Neonatal ventral hippocampal lesions attenuate the nucleus accumbens dopamine response to stress: an electrochemical study in the adult rat

Aripiprazole attenuates the medial prefrontal cortex morphological and biochemical alterations in rats with neonatal ventral hippocampus lesion

Schizophrenia is a neurodevelopmental disorder characterized by a loss of dendritic spines in the medial prefrontal cortex (mPFC). Multiple subclinical and clinical studies have evidenced the ability of antipsychotics to improve neuroplasticity. In this study, it was evaluated the effect of the atypical antipsychotic aripiprazole (ARI) on the behavioral and mPFC neuronal disturbances of rats with neonatal ventral hippocampus lesion (nVHL), which is a heuristic developmental model relevant to the study of schizophrenia. ARI attenuated open field hyperlocomotion in the rats with nVHL. Also, ARI ameliorated structural neuroplasticity disturbances of the mPFC layer 3 pyramidal cells, but not in the layer 5 neurons. These effects can be associated with the ARI capability of increasing brain-derived neurotrophic factor (BDNF) levels. Moreover, in the animals with nVHL, ARI attenuated the immunoreactivity for some oxidative stress-related molecules such as the nitric oxide synthase 2 (NOS-2), 3-nitrotyrosine (3-NT), and cyclooxygenase 2 (COX-2), as well as the reactive astrogliosis in the mPFC. These results contribute to current knowledge about the neurotrophic, anti-inflammatory, and antioxidant properties of antipsychotics which may be contributing to their clinical effects and envision promising therapeutic targets for the treatment of schizophrenia.

Circannual changes in stress and feeding hormones and their effect on food-seeking behaviors

Seasonal fluctuations in food availability show a tight association with seasonal variations in body weight and food intake. Seasonal variations in food intake, energy storage, and expenditure appear to be a widespread phenomenon suggesting they may have evolved in anticipation for changing environmental demands. These cycles appear to be driven by changes in external daylength acting on neuroendocrine pathways. A number of neuroendocrine pathways, two of which are the endocrine mechanisms underlying feeding and stress, appear to show seasonal changes in both their circulating levels and reactivity. As such, variation in the level or reactivity to these hormones may be crucial factors in the control of seasonal variations in food-seeking behaviors. The present review examines the relationship between feeding behavior and seasonal changes in circulating hormones. We hypothesize that seasonal changes in circulating levels of glucocorticoids and the feeding-related hormones ghrelin and leptin contribute to seasonal fluctuations in feeding-related behaviors. This review will focus on the seasonal circulating levels of these hormones as well as sensitivity to these hormones in the modulation of food-seeking behaviors.

Reduction in cholinergic interneuron density in the nucleus accumbens attenuates local extracellular dopamine release in response to stress or amphetamine

Depletion of cholinergic interneurons in the ventral striatum (nucleus accumbens or N.Acc.) in adult rats increases the locomotor activating effects of amphetamine. It also impairs sensorimotor gating processes, an effect reversed by the antipsychotic haloperidol. These behavioral effects are suggestive of pronounced hyper-responsiveness of the mesolimbic dopamine (DA) projection to the N.Acc. However, it is unclear whether local cholinergic depletion results predominantly in exaggerated presynaptic DA release or a postsynaptic upregulation of DAergic function. The purpose of the present study is to test the former possibility by employing in vivo voltammetry to examine changes in the levels of extracellular DA within the N.Acc. in response to either mild tail pinch stress or amphetamine administration. While both cholinergic-lesioned and control rats showed reliable stress-induced increases in extracellular DA on two consecutive test days, those in the lesioned rats were significantly less pronounced. In response to amphetamine, a separate cohort of lesioned rats also exhibited smaller increases in extracellular DA release than controls, despite showing greater locomotor activity. Moreover, the increased behavioral response to amphetamine in lesioned rats coincided temporally with decreasing levels of DA in the N.Acc. The results confirm that cholinergic depletion within the N.Acc. suppresses presynaptic DA release and suggest that lesion-induced behavioral effects are more likely due to postsynaptic DA receptor upregulation. The results are also discussed in the context of schizophrenia, where post mortem studies have revealed a selective loss of cholinergic interneurons within the ventral striatum.

Neonatal disconnection of the rat hippocampus: a neurodevelopmental model of schizophrenia

In the context of our current knowledge about schizophrenia, heuristic models of psychiatric disorders may be used to test the plausibility of theories developed on the basis of new emerging biological findings, explore mechanisms of schizophrenia-like phenomena, and develop potential new treatments. In a series of studies, we have shown that neonatal excitotoxic lesions of the rat ventral hippocampus (VH) may serve as a heuristic model. The model appears to mimic a spectrum of neurobiological and behavioral features of schizophrenia, including functional pathology in presumably critical brain regions interconnected with the hippocampal formation and targeted by antipsychotic drugs (the striatum/nucleus accumbens and the prefrontal cortex), and leads in adolescence or early adulthood to the emergence of abnormalities in a number of dopamine-related behaviors. Moreover, our data show that even transient inactivation of the VH during a critical period of development, which produces subtle, if any, anatomical changes in the hippocampus, may be sufficient to disrupt normal maturation of the prefrontal cortex (and perhaps, other interconnected latematuring regions) and trigger behavioral changes similar to those observed in animals with the permanent excitotoxic lesion. These results represent a potential new model of aspects of schizophrenia without a gross anatomical lesion.

Stress, neurotransmitters, corticosterone and body-brain integration

Stress can be defined as a brain-body reaction towards stimuli arising from the environment or from internal cues that are interpreted as a disruption of homeostasis. The organization of the response to a stressful situation involves not only the activity of different types of neurotransmitter systems in several areas of the limbic system, but also the response of neurons in these areas to several other chemicals and hormones, chiefly glucocorticoids, released from peripheral organs and glands. Thus, stress is probably the process through which body-brain integration plays a major role. Here we review first the responses to an acute stress in terms of neurotransmitters such as dopamine, acetylcholine, glutamate and GABA in areas of the brain involved in the regulation of stress responses. These areas include the prefrontal cortex, amygdala, hippocampus and nucleus accumbens and the interaction among those areas. Then, we consider the role of glucocorticoids and review some recent data about the interaction of these steroids with several neurotransmitters in those same areas of the brain. Also the actions of other substances (neuromodulators) released from peripheral organs such as the pancreas, liver or gonads (insulin, IGF-1, estrogens) are reviewed. The role of an environmental enrichment on these same responses is also discussed. Finally a section is devoted to put into perspective all these environmental-brain-body-brain interactions during stress and their consequences on aging. It is concluded that the integrative perspective framed in this review is relevant for better understanding of how the organism responds to stressful challenges and how this can be modified through different environmental conditions during the process of aging. This article is part of a Special Issue entitled: Brain Integration.

