neuroprotective efficacy of lipoic acid in acrylamide...

American Journal of Life Science Researches

www.worldofresearches.com

100 Jan, 2015

© 2014, World of Researches Publication

Am. J. Life. Sci. Res. Vol. 3, Issue 1, 100-111, 2015

ISSN: 2332-0206 (Online) ISSN: 2375-7485 (Print)

Neuroprotective Efficacy of lipoic acid in Acrylamide-

Induced Neuropathy in Rats: Behavioral and

Histopathological evidence

Rashed R. Rashed and Hossam G. Tohamy

Department of Animal Husb. and Animal Wealth Develop. Fac. of Vet. Medicine

Alex. Univ. Egypt.

Department of Pathology Faculty of Veterinary Medicine Alexandria University.

Egypt.

*Corresponding Author: Rashed R. Rashed

Email: [email protected].

INTRODUCTION

Many chemicals with broad industrials, pharmaceutical and agricultural

application produce a neurotoxic syndrome in humans and experimental animals

involving weight loss, skeletal muscle weakness and ataxia1, 2and multifocal

Abstract: The primary objective of this investigation was to assess the neuroprotective efficacy

of lipoic acid in an acrylamide (ACR) neuropathy model in rats. To this end, albino males rat were

given 50 mg ACR in drinking water, with or without lipoic acid in the diet for four weeks. A group

of untreated controls was also included in the study. All ACR-treated animals exhibited

progressive neurotoxicity as judged by landing feet spread distance and learning ability (take

along time to solve the maze). While among lipoic acid co-administrated, lipoic acid didn't

prevent the effect of ACR but it slightly decreased the severity and delayed the appearance of

signs of ACR toxicity . ACR treatment decreased significantly the time spend feeding, drinking

frequencies, sitting time, walking and running frequencies and scratching frequencies while

increased significantly time spend lying. Moreover, ACR treatment increased frequencies of

exploration . From pathological point of view, this study revealed brain lesions in rats treated

with ACR alone and ACR with lipoic acid. The cerebrum lesions were characterized by the

presence of pyknotic neuron, central chromatolysis, satellitosis, neuronophagia and finally focal

gliosis. The cerebellum of rats treated with ACR alone exhibited congestion of blood vessel and

pyknotic purkinje cells while in rats received ACR and lipoic acid showed mild pyknotic purkinje

cells.

Keywords: Neuroprotective, Efficacy, lipoic acid, Acrylamide-Induced Neuropathy, Rats,

Behavioral, Histopathological evidence.

ORIGINAL ARTICLE Received 9 Oct. 2014 Accepted 14 Dec. 2014

Neuroprotective Efficacy of lipoic acid in Acrylamide-Induced …

neurofilamentous swelling and eventual degenerations beginning from the distal

ends of peripheral nerve axons have been traditionally thought as hallmark

morphological features of acrylamide (ACR)-induced neuropathy3 . The initial

target of ACR appears to be the nerve terminals in both central and peripheral

nervous systems, resulting in autonomic, behavioral, sensory, motor

disturban es4. Mechanisms underlying the diverse neurotoxicity remain 7

controversial. approaches to reducing its toxic effects should be established.

Morphologic studies have suggested that these functional effects are associated

with distal axon injury in central and peripheral nervous systems. This type of

toxic neuropathy and is characterized by multifocal swelling of distal axon regions

and eventual retrograde axon degeneration with sparing of more proximal

sections . ACR monomer considered to be prototypical among chemicals that 1

produce distal axonopathy found that all ACR treated animals exhibited hind 5,6

limb splay, ataxia and muscle weakness with a progressive increase in gait scores

and a progressive decrease in weight studied the efficacy of eugenol and 7

isoeugenol in ACR induced neuropathy in rats and found that rats receiving ACR a

lone developed progressive gait abnormalities during the experimental period.

