tetha-burst stimulation kandel cap 1

Brief O-Burst Stimulation Induces a Transcription-Dependent Late Phase of LTP Requiring cAMP in Area CA I of the Mouse Hippocampus P e t e r V. N g u y e n I a n d Er ic R. K a n d e l 2

Howard Hughes Medical Institute and Center for Neurobiology and Behavior College of Physicians and Surgeons of Columbia University New York, New York 10032

Abstract

Memory storage in the m a m m a l i a n bra in can be divided into a shor t - term phase that is i ndependen t of new prote in synthesis and a long- term phase that requires synthesis of new RNA and proteins. A cellular model for these two phases has emerged f rom studies of long-term potent ia t ion (LTP) in the three major excitatory synaptic pathways in the h ippocampus . One especially effective protocol for inducing robust and persistent LTP is "O-burst" st imulation, which is designed to mimic the firing pat terns of h ippocampa l neurons recorded dur ing explora tory behavior in intact awake animals. Unlike LTP induced by non-O tetanization regimens, little is k n o w n about the biochemical mechan i sms under ly ing O-burst LTP in the h ippocampus . In the presen t study, we examined O-burst LTP in the Schaffer collateral pathway. We found that 3 sec of O-burst s t imulat ion induced a robust and persis tent potent iat ion (O L-LTP) in mouse h ippocampa l slices. This O L-LTP was dependen t on NMDA receptor activation. The initial or early phase of O-LTP did not require ei ther protein or RNA synthesis and was independen t of cAMP-dependent prote in kinase (PKA) activation. In contrast, the late phase of O-LTP required synthesis of proteins and RNA and was blocked by inhibitors of PKA.

1Present address: Center for Neuroscience Research, Mc- Gill University, Montreal General Hospital Research In- stitute, Montreal, Quebec, Canada H3G 1A4 ZCorresponding author.

Prior induction of O-LTP also occluded the potentiat ion elicited by chemical activation of PKA. Our results show that, like non-O LTP, O-induced LTP in area CA1 of the mouse h ippocampus also involves transcript ion, translation, and PKA and suggest that cAMP-mediated gene t ranscr ipt ion may be a c o m m o n mechan i sm responsible for the late phases of LTP induced by both O and non-O pat terns of stimulation.

Introduction

Memory storage consists of at least two distinct temporal phases: short-term memory, lasting minutes to hours, and long-term memory, which may persist for days, weeks, or even longer (for reviews, see Polster et al. 1991; Squire 1992). Brief inhibition of either protein synthesis or transcription selectively blocks induction of long-term memory without affecting short-term memory (Davis and Squire 1984; Castellucci et al. 1989; Crow and Forrester 1990; Tully et al. 1994). In contrast to its induction, maintenance of long-term memory is independent of new protein synthesis and transcription (Davis and Squire 1984).

Cell biological studies of the conversion of short- to long-term memory in invertebrates have revealed some of the molecular mechanisms underlying this transition. In the marine snail, Aply- sia, studies of memory for sensitization of the gill- and siphon-withdrawal reflexes have shown that a clear distinction exists between the mechanisms involved in short-term and long-term presynaptic facilitation (a cellular mechanism contributing to sensitization). Short-term facilitation involves post-

LEARNING & MEMORY 4:230-243 �9 1997 by Cold Spring Harbor Laboratory Press ISSN1072-0502/97 $5.00

& 230

L E A R N / N G M E M O R Y

Cold Spring Harbor Laboratory Press on May 4, 2016 - Published by learnmem.cshlp.orgDownloaded from

http://learnmem.cshlp.org/

http://www.cshlpress.com

O-BURST L TP IN THE MOUSE HIPPOCAMPUS

translation modification of pre-existing proteins and is mediated by cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) (Castellucci et al. 1980; Montarolo et al. 1986; Ghirardi et al. 1992; Byrne et al. 1993). Long-term facilitation, in contrast, requires new protein synthesis and cAMP- mediated gene expression, through activation of cAMP response element binding-1 (CREB-1) and relief from repression of CREB-2 (Montarolo et al. 1986; Dash et al. 1990; Alberini et al. 1994; Bartsch et al. 1995), and also involves growth of new synaptic connections (Glanzman et al. 1990; Nazif et al. 1991). Similarly, studies on Drosophila suggest that short-term memory and learning require PKA, whereas long-term memory requires CREB-initiated gene expression (Tully et al. 1994; Yin et al. 1994; for mouse data, see Bourtchouladze et al. 1994).

Mechanisms similar to those revealed in Aply- sia and Drosophila may also underlie explicit memory storage in the mammalian brain (for reviews, see Abel et al. 1995; Nguyen et al. 1995). Explicit learning involves the acquisition of information about people, places, and things and is critically dependent on structures within the temporal lobe, including the hippocampus (Scoville and Mil- ner 1957; Hirsh 1974). Within the hippocampus, there are three major serial excitatory synaptic pathways: the perforant, mossy fiber, and Schaffer collateral pathways that connect the entorhinal cortex to the dentate gyrus, the dentate gyrus to area CA3, and area CA3 to area CA1, respectively (Andersen et al. 1977; Amaral 1993). Damage to any one of these three serial pathways is thought to be sufficient to severely impair memory in humans (Zola-Morgan et al. 1986).

Hippocampal neurons can undergo long-lasting increases in synaptic efficacy after brief high- frequency stimulation of any of the three excitatory pathways (Bliss and Lomo 1973). In awake animals, the activity-dependent increase in synaptic strength can last for hours to days and is called long-term potentiation (LTP). LTP has been studied extensively in hippocampal slices (Andersen et al. 1977; for review, see Bliss and Collingridge 1993). As with behavioral memory, LTP in all three hippocampal regions consists of at least two bio- chemically distinct temporal phases. There is an early phase lasting 1-2 hr that is independent of protein and RNA synthesis and a later, more persistent phase (L-LTP), beginning after 1-2 hr and lasting up to 8 hr in slices (for review, see Huang et al. 1996a). This L-LTP requires new protein and RNA synthesis, and PKA activation for its full ex-

pression (Frey et al. 1993; Matthies and Reymann 1993; Huang and Kandel 1994; Huang et al. 1994; Nguyen et al. 1994; Nguyen and Kandel 1996).

Stimulation protocols for LTP induction in the hippocampus vary considerably, but LTP is typi- cally induced by applying 1-sec trains of high-frequency (100-Hz) stimulation (Bliss and Lomo 1973; Bliss and Collingridge 1993). It is unclear whether hippocampal neurons in vivo fire at 100 Hz for a full second. Pyramidal cells in CA1 commonly fire short (30- to 40-msec) bursts of three to four spikes (Kandel and Spencer 1961; Ranck 1973), with the bursts being repeated at the "O" frequency (Green et al. 1960). O is a 5- to 12-Hz electroencephalo- graphic wave that appears when animals are engaged in exploratory, attentive behavior (Grastyan et al. 1959; Vanderwolf 1969; Bland 1986). O rhythm may initiate LTP, because brief 30-msec bursts of stimuli (100 Hz) delivered repeatedly at 5 Hz for 1-2 sec ("O-burst" stimulation) effectively induces LTP in the rat hippocampus in vitro (Lar- son and Lynch 1986; Larson et al. 1986) and in vivo (Staubli and Lynch 1987).

Numerous studies have recently explored the biochemical mechanisms of L-LTP in hippocampal slices (for review, see Abel et al. 1995; Nguyen et al. 1995). These experiments have used 1-sec tet- ani and have shown that L-LTP requires macromolecular synthesis and PKA recruitment. In contrast, little is known about the biochemical mechanisms of L-LTP induced by O-burst stimulation.