Chronic administration of the neurotrophic agent cerebrolysin ameliorates the behavioral and morphological changes induced by neonatal ventral hippocampus lesion in a rat model of schizophrenia

Neonatal ventral hippocampal lesion (nVHL) in rats has been widely used as a neurodevelopmental model to mimic schizophrenia-like behaviors. Recently, we reported that nVHLs result in dendritic retraction and spine loss in prefrontal cortex (PFC) pyramidal neurons and medium spiny neurons of the nucleus accumbens (NAcc). Cerebrolysin (Cbl), a neurotrophic peptide mixture, has been reported to ameliorate the synaptic and dendritic pathology in models of aging and neurodevelopmental disorder such as Rett syndrome. This study sought to determine whether Cbl was capable of reducing behavioral and neuronal alterations in nVHL rats. The behavioral analysis included locomotor activity induced by novel environment and amphetamine, social interaction, and sensoriomotor gating. The morphological evaluation included dendritic analysis by using the Golgi-Cox procedure and stereology to quantify the total cell number in PFC and NAcc. Behavioral data show a reduction in the hyperresponsiveness to novel environment- and amphetamine-induced locomotion, with an increase in the total time spent in social interactions and in prepulse inhibition in Cbl-treated nVHL rats. In addition, neuropathological analysis of the limbic regions also showed amelioration of dendritic retraction and spine loss in Cbl-treated nVHL rats. Cbl treatment also ameliorated dendritic pathology and neuronal loss in the PFC and NAcc in nVHL rats. This study demonstrates that Cbl promotes behavioral improvements and recovery of dendritic neuronal damage in postpubertal nVHL rats and suggests that Cbl may have neurotrophic effects in this neurodevelopmental model of schizophrenia. These findings support the possibility that Cbl has beneficial effects in the management of schizophrenia symptoms.

Animal models of schizophrenia

Developing reliable, predictive animal models for complex psychiatric disorders, such as schizophrenia, is essential to increase our understanding of the neurobiological basis of the disorder and for the development of novel drugs with improved therapeutic efficacy. All available animal models of schizophrenia fit into four different induction categories: developmental, drug-induced, lesion or genetic manipulation, and the best characterized examples of each type are reviewed herein. Most rodent models have behavioural phenotype changes that resemble 'positive-like' symptoms of schizophrenia, probably reflecting altered mesolimbic dopamine function, but fewer models also show altered social interaction, and learning and memory impairment, analogous to negative and cognitive symptoms of schizophrenia respectively. The negative and cognitive impairments in schizophrenia are resistant to treatment with current antipsychotics, even after remission of the psychosis, which limits their therapeutic efficacy. The MATRICS initiative developed a consensus on the core cognitive deficits of schizophrenic patients, and recommended a standardized test battery to evaluate them. More recently, work has begun to identify specific rodent behavioural tasks with translational relevance to specific cognitive domains affected in schizophrenia, and where available this review focuses on reporting the effect of current and potential antipsychotics on these tasks. The review also highlights the need to develop more comprehensive animal models that more adequately replicate deficits in negative and cognitive symptoms. Increasing information on the neurochemical and structural CNS changes accompanying each model will also help assess treatments that prevent the development of schizophrenia rather than treating the symptoms, another pivotal change required to enable new more effective therapeutic strategies to be developed.

Cortical disinhibition in the neonatal ventral hippocampal lesion model of schizophrenia: new vistas on possible therapeutic approaches

The neonatal ventral hippocampal lesion (NVHL) model of schizophrenia has been extensively used in many laboratories over the past couple of decades. With more than 120 publications from over 15 research groups, this developmental model yields a number of schizophrenia-relevant behavioral, neurochemical and electrophysiological deficits. An important aspect of this model is the delayed emergence of alterations, typically during adolescence despite the manipulation that causes them having been performed during the first postnatal week. Such delayed timing reflects the periadolescent onset of schizophrenia symptoms and may be related to the protracted maturation of cortical circuits, affected in both the disease and the NVHL model. Here, I will review the work we have done regarding the maturation of prefrontal cortical-accumbens circuits during adolescence, and how this maturation is affected in rats with a NVHL. One of the principal elements affected in NVHL rats is the dopamine modulation of prefrontal cortical interneurons, and this finding is convergent with data from many other developmental, genetic and pharmacological models. An altered maturation of interneuron function would yield a disinhibited cortex, and this opens the way to novel therapeutic approaches for treatment and even prevention of schizophrenia.

Cholinergic depletion in the nucleus accumbens: effects on amphetamine response and sensorimotor gating

A delicate balance between dopaminergic and cholinergic activity in the ventral striatum or nucleus accumbens (N.Acc) appears to be important for optimal performance of a wide range of behaviours. While functional interactions between these systems are complex, some data suggest that acetylcholine in the N.Acc. may dampen the effects of excessive dopamine (DA) release. We proposed that a reduction in the density of cholinergic interneurons in the N.Acc would result in behavioural alterations suggestive of a hyper-responsiveness of the N.Acc DA system. The present study aimed to produce a sustainable depletion of cholinergic neurons in the N.Acc in the rat and study the effects of such lesions on DA-dependent behaviour. A novel saporin immunotoxin targeting choline acetyltransferase was microinjected bilaterally into the N.Acc of adult rats. We confirmed histologically that two weeks post-injection, animals show a local, selective depletion of cholinergic interneurons (mean cell loss of 44%). Cholinergic-depleted rats showed a marked increase in the locomotor activating effects of amphetamine. In addition, such lesions induced a disruption of sensorimotor gating processes, reflected in a reduction in the prepulse inhibition of the acoustic startle response, which was reversed by haloperidol. These data are suggestive of pronounced hyper-responsiveness of the meso-accumbens DA system which may be of relevance to the pathophysiology of schizophrenia, a condition where selective reduction in the number of ventral striatal cholinergic neurons has been demonstrated.

Ventral and dorsal striatal dopamine efflux and behavior in rats with simple vs. co-morbid histories of cocaine sensitization and neonatal ventral hippocampal lesions

RATIONAL

Exposing animal models of mental illness to addictive drugs provides an approach to understanding the neural etiology of dual diagnosis disorders. Previous studies have shown that neonatal ventral hippocampal lesions (NVHL) in rats produce features of both schizophrenia and addiction vulnerability.

OBJECTIVE

This study investigated ventral and dorsal striatal dopamine (DA) efflux in NVHL rats combined with behavioral sensitization to cocaine.

METHODS

Adult NVHL vs. SHAM-operated rats underwent a 5-day injection series of cocaine (15 mg/kg/day) vs. saline. One week later, rats were cannulated in nucleus accumbens SHELL, CORE, or caudate-putamen. Another week later, in vivo microdialysis sampled DA during locomotor testing in which a single cocaine injection (15 mg/kg) was delivered.

RESULTS

NVHLs and cocaine history significantly increased behavioral activation approximately 2-fold over SHAM-saline history rats. DA efflux curves corresponded time dependently with the cocaine injection and locomotor curves and varied significantly by striatal region: Baseline DA levels increased 5-fold while cocaine-stimulated DA efflux decreased by half across a ventral to dorsal striatal gradient. However, NVHLs, prior cocaine history, and individual differences in behavior were not underpinned by differential DA efflux overall or within any striatal region.

