CNS autoimmune response in the MAM/pilocarpine rat model of epileptogenic cortical malformation.

The development of seizures in epilepsy syndromes associated with malformations of cortical development (MCDs) has traditionally been attributed to intrinsic cortical alterations resulting from abnormal network excitability. However, recent analyses at single-cell resolution of human brain samples from MCD patients have indicated the possible involvement of adaptive immunity in the pathogenesis of these disorders. By exploiting the MethylAzoxyMethanol (MAM)/pilocarpine (MP) rat model of drug-resistant epilepsy associated with MCD, we show here that the occurrence of status epilepticus and subsequent spontaneous recurrent seizures in the malformed, but not in the normal brain, are associated with the outbreak of a destructive autoimmune response with encephalitis-like features, involving components of both cell-mediated and humoral immune responses. The MP brain is characterized by blood-brain barrier dysfunction, marked and persisting CD8+ T cell invasion of the brain parenchyma, meningeal B cell accumulation, and complement-dependent cytotoxicity mediated by antineuronal antibodies. Furthermore, the therapeutic treatment of MP rats with the immunomodulatory drug fingolimod promotes both antiepileptogenic and neuroprotective effects. Collectively, these data show that the MP rat could serve as a translational model of epileptogenic cortical malformations associated with a central nervous system autoimmune response. This work indicates that a preexisting brain maldevelopment predisposes to a secondary autoimmune response, which acts as a precipitating factor for epilepsy and suggests immune intervention as a therapeutic option to be further explored in epileptic syndromes associated with MCDs.

Sex differences in neuronal oscillatory activity and memory in the methylazoxymethanol acetate model of schizophrenia.

The methylazoxymethanol acetate (MAM) rodent model is used to study aspects of schizophrenia. However, numerous studies that have employed this model have used only males, resulting in a dearth of knowledge on sex differences in brain function and behaviour. The purpose of this study was to determine whether differences exist between male and female MAM rats in neuronal oscillatory function within and between the prefrontal cortex (PFC), ventral hippocampus (vHIP) and thalamus, behaviour, and in proteins linked to schizophrenia neuropathology. We showed that female MAM animals exhibited region-specific alterations in theta power, elevated low and high gamma power in all regions, and elevated PFC-thalamus high gamma coherence. Male MAM rats had elevated beta and low gamma power in PFC, and elevated vHIP-thalamus coherence. MAM females displayed impaired reversal learning whereas MAM males showed impairments in spatial memory. Glycogen synthase kinase-3 (GSK-3) was altered in the thalamus, with female MAM rats displaying elevated GSK-3α phosphorylation. Male MAM rats showed higher expression and phosphorylation GSK-3α, and higher expression of GSK-ß. Sex-specific changes in phosphorylated Tau levels were observed in a region-specific manner. These findings demonstrate there are notable sex differences in behaviour, oscillatory network function, and GSK-3 signaling in MAM rats, thus highlighting the importance of inclusion of both sexes when using this model to study schizophrenia.

Early developmental changes in a rat model of malformations of cortical development: Abnormal neuronal migration and altered response to NMDA-induced excitotoxic injury.

Malformations of cortical development (MCDs) are caused by abnormal neuronal migration processes during the fetal period and are a major cause of intractable epilepsy in infancy. However, the timing of hyperexcitability or epileptogenesis in MCDs remains unclear. To identify the early developmental changes in the brain of the MCD rat model, which exhibits increased seizure susceptibility during infancy (P12-15), we analyzed the pathological changes in the brains of MCD model rats during the neonatal period and tested NMDA-induced seizure susceptibility. Pregnant rats were injected with two doses of methylazoxymethanol acetate (MAM, 15 mg/kg, i.p.) to induce MCD, while controls were administered normal saline. The cortical development of the offspring was measured by performing magnetic resonance imaging (MRI) on postnatal days (P) 1, 5, and 8. At P8, some rats were sacrificed for immunofluorescence, Golgi staining, and Western analysis. In another set of rats, the number and latency to onset of spasms were monitored for 90 min after the NMDA (5 mg/kg i.p.) injection at P8. In MCD rats, in vivo MR imaging showed smaller brain volume and thinner cortex from day 1 after birth (p < 0.001). Golgi staining and immunofluorescence revealed abnormal neuronal migration, with a reduced number of neuronal cell populations and less dendritic arborization at P8. Furthermore, MCD rats exhibited a significant reduction in the expression of NMDA receptors and AMPAR4, along with an increase in AMPAR3 expression (p < 0.05). Although there was no difference in the latency to seizure onset between MCD rats and controls, the MCD rats survived significantly longer than the controls. These results provide insights into the early developmental changes in the cortex of a MCD rat model and suggest that delayed and abnormal neuronal development in the immature brain is associated with a blunted response to NMDA-induced excitotoxic injury. These developmental changes may be involved in the sudden onset of epilepsy in patients with MCD or prenatal brain injury.