Among rats receiving the spine active principles the onset of gait abnormalities

were delayed band occurred from week 3 onwards indicating their protective

effect. However after 4 weeks, all ACR treated rats developed characteristic

symptoms such as foot splay, twisting hind limbs, difficulty in ambulation and

increase landing foot spread distance. The pattern and strength of synaptic

connections are widely believed to code memory traces. Long-term potentiation

of synaptic strength (LTP) is correlated with behaviorally relevant memory

function: reductions in LTP cause memory impairments , whereas increases in 8,9

LTP are associated with enhancement of learning and memory . However, 10,11,12

the ability to store new information in neural networks depends on the degree of

plasticity of synaptic connections, as well as the number of available connections.

Therefore, number of synapses should be critical for learning and memory too.

Indeed, loss of synapses is correlated with age-dependent memory decline in

rats. , while hormones and neuropeptides, such as estrogen , 13,14,15 16

neurotophins insulin/IGF , and ghrelin , increase synaptic density and 17 , 18,19 18

improve memory. Diet, in conjunction with environmental factors, has a crucial

role in shaping brain cognitive capacity . Therefore, searching for dietary 20

components that can increase the number and plasticity of synapses might yield

new strategies to enhance learning and memory functions.

MATERIALS AND METHODS

This experiment was carried out in the laboratory animal unit of the

department of animal husbandry and animal wealth development, faculty of

veterinary medicine, Alexandria University, Egypt, during the period from

February to March 2014.

Animals : 36 male albino rats obtained from department of forensic

medicine, faculty of veterinary medicine, Alexandria University, Egypt, and

Rashed and Tohamy, 2015

102 January 2015

average weight about 160gm were randomly divided into 4 equal groups and

distributed as 9 rats/cage. The first group control group and the second received

50mg acrylamide/kg body weight. In drinking water, the third received 50mg

acrylamide in drinking water and lipoic acid in basal diet and the fourth group

received lipoic acid in basal diet. Acrylamide was dissolved at the concentration of

0.02% (w/v; corresponding to 2.8mM) in distilled water for administrations' and

lipoic acid was given at dose 0.5% (wt/wt) mixed into basal diet. Animals were

housed in open system door and provided with galvanized wire cage batteries

(55×45×30 cm/cage) and 14 -16 h of light/day. Daily temperature was ranged

between 16 to 25o C and 50 to 60% relative humidity. Food was provided ad-

libtium with commercial pelted diet contained the following nutrients. Crude

protein 16.3%, Crude fiber 3.5%, Fat 6.8%. Rats fed the ration from feeding trough

and drinking water from water trough.

Behavioral tests:

I. Behavioral observations : Animals were identified by using color paint on

their back and the behavioral observation were carried out during day light,

using focal sample according to and the behavior patterns recorded are: 21

A. Ingestive behavior: A.1.Feeding:(min/hr.): The time spent (min.) by rats in

eating food. A.2. drinking:( freq/hr.): Frequency of taking water from water

trough.

B. Resting behavior: B.1.Lying :( min/hr.): The time spent (min) by rats in a

lying or sleeping. B.2.sitting up :( min/hr.): Either idles standing or doing

some maintenance activities.

C. Movement activities: C.1: Walking :( freq/hr.): Slow symmetrical gait taking

one step or more. C.2. running :( freq/hr.): Fast movement by the rat.

D. Body care behaviors: D.1.Scratching :( freq/hr.): Include friction of head

and/or shoulder region by hind feet. D.2. Licking: (freq/hr): licking of the body by

their tongue.

E. Investigatory behavior :( freq/hr): In investigatory behavior the rats

explore the surrounding environment by sniffing feeding and water troughs,

walls, floor or others.

II. Behavioral index:

II.1. Landing foot spread distance (LFSD): LFSD was measured as the fourth

digit of the hind limbs of the rats was colored with ink and dropped from a

height 30 cm in a horizontal position. The distance between the fourth

digits of each hind limb on landing was measured. The procedure was

repeated three times for each rat and the average was recorded. The

mean± SE was calculated for each group.

II.2. learning ability: ability to solve maze II.2.1. The Morris water maze is a 9

large round tub of opaque water with powdered milk) with two small

hidden platforms located 1-2cm under water's surface. The rat is placed on

a start platform. The rat swims around until it finds the other platform to


stand on. External cues, such as patterns or the standing researcher, are

placed around the pool in the same spot every time to help the rat learn

where the end platform is. The researcher measures how long it takes for a

rat to find hidden plat form.