In the present study, we asked the following questions: Can L-LTP be induced in area CA1 of hippocampal slices by applying brief O-burst stimulation? Is PKA activity essential for induction of O L-LTP? Are protein synthesis and gene transcription critical for O L-LTP and, if so, when are these processes engaged?

Materials and Methods

Adult (7- to 11-week old) male C57BL/6J mice (The Jackson Laboratory) were decapitated, and their brains were rapidly removed and immersed in cold (4~ artificial cerebrospinal fluid (ACSF). Iso- lated hippocampi were cut transversely (400-1am thickness) with a McIlwain tissue chopper, and the resulting slices were placed on a nylon mesh in an interface chamber maintained at 28~ Slices were continuously superfused with ACSF (1 ml/min) bubbled with a mixture of 95% 02 and 5% CO 2 and were allowed to recover for 60-90 min before re-

& 231





Nguyen and Kandel

cordings were at tempted. The composi t ion of the ACSF solution was as follows (125 mM NaC1, 1.5 mM MgSO4, 4.5 m i KC1, 26 m i NaHCO3, 2.5 m i CaC12, 1 mM NaH2PO4, and 10 m i glucose.

For extracellular st imulation of the Schaffer collateral pathway, a bipolar n i cke l - ch romium electrode (Medwire Corp.) was placed in the stratum radiatum layer of area CA1. Extracellular field EPSPs were recorded wi th a glass microelectrode (5- to 8-M~ resistance) filled wi th ACSF and posi- t ioned in stratum radiatum of area CA1. For all exper iments , test stimuli (0.05-msec pulse width) were del ivered o n c e / m i n , and the stimulus intensity was set to give basel ine field EPSP slopes -40% of maximal evoked slopes. Slices that showed maximal field EPSP sizes <3 mV were rejected.

LTP was induced by applying 3 sec of continu- ous O-burst stimulation: 15 bursts of four pulses at 100 Hz, wi th an interburst interval of 200 msec. For some exper iments , LTP was induced by giving an equivalent n u m b e r of pulses wi th in 1 sec (i.e., a single 1-sec train of 60 Hz).

All drugs were made fresh in perfusate, except for act inomycin-D (dissolved in 0.05% ethanol final concentra t ion) and KT-5720 (dissolved in 0.1% DMSO final concentrat ion) .

Student 's unpai red t-test was used for all statis- tical compar isons of m e a n field EPSP slopes.

Resul ts

O-BURST STIMULATION INDUCES LONG-LASTING POTENTIATION IN AREA CA1 OF MOUSE HIPPOCAMPAL SLICES

Previous studies have shown that O-burst s t imulation can induce robust and persistent facilitation of t ransmission in area CA1 of intact animals and rat h ippocampa l slices (Larson et al. 1986; Staubli and Lynch 1987). In contrast, little is k n o w n about the b iochemica l mechan i sms responsible for O-burst LTP in the mouse h ippocampus . As an initial step toward characterizing the bio- chemica l pa thways that may contr ibute to O-burst LTP, we tested for the induct ion of L-LTP in mouse h ippocampa l slices by applying 3 sec of O-burst st imulation to the Schaffer col la tera l -commissural pathway. We found that O-burst st imulation yielded a robust and stable facilitation of synaptic t ransmission that persis ted for 3 -6 hr (Fig. 1A; 6-hr data not shown). Mean values for field excitatory postsynapt ic potential (fEPSP) slopes at 1, 2, and 3

hr after O-burst st imulation were 186_+ 7%, 170 _ 7%, and 174 _+ 6% of baseline, respectively (n = 12 slices from six animals) (Fig. 1A).

Is this O-induced L-LTP dependen t on NMDA receptor activation? In the presence of 100 ~IM APV (2-amino-5-phosphonovalerate), an NMDA receptor antagonist, 3-sec O-burst st imulation failed to potentiate t ransmission in area CA1 (Fig. 1B). This block of LTP induct ion was reversed wi th washout of APV (Fig. 1B). Hence, these exper iments show that, like earlier studies on rat h ippocampa l LTP induced by O-bursts (Larson and Lynch 1988), O-LTP induct ion in area CA1 of mouse h ippocam- pal slices is dependen t on NMDA receptor activation.

Can the temporal pat tern of st imulation critically shape the duration of synaptic potentiation? We addressed this quest ion by applying the same total n u m b e r of st imulus pulses (60) in a temporally compressed manner . After a 1-sec train of 60- Hz stimulation, t ransmission in the Schaffer collat- e ra l -commissura l pa thway was facilitated to a lesser degree than fol lowing O-burst st imulation (Fig. 1A). Mean fEPSP slopes in 60-Hz slices were 117 _+ 11%, 117 _+ 9%, and 112 + 8% after 1, 2, and 3 hrs, respectively (n = 6). These values were significantly lower than those observed in O-burst slices ( P < 0 . 0 2 ) . These results indicate that O-burst st imulation is a very effective protocol for induct ion of stable, long-lasting potent iat ion in area CA1 of mouse h ippocampa l slices and that the temporal spacing of stimulus pulses is critical for producing such robust synaptic plasticity.

TRANSCRIPTION AND TRANSLATION ARE REQUIRED FOR EXPRESSION OF LATE PHASES OF O-BURST LTP

We then explored the putative roles of RNA synthesis and translation in the express ion of O L-LTP in mouse h ippocampa l slices. In the presence of 40 ILIM act inomycin D (ACT-D; appl ied for 1 hr beginning 30 min before O), a transcriptional inhibitor, 3 sec of O-burst st imulation induced LTP that gradually decayed to 125 _+ 5% and 114 + 9% (n = 6) of pre-O baseline after 90 min and 3 hr, respectively (Fig. 2A). W h e n ACT-D was appl ied for 1 hr beginning 30 min after O, the levels of potent iat ion were then 158 _ 7% and 160 _+ 3% ( n = 4 ) after 90 min and 3 hr, respect ively (P < 0.02; Fig. 2A). Hence, there exists a t ime window of t ranscript ion critical for full main tenance of

L E A R N / N G & 232

M E M O R Y




O-BURST L TP IN THE M O U S E HIPPOCAMPUS

A

(D e"

oO

0

fa. o oe~ 13. O9 n LU -o .o_ LL

B

300

250

200

150

100

50

0 -

-30

~ , l s

L~.~lkZa-'-

r �9 �9 t , i . i �9 . - r - T

0 30 60 90 120 150 1 B0

Time (min)

THETA, 3s n=12

60 Hz, ls n=6

300

�9 -= 2so

"*~ 200

ca. 150

m 1011 Q.

'" t "o .~ 50 100gM APV " r

0 , d �9 �9 , - �9 , �9 �9 . ~ " - ' - ' - ' - " 1 --20 0 20 40 60 80

Time (min)

THETA, 3s n=12

APV, n=4

Figure 1: O-Burst, but not 60-Hz stimulation, leads to L-LTP of synaptic transmission in area CA1 of mouse hippocampal slices. (A) A brief episode (3 sec) of O-pattern stimulation elicited L-LTP that persisted for at least 3 hr, whereas the same number of stimulus pulses applied in a compressed fashion (60 Hz, 1 sec) produced a gradually decaying form of synaptic facilitation. O or 60-Hz stimulation was applied at the time marked by the arrow. Sample fEPSP traces were recorded 15 min before and 3 hr after O. Scale bars, 2 mV, 10 msec. (B) LTP produced by O-burst stimulation is dependent on NMDA receptor activation. In the presence of 100 ~IM

APV, O-burst stimulation (at arrow) failed to elicit any potentiation. Washout of APV, followed by a second episode of O-burst stimulation (3 sec) at about 65 min, resulted in some potentiation (A). The upper curve (r-l) shows data identical to the O curve of A.