Olanzapine, but not haloperidol, exerts pronounced acute metabolic effects in the methylazoxymethanol rat model.

AIM: Widely used second-generation antipsychotics are associated with adverse metabolic effects, contributing to increased cardiovascular mortality. To develop strategies to prevent or treat adverse metabolic effects, preclinical models have a clear role in uncovering underlying molecular mechanisms. However, with few exceptions, preclinical studies have been performed in healthy animals, neglecting the contribution of dysmetabolic features inherent to psychotic disorders. METHODS: In this study, methylazoxymethanol acetate (MAM) was prenatally administered to pregnant Sprague-Dawley rats at gestational day 17 to induce a well-validated neurodevelopmental model of schizophrenia mimicking its assumed pathogenesis with persistent phenotype. Against this background, the dysmetabolic effects of acute treatment with olanzapine and haloperidol were examined in female rats. RESULTS: Prenatally MAM-exposed animals exhibited several metabolic features, including lipid disturbances. Half of the MAM rats exposed to olanzapine had pronounced serum lipid profile alteration compared to non-MAM controls, interpreted as a reflection of a delicate MAM-induced metabolic balance disrupted by olanzapine. In accordance with the drugs' clinical metabolic profiles, olanzapine-associated dysmetabolic effects were more pronounced than haloperidol-associated dysmetabolic effects in non-MAM rats and rats exposed to MAM. CONCLUSION: Our results demonstrate metabolic vulnerability in female prenatally MAM-exposed rats, indicating that findings from healthy animals likely provide an underestimated impression of metabolic dysfunction associated with antipsychotics. In the context of metabolic disturbances, neurodevelopmental models possess a relevant background, and the search for adequate animal models should receive more attention within the field of experimental psychopharmacology.

Pro-social and pro-cognitive effects of LIT-001, a novel oxytocin receptor agonist in a neurodevelopmental model of schizophrenia.

Social and cognitive dysfunctions are the most persistent symptoms of schizophrenia. Since oxytocin (OXT) is known to play a role in social functions and modulates cognitive processes, we investigated the effects of a novel, nonpeptide, selective OXT receptor agonist, LIT-001, in a neurodevelopmental model of schizophrenia. Administration of methylazoxymethanol acetate (MAM; 22 mg/kg) on the 17th day of rat pregnancy is known to cause developmental disturbances of the brain, which lead to schizophrenia-like symptomatology in the offspring. Here, we examined the effects of acutely administered LIT-001 (1, 3, and 10 mg/kg) in MAM-exposed males and females on social behaviour, communication and cognition. We report that MAM-treated adult male and female rats displayed reduced social behaviour, ultrasonic communication and novel object recognition test performance. LIT-001 partially reversed these deficits, increasing the total social interaction time and the number of 'positive', highly-modulated 50 kHz ultrasonic calls in male rats. The compound ameliorated MAM-induced deficits in object discrimination in both sexes. Present results confirm the pro-social activity of LIT-001 and demonstrate its pro-cognitive effects following acute administration.

Sex-dependent emergence of prepubertal social dysfunction and augmented dopamine activity in a neurodevelopmental rodent model relevant for schizophrenia.

