The circadian system: A neglected player in neurodevelopmental disorders.

Patients with neurodevelopmental disorders, such as autism spectrum disorder, often display abnormal circadian rhythms. The role of the circadian system in these disorders has gained considerable attention over the last decades. Yet, it remains largely unknown how these disruptions occur and to what extent they contribute to the disorders' development. In this review, we examine circadian system dysregulation as observed in patients and animal models of neurodevelopmental disorders. Second, we explore whether circadian rhythm disruptions constitute a risk factor for neurodevelopmental disorders from studies in humans and model organisms. Lastly, we focus on the impact of psychiatric medications on circadian rhythms and the potential benefits of chronotherapy. The literature reveals that patients with neurodevelopmental disorders display altered sleep-wake cycles and melatonin rhythms/levels in a heterogeneous manner, and model organisms used to study these disorders appear to support that circadian dysfunction may be an inherent characteristic of neurodevelopmental disorders. Furthermore, the pre-clinical and clinical evidence indicates that circadian disruption at the environmental and genetic levels may contribute to the behavioural changes observed in these disorders. Finally, studies suggest that psychiatric medications, particularly those prescribed for attention-deficit/hyperactivity disorder and schizophrenia, can have direct effects on the circadian system and that chronotherapy may be leveraged to offset some of these side effects. This review highlights that circadian system dysfunction is likely a core pathological feature of neurodevelopmental disorders and that further research is required to elucidate this relationship.

Altered excitatory and decreased inhibitory transmission in the prefrontal cortex of male mice with early developmental disruption to the ventral hippocampus.

Ventral hippocampal (vHPC)-prefrontal cortical (PFC) pathway dysfunction is a core neuroimaging feature of schizophrenia. However, mechanisms underlying impaired connectivity within this pathway remain poorly understood. The vHPC has direct projections to the PFC that help shape its maturation. Here, we wanted to investigate the effects of early developmental vHPC perturbations on long-term functional PFC organization. Using whole-cell recordings to assess PFC cellular activity in transgenic male mouse lines, we show early developmental disconnection of vHPC inputs, by excitotoxic lesion or cell-specific ablations, impairs pyramidal cell firing output and produces a persistent increase in excitatory and decrease in inhibitory synaptic inputs onto pyramidal cells. We show this effect is specific to excitatory vHPC projection cell ablation. We further identify PV-interneurons as a source of deficit in inhibitory transmission. We find PV-interneurons are reduced in density, show a reduced ability to sustain high-frequency firing, and show deficits in excitatory inputs that emerge over time. We additionally show differences in vulnerabilities to early developmental vHPC disconnection, wherein PFC PV-interneurons but not pyramidal cells show deficits in NMDA receptor-mediated current. Our results highlight mechanisms by which the PFC adapts to early developmental vHPC perturbations, providing insights into schizophrenia circuit pathology.

Altered circadian rhythms in a mouse model of neurodevelopmental disorders based on prenatal maternal immune activation.

Individuals with neurodevelopmental disorders, such as schizophrenia and autism spectrum disorder, exhibit various sleep and circadian rhythm disturbances that often persist and worsen throughout the lifespan. To study the interaction between circadian rhythm disruption and neurodevelopmental disorders, we utilized a mouse model based on prenatal maternal immune activation (MIA). We hypothesized that MIA exposure would lead to impaired circadian locomotor activity rhythms in adult mouse offspring. We induced MIA by injecting pregnant dams with polyinosinic:polycytidylic acid (poly IC) at embryonic day 9.5, then aged resulting offspring to adulthood. We first confirmed that poly IC injection in pregnant dams elevated plasma levels of pro- and anti-inflammatory cytokines and chemokines. We then placed adult offspring in running wheels and subjected them to various lighting conditions. Overall, poly IC-exposed male offspring exhibited altered locomotor activity rhythms, reminiscent of individuals with neurodevelopmental disorders. In particular, we report increased (subjective) day activity across 3 different lighting conditions: 12 h of light, 12 h of dark (12:12LD), constant darkness (DD) and constant light. Further data analysis indicated that this was driven by increased activity in the beginning of the (subjective) day in 12:12LD and DD, and at the end of the day in 12:12LD. This effect was sex-dependent, as in utero poly IC exposure led overall to much milder alterations in locomotor activity rhythms in female offspring than in male offspring. We also confirmed that the observed behavioral impairments in adult poly IC-exposed offspring were not due to differences in maternal behavior. These data further our understanding of the link between circadian rhythm disruption and neurodevelopmental disorders and may have implications for mitigating risk to the disorders and/or informing the development of circadian-based therapies.

