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Schizophrenia is a mental disorder characterized by cognitive impairments, specifically deficits in social recognition memory (SRM). Abnormal hippocampal neurogenesis has been implicated in these deficits. Due to the pathogenetic heterogeneity of schizophrenia, studying the hippocampal neurogenesis and SRM in two models with prenatal and postnatal defects could enhance our understanding of the developmental aspects of the biological susceptibility to schizophrenia. Here, we examined SRM and hippocampal neurogenesis in two developmental models of schizophrenia: gestational exposure to methylazoxymethanol acetate (MAM) and postweaning social isolation (SI). Our findings revealed that gestational MAM exposure induced a decay of social memory while postweaning SI led to impaired social memory formation and decay. In both models, we observed a correlation between impaired SRM and reduced number, and abnormal differentiation and less complex morphology of hippocampal neurons. These results indicate that aberrant hippocampal neurogenesis may contribute to the deficits of SRM in both models, and these abnormalities may be a shared underlying pathogenic factor in developmental models of schizophrenia, regardless of prenatal and postnatal pathogenesis., (© 2024 Federation of American Societies for Experimental Biology.)

Neurodevelopmental abnormalities are considered to be one of the important causes of schizophrenia. The offspring of methylazoxymethanol acetate (MAM)-exposed mice are recognized for the dysregulation of neurodevelopment and are well-characterized with schizophrenia-like phenotypes. However, the inhibition-related properties of the medial prefrontal cortex (mPFC) and hippocampus throughout adolescence and adulthood have not been systematically elucidated. In this study, both 10 and 15 mg/kg MAM-exposed mice exhibited schizophrenia-related phenotypes in both adolescence and adulthood, including spontaneous locomotion hyperactivity and deficits in prepulse inhibition. We observed that there was an obvious parvalbumin (PV) loss in the mPFC and hippocampus of MAM-exposed mice, extending from adolescence to adulthood. Moreover, the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidal neurons at mPFC and hippocampus was significantly dampened in the 10 and 15 mg/kg MAM-exposed mice. Furthermore, the firing rate of putative pyramidal neurons in mPFC and hippocampus was increased, while that of putative inhibitory neurons was decreased during both adolescence and adulthood. In conclusion, PV loss in mPFC and hippocampus of MAM-exposed mice may contribute to the impaired inhibitory function leading to the attenuation of inhibition in the brain both in vitro and in vivo., Competing Interests: The authors declare no competing financial interests., (Copyright © 2024 He et al.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

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., (© 2023 The Authors. CNS Neuroscience & Therapeutics published by John Wiley & Sons Ltd.)

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., Competing Interests: Conflicts of interest The authors declare that they have no conflicts of interest to disclose., (Copyright © 2023. Published by Elsevier B.V.)

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., Competing Interests: Declaration of competing interest MRC has no competing financial interests. AAG received funds from the following organizations: Newron, Merck, SynAgile, Alkermes, Lundbeck, Takeda, Roche, and Lyra., (Copyright © 2023 Elsevier B.V. All rights reserved.)

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.

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., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Gestational methylazoxymethanol acetate (MAM) treatment produces offspring with adult phenotype relevant to schizophrenia, including positive- and negative-like symptoms, cognitive deficits, dopaminergic dysfunction, structural and functional abnormalities. Here we show that adult rats prenatally treated with MAM at gestational day 17 display significant increase in dopamine D3 receptor (D3) mRNA expression in prefrontal cortex (PFC), hippocampus and nucleus accumbens, accompanied by increased expression of dopamine D2 receptor (D2) mRNA exclusively in the PFC. Furthermore, a significant change in the blood perfusion at the level of the circle of Willis and hippocampus, paralleled by the enlargement of lateral ventricles, was also detected by magnetic resonance imaging (MRI) techniques. Peripubertal treatment with the non-euphoric phytocannabinoid cannabidiol (30 mg/kg) from postnatal day (PND) 19 to PND 39 was able to reverse in MAM exposed rats: i) the up-regulation of the dopamine D3 receptor mRNA (only partially prevented by haloperidol 0.6 mg/kg/day); and ii) the regional blood flow changes in MAM exposed rats. Molecular modelling predicted that cannabidiol could bind preferentially to dopamine D3 receptor, where it may act as a partial agonist according to conformation of ionic-lock, which is highly conserved in GPCRs. In summary, our results demonstrate that the mRNA expression of both dopamine D2 and D3 receptors is altered in the MAM model; however only the transcript levels of D3 are affected by cannabidiol treatment, likely suggesting that this gene might not only contribute to the schizophrenia symptoms but also represent an unexplored target for the antipsychotic activity of cannabidiol., Competing Interests: Declaration of Competing Interest VD is a consultant for GW Pharmaceuticals, UK, and FAI, FP and VD receive funding from GW Pharmaceuticals, UK. CTW is employed by Boehringer Ingelheime Pharma & Co KG which did not influence design, analysis and interpretation of the study., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Social dysfunction is among the core symptoms of schizophrenia. The neuropeptides oxytocin (OXT) and vasopressin (VP) are involved in the regulation of social behaviour and social cognition. There are indications that both of these neurotransmitter systems are altered in schizophrenia. Prenatal (embryonic day 17) exposure to the neurotoxin methylazoxymethanol acetate (MAM; 22 mg/kg) leads to a schizophrenia-like phenotype in rats and has been used as a model of schizophrenia symptoms. Here, we examined the social phenotype of MAM-exposed female and male rats and measured concentrations of OXT, VP and their specific receptors in various brain areas involved in the control of social behaviour. We report decreases in social behaviour and ultrasonic vocalisations (USVs) in the MAM rats during social encounters. Specifically, the duration of social interactions and number of corresponding USVs were reduced in this group. In the MAM rats, "positive" 50-kHz USVs were flatter, i.e., displayed lower bandwidth, a greater percentage of "short" calls and lower percentage of frequency-modulated calls. The MAM animals exhibited diminished interest towards social stimuli in olfactory preference tests. In the resident-intruder test, MAM exposure reduced dominance behaviour only in the males. We also report cognitive impairments, including reduced novel object recognition and cognitive inflexibility in the attentional set shifting test, and decreased OXT and OXT receptor concentrations in the prefrontal cortex and hypothalamus and VP and VP receptors in the hypothalamus in the MAM rats. Deficits in central OXT and VP systems may underlie abnormalities present in the MAM model of schizophrenia., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest., (Copyright © 2020. Published by Elsevier Ltd.)

Introduction: Patients with schizophrenia (SCZ) smoke at a rate of 4-5 times higher than the general population, contributing to negative health consequences in this group. One possible explanation for this increased smoking is that individuals with SCZ find nicotine (NIC) more reinforcing. However, data supporting this possibility are limited., Methods: The present experiments examined self-administration of NIC, alone or in combination with other reinforcers, across a range of doses in the methylazoxymethanol acetate (MAM) rodent model of SCZ., Results: MAM and control animals did not differ in NIC self-administration across a range of doses and schedules of reinforcement, in both standard 1-hour self-administration sessions and 23-hour extended access sessions. However, MAM animals responded less for sucrose or reinforcing visual stimuli alone or when paired with NIC., Conclusions: To the extent that MAM-treated rats are a valid model of SCZ, these results suggest that increased NIC reinforcement does not account for increased smoking in SCZ patients., Implications: This study is the first to utilize nicotine self-administration, the gold standard for studying nicotine reinforcement, in the methylazoxymethanol acetate model of schizophrenia, which is arguably the most comprehensive animal model of the disease currently available. Our assessment found no evidence of increased nicotine reinforcement in methylazoxymethanol acetate animals, suggesting that increased reinforcement may not perpetuate increased smoking in schizophrenia patients., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved.For permissions, please e-mail: journals.permissions@oup.com.)