CONCLUSION

Differences in ventral/dorsal striatal DA efflux are not present in and are not required for producing differential levels of acute cocaine-induced behavioral activation in NVHLs with and without a behaviorally sensitizing cocaine history. These findings suggest other neurotransmitter systems, and alterations in striatal network function post-synaptic to DA transmission are more important to understanding the interactive effects of addictive drugs and mental illness.

Early postnatal exposure to methylphenidate alters stress reactivity and increases hippocampal ectopic granule cells in adult rats

To mimic clinical treatment with methylphenidate (MPH; Ritalin) for attention deficit/hyperactivity disorder (ADHD), rat pups were injected with MPH (5 mg/kg, i.p.) or placebo twice daily during their nocturnal active phase from postnatal day (PND) 7-35. Thirty-nine days after the last MPH administration (PND 76), four litters of rats experienced stressful conditions during the 2003 New York City blackout. MPH-treated rats that endured the blackout lost more weight and regained it at a slower pace than controls (p<0.05; N=7-11 per group). Furthermore, MPH-treated rats had elevated systolic arterial blood pressure (from 115.6+/-1.2 to 126+/-1.8 mmHg; p<0.05), assessed on PND 130 by tail cuff plethysmography. Immunocytochemical studies of transmitter systems in the brain demonstrated rearrangements of catecholamine and neuropeptide Y fibers in select brain regions at PND 135, which did not differ between blackout and control groups. However, MPH-treated rats that endured the blackout had more ectopic granule cells in the hilus of the dorsal hippocampal dentate gyrus compared to controls at PND 135 (p<0.05; N=6 per group). These findings indicate that early postnatal exposure to high therapeutic doses of MPH can have long lasting effects on the plasticity of select brain regions and can induce changes in the reactivity to stress that persist into adulthood.

The neonatal ventral hippocampal lesion as a heuristic neurodevelopmental model of schizophrenia

Traditionally, animal models of schizophrenia were predominantly pharmacological constructs focused on phenomena linked to dopamine and glutamate neurotransmitter systems, and were created by direct perturbations of these systems. A number of developmental models were subsequently generated that allowed testing of hypotheses about the origin of the disease, mimicked a wider array of clinical and neurobiological features of schizophrenia, and opened new avenues for developing novel treatment strategies. The most thoroughly characterized (approximately 100 primary research articles) is the neonatal ventral hippocampal lesion (NVHL) model, which is the subject of this review. We highlight its advantages and limitations, and how it may offer clues about the extent to which positive, negative, cognitive, and other aspects of schizophrenia, including addiction vulnerability, represent inter-related pathophysiological mechanisms.

A neonatal ventral hippocampal lesion causes functional deficits in adult prefrontal cortical interneurons

Animals with a neonatal ventral hippocampal lesion (NVHL) develop abnormal behaviors during or after adolescence, suggesting that early insults can have delayed consequences. Many of these behaviors depend on the prefrontal cortex (PFC), and we have reported that PFC pyramidal neurons of adult rats with an NVHL respond to stimulation of the ventral tegmental area with an increase in firing instead of the characteristic decrease. As the dopamine modulation of cortical interneurons matures during adolescence, these findings raise the possibility that maturation of local inhibitory circuits within the PFC may have been altered in NVHL rats. Here, we assessed the state of PFC interneurons in NVHL rats with in situ hybridization measures of the mRNAs for the calcium binding protein parvalbumin (PV) and the GABA synthesizing enzyme GAD(67), as well as with electrophysiological measures of interneuron function. Although no differences were observed with PV or GAD(67), whole-cell recordings in slices revealed abnormal responses to the D(2) agonist quinpirole in interneurons from NVHL rats. The loss of D(2) modulation of local inhibition in slices from NVHL rats was also evident in the absence of a lasting component in the D(2) attenuation of excitatory synaptic responses in pyramidal neurons, which in sham treated rats was picrotoxin sensitive. The results suggest that the neonatal lesion causes improper maturation, but not loss, of PFC interneurons during adolescence, a finding consistent with current interpretations of imaging data in schizophrenia that suggest a hyperactive, "noisy" cortex underlying dysfunction in the PFC and other cortical areas.

Enhanced methamphetamine self-administration in a neurodevelopmental rat model of schizophrenia

RATIONALE

Substance abuse is more prevalent among patients with schizophrenia than in the general population. The considerable overlap in neurobiological disruptions thought to underlie each condition suggests that addictive behavior may represent a primary symptom of schizophrenia.

OBJECTIVE

This study investigated drug-seeking in a neurodevelopmental animal model of schizophrenia, the neonatal ventral hippocampal lesion (NVHL) model.

MATERIALS AND METHODS

At postnatal day 7, rats received an excitotoxic ventral hippocampus lesion or a sham procedure and were trained as adults to self-administer methamphetamine (0.1 mg/kg/infusion) or respond for natural reinforcement (water or food).

RESULTS

NVHL rats were faster than shams to acquire the operant response for either drug self-administration or water reinforcement, suggesting that simple instrumental learning may be enhanced in these animals. NVHL and sham rats displayed no differences in fixed-ratio (FR) responding for either methamphetamine or food, and both groups of animals were equally sensitive to methamphetamine dose changes (0.05, 0.1, or 0.2 mg/kg/infusion). However, under a progressive-ratio (PR) schedule, NVHL animals reached significantly higher break points (NVHL 18 infusions; sham 12 infusions) for methamphetamine but not food reinforcement, suggesting enhanced motivation to acquire drug and/or elevated incentive value of the drug that did not generalize to another form of reinforcement.

CONCLUSIONS

These data indicate that developmental disruption of the hippocampus elevates rats' vulnerability to drug-seeking behavior under PR conditions. Furthermore, drug self-administration in the NVHL animal emulates addictive behavior in schizophrenia, making this model useful for investigating the mechanisms of dual diagnosis, including the neurobiological and behavioral similarities between addiction and schizophrenia.

Emergence of stereotypies in juvenile monkeys (Macaca mulatta) with neonatal amygdala or hippocampus lesions

The emergence of stereotypies was examined in juvenile rhesus monkeys (Macaca mulatta) who, at 2 weeks of postnatal age, received selective bilateral ibotenic acid lesions of the amygdala (N = 8) or hippocampus (N = 8). The lesion groups were compared to age-matched control subjects that received a sham surgical procedure (N = 8). All subjects were maternally reared for the first 6 months and provided access to social groups throughout development. Pronounced stereotypies were not observed in any of the experimental groups during the first year of life. However, between 1 to 2 years of age, both amygdala- and hippocampus-lesioned subjects began to exhibit stereotypies. When observed as juveniles, both amygdala- and hippocampus-lesioned subjects consistently produced more stereotypies than the control subjects in a variety of contexts. More interesting, neonatal lesions of either the amygdala or hippocampus resulted in unique repertoires of repetitive behaviors. Amygdala-lesioned subjects exhibited more self-directed stereotypies and the hippocampus-lesioned subjects displayed more head-twisting. We discuss these results in relation to the neurobiological basis of repetitive stereotypies in neurodevelopmental disorders, such as autism.

