Kazuya Toriumi

GABAergic Precursor Transplantation into the Prefrontal Cortex Prevents Phencyclidine-Induced Cognitive Deficits

Phencyclidine (PCP) is a noncompetitive NMDA receptor antagonist, and it induces schizophreniform cognitive deficits in healthy humans and similar cognitive deficits in rodents. Although the PCP-induced cognitive deficits appear to be accompanied and possibly caused by dysfunction of GABAergic inhibitory interneurons in the prefrontal cortex (PFC), the potential benefit(s) of GABAergic interneuron manipulations on PCP-induced cognitive deficits remains unexplored. In this study we show that when embryonic medial ganglionic eminence (MGE) cells, many of which differentiate into cortical GABAergic interneurons in situ, were grafted into the medial PFC (mPFC) of neonatal mice, they differentiated into a specific class of GABAergic interneurons and became functionally integrated into the host neuronal circuitry in adults. Prior MGE cell transplantation into the mPFC significantly prevented the induction of cognitive and sensory-motor gating deficits by PCP. The preventive effects were not reproduced by either transplantation of cortical projection neuron precursors into the mPFC or transplantation of MGE cells into the occipital cortex. The preventive effects of MGE cell transplantation into the mPFC were accompanied by activation of callosal projection neurons in the mPFC. These findings suggest that increasing GABAergic interneuron precursors in the PFC may contribute to the development of a cell-based approach as a novel means of modulating the PFC neuronal circuitry and preventing schizophreniform cognitive deficits.

Exposure to enriched environments during adolescence prevents abnormal behaviours associated with histone deacetylation in phencyclidine-treated mice

Enriched environments (EEs) during development have been shown to influence adult behaviour. Environmental conditions during childhood may contribute to the onset and/or pathology of schizophrenia; however, it remains unclear whether EE might prevent the development of schizophrenia. Herein, we investigated the effects of EE during adolescence on phencyclidine (PCP)-induced abnormal behaviour, a proposed schizophrenic endophenotype. Male ICR mice (3 wk old) were exposed to an EE for 4 wk and then treated with PCP for 2 wk. The EE potentiated the acute PCP treatment-induced hyperlocomotion in the locomotor test and prevented chronic PCP treatment-induced impairments of social behaviour and recognition memory in the social interaction and novel object recognition tests. It also prevented the PCP-induced decrease of acetylated Lys9 in histone H3-positive cells and increase of the histone deacetylase (HDAC)5 level in the prefrontal cortex. To investigate whether the histone modification during adolescence might be critical for the effect of EE, 3-wk-old mice were first treated with sodium butyrate (SB; an HDAC inhibitor) for 4 wk and then treated with PCP for 2 wk. Chronic SB treatment during adolescence mimicked the effects of EE, including potentiation of hyperlocomotion induced by acute PCP treatment and prevention of social and cognitive impairments, decrease of acetylated Lys9 in histone H3-positive cells and increase of the HDAC5 level in the prefrontal cortex associated with chronic PCP treatment. Our results suggest that EEs prevent PCP-induced abnormal behaviour associated with histone deacetylation. EEs during childhood might prove to be a novel strategy for prophylaxis against schizophrenia.

Prenatal NMDA Receptor Antagonism Impaired Proliferation of Neuronal Progenitor, Leading to Fewer Glutamatergic Neurons in the Prefrontal Cortex