Glutamate receptors play a crucial pathogenic role in brain damage induced by status epilepticus (SE). SE may initiate NMDAR-dependent excitotoxicity through the production of oxidative damage mediated by the activation of a ternary complex formed by the NMDA receptor, the post-synaptic density scaffolding protein 95 (PSD95) and the neuronal NO synthase (nNOS). The inhibition of the protein-protein-interaction (PPI) of the NMDAR-PSD95-nNOS complex is one of the most intriguing challenges recently developed to reduce neuronal death in both animal models and in patients with cerebral ischemia. We took advantage of this promising approach to verify whether early administration of a neuroprotective NMDAR-PSD95-nNOS PPI inhibitor preserves the brain from SE-induced damage in a model of acquired cortical dysplasia, the methylazoxymethanol (MAM)/pilocarpine rat. Pilocarpine-induced SE rapidly determined neurodegenerative changes mediated by a NMDAR-downstream neurotoxic pathway in MAM rats. We demonstrated that SE rapidly induces NMDAR activation, nNOS membrane translocation, PSD95-nNOS molecular interaction associated with neuronal and glial peroxynitrite accumulation in the neocortex of MAM-pilocarpine rats. These changes were paralleled by rapid c-fos overexpression and by progressive spectrin proteolysis, suggestive of calpain activity and irreversible cytoskeletal damage. Early administration of a cell-penetrating Tat-N-dimer peptide inhibitor of NMDAR-PSD95-nNOS PPI during SE significantly rescued the MAM-pilocarpine rats from SE-induced mortality, reduced the number of degenerating neurons, decreased neuronal c-fos activation, peroxynitrite formation and cytoskeletal degradation and prevented astrogliosis. Our findings suggest an overall neuroprotective effect of blocking PSD95-nNOS protein-protein-interaction against SE insult., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Clinical studies consistently report structural impairments (i.e.: ventricular enlargement, decreased volume of anterior cingulate cortex or hippocampus) and functional abnormalities including changes in regional cerebral blood flow in individuals suffering from schizophrenia, which can be evaluated by magnetic resonance imaging (MRI) techniques. The aim of this study was to assess cerebral blood perfusion in several schizophrenia-related brain regions using Arterial Spin Labelling MRI (ASL MRI, 9.4 T Bruker BioSpec 94/30USR scanner) in rats. In this study, prenatal exposure to methylazoxymethanol acetate (MAM, 22 mg/kg) at gestational day (GD) 17 and the perinatal treatment with Δ-9-tetrahydrocannabinol (THC, 5 mg/kg) from GD15 to postnatal day 9 elicited behavioral deficits consistent with schizophrenia-like phenotype, which is in agreement with the neurodevelopmental hypothesis of schizophrenia. In MAM exposed rats a significant enlargement of lateral ventricles and perfusion changes (i.e.: increased blood perfusion in the circle of Willis and sensorimotor cortex and decreased perfusion in hippocampus) were detected. On the other hand, the THC perinatally exposed rats did not show differences in the cerebral blood perfusion in any region of interest. These results suggest that although both pre/perinatal insults showed some of the schizophrenia-like deficits, these are not strictly related to distinct hemodynamic features.

Social isolation (SI) during adolescence may induce schizophrenia-like behavior. In the present study, we investigated whether adolescent SI might affect the development of schizophrenia-like behavior in the MAM-E17 neurodevelopmental model of schizophrenia. Rats were socially isolated for 10 days during adolescence (postnatal days (P) 30-40), followed by resocialization until late adolescence (P45-P48) or early adulthood (P70-P75); behavioral and neurochemical studies were performed at these ages. The behavioral studies analyzed locomotor activity, social interaction, recognition memory, and sensorimotor gating; GAD65 and GAD67 protein levels were measured in the prefrontal cortex. The results showed that SI did not affect locomotor activity, but it prevented the social interaction deficits induced by MAM administration at both of the analyzed age points. However, SI induced a deficit in recognition memory in the MAM group during adolescence, which was not observed in the MAM-treated, socially housed rats at this age. In adulthood, impairments in recognition memory were detected in both MAM groups. In contrast, SI did not accelerate the appearance of sensorimotor gating deficits in MAM animals during adolescence, and sensorimotor gating impairments were observed in both MAM groups during adulthood. Adolescent SI rearing did not affect any examined behavioral responses in the VEH-treated groups. SI altered the levels of GAD65 and GAD67 proteins during adolescence in both groups; however, the decrease in the level of GAD65 protein was observed only in the adult MAM-SI group. Thus, SI rearing during a defined period of adolescence might have specific effects on the emergence of schizophrenia-like abnormalities in MAM-treated animals.

Background: Melatonin, which is an antioxidant and neuroprotective agent, can be an effective treatment for neurological disorders. We assessed the effect of melatonin administration on histological changes, antioxidant enzyme levels, and behavioral changes in a neonate mouse model of cortical malformation., Materials and Methods: Cortical malformation was induced by two injections of 15 mg/kg methylazoxymethanol (MAM) on gestational day 15 (E15). Pregnant Balb/c mice were randomly divided into the following six groups: Control (CO), Melatonin (MEL), Luzindole (LUZ), MAM, MEL + MAM1 (co-treatment), and MEL + MAM2 (pretreatment). Melatonin was intraperitoneally injected at a dose of 10 mg/kg daily (from E15 until delivery of from E6 for 20 days after delivery). On postnatal day 31, the activity and anxiety of mice were assessed by open field and elevated plus maze tests, respectively. Histopathological changes in the neonate cortex were studied using hematoxylin and eosin staining and neurofilament immunohistochemistry. Enzyme-linked immunosorbent assays were used to measure the activity of nitric oxide (NO), malondialdehyde (MDA), and antioxidant enzymes, including catalase (CAT), super oxide dismutase (SOD), and glutathione peroxidase (GPX)., Results: In the behavioral assessment of neonate mice, a significant increase in the crossing activity and decrease in anxiety were recorded in groups treated with MAM plus melatonin. In histological examination, heterotopic, dysmorphic, and ectopic cells, as well as dyslamination, were seen in the MAM and LUZ groups. However, these defects were attenuated in the MAM plus melatonin groups. Significant reductions were recorded in the SOD and GPX levels in the MAM and LUZ groups compared to the control, while the NO level was increased in these groups. Groups that received MAM plus melatonin showed significant increases in the levels of SOD and GPX and a significant decrease in the level of NO, compared to the MAM group., Conclusion: Melatonin increased the crossing activity and decreased the anxiety in the treated mice of the neonate mouse model of cortical malformation. Histologically, the administration of exogenous melatonin in pregnant mice and their neonates had a protective effect on the cerebral cortex of neonates. Also, this effect is elicited by decreasing NO and increasing antioxidative enzymes., (Copyright © 2018 ISDN. Published by Elsevier Ltd. All rights reserved.)

