maternal exposure to bacterial endotoxin during pregnancy enhances amphetamine-induced locomotion...
TRANSCRIPT
Maternal exposure to bacterial endotoxin during pregnancyenhances amphetamine-induced locomotion and startle responses in
adult rat offspring
Marie-Eve Fortier, Ridha Joober, Giamal N. Luheshi, Patricia Boksa*
Departments of Psychiatry and Neurology and Neurosurgery, McGill University, Douglas Hospital Research Centre, 6875 LaSalle Boulevard,
Verdun, Quebec, Canada H4H 1R3
Received 24 March 2003; received in revised form 10 August 2003; accepted 15 October 2003
Abstract
An increased incidence of schizophrenia has been associated with several perinatal insults, most notably maternal infection dur-ing pregnancy and perinatal hypoxia. This study used a rat model to directly test if maternal exposure to bacterial endotoxin(lipopolysaccharide, LPS) during pregnancy alters behaviors relevant to schizophrenia, in offspring at adulthood. The study also
tested if postnatal anoxia interacted with gestational LPS exposure to affect behavior. At adulthood, offspring from dams admi-nistered LPS on days 18 and 19 of pregnancy showed significantly increased amphetamine-induced locomotion, compared tooffspring from saline-treated dams. A period of anoxia on postnatal day 7 had no effect on amphetamine-induced locomotion and
there was no interaction between effects of gestational LPS and postnatal anoxia on this behavior. Offspring from LPS-treateddams also showed enhanced acoustic startle responses as adults, compared to offspring from saline-treated dams. In offspringtested for pre-pulse inhibition (PPI) of acoustic startle and for apomorphine modulation of PPI, no effects of either gestationalLPS or of postnatal anoxia and no interactions between LPS and anoxia were observed. It is concluded that maternal LPS exposure
during pregnancy in the rat may be a useful model to study mechanisms responsible for effects of maternal infection on behaviorsrelevant to schizophrenia, in offspring.# 2003 Elsevier Ltd. All rights reserved.
Keywords: Behavior; Dopamine; Endotoxin; Perinatal; Hypoxia; Lipopolysaccharide; Maternal infection; Schizophrenia; Startle
1. Introduction
Substantial epidemiologic evidence points to in uteroand perinatal insults as etiological factors in schizo-phrenia. In particular, increased incidence ofschizophrenia has been observed following maternalinfections with either viral or bacterial pathogens duringpregnancy (e.g., Watson et al., 1984; Barr et al., 1990;O’Callaghan et al., 1994; Suvisaari et al., 1999; Brown etal., 2000). This suggests that infection during pregnancymight contribute to the pathophysiology of schizo-phrenia through adverse effects on brain development.In this context, animal models may prove useful todirectly test if infection during gestation produces longterm changes in CNS functions relevant to schizo-phrenia.
Several groups have administered viruses to neonatalrodents shortly after birth to model effects of perinatalinfection on later behavior (Solbrig et al., 1998; Roths-child et al., 1999; Engel et al., 2000; Pletnikov et al.,2002), while one recent study has administered humaninfluenza virus to mice during gestation on embryonicday 9.5 (E9.5) resulting in offspring with deficits insocial interaction and other behaviors relevant to schi-zophrenia (Shi et al., 2003). Modeling of bacterialinfections during pregnancy has recently been approa-ched by using maternal administration of lipoly-saccharide (LPS), a component of the cell wall of gramnegative bacteria (Borrell et al., 2002). Systemic admin-istration of LPS is a widely accepted model of infection,resulting in reproducible production of fever andinduction of pro-inflammatory cytokines, the mainchemical mediators of the host defense response toinfection (Luheshi and Rothwell, 1996; Larson andDunn, 2001). Compared to live pathogens, use of LPSconfers control over time course and dose of endotoxin
0022-3956/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpsychires.2003.10.001
Journal of Psychiatric Research 38 (2004) 335–345
www.elsevier.com/locate/jpsychires
* Corresponding author. Tel.: +1-514-761-6131x5928; fax: +1-
514-762-3034.
E-mail address: [email protected] (P. Boksa).
exposure, thus reducing potential variability and allow-ing identification of windows of vulnerability and dose-related effects.
Therefore, the first aim of this study was to test if LPSadministration to rat dams during pregnancy produceslong term changes, in offspring, in behaviors relevant toschizophrenia. The behaviors tested were amphetamine(AMPH)-induced locomotion, pre-pulse inhibition(PPI) of acoustic startle and apomorphine disruption ofPPI. In rodents, locomotion in response to low doseAMPH is routinely used as a behavioral indicator ofactivity in the mesolimbic dopamine (DA) pathway(Castall et al., 1977; Porrino et al., 1984), and there isnow compelling in vivo imaging evidence for a dysre-gulation of presynaptic striatal dopaminergic functionin the genesis of positive symptoms of schizophrenia(Laruelle et al., 1996, 1999; Breier et al, 1997; Abi-Dargham et al., 1998; Laruelle and Abi-Dargham,1999). PPI is a form of sensorimotor gating that is con-served across species and is defined as an inhibition ofthe startle response when a low intensity stimulus, theprepulse, precedes the startling stimulus. Deficits in PPIin schizophrenic compared to control subjects have beenreproducibly observed in numerous studies (Braff et al.,2001). Strong evidence indicates that PPI is regulated bynucleus accumbens dopaminergic mechanisms, and dis-ruption of PPI by DA agonists like apomorphine is afrequently used animal model of PPI deficits in schizo-phrenic subjects (Geyer et al., 2001).
In addition to maternal infection during pregnancy,obstetric complications, particularly those involvingneonatal hypoxia at the time of labor and delivery, arealso associated with an increased incidence of schizo-phrenia (McNeil et al., 2000). This raises the question asto whether there might be interactive or additive effectsof maternal infection and perinatal hypoxia on CNSfunction. Support for such an interaction has been pro-vided in animal models of brain injury, where priorexposure to LPS has been reported to alter the degree ofdamage incurred by a later hypoxic-ischemic insult,under some conditions. For example, in adult rats, LPSpriming 3-4 days before middle cerebral artery occlusionprovides protection against hypoxia-ischemia inducedCNS injury, through a mechanism mediated by thecytokine, tumor necrosis factor-a (TNF-a) (Tasaki etal., 1997; Dawson et al., 1999). In contrast, LPS admi-nistered to immature rats 1–4 h before hypoxic-ischemicinsult actually enhances neuronal cell damage (Eklind etal., 2001; Coumans et al., 2003). It is not known if LPSpre-exposure might interact with milder global hypoxicinsult in immature brain to affect more subtle CNSfunctions, and whether this interaction may occur overa longer time interval of several days between insults.Thus, the second aim of this study was to test if gesta-tional LPS and later global anoxic insult, at postnatalday 7, interact to affect behavior in adult offspring.