O-burst LTP; this time period extends from O stimulation to 30 min after induction of potentiation.

A requirement for gene transcription suggests further that protein synthesis may be involved in the expression of O-LTP. To test this hypothesis, we applied anisomycin (30 ~M, for 1 hr starting 30 min before O) to mouse hippocampal slices and observed that potentiation in area CA1, as in the ACT-D experiments, decayed slowly to near baseline values: Mean fEPSP slopes after 3 hr were 116 +_ 6% (n = 6) in drug-treated slices and 161 + 8% (n = 6) in drug-free controls (P < 0.05) (Fig. 2B).

These experiments show that O-LTP in area CA1 of mouse hippocampal slices requires RNA

synthesis and translation for full expression. Fur- thermore, in the presence of these inhibitors of transcription and translation, the later phases of LTP were absent.

INHIBITORS OF cAMP-DEPENDENT PROTEIN KINASE BLOCK THE LATE PHASES OF LTP INDUCED BY O-BURST STIMULATION IN AREA CA1

Which biochemical signal transduction pathways are involved in the induction of O-LTP? One candidate is the cAMP-PKA pathway, which has been shown to be critical for expression of the late phases of hippocampal LTP induced by non-O patterns of tetanization (Frey et al. 1993; Huang and

& 233

L E A R N I N G M E M O R Y




Nguyen and Kandel

A 300

.c 25O u~

m e~ ",- 200 o g

150 o

0.. r/) 100 Q.. LU " 10

.'~ 50 u_

B

Figure 2: Transcription and protein syn- 30o] thesis are necessary for express ion of O- in -

duced L-LTP. (A) Application of 40 IJM ~ 250

ACT-D, a transcriptional inhibitor, blocked u )

the late stages of LTP induced by 3 sec of ~ 200 O-burst stimulation, but only when the ~6 drug was given before and after stimula-

150 tion (lower curve, A). Later application of ~.

o ACT-D (beginning 30 min after O) failed to

100 affect L-LTP (upper curve, R). (B) Aniso- r mycin, a protein synthesis inhibitor, o. blocked L-LTP when applied for 1 hr over- _~ lapping with O (lower curve, I-1). Sample iT_ traces were measured 15 min before and 3 hr after O in both A and B. Scale bars, 2 mV, 10 msec.

0 - 3 0

~ ACT-D, Late n--4

~ . ~ - - - - " ' l ' ~ ' ~ ~ ACT- D, Early = P ' - - - n=6

ACT-D, 40p.M ,1 ~ ACT-D, 401.[M

�9 i - �9 i �9 �9 i �9 �9 i �9 �9 i �9 - i = ' �9 i

0 30 60 90 120 150 180

Time (rain)

30"" I

Control, ~ ' ~ "

,.]Ii=r - = ~ Anisomycin n--6

50 Anisomycin, 30~M

,f 0 ~ �9 i - �9 i - - | �9 - i "- " ' " ' , ' i �9 �9 | - �9 i

-30 o 30 so 90 12o '=so 1so

Time (min)

Kandel 1994; Huang et al. 1994; Nguyen and Kan- del 1996).

Using two different inhibitors of PKA, we tested the hypothesis that PKA activation is necessary for induction of the late phases of O-LTP. A brief application of KT-5720 (1 laM, bath-applied for 30 min beginning 15 min before O), an inhibitor of the catalytic subunit of PKA (Kase et al. 1987), did not affect initial induction of O-LTP (Fig. 3A), but caused a relatively rapid decay of potentiation to baseline values: Mean fEPSP slopes measured 60 min and 3 hr after 3 sec of O stimulation were 123 + 5% and 109 -+ 6%, respectively (n = 6). When KT-5720 was applied slightly later (starting 30 min after O), potentiation was intact: Mean fEPSP slopes recorded 60 min and 3 hr post-O were

186 + 6% and 174 + 6%, respectively (n = 4; P < 0.05).

A second inhibitor of PKA, Rp-cAMPS (100 pM, applied for 30 min starting 15 min before O), also blocked the later phases of O-LTP (Fig. 3B). Mean fEPSP slopes recorded 3 hr after O in drug-treated and drug-free slices were 106 _+ 10% (n - 5) and 161 _+ 9% (n = 5), respectively (P < 0.05). Unlike KT-5720, Rp-cAMPS is known to act on the regulatory subtmit of PKA, preventing its dissociation from the catalytic subunits and thereby maintain- ing PKA in its inactive tetrameric form (Dostmann 1995).

These results show that PKA activation is cru- cial for full expression of the late phases of O-LTP in area CA1 of the mouse hippocampus and sug-

L E A R N / N G & 2 3 4

M E M O R Y





A

C

U~ 03

J~

0

CL _9o O9 13. i f ) 0_ UJ

LL

B

.c_

300

250 -~

200

Early P

~ q5720, Late n=4

15O

100 f " - " "-'~' - -- KT5720, Early

n=6

- - - " K T 5 7 2 0 , gM l I , I i

0 �9 i �9 �9 i �9 * i �9 �9 �9

- 3 0 0 30 60 90 120 150 180

300

250

�9 ,- 200 o g Q. 150

o

100

LU "10 "~ 50 LL

Time (min)

0 - 3 0

~ AMPS, E a r l y . ~ P S , Late

c A M P S , Late fl=5

Rp-cAMPS, Early n=5

Rp-cAMPS, 1001~M Rp-cAMPS, 1001aM

/

; | �9 �9 | �9 - | �9 . ' ' l �9 �9 | �9 �9 i �9 �9 !

0 30 60 90 120 150 180

Time (min)

Figure 3: Inhibitors of PKA block expression of L-LTP following O-burst stimulation. (A) KT-5720, an inhibitor of the catalytic subunit of PKA, elicited a gradual decay of O-induced LTP when application overlapped with O (KT5720 Early, lower curve) but had no effect on L-LTP when applied 30 min after O (KT5720 Late, upper curve). (B) Rp- cAMPS, an inhibitor of PKA that acts on the regulatory subunit, also prevented expression of L-LTP following O, but only when application of drug overlapped O-burst stimulation (lower curve). Later administration of Rp-cAMPS failed to affect L-LTP expression (upper curve). Traces were recorded 15 min before and 2 hr after O. Scale bars, 2 mV, 10 msec.

gest that, like some forms of LTP induced by non-O patterns of high-frequency stimulation, the late phases of O-LTP also depend on activity-dependent recruitment of PKA in hippocampal neurons. Fur- thermore, a critical period of PKA activation appears to be required for the late phases of O-LTP.

A cAMP ANALOG PRODUCES LONG-LASTING POTENTIATION THAT IS OCCLUDED BY PRIOR O-BURST STIMULATION

If the cAMP-PKA signal transduction pathway is critically involved in O-LTP, then induction of LTP by O-burst stimulation should occlude subsequent potentiation produced by chemical activa-

tion of PKA. We tested this idea by first applying Sp-cAMPS (100 ~M, given for 15 min) to mouse hippocampal slices (Fig. 4A). This activator of PKA produced an initial transient depression of transmission in area CA1, followed by a gradual facilitation that reached plateau values of 165 _+ 9% and 167 + 3% (n - 5) 90 min and 2 hr after application, respectively (Fig. 4A).