The methylazoxymethanol acetate (MAM) rodent neurodevelopmental model of schizophrenia exhibits aberrant dopamine system activation attributed to hippocampal dysfunction. Context discrimination is a component of numerous behavioral and cognitive functions and relies on intact hippocampal processing. The present study explored context processing behaviors, along with dopamine system activation, during fear learning in the MAM model. Male offspring of dams treated with MAM (20mg/kg, i.p.) or saline on gestational day 17 were used for electrophysiological and behavioral experiments. Animals were tested on the immediate shock fear conditioning paradigm, with either different pre-conditioning contexts or varying amounts of context pre-exposure (0-10 sessions). Amphetamine-induced locomotor activity and dopamine neural activity was measured 1-week after fear conditioning. Saline, but not MAM animals, demonstrated enhanced fear responses following a single context pre-exposure in the conditioning context. One week following fear learning, saline rats with 2 or 7min of context pre-exposure prior to fear conditioning also demonstrated enhanced amphetamine-induced locomotor response relative to MAM animals. Dopamine neuron recordings showed fear learning-induced reductions in spontaneous dopamine neural activity in MAM rats that was further reduced by amphetamine. Apomorphine administration confirmed that reductions in dopamine neuron activity in MAM animals resulted from over excitation, or depolarization block. These data show a behavioral insensitivity to contextual stimuli in MAM rats that coincide with a less dynamic dopamine response after fear learning., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Environmental enrichment (EE) mediates recovery from sensory, motor, and cognitive deficits and emotional abnormalities. In the present study, we examined the effects of EE on locomotor activity and neuronal activity in the amygdala in control and methylazoxymethanol acetate (MAM)-induced micrencephalic rats after challenge in a novel open field. Control rats housed in EE (CR) showed reduced locomotor activity compared to rats housed in a conventional cage (CC), whereas hyperactivity was seen in MAM rats housed in a conventional cage (MC) and in MAM rats housed in EE (MR). Novel open field exposure in both CC and MC resulted in a marked increase in Fos expression in the anterior and posterior parts of the basolateral amygdaloid nucleus, basomedial nucleus, and medial nucleus, whereas these increases in expression were not observed in CR. The effect of EE on Fos expression in the amygdala was different in MR exposed to a novel open field compared to CR. Furthermore, we observed a quite different pattern of Fos expression in the central nucleus of the amygdala between control and MAM rats. The present results suggest that neuronal activity in the amygdala that responds to anxiety is altered in MAM rats, especially when the rats are reared in EE. These alterations may cause behavioral differences between control and MAM rats., (© 2017 Japanese Teratology Society.)

Schizophrenia (SCZ) is characterized not only by psychosis, but also by working memory and executive functioning deficiencies, processes that rely on the prefrontal cortex (PFC). Because these cognitive impairments emerge prior to psychosis onset, we investigated synaptic function during development in the neurodevelopmental methylazoxymethanol (MAM) model for SCZ. Specifically, we hypothesize that N-methyl-D-aspartate receptor (NMDAR) hypofunction is attributable to reductions in the NR2B subunit through aberrant epigenetic regulation of gene expression, resulting in deficient synaptic physiology and PFC-dependent cognitive dysfunction, a hallmark of SCZ. Using western blot and whole-cell patch-clamp electrophysiology, we found that the levels of synaptic NR2B protein are significantly decreased in juvenile MAM animals, and the function of NMDARs is substantially compromised. Both NMDA-mEPSCs and synaptic NMDA-eEPSCs are significantly reduced in prelimbic PFC (plPFC). This protein loss during the juvenile period is correlated with an aberrant increase in enrichment of the epigenetic transcriptional repressor RE1-silencing transcription factor (REST) and the repressive histone marker H3K27me3 at the Grin2b promoter, as assayed by ChIP-quantitative polymerase chain reaction. Glutamate hypofunction has been a prominent hypothesis in the understanding of SCZ pathology; however, little attention has been given to the NMDAR system in the developing PFC in models for SCZ. Our work is the first to confirm that NMDAR hypofunction is a feature of early postnatal development, with epigenetic hyper-repression of the Grin2b promoter being a contributing factor. The selective loss of NR2B protein and subsequent synaptic dysfunction weakens plPFC function during development and may underlie early cognitive impairments in SCZ models and patients. Read the Editorial Highlight for this article on page 264., (© 2017 International Society for Neurochemistry.)

Genotoxic carcinogens pose great hazard to human health. Uncertainty of current risk assessment strategies and long latency periods between first carcinogen exposure and diagnosis of tumors have raised interest in predictive biomarkers. Initial DNA adduct formation is a necessary step for genotoxin induced carcinogenesis. However, as DNA adducts not always translate into tumorigenesis, their predictive value is limited. Here we hypothesize that the combined analysis of pro-mutagenic DNA adducts along with time-matched gene expression changes could serve as a superior prediction tool for genotoxic carcinogenesis. Eker rats, heterozygous for the tuberous sclerosis (Tsc2) tumor suppressor gene and thus highly susceptible towards genotoxic renal carcinogens, were continuously treated with the DNA alkylating carcinogen methylazoxymethanol acetate (MAMAc). Two weeks of MAMAc treatment resulted in a time-dependent increase of O 6 -methylguanine and N7-methylguanine adducts in the kidney cortex, which was however not reflected by significant expression changes of cyto-protective genes involved in DNA repair, cell cycle arrest or apoptosis. Instead, we found a transcriptional regulation of genes involved in the tumor-related MAPK, FoxO and TGF-beta pathways. Continuous MAMAc treatment for up to 6 months resulted in a mild but significant increase of cancerous lesions. In summary, the combined analysis of DNA adducts and early gene expression changes could serve as a suitable predictive tool for genotoxicant-induced carcinogenesis.

Rationale: Impairments in attention and inhibitory control are endophenotypic markers of neuropsychiatric disorders such as schizophrenia and represent key targets for therapeutic management. Robust preclinical models and assays sensitive to clinically relevant treatments are crucial for improving cognitive enhancement strategies., Objectives: We assessed a rodent model with neural and behavioral features relevant to schizophrenia (gestational day 17 methylazoxymethanol acetate treatment (MAM-E17)) on a novel test of attention and executive function, and examined the impact of putative nootropic drugs., Methods: MAM-E17 and sham control rats were trained on a novel touchscreen-based rodent continuous performance test (rCPT) designed to closely mimic the human CPT paradigm. Performance following acute, systemic treatment with an array of pharmacological compounds was investigated., Results: Two cohorts of MAM-E17 rats were impaired on rCPT performance including deficits in sensitivity (d') and increased false alarm rates (FARs). Sulpiride (0-30 mg/kg) dose-dependently reduced elevated FAR in MAM-E17 rats whereas low-dose modafinil (8 mg/kg) only improved d' in sham controls. ABT-594 (5.9-19.4 μg/kg) and modafinil (64 mg/kg) showed expected stimulant-like effects, while LSN2463359 (5 mg/kg), RO493858 (10 mg/kg), atomoxetine (0.3-1 mg/kg), and sulpiride (30 mg/kg) showed expected suppressant effects on performance across all animals. Donepezil (0.1-1 mg/kg) showed near-significant enhancements in d', and EVP-6124 (0.3-3 mg/kg) exerted no effects in the rCPT paradigm., Conclusion: The MAM-E17 model exhibits robust and replicable impairments in rCPT performance that resemble attention and inhibitory control deficits seen in schizophrenia. Pharmacological profiles were highly consistent with known drug effects on cognition in preclinical and clinical studies. The rCPT is a sensitive and reliable tool with high translational potential for understanding the etiology and treatment of disorders affecting attention and executive dysfunction.