Twenty years of dopamine research: individual differences in the response of accumbal dopamine to environmental and pharmacological challenges

Individual differences in the dopaminergic system of the nucleus accumbens of rats have extensively been reported. These individual differences have frequently been used to explain individual differences in response to environmental and pharmacological challenges. Remarkably, only little attention is paid to the factors that underlie these individual differences. This review gives an overview of the studies that have been performed in our institute during the last 20 years to investigate individual differences in accumbal dopamine release. Data are summarised demonstrating that individual differences in accumbal dopamine release are due to individual differences in: the functional reactivity of the noradrenergic system, the accumbal concentration of vesicular monoamine transporters and tyrosine hydroxylase as well as in the quantal size of the presynaptic pools of dopamine. Our data are embedded in the available literature to create a model that illustrates the putative hardware giving rise to the individual-specific release of accumbal dopamine. An important role is contributed to individual differences in the reactivity of the: hypothalamic-pituitary-adrenal axes, the reactivity of second messenger systems as well in the aminergic reactivity of the accumbens shell and core. The consequences of the individual-specific make-up and reactivity of the nucleus accumbens on the regulation of behaviour and the response to drugs of abuse will also be discussed. Apart from agents that interact with dopaminergic receptors, re-uptake or breakdown, noradrenergic agents as well as agents that interact with vesicular monoamine transporters or tyrosine hydroxylase are suggested to have therapeutic effects in subjects that are suffering from diseases in which the dopaminergic system is disturbed.

Methylphenidate administration to juvenile rats alters brain areas involved in cognition, motivated behaviors, appetite, and stress

Thousands of children receive methylphenidate (MPH; Ritalin) for attention deficit/hyperactivity disorder (ADHD), yet the long-term neurochemical consequences of MPH treatment are unknown. To mimic clinical Ritalin treatment in children, male rats were injected with MPH (5 mg/kg) or vehicle twice daily from postnatal day 7 (PND7)-PND35. At the end of administration (PND35) or in adulthood (PND135), brain sections from littermate pairs were immunocytochemically labeled for neurotransmitters and cytological markers in 16 regions implicated in MPH effects and/or ADHD etiology. At PND35, the medial prefrontal cortex (mPFC) of rats given MPH showed 55% greater immunoreactivity (-ir) for the catecholamine marker tyrosine hydroxylase (TH), 60% more Nissl-stained cells, and 40% less norepinephrine transporter (NET)-ir density. In hippocampal dentate gyrus, MPH-receiving rats showed a 51% decrease in NET-ir density and a 61% expanded distribution of the new-cell marker PSA-NCAM (polysialylated form of neural cell adhesion molecule). In medial striatum, TH-ir decreased by 21%, and in hypothalamus neuropeptide Y-ir increased by 10% in MPH-exposed rats. At PND135, MPH-exposed rats exhibited decreased anxiety in the elevated plus-maze and a trend for decreased TH-ir in the mPFC. Neither PND35 nor PND135 rats showed major structural differences with MPH exposure. These findings suggest that developmental exposure to high therapeutic doses of MPH has short-term effects on select neurotransmitters in brain regions involved in motivated behaviors, cognition, appetite, and stress. Although the observed neuroanatomical changes largely resolve with time, chronic modulation of young brains with MPH may exert effects on brain neurochemistry that modify some behaviors even in adulthood.

Alterations in GABAA receptor expression in neonatal ventral hippocampal lesioned rats: Comparison of prepubertal and postpubertal periods

Rats with neonatal ventral hippocampal lesions (NVHL) have been studied as a neurodevelopmental animal model of schizophrenia. NVHL rats exhibit postpubertal emergence of hyperresponsiveness to stress, suggesting increased mesolimbic dopamine (DA) activity. However, previous studies have not yielded clear evidence of this. Disturbances in the gamma-amino-butyric acid (GABA)-ergic system as well as the dopaminergic system are thought to be present in schizophrenia. To determine whether GABA(A) receptors play a role in the abnormal postpubertal behavior in NVHL rats, we compared changes in expression of mRNA of GABA(A) receptor subunits and in [(35)S] t-butylbicyclophosphorothionate ([(35)S] TBPS) binding in the prepubertal and postpubertal periods. Male pups were lesioned with ibotenic acid at postnatal day 7 (PD 7), and in situ hybridization and quantitative autoradiography were then performed. In NVHL rats, alpha1 subunit mRNA expression in prefrontal cortex was decreased at PD 35 (prepubertal period; by 21.7%), but increased at PD 56 (postpubertal period; by 21.4%) when compared with sham controls. beta2 subunit mRNA expression was increased in PFC in the postpubertal period (by 24.3%). beta3 subunit mRNA expression was increased in the caudate-putamen in the postpubertal period (by 37.2%). [(35)S] TBPS binding was increased in PFC only in the postpubertal period (by 17.7%). These findings suggest that dysfunction of the GABAergic system exists in NVHL rats. Furthermore, developmental and regional changes in GABA(A) receptor expression appear to occur in compensation for the attenuation of GABAergic system activity in NVHL rats.

Peri-pubertal maturation after developmental disturbance: a model for psychosis onset in the rat

Schizophrenia is thought to be associated with abnormalities during neurodevelopment although those disturbances usually remain silent until puberty; suggesting that postnatal brain maturation precipitates the emergence of psychosis. In an attempt to model neurodevelopmental defects in the rat, brain cellular proliferation was briefly interrupted with methylazoxymethanol (MAM) during late gestation at embryonic day 17 (E17). The litters were explored at pre- and post-puberty and compared with E17 saline-injected rats. We measured spontaneous and provoked locomotion, working memory test, social interaction, and prepulse inhibition (PPI). As compared with the saline-exposed rats, the E17 MAM-exposed rats exhibited spontaneous hyperactivity that emerged only after puberty. At adulthood, they also exhibited hypersensitivity to the locomotor activating effects of a mild stress and a glutamatergic N-methyl-D-aspartate receptor antagonist (MK-801), as well as PPI deficits whereas before puberty no perturbations were observed. In addition, spatial working memory did not undergo the normal peri-pubertal maturation seen in the sham rats. Social interaction deficits were observed in MAM rats, at both pre- and post-puberty. Our study further confirms that transient prenatal disruption of neurogenesis by MAM at E17 is a valid behavioral model for schizophrenia as it is able to reproduce some fundamental features of schizophrenia with respect to both phenomenology and temporal pattern of the onset of symptoms and deficits.