In a separate group of slices, we next gave 3 sec of O-burst stimulation, decreased the stimulus intensity to bring transmission back down to baseline levels immediately after O, and applied 100 ~M Sp-cAMPS for 15 min, beginning 5 min before O-burst stimulation (Fig. 4B). The level of potentiation measured immediately after O-burst stimulation was 172 + 14% (n - 4). More importantly,

L E A R N I N G & 235

M E M O R Y




Nguyen and Kandel

A 300

250

.IQ

"6 200 g

150 o 03 n 100 co n uJ "o 50 ._r LL

~ l O O p M I

n=5

Sp-cAMPS, 100p.M

-30 ; 3'0 6'0 9'0 1;0 " Time (min)

B 300

250 . - -

,,.. 200 o

g ~0 150

o oo n 100 o') n uJ "o 50 ._r LL

a

b__

c_

c n=4

Sp-cAMPS, lOOpM

-30 0 30 60 90 120 150 180

Time (rain)

Figure 4: O-Burst stimulation occludes synaptic potentiation produced by an analog of cAMP. (A) A brief, 15-min application of Sp-cAMPS, an activator of PKA, elicited a transient depression and then a long-lasting facilitation of synaptic transmission in area CAl. Sample traces were recorded 15 min before and 2 hr after onset of Sp-cAMPS application. (B) O-Burst stimulation (3 ser at arrow) given 5 min after the onset of application of Sp-cAMPS prevented subsequent potentiation by Sp- cAMPS. Note that the initial depression seen in A was less pronounced here, perhaps because of overlapping facilitation induced by O-burst stimulation. Sample traces were recorded at marked times. Trace b was measured immediately after O. Scale bars, 2 mV, 10 msec.

we found that Sp-cAMPS did not produce signifi- cant facilitation of transmission in area CA1 following O-burst stimulation: Mean fEPSP slopes measured 1 hr, 90 min, and 2 hr after Sp-cAMPS application were 109_+13%, 91_+6%, and 99-+8% (n = 4), respectively. These values were not significantly different from pre-O baseline measurements (P > O. 5). A marked depression of transmission was

absent during Sp-cAMPS application following O stimulation (Fig. 4B). This may have stemmed from facilitatory processes induced in CA1 pyramidal cells by O, which would mask the depression induced by Sp-cAMPS.

These findings complement those obtained with pharmacological inhibitors of PKA, strongly supporting the idea that O-burst stimulation acti- vates the cAMP-PKA signal transduction pathway, which, in turn, triggers molecular events that are necessary for expression of the late stages of O-LTP in area CA1.

SHORT-LASTING POTENTIATION INDUCED BY A COMPRESSED PATTERN OF STIMULATION REQUIRES NEITHER TRANSCRIPTION NOR PKA ACTIVATION

It is clear that O-burst stimulation induces long-lasting potentiation that is dependent on transcription and PKA activation, whereas a temporally compressed pattern of stimulation that uses the same number of stimulus pulses fails to produce persistent and robust facilitation. Does such short- lasting potentiation also require gene transcription and PKA activity?

To address this question, we applied 1 sec of 60-Hz stimulation to the Schaffer collateral-commissural pathway of mouse hippocampal slices in the presence of either ACT-D (Fig. 5A) or Rp- cAMPS (Fig. 5B). In the absence of either drug, levels of transmission were moderately potentiated for a relatively short period of time: Mean fEPSP slopes measured 2 hr after 60-Hz stimulation in the two control groups were 118 _+ 7% and 116 + 9% of baseline values (n - 5 for each group). In the presence of the transcriptional inhibitor ACT-D (40 HM applied for 1 hr, Fig. 5A), the mean fEPSP slope recorded 2 hr after 60-Hz stimulation was 110 + 5% (n - 5), which was not significantly different from drug-free controls (P > 0.5). Rp-cAMPS (100 ~aM), a PKA inhibitor, also did not affect potentiation after 2 hr: The mean fEPSP slope measured here was 118 + 8% (n = 5; P > 0.5; Fig. 5B).

The results of these experiments suggest that the temporal pattern of stimulation leading to synaptic potentiation in the hippocampus can deter- mine the particular biochemical requirements and duration of facilitation induced. Specifically, a temporally compressed pattern of stimulation (60 Hz, 1 sec) was less effective in eliciting a transcription- and cAMP-dependent form of long-lasting potentia-

L E A R N / N G & 236

M E M O R Y




O-BURST L IP IN THE MOUSE HIPPOCAMPUS

A ~" 300 1

._r 250 -~

] "6 2oo

r 150 o 09 C L 100 CO O. I.U -o 5o (D LE

60 Hz, ls

~ ~ ~ ~ i ~ ~ - D , n=5

, Control, n=5

ACT-D, 40~d~

30 0 30 60 90 120

Time (min)

300

250

"~ 200 =. "6

150 o cO o.. 100 co o,. LU

50

60 Hz, ls

Rp-cAMPS, n=5

Da~ l~ l~ Control, n=5

R ~ M ~ S , 100~M m

0 . . , -30 0

, . . , . . , . . ,

30 60 90 120

Time (min)

Figure 5: A compressed pattern of stimulation elicits only short-lasting potentiation that is independent of transcription and PKA. (A) A brief, 1-sec train of 60 Hz produced short-lasting facilitation in slices treated with ACT-D (a transcriptional inhibitor; I-1) that was indistin- guishable from control slices (A). (B) The same stimulation pattern still elicited a transient facilitation that was not significantly different between control slices (A) and slices treated with a PKA inhibitor, Rp-cAMPS (I-1).

tion than was a more temporally spaced, O-burst pattern of activation.

D i s c u s s i o n

A COMPARISON OF L-LTP INDUCED BY O AND NON-O PATTERNS OF STIMULATION

Many recent experiments have shown that multiple trains (three or more) of 100-Hz stimulation are needed to produce L-LTP lasting 3 hr or more (Frey et al. 1993; Matthies and Reymann 1993; Huang and Kandel 1994; Huang et al. 1994; Nguyen et al. 1994; Nguyen and Kandel 1996). In all three hippocampal regions (dentate gyrus, CA3, CA1), this L-LTP requires protein and RNA synthe-

sis and is mediated by PKA and cAMP (Frey et al. 1993; Matthies and Reymann 1993; Huang et al. 1994; Nguyen et al. 1994; Nguyen and Kandel 1996). In contrast, short-lasting potentiation that decays to baseline within 2 hr does not require macromolecular synthesis and is induced with fewer stimulus trains (Huang and Kandel 1994; Nguyen and Kandel 1996).

Our results with O-burst L-LTP show (for the first time in mouse hippocampal slices) that, like conventional L-LTP, O L-LTP in the CA1 region requires the synthesis of new protein and RNA, as well as PKA recruitment. The necessity for transcription and PKA activity occurred during a critical time window overlapping with b-burst stimulation, because delayed post-O application of inhibitors of either transciption or PKA failed to block O L-LTP.