Schizophrenia is a neurodevelopmental psychiatric disorder that often emerges in adolescence, is characterized by social dysfunction, and has an earlier onset in men. These features have been replicated in rats exposed to the mitotoxin methylazoxymethanol acetate (MAM) on gestational day (GD) 17, which as adults exhibit behavioral impairments and dopamine (DA) system changes consistent with a schizophrenia-relevant rodent model. In humans, social withdrawal is a negative symptom that often precedes disease onset and DA system dysfunction and is more pronounced in men. Children and adolescents at high-risk for schizophrenia exhibit social deficits prior to psychotic symptoms (i.e., prodromal phase), which can be used as a predictive marker for future psychopathology. Adult MAM rats also exhibit deficient social interaction, but less is known regarding the emergence of social dysfunction in this model, whether it varies by sex, and whether it is linked to disrupted DA function. To this end, we characterized the ontogeny of social and DA dysfunction in male and female MAM rats during the prepubertal period (postnatal days 33-43) and found sex-specific changes in motivated social behaviors (play, approach) and DA function. Male MAM rats exhibited reduced social approach and increased VTA DA neuron activity compared to saline-treated (SAL) males, whereas female MAM rats exhibited enhanced play behaviors compared to SAL females but no changes in social approach or VTA population activity during this period. These findings demonstrate sex differences in the emergence of social and DA deficits in the MAM model, in which females exhibit delayed emergence.

Congenital blindness does not protect against a schizophrenia-related phenotype in rodents.

BACKGROUND: In 1950, Drs. Chevigny and Braverman authored a book about people's attitudes and prejudices toward the blind, noting that out of the thousands of schizophrenia patients they and others had treated, not one was blind. This led some to the intriguing hypothesis that congenital blindness may provide protection against schizophrenia. In this study, we directly examined whether congenital blindness protects against a schizophrenia-related phenotype in the methylazoxymethanol acetate (MAM) rodent model. DESIGN: Enucleation surgeries were performed on pups of MAM- or saline-treated rats on post-natal day 10. Once pups reached adulthood, male and female rats were evaluated for schizophrenia-like phenotypes using behavioral and electrophysiological measures. Consistent with previous work, MAM-treated rats display elevated dopamine neuron population activity, deficits in pre-pulse inhibition of startle, and hypersensitivity to psychomotor stimulants. RESULTS: Blindness did not protect against any of the MAM-induced phenotypes. Surprisingly, blindness in saline-treated rats caused changes in behavior and dopamine neuron activity. To examine the circadian rhythms of enucleated rats, we performed non-invasive measurements of corticosterone, a steroid hormone known to vary across the light/dark period, revealing blind rats display aberrant (non-cycling) corticosterone levels. CONCLUSIONS: Alterations in dopamine neuron activity and associated behaviors observed in blind rats are likely secondary to aberrant circadian regulation. This is the first preclinical study examining whether congenital blindness protects against a schizophrenia-like phenotype. While support of this hypothesis would have led to novel avenues of research and potential novel therapies, the results of current study suggest that blindness does not protect against schizophrenia.

Use of prepubertal environment enrichment to prevent dopamine dysregulation in a neurodevelopmental rat model of schizophrenia risk.

Here, we present a protocol for delivering environmental enrichment (EE) in discrete postnatal windows to prevent long-term dopamine neuron dysfunctions in a neurodevelopmental rat model of schizophrenia risk. We describe generation of the schizophrenia model through prenatal treatment of rats with methylazoxymethanol acetate (the MAM model) and the saline-treated controls. We then detail the 10-day or 20-day EE paradigms applied on male rats at different ages. This protocol also includes preparation of control groups in regular environment (RE) cages for comparison. For complete details on the use and execution of this protocol, please refer to Zhu and Grace (2021).

Early Blockade of CB1 Receptors Ameliorates Schizophrenia-like Alterations in the Neurodevelopmental MAM Model of Schizophrenia.