Opposing alterations in excitation and inhibition of layer 5 medial prefrontal cortex pyramidal neurons following neonatal ventral hippocampal lesion.

Cognitive abnormalities in schizophrenia reflect deficits in prefrontal cortical function, which could be related to attrition of dendritic structures of prefrontal cortical neurons. Schizophrenia-related prefrontal deficits have been modeled in postpubertal neonatal ventral hippocampal lesioned (NVHL) rats, which displayed a loss of dendritic complexity and spines in layer 3 pyramidal neurons in the medial prefrontal cortex (mPFC). The influence of dendritic attrition on synaptic function and neuronal excitability in the mPFC remains poorly understood. Here, we performed electrophysiological recordings of layer 5 mPFC pyramidal neurons from postpubertal (postnatal 40-60 days) NVHL rats and sham-operated controls. We found that the dendritic length, complexity, and spine density of neurobiotin-labeled layer 5 mPFC pyramidal neurons in NVHL rats were significantly lower than those in sham-operated rats. However, the excitability of layer 5 mPFC pyramidal neurons remained unchanged after NVHL. We found no significant changes in the expression of vesicular glutamate and γ-aminobutyric acid transporters after NVHL. Intriguingly, NVHL increased the amplitude of action potential-independent miniature excitatory postsynaptic currents and decreased the frequency of miniature inhibitory postsynaptic currents. These opposing alterations in excitatory and inhibitory synapses, possibly shifting basal synaptic activity toward increased excitation, could be cellular substrates for mPFC functional deficits reported in NVHL rats.

Loss of dysbindin-1 in excitatory neurons in mice impacts NMDAR-dependent behaviors, neuronal morphology and synaptic transmission in the ventral hippocampus.

Dysbindin-1, a protein encoded by the schizophrenia susceptibility gene DTNBP1, is reduced in the hippocampus of schizophrenia patients. It is expressed in various cellular populations of the brain and implicated in dopaminergic and glutamatergic transmission. To investigate the impact of reduced dysbindin-1 in excitatory cells on hippocampal-associated behaviors and synaptic transmission, we developed a conditional knockout mouse model with deletion of dysbindin-1 gene in CaMKIIα expressing cells. We found that dysbindin-1 reduction in CaMKII expressing cells resulted in impaired spatial and social memories, and attenuation of the effects of glutamate N-methyl-d-asparate receptor (NMDAR) antagonist MK801 on locomotor activity and prepulse inhibition of startle (PPI). Dysbindin-1 deficiency in CaMKII expressing cells also resulted in reduced protein levels of NMDAR subunit GluN1 and GluN2B. These changes were associated with increased expression of immature dendritic spines in basiliar dendrites and abnormalities in excitatory synaptic transmission in the ventral hippocampus. These results highlight the functional relevance of dysbindin-1 in excitatory cells and its implication in schizophrenia-related pathologies.

Schizophrenia-like features in transgenic mice overexpressing human HO-1 in the astrocytic compartment.

Delineation of key molecules that act epigenetically to transduce diverse stressors into established patterns of disease would facilitate the advent of preventive and disease-modifying therapeutics for a host of neurological disorders. Herein, we demonstrate that selective overexpression of the stress protein heme oxygenase-1 (HO-1) in astrocytes of novel GFAP.HMOX1 transgenic mice results in subcortical oxidative stress and mitochondrial damage/autophagy; diminished neuronal reelin content (males); induction of Nurr1 and Pitx3 with attendant suppression of their targeting miRNAs, 145 and 133b; increased tyrosine hydroxylase and α-synuclein expression with downregulation of the targeting miR-7b of the latter; augmented dopamine and serotonin levels in basal ganglia; reduced D1 receptor binding in nucleus accumbens; axodendritic pathology and altered hippocampal cytoarchitectonics; impaired neurovascular coupling; attenuated prepulse inhibition (males); and hyperkinetic behavior. The GFAP.HMOX1 neurophenotype bears resemblances to human schizophrenia and other neurodevelopmental conditions and implicates glial HO-1 as a prime transducer of inimical (endogenous and environmental) influences on the development of monoaminergic circuitry. Containment of the glial HO-1 response to noxious stimuli at strategic points of the life cycle may afford novel opportunities for the effective management of human neurodevelopmental and neurodegenerative conditions.