Ketamine may prove to be a potential candidate in treating the widespread drug addiction/substance abuse epidemic among patients with schizophrenia. Clinical studies have shown ketamine to reduce cocaine and heroin cravings. However, the use of ketamine remains controversial as it may exacerbate the symptoms of schizophrenia. Therefore, the aim of this study is to characterize the effects of ketamine on drug addiction in schizophrenia using the methylazoxymethanol (MAM) acetate rat model on operant IV methamphetamine (METH) self-administration. MAM was administered intraperitoneally (22 mg/kg) on gestational day 17. Locomotor activity test and later IV self-administration (IVSA) were then performed in the male offspring followed by a period of forced abstinence and relapse of METH taking. After reaching stable intakes in the relapse phase, ketamine (5 mg/kg) was administered intraperitoneally 30 min prior to the self-administration session. As documented previously, the MAM rats showed a lack of habituation in the locomotor activity test but developed stable maintenance of METH self-administration with no difference in operant behaviour to control animals. Results show that ketamine treatment significantly reduced the METH intake in the control animals but not in MAM animals. Ketamine effect on METH self-administration may be explained by increased glutamatergic signalling in the prefrontal cortex caused by the N-methyl-D-aspartate antagonism and disinhibition of GABA interneurons which was shown to be impaired in the MAM rats. This mechanism may at least partly explain the clinically proven anti-craving potential of ketamine and allow development of more specific anti-craving medications with fewer risks.

Prenatal interventions may offer an immense opportunity in therapeutic protocols of malformations of cortical development (MCD). Epidermal neural crest stem cells (EPI-NCSCs) of the hair follicle bulge exhibit features of both embryonic and adult stem cells; these cells maintain their neurologic differentiation capability because of their neural crest origin. However, it is unknown if prenatal use of EPI-NCSCs could be beneficial in targeting methylazoxymethanol (MAM)-induced MCD, which further addressed in the present work. EPI-NCSCs were prenatally infused to the MAM-exposed mice. Thicknesses of various cerebral cortex areas as well as corpus callosum was measured; there were markedly decrease in MAM group (p < .001 vs. untreated), but a significant increase in EPI-NCSC group (p < .05 vs. MAM), except for corpus callosum. Real-time PCR analysis showed high expressions for absent, small, or homeotic 2-like protein, nestin, doublecortin (DCX), neuronal specific nuclei protein (NeuN), and glial fibrillary acidic protein (GFAP) in MAM group (p < .001 vs. untreated), except for G-protein-coupled C-X-C chemokine receptor type 4 (CXCR4) and CXC motif ligand 12 (CXCL12), whereas there were low expressions in EPI-NCSCs group (p < .01 vs. MAM). Immunohistochemistry of NeuN, GFAP, ionized calcium-binding adapter molecule (Iba1), and oligodendrocyte lineage transcription factor 2 (Olig2) was also revealed the same pattern as real-time PCR (p < .001 MAM vs. untreated, and p < .05 EPI-NCSCs vs. MAM). Our findings suggest prenatal use of EPI-NCSCs as a possible candidate for cell-based therapy of cortical injury through affecting neural markers and their relationship with glial., (© 2016 Wiley Periodicals, Inc.)

In addition to prefrontal cortex (PFC) and hippocampus, amygdala may have a role in the pathophysiology of schizophrenia, given its pivotal role in emotion and extensive connectivity with the PFC and hippocampus. Moreover, abnormal activities of amygdala may be related to the anxiety observed in schizophrenia patients and at-risk adolescents. These at-risk subjects demonstrated heightened levels of anxiety, which are correlated with the onset of psychosis later in life. Similarly, rats that received methyl azoxymethanol acetate (MAM) gestationally exhibited higher levels of anxiety peripubertally. In the current study, the heightened anxiety was also observed in adult MAM animals, as well as higher firing rates of BLA neurons in both peripubertal and adult MAM rats. In addition, the power of BLA theta oscillations of adult MAM rats showed a larger increase in response to conditioned stimuli (CS). We showed previously that administration of the antianxiety drug diazepam during the peripubertal period prevents the hyperdopaminergic state in adult MAM rats. In this study, we found that peripubertal diazepam treatment reduced heightened anxiety, decreased BLA neuron firing rates and attenuated the CS-induced increase in BLA theta power in adult MAM rats, supporting a persistent normalization by this treatment. This study provides a link between BLA hyperactivity and anxiety in schizophrenia model rats and that circumvention of stress may prevent the emergence of pathology in the adult.

Schizophrenia is a chronic disease that has been hypothesized to be linked to neurodevelopmental abnormalities. Schizophrenia patients exhibit impairments in basic sensory processing including sensory gating deficits in P50 and mismatch negativity (MMN). Neuronal nicotinic acetylcholine receptor (nAChR) agonists have been reported to attenuate these deficits. Gestational exposure of rats to methylazoxymethanol acetate (MAM) at embryonic day 17 leads to developmental disruption of the limbic-cortical system. MAM exposed offspring show neuropathological and behavioral changes that have similarities with those seen in schizophrenia. In this study, we aimed to assess whether N40 auditory sensory gating (the rodent form of P50 gating) and MMN deficits as measures of auditory evoked potential (AEP) electroencephalography (EEG) are present in MAM rats and whether nAChR agonists could attend the deficit. E17 male MAM and sham rats were implanted with cortical electrodes at 2 months of age. EEG recordings evaluating N40 gating and MMN paradigms were done comparing effects of vehicle (saline), nicotine and the α7 agonist ABT-107. Deficits were seen for MAM rats compared to sham animals in both N40 auditory sensory gating and MMN AEP recordings. There was a strong trend for N40 deficits to be attenuated by both nicotine (0.16mg/kg i.p. base) and ABT-107 (1.0mg/kg i.p. base). MMN deficits were significantly attenuated by ABT-107 but not by nicotine. These data support the MAM model as a useful tool for translating pharmacodynamic effects in clinical medicine studies of novel therapeutic treatments for schizophrenia., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Altered activity of the nucleus accumbens (NAc) is thought to be a core feature of schizophrenia and animal models of the disease. Abnormal high frequency oscillations (HFO) in the rat NAc have been associated with pharmacological models of schizophrenia, in particular the N-methyl-d-aspartate receptor (NMDAR) hypofunction model. Here, we tested the hypothesis that abnormal HFO are also associated with a neurodevelopmental rat model., Methods: Using prenatal administration of the mitotoxin methylazoxymethanol acetate (MAM) we obtained the offspring MAM rats. Adult MAM and Sham rats were implanted with electrodes, for local field potential recordings, in the NAc., Results: Spontaneous HFO (spHFO) in MAM rats were characterized by increased power and frequency relative to Sham rats. MK801 dose-dependently increased the power of HFO in both groups. However, the dose-dependent increase in HFO frequency found in Sham rats was occluded in MAM rats. The antipsychotic compound, clozapine reduced the frequency of HFO which was similar in both MAM and Sham rats. Further, HFO were modulated in a similar manner by delta oscillations in both MAM and Sham rats., Conclusion: Together these findings suggest that increased HFO frequency represents an important feature in certain animal models of schizophrenia. These findings support the hypothesis that altered functioning of the NAc is a core feature in animal models of schizophrenia., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Schizophrenia is a serious neuropsychiatric disorder. Several brain structures, neurotransmitter systems, genetic and environmental risk factors are suspected in the background. Because of its complexity the mechanism of the disorder is not known exactly, so the treatment of patients is unsolved. In the research of schizophrenia application of the rodent models is widespread. In this study one of these models based on the effect of methylazoxymethanol- acetate (MAM) is described, which is a neurodevelopmental, validated rat model. This antimitotic agent is able to evoke a number of schizophrenic symptomes temporarily disrupting the prenatal neurogenesis. The model reproduces numerous histological and neurophysiological changes of the human disorder, moreover it also represents several behavioral and cognitive phenomena resembling those in schizophrenia. A salient advantage of the model is the demonstration of the diachronic feature of the disorder, that is, postpubertal appearance of the positive symptoms. This model provides widespread opportunities for manipulations of the symptoms, so that using it in the future investigations can lead to a better understanding of this disorder.