N-methyl-D-aspartate (NMDA) receptor is a glutamate receptor which has an important role on mammalian brain development. We have reported that prenatal treatment with phencyclidine (PCP), a NMDA receptor antagonist, induces long-lasting behavioral deficits and neurochemical changes. However, the mechanism by which the prenatal antagonism of NMDA receptor affects neurodevelopment, resulting in behavioral deficits, has remained unclear. Here, we report that prenatal NMDA receptor antagonism impaired the proliferation of neuronal progenitors, leading to a decrease in the progenitor pool in the ventricular and the subventricular zone. Furthermore, using a PCR array focused on neurogenesis and neuronal stem cells, we evaluated changes in gene expression causing the impairment of neuronal progenitor proliferation and found aberrant gene expression, such as Notch2 and Ntn1, in prenatal PCP-treated mice. Consequently, the density of glutamatergic neurons in the prefrontal cortex was decreased, probably resulting in glutamatergic hypofunction. Prenatal PCP-treated mice displayed behavioral deficits in cognitive memory and sensorimotor gating until adulthood. These findings suggest that NMDA receptors regulate the proliferation and maturation of progenitor cells for glutamatergic neuron during neurodevelopment, probably via the regulation of gene expression.

Clozapine ameliorates epigenetic and behavioral abnormalities induced by phencyclidine through activation of dopamine D1 receptor.

Accumulating evidence suggests that dysregulation of histone modification is involved in the pathogenesis and/or pathophysiology of psychiatric disorders. However, the abnormalities in histone modification in the animal model of schizophrenia and the efficacy of antipsychotics for such abnormalities remain unclear. Here, we investigated the involvement of histone modification in phencyclidine-induced behavioral abnormalities and the effects of antipsychotics on these abnormalities. After repeated phencyclidine (10 mg/kg) treatment for 14 consecutive days, mice were treated with antipsychotics (clozapine or haloperidol) or the histone deacetylase inhibitor sodium butyrate for 7 d. Repeated phencyclidine treatments induced memory impairment and social deficit in the mice. The acetylation of histone H3 at lysine 9 residues decreased in the prefrontal cortex with phencyclidine treatment, whereas the expression level of histone deacetylase 5 increased. In addition, the phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II in the nucleus decreased in the prefrontal cortex of phencyclidine-treated mice. These behavioral and epigenetic changes in phencyclidine-treated mice were attenuated by clozapine and sodium butyrate but not by haloperidol. The dopamine D1 receptor antagonist SCH-23390 blocked the ameliorating effects of clozapine but not of sodium butyrate. Furthermore, clozapine and sodium butyrate attenuated the decrease in expression level of GABAergic system-related genes in the prefrontal cortex of phencyclidine-treated mice. These findings suggest that the antipsychotic effect of clozapine develops, at least in part, through epigenetic modification by activation of the dopamine D1 receptor in the prefrontal cortex.

Clinical Features of Schizophrenia With Enhanced Carbonyl Stress

Accumulating evidence suggests that advanced glycation end products, generated as a consequence of facilitated carbonyl stress, are implicated in the development of a variety of diseases. These diseases include neurodegenerative illnesses, such as Alzheimer disease. Pyridoxamine is one of the 3 forms of vitamin B6, and it acts by combating carbonyl stress and inhibiting the formation of AGEs. Depletion of pyridoxamine due to enhanced carbonyl stress eventually leads to a decrease in the other forms of vitamin B6, namely pyridoxal and pyridoxine. We previously reported that higher levels of plasma pentosidine, a well-known biomarker for advanced glycation end products, and decreased serum pyridoxal levels were found in a subpopulation of schizophrenic patients. However, there is as yet no clinical characterization of this subset of schizophrenia. In this study, we found that these patients shared many clinical features with treatment-resistant schizophrenia. These include a higher proportion of inpatients, low educational status, longer durations of hospitalization, and higher doses of antipsychotic medication, compared with patients without carbonyl stress. Interestingly, psychopathological symptoms showed a tendency towards negative association with serum vitamin B6 levels. Our results support the idea that treatment regimes reducing carbonyl stress, such as supplementation of pyridoxamine, could provide novel therapeutic benefits for this subgroup of patients.