The experimental design of the current study con-sisted of administering either LPS or saline to rat damson days 18 and 19 of pregnancy (E18, E19). On post-natal day 7 (P7), male offspring from these dams wereplaced in a chamber containing either 100% N2 (anoxia)or air (air control) for 7 min. At adulthood, the off-spring were behaviorally tested for AMPH-inducedlocomotion, acoustic startle responses, PPI of startleand apomorphine disruption of PPI.
The epidemiology of schizophrenia suggests that thelate 2nd trimester of human pregnancy may be a periodof increased fetal vulnerability to maternal infection(Barr et al., 1990; O’Callaghan et al., 1994; Suvisaari etal., 1999; Brown et al., 2000). Rat CNS is devel-opmentally less mature than is human, with rat brain atapproximately postnatal day 7–14 estimated to bedevelopmentally equivalent to newborn human brain(Romijn et al., 1991; Avishai-Eliner et al., 2002). ThusLPS should be administered near term in the pregnantrat (gestation length=22 days) to mimic late 2nd tri-mester infection in humans. However rats (and otherspecies) have high mortality rates very near term (E20–E22) in response to doses of LPS that produce fever andno mortality in non-pregnant rats and in pregnant ratsbefore E20 (Martin et al., 1995). Thus, in the currentexperiments LPS was administered on E18 and E19, tomimic an acute maternal infection during pregnancy.Anoxia was delivered on P7 since rat brain at this age isnearing the developmental stage of the human brain atbirth, a time when humans experience labor and deliv-ery complications involving hypoxia that are associatedwith increased schizophrenia. In addition, rat brainshows enhanced vulnerability to hypoxic damage at thisearly postnatal time (Slotkin et al., 1986; Jensen et al.,1991; Yager et al., 1996).
2. Materials and methods
2.1. Gestational LPS and postnatal anoxia treatment;experimental design
All procedures were performed in accordance with theguidelines established by the Canadian Council on Ani-mal Care and were approved by the McGill UniversityAnimal Care Committee. For gestational LPS treat-ment, timed pregnant Sprague–Dawley rats (CharlesRiver, Quebec, Canada) were injected on day 18 and 19of pregnancy as follows: 13 pregnant rats were injectedintraperitoneally with 50 mg/kg LPS (Sigma L2755 fromEscherichia coli, serotype 0128:B12) and 10 were injec-ted with saline (control), once daily. Offspring in groupsreceiving gestational LPS were thus derived from 13separate dams, while those in groups receiving gesta-tional saline were derived from 10 separate dams. 50 mg/kg LPS was chosen as a dose producing significant fever
336 M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345
and induction of serum cytokines (interleukin-6, IL-6)in dose–response studies in non-pregnant rats (data notshown), and no reduction in survival when administeredto pregnant rats on E18 and E19.
On the day of birth, a small quantity of indelible inkwas injected into one of the paws of each pup to identifyanimals from different birth groups. Pups were cross-fostered with surrogate dams in mixed litters. Only malepups were retained for the study. On P7, half of thepups born from both LPS-treated mothers and saline-treated mothers were subjected to anoxia. For this, eachpup was placed for 7 min in a chamber containing 100%N2 (flow rate=9 liters per min) at 34 �C. Pups weregiven a 10 min recovery period before being returned totheir foster dam. The other half of the pups (from bothLPS-treated and saline-treated mothers) received con-trol treatment on P7; this consisted of placing the pupfor 7 min in a chamber with ambient air at 34 �C,instead of N2. Pups were weaned at 21 days of age andgrown to adulthood. Animals were group housed (twoanimals/cage) in random treatment combinations andmaintained on a 12 h:12 h light:dark cycle (lights on at8:00 h) with free access to food and water. Behavioraltesting of these offspring began at 70 days of age.
For behavioural testing, all animals were first testedfor baseline PPI of acoustic startle. One week later theanimals were tested for AMPH-induced locomotion.The next week the animals were tested for PPI afterreceiving a saline injection, and one week later they weretested for PPI after apomorphine administration.
2.2. Average startle response (ASR) and PPI ofacoustic startle
Startle reactivity was measured using two SR-LABstartle apparatuses (San Diego Instruments, San Diego,USA). Each sound attenuated startle chambercontained a clear Plexiglas cylinder resting on a piezo-electric transducer that detected the vibrations causedby the movements of the animals. A computer controlunit stored startle responses and controlled the timingand presentation of acoustic stimuli. A SR-LAB cali-bration unit was used to produce consistent responsesensitivity across chambers and trials.
Testing took place between 9:00 and 17:00 h. Eachtest session began with a 5 min acclimatization period inthe presence of 70 dB white noise, which continuedthroughout the session. One orienting pulse alone trial(120 dB for 30 ms) was then presented, which wasexcluded from the data analysis. Next, 11 pulse alonetrials (120 dB for 30 ms), five null trials with no stimulus,and five prepulse+pulse trials at each of five differentprepulse intensities were presented, in a pseudo-randomorder and with an average intertrial interval of 17 s(range: 9–29 s). The prepulse+pulse trials consisted of a30 ms prepulse (at 73, 76, 79, 82 or 85 dB), followed by
a 70 ms delay, then a startle pulse (120 dB, 30 ms). Thetesting session lasted 15 min. When assessing effects ofsaline injection or of apomorphine on PPI, saline orapomorphine (0.18 mg/kg) was injected 10 min beforethe animal was placed in the startle apparatus andtested for PPI using the protocol described above.
For each animal, a background startle value (averageof the 5 null trials) was subtracted from the startleamplitude of the pulse alone and prepulse+pulse trialsbefore further calculations were performed. Prepulseinhibition is expressed as % PPI, defined as (1�[startleamplitude on prepulse+pulse trial/mean startle ampli-tude on pulse alone trials])�100.
2.3. Amphetamine (AMPH)-induced locomotion
Locomotor activity was monitored using 11 activitychambers (30�40�40 cm), each equipped with twoparallel infrared light beams aligned with photoelectricswitches. The consecutive interruption of the two beamswas recorded as one locomotor act. Each test sessionbegan with 1 h of habituation, followed by saline injec-tion and another hour of recording. D-amphetaminesulphate (0.5 mg/kg) was then injected subcutaneouslyand locomotor activity was recorded for an additional 2h. Data are presented as locomotor acts (photocellcounts) summed for each successive 10 min interval.
2.4. Data analysis
Data analyses for baseline ASR and for effects ofapomorphine on ASR were performed using two-wayanalysis of variance (ANOVA) with gestational LPStreatment and postnatal anoxia as between-subject fac-tors. Data for baseline PPI and PPI modulated by apo-morphine were analyzed using three-way ANOVA, withLPS treatment and anoxia as between-subject factors,and prepulse intensity as a within-subject repeatedmeasure. Similarly, data analyses for locomotor activitywere performed using three-way ANOVA, with LPStreatment and anoxia as between-subject factors, andtime as a within-subject repeated measure. Separateanalyses were performed on data for baseline locomo-tion during habituation, for locomotion following salineand for locomotion after AMPH administration. Post-hoc Newman–Keuls tests were performed, where indi-cated, to assess differences between treatments at onespecific time-point or prepulse intensity.