The aim of the study was to find whether spatial memory impairment and disruption in locomotor activity were found in prenatally stressed rats (PSG) or prenatally methylazoxymethanol acetate-treated rats (MAMG). In addition to this, we examined basal plasma corticosterone level as well as brain-derived neurothropic factor (BDNF) in the PSG and MAMG rats. The effect of prenatal stress (stress paradigm between 14 and 21 day of gestation) and methylazoxymethanol acetate (MAM) administration (17 day of gestation) to the female Wistar rats were studied on the male offspring in the Morris Water Maze (spatial memory) and locomotor activity test. Through Morris Water Maze rats were injected with saline 4 times (on 1, 7, 14 and 21 day of testing) while in locomotor activity test saline was injected only once. Corticosterone level was measured using ELISA Kit while BDNF levels were assessed using ELISA Chemikine TM BDNF kit. Results indicate that both PSG and MAMG rats deteriorate spatial memory as well as increase locomotor activity compared to the control group. Biochemical studies indicate that basal plasma corticosterone level increased in both PSG and MAMG rats compared to the control group. Analyses of the BDNF level, on the other hand, have shown decrease of the neurothropin level in both hippocampus and prefrontal cortex (PFC) in both PSG and MAMG groups of rats. As shown by the obtained results, both the prenatal stress model and prenatal MAM administration model generate a number of behavioural (e.g. spatial memory disorders, increased locomotor activity) and biochemical (e.g. increased corticosterone and decreased BDNF levels) changes in the examined offspring, Thus, these models can be successfully used in the efficacy analysis of the pharmacotherapy applied.

Alteration in normal hippocampal (HPC) function attributed to reduced parvalbumin (PV) expression has been consistently reported in schizophrenia patients and in animal models of schizophrenia. However, it is unclear whether there is an overall loss of interneurons as opposed to a reduction in activity-dependent PV content. Co-expression of PV and the constitutively expressed substance P (SP)-receptor protein has been utilized in other models to ascertain the degree of cell survival, as opposed to reduction in activity-dependent PV content, in the HPC. The present study measured the co-expression of PV and SP-receptors in the dentate and dorsal and ventral CA3 subregions of the HPC in the methylazoymethanol acetate (MAM) rat neurodevelopmental model of schizophrenia. In addition, these changes were compared at the post-natal day 27 (PND27) and post-natal day 240 (PND > 240) time points. Brains from PND27 and PND > 240 MAM (n = 8) and saline (SAL, n = 8) treated offspring were immunohistochemically processed for the co-expression of PV and SP-receptors. The dorsal dentate, dorsal CA3 and ventral CA3 subregions of PND27 and PND > 240 MAM rats demonstrated significant reductions in PV but not SP-receptor expression, signifying a loss of PV-content. In contrast, in the ventral dentate the co-expression of PV and SP-receptors was significantly reduced only in PND > 240 MAM animals, suggesting a reduction in cell number. While MAM-induced reduction of PV content occurs in CA3 of dorsal and ventral HPC, the most substantial loss of interneuron number is localized to the ventral dentate of PND > 240 animals. The disparate loss of PV in HPC subregions likely impacts intra-HPC network activity in MAM rats.

Schizophrenia is characterized by alterations in cortico-limbic processes believed to involve modifications in activity within the prefrontal cortex (PFC) and the hippocampus. The nucleus accumbens (NAc) integrates information from these 2 brain regions and is involved in cognitive and psychomotor functions that are disrupted in schizophrenia, indicating an important role for this structure in the pathophysiology of this disorder. In this study, we used in vivo electrophysiological recordings from the NAc and the PFC of adult rats and the MAM developmental disruption rodent model of schizophrenia to explore the influence of the medial PFC on the hippocampal-accumbens pathway. We found that, in MAM-treated rats, tetanization of hippocampal inputs to the NAc produce opposite synaptic plasticity compared with controls, which is a consequence of alterations in the hippocampal-mPFC pathway. Moreover, we show that administration of the D2-receptor-blocking antipsychotic drug sulpiride either systemically or directly into the mPFC reverses the alterations in the MAM rat. Therefore, specific disruptions in cortical and hippocampal inputs in the MAM-treated rat abnormally alter plasticity in subcortical structures. Moreover, our results suggest that, in the presence of antipsychotic drugs, the disrupted plasticities are normalized, supporting a role for this mechanism in antipsychotic drug action in schizophrenia.

Trials of novel compounds for the treatment of schizophrenia are typically tested in patients following brief withdrawal of ongoing medication despite known long-term changes in the dopamine (DA) system following chronic antipsychotic drug therapy. The present study explored the impact of withdrawal from repeated haloperidol (HAL) treatment, as well as the response to a novel α5 gamma-aminobutyric acid (GABA(A)) receptor positive allosteric modulator (α5PAM), on the activity of the DA system in the methylazoxymethanol acetate (MAM) neurodevelopmental model of schizophrenia. Electrophysiological recordings were conducted from DA neurons in the ventral tegmental area of MAM and saline (SAL) rats following 7-day withdrawal from repeated HAL (21 d, 0.6 mg/kg, orally). In separate animals, amphetamine-induced locomotion was measured to assess changes in DA behavioral sensitivity. SAL rats withdrawn from HAL demonstrated reduced spontaneous DA neuron activity along with an enhanced locomotor response to amphetamine, indicative of the development of DA supersensitivity. Both α5PAM treatment and ventral hippocampal (vHPC) inactivation reversed the DA neuron depolarization block following HAL withdrawal in SAL rats. In contrast, MAM rats withdrawn from HAL exhibited reduced spontaneous DA activity and enhanced locomotor response to amphetamine compared with untreated SAL rats; however, this condition was unresponsive to α5PAM treatment or vHPC inactivation. Withdrawal from prior HAL treatment interferes with the therapeutic actions of this novel treatment in the MAM model of schizophrenia. Consequently, testing novel compounds on chronically treated schizophrenia patients may be ineffective.