Behavioral and cellular responses to circadian disruption and prenatal immune activation in mice.

Most individuals with neurodevelopmental disorders (NDDs), including schizophrenia and autism spectrum disorders, experience disruptions in sleep and circadian rhythms. Epidemiological studies indicate that exposure to prenatal infection increases the risk of developing NDDs. We studied how environmental circadian disruption contributes to NDDs using maternal immune activation (MIA) in mice, which models prenatal infection. Pregnant dams were injected with viral mimetic poly IC (or saline) at E9.5. Adult poly IC- and saline-exposed offspring were subjected to 4 weeks of each of the following: standard lighting (LD1), constant light (LL) and standard lighting again (LD2). Behavioral tests were conducted in the last 12 days of each condition. Poly IC exposure led to significant behavioral differences, including reduced sociability (males only) and deficits in prepulse inhibition. Interestingly, poly IC exposure led to reduced sociability specifically when males were tested after LL exposure. Mice were exposed again to either LD or LL for 4 weeks and microglia were characterized. Notably, poly IC exposure led to increased microglial morphology index and density in dentate gyrus, an effect attenuated by LL exposure. Our findings highlight interactions between circadian disruption and prenatal infection, which has implications in informing the development of circadian-based therapies for individuals with NDDs.

Exposure to Circadian Disruption During Adolescence Interacts With a Genetic Risk Factor to Modify Schizophrenia-relevant Behaviors in a Sex-dependent Manner.

DTNBP1 is a gene associated with schizophrenia. Postmortem studies found a reduced expression of DTNBP1 in regions associated with schizophrenia in patients' brains. Sandy (Sdy) mice have a loss-of-function mutation in Dtnbp1 gene, resulting in behavioral deficits and brain changes similar to those seen in patients with schizophrenia. We previously showed that exposing adult Sdy mice to circadian disruption led to an exacerbation of schizophrenia-relevant behaviors. Here we asked whether the interaction between this genetic risk factor and circadian disruption occurs during adolescence, a period when environmental insults can promote schizophrenia symptoms, and whether sex affects this interaction. Starting at postnatal day 21, wild-type (WT) and Sdy males and females were housed for 4 weeks either in a 12 h light:12 h dark (LD 12:12) cycle or under chronic jetlag (CJL). Then, after 2 weeks in LD 12:12, behavioral assessments were conducted, including elevated plus maze (EPM), novel object recognition (NOR), social interaction, and prepulse inhibition (PPI) of acoustic startle. NOR and social novelty tests showed that, surprisingly, CJL during adolescence had opposite effects on WT and Sdy males, that is, behavioral deficits in WT males while rescuing preexisting deficits in Sdy mice. CJL led to decreased sociability in WT and Sdy mice while decreasing PPI only in females. Sdy mice showed decreased anxiety-like behavior compared with wild-type (WT), which was further accentuated by CJL in males. Thus, circadian disruption during adolescence, on its own or in association with Dtnbp1 mutation, can influence cognition, sociability, sensorimotor gating, and anxiety-like behaviors in a sex-dependent manner.

Alterations in prefrontal cortical neuregulin-1 levels in post-pubertal rats with neonatal ventral hippocampal lesions.

Genetic studies in humans have implicated the gene encoding neuregulin-1 (NRG-1) as a candidate susceptibility gene for schizophrenia. Furthermore, it has been suggested that NRG-1 is involved in regulating the expression and function of the N-methyl-D-aspartate receptor and the GABAA receptor in several brain areas, including the prefrontal cortex (PFC), the hippocampus, and the cerebellum. Neonatal ventral hippocampal lesioned (NVHL) rats have been considered as a putative model for schizophrenia with characteristic post-pubertal alteration in response to stress and neuroleptics. In this study, we examined NRG-1, erb-b2 receptor tyrosine kinase 4 (erbB4), and phospho-erbB4 (p-erbB4) levels in the PFC and the distribution of NRG-1 in the NVHL rats by using immunoblotting and immunohistochemical analyses. Neonatal lesions were induced by bilateral injection of ibotenic acid in the ventral hippocampus of postnatal day 7 Sprague-Dawley (SD)-rats. NVHL rats showed significantly decreased levels of NRG-1 and p-erbB4 in the PFC compared to sham controls at post-pubertal period, while the level of erbB4 did not differ between sham and NVHL rats. Moreover, microinjection of NRG-1 into the mPFC improved NVHL-induced prepulse inhibition deficits. Our study suggests PFC NRG-1 alteration as a potential mechanism in schizophrenia-like behaviors in the NVHL model.