Enhanced locomotor activity in adult rats with neonatal administration ofN-omega-nitro-L-arginine

Nitric oxide (NO) is a neuronal messenger molecule that plays important roles in the development, maintenance, and functional modifications of brain circuits. We investigated whether the NO levels at different postnatal day (P) periods of the brain develop interference with the locomotion in a novel environment during the postpuberal age (P60). First, using the determination of the nitrite accumulation, we evaluated whether treatment with the NO-synthase inhibitor N-nitro-L-arginine (L-NNA) during different neonatal ages (P1 to P3, P4 to P6, and P7 to P9) affected the levels of NO activity in different regions in the neonatal brain of the rat. We then evaluated whether the locomotor activity in the adult rat (P60) is affected by the blocking of the neonatal NO-activity during a specific period of the development of the nervous system. Neonatal rats with L-NNA administration at P4 to P6 and P7 to P9 show a significant decrease in the levels of NO activity in all the brain regions. However, the blocking of NO synthesis during the neonatal period between P4 to P6 produced an increase in the locomotion after puberty. These data suggest that during a specific step in the development of the brain, the NO levels may play a critical role in the structures that control the spontaneous locomotion in a novel environment after puberty.

Strain differences of dopamine receptor levels and dopamine related behaviors in rats

Here we have investigated whether differences in levels of dopamine D1-like, D2-like receptors, dopamine D3 receptors, and dopamine transporter could be related to behaviors such as immobility response and locomotion between Wistar rats and Sprague-Dawley rats. The levels of the dopamine receptors and transporter were measured by autoradiographic study at the level of basal ganglia and the limbic subregion. The behavioral study was done by open-field and immobility response tests. The Wistar rats exhibited a higher level of D1 receptor binding in the basal ganglia subregions than Sprague-Dawley rats. The Wistar rats have higher levels of dopamine D2 receptor binding and dopamine transporter binding in the dorsolateral part of the caudate-putamen. In addition, the dopamine transporter binding were also higher in the Wistar rats than in Sprague-Dawley rats in the ventral part of the caudate-putamen and nucleus accumbens core. However, there were no differences in the level of D3 receptor binding in the limbic or basal ganglia subregions between these two strains. In Wistar rats, the duration of the immobility responses was longer and with less locomotor activity after these immobility responses compared with Sprague-Dawley rats. These data suggest that the differences in dopamine receptors in these two rat strains may in part relate to the behavioral differences reported in these two strains.

Effect of excitotoxic lesions of the neonatal ventral hippocampus on the immobility response in rats

Rats with neonatal ventral hippocampal (nVH) lesions show postpubertal hypersensitivity to dopamine agonists, which may be reversed by neuroleptic treatment. In addition, the immobility response (IR) may be regulated by dopaminergic activity. We investigated the influence of the IR caused by clamping the neck of rats that had received bilateral ibotenic acid lesions of the ventral hippocampus at postnatal day 7 (PD7). At both ages, prepubertal (PD35) and postpubertal (PD56), the duration of the IR was significantly increased in animals with lesions when compared to controls. These findings indicate that nVH damage results in behavioral changes, such as enhancement of the IR, related to mesolimbic dopaminergic transmission.

Alterations in dendritic morphology of prefrontal cortical and nucleus accumbens neurons in post-pubertal rats after neonatal excitotoxic lesions of the ventral hippocampus

Neonatal ventral hippocampal (nVH) lesions in rats result in adult onset of a number of behavioral and cognitive abnormalities analogous to those seen in schizophrenia, including hyperresponsiveness to stress and psychostimulants and deficits in working memory, sensorimotor gating and social interaction. Molecular and neurochemical alterations in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) of nVH-lesioned animals suggest developmental reorganization of these structures following neonatal lesions. To determine whether nVH lesions lead to neuronal morphological changes, we investigated the effect of nVH lesion on dendritic structure and spine density of pyramidal neurons of the PFC and medium spiny neurons of the NAcc. Bilateral ibotenic acid-induced lesion of the VH was made in Sprague-Dawley pups at postnatal day 7 (P7); and at P70, neuronal morphology was quantified by modified Golgi-Cox staining. The results show that length of basilar dendrites and branching and the density of dendritic spines on layer 3 pyramidal neurons were significantly decreased in rats with nVH lesions. Medium spiny neurons from the NAcc showed a decrease in the density of dendritic spines without significant changes in dendritic length or arborization. The data, comparable to those observed in the PFC of schizophrenic patients, suggest that developmental loss of excitatory projections from the VH may lead to altered neuronal plasticity in the PFC and the NAcc that may contribute to the behavioral changes in these animals.

Effects of neonatal ventral hippocampal lesion in rats on stress-induced acetylcholine release in the prefrontal cortex

Excitotoxic neonatal ventral hippocampus (NVH) lesions in rats result in characteristic post-pubertal hyper-responsiveness to stress and cognitive abnormalities analogous to those described in schizophrenia and suggestive of alterations in dopamine (DA) neurotransmission. Converging lines of evidence also point to dysfunctions in the cortical cholinergic system in neuropsychiatric disorders. In previous studies, we observed alterations in dopaminergic modulation of acetylcholine (Ach) release in the prefrontal cortex (PFC) in post-pubertal NVH-lesioned rats. These two neurotransmitter systems are involved in the stress response as PFC release of DA and Ach is enhanced in response to some stressful stimuli. As adult NVH-lesioned rats are behaviorally more reactive to stress, we investigated the effects of NVH lesions on tail-pinch stress-induced Ach and DA release in the PFC. Using in vivo microdialysis, we observed that tail-pinch stress resulted in significantly greater increases in prefrontal cortical Ach release in post-pubertal NVH-lesioned rats (220% baseline) compared with sham-operated controls (135% baseline). Systemic administration of the D1-like receptor antagonist SCH 23390 (0.5 mg/kg i.p.) or the D2-like receptor antagonist haloperidol (0.2 mg/kg i.p.), as well as intra-PFC administration of the D2-like antagonist sulpiride (100 microm), reduced stress-induced Ach release in PFC of adult NVH-lesioned rats. By contrast, intra-PFC administration of SCH 23390 (100 microm) failed to affect stress-induced Ach release in PFC of NVH-lesioned rats. Interestingly, using in vivo voltammetry, stress-induced stimulation of PFC DA release was found to be attenuated in adult NVH-lesioned rats. Taken together, these data suggest developmentally specific reorganization of prefrontal cortical cholinergic innervation notably regarding its regulation by DA neurotransmission.

The supramammillary area: its organization, functions and relationship to the hippocampus

The supramammillary area of the hypothalamus, although small in size, can have profound modulatory effects on the hippocampal formation and related temporal cortex. It can control hippocampal plasticity and also has recently been shown to contain cells that determine the frequency of hippocampal rhythmical slow activity (theta rhythm). We review here its organization and anatomical connections providing an atlas and a new nomenclature. We then review its functions particularly in relation to its links with the hippocampus. Much of its control of behaviour and its differential activation by specific classes of stimuli is consistent with a tight relationship with the hippocampus. However, its ascending connections involve not only caudal areas of the cortex with close links to the hippocampus but also reciprocal connections with more rostral areas such as the infralimbic and anterior cingulate cortices. These latter areas appear to be the most rostral part of a network that, via the medial septum, hippocampus and lateral septum, is topographically mapped into the hypothalamus. The supramammillary area is thus diffusely connected with areas that control emotion and cognition and receives more topographically specific return information from areas that control cognition while also receiving ascending information from brain stem areas involved in emotion. We suggest that it is a key part of a network that recursively transforms information to achieve integration of cognitive and emotional aspects of goal-directed behaviour.