Cortical dysplasia (CD) associates with clinical pathologies, including epilepsy and mental retardation. CD results from impaired migration of immature neurons to their cortical targets, leading to clustering of neural cells and changes in cortical properties. We developed a CD model by administering methylazoxymethanol (MAM), an anti-mitotic, to pregnant ferrets on embryonic day 33; this leads to reduction in cortical thickness in addition to redistribution and increased expression of GABAA receptors (GABAAR). We evaluated the impact of MAM treatment on GABAAR-mediated synaptic transmission in postnatal day 0-1 neurons, leaving the ganglionic eminence (GE) and in layer 2/3 pyramidal cells of postnatal day 28-38 ferrets. Embryonic day 33 MAM treatment significantly increases the amplitude and frequency of spontaneous GABAAR-mediated inhibitory postsynaptic currents (IPSCs) in the cells leaving the GE. In older MAM-treated animals, the amplitude and frequency of GABAAR-mediated spontaneous IPSCs in layer 2/3 pyramidal cells is increased, as are the amplitude and frequency of miniature IPSCs. The kinetics of GABAAR opening also altered following treatment with MAM. Western blot analysis shows that the expression of the GABAAα3R and GABAAγ2R subunits amplified in our model animals. We did not observe any significant change in the passive properties of either the layer 2/3 pyramidal cells or cells leaving the GE after MAM treatment. These observations reinforce the idea that synaptic neurotransmission through GABAAR enhances following treatment with MAM and coincides with our finding of increased GABAAαR expression within the upper cortical layers. Overall, we demonstrate that small amounts of toxins delivered during corticogenesis can result in long-lasting changes in ambient expression of GABAAR that influence intrinsic neuronal properties.

Developmental neurotoxicity (DNT) of environmental chemicals is a serious threat to human health. Current DNT testing guidelines propose investigations in rodents, which require large numbers of animals. With regard to the "3Rs" (reduction, replacement, and refinement) of animal testing, alternative testing strategies are needed in order to refine and reduce animal experiments and allow faster and less expensive screening. The goal of this study was to establish components for a human cell-based test system to assess DNT potential of chemicals at an early stage of brain development. A human neural precursor cell line should be tested for suitability for semi-automated high-throughput DNT screening. We established assays suitable for detecting disturbances in two basic processes of brain development in 96-well scale: neuronal differentiation and migration using the human Ntera2 (NT2) cell line. We assessed the effects of four test compounds with well-established DNT potential in comparison with three compounds without specific DNT potential. We found that human NT2 cell cultures treated with the morphogen, retinoic acid, imitate neuronal differentiation, and migration in vitro. The developmental neurotoxicants methylmercury chloride, sodium arsenite, sodium valproate, and methylazoxymethanol significantly reduced the expression of the neuronal marker β-tubulin type III and decreased the migration distance in developing NT2 cells. Both endpoints, differentiation and migration, can be read out directly in a standard fluorescence plate reader, enabling high-throughput screening. We conclude that NT2 cell tests are likely to become valuable components of a human cell-based modular in vitro DNT test systems.

Schizophrenia is believed to arise from an interaction of genetic predisposition and adverse environmental factors, with stress being a primary variable. We propose that alleviating anxiety produced in response to stress during a sensitive developmental period may circumvent the dopamine (DA) system alterations that may correspond to psychosis in adults. This was tested in a developmental rat model of schizophrenia based on prenatal administration of the mitotoxin methyl azoxymethanol acetate (MAM). MAM administration leads to a hyperdopaminergic state consisting of an increase in the number of DA neurons firing spontaneously, which correlates with an increased behavioral response to amphetamine. MAM-treated rats exhibited a heightened level of anxiety during adolescence. Peripubertal administration of the antianxiety agent diazepam was found to prevent the increase in DA neuron activity and blunt the behavioral hyperresponsivity to amphetamine in these rats. These data suggest that the pathophysiological factors leading to the onset of psychosis in early adulthood may be circumvented by controlling the response to stress during the peripubertal period.

Evidence indicates that the prefrontal cortex and its regulation by afferent inputs are disrupted in schizophrenia. Using a validated rat model of schizophrenia based on prenatal administration of the mitotoxin methyl azoxymethanol acetate (MAM), we examined the convergent projections from the ventral hippocampus (vHipp) and the basolateral amygdala (BLA) in the medial prefrontal cortex (mPFC). In vivo extracellular recordings were done in anesthetized rats to assess how prior stimulation of the BLA or vHipp input to the mPFC affected mPFC responses to subsequent stimulation of these regions. The interstimulus interval (ISI) of the BLA and vHipp pulse stimulation was varied randomly between 0 and 130 ms, and the probability of evoked spike response in the mPFC measured. We found that BLA input increased vHipp-evoked spike probability at ISIs 40-130 ms, but decreased spike probability at ISIs 10-20 ms. This would be consistent with activation of inhibitory interneurons at shorter ISIs by BLA stimulation. In contrast, in MAM-treated rats BLA stimulation increased vHipp-evoked spike probability in mPFC at all ISIs tested. Given that interneurons are driven primarily by N-methyl-D-aspartate (NMDA) channel activation, the effects of the NMDA channel blocker, phencyclidine (PCP), were tested. PCP was found to completely attenuate the inhibitory effect of BLA input on vHipp-evoked responses in mPFC at shorter ISIs, causing the response in control rats treated with PCP to resemble that observed in the MAM rat. In contrast to the effects of BLA stimulation on vHipp-mPFC-evoked responses, there was no inhibitory period when examining the effects of vHipp stimulation on BLA-mPFC-evoked responses in control rats, but in MAM-treated rats there was a significant inhibition at short intervals. Thus, both affective input arising from the BLA and context-dependent input from the vHipp exert a modulatory effect on mPFC neural activity in response to these inputs. Whereas the BLA potentiated vHipp input to the mPFC at long intervals, there was a short-interval inhibitory period that appeared to be mediated by an NMDA-dependent drive of interneurons. This inhibitory modulation was absent in the model of schizophrenia and following PCP, which is consistent with an interneuron disruption in this disorder.

Subcortical dopamine system dysregulation has been suggested to underlie the positive symptoms of schizophrenia. Recent preclinical investigations and human imaging studies have proposed that the augmented dopamine system function observed in schizophrenia patients may be secondary to aberrant hippocampal activity. Thus, we posit that the hippocampus represents a novel therapeutic target for the treatment of schizophrenia. Here we provide evidence of the effectiveness of a unique approach aimed at decreasing hippocampal function in a rodent model of schizophrenia. Specifically, in a rodent model of schizophrenia, we demonstrate that ventral hippocampal (vHipp) deep brain stimulation (DBS) can normalize aberrant dopamine neuron activity and behaviours associated with positive symptoms. In addition, we provide evidence that this approach may also be effective in restoring deficits in cognitive function, often left unaltered by conventional antipsychotic medications. Therefore, we have provided initial preclinical evidence demonstrating the feasibility of hippocampal DBS as a potential novel approach for the treatment of schizophrenia.