2.5. Plasma Interleukin-6 (IL-6) levels
The cytokine, IL-6, is an important mediator of feverand readily detectible in the circulation of febrile ani-mals in response to systemic administration of LPS(Cartmell et al., 2000). In the present study, plasma IL-6levels were measured to confirm that the dose of LPS
M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345 337
administered to pregnant rat dams effectively elicited acytokine response. Pregnant rat dams received injec-tions of LPS (50 mg/kg, n=7) or saline (n=5) on E18and on E19. Three hours after the last LPS or salineinjection, animals were rapidly decapitated and a sam-ple of trunk blood was collected into sterile tubes con-taining pyrogen-free heparin (10 U/ml). Samples werecentrifuged (5300 g, 4 �C, 10 min) and plasma stored at�70 �C until assayed. Plasma was analyzed for IL-6using a rat specific ELISA (kindly provided by Dr. Ste-phen Poole, National Institute for Biological Standardsand Control, NIBSC, UK) as described previously(Rees et al., 1999; Cartmell et al., 2000). Intra- andinterassay co-efficients of variability for the IL-6 assaywere <5% and the detection limit was 20 pg/ml.
3. Results
The design of this study generated 4 experimentalgroups of offspring, i.e., those receiving gestationalLPS+postnatal anoxia (LPS+anoxia group, n=14),gestational LPS+postnatal air (LPS group, n=18);gestational saline+postnatal anoxia (Anoxia group,n=9) or gestational saline+postnatal air (Controlgroup, n=13). At adulthood, these offspring werebehaviorally tested for amphetamine-induced locomo-tion, acoustic startle responses, PPI of startle and apo-morphine disruption of PPI.
3.1. Survival, plasma interleukin-6, gestation length, andweight
Plasma IL-6 levels were measured to confirm that LPSelicited a cytokine response in pregnant rats. Table 1ashows that dams injected with LPS on E18 and E19 hadsignificantly higher levels of plasma IL-6 on E19, incomparison to saline-injected dams.
Dams injected with LPS on E18 and E19 exhibitedclear signs of sickness-type behaviors includingdecreased locomotor activity, piloerection and generalmalaise for up to 12h post injection. These are typicalresponses to endotoxin exposure in rats. Survival ofdams treated with either LPS or saline during gestationwas 100%. Gestation length was similar for LPS- andsaline treated dams (Table 1a), indicating that this doseof LPS does not induce premature labor. However thepercentage of stillborn pups was somewhat greater fromLPS-treated (6/142=4.2%) compared to saline treateddams (1/124=0.8%). In preliminary experiments, wedetermined that 7 min of anoxia (100% N2) on P7 wasthe length of anoxia at which considerable acute mor-tality occurred. Exposure of pups to 7 min of anoxia onP7 resulted in the death of 17.9% (5/28) of the pupson the day of treatment, while no air-treated pups (0/31)died on P7. For animals who lived until P8, long term
survival until adulthood was 100% in all four experi-mental groups. There were no significant group differ-ences in body weight of offspring from birth through toadulthood (Table 1b).
3.2. AMPH-induced locomotion in adult offspring
On the day of locomotor testing, the four experi-mental groups were tested for baseline locomotion (1 h),followed by locomotor responses to saline (1 h) and tolow dose (0.5 mg/kg) AMPH (2 h).
Three way ANOVA of baseline locomotion revealed asignificant LPS�time interaction (F5,245=2.476,P=0.033), but no significant effect of anoxia(F1,49=0.863, P=0.357) and no significant interactionsof anoxia with LPS or time (Anoxia�LPS: F1,49=1.489,P=0.228; Anoxia�time: F5,245=0.130, P=0.985;Anoxia�LPS�time: F5,245=0.456, P=0.809). Threeway ANOVA of saline-induced locomotion showed nosignificant effects of LPS (F1,49=2.278, P=0.138) or ofanoxia (F1,49=0.093, P=0.761) and no interactions(LPS�time: F5,245=0.314, P=0.904; Anoxia�time:F5,245=0.818, P=0.538; Anoxia�LPS: F1,49=0.964,P=0.331; Anoxia�LPS�time: F5,245=1.057,P=0.385). Three way ANOVA of locomotion inresponse to low dose (0.5 mg/kg) AMPH revealed asignificant LPS�time interaction (F11,495=2.441,P=0.006), but no significant effect of anoxia(F1,45=0.014, P=0.908) and no interactions of anoxiawith LPS or time (Anoxia�LPS: F1,45=0.076, P=0.783;Anoxia�time: F11,495=0.558, P=0.862; Anoxia�LPS�time: F11,495=1.285, P=0.229).
Table 1
(a) Maternal plasma interleukin-6 levels, length of gestation and (b)
offspring weights after treatment with gestational lipopolysaccharide
(LPS) and/or postnatal anoxia
(a)
Gestational LPS Gestational salineInterleukin-6 levels in maternal
plasma (pg/ml�SEM)
1846�217 (n=7)*
136�41 (n=5)Gestation length
(mean # of days�SEM)
22.6�0.1 (n=13)
22.1�0.1 (n=10)(b)
Weight (g)�SEM of offspring on postnatal day:P1
P7 P10 P70 P100LPS+Anoxia
6.5�0.2 16.0�0.4 20.4�0.4 434.6�12.2 520.0�12.0LPS
6.3�0.3 16.1�0.5 20.9�0.4 428.0�7.1 519.4�9.1Anoxia
6.3�0.3 15.8�1.0 20.1�0.9 426.7�12.4 528.3�15.8Control
6.7�0.3 15.6�1.1 20.6�0.7 425.7�8.0 512.9�8.6Rat dams were administered LPS (50 mg/kg) or saline on days 18 and
19 of pregnancy. On postnatal day 7 (P7), their offspring were exposed
to either 100% N2 (anoxia) or air (air control) for 7 min. Offspring
were then grown to adulthood. Using a separate cohort of dams, IL-6
was measured in maternal blood samples taken 3 h after the last LPS
or saline injection.
* Significantly different from values for saline-treated dams at
P<0.001.
338 M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345
Since there were no significant interactions betweengestational LPS and postnatal anoxia, effects of thesetwo treatments are shown separately in Figs. 1 and 2.Fig. 1 shows the effects of gestational LPS on locomo-tion in the subsample of offspring that were treated withair (control treatment) on P7 (omitting those treatedwith anoxia on P7). Offspring from LPS-treated damsshowed significantly greater stimulation of locomotoractivity at 30, 40 and 50 min after AMPH administra-tion (t=150, 160 and 170 min in Fig. 1), compared tooffspring from saline-treated dams. When data from thetotal sample of offspring (i.e. those treated with bothanoxia and air at P7) were included in the analysis ofeffects of gestational LPS, a similar result was obtained,i.e. offspring from LPS-treated dams again showed sig-nificantly greater locomotion at 30 (P<0.01), 40(P<0.01) and 50 (P<0.05) min after AMPH adminis-tration, compared to offspring from saline-treated dams(data not shown).