2.2: Plus Maze: Rat was allotted individually to the center of the maze and

measure the time elapsed to the closed arm and the time elapsed to reach the

open arm and the frequencies in the close and the open arm for each rat in 3

minutes.

III. Pathological indication: The tissues were fixed in 10% buffered formalin

solution and embedded in paraffin. Tissue sections of 3 -5 µm thickness

were stained with hematoxylin and eosin. The slides were then evaluated

under light microscope.

1.3: Statistical analysis:

The behavioral were analyzed by Statistical Analysis System , Nested 22

design analysis of variance. b-The leg splay and the time elapsed in both

plus and water maze were analyzed using Statistical analysis system .The 22

frequencies in closed and open arms of plus maze and the scores of

pathological were analyzed using wilcoxon scores (rank sums) for variables

frequencies.

RESULTS

Table 1: Showing the effect of acrylamide with or without lipoic acid on behavior of rats.

Treatment feeding Min/hr Drinking

Freq/hr

Sitting up Min/hr

Control 17.89±2.90a 1.05± 0.15a 34.74±2.69a

Acrylamide 12.80±2.00b 0.03±0.01b 15.60±2.10c

Acrylamide+lipoi

c

11.20±2.37b 0.24±0.09b 22.80±2.37b

lipoic 12.60±1.16b 0.24±0.09b 33.00±1.85a

Treatment Lying Min/hr Walking Freq/hr Running Freq/hr

Control 7.47±1.16b 4.37±0.65a 0.58±0.13a

Acrylamide 31.60±3.04a 0.08±0.01b 0.00±0.00b

Acrylamide+lipoi

c

26.08±3.17a 0.80±0.18c 0.08±0.06bc

lipoic 14.40±1.81b 2.88±0.43b 0.28±0.09b

Treatment Licking Freq/hr Scratching Freq/hr Exploration other

Freq/hr

Control 1.32±0.23a 1.58±0.31a 0.16±0.08a

Acrylamide 0.56±0.13b 0.24±0.09b 0.00±0.00b

Acrylamide+lipoi

c

0.08±0.06c 0.24±0.09b 0.08±0.06ab

lipoic 0.16±0.08c 0.52±0.15b 0.04±0.03ab

Treatment Exploration cage


104 January 2015

Freq/hr

Control 0.37±0.10a

Acrylamide 0.40±0.13a

Acrylamide+lipoi

c

0.00±0.00b

lipoic 0.16±0.08ab

All values are means ±SE, n=9

Values with different letters at the same raw are significantly different at (p<0.05)

Table 1 shows the effect of acrylamide on behavior of male rats as the control

group has the highest feeding time and significantly more than acrylamide treated

rats while the lowest feeding time observed in acrylamide + lipoic acid group.

Moreover, addition of acrylamide in water decreases significantly drinking

frequencies than control groups. As the sitting up time increased in control and

lipoic acid groups it decreased in both acrylamide and acrylamide + lipoic acid

groups on contrast the lying time increased in acrylamide and Acrylamide+ lipoic

acid groups due to neurotoxic effect of acrylamide and muscle weakness lead the

rat unable to stand so taking resting time in lying position.

The number of walking and running frequencies were found to be decreased

significantly in both acrylamide and acrylamide + lipoic than control and lipoic

acid groups this because neurotoxic effect and muscles weakness and the gait

inability to support body weight, dragging hind limbs, inability to rear.

Licking was higher in control group followed by acrylamide treated group

while the lowest frequencies observed in acrylamide + lipoic acid groups, on

contrast scratching frequencies decreased in both acrylamide and acrylamide +

lipoic acid groups. However other exploration was lower in control group on

contrast the cage exploration was higher in ACR group followed by control group

and the lowest observed in ACR+ lipoic acid group

Table 2 : Effect of acrylamide with or without lipoic acid on learning ability and landing leg

spread distance of rats.

Treatment Latency to

solve water

maze

(seconds).