What makes b-burst stimulation an especially effective protocol for induction of LTP? Stimulation of hippocampal afferents initiates EPSPs in pyramidal cells but also recruits IPSPs in these cells by means of feed-forward activation of interneurons (Alger and Nicoll 1982). These feed-forward IPSPs become refractory for 200-500 msec thereafter (McCarren and Alger 1985). Hence, the O interburst interval of 200 msec delineates a period when IPSPs are difficult to recruit. Repeated application of brief bursts of stimuli, at the 5-Hz O frequency, allows for more effective temporal sum- mation of EPSPs in the absence of strong feed-forward inhibition that would otherwise truncate excitatory transmission. Modest LTP can be produced by preceding a single brief burst with a priming pulse at a 200-msec interval (Rose and Dunwiddie 1986; Diamond et al. 1988), and robust LTP can be elicited with as few as 10 bursts (40 pulses) delivered at the O frequency (Larson and Lynch 1986; Larson et al. 1986; Staubli and Lynch 1987). Spaced stimulation at the O frequency of 5 Hz or at much lower interburst frequencies (e.g., 1-sec duration trains of 100 Hz given every 1-10 min), may favor L-LTP expression because transcription (a requirement for L-LTP expression, for review, see Huang et al. 1996a) may be more strongly activated after such protocols. There is evidence that CREB expression is increased after repeated spaced stimulation leading to L-LTP in hippocampal neurons but not after single-train compressed stimulation (Impey et al. 1996). Brief, compressed stimulation patterns may fail to induce L-LTP because such protocols do not elicit sufficient calcium influx through NMDA receptor chan-

L E A R N i N G M E M O R Y




Nguyen and Kandel

nels and through voltage-gated calcium channels (e.g., L-type Ca 2+ channels) to trigger gene expression (for review, see Gallin and Greenberg 1995; see also Malenka 1991). Recent work indicates that L-type Ca 2+ channels may play a role in eliciting synapse-to-nucleus signaling involving CREB phosphorylation (Deisseroth et al. 1996). These channels have slow inactivation kinetics and high activation thresholds, which would favor stronger, more prolonged (i.e., temporally spaced) depolar- ization regimens for eliciting greater Ca 2+ influx over the longer stimulation regimens required for effective L-LTP induction (Bito et al. 1996; Deis- seroth et al. 1996). Also, recovery from protein phosphorylation may be slower following spaced stimulation protocols (Bito et al. 1996), and this may facilitate expression of more persistent forms of synaptic potentiation (for review, see Huang et al. 1996a).

Our present results extend earlier work in rats (Larson and Lynch 1986, 1988; Larson et al. 1986) by showing that temporally spaced patterns of stimulation are not only effective for initiating LTP but are also very effective for producing long-lasting, robust L-LTP in mouse hippocampal slices. In contrast, delivering the same total number of pulses in a temporally compressed fashion (60 Hz, 1 sec) did not elicit long-lasting facilitation in area CA1. This latter protocol induced only a transient potentiation that, unlike O-burst L-LTP, was independent of transcription and PKA activation. In ret- rospect, our present findings are in agreement with, and further extend, earlier experiments that have shown effective L-LTP induction in all three hippocampal regions by repeated application of 1-sec-duration, lO0-Hz trains spaced 1-10 min apart (Frey et al. 1993; Matthies and Reymann 1993; Huang et al. 1994; Nguyen and Kandel 1996).

Which induction protocol is most suited for producing L-LTP? The present study does not pro- vide any evidence to suggest that one single protocol is the most appropriate for inducing L-LTP. It is evident that a number of different stimulation regimens, varying in strength and duration, can induce robust L-LTP. Our findings do indicate, however, that despite its more subtle temporal characteristics, a O-burst pattern of stimulation can none- theless invoke subcellular mechanisms and signal transduction pathways that are, at least superfi- cially, identical to those involved in non-O L-LTP. Hence, a similar and conserved molecular program of events, involving NMDA receptor activation,

cAMP, PKA, transcription, and translation, may underlie L-LTP induced by a variety of stimulus patterns.

RELATIONSHIP BETWEEN O-BURST LTP, FIRING PATTERNS OF HIPPOCAMPAL NEURONS, AND SOME FORMS OF LEARNING AND MEMORY

The first evidence to link the electrical activity of CA1 neurons to spatial processes was provided through chronic single-unit recordings made by O'Keefe and Dostrovsky (1971). They found that CA1 pyramidal cells fired selectively when awake, unrestrained rats were placed in specific locations in a defined environment during spatial explora- tion. These "place cells" encoded spatial relation- ships between distal cues, as well as direction and speed of movement (Olton et al. 1978; O'Keefe 1979). It is known that CA1 pyramidal cells fire in short bursts of two to seven spikes ("complex spike" bursts) lasting 30 msec (Ranck 1973; Fox and Ranck 1981; Muller et al. 1987; Thompson and Best 1989). In rats exploring new surroundings, this firing pattern occurs in conjunction with a cholinergically regulated, 5-Hz O rhythm of mem- brane potential oscillations (Vanderwoff 1969; Bland 1986; Eichenbaum et al. 1987; Muller et al. 1987; Otto et al. 1991; Lee et al. 1994; Ylinen et al. 1995).

What is the relationship between O-burst firing of CA1 pyramidal neurons and LTP induction? In isolation, a single 30-msec burst of four pulses does not generally produce robust LTP (but see Huerta and Lisman 1995), but several bursts repeated with a 200-msec interburst interval (O frequency) induces substantial LTP in vivo and in vitro (Larson and Lynch 1986; Larson et al. 1986; Rose and Dunwiddie 1986; Staubli and Lynch 1987; Diamond et al. 1988; Pavlides et al. 1988). Hippocampal pyramidal cells fire in bursts similar to the O pattern found to be optimal for LTP induction, when rats are sampling odors in an olfactory learning task (Otto et al. 1991). These collec- tive studies all support the notion that natural patterns of hippocampal neuronal activity, observed during learning, can induce robust LTP. Hence, there is ample evidence to believe that the molecular events invoked after O stimulation occur during learning and lead to long-term synaptic plasticity that may underlie the consolidation of long-term memory. Also, there appears to be a strong corre- lation between O-burst firing of hippocampal CA1

& 238






neurons, synaptic LTP induced by this firing in these same neurons, and some kinds of learning in the intact animal (Otto et al. 1991; Huerta and Lis- man 1995).

WHICH cAMP-INDUCIBLE GENES ARE CRITICAL FOR O-BURST L-LTP?

L-LTP in all three regions of the rat hippocampus requires transcription and translation and can be mimicked by pharmacological activation of PKA and the cAMP signal transduction pathway (Frey et al. 1993; Huang et al. 1994; Huang and Kandel 1994; Nguyen et al. 1994; Nguyen and Kandel 1996; see also Chavez-Noriega and Stevens 1994). Our observations that O L-LTP was blocked by inhibitors of either gene transcription or PKA suggest that cAMP-inducible genes are involved in L- LTP in area CA1 of the mouse hippocampus. Ge- netic evidence supporting this idea derives from the observations that selective ablation of the ot and 8 isoforms of CREB eliminated LTP and long- term memory in mice, without affecting short-term memory (Bourtchouladze et al. 1994). Also, a ga- lactosidase reporter gene driven by CRE (_cAMP response _element) is induced during L-LTP (Impey et al. 1996). These studies thus show that a cAMP- modulated transcription factor, CREB, may activate downstream effector genes for L-LTP expression in the hippocampus. It is not yet known whether O-burst L-LTP depends on CREB-activated gene expression.

Mthough our study has implicated PKA in the late phase of O-LTP, we cannot rule out a role for PKA in the early stages (1-2 hr post-O) of potentiation (see Blitzer et al. 1995). The early phase may be less sensitive to disruption by the modest concentrations of PKA inhibitors used here and may in fact be disrupted by higher concentrations of inhibitors or by more extended application of the inhibitors. However, at higher drug concentrations, other kinases may be affected and the speci- ficity of action of these inhibitors may be compro- mised. Also, a recent study using transgenic overexpression of an inhibitory subunit of PKA (Abel et al. 1997) has shown that short-lasting potentiation induced by one or two 100-Hz trains is normal, whereas L-LTP induced by four trains is selectively disrupted. Hence, the available evidence to date argues for a critical and apparently selective role for PKA in the late phase of LTP.

In Aplysia, long-term (but not short-term) fa-

cilitation is mediated by translocation of the catalytic subunit of PKA to the nucleus of sensory neurons (Bacskai et al. 1993), where it may phosphory- late CREB and other transcription factors that switch on cAMP-inducible immediate-early genes (Dash et al. 1990; Kaang et al. 1993). One gene that is induced in sensory neurons by cAMP is the Aply- sia homolog of the mammalian transcription factor C/EBP (ApC/EBP; Alberini et al. 1994). Blocking the function of ApC/EBP in sensory neurons blocks long-term but not short-term facilitation (A1- berini et al. 1994).