Fig. 2 shows that anoxia on P7 had no significanteffect on locomotor activity at adulthood. The figureshows effects of postnatal anoxia in the subsample ofoffspring treated with saline (control treatment) dur-ing gestation (omitting those treated with LPS duringgestation). For baseline, saline-induced and AMPH-induced locomotor activity, there were no significantdifferences between anoxia- and air-treated animals.Similarly no effects of postnatal anoxia on locomotionwere found, when the analysis included the total sample
of offspring treated with both LPS and saline duringgestation (data not shown).
3.3. Acoustic startle responses in adult offspring
Three way ANOVA of data for baseline acousticstartle responses (ASR) indicated a significant effect oftrial (F10,490=24.045, P<0.0001) across all experi-mental groups. Post hoc analysis of the trial effectrevealed that ASRs during trials 1, 2 and 3 were sig-nificantly different from ASRs during trials 4–11 (allPs<0.0001), and that there were no significant differ-ences in ASR within trials 4–11 (all Ps>0.579) (Fig. 3a).Thus it appeared as if all experimental animals requiredan habituation of three startle trials in order to attainstable and reproducible ASR across the next eight trials(trials 4–11). Therefore in subsequent analyses of startleresponse, we discarded data from the first threestartle trials, and performed analysis on average ASRfrom trials 4–11. (Similarly for analyses of PPI data inSection 3.4, we discarded data from prepulse+pulsetrials that were intercalated between the first three star-tle trials. This resulted in the elimination of one trial ateach of the five prepulse intensities, and average resultsfrom the four remaining trials at each prepulse intensitywere included in the analyses.)
Using average ASR from the last eight startle trials(trials 4–11) as the measure of ASR for each animal,two way ANOVA on baseline ASR data showed a
Fig. 1. Effects of LPS during gestation on AMPH-induced locomo-
tion in adult offspring. Rat dams were administered LPS (50 mg/kg) or
saline on days 18 and 19 of pregnancy. On postnatal day 7 (P7), their
offspring were exposed to either 100% N2 (anoxia) or air (air control)
for 7 min. At adulthood, offspring were tested for baseline locomo-
tion, followed by locomotor responses to saline and to low dose (0.5
mg/kg) AMPH. Since no significant interactions between LPS�anoxia
were observed, the figure shows the effects of gestational LPS on
locomotion in the subsample of offspring treated with air (control
treatment) at P7. Asterisks denote values significantly different from
saline during gestation at P<0.05 (*) and P<0.01 (**). LPS during
gestation significantly enhanced AMPH-induced locomotion in adult
offspring.
Fig. 2. Effects of postnatal anoxia on AMPH-induced locomotion in
adult offspring. Rats were administered LPS or saline during gesta-
tion, followed by anoxia or air on postnatal day 7. At adulthood, they
were tested for locomotor responses at baseline and in response to
saline and to low dose (0.5 mg/kg) AMPH. Since no significant inter-
actions between LPS�anoxia were observed, the figure shows the
effects of postnatal anoxia on locomotion in the subsample of off-
spring treated with saline (control treatment) during gestation. Post-
natal anoxia had no significant effect on AMPH-induced locomotion
in adult offspring.
M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345 339
significant effect of LPS (F1,49=4.622, P=0.037), butno effect of anoxia (F1,49=0.025, P=0.876) and noLPS�anoxia interaction (F1,49=0.011, P=0.917). Alloffspring receiving gestational LPS showed significantlyincreased baseline ASRs, compared to those receivingsaline injections during gestation (Fig. 3a and b).Anoxia on P7 had no effect on ASR at adulthood.
Apomorphine significantly (P<0.01) enhanced ASRin all experimental groups of animals. For ASR afterapomorphine administration, two way ANOVA showedno significant effect of LPS (F1,53=1.361, P=0.249) orof anoxia (F1,53=0.053, P=0.818) and no LPS�anoxiainteraction (F1,53=0.181, P=0.672). Thus gestationalLPS and postnatal anoxia had no effects on apomor-phine-induced ASR in adult offspring (Fig. 3c).
3.4. PPI of acoustic startle in adult offspring
Three way ANOVA of data for baseline PPI ofacoustic startle showed no significant effects of LPS(F1,49=0.004, P=0.950) or of anoxia (F1,49=2.249,P=0.140) and no interactions (LPS�prepulse inten-sity: F4,196=1.188, P=0.317; Anoxia�prepulseintensity: F4,196=0.894, P=0.468; Anoxia�LPS:F1,49=0.019, P=0.891; Anoxia�LPS�prepulse inten-sity: F4,196=0.564, P=0.689). Thus both gestationalLPS and postnatal anoxia were without effect on PPI inadult offspring, under conditions of the present experi-ment, and the two insults did not interact to affect PPI(Table 2a).
Three way ANOVA of data for PPI after apomor-phine showed no significant effects of LPS (F1,51=1.077,P=0.304) or of anoxia (F1,51=0.968, P=0.330) and nointeractions (LPS�prepulse intensity: F4,204=0.456,P=0.768; Anoxia�prepulse intensity: F4,204=0.874,P=0.480; Anoxia�LPS: F1,51=1.513, P=0.224; Anox-ia�LPS�prepulse intensity: F4,204=1.053, P=0.381).The low dose of apomorphine used significantly(P<0.05) inhibited PPI only at the 81 dB prepulseintensity, for all experimental groups. Thus, both gesta-tional LPS and postnatal anoxia were without effect onapomorphine modulation of PPI in adult offspring(Table 2b).
4. Discussion
The main finding of this study is that administrationof bacterial endotoxin to rat dams on days 18 and 19 ofpregnancy produces long-term enhancement of AMPH-induced locomotion and of acoustic startle responses inthe resulting offspring. Pharmacologic lesioning andimaging studies indicate that locomotion in response tolow dose AMPH in the rat largely reflects activity in themidbrain-ventral striatal (nucleus accumbens) DApathway (Castall et al., 1977; Porrino et al., 1984).
There is substantial evidence that dysregulation of sub-cortical DA function plays a critical role in the patho-physiology of schizophrenia. For example, drugs likeAMPH, which enhance DA transmission, can exacer-bate psychotic symptoms in schizophrenic subjects andinduce a schizophrenia-like syndrome with chronic usein normals (reviewed by Yui et al., 1999). More recently,in vivo imaging studies have provided more direct evi-dence that enhanced subcortical DA activity may con-tribute to positive symptoms of schizophrenia. Thesestudies demonstrated that, compared to controls,untreated schizophrenic subjects show enhanced striatalDA release in response to AMPH, that correlates withworsening of psychotic symptoms (Laruelle et al., 1996,1999; Breier et al, 1997; Abi-Dargham et al., 1998; Lar-uelle and Abi-Dargham, 1999). Our findings withgestational LPS in the rat model support the idea thatmaternal infection during pregnancy could contributeto the genesis of such subcortical dopaminergic over-activity in schizophrenia.