Latency in open

arm plus maze

at 3rd week

(seconds)

Latency in

closed arm

plus maze at

3rd week

(seconds)

Latency in

open arm

plus maze at

4th week

(seconds)

Control 6.00±0.41b 126.0± 13.16a 54.0±12.97b 114.0±8.54a

Acrylamide 12.50±1.44a 48.0±14.24b 132.0±14.2a 65.0±8.54b

Acrylamide+lipoic 10.50±0.96ab 35.6±6.96b 120.8±18.98a 18.0 ± 6.65c

lipoic 6.40±2.11b 142.6± 5.91a 37.4± 5.69b 120.8 ± 6.32a

Treatment Latency in closed arm plus maze

at 4th week seconds

Landing leg

spread

distance (cm)


Control 66.0±13.92c 6.63±0.26b

Acrylamide 115.0± 8.54b 9.75±1.26a

Acrylamide+lipoic 162.0± 6.64a 8.50±0.63a

lipoic 59.2± 6.32c 5.56±0.22b

All values are means ±SE, n=10

Values with different letters at the same raw are significantly different at (p<0.05)

Table 3: Wilcoxon scores (rank sums) for variables frequencies of acrylamide with or without

lipoic acid for open and closed arm in plus maze during the third and the fourth

week after treatment.

Treatment Freq open 3rd

week

Freq closed 3rd

week

Freq open 4th

week

Freq closed 4th

week

Control 15.50 12.80 13.60 13.80

ACR 7.00 5.50 10.20 10.60

ACR+Lipioc 8.10 12.00 4.80 8.80

Lipoic 11.40 11.70 13.40 8.80

Chi-Square 6.6981 5.2235 8.3382 3.3537

DF 3 3 3 3

Pr > Chi-

Square

0.0822 0.1561 0.0395* 0.3402

* Significantly difference from ACR treated group p≤0.05.

Learning ability: 1. Morris water maze: Rat has a well-developed central

nervous system and memory system and has the ability to solve maze so in

control group rats solve water maze in a little time 6.00± 0.41 Sec while the

longer time taken by ACR group was 12.50 ±1.44 Sec followed by ACR+ lipoic

acid group then group. 2. Plus maze: ACR treated group take a long time to

solve plus maze as the rat take a long time in the closed arm 132.0±14.2 sec

after exposure by three weeks while take short time in the open arm

48.0±14.24 sec as compared with control group 126.0± 13.16 sec in open and

54.0±12.97 sec in closed arm.

After exposure by 4 weeks the rats in lipoic + ACR spent a short period

in open arm 18.0 ± 6.65 sec and a long period 162.0± 6.64 sec in the closed arm

while in ACR treated group was 65.0±8.54 sec in open arm and 115.0± 8.54 sec

in closed arm moreover the highest time observed in open arm was for lipoic

acid 120.8 ± 6.32sec and the lowest time 59.2± 6.32 sec in closed arm. Data for

the frequencies in open and in closed arm of plus maze presented in table(3)

revealed that higher frequency in open arm was for control groups after 3 and

4 week followed by lipoic acid group and the lowest frequencies observed in

the treated ACR and ACR+ lipoic acid group.


106 January 2015

Landing Foot Spread Distance (LFSD): A significant and a progressive

increase in landing feed spread distance LFSD measurement were evident

among ACR administered rats. Both ACR and ACR+ lipoic showed the LFSD

9.75±1.26cm and 8.50±0.63cm respectively while in control and lipoic groups

was 6.63±0.26cm and 5.56±0.22cm respectively.

Fig. (1): Photomicrograph of rate cerebrum treated with ACR (HE X. 250). (A) Mild

perivascular cuffing (arrows) with minor hemorrhage. (B) Shrunken, eosinophilic

cytoplasm, hyper chromatic or pyknotic nuclei and widening neuropils. (C&D) central

chromatolysis (arrow) and ghost neuron (arrow head). (E) Satellitosis around

degenerated neurons (arrow head) and neuronophagia (arrows). (F) Focal gliosis (A).