In agreement with the neurodevelopmental hypothesis of schizophrenia, prenatal exposure of Sprague-Dawley rats to the antimitotic agent methylazoxymethanol acetate (MAM) at gestational day 17 produces long-lasting behavioral alterations such as social withdrawal and cognitive impairment in adulthood, mimicking a schizophrenia-like phenotype. These abnormalities were preceded at neonatal age both by the delayed appearance of neonatal reflexes, an index of impaired brain maturation, and by higher 2-arachidonoylglycerol (2-AG) brain levels. Schizophrenia-like deficits were reversed by early treatment [from postnatal day (PND) 2 to PND 8] with the CB1 antagonist/inverse agonist AM251 (0.5 mg/kg/day). By contrast, early CB1 blockade affected the behavioral performance of control rats which was paralleled by enhanced 2-AG content in the prefrontal cortex (PFC). These results suggest that prenatal MAM insult leads to premorbid anomalies at neonatal age via altered tone of the endocannabinoid system, which may be considered as an early marker preceding the development of schizophrenia-like alterations in adulthood.

LY395756 promotes NR2B expression via activation of AKT/CREB signaling in the juvenile methylazoxymethanol mice model of schizophrenia.

INTRODUCTION: Synaptic N-methyl-d-aspartate receptor subtype 2B(NR2B) is significantly reduced in prefrontal cortex (PFC) in the neurodevelopmental methylazoxymethanol (MAM) model of schizophrenia (SCZ). Recent research has shown that LY395756 can effectively restore NR2B levels and improve cognitive performance in juvenile MAM mice model. However, the underlying mechanisms of these beneficial effects remain unclear. MATERIALS AND METHODS: Juvenile MAM mice model of SCZ is used in our study. Synaptic membrane protein levels were examined by western blotting under different treatment conditions. Interaction of cAMP-response element binding protein (CREB) and the promoter of NR2B was detected by the chromatin immunoprecipitation (ChIP) assay. Further examination of signaling pathway that mediates NR2B expression was also investigated by western blotting. RESULTS: In the PFC of the juvenile MAM mice schizophrenia model, CREB was found to directly bind with the promoter of NR2B. LY395756 activated the phosphorylation of AKT. Phosphorylated AKT subsequently induced the phosphorylation of CREB, and the activated CREB promoted the expression of NR2B. Subsequent experiments showed that the dephosphorylation of CREB induced by protein phosphatase 1 (PP1) can inhibit NR2B levels. Taken together, these findings support that the AKT/CREB signaling pathway is essential for the promoting effect of LY395756 on synaptic NR2B in PFC in juvenile MAM mice SCZ model. CONCLUSIONS: Our investigation has identified a novel mechanism by which LY395756 increases NR2B expression in juvenile MAM mice SCZ model. The AKT/CREB signaling pathway warrants further research as a potential direction for clinical treatment of SCZ.

GABAA and NMDA receptor density alterations and their behavioral correlates in the gestational methylazoxymethanol acetate model for schizophrenia.

Hippocampal hyperactivity driven by GABAergic interneuron deficits and NMDA receptor hypofunction is associated with the hyperdopaminergic state often observed in schizophrenia. Furthermore, previous research in the methylazoxymethanol acetate (MAM) rat model has demonstrated that repeated peripubertal diazepam administration can prevent the emergence of adult hippocampal hyperactivity, dopamine-system hyperactivity, and associated psychosis-relevant behaviors. Here, we sought to characterize hippocampal GABAA and NMDA receptors in MAM-treated rats and to elucidate the receptor mechanisms underlying the promising effects of peripubertal diazepam exposure. Quantitative receptor autoradiography was used to measure receptor density in the dorsal hippocampus CA1, ventral hippocampus CA1, and ventral subiculum. Specifically, [3H]-Ro15-4513 was used to quantify the density of α5GABAA receptors (α5GABAAR), [3H]-flumazenil to quantify α1-3;5GABAAR, and [3H]-MK801 to quantify NMDA receptors. MAM rats exhibited anxiety and schizophrenia-relevant behaviors as measured by elevated plus maze and amphetamine-induced hyperlocomotion (AIH), although diazepam only partially rescued these behaviors. α5GABAAR density was reduced in MAM-treated rats in all hippocampal sub-regions, and negatively correlated with AIH. Ventral hippocampus CA1 α5GABAAR density was positively correlated with anxiety-like behavior. Dorsal hippocampus CA1 NMDA receptor density was increased in MAM-treated rats, and positively correlated with AIH. [3H]-flumazenil revealed no significant effects. Finally, we found no significant effect of diazepam treatment on receptor densities, potentially related to the only partial rescue of schizophrenia-relevant phenotypes. Overall, our findings provide first evidence of α5GABAAR and NMDA receptor abnormalities in the MAM model, suggesting that more selective pharmacological agents may become a novel therapeutic mechanism in schizophrenia.