Neurodevelopmental insights into circuit dysconnectivity in schizophrenia.

Schizophrenia is increasingly being recognized as a disorder of brain circuits of developmental origin. Animal models, however, have been technically limited in exploring the effects of early developmental circuit abnormalities on the maturation of the brain and associated behavioural outputs. This review discusses evidence of the developmental emergence of circuit abnormalities in schizophrenia, followed by a critical assessment on how animal models need to be adapted through optimized tools in order to spatially and temporally manipulate early developmental events, thereby providing insight into the causal contribution of developmental perturbations to schizophrenia.

Mice with dopaminergic neuron-specific deletion of DTNBP-1 gene show blunted nucleus accumbens dopamine release and associated behaviors.

Reduced expression of a schizophrenia-associated gene Dystrobrevin Binding Protein 1 (DTNBP1) and its protein product dysbindin-1, has been reported in the brains of schizophrenia patients. DTNBP1-null mutant Sdy (Sandy) mice exhibit several behavioral features relevant to schizophrenia. Changes in dopaminergic as well as glutamatergic and GABAergic neurotransmission in cortico-limbic regions have been reported in Sdy mice. Since dysbindin-1 is expressed in multiple brain regions, it is not known whether dopamine (DA) changes observed in Sdy null mutants are due to dysbindin-1 deficiency in DAergic neurons specifically. Here, using a mouse line with conditional knockout (cKO) of DTNBP1 in DA neurons, we studied the effects of dysbindin-1 deficiency on DA release and DA-dependent behaviors. Spontaneous locomotor activity of cKO mice in novel environment was significantly reduced initially but was comparable at later time points with littermate controls. However, the locomotion-enhancing effect of a low dose of d-amphetamine (d-AMPH; 2.5 mg/kg, ip) was significantly attenuated in the cKO mice suggesting a dampened mesolimbic DA transmission. Similarly, the prepulse inhibition disrupting effect of d-AMPH was found to be significantly reduced in the mutant mice. No significant differences between the cKO and control mice were observed in tests of anxiety, spatial learning and memory and social interaction. In- vivo microdialysis in the nucleus accumbens (NAc) showed a decrease in d-AMPH-induced extracellular DA release in the cKO mice. No significant alterations in protein levels of DA transporter, phosphorylated CaM kinase-II or Akt308 in the NAc were observed in the cKO mice. Taken together, our data suggest an important role of dysbindin-1 in maintaining mesolimbic DA tone and call for further investigations identifying mechanisms linking dysbindin-1, DA and schizophrenia.

Are Circadian Disturbances a Core Pathophysiological Component of Schizophrenia?

Schizophrenia is a multifactorial disorder caused by a combination of genetic variations and exposure to environmental insults. Sleep and circadian rhythm disturbances are a prominent and ubiquitous feature of many psychiatric disorders, including schizophrenia. There is growing interest in uncovering the mechanistic link between schizophrenia and circadian rhythms, which may directly affect disorder outcomes. In this review, we explore the interaction between schizophrenia and circadian rhythms from 2 complementary angles. First, we review evidence that sleep and circadian rhythm disturbances constitute a fundamental component of schizophrenia, as supported by both human studies and animal models with genetic mutations related to schizophrenia. Second, we discuss the idea that circadian rhythm disruption interacts with existing risk factors for schizophrenia to promote schizophrenia-relevant behavioral and neurobiological abnormalities. Understanding the mechanistic link between schizophrenia and circadian rhythms will have implications for mitigating risk to the disorder and informing the development of circadian-based therapies.

Role of prefrontal cortical 5-HT2A receptors and serotonin transporter in the behavioral deficits in post-pubertal rats following neonatal lesion of the ventral hippocampus.