Cerebrum:

Cerebrum of ACR treated rates showed moderate perivascular monocytic

aggregation (fig.1A), small shurenked pyknotic neuron with widening neuropills

(fig. 1B). Central chromatolysis where the chromatolytic cells are swollen and

rounded, rather than having the normal angulated appearance and the nucleus

becomes eccentric. Nissl granules clear from the central region of the cell body,

leaving this zone with a smooth ground-glass appearance (Fig. 1 C&D). The

cerebral cortex in ACR-intoxicated rats exhibited Perineuronal satellitosis as

surrounding small degenerated neurons, the microglia invade and phagocytize

the degenerated neurons in the process called neurophagia (fig. 1E) and focal

gliosis (fig. 1F).

Fig. (2): Photomicrograph of rate cerebellum stained with hematoxylin and eosin (HE X. 250). (A)The

histoarchitecture of the cerebellum is intact in the control rate. (B) Congestion of blood vessel (arrow) (C)

moderate to severe pyknotic Purkinje cells (arrowheads) in rates received ACR. (D) mild pyknotic purkinje

cells (arrowheads) in rate received ACR in addition Lipoic acid


108 January 2015

Cerebellum:

Cerebellum of control group showed normal histology (fig. 2A). While in ACR

toxicated rats showed congestion of blood vessel (fig. 2 B) and moderate to

severe pyknotic Purkinje cells (fig. 2 C). Moreover, mild pyknotic Purkinje cells (fig.

2 D) was noticed in Lipoic acid supplemented rats

Table 4: Wilcoxon scores (rank sums) for incidence and Severity of histopathological Lesions.

Lesions Incidence and Severity of Histopathological Lesions

Treatment ACR ACR+Lipoic

Organ/ histopathological changes

pyknotic nuclei and widening

neuropils

10 (0/ 2/ 5/ 3) 10 (1/5/4/0) *

central chromatolysis

(±/+/++/+++)

10 (0/ 1/ 6 / 3) 10 (1/ 5/ 4/ 0)*

ghost neuron 10 (0/ 2/ 4/ 4) 10(3/ 4/ 3/ 0)**

Cerebrocortical satellitosis 10 (0/ 4/ 6/ 0) 10 (5/ 4/ 1/ 0)

Cerebrocortical neurophagia 10 (0/ 2/ 3 / 5) 10 (6/ 3/ 1/ 0)**

Perivascular monocytic

aggregations

10 (3/ 3 /4 / 0) 10 (5/ 3/ 2/ 0)

Cerebellum: Congestion of

blood vessels

10 (0/ 3/ 4/ 3) 10 (4/ 3/ 3/ 0)*

Pyknotic pyrkanji cells 10 (1/3 /4 / 2) 10(4/ 5/1 / 0)*

Normal (-) Mild (+) Moderate (++) Severe (+++)

*,**Significantly difference from ACR alone treated group p≤0.05, p ≤ 0.01

Number of animal examined (Minimal (±/)/ Mild (+) /Moderate (++)/ Severe (+++))

The tissues were fixed in 10 % buffered formalin solution and embedded in

paraffin. Tissue sections of 3 -5 µm thickness were stained with hematoxylin and

eosin. The slides were then evaluated under light microscope

DISCUSSION

Behavior patterns: Ataxia and hind limb muscle weakness are the primary

neurological defects associated with induction of distal axonopathy by chemicals

such as ACR . The value and effectiveness of research concerning axonopathic 5,1

mechanisms can be improved by assessment of onset, duration and magnitude of

neurological defects. Such information provides a rational basis for selection of

experimental endpoints that accurately reflect various stages of neurotoxicity and

subsequent data interpretation where establishing the path physiologic relevance

of biochemical/ molecular parameter in critical. Several neurological measures (e.g.

gait, hind limb foot splay distance) have been used as indices of developing

neurotoxicity in previous investigations, however, the change in behavior, learning

ability and using of lipoic acid as a protective agent were studied in our research.