While gestational LPS increased acoustic startleresponses in adult offspring, this insult was withouteffect on PPI of startle or on apomorphine modulationof PPI. Enhanced ASR (i.e. deficits in habituation ofASR) in schizophrenic subjects compared to controlshas been reported in several studies, particularly inparadigms utilizing a series of pulse alone trials (with nopre-pulse trials) to determine habituation (Geyer andBraff, 1982; Bolino et al., 1992; Braff et al., 1992; Par-wani et al., 2000). The finding of deficient habituation ofASR appears, however, to be less robust than is thefinding of PPI deficits in schizophrenia (Braff et al.,2001).
In experiments in which LPS (1 mg/kg) was adminis-tered to pregnant rats every second day throughoutpregnancy, Borrell et al. (2002) have recently reporteddisrupted PPI of startle using either an acoustic pre-pulse of 55dB or a photic pre-pulse, in adult offspring.Differences in timing or dosage of LPS exposure mayaccount for the differing behavioral alterations in theirstudy versus ours (i.e., reduced PPI versus enhancedAMPH-induced locomotion and ASR). LPS adminis-tered on E18 and E19 may more closely mimic an acutesecond trimester infection in humans. The model ofBorrell et al. may approximate a chronic infection dur-ing the first and second trimester of pregnancy,although tolerance to repeated LPS is known to develop(West and Heagy, 2002). Enhanced AMPH-inducedrelease of striatal DA appears to be associated withexacerbations of psychotic symptomatology (Laruelleand Abi-Dargham, 1999), while PPI deficits correlatewith cognitive symptoms such as thought disorder anddistractibility (Karper et al., 1996; Perry et al., 1999;Braff et al., 2001). Thus, comparison of our findings tothose of Borrell et al. suggest that it may be possibleto model differing aspects of the schizophrenic pheno-
340 M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345
Fig. 3. Effects of LPS during gestation and of postnatal anoxia on baseline and apomorphine-induced acoustic startle responses (ASR) in adult
offspring. Rats were administered LPS or saline during gestation, followed by anoxia or air on postnatal day 7, and were tested for acoustic startle
responses at adulthood. (a) shows baseline ASRs across 11 successive trials in the four experimental groups, i.e., animals receiving gestational
LPS+postnatal anoxia (LPS+Anoxia), gestational LPS+postnatal air (LPS); gestational saline+postnatal anoxia (Anoxia) or gestational sali-
ne+postnatal air (Control). For all experimental groups, ASRs during trials 1, 2 and 3 were significantly different from ASRs during trials 4–11
(Ps<0.0001). (b) shows average baseline ASR (from trials 4–11) for each of the four experimental groups. *=significantly different at P<0.05. LPS
during gestation significantly increased ASR at adulthood. Postnatal anoxia had no effect on ASR and there was no interaction between
LPS�anoxia. (c) shows average apomorphine-induced ASR (from trials 4–11) for each of the four experimental groups. LPS during gestation and
postnatal anoxia had no significant effects on apomorphine-induced ASR.
M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345 341
type by administering LPS during different times of gesta-tion in the rat. In addition, the current study employed aparadigm of cross-fostering of pups with untreated sur-rogate dams, while animals in the study by Borrell et al.appear to have been raised postnatally by their originalLPS- or saline-treated mothers. Differential postnatalmaternal care may have contributed to behavioral find-ings in the latter study, since maternal deprivation hasbeen reported to have long term effects on both PPI andAMPH-induced locomotion in offspring (Zimmerbergand Shartrand, 1992; Matthews et al., 1996; Ellenbroekand Cools, 2002; Meaney et al., 2002).
LPS administration induces production of pro-inflammatory cytokines, most prominently IL-1b, IL-6and TNF-a, which collectively mediate defense respon-ses to systemic infection including fever, hypophagia,enhancement of slow wave sleep, sickness behavior andglucocorticoid secretion, primarily via direct actions inthe CNS (Luheshi and Rothwell, 1996; Larson andDunn, 2001). In addition to affecting adult CNS func-tion, cytokines have multiple effects on developing neu-rons, making them prime candidates as mediators ofeffects of maternal infection on fetal brain development.
For example, LPS, IL-1, IL-6 and/or TNF-a influenceconversion of mesencephalic progenitor cells into dif-ferentiated DA neurons and survival of embryonicdopaminergic and serotoninergic neurons in vitro (vonCoelln et al., 1995; Jarskog et al., 1997; Ling et al.,1998). Cultured DA neurons are selectively injured bylow doses of LPS that have no effect on developinghippocampal or cortical neurons (Kim et al., 2000). IL-1b has also been reported to regulate expression ofneurotrophic molecules, such as brain-derived neuro-trophic factor, a potent regulator of the survival anddifferentiation of DA neurons, as well as nerve growthfactor (Lapchak et al., 1993; Heese et al., 1998). In ourstudy, pregnant rat dams administered LPS on E18/19had increased levels of plasma IL-6, confirming that thedose of LPS used elicited a cytokine response in theseanimals. LPS administered to rats dams on E18 has alsobeen shown to increase IL-1b and TNF-a mRNA infetal brain (Cai et al., 2000), while increased IL-1b, IL-6and TNF-a in the placenta and a small decrease in fetalbrain TNF-a have been reported following LPS on E16(Urakubo et al., 2001). Independent of other effects ofcytokines, LPS-induced fever might also affect braindevelopment. For example, heat stress early in gestationhas been reported to produce gross CNS anomalies indeveloping rodents (Mottola et al., 1993; Yitzhakie etal., 1999).
In addition to affecting development of dopaminergicsystems, prenatal LPS may lead to lasting dysregulationof cytokine function in offspring as adults, and resultingdysregulation of cytokine-DA interactions in adultbrain. In this context, Borell et al. (2002) reported thatLPS administration throughout pregnancy results in
offspring with increased serum IL-6 as adults. ElevatedIL-6 levels may alter DA function since systemic IL-6administration in adult rats has been reported to altercentral DA turnover and enhance AMPH-inducedlocomotor activity (Zalcman et al., 1994, 1999; Song etal., 1999). Another possible mechanisms by whichmaternal LPS might increase AMPH-induced locomo-tion in offspring is by decreasing AMPH metabolismdue to LPS effects on liver drug metabolizing enzymesor other processes in offspring, although this mechanismwould not account for effects of prenatal LPS on ASR.