In mice, genetic ablation of either a catalytic subunit (O13-1) or a regulatory subunit (RI-[3) of PKA eliminates the late phase of LTP in areas CA1 and CA3 (Huang et al. 1995; Qi et al. 1996). Over- expression of an inhibitory form of a PKA regulatory subunit (RI-00 also eliminates L-LTP in area CA1 (Abel et al. 1997), suggesting that in the hippocampus, as in Aplysia, cAMP and PKA may play a role in the recruitment of transcription factors (e.g., CREB, C/EBP) for L-LTP expression.

Which effector genes are recruited during O L-LTP? To date, no previous study has examined the roles of gene induction and protein synthesis in L-LTP induced by O-burst stimulation. That O L-LTP was blocked by transcriptional and translational inhibitors suggests that late effector genes and the proteins encoded by them may be recruited after O-burst stimulation. Some candidate genes that may be activated during L-LTP are those encoding tissue-plasminogen activator (Qian et al. 1993; Frey et al. 1995; Huang et al. 1996b), cell adhesion mol- ecules (Bailey et al. 1992; Mayford et al. 1992; Cre- mer et al. 1994), and voltage-dependent K + channels (Kaang et al. 1992). The latter are particularly noteworthy, because their expression levels can shape synaptic efficacy (Kaang et al. 1992) and can be regulated by cAMP and CREB (Mori et al. 1993). If hippocampal LTP, like long-term facilitation in Aplysia (Bailey and Kandel 1993), involves an or- ganized repertoire of synaptic growth and differ- entiation (Desmond and Levy 1986a,b; Lisman and Harris 1993; Edwards 1995), then these genes may very well prove to be pivotal for triggering structural changes during L-LTP.

Acknowledgments We thank Irma Trumpet, Harriet Ayers, and Chuck Lain

for preparing the manuscript and Danny Winder for critical comments. This work was supported by the Howard Hughes Medical Institute and grant MH 45923-07 to E.R.K.P.V.N. is





Nguyen and Kandel

a fellow of the Medical Research Council of Canada. E.R.K. is Senior Investigator of the Howard Hughes Medical Institute.

The publication costs of this article were defrayed in part by payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

References Abel, T., C. Alberini, M. Ghirardi, Y.-Y. Huang, P. Nguyen, and E.R. Kandel. 1995. Steps toward a molecular definition of memory consolidation. In Memory distortion (ed. D.L. Schacter), Chapter 11, pp. 298-325. Harvard University Press, Cambridge, MA.

Abel, T., P. Nguyen, M. Barad, T.A.S. Deuel, E.R. Kandel, and R. Bourtchouladze. 1997. Genetic demonstration of a role for PKA in the late phase of LTP and in hippocampus-based long-term memory. Cell 88: 615-626.

Alberini, C., M. Ghirardi, R. Metz, and E.R. Kandel. 1994. C/EBP is an immediate-early gene required for the consolidation of long-term facilitation in Aplysia. Cell 76:1099-1114.

Alger, B.E. and R. Nicoll. 1982. Feed-forward dendritic inhibition in rat hippocampal pyramidal neurons studied in vitro. J. Physiol. (Lond.) 328" 105-123.

Amaral, D.G. 1993. Emerging principles of intrinsic hippocampal organization. Curr. Opin. Neurobiol. 3" 225-229.

Andersen, P., S.H. Sundberg, O. Sven, and H. Wigstr6m. 1977. Specific long-lasting potentiation of synaptic transmission in hippocampal slices. Nature 266: 736-737.

Bacskai, B.J., B. Hochner, M. Mahaut-Smith, S.R. Adams, B.-K. Kaang, E.R. Kandel, and R.Y. Tsien. 1993. Spatially resolved dynamics of cAMP and protein kinase A subunits in Aplysia sensory neurons. Science 260" 222-226.

Bailey, C.H. and E.R. Kandel. 1993. Structural changes accompanying memory storage. Annu. Rev. Physiol. 55: 397-426.

Bailey, C.H., M. Chen, F. Keller, and E.R. Kandel. 1992. Serotonin-mediated endocytosis of apCAM: An early step of learning-related synaptic growth in Aplysia. Science 256: 645-649.

Bartsch, D., M. Ghirardi, P.A. Skehel, K.A. Karl, S.P. Herder, M. Chen, C.H. Bailey, and E.R. Kandel. 1995. Aplysia CREB2 represses long-term facilitation: Relief of repression converts transient facilitation into long-term functional and structural change. Cell 83: 979-992.

Bito, H., K. Deisseroth, and R.W. Tsien. 1996. CREB phosphorylation and dephosphorylation: A Ca 2§ and stimulus duration-dependent switch for hippocampal gene expression. Cell 87" 1203-1214.

Bland, B.H. 1986. The physiology and pharmacology of

hippocampal formation theta rhythms. Prog. Neurobiol. 26" 1-54.

Bliss, T.V.P. and G.L. Collingridge. 1993. A synaptic model of memory: Long-term potentiation in the hippocampus. Nature 361 : 31-39.

Bliss, T.V.P. and G.L. Lomo. 1973. Long-lasting potentiation of synaptic transmission in the dentate area of the anesthetized rabbit following stimulation of the perforant path. J. Physiol. (Lond.) 232" 331-356.

Blitzer, R.D., T. Wong, R. Nouranifar, R. lyengar, and E.M. Landau. 1995. Postsynaptic cAMP pathway gates early LTP in hippocampal CA1 region. Neuron 15:1403-1414.

Bourtchouladze, R., B. Frenguelli, D. Cioffi, J. Blendy, G. Schutz, and A.J. Silva. 1994. Deficient long-term memory in mice with a targeted mutation of the cAMP responsive element binding (CREB) protein. Cell 79: 59-68.

Byrne, J.H., R. Zwartjes, R. Homayouni, S.S. Critz, and A. Eskin. 1993. Roles of second messenger pathways in neuronal plasticity and in learning and memory: Insights gained from Aplysia. Adv. Second Messenger Phosphoprotein Res. 27" 47-108.

Castellucci, V.F., E.R. Kandel, J.H. Schwartz, F.D. Wilson, A.C. Nairn, and P. Greengard. 1980. Intracellular injection of the catalytic subunit of cyclic AMP-dependent protein kinase simulates facilitation of transmitter release underlying behavioral sensitization in Aplysia. Proc. Natl. Acad. Sci. 77: 7492-7496.

Castellucci, V.F., H. Blumenfeld, P. Goelet, and E.R. Kandel. 1989. Inhibitor of protein synthesis blocks long-term behavioral sensitization in the isolated gill-withdrawal reflex of Aplysia. J. Neurobiol. 20: 1-9.

Chavez-Noriega, L.E. and C.F. Stevens. 1994. Increased transmitter release at excitatory synapses produced by direct activation of adenylate cyclase in rat hippocampal slices. J. Neurosci. 14:310-317.

Cremer, H., R. Lange, A. Christoph, M. Plomann, G. Vopper, J. Roes, R. Brown, S. Baldwin, P. Kraemer, S. Scheff et al. 1994. Inactivation of the N-CAM gene in mice results in size reduction of the olfactory bulb and deficits in spatial learning. Nature 367: 455-459.

Crow, T. and J. Forrester. 1990. Inhibition of protein synthesis blocks long-term enhancement of generator potentials produced by one-trial in vivo conditioning in Hermissenda. Proc. Natl. Acad. Sci. 87: 4490-4494.