The results of this study suggest that rat behavior were affected by acrylamide as

the feeding time was found to be decreased in both acrylamide and acrylamide +


lipoic acid groups moreover the drinking frequency were lower in rats of both

groups. Sitting up time was also lower in both acrylamide and lipoic acid +

acrylamide groups while taking much resting time in lying position this because

acrylamide affect nerve axons and caused muscle weakness leading the rats

unable to support their bodies during sitting up so take more resting time in lying

position these results similar to those obtained by whose found that the initial 4

target of ACR appears to be the nerve terminals in both central and peripheral

nervous systems, resulting in autonomic, behavioral, sensory, motor disturbances

and muscle weakness. Movement activities (walking and running frequencies) were

higher in control and lipoic acid groups than acrylamide and acrylamide + lipoic

acid groups and the difference was significantly different as the ACR caused

progressive muscle weakness and nerve injuries resulting in motor disturbances

similar results obtained by . Licking was higher in control group followed by 4

acrylamide treated group while the lowest frequencies observed in acrylamide +

lipoic acid groups, on contrast scratching frequencies decreased in both acrylamide

and acrylamide + lipoic acid groups this because the ACR affect nerve terminals

and caused muscle weakness so the ability of rat to using hind limbs in scratching

their bodies decreased while increased using tongue in licking their bodies.

However other exploration was lower in control group on contrast the cage

exploration was higher in ACR group followed by control group and the lowest

observed in ACR+ lipoic acid group this was for ACR affect the memory system so

the rat ignore the land marks of the surrounding environment leading to increased

the exploration to investigate the surrounding environment.

Landing Hind limb Foot Splay In the present study landing hind limb foot

splay distance was also shown to be a sensitive index of developing ACR-induced

neurotoxicity. Our findings are consistent with earlier research that characterized

this neurologic end point during different ACR exposure conditions . intoxication 1

at the 50 mg/kg per day dose-rate significantly increased landing hind limb foot

splay, i.e. rats in both the exposure ACR and ACR+Lipoic exhibited initial foot

spread distances of approximately (9.75±1.26cm vs. 8.50±0.63cm respectively)

while in control group decreased to 6.63±0.26cm this results are in agreement with

the findings of . 4,7

Learning ability; Rats have a will developed memory system as they have the

ability to solve maze as in control groups rats take a shorter time to solve Morris

water maze than ACR treated group which has neurotoxic effect and caused a

nerve damage and these results emphasized that Long-term potentiation of

synaptic strength (LTP) is correlated with behaviorally relevant memory function:

reductions in LTP cause memory impairments , whereas increases in LTP are 8,9

associated with enhancement of learning and memory . However, the ability to 11,12

store new information in neural networks depends on the degree of plasticity of

synaptic connections, as well as the number of available connections. Therefore,

number of synapses should be critical for learning and memory too. Indeed, loss of

synapses is correlated with age-dependent memory decline in rats . 14,15

Pathological and histopathological changes


110 January 2015

In the present study, the cerebrum of ACR treated rate showed small

shurenked pyknotic neuron with widening neuropills, Central chromatolysis is best

appreciated in large neurons of some of the brain stem nuclei, in the spinal motor

neurons, and peripheral ganglia. Cerebrocortical degenerated neuron undergo

satellitosis, neurophagia and focal gliosis. The cerebellum exhibited moderate to

severe pyknotic Purkinji cells. Finally we found that supplementation of Lipoic acid

not give the protection against ACR induced neurotoxicity but only decrease the

severity of the histopathological lesions.

Conclusions

In this study lipoic acid didn't prevent the neurotoxic effects of acrylamide but it

decreased the severity and delayed the appearance of the signs. More research are

needed to follow the neuroprotective effect of lipoic acid with a small doses of

acrylamide.

REFERENCES

1. Spencer, P.S., Schaumburg, H.H. (1974). A review of acrylamide

neurotoxicity. Part II. Experimental animal neurotoxicity. Phytother

Res;16:256-260.

2. Le Qusene, P.M. (1985). Clinical and morphological finding in acrylamide

toxicity. Neurotoxicology ; 6:17-24.

3. LoPachin, R.M., & Lehning, E.J. (1994). Acrylamide induced distal axon

degeneration: a proposed mechanism of action. Neur-toxicology; 15:247-

259.

4. LoPachin, R.M., Balaban, C.D., Ross, J.F. (2003). Acrylamide axonapathy

revisited.Toxicol. Apppl.Pharmacol;188:135-153.