In the current study, 7 min of anoxia on P7had no effect on baseline or AMPH-induced locomotionand no effect on PPI or apomorphine modulation ofPPI, at adulthood. This finding is in agreement withprevious reports on behavioral effects of postnatalanoxia in the rat. Postnatal anoxia administered on P1(Speiser et al., 1983), P2 (Iuvone et al., 1996), P4 (Shi-momura and Ohta, 1988), P5 or P10 (Jensen et al.,1992) has been reported to produce transient baselinehyperactivity in rats as adolescents but no lasting effectson locomotion in adulthood. With repeated anoxicinsults (at P2 and P6) or chronic mild (P2–P6) or episo-dic (P7–P11) hypoxia, hypoactivity or hyperactivityhave been observed at adulthood (Lun et al., 1990;Nyakas et al., 1991; Decker et al., 2003). None of theseprevious studies have reported on AMPH-inducedlocomotion or PPI, although spatial and workingmemory deficits at adulthood have been observed insome models of postnatal anoxia (Iuvone et al., 1996;Decker et al., 2003). In contrast to the lack of effect ofacute postnatal anoxia, we have previously reportedthat the subtle insult of Caesarean section (C-section)birth is sufficient to produce lasting increases in AMPH-induced locomotion in rats and guinea pigs (El-Khodorand Boksa, 1998; Vaillancourt and Boksa, 1998, 2000).Addition of 15 min of anoxia to the C-section proceduredid not exacerbate or ameliorate the C-section-inducedeffect on AMPH-induced locomotion in the rat. How-ever in the guinea pig, a model with greater CNSmaturity than the rat, C-section with 1–2 min of addi-tional birth anoxia resulted in further changes inAMPH-induced locomotion, compared to C-sectionalone. Thus it appears as if dopaminergic systems mightexhibit greater susceptibility to long term dysregulationby subtle insults during pregnancy and at birth (gesta-tional LPS, C-section birth, birth anoxia), compared torelative resistance to acute postnatal anoxia.
We observed no interaction between effects of gesta-tional LPS and postnatal anoxia on behavior at adult-hood. Thus pre-exposure to LPS during gestation didnot sensitize the animals to effects of postnatal anoxia atP7, and effects of gestational LPS were neither exacer-bated nor ameliorated by later exposure to postnatalanoxia. LPS pre-exposure 1–4 h before hypoxic-ischemic or excitotoxic insult has been reported to
342 M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345
exacerbate neuronal injury in immature rats (Lee et al.,2000; Eklind et al., 2001; Coumans et al., 2003). Toge-ther with our findings, this suggests that the sensitizingeffects of LPS exposure may be only short-lived, andthat LPS and anoxia might have interactive effects onimmature brain only when administered in close tem-poral proximity.
In conclusion, maternal exposure to bacterialendotoxin during pregnancy resulted in long termchanges in behaviors relevant to schizophrenia, whilepostnatal anoxia on P7 was without effect and the twoinsults did not interact. Animal modeling of obstetricinsults may contribute to an understanding of thetypes of complications that have the most pronouncedimpact on specific CNS systems and their mechanismsof action.
Acknowledgements
Supported by grants from the Canadian Institutes ofHealth Research (PB, RJ, GNL) and Young Investi-gator Awards from the National Alliance for Researchon Schizophrenia and Depression, USA (RJ, GNL).
References
Abi-Dargham A, Gil R, Krystal J, Baldwin RM, Seibyl JP, Bowers M,
et al. Increased striatal dopamine transmission in schizophrenia:
confirmation in a second cohort. American Journal of Psychiatry
1998;155:761–7.
Avishai-Eliner S, Brunson KL, Sandman CA, Baram TZ. Stressed-
out, or in (utero)? Trends in Neurosciences 2002;25:518–24.
Barr CE, Mednick SA, Munk-Jorgensen P. Exposure to influenza
epidemics during gestation and adult schizophrenia. A 40-year
study. Archives of General Psychiatry 1990;47:869–74.
Bolino F, Manna V, Di Cicco L, Di Michele V, Daneluzzo E, Rossi A,
et al. Startle reflex habituation in functional psychoses: a controlled
study. Neuroscience Letters 1992;145:126–8.
Borrell J, Vela JM, Arevalo-Martin A, Molina-Holgado E, Guaza C.
Prenatal immune challenge disrupts sensorimotor gating in adult
rats. Implications for the etiopathogenesis of schizophrenia. Neuro-
psychopharmacology 2002;26:204–15.
Braff DL, Geyer MA, Swerdlow NR. Human studies of prepulse
inhibition of startle: normal subjects, patient groups, and pharma-
cological studies. Psychopharmacology 2001;156:234–58.
Braff DL, Grillon C, Geyer MA. Gating and habituation of the startle
reflex in schizophrenic patients. Archives of General Psychiatry
1992;49:206–15.
Breier A, Su T-P, Saunders R, Carson RE, Kolachana BS, de Barto-
lomeis A, et al. Schizophrenia is associated with elevated ampheta-
mine-induced synaptic dopamine concentrations: evidence from a
novel positron emission tomography method. Proceedings of the
National Academy of Sciences USA 1997;94:2569–74.
Brown AS, Schaefer CA, Wyatt RJ, Goetz R, Begg MD, Gorman
JM, et al. Maternal exposure to respiratory infections and adult
schizophrenia spectrum disorders: a prospective birth cohort study.
Schizophrenia Bulletin 2000;26:287–95.
Cai Z, Pan ZL, Pang Y, Evans OB, Rhodes PG. Cytokine induction in
fetal rat brains and brain injury in neonatal rats after maternal
lipopolysaccharide administration. Pediatric Research 2000;47:64–
72.
Cartmell T, Poole S, Turnbull AV, Rothwell NJ, Luheshi GN. Circu-
lating interleukin-6 mediates the febrile response to localised
inflammation in rats. Journal of Physiology 2000;526:653–61.
Castall B, Marsden CD, Naylor RJ, Pycock CJ. Stereotyped
behaviour patterns and hyperactivity induced by amphetamine and
apomorphine after discrete 6-hydroxydopamine lesions of extra-
pyramidal and mesolimbic nuclei. Brain Research 1977;123:89–111.
Coumans AB, Middelanis JS, Garnier Y, Vaihinger HM, Leib SL,
Von Duering MU, et al. Intracisternal application of endotoxin
enhances the susceptibility to subsequent hypoxic-ischemic brain
damage in neonatal rats. Pediatric Research 2003;53:770–5.
Dawson DA, Furuya K, Gotoh J, Nakao Y, Hallenbeck JM. Cere-
brovascular hemodynamics and ischemic tolerance: lipopoly-
saccharide-induced resistance to focal cerebral ischemia is not due
to changes in severity of the initial ischemic insult, but is associated
with preservation of microvascular perfusion. Journal of Cerebral
Blood Flow and Metabolism 1999;19:616–23.
Decker MJ, Hue GE, Caudle WM, Miller GW, Keating GL, Rye DB.
Episodic neonatal hypoxia evokes executive dysfunction and
regionally specific alterations in markers of dopamine signalling.
Neuroscience 2003;117:417–25.