Nicotine Administration Normalizes Behavioral and Neurophysiological Perturbations in the MAM Rodent Model of Schizophrenia.

BACKGROUND: The present study utilized the methylazoxymethanol (MAM) neurodevelopmental rodent model of schizophrenia (SCZ) to evaluate the hypothesis that individuals with SCZ smoke in an attempt to "self-medicate" their symptoms through nicotine (NIC) intake. METHODS: To explore this question, we examined the effects of acute and chronic administration of NIC in 2 established behavioral tests known to be disrupted in the MAM model: prepulse inhibition of startle and novel object recognition. Additionally, we assessed the effects of acute and chronic NIC on 2 indices of the pathophysiology of SCZ modeled by MAM, elevated dopamine neuron population activity in the ventral tegmental area and neuronal activity in the ventral hippocampus, using in vivo electrophysiological recordings. RESULTS: Our findings demonstrated that both acute and chronic administration of NIC significantly improved deficits in prepulse inhibition of startle and novel object recognition among MAM rats and normalized elevated ventral tegmental area and ventral hippocampal neuronal activity in these animals. CONCLUSION: Together, these findings of NIC-induced improvement of deficits lend support for a "self-medication" hypothesis behind increased cigarette smoking in SCZ and illustrate the potential utility of nicotinic modulation in future pharmacotherapies for certain SCZ symptoms.

Frontal-posterior functional imbalance and aberrant function developmental patterns in schizophrenia.

Schizophrenia (SZ) is a neurodevelopmental disorder. There remain significant gaps in understanding the neural trajectory across development in SZ. A major research focus is to clarify the developmental functional changes of SZ and to identify the specific timing, the specific brain regions, and the underlying mechanisms of brain alterations during SZ development. Regional homogeneity (ReHo) characterizing brain function was collected and analyzed on humans with SZ (hSZ) and healthy controls (HC) cross-sectionally, and methylazoxymethanol acetate (MAM) rats, a neurodevelopmental model of SZ, and vehicle rats longitudinally from adolescence to adulthood. Metabolomic and proteomic profiling in adult MAM rats and vehicle rats was examined and bioanalyzed. Compared to HC or adult vehicle rats, similar ReHo alterations were observed in hSZ and adult MAM rats, characterized by increased frontal (medial prefrontal and orbitofrontal cortices) and decreased posterior (visual and associated cortices) ReHo. Longitudinal analysis of MAM rats showed aberrant ReHo patterns as decreased posterior ReHo in adolescence and increased frontal and decreased posterior ReHo in adulthood. Accordingly, it was suggested that the visual cortex was a critical locus and adolescence was a sensitive window in SZ development. In addition, metabolic and proteomic alterations in adult MAM rats suggested that central carbon metabolism disturbance and mitochondrial dysfunction were the potential mechanisms underlying the ReHo alterations. This study proposed frontal-posterior functional imbalance and aberrant function developmental patterns in SZ, suggesting that the adolescent visual cortex was a critical locus and a sensitive window in SZ development. These findings from linking data between hSZ and MAM rats may have a significant translational contribution to the development of effective therapies in SZ.

Inhibition of BET Proteins during Adolescence Affects Prefrontal Cortical Development: Relevance to Schizophrenia.