Neonatal ventral hippocampus lesion alters the dopamine content in the limbic regions in postpubertal rats

The neonatal ventral Hippocampus (nVH) lesion in rats has been used as a model to test the hypothesis that early neurodevelopmental abnormalities lead to behavioral changes putatively linked to schizophrenia. The schizophrenic patients tend to social isolation. In addition, considerable evidence from behavioral and neurochemistry studies strongly implicate the dopamine (DA) system and the medial part of the prefrontal cortex (mPFC) in the pathophysiology of the social isolation syndrome. In order to assess effects of the postweaning social isolation (pwSI) on the DA system of the nVH lesions, we investigated the DA content and its metabolite, DOPAC in different limbic subregions in rats postpubertally at postnatal day (P) 78 following nVH lesions at P7 with and without pwSI for 8 weeks. The DA and DOPAC were measured by HPLC with electrochemical detection. The nVH lesion induces increase in the DA content in the hippocampus with no effect in the mPFC, nucleus accumbens and caudate-putamen, while the pwSI induces major increase in the DA content in limbic subregions such as the mPFC, nucleus accumbens and hipocampus with opposite effect in the caudate-putamen. These results suggest that while pwSI has an effect in the postpubertal content of DA in both sham and nVH lesions in rats, the nVH-lesioned rats appear to be affected to a greater extent than the sham animals underscoring the influence of pwSI differences in the development of behaviors in the nVH-lesioned animals.

Anoxia at birth induced hyperresponsiveness to amphetamine and stress in postpubertal rats

Several evidences suggest that transient global anoxia after Caeraean section birth in rats produces behavioral changes related to dopaminergic transmission. However, all of the reports tested the behavioral changes in adult rats. Here we investigated the role of perinatal anoxia on behavioral paradigms related to dopamine (DA) such as novel environment, saline injection, D-amphetamine, apomorphine and stress-induced changes in locomotor activity at prepubertal and postpubertal ages. All these dimensions of behavior can be affected in schizophrenia. Caesarean section birth with or without an additional period of anoxia was performed in Sprague-Dawley rats and their behaviors were studied at P35 and P56, respectively. In addition, a third group of animals born vaginally served as control. No significant differences in saline injection and D-amphetamine-induced locomotion were observed when the three groups of rats at P35 were compared. However, stress-induced locomotor activity was significantly increased in the Caesarean birth plus anoxia at P35, while after puberty (at P56), saline injection, D-amphetamine and stress-induced locomotion were significantly enhanced in the Caesarean birth plus anoxia compared to its control groups. The data suggests that anoxia at birth mediates differently the functional development and maturation of DA behaviors in adult rats.

Neonatal ventral hippocampus lesion leads to reductions in nerve growth factor inducible-B mRNA in the prefrontal cortex and increased amphetamine response in the nucleus accumbens and dorsal striatum

Converging evidence in schizophrenia suggests prefrontal cortical neuronal deficits that correlate with exaggerated subcortical dopamine (DA) functions: Excitotoxic lesion of the ventral hippocampus (VH) in neonatal rats is widely considered a putative animal model of schizophrenia as they lead to characteristic post-pubertal emergence of behavioral and cognitive abnormalities suggesting a developmental change in the neural circuits comprising the prefrontal cortex (PFC) and subcortical DA. Nerve growth factor inducible-B (NGFI-B, also known as Nur77), an orphan nuclear receptor and transcriptional regulator, is constitutively expressed in the target structures of DA pathways. It acts as an immediate early gene with rapid modulation of its mRNA expression by stress, DA and antipsychotic drugs. The present study assessed the effects of neonatal VH (nVH) lesion and amphetamine treatment on the expression of NGFI-B mRNA in pre- and post-pubertal rats. Sprague-Dawley rat pups received bilateral injection of ibotenic acid or phosphate buffered saline in VH at postnatal (PD) 7. At PD35 and PD56, groups of sham and lesioned animals were administered with D-amphetamine (1.5 mg/kg) or saline and killed 20 min later. In situ hybridization analyses showed that the basal level of NGFI-B mRNA in saline-treated lesioned rats was significantly reduced in the medial PFC (mPFC) and cingulate cortex (CC) only at post-pubertal (PD56) age. No significant difference in NGFI-B mRNA levels was seen in the dorsal striatum or nucleus accumbens (NAcc). Amphetamine treatment increased the expression of NGFI-B mRNA in the mPFC, CC, striatum and NAcc in both control and lesioned animals of both ages. Interestingly, however, striatal and NAcc regions of lesioned rats showed a significantly greater effect of amphetamine at PD56. The data suggest that nVH lesions lead to delayed changes in PFC gene expression along with functional DAergic hyperactivity in subcortical regions.

The neonatal ventral hippocampal lesion model of schizophrenia: effects on dopamine and GABA mRNA markers in the rat midbrain

The neonatal ventral hippocampal lesion in the rat has been used as a model of schizophrenia, a human disorder associated with changes in markers of dopamine and gamma-aminobutyric acid (GABA) circuits in various regions of the brain. We investigated whether alterations in mRNA markers related to the activity of midbrain dopaminergic and GABAergic neurons are associated with this model. We used in situ hybridization histochemistry to assess expression of mRNAs for dopamine transporter (DAT), tyrosine hydroxylase (TH) and glutamate decarboxylase-67 (GAD67) in the midbrain of adult rats with neonatal and adult ibotenic acid lesions of the ventral hippocampus. Neonatally lesioned rats showed in adulthood significantly reduced expression of DAT mRNA in the substantia nigra and the ventral tegmental area but no changes in the expression of TH and GAD67 mRNAs in these midbrain regions. Adult lesioned rats showed no changes in the expression of any of these genes. As the neonatal ventral hippocampal lesion reproduces many aspects of schizophrenia and is used as an animal model of this disorder, these results suggest that the reduction in DAT mRNA could result from developmental neuropathology in the ventral hippocampus and may thus represent a molecular substrate of the disease process.