Eklind S, Mallard C, Leverin AL, Gilland E, Blomgren K, Mattsby-
Baltzer I, et al. Bacterial endotoxin sensitizes the immature brain to
hypoxic–ischaemic injury. European Journal of Neuroscience 2001;
13:1101–6.
El-Khodor BF, Boksa P. Birth insult increases amphetamine-induced
behavioral responses in the adult rat. Neuroscience 1998;87:893–
904.
Ellenbroek BA, Cools AR. Early maternal deprivation and prepulse
inhibition: the role of the postdeprivation environment. Pharma-
cology Biochemistry and Behavior 2002;73:177–84.
Engel JA, Zhang J, Bergstrom T, Conradi N, Forkstam C, Liljeroth
A, et al. Neonatal herpes simplex virus type 1 brain infection affects
Table 2
Effects of LPS during gestation and of postnatal anoxia on baseline
pre-pulse inhibition (PPI) of acoustic startle (a) and on PPI after
apomophine (b), in adult offspring
(a) Baseline PPI
% PPI at pre-pulse intensity of
73dB
76dB 79dB 82dB 85dBLPS+Anoxia
29.1�7.1 42.0�5.2 60.4�5.1 69.3�4.0 77.0 �3.9LPS
16.0�8.2 41.1�6.1 55.8�5.6 60.5�7.1 72.4�7.8Anoxia
45.1�8.0 56.7�7.4 70.7�9.1 71.9�7.8 78.4�8.6Control
16.1�8.3 46.6�7.1 63.0�6.5 69.6�3.7 71.5�5.1(a) PPI after apomorphine
% PPI at pre-pulse intensity of
73dB
76dB 79dB 82dB 85dBLPS+Anoxia
37.4�10.3 23.1�10.6 57.8�7.1 72.7�6.2 84.9�4.7LPS
36.6�8.34 23.5�7.6 61.2�4.0 73.5�4.6 84.0�2.3Anoxia
44.3�10.1 39.9�7.9 52.1�9.6 71.2�5.8 80.2�4.4Control
37.4�9.8 4.1�10.7 48.0�7.6 60.0�9.2 76.5�3.8Rats were administered LPS or saline during gestation, followed by
anoxia or air on postnatal day 7. They were tested for baseline PPI
and apomorphine (0.18 mg/kg) modulation of PPI at adulthood.
Gestational LPS and postnatal anoxia alone or in combination had no
significant effects on either baseline PPI or PPI after apomorphine.
M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345 343
the development of sensorimotor gating in rats. Brain Research
2000;863:233–40.
Geyer MA, Braff DL. Habituation of the blink reflex in normals and
schizophrenic patients. Psychophysiology 1982;19:1–6.
Geyer MA, Krebs-Thomson K, Braff DL, Swerdlow NR. Pharmaco-
logical studies of prepulse inhibition models of sensorimotor gating
deficits in schizophrenia: a decade in review. Psychopharmacology
2001;156:117–54.
Heese K, Hock C, Otten U. Inflammatory signals induce neurotrophin
expression in human microglial cells. Journal of Neurochemistry
1998;70:699–707.
Iuvone L, Geloso MC, Dell’Anna E. Changes in open field behavior,
spatial memory, and hippocampal parvalbumin immunoreactivity
following enrichment in rats exposed to neonatal anoxia. Experi-
mental Neurology 1996;139:25–33.
Jarskog LF, Xiao H, Wilkie MB, Lauder JM, Gilmore JH. Cytokine
regulation of embryonic rat dopamine and serotonin neuronal sur-
vival in vitro. International Journal of Developmental Neuroscience
1997;15:711–6.
Jensen FE, Applegate CD, Holtzman D, Belin TR, Burchfiel JL. Epi-
leptogenic effect of hypoxia in the immature rodent brain. Annals of
Neurology 1991;29:629–37.
Jensen FE, Holmes GL, Lombroso CT, Blume HK, Firkusny IR.
Age-dependent changes in long-term seizure susceptibility and
behavior after hypoxia in rats. Epilepsia 1992;33:971–80.
Karper LP, Freeman GK, Grillon C, Morgan CA 3rd, Charney DS,
Krystal JH. Preliminary evidence of an association between sensor-
imotor gating and distractibility in psychosis. Journal of Neuro-
psychiatry and Clinical Neuroscience 1996;8:60–6.
Kim WG, Mohney RP, Wilson B, Jeohn GH, Liu B, Hong JS.
Regional difference in susceptibility to lipopolysaccharide-induced
neurotoxicity in the rat brain: role of microglia. Journal of Neuro-
science 2000;20:6309–16.
Lapchak PA, Araujo DM, Hefti F. Systemic interleukin-1 beta
decreases brain-derived neurotrophic factor messenger RNA
expression in the rat hippocampal formation. Neuroscience 1993;53:
297–301.
Larson SJ, Dunn AJ. Behavioral effects of cytokines. Brain, Behavior,
and Immunity 2001;15:371–87.
Laruelle M, Abi-Dargham A. Dopamine as the wind of the psychotic
fire: new evidence from brain imaging studies. Journal of Psycho-
pharmacology 1999;13:358–71.
Laruelle M, Abi-Dargham A, Gil R, Kegeles L, Innis RB. Increased
dopamine transmission in schizophrenia:relationship to illness
phase. Biological Psychiatry 1999;46:56–72.
Laruelle M, Abi-Dargham A, van Dyck CH, Gil R, D’Souza CD,
Erdos J, et al. Single photon emission computerized tomography
imaging of amphetamine-induced dopamine release in drug-free
schizophrenic subjects. Proceedings of the National Academy of
Sciences USA 1996;93:9235–40.
Lee SH, Han SH, Lee KW. Kainic acid-induced seizures cause neuro-
nal death in infant rats pretreated with lipopolysaccharide. Neuro-
report 2000;11:507–10.
Ling ZD, Potter ED, Lipton JW, Carvey PM. Differentiation of
mesencephalic progenitor cells into dopaminergic neurons by cyto-
kines. Experimental Neurology 1998;149:411–23.
Luheshi G, Rothwell N. Cytokines and fever. International Archives
of Allergy Immunology 1996;109:301–7.
Lun A, Dominick B, Gross J. An animal model of perinatal hypoxic
brain damage: behavioural aspects. Biomedica Biochimica Acta
1990;49:1021–6.
Martin SM, Malkinson TJ, Veale WL, Pittman QJ. Fever in pregnant,
parturient, and lactating rats. American Journal of Physiology 1995;
268:R919–0R923.
Matthews K, Hall FS, Wilkinson LS, Robbins TW. Retarded acqui-
sition and reduced expression of conditioned locomotor activity in
adult rats following repeated early maternal separation: effects of
prefeeding, d-amphetamine, dopamine antagonists and clonidine.
Psychopharmacology 1996;126:75–84.
McNeil TF, Cantor-Graae E, Ismail B. Obstetric complications and
congenital malformation in schizophrenia. Brain Research Reviews
2000;31:166–78.