Neonatal ventral hippocampal-lesioned (NVHL) rats have been shown to display neurochemical and behavioral abnormalities at adulthood, analogous to some of those seen in schizophrenia. Serotonergic neurotransmission is implicated the pathophysiology and treatment of schizophrenia. In this study, we evaluated possible role of serotonergic transmission is the behaviors of NVHL-lesioned rats. Bilateral lesions to the ventral hippocampus (VH) in rat pups were made using the excitotoxin ibotenic acid. We investigated 5-HT2A-receptor and SERT binding sites in cortical and subcortical areas in post-pubertal NVHL and sham-lesioned rats, using quantitative receptor autoradiography. We compared a 5-HT-dependent behavior in NVHL and sham animals, the wet-dog shake response (WDSr) to a 5-HT2A receptor agonist DOI. In addition, we studied prepulse inhibition (PPI) of startle responses in NVHL and Sham-lesioned animals treated with antipsychotic drugs haloperidol, risperidone and clozapine and 5-HT2A antagonists ketanserin or MDL100907. The WDSr elicited by DOI was enhanced in post-pubertal NVHL rats compared to sham-lesioned controls. Moreover, post-pubertal NVHL rats exhibited PPI deficits which was reversed by atypical antipsychotics, ketanserin and MDL100907. A significant increase in 5-HT2A-like receptor binding was observed in the medial prefrontal cortex (mPFC) in post-pubertal NVHL rats without any significant change in the striatum and ventral pallidum. A significant increase in SERT-like binding was also observed in the mPFC and striatum of NVHL rats at pre-pubertal period; however, at post-pubertal age, the binding remained elevated in mPFC only. These data suggest that increased prefrontal cortical 5-HT transmission may play a role in the behavioral deficits observed in this neurodevelopmental model of schizophrenia.

Prenatal immune challenge induces developmental changes in the morphology of pyramidal neurons of the prefrontal cortex and hippocampus in rats.

The neural mechanisms by which maternal infections increase the risk for schizophrenia are poorly understood; however, animal models using maternal administration of immune activators suggest a role for cytokine imbalance in maternal/fetal compartments. As cytokines can potentially affect multiple aspects of neuronal development and the neuropathology of schizophrenia is believed to involve subtle temporo-limbic neurodevelopmental alterations, we investigated morphological development of the pyramidal neurons of the medial prefrontal cortex (mPFC) and hippocampus in rats that were prenatally challenged with the immune activator lipopolysaccharide (LPS). Pregnant Sprague-Dawley rats were administered with LPS (at E15- E16) or saline. The brains of offspring were processed for Golgi-Cox staining at postnatal days 10, 35 and 60. Dendritic length, branching, spine density and structure were quantified using Neurolucida software. At all ages, dendritic arbor was significantly reduced in mPFC and CA1 neurons of LPS-treated animals. Dendritic length was significantly reduced in the mPFC neurons of LPS group at P10 and 35 but returned to control values at P60. Opposite pattern was observed in CA1 region of LPS animals (normal values at P10 and 35, but a reduction at P60). LPS treatment significantly altered the structure of CA1 dendritic spines at P10. Spine density was found to be significantly lower only in layer V mPFC of P60 LPS rats. The study provides the first evidence that prenatal exposure to an immune activator dynamically affects spatio-temporal development of pyramidal neurons in mPFC and hippocampal that can potentially lead to aberrant neuronal connectivity and functions of these structures.

Altered netrin-1 receptor expression in dopamine terminal regions following neonatal ventral hippocampal lesions in the rat.

Neonatal ventral hippocampal (nVH) lesions in rats, which model certain features of schizophrenia, alter dopamine (DA)-mediated behaviors in adulthood. The precise mechanisms underlying these effects remain elusive; however, neuronal reorganization within the medial prefrontal cortex (mPFC) has been suggested. Netrins are developmental cues that organize brain wiring, including the mesocorticolimbic DA circuitry. We showed recently that the netrin-1 receptors DCC and UNC5H are highly expressed by DA neurons and that variation in DCC levels during development lead to profound changes in mesocorticolimbic DA function and behavior in adulthood. We hypothesized that changes in netrin-1 receptor function could be one of the mechanisms producing enduring changes in DA function in nVH-lesioned animals. To begin to explore this idea, we examined the effects of nVH lesions on DCC and UNC5H expression in brain regions receiving robust DA innervation; the mPFC, striatum, and nucleus accumbens (NAcc) at three developmental time points; 3 days after lesion, before puberty and during early adulthood. Expression was also examined in the cerebellar simple lobule; a brain region deprived of DA innervation. Neonatal VH lesions produced dynamic changes in DCC expression in the mPFC and NAcc. The direction and magnitude of these changes depended on the developmental age and brain region examined and were specific to regions receiving DA innervation. Although further studies are required to understand the functional significance of these changes, these results raise the interesting possibility that nVH lesions, and perinatal insults in general, may exert their neuronal reorganizational effects by modulating netrin-1 function.

Altered expression and alpha-1 adrenergic receptor mediated activity of protein kinase C in the prefrontal cortex of rats with neonatal ventral hippocampus lesions.