Post-pubertal adrenergic changes in rats with neonatal lesions of the ventral hippocampus

Lesions of the ventral hippocampus (VH) in neonatal rats result in post-pubertal alterations in a number of cognitive, social and motor behaviors that bear some analogy to schizophrenia. Increased sensitivity to stress and psychostimulants and prefrontal functional changes in the lesioned animals suggest an involvement of the mesocorticolimbic dopamine (DA) system. DA and norepinephrine (NE) interact in a number of ways in the medial prefrontal cortex (mPFC) to influence each other's functions. In order to assess the role of adrenergic system in the behavioral responses of neonatal VH (nVH) lesioned animals, we first examined cortical and subcortical bindings of alpha-1 and alpha-2 adrenergic receptors using [3H]-prazosin and [3H]-rauwolscine respectively, and the norepinephrine transporter (NET) using [3H]-nisoxetine. Sprague-Dawley rat pups, at post-natal day (PD) 7, received bilateral injections of ibotenic acid in the VH and were sacrificed pre (PD35)- and post (PD56)-pubertally. A significant increase in [3H]-prazosin binding was observed in the frontal and cingulate cortices of lesioned rats at PD56 without any significant change in the caudate putamen or nucleus accumbens. No significant difference was seen in [3H]-rauwolscine binding. A significant upregulation of NET binding was observed in subregions of the PFC and nucleus accumbens of PD56 lesioned rats. The functional relevance of changes in adrenergic markers on amphetamine-induced locomotor activity was examined by pre-treatment of PD56 rats with prazosin, an alpha-1 receptor antagonist. Prazosin at doses of 1.0 or 2.0 mg/kg ip significantly reduced amphetamine-induced locomotion in sham but not in PD56 lesioned animals. Taken together, these results suggest that alterations in prefrontal alpha-1 receptors likely contribute to altered behavioral responses observed in post-pubertal VH lesioned rats.

Prepulse inhibition deficits of the startle reflex in neonatal ventral hippocampal-lesioned rats: reversal by glycine and a glycine transporter inhibitor

BACKGROUND

Neonatal ventral hippocampal (NVH) lesions in rats induce behavioral abnormalities at adulthood thought to simulate some aspects of the positive, negative, and cognitive deficits classically observed in schizophrenic patients. Such lesions induce a postpubertal emergence of prepulse inhibition (PPI) deficits of the startle reflex reminiscent of the sensorimotor gating deficits observed in a majority of schizophrenic patients. To study the potential involvement of the glycinergic neurotransmission in such deficits, we investigated the capacity of glycine (an obligatory N-methyl-D-aspartate [NMDA] receptor co-agonist) and ORG 24598 (a selective glycine transporter 1 inhibitor) to reverse NVH lesion-induced PPI deficits in rats.

METHODS

Ibotenic acid was injected bilaterally into the ventral hippocampus of 7-day-old pups. Prepulse inhibition of the startle reflex was measured at adulthood.

RESULTS

Glycine (.8 and 1.6 g/kg IP) and ORG 24598 (10 mg/kg IP) fully and partially reversed lesion-induced PPI deficits, respectively.

CONCLUSIONS

These findings confirm that an impaired glutamatergic neurotransmission may be responsible for PPI deficits exhibited by NVH-lesioned rats and support the hypoglutamatergic hypothesis of schizophrenia. They also suggest that drugs acting either directly at the NMDA receptor glycine site or indirectly on the glycine transporter 1 could offer promising targets for the development of novel therapies for schizophrenia.

Phencyclidine exacerbates attentional deficits in a neurodevelopmental rat model of schizophrenia

Schizophrenia is characterized by severe abnormalities in cognition, including disordered attention. In the rat, neonatal ventral hippocampal (NVH) lesions induce behavioral abnormalities at adulthood thought to simulate some aspects of the symptomatology of schizophrenia. Here, we compared the effects of NVH and adult ventral hippocampal (AVH) lesions on attentional performance as assessed by the five-choice serial reaction time task (5-CSRTT). NVH-lesioned rats were slower to acquire the task than AVH-lesioned and control animals. When training was complete, NVH- and AVH-lesioned animals exhibited stable but disrupted performance under standard conditions, thus emphasizing an implication of VH in visual attentional processes. Variations in task parameters induced a significantly greater disruption in NVH- and AVH-lesioned groups as compared to controls. NVH-lesioned rats were also hyper-responsive to the disruptive effects of a high dose of phencyclidine (PCP) (3 mg/kg). In contrast, amphetamine (0.4-0.8 mg/kg) had a similar effect in control and VH-lesioned rats. Thus, NVH-lesioned rats were impaired in the acquisition of stable performance in the 5-CSRTT, and were hypersensitive to the cognitive-impairing effects of PCP.

Early environment contributes to developmental disruption of MPFC after neonatal ventral hippocampal lesions in rats

Using a putative animal model of schizophrenia, neonatal rat ventral hippocampal (VH) lesions, combined with cross-fostering Lewis and Fisher rats, we previously demonstrated that the postpubertal expression of amphetamine-induced hyperlocomotion after lesioning depends on the early environment of the pups. However, an important question that emerged from our studies was whether the early environment leads to sparing of function within the VH or to the disruption of another structure, such as the medial prefrontal cortex (MPFC). To answer this question, we took advantage of the natural variation in maternal care of Sprague-Dawley rat dams and separated them into high and low arched back nursing (ABN) groups. Then, on postnatal day 7 (PD7) the pups from the two groups of dams were lesioned in the VH. As a measure of VH function, the rats were tested in a reference memory paradigm, which demonstrated that nVH-lesioned rats raised by high or low ABN dams had pronounced deficits, suggesting that VH functions are not fully spared. Next, the integrity of the MPFC was tested in a number of paradigms in which MPFC function has been implicated. In all three paradigms a similar result was found, that only lesioned rats raised by high ABN dams displayed deficits, such as a lack of MPFC control of amphetamine-induced locomotion, decreased working memory, and decreased anxiety. These results suggest that the early environment does not affect the recovery of the VH to nVH lesion. Rather, the early environment interacts with nVH lesions in such a way that disrupts the development and function of MPFC.

Decreased dendritic spine density on prefrontal cortical and hippocampal pyramidal neurons in postweaning social isolation rats

The effects of postweaning social isolation (pwSI) on the morphology of the pyramidal neurons from the medial part of the prefrontal cortex (mPFC) and hippocampus were investigated in rats. The animals were weaned on day 21 postnatal (P21) and isolated 8 weeks. After the isolation period, locomotor activity was evaluated through 60 min in the locomotor activity chambers and the animals were sacrificed by overdoses of sodium pentobarbital and perfused intracardially with 0.9% saline solution. The brains were removed, processed by the Golgi-Cox stain and analyzed by the Sholl method. The locomotor activity in the novel environment from the isolated rats was increased with respect to the controls. The dendritic morphology clearly showed that the pwSI animals presented a decrease in dendritic length of pyramidal cells from the CA1 of the hippocampus without changes in the pyramidal neurons of the mPFC. However, the density of dendritic spines was decreased in the pyramidal cells from mPFC and Hippocampus. In addition, the Sholl analyses showed that pwSI produced a decrease in the number of sholl intersections compared with the control group only in the hippocampus region. The present results suggest that pwSI may in part affect the dendritic morphology in the limbic structures such as mPFC and hippocampus that are implicated in schizophrenia.