5. Asbury, A.K., & Brown, M.J. (1980). The evolution of structural changes in

distal axonopathy. In: Spencer PS, Schaumberg HH, editors. Experimental

and clinical neurotoxicology, 1st ed. Baltimore, MD: Williams & Wilkins Co:

179-92.

6. Kyoung, Y.L., Makoto, S., Kuroiwa. H.T., Kaoru, I., Hiroshi, N., Tokutaro, M., &

Masao, H. (2005). Chemoprevention of acrylamamide toxicity by

antioxidative agents in rats-effective suppression of testicular toxicity by

phenylethyl isothiocyanate. Oragan toxicicity and mechanisms; 79:531-451.

7. Sathya, N. Prasad. (2013) Neuroprotective efficacy of eugenol and

isoeugenol in acrylamide induced neuropathy in rats:behavioral and

biochemical evidence.Neurochemical res; 38:330-345.

8. Barnes, C.A. (1979). Memory deficits associated with senescence: a

neurophysiological and behavioral study in the rat. J. Comp. Physiol.

Psychol; 93, 74–104.

9. Morris, R.G., Anderson, E., Lynch, G.S., and Baudry, M. (1986). Selective

impairment of learning and blockade of long-term potentiation by an N-

methyl-D-aspartate receptor antagonist, AP5. Nature;319, 774–776.


10. Lee, Y.S., and Silva, A.J. (2009). The molecular and cellular biology of

enhanced cognition. Nat. Rev. Neurosci; 10, 126–140.

11. Martin, S.J., Grimwood, P.D., & Morris, R.G. (2000). Synaptic plasticity and

memory: an evaluation of the hypothesis. Annu. Rev. Neurosci; 23, 649–

711.

12. Nakazawa, K., McHugh, T.J., Wilson, M.A., and Tonegawa, S. (2004). NMDA

receptors, place cells and hippocampal spatial memory. Nat. Rev. Neurosci;

5, 361–372

13. Burke, S.N., & Barnes, C.A. (2006). Neural plasticity in the ageing brain. Nat.

Rev. Neurosci; 7, 30–40.

14. Smith, T.D., Adams, M.M., Gallagher, M., Morrison, J.H., & Rapp, P.R. (2000).

Circuit-specific alterations in hippocampal synaptophysin immunoreactivity

predict spatial learning impairment in aged rats. J. Neurosci; 20, 6587–

6593.

15. Wilson, I.A., Gallagher, M., Eichenbaum, H., & Tanila, H. (2006).

Neurocognitive aging: prior memories hinder new hippocampal encoding.

Trends Neurosci; 29, 662–670.

16. Li, C., Brake, W.G., Romeo, R.D., Dunlop, J.C., Gordon, M., Buzescu, R.,

Magarinos, A.M., Allen, P.B., Greengard, P., Luine, V., & McEwen, B.S. (2004).

Estrogen alters hippocampal dendritic spine shape and enhances synaptic

protein immunoreactivity and spatial memory in female mice. Proc. Natl.

Acad. Sci. USA ; 101, 2185–2190.

17. Vicario-Abejo´, n.C., Owens, D., McKay, R., & Segal, M. (2002). Role of

neurotrophins in central synapse formation and stabilization. Nat. Rev.

Neurosci;3, 965–974.

18. Lichtenwalner, R.J., Forbes, M.E., Bennett, S.A., Lynch, C.D., Sonntag, W.E., &

Riddle, D.R. (2001). Intracerebroventricular infusion of insulin-like growth

factor-I ameliorates the age-related decline in hippocampal neurogenesis.

Neuroscience 107, 603–613.

19. O’Kusky, J.R., Ye, P., & D’Ercole, A.J. (2000). Insulin-like growth factor-I

promotes neurogenesis and synaptogenesis in the hippocampal dentate

gyrus during postnatal development. J. Neurosci; 20, 8435–8442.

20. Go´ mez-Pinilla, F. (2008). Brain foods: the effects of nutrients on brain

function. Nat. Rev. Neurosci; 9, 568–578.

21. Martin, P. & Fars, P. B. (1986). Measuring behavior an introductory guide,

Pp. 48.58 Cambridge, University press, Cambridge, London.

neuroprotective efficacy of lipoic acid in acrylamide...

Documents