BACKGROUND: The present study investigated the role of proteins from the bromodomain and extra-terminal (BET) family in schizophrenia-like abnormalities in a neurodevelopmental model of schizophrenia induced by prenatal methylazoxymethanol (MAM) administration (MAM-E17). METHODS: An inhibitor of BET proteins, JQ1, was administered during adolescence on postnatal days (P) 23-P29, and behavioural responses (sensorimotor gating, recognition memory) and prefrontal cortical (mPFC) function (long-term potentiation (LTP), molecular and proteomic analyses) studies were performed in adult males and females. RESULTS: Deficits in sensorimotor gating and recognition memory were observed only in MAM-treated males. However, adolescent JQ1 treatment affected animals of both sexes in the control but not MAM-treated groups and reduced behavioural responses in both sexes. An electrophysiological study showed LTP impairments only in male MAM-treated animals, and JQ1 did not affect LTP in the mPFC. In contrast, MAM did not affect activity-dependent gene expression, but JQ1 altered gene expression in both sexes. A proteomic study revealed alterations in MAM-treated groups mainly in males, while JQ1 affected both sexes. CONCLUSIONS: MAM-induced schizophrenia-like abnormalities were observed only in males, while adolescent JQ1 treatment affected memory recognition and altered the molecular and proteomic landscape in the mPFC of both sexes. Thus, transient adolescent inhibition of the BET family might prompt permanent alterations in the mPFC.

Thalamic reticular nucleus impairments and abnormal prefrontal control of dopamine system in a developmental model of schizophrenia: prevention by N-acetylcysteine.

Recent evidence showed thalamic abnormalities in schizophrenia involving disruptions to the parvalbumin neurons in the thalamic reticular nucleus (TRN). However, their functional consequences, as well as a potential linkage to oxidative stress, are unclear. The TRN is posited to gate prefrontal control of dopamine neuron activity in the ventral tegmental area (VTA). Thus, we hypothesized that schizophrenia-related TRN abnormalities might contribute to dopamine dysregulation, a well-known feature of the disorder. To test this, in adult rats exposed prenatally to methylazoxymethanol acetate (MAM rats), oxidative impairments to the parvalbumin neurons in the anterior TRN were assessed by immunohistochemistry. Using in vivo electrophysiology, we investigated whether inactivation of the prefrontal cortex would produce differential effects on VTA dopamine neurons in MAM rats. We show that MAM rats displayed reduced markers of parvalbumin and wisteria floribunda agglutinin-labeled perineuronal nets, correlating with increased markers of oxidative stress (8-oxo-7, 8-dihydro-20-deoxyguanosine, and 3-nitrotyrosine). Moreover, MAM rats displayed heightened baseline and abnormal prefrontal control of VTA dopamine neuron activity, as tetrodotoxin-induced inactivation of the infralimbic prefrontal cortex decreased the dopamine population activity, contrary to the normal increase in controls. Such dopamine neuron dysregulation was recapitulated by enzymatic perineuronal net digestion in the TRN of normal rats. Furthermore, juvenile (postnatal day 11-25) antioxidant treatment (N-acetyl-cysteine, 900 mg/L drinking water) prevented all these impairments in MAM rats. Our findings suggest that early accumulation of oxidative stress in the TRN may shape the later onset of schizophrenia pathophysiology, highlighting redox regulation as a potential target for early intervention.

Reduced risk aversion and impaired short-term memory in juvenile rats with malformation of cortical development.

Malformation of cortical developments (MCDs) is currently an incurable disease and is associated with significant neuropsychological problems, such as intellectual disability, epilepsy, and anxiety disorders from a young age. Development of a suitable animal model and pathophysiological study is therefore necessary to better understand and treat MCDs from being an incurable disease. The Y-maze, open field, and fear conditioning studies were performed at postnatal days 40-44 to validate the behavioral phenotypes of the existing rat model of MCD with prenatal methylazoxymethanol exposure at their developmental period. The study results show that juvenile rats with MCD spent significantly less time inside the novel arms in Y-maze and less time in the peripheral zones of the open field. Additionally, the rats with MCDs showed attenuated freezing behavior to sound and light cues as well as to context after fear conditioning. This comprehensive behavioral analysis of rats with MCDs at the juvenile period indicate a lack of spatial memory, decreased anxiety, and learning disability in these rats, which is compatible with the human behavioral phenotype of MCDs and can be used as the behavioral biomarkers for future translational research.

Peripubertal mGluR2/3 Agonist Treatment Prevents Hippocampal Dysfunction and Dopamine System Hyperactivity in Adulthood in MAM Model of Schizophrenia.