The neonatal ventral hippocampus (nVH) lesion in rats captures many features of schizophrenia at the levels of behavior and neurobiological markers. We have previously reported enhanced expression of alpha-1 adrenergic receptors (AR) in the prefrontal cortex (PFC) of postpubertal nVH-lesioned rats and proposed that enhanced alpha-1 AR signaling might participate in some of the behavioral abnormalities observed in the nVH-lesioned rats. To assess the components of alpha-1 adrenergic signaling in nVH-lesion rats, we examined prefrontal cortical expression of protein kinase C (PKC) subtypes by Western blotting and alpha-1 AR-stimulated PKC activity by in vitro enzyme assay in postpubertal animals. Neonatal VH-lesioned animals showed significantly increased expression of membrane-bound PKC-alpha and the phosphorylated form of PKC. Cytosolic PKC-beta II and PKC-gamma expression were found to be decreased in the PFC of lesioned animals with no change in the expression of PKC-beta I either in the cytosol or membrane. PKC activity assays showed an increase in basal PKC activity in the PFC slices of nVH-lesioned animals. Stimulation of alpha-1 adrenergic receptor with different concentrations of the agonist phenylephrine (PE), while increasing PKC activity in the sham-lesioned animals surprisingly decreased the activity in nVH-lesioned animals. Increased basal levels as well as activity of prefrontal PKC and its anomalous regulation by alpha-1 adrenergic receptors may participate in the cognitive and stress-induced behavioral alterations in nVH-lesioned animals.

Prenatal treatment with methylazoxymethanol acetate as a neurodevelopmental disruption model of schizophrenia in mice.

Methylazoxymethanol (MAM)-treated pregnant rat at gestation day (GD) 17 has been shown to be a valuable developmental animal model for schizophrenia. Yet, this model remains to be established in mice. In the present study, we examined behavioral, cytoarchitectural, and neurochemical changes in the offspring of MAM-treated mice and validated the model's face, construct and predictive validities. We found that in contrast to a single injection of MAM to dams at GD 15, 16 or 17, its daily administration from GD 15 to 17 led to deficits in prepulse inhibition (PPI) of startle in the post-pubertal offspring. In addition, we observed behavioral deficits in working memory and social interactions, as well as an increase in locomotor activity induced by the NMDA antagonist MK-801 in GD15-17 MAM offspring. These animals also showed a reduction in the volume of the prefrontal cortex (PFC) and hippocampus, neuroanatomical changes such as discontinuities and heterotopias in the hippocampus, and an increase of DA level and DOPAC/DA ratio in the medial PFC. Atypical antipsychotic drugs clozapine, risperidone, and aripiprazole, but not the typical drug haloperidol, reversed the deficit in PPI and social withdrawal in the offspring of MAM-treated dams. In contrast, MK-801-induced hyperactivity in MAM mice was reversed by both and typical or atypical antipsychotic drugs. Taken together, the treatment of pregnant mice with MAM during GD 15-17 offers a new approach to study neurobiological mechanisms involved in the pathogenesis of schizophrenia.

Microglia in the developing prefrontal cortex of rats show dynamic changes following neonatal disconnection of the ventral hippocampus.

Impaired ventral hippocampal (VH)-prefrontal cortex (PFC) connectivity is implicated in many cognitive and behavioral disorders. Excitotoxic neonatal VH (nVH) lesion in rat pups has been shown to induce synaptic pruning in the PFC as well as behavioral changes of relevance to developmental neuropsychiatric disorders. In the current study, we hypothesized that microglia, immune cells required for proper brain development and plasticity, may play a role in the development of abnormal behaviors in the nVH-lesioned animals. Ibotenic acid-induced nVH lesion was induced in postnatal day (P)7 male rats. Developmental changes in microglial density, morphology, ultrastructure and gene expression were analyzed in the PFC at P20 and P60. Our results revealed increased microglial reactivity and phagocytic activity in the lesioned rats at P20. Increased mRNA levels of C3 and C1q, complement molecules involved in synaptic pruning, were concomitantly observed. Diminished, but maintained, microglial reactivity and reduced antioxidative defenses were identified in lesioned rats at P60. Behavioral deficits were significantly reduced in the post-pubertal rats by suppressing microglial reactivity by a one-week minocycline treatment immediately after the lesion, These results suggest that early-life disconnection of the VH has long-lasting consequences for microglial functions in the connected structures. Alterations in microglia may underlie synaptic reorganization and behavioral deficits observed following neonatal VH disconnection.