Meaney MJ, Brake W, Gratton A. Environmental regulation of the
development of mesolimbic dopamine systems: a neurobiological
mechanism for vulnerability to drug abuse? Psychoneur-
oendocrinology 2002;27:127–38.
Mottola MF, Fitzgerald HM, Wilson NC, Taylor AW. Effect of water
temperature on exercise-induced maternal hyperthermia on fetal
development in rats. International Journal of Sports Medicine 1993;
14:248–51.
Nyakas C, Markel E, Schuurman T, Luiten PG. Impaired learning
and abnormal open-field behaviours of rats after early postnatal
anoxia and the beneficial effect of the calcium antagonist nimodi-
pine. European Journal of Neuroscience 1991;3:168–74.
O’Callaghan E, Sham PC, Takei N, Murray G, Glover G, Hare EH, et
al. The relationship of schizophrenic births to 16 infectious diseases.
British Journal of Psychiatry 1994;165:353–6.
Parwani A, Duncan EJ, Bartlett E, Madonick SH, Efferen TR, Rajan
R, et al. Impaired prepulse inhibition of acoustic startle in schizo-
phrenia. Biological Psychiatry 2000;47:662–9.
Perry W, Geyer MA, Braff DL. Sensorimotor gating and thought dis-
turbance measured in close temporal proximity in schizophrenic
patients. Archives of General Psychiatry 1999;56:277–81.
Pletnikov MV, Rubin SA, Vogel MW, Moran TH, Carbone KM.
Effects of genetic background on neonatal Borna disease virus
infection-induced neurodevelopmental damage. I. Brain pathology
and behavioral deficits. Brain Research 2002;944:97–107.
Porrino LJ, Lucignani G, Dow-Edwards D, Sokoloff L. Correlation of
dose-dependent effects of acute amphetamine administration on
behavior and local cerebral metabolism in rats. Brain Research
1984;307:311–20.
Rees G, Ball C, Ward HL, Gee CK, Tarrant G, Mistry Y, et al. Rat
interleukin 6: expression in recombinant Escherichia coli. Cytokine
1999;11:95–103.
Romijn HJ, Hofman MA, Gramsbergen A. At what age is the devel-
oping cerebral cortex of the rat comparable to that of the full-term
newborn human baby? Early Human Development 1991;26:61–7.
Rothschild DM, O’Grady M, Wecker L. Neonatal cytomegalovirus
exposure decreases prepulse inhibition in adult rats: implications for
schizophrenia. Journal of Neuroscience Research 1999;57:429–34.
Shi L, Fatemi SH, Sidwell RW, Patterson PH. Maternal influenza
infection causes marked behavioral and pharmacological changes in
the offspring. Journal of Neuroscience 2003;23:297–302.
Shimomura C, Ohta H. Behavioral abnormalities and seizure suscept-
ibility in rat after neonatal anoxia. Brain Development 1988;10:160–
3.
Slotkin TA, Cowdery TS, Orband L, Pachman S, Whitmore WL.
Effects of neonatal hypoxia on brain development in the rat:
immediate and long-term biochemical alterations in discrete regions.
Brain Research 1986;374:63–74.
Solbrig MV, Koob GF, Lipkin WI. Cocaine sensitivity in Borna dis-
ease virus-infected rats. Pharmacology Biochemistry and Behavior
1998;59:1047–52.
Song C, Merali Z, Anisman H. Variations of nucleus accumbens
dopamine and serotonin following systemic interleukin-1, inter-
leukin-2 or interleukin-6 treatment. Neuroscience 1999;88:823–36.
Speiser Z, Korczyn AD, Teplitzky I, Gitter S. Hyperactivity in rats
following postnatal anoxia. Behavioral Brain Research 1983;7:379–
82.
Suvisaari J, Haukka J, Tanskanen A, Hovi T, Lonnqvist J. Associ-
ation between prenatal exposure to poliovirus infection and adult
schizophrenia. American Journal of Psychiatry 1999;156:1100–2.
Tasaki K, Ruetzler CA, Ohtsuki T, Martin D, Nawashiro H, Hallen-
beck JM. Lipopolysaccharide pre-treatment induces resistance
344 M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345
against subsequent focal cerebral ischemic damage in spontaneously
hypertensive rats. Brain Research 1997;748:267–70.
Urakubo A, Jarskog LF, Lieberman JA, Gilmore JH. Prenatal expo-
sure to maternal infection alters cytokine expression in the placenta,
amniotic fluid, and fetal brain. Schizophrenia Research 2001;47:27–36.
Vaillancourt C, Boksa P. Caesarean section birth with general anes-
thesia increases dopamine-mediated behavior in the adult rat. Neu-
roreport 1998;9:2953–9.
Vaillancourt C, Boksa P. Birth insult alters dopamine-mediated beha-
vior in a precocial species, the guinea pig. Implications for schizo-
phrenia. Neuropsychopharmacology 2000;23:654–66.
von Coelln R, Unsicker K, Krieglstein K. Screening of interleukins for
survival-promoting effects on cultured mesencephalic dopaminergic
neurons from embryonic rat brain. Developmental Brain Research
1995;89:150–4.
Watson CG, Kucala T, Tilleskjor C, Jacobs L. Schizophrenic birth
seasonality in relation to the incidence of infectious diseases and
temperature extremes. Archives of General Psychiatry 1984;41:85–90.
West MA, Heagy W. Endotoxin tolerance: a review. Critical Care
Medicine 2002;30:S64–0S73.
Yager JY, Shuaib A, Thornhill J. The effect of age on susceptibility to
brain damage in a model of global hemispheric hypoxia-ischemia.
Developmental Brain Research 1996;93:143–54.
Yitzhakie D, Torchinsky A, Savion S, Toder V. Maternal immuno-
potentiation affects the teratogenic response to hyperthermia. Jour-
nal of Reproductive Immunology 1999;45:49–66.
Yui K, Goto K, Ikemoto S, Ishiguro T, Angrist B, Duncan GE, et al.
Neurobiological basis of relapse prediction in stimulant-induced
psychosis and schizophrenia: role of sensitisation. Molecular Psy-
chiatry 1999;4:512–23.
Zalcman S, Green-Johnson JM, Murray L, Nance DM, Dyck D,
Anisman H, et al. Cytokine-specific central monoamine altera-
tions induced by interleukin-1,-2 and-6. Brain Research 1994;643:
40–9.
Zalcman S, Savina I, Wise RA. Interleukin-6 increases sensitivity to
the locomotor stimulating effects of amphetamine in rats. Brain
Research 1999;847:276–83.
Zimmerberg B, Shartrand AM. Temperature-dependent effects of
maternal separation on growth, activity, and amphetamine sensitiv-
ity in the rat. Developmental Psychobiology 1992;25:213–26.
M.-E. Fortier et al. / Journal of Psychiatric Research 38 (2004) 335–345 345