Developmental perturbations during adolescence have been hypothesized to be a risk factor for the onset of several neuropsychiatric diseases. However the physiological alterations that result from such insults are incompletely understood. We investigated whether a defined perturbation during adolescence affected hippocampus-dependent sensorimotor gating functions, a proposed endophenotype in several psychiatric diseases, most notably schizophrenia. The developmental perturbation was induced during adolescence in mice using an antimitotic agent, methylazoxymethanol acetate (MAM), during postnatal weeks (PW) 4-6. MAM-treated mice showed a decrease in hippocampal neurogenesis immediately after treatment, which was restored by PW10 in adulthood. However, the mice treated with MAM during adolescent stages exhibited a persistent sensorimotor gating deficiency and a reduction in prepulse inhibition-related activation of hippocampal and prefrontal neurons in adulthood. Cellular analyses found a reduction of GABAergic inhibitory neurons and abnormal dendritic morphology of immature neurons in the dentate gyrus (DG). Interestingly, bilateral infusion of muscimol, a GABAA receptor agonist, into the DG region reversed the prepulse inhibition abnormality in MAM-treated mice. Furthermore, the behavioral deficits together with the decrease in the number of GABAergic neurons in this MAM model were rescued by exposure to an enriched environment during a defined critical adolescent period. These observations suggest a possible role for GABAergic interneurons in the DG during adolescence. This role may be related to the establishment of neural circuitry required for sensorimotor gating. It is plausible that changes in neurogenesis during this window may affect the survival of GABAergic interneurons, although this link needs to be causally addressed.

The nucleus accumbens (NAc) receives converging inputs from the medial prefrontal cortex (mPFC) and the hippocampus which have competitive interactions in the NAc to influence motivational drive. We have previously shown altered synaptic plasticity in the hippocampal-NAc pathway in the methylazoxymethanol acetate (MAM) developmental model of schizophrenia in rodents that is dependent on cortical inputs. Thus, because mPFC-hippocampal balance is known to be partially altered in this model, we investigated potential pathological changes in the hippocampal influence over cortex-driven NAc spike activity. Here we show that the reciprocal interaction between the hippocampus and mPFC is absent in MAM animals but is able to be reinstated with administration of the antipsychotic drug, sulpiride. The lack of interaction between these structures in this model could explain the attentional deficits in schizophrenia patients and shed light onto their inability to focus on a single task.

The N-methyl-D-aspartate (NMDA) receptor has long been associated with learning and memory processes as well as diseased states, particularly in schizophrenia (SZ). Additionally, SZ is increasingly recognized as a neurodevelopmental disorder with cognitive impairments often preceding the onset of psychosis. However, the cause of these cognitive deficits and what initiates the pathological process is unknown. Growing evidence has implicated the glutamate system and, in particular, N-methyl-D-aspartate receptor (NMDAR) dysfunction in the pathophysiology of SZ. Yet, the vast majority of SZ-related research has focused on NMDAR function in adults leaving the role of NMDARs during development uncharacterized. We used the prenatal methylazoxymethanol acetate (MAM, E17) exposure model to determine the alterations of NMDAR protein levels and function, as well as associated cognitive deficits during development. We found that MAM-exposed animals have significantly altered NMDAR protein levels and function in the juvenile and adolescent hippocampus. Furthermore, these changes are associated with learning and memory deficits in the Morris Water Maze. Thus, in the prenatal MAM-exposure SZ model, NMDAR expression and function is altered during the critical period of hippocampal development. These changes may be involved in disease initiation and cognitive impairment in the early stage of SZ.

Developmental neurotoxicity (DNT) testing assesses potentially adverse effects on the developing nervous system. The present DNT study was conducted to generate historical data with the Wistar Han (WH) and Sprague Dawley (SD) rat strains, commonly used in Europe and the US, respectively. Potential differences between these strains in DNT endpoints have not been extensively investigated. Motor activity, startle response, learning and memory testing, and neurological (quantitative and qualitative) examinations were conducted using three groups of control, prenatally exposed (to Methylazoxymethanol [MAM] on gestation Day 15) and acutely treated (with IDPN, MK-801 or Chlorpromazine) animals for each strain. The positive controls produced clear effects in most endpoints investigated, with limited functional differences in baseline behavior and positive control sensitivity. However, SD rats were considerably more susceptible to MAM-induced learning and memory impairments and neurological damage. These data highlight differential sensitivity between the strains, which may require risk assessment consideration for developmental neurotoxicants., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Prenatal exposure of methylazoxymethanol acetate, a DNA methylating agent, to pregnant rats on embryonic day 15 is known to produce hippocampal malformation and laminar disorganization of the cerebral cortex. However, there are few studies to demonstrate developmental processes of abnormal structures in the hippocampus. In the present study, we examined complete serial sections of rat brains on postnatal day 0 to 2, which pretreated with methylazoxymethanol acetate on embryonic day 15. At birth, massive cellular clusters were found under the white matter of the cerebral cortex and then, a part of these clusters entered into the hippocampal CA1 sector on postnatal day 2. These ectopic cellular clusters in the CA1 were immunoreactive to anti-calbindin antibody, suggesting that the origin of these cellular clusters is equivalent to that of the cortical layer II/III neurons. Next, we injected FluoroGold into the lateral septal nucleus to examine hippocampo-septal projection. FluoroGold-labeled neurons were scattered in the ectopic cellular cluster, implying that CA1 pyramidal neurons project normally to the lateral septal nucleus. In conclusion, a majority of neurons found in the ectopic cellular cluster caused by prenatal methylazoxymethanol treatment is derived from cortical neurons, and some intrinsic pyramidal neurons in the CA1 of hippocampus are scattered throughout the ectopic cellular cluster., (© 2012 The Authors. Congenital Anomalies © 2012 Japanese Teratology Society.)