Pomaglumetad methionil (POM), a group 2 metabotropic glutamate receptor (mGluR2/3) agonist, showed promise as a novel antipsychotic in preclinical research but failed to show efficacy in clinical trials, though it has been suggested that it may be effective in certain patient populations, including early in disease patients. We used the methyazoxymethanol acetate (MAM) rat model of schizophrenia to determine whether POM may prevent the development of dopamine (DA) system dysfunction in a model representative of the hyperdopaminergic state thought to underlie psychosis, compared to control (SAL) rats. MAM and SAL rats were administered either POM (3 mg/kg, i.p.), vehicle (1 ml/kg), or no injection during postnatal day (PD) 31-40. In either late adolescence (PD 47-56) or adulthood (PD 83-96), novel object recognition (NOR) was tested, followed by anesthetized in vivo electrophysiological recordings of VTA DA neuron activity or ventral hippocampal (vHPC) pyramidal neuron activity. MAM rats treated with POM demonstrated increased NOR in adulthood compared to no injection MAM rats, but not compared to vehicle-treated MAM rats. POM-treated MAM rats demonstrated normalized DA neuron population activity and vHPC pyramidal neuron activity compared to vehicle and no injection MAM rats in both late adolescence and adulthood. No significant differences were observed across treatment groups in SAL rats. These results suggest that peripubertal mGluR2/3 agonist administration can prevent the emergence of vHPC pyramidal neuron hyperactivity and increased DA neuron population activity in adult MAM rats.

Effects of methylazoxymethanol-induced micrencephaly on parvalbumin-positive GABAergic interneurons in the rat rostral basolateral amygdala.

The amygdala plays a crucial role in anxiety-related behavior and various neuropsychiatric disorders. The offspring of dams, administered methylazoxymethanol acetate (MAM) intraperitoneally at gestational day 15, exhibit micrencephaly and anxiety-related behavior, such as hyperactivity in rearing and crossing behavior, alongside a distinct Fos expression profile in the basolateral (BLA) and central amygdala. However, the histochemical underpinnings of these changes remain to be elucidated. To determine the histochemical alterations in MAM-induced model rats, we performed Nissl staining, immunohistochemistry for parvalbumin (PV) or calbindin (Calb), and immunohistochemistry for PV in conjunction with in situ hybridization for glutamate decarboxylase (GAD). We compared immunoreactivity in the BLA between normal and MAM-induced model rats and observed a significant decrease in the number of PV-positive neurons in MAM-induced model rats; however, no significant differences in the number of Nissl- and Calb-positive neurons were observed. We did not detect any significant between-group differences with regards to the effects of environmental enrichment on the number of PV-positive neurons in the BLA. Double-labeling for GAD and PV revealed that many PV-positive neurons colocalized with digoxigenin-GAD65/67 signals. In addition, GAD/PV double-positive neurons and the total number of GAD-positive neurons in the BLA were lower in the MAM-induced model rats. These results indicate that histochemical alterations observed in the BLA of the MAM-induced model rats may attribute to an aberrant GABAergic inhibitory system.

Prenatal MAM treatment altered fear conditioning following social isolation: Relevance to schizophrenia.

Adolescent social isolation (SI) might change the trajectory of brain development. In the present study, we investigated the effect of short-term adolescent SI on fear memory, anxiety and protein levels in the adult medial prefrontal cortex of rats prenatally treated with methylazoxymethanol, MAM-E17 model of schizophrenia. The animals were maintained in standard housing (SH) or social isolation (P30-P40, SI) conditions. Behavioural tests (trace or delay fear conditioning, light/dark box) were performed in late adolescence and early adulthood. The results showed that MAM treatment did not alter fear memory, which was investigated with the use of either trace or delay fear conditioning, at any age, and SI decreased the fear response in adult control animals only under trace conditioning. Neither MAM nor SI influenced anxiety-related behaviour measured in the light/dark box. A proteomics study showed that both MAM and SI changed the protein levels related to synapse maturation and cytoskeletal organization, energy transfer and metabolic processes. Prenatal or adolescent environmental factors are able to change the expression of proteins that are correlated with behavioural impairments. Moreover, SI reversed some alterations in proteins induced by MAM. Thus, normally developing brains showed different responses to adolescent SI than those with altering courses of MAM administration.