Gene expression in dopamine and GABA systems in an animal model of schizophrenia: effects of antipsychotic drugs

We used in situ hybridization histochemistry to assess expression of dopamine receptors (D1R, D2R and D3R), neurotensin, proenkephalin and glutamate decarboxylase-67 (GAD67) in the prefrontal cortex, striatum, and/or nucleus accumbens in adult rats with neonatal ventral hippocampal (VH) lesions and in control animals after acute and chronic treatment with antipsychotic drugs clozapine and haloperidol. We also acquired these measures in a separate cohort of treatment-naïve sham and neonatally VH-lesioned rats used as an animal model of schizophrenia. Our results indicate that the neonatal VH lesion did not alter expression of D1R, D3R, neurotensin or proenkephalin expression in any brain region examined. However, D2R mRNA expression was down-regulated in the striatum, GAD67 mRNA was down-regulated in the prefrontal cortex and prodynorphin mRNA was up-regulated in the striatum of the VH-lesioned rats as compared with sham controls. Antipsychotic drugs did not alter expression of D1R, D2R or D3R receptor mRNAs but elevated neurotensin and proenkephalin expression in both groups of rats; patterns of changes were dependent on the duration of treatment and brain area examined. GAD67 mRNA was up-regulated by chronic antispychotics in the nucleus accumbens and the striatum and by chronic haloperidol in the prefrontal cortex in both sham and lesioned rats. These results indicate that the developmental VH lesion changed the striatal expression of D2R and prodynorphin and robustly compromised prefrontal GAD67 expression but did not modify drug-induced expression of any genes examined in this study.

Comparative behavioral changes between male and female postpubertal rats following neonatal excitotoxic lesions of the ventral hippocampus

Neonatal ventral hippocampal (nVH) lesioned male rat has been used as a model to test the hypothesis that early neurodevelopmental abnormalities lead to behavioral changes putatively linked to schizophrenia. There are significant gender differences in schizophrenia with male and female individuals differing in the age of onset, course and outcome of the disorder. In order to assess whether the behavioral effects of nVH lesions extend to or are different in female rats, we investigated spontaneous locomotion, grooming, social interactions and spatial memory in male and female rats post-pubertally at postnatal day (P) 56 following bilateral ibotenic acid of the ventral hippocampus at P7. The spontaneous locomotor activity in a novel environment of both male and female nVH lesioned rats was significantly enhanced compared to their respective sham-operated controls. In tests of social interactions, the number of encounters was significantly decreased in female lesioned rats, whereas the male nVH lesioned rats showed a significantly reduced duration of active social interactions. Furthermore, Morris water maze test showed a deficit of spatial learning/memory in only male lesioned rats with significant decrease in the latency to find hidden platform. These results suggest that while nVH lesions affect post-pubertal behavior in both sexes of rats, the males appear to be affected to a greater extent than the females underscoring the influence of sex differences in the development of behaviors in the nVH lesioned animals.

Neonatal ventral hippocampal damage modifies serum corticosterone and dopamine release responses to acute footshock in adult Sprague-Dawley rats

Rats with excitotoxic neonatal ventral hippocampal lesions (NVHL) manifest in early adulthood a variety of behavioral and neurochemical abnormalities mimicking those seen in patients with schizophrenia. Some of these aberrations implicate malfunction of the midbrain dopamine systems. We studied NVHL effects on dopamine release in the rat frontal cortex, nucleus accumbens, and striatum during acute stress caused by inescapable continuous footshock (0.45 mA). Serum total corticosterone and prolactin levels were used as peripheral indices of stress. As an indirect index of dopamine release, tissue 3-methoxytyramine levels attained in vivo 10 min after monoamine oxidase inhibition was assayed in rats sacrificed by instantaneous microwave fixation of the brain tissue. Nonshocked NVHL rats showed significantly less nucleus accumbens' 3-methoxytyramine accumulation than their sham counterparts. Frontal cortical 3-methoxytyramine levels rose similarly after 20-min footshock in both groups of rats, but while it normalized after 60-min footshock in the sham rats, it did not decrease in the NVHL rats. Nucleus accumbens' 3-methoxytyramine was significantly elevated after either 20-min or 60-min footshock in both groups, whereas striatal 3-methoxytyramine was significantly elevated in the NVHL rats only. Serum corticosterone showed similar elevations in the sham and NVHL rats, but the patterns differed in that there was no attenuation after 60-min footshock in the latter. The lesion did not affect serum prolactin response. These data indicate that neonatal ventral hippocampal damage enhances and prolongs certain neural and neuroendocrine responses to acute physical stressor(s), and thus may affect adaptation and enhance detrimental effects of stress.

A neurodevelopmental model of schizophrenia: neonatal disconnection of the hippocampus

In the context of our current knowledge about schizophrenia, heuristic models of psychiatric disorders may be used to test the plausibility of theories developed on the basis of new emerging biological findings, explore mechanisms of schizophrenia-like phenomena, and develop potential new treatments. In a series of studies, we have shown that neonatal excitotoxic lesions of the rat ventral hippocampus (VH) may serve as a heuristic model. The model appears to mimic a spectrum of neurobiological and behavioral features of schizophrenia, including functional pathology in presumably critical brain regions interconnected with the hippocampal formation and targeted by antipsychotic drugs - the striatum/nucleus accumbens and the prefrontal cortex, and leads in adolescence or early adulthood to the emergence of abnormalities in a number of dopamine related behaviors. Moreover, our data show that even transient inactivation of the ventral hippocampus during a critical period of development, that produces subtle, if any, anatomical changes in the hippocampus, may be sufficient to disrupt normal maturation of the prefrontal cortex (and perhaps, other interconnected late maturing regions) and trigger behavioral changes similar to those observed in animals with the permanent excitotoxic lesion. These results represent a potential new model of aspects of schizophrenia without a gross anatomical lesion.

Adaptation and habituation to an open field and responses to various stressful events in animals with neonatal lesions in the amygdala or ventral hippocampus

A rat model of neurodevelopmental psychopathological disorders, designed to determine neurodevelopmental deficits following damage to the brain early in life, was used to investigate behavioural changes in adaptation and habituation to an open field and responses to different kinds of stressful events. Animals with bilateral ibotenic acid lesions in the amygdala or ventral hippocampus on day 7 or 21 of life were compared to sham-operated animals. According to the model it was assumed that behavioural changes in animals lesioned on day 7, but not in animals lesioned on day 21 of life, were caused by maldevelopment of one or more structures connected to the damaged area. Animals lesioned in the amygdala or ventral hippocampus on day 7, but not animals lesioned in these structures on day 21 of life, displayed decreased (within-session) adaptation and (between-session) habituation to the open field and a decrease in immobility in the forced swim test, whereas only animals lesioned in the amygdala displayed enhanced general activity. These results were indicative of neurodevelopmental deficits. No changes in stress-induced hyperthermia were found, while animals lesioned in the amygdala both on day 7 or 21 of life exhibited decreased conditioned ultrasonic vocalizations. These latter results suggest that the amygdala is implicated in the conditioned stress-induced response. The contribution of the present findings to the animal model of neurodevelopmental disorders like schizophrenia and possible brain structures and neurotransmitter systems involved in the neurodevelopmental deficits are discussed.