The risk of developing schizophrenia has been linked to perturbations in embryonic development, but the physiological alterations that result from such insults are incompletely understood. Here, we have investigated aspects of hippocampal physiology in a proposed neurodevelopmental model of schizophrenia, induced during gestation in rats by injection of the antimitotic agent methylazoxymethanol acetate (MAM) at embryonic day 17 (MAM(E17)). We observed a reduction in synaptic innervation and synaptic transmission in the dorsal hippocampus of MAM(E17) treated rats, accompanied by a pronounced increase in CA1 pyramidal neuron excitability. Pharmacological investigations suggested that a deficit in GABAergic inhibition could account for the increase in excitability; furthermore, some aspects of the hyper-excitability could be normalised by the GABA(A) receptor (GABA(A)R) potentiator diazepam. Despite these alterations, two major forms of synaptic plasticity, long-term potentiation (LTP) and long-term depression (LTD) could be readily induced. In contrast, there was a substantial deficit in the reversal of LTP, depotentiation. These findings suggest that delivering neurodevelopmental insults at E17 may offer insights into some of the physiological alterations that underlie behavioural and cognitive symptoms observed in schizophrenia., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Neuroanatomical, electrophysiological and behavioural abnormalities following timed prenatal methylazoxymethanol acetate (MAM) treatment in rats model changes observed in schizophrenia. In particular, MAM treatment on gestational day 17 (E17) preferentially disrupts limbic-cortical circuits, and is a promising animal model of schizophrenia. The hypersensitivity of this model to the NMDA receptor antagonist-induced hyperactivity has been proposed to mimic the increase in sensitivity observed in schizophrenia patients following PCP and Ketamine administration. However, how this increase in sensitivity in both patients and animals translates to differences in EEG oscillatory activity is unknown. In this study we have shown that MAM-E17 treated animals have an increased response to the hyperlocomotor and wake promoting effects of Ketamine, PCP, and MK801 but not to the competitive antagonist SDZ 220,581. These behavioural changes were accompanied by altered EEG responses to the NMDAR antagonists, most evident in the gamma and high frequency (HFO) ranges; altered sensitivity of these neuronal network oscillations in MAM-exposed rats is regionally selective, and reflects altered interneuronal function in this neurodevelopmental model., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Purpose: Periventricular nodular heterotopia (PNH) is, in humans, often associated with difficult-to-control epilepsy. However, there is considerable controversy about the role of the PNH in seizure generation and spread. To study this issue, we have used a rat model in which injection of methylazoxymethanol (MAM) into pregnant rat dams produces offspring with nodular heterotopia-like brain abnormalities., Methods: Electrophysiologic methods were used to examine the activity of the MAM-induced PNH relative to activity in the neighboring hippocampus and overlying neocortex. Recordings were obtained simultaneously from these three structures in slice preparations from MAM-exposed rats and in intact animals. Bath application or systemic injection of bicuculline was used to induce epileptiform activity., Key Findings: In the in vitro slice, epileptiform discharge was generally initiated in hippocampus. In some cases, independent PNH discharge occurred, but the PNH never "led" discharges in hippocampus or neocortex. Intracellular recordings from PNH neurons confirmed that these cells received synaptic drive from both hippocampus and neocortex, and sent axonal projections to these structures-consistent with anatomic observations of biocytin-injected PNH cells. In intact animal preparations, bicuculline injection resulted in epileptiform discharge in all experiments, with a period of ictal-like electrographic activity typically initiated within 2-3 min after drug injection. In almost all animals, the onset of ictus was seen synchronously across PNH, hippocampal, and neocortical electrodes; in a few cases, the PNH electrode (histologically confirmed) did not participate, but in no case was activity initiated in the PNH electrode. Interictal discharge was also synchronized across all three electrodes; again, the PNH never "led" the other two electrodes, and typically followed (onset several milliseconds after hippocampal/neocortical discharge onset)., Significance: These results do not support the hypothesis that the PNH lesion is the primary epileptogenic site, since it does not initiate or lead epileptiform activity that subsequently propagates to other brain regions., (Wiley Periodicals, Inc. © 2011 International League Against Epilepsy.)

Western Pacific amyotrophic lateral sclerosis and parkinsonism-dementia complex, a disappearing neurodegenerative disease linked to use of the neurotoxic cycad plant for food and/or medicine, is intensively studied because the neuropathology (tauopathy) is similar to that of Alzheimer's disease. Cycads contain neurotoxic and genotoxic principles, notably cycasin and methylazoxymethanol, the latter sharing chemical relations with nitrosamines, which are derived from nitrates and nitrites in preserved meats and fertilizers, and also used in the rubber and leather industries. This review includes new data that influence understanding of the neurobiological actions of cycad and related genotoxins and the putative mechanisms by which they might trigger neurodegenerative disease.

Repeated administration of antipsychotic drugs to normal rats has been shown to induce a state of dopamine neuron inactivation known as depolarization block, which correlates with the ability of the drugs to exhibit antipsychotic efficacy and extrapyramidal side effects in schizophrenia patients. Nonetheless, in normal rats depolarization block requires weeks of antipsychotic drug administration, whereas schizophrenia patients exhibit initial effects soon after initiating antipsychotic drug treatment. We now report that, in a developmental disruption rat model of schizophrenia [methyl-azoxymethanol acetate (20 mg/kg, i.p.) injected into G17 pregnant female rats, with offspring tested as adults], the extant hyperdopaminergic state combines with the excitatory actions of a first- (haloperidol; 0.6 mg/kg, i.p.) and a second- (sertindole; 2.5 mg/kg, i.p.) generation antipsychotic drug to rapidly induce depolarization block in ventral tegmental area dopamine neurons. Acute injection of either antipsychotic drug induced an immediate reduction in the number of spontaneously active dopamine neurons (cells per electrode track; termed population activity). Repeated administration of either antipsychotic drug for 1, 3, 7, 15, and 21 d continued to reduce dopamine neuron population activity. Both acute and repeated effects on population activity were reversed by acute apomorphine injections, which is consistent with the reversal of dopamine neuron depolarization block. Although this action may account for the effects of D2 antagonist drugs on alleviating psychosis and the lack of development of tolerance in humans, the drugs appear to do so by inducing an offsetting deficit rather than attacking the primary pathology present in schizophrenia.

Schizophrenia is a highly familial, neurodevelopmental disorder that is associated with several neuropsychiatric, psychological, and neuropathological features. Although pharmacological animal models of dopaminergic and glutamatergic dysfunction have helped advance our understanding of the disease biology, there is a clear need for translational models that capture the neuropathological and functional manifestations associated with the intermediate phenotype and the clinical illness. Neuroimaging of preclinical neurodevelopmental approaches such as methylazoxymethanol acetate (MAM) exposure may afford a powerful translational tool to establish endpoints with greater congruency across animals and humans. Using in vivo volumetric magnetic resonance imaging (MRI), manganese-enhanced MRI, and diffusion tensor imaging (DTI), we investigated morphological and cytoarchitectural changes of brain structures in MAM-exposed rats, a neurodevelopmental model of schizophrenia. Compared to saline-exposed controls, MAM-exposed rats showed significant enlargement of lateral and third ventricles as well as reduced hippocampal volumes, which is consistent with findings observed in schizophrenia. In addition, DTI revealed that diffusion fractional anisotropy retrieved from corpus callosum and cingulum were significantly decreased in MAM-exposed rats, suggesting that demyelination occurred in these white-matter fiber tracts. Imaging findings were confirmed by conducting histological analysis using hematoxylin and eosin and Luxol fast blue stainings. In summary, structural abnormalities resulting from a MAM environmental challenge parallel cerebral pathology observed in schizophrenia. The MAM model incorporating noninvasive imaging techniques may therefore serve as an improved translational research tool for assessing new treatments for schizophrenia., (Copyright © 2010 Wiley-Liss, Inc.)

Methylazoxymethanol (MAM), the genotoxic metabolite of the cycad azoxyglucoside cycasin, induces genetic alterations in bacteria, yeast, plants, insects and mammalian cells, but adult nerve cells are thought to be unaffected. We show that the brains of adult C57BL6 wild-type mice treated with a single systemic dose of MAM acetate display DNA damage (O⁶-methyldeoxyguanosine lesions, O⁶-mG) that remains constant up to 7 days post-treatment. By contrast, MAM-treated mice lacking a functional gene encoding the DNA repair enzyme O⁶-mG DNA methyltransferase (MGMT) showed elevated O⁶-mG DNA damage starting at 48 hours post-treatment. The DNA damage was linked to changes in the expression of genes in cell-signaling pathways associated with cancer, human neurodegenerative disease, and neurodevelopmental disorders. These data are consistent with the established developmental neurotoxic and carcinogenic properties of MAM in rodents. They also support the hypothesis that early-life exposure to MAM-glucoside (cycasin) has an etiological association with a declining, prototypical neurodegenerative disease seen in Guam, Japan, and New Guinea populations that formerly used the neurotoxic cycad plant for food or medicine, or both. These findings suggest environmental genotoxins, specifically MAM, target common pathways involved in neurodegeneration and cancer, the outcome depending on whether the cell can divide (cancer) or not (neurodegeneration). Exposure to MAM-related environmental genotoxins may have relevance to the etiology of related tauopathies, notably, Alzheimer's disease.