Dash, P.K., B. Hochner, and E.R. Kandel. 1990. Injection of cAMP-responsive element into the nucleus of Aplysia sensory neurons blocks long-term facilitation. Nature 345" 718-721.

Davis, H.P. and L.R. Squire. 1984. Protein synthesis and memory: A review. Psychol. Bull. 96: 518-559.

Deisseroth, K., H. Bito, and R.W. Tsien. 1996. Signaling from

& 240






synapse to nucleus: Postsynaptic CREB phosphorylation during multiple forms of hippocampal synaptic plasticity. Neuron 16:89-101.

Desmond, N.L. and W.B. Levy. 1986a. Changes in the numerical density of synaptic contacts with LTP in hippocampal dentate gyrus. J. Comp. Neurol. 253: 466475.

- - . 1986b. Changes in the postsynaptic density with LTP in the dentate gyrus. J. Comp. Neurol. 253" 476-482.

Diamond, D.M., T.V. Dunwiddie, and G.M. Rose. 1988. Characterization of hippocampal primed burst potentiation in vitro and in awake rats. J. Neurosci. 8: 4079-4088.

Dostmann, W.R.G. 1995. Rp-cAMPS inhibits the cAMP-dependent protein kinase by blocking the cAMP-induced conformational transition. FEBS Lett. 375: 231-234.

Edwards, F.A. 1995. Anatomy and electrophysiology of fast central synapses lead to a structural model for LTP. Physiol. Rev. 75: 759-787.

Eichenbaum, H., M. Kuperstein, A. Fagan, and J. Nagode. 1987. Cue-sampling and goal approach correlates of hippocampal unit activity in rats performing an odor discrimination task. J. Neurosci. 7: 716-732.

Fox, S.E. and R.B. Ranck, Jr. 1981. Electrophysiological characteristics of hippocampal complex-spike cells and theta cells. Exp. Brain Res. 41 �9 399-410.

Frey, U., Y.-Y. Huang, and E.R. Kandel. 1993. Effects of cAMP simulate a late stage of LTP in hippocampal CA1 neurons. Science 260" 1661-1664.

Frey, U., M. Muler, and D. Kuhl. 1995. A different form of long-term potentiation revealed in tissue plasminogen activator mutant mice. J. Neurosci. 16." 2057-2063.

Gallin, W.J. and M.E. Greenberg. 1995. Calcium regulation of gene expression in neurons: The mode of entry matters. Curr. Opin. Neurobiol. 5: 367-374.

Ghirardi, M., O. Braha, B. Hochner, P.G. Montarolo, E.R. Kandel, and N. Dale. 1992. Roles of PKA and PKC in facilitation of evoked and spontaneous transmitter release at depressed and nondepressed synapses in Aplysia sensory neurons. Neuron 9: 479-489.

Glanzman, D.L., E.R. Kandel, and S. Schacher. 1990. Target-dependent structural changes accompanying long-term synaptic facilitation in Aplysia neurons. Science 249: 799-802.

Grastyan, E., K. Lissak, I. Madarasz, and H. Donhoffer. 1959. Hippocampal electrical activity during the development of conditioned reflexes. Electroenceph. Clin. Neurophysiol. 11 : 409-430.

Green, J.D., D.S. Maxwell, W.J. Schindler, and C. Stumpf. 1960. Rabbit EEG theta rhythm: Its anatomical source and

relation to activity in single neurons. J. Neurophysiol. 23: 403-420.

Hirsh, R. 1974. The hippocampus and contextual retrieval of information from memory: A theory. Behav. Biol. 12" 421-444.

Huang, Y.-Y. and E.R. Kandel. 1994. Recruitment of long-lasting and protein kinase A-dependent long-term potentiation in the CA1 region of hippocampus requires repeated tetanization. Learn. & Mem. 1" 74-82.

Huang, Y.-Y., X.-C. Li, and E.R. Kandel. 1994. cAMP contributes to mossy fiber LTP by initiating both a covalently-mediated early phase and macromolecular synthesis-dependent late phase. Cell 79: 69-79.

Huang, Y.-Y., E.R. Kandel, L. Varshavsky, E.P. Brandon, M. Qi, R.L. Idzerda, G.S. McKnight, and R. Bourtchouladze. 1995. A genetic test of the effects of mutations in PKA on mossy fiber LTP and its relation to spatial and contextual learning. Cell 83: 1211-1222.

Huang, Y.-Y., P.V. Nguyen, T. Abel, and E.R. Kandel. 1996a. Long-lasting forms of synaptic potentiation in the mammalian hippocampus. Learn. & Mem. 3: 74-85.

Huang, Y.-Y., M.E. Bach, H.-P. Lipp, M. Zhuo, D.P. Wolfer, R.D. Hawkins, L. Schoonjians, E.R. Kandel, J.-M. Godfraind, R. Mulligan, D. Collen, and P. Carmeliet. 1996b. Mice lacking the gene encoding tissue-type plasminogen activator show a selective interference with late-phase long-term potentiation in both Schaffer collateral and mossy fiber pathways. Proc. Natl. Acad. Sci. 93: 8699-8704.

Huerta, P.T. and J.E. Lisman. 1995. Bidirectional synaptic plasticity induced by a single burst during cholinergic theta oscillation in CA1 in vitro. Neuron 15" 1053-1063.

Impey, S., M. Mark, E.C. Villacres, S. Poser, C. Chavkin, and D.R. Storm. 1996. Induction of CRE-mediated gene expression by stimuli that generate long-lasting LTP in area CA1 of the hippocampus. Neuron 16" 973-982.

Kaang, B.-K., P.J. Pfaffinger, S.G.N. Grant, E.R. Kandel, and Y. Furukawa. 1992. Overexpression of an Aplysia Shaker K § channel gene modifies the electrical properties and synaptic efficacy of identified Aplysia neurons. Proc. Natl. Acad. Sci. 89: 1133-1137.

Kaang, B.-K., E.R. Kandel, and S.G.N. Grant. 1993. Activation of cAMP-responsive genes by stimuli that produce long-term facilitation in Aplysia sensory neurons. Neuron 10" 427-435.

Kandel, E.R. and W.A. Spencer. 1961. Electrophysiology of hippocampal neurons. II. After-potentials and repetitive firing. J. Neurophysiol. 24: 243-259.

Kase, H., K. Iwahashi, S. Nakanishi, Y. Matsuda, K. Yamada, M. Takahashi, C. Murakata, A. Sato, and M. Kaneko. 1987. K-252 compounds, novel and potent inhibitors of PKC and

& 241

L E A R N I N G M E M O R Y




Nguyen and Kandel

cyclic nucleotide-dependent protein kinases. Biochem. Biophys. Res. Commun. 142" 436-440.

Larson, J. and G. Lynch�9 1986. Induction of synaptic potentiation in hippocampus by patterned stimulation involves two events. Science 232" 985-988.

�9 1988. Role of NMDA receptors in the induction of synaptic potentiation by burst stimulation patterned after the hippocampal theta rhythm. Brain Res. 441 �9 111-118.

Larson, J., D. Wong, and G. Lynch. 1986. Patterned stimulation at the theta frequency is optimal for induction of hippocampal LTP. Brain Res. 368" 347-350.

Lee, M.G., J.J. Chrobak, A. Sik, R.G. Wiley, and G. Buzsaki. 1994. Hippocampal theta activity following selective lesion of the septal cholinergic system. Neuroscience 62" 1033-1047.

Lisman, J.E. and K.M. Harris. 1993. Quantal analysis and synaptic anatomy: Integrating two views of hippocampal plasticity. Trends Neurosci. 16:141-147.

Malenka, R.C. 1991. Postsynaptic factors control the duration of synaptic enhancement in area CA1 of the hippocampus. Neuron 6" 53-60.

Matthies, H. and K.G. Reymann. 1993. Protein kinase A inhibitors prevent the maintenance of hippocampal LTP. NeuroReport 4" 712-714.

Mayford, M., A. Barzilai, F. Keller, S. Schacher, and E.R. Kandel. 1992. Modulation of an NCAM-related adhesion molecule with long-term synaptic plasticity in Aplysia. Science 256' 638-644.

McCarren, M. and B.E. Alger�9 1985. Use-dependent depression of IPSPs in rat hippocampal pyramidal cells in vitro. J. Physiol. (Lond.) 53: 557-571.

Montarolo, P., P. Goelet, V.F. Castellucci, J. Morgan, E.R. Kandel, and S. Schacher. 1986. A critical period for macromolecular synthesis in long-term heterosynaptic facilitation in Aplysia. Science 234" 1249-1254.

Mori, Y., H. Matsubara, E. Folco, A. Siegel, and G. Koren. 1993. Transcription of a mammalian voltage-gated potassium channel is regulated by cAMP in a cell-specific manner. J. Biol. Chem. 268" 26482-26493.

Muller, R.U., J.L. Kubie, and J.B. Ranck. 1987. Spatial firing patterns of hippocampal complex-spike cells in a fixed environment. J. Neurosci. 7" 1935-1950.

Nazif, F.A., J.H. Byrne, and L.J. Cleary. 1991. cAMP induces long-term morphological changes in sensory neurons of Aplysia. Brain Res. 539" 324-327.

Nguyen, P.V. and E.R. Kandel. 1996. A macromolecular synthesis-dependent late phase of LTP requiring cAMP in the medial perforant pathway of rat hippocampal slices. J. Neurosci. 16:3189-3198.

Nguyen, P.V., T. Abel, and E.R. Kandel. 1994. Requirement of a critical period of transcription for induction of a late phase of LTP. Science 265:1104-1107.

Nguyen, P.V., C.M. Alberini, Y.-Y. Huang, M. Ghirardi, T. Abel, and E.R. Kandel. 1995. Genes, synapses and long-term memory. In Challenges and perspectives in neuroscience (ed. D. Ottoson), pp. 213-237. Elsevier, Oxford, UK.

O'Keefe, J. 1979. A review of the hippocampal place cells. Prog. Neurobiol. 13" 419-439.

O'Keefe, J. and J. Dostrovsky. 1971. The hippocampus as a spatial map: Preliminary evidence from unit activity in the freely-moving rat. Brain Res. 34" 171-175.

Olton, D.S., M. Branch, and P.J. Best. 1978. Spatial correlates of hippocampal unit activity. Exp. Neurol. 58" 387-409.

Otto, T., H. Eichenbaum, S.I. Wiener, and C.G. Wible. 1991. Learning-related patterns of CA1 spike trains parallel stimulation parameters optimal for inducing hippocampal LTP. Hippocampus 1 : 181-192.

Pavlides, G., Y. Greenstein, M. Grudman, and J. Winson. 1988. LTP in the dentate gyrus is induced preferentially on the positive phase of theta rhythm. Brain Res. 439" 383-387.

Polster, M., L. Nadel, and D. Schacter. 1991. Cognitive neuroscience analysis of memory: A historical perspective. J. Cognitive Neurosci. 3" 95-116.

Qi, M., M. Zhuo, B.S. Sk~lhegg, E.P. Brandon, E.R. Kandel, G.S. McKnight, and R.L. Idzerda. 1996. Impaired hippocampal plasticity in mice lacking the C[31 catalytic subunit of cAMP-dependent protein kinase. Proc. Natl. Acad. Sci. 93:1571-1576.

Qian, z., M.E. Gilbert, M.E. Colicos, E.R. Kandel, and D. Kuhl. 1993. Tissue-plasminogen activator is induced as an immediate-early gene during seizure, kindling and long-term potentiation. Nature 361 : 453-457.

Ranck, R.B., Jr. 1973. Studies on single neurons in dorsal hippocampal formation and septum in unrestrained rats. Exp. Neurol. 41 : 462-531.

Rose, G.M. and T.V. Dunwiddie. 1986. Induction of hippocampal LTP using physiologically patterned stimulation. Neurosci. Lett. 69" 244-248.

Scoville, W.B. and B. Milner. 1957. Loss of recent memory after bilateral hippocampal lesions. J. Neurol. Neurosurg. Psychiat. 20:11-21.

Squire, L.R. 1992. Memory and the hippocampus: A synthesis from findings with rats, monkeys, and humans. Psychol. Rev. 99" 195-231.

Staubli, U. and G. Lynch. 1987. Stable hippocampal LTP elicited by "theta" pattern stimulation. Brain Res. 435: 227-234.

L E A R N I N G & 242

M E M O R Y




& 243

O-BURST L TP IN THE M O U S E HIPPOCAMPUS

Thompson, L.T. and P.J. Best. 1989. Place cells and silent cells in the hippocampus of freely behaving rats. J. Neurosci. 9" 2382-2390.

Tully, T., T. Preat, S. C. Boynton, M. DeIVechhio. 1994. Genetic dissection of consolidated memory in Drosophila melanogaster. Cell 79: 35-47.

Vanderwolf, C.H. 1969. Hippocampal electrical activity and voluntary movement in the rat. Electroenceph. Clin. Neurophysiol. 26" 407-418.

Yin, J.C.P., J.S. Wallach, M. DelVecchio, E.L. Wilder, H. Zhuo, W.G. Quinn, and T. Tully. 1994. Induction of a dominant-negative CREB transgene specifically blocks long-term memory in Drosophila. Cell 79" 49-58.

Ylinen, A., I. Soltesz, A. Bragin, M. Penttonen, A. Sik, and G. Buzsaki. 1995. Intracelular correlates of hippocampal theta rhythm in identified pyramidal cells, granule cells, and basket cells. Hippocampus 5: 78-90.

Zola-Morgan, S., L.R. Squire, and D.G. Amaral. 1986. Human amnesia and the medial temporal region: Enduring memory impairment after a bilateral lesion limited to field CA1 of the hippocampus. J. Neurosci. 6" 2950-2967.

Received February 18, 1997; accepted in revised form April 9, 1997.

L E A R N I N G M E M 0 R Y




10.1101/lm.4.2.230Access the most recent version at doi: 1997 4: 230-243 Learn. Mem.

P V Nguyen and E R Kandel hippocampus.phase of LTP requiring cAMP in area CA1 of the mouse Brief theta-burst stimulation induces a transcription-dependent late

References

http://learnmem.cshlp.org/content/4/2/230.full.html#ref-list-1

This article cites 84 articles, 26 of which can be accessed free at:

ServiceEmail Alerting

click here.top right corner of the article or

Receive free email alerts when new articles cite this article - sign up in the box at the

http://learnmem.cshlp.org/subscriptionsgo to: Learning & Memory To subscribe to

Copyright © Cold Spring Harbor Laboratory Press


http://learnmem.cshlp.org/lookup/doi/10.1101/lm.4.2.230

http://learnmem.cshlp.org/content/4/2/230.full.html#ref-list-1

http://learnmem.cshlp.org/cgi/alerts/ctalert?alertType=citedby&addAlert=cited_by&saveAlert=no&cited_by_criteria_resid=learnmem;4/2/230&return_type=article&return_url=http://learnmem.cshlp.org/content/4/2/230.full.pdf

http://learnmem.cshlp.org/subscriptions



tetha-burst stimulation kandel cap 1

Documents