Prenatal Nicotine Exposure Impairs the Proliferation of Neuronal Progenitors, Leading to Fewer Glutamatergic Neurons in the Medial Prefrontal Cortex

Cigarette smoking during pregnancy is associated with various disabilities in the offspring such as attention deficit/hyperactivity disorder, learning disabilities, and persistent anxiety. We have reported that nicotine exposure in female mice during pregnancy, in particular from embryonic day 14 (E14) to postnatal day 0 (P0), induces long-lasting behavioral deficits in offspring. However, the mechanism by which prenatal nicotine exposure (PNE) affects neurodevelopment, resulting in behavioral deficits, has remained unclear. Here, we report that PNE disrupted the proliferation of neuronal progenitors, leading to a decrease in the progenitor pool in the ventricular and subventricular zones. In addition, using a cumulative 5-bromo-2′-deoxyuridine labeling assay, we evaluated the rate of cell cycle progression causing the impairment of neuronal progenitor proliferation, and uncovered anomalous cell cycle kinetics in mice with PNE. Accordingly, the density of glutamatergic neurons in the medial prefrontal cortex (medial PFC) was reduced, implying glutamatergic dysregulation. Mice with PNE exhibited behavioral impairments in attentional function and behavioral flexibility in adulthood, and the deficits were ameliorated by microinjection of D-cycloserine into the PFC. Collectively, our findings suggest that PNE affects the proliferation and maturation of progenitor cells to glutamatergic neuron during neurodevelopment in the medial PFC, which may be associated with cognitive deficits in the offspring.

Prenatal exposure to PCP produces behavioral deficits accompanied by the overexpression of GLAST in the prefrontal cortex of postpubertal mice.

Altered glutamatergic neurotransmission in the prefrontal cortex (PFC) has been implicated in a myriad of neuropsychiatric disorders. We previously reported that prenatal exposure to PCP produced long-lasting behavioral deficits, accompanied by the abnormal expression and dysfunction of NMDA receptors. In addition, these behavioral changes were attenuated by clozapine treatment. However, whether the prenatal exposure adversely affects pre-synaptic glutamatergic neurotransmission in postpubertal mice remains unknown. In the present study, we investigated the involvement of prefrontal glutamatergic neurotransmission in the impairment of cognitive and emotional behavior after prenatal PCP treatment (5mg/kg/day) from E6 to E18 in mice. The PCP-treated mice showed an impairment of recognition memory in a novel object recognition test and enhancement of immobility in a forced swimming test at 8 weeks of age. Moreover, the prenatal treatment reduced the extracellular glutamate level, but increased the expression of a glial glutamate transporter (GLAST) in the PFC. The microinjection of DL-threo-β-benzyloxyaspartate (DL-TBOA, 10 nmol/site/bilaterally), a potent blocker of glutamate transporters, reversed these behavioral deficits by enhancing the prefrontal glutamatergic neurotransmission. Taken together, prenatal exposure to PCP produced impairments of long-term memory and emotional function which are associated with abnormalities of pre-synaptic glutamate transmission in the PFC of postpubertal mice. These findings suggest the prenatal inhibition of NMDA receptor function to contribute partly to the pathophysiology of neurodevelopment-related disorders, such as schizophrenia.

Prenatal exposure to phencyclidine produces abnormal behaviour and NMDA receptor expression in postpubertal mice

Several studies have shown the disruptive effects of non-competitive N-methyl-d-aspartate (NMDA) receptor antagonists on neurobehavioural development. Based on the neurodevelopment hypothesis of schizophrenia, there is growing interest in animal models treated with NMDA antagonists at developing stages to investigate the pathogenesis of psychological disturbances in humans. Previous studies have reported that perinatal treatment with phencyclidine (PCP) impairs the development of neuronal systems and induces schizophrenia-like behaviour. However, the adverse effects of prenatal exposure to PCP on behaviour and the function of NMDA receptors are not well understood. This study investigated the long-term effects of prenatal exposure to PCP in mice. The prenatal PCP-treated mice showed hypersensitivity to a low dose of PCP in locomotor activity and impairment of recognition memory in the novel object recognition test at age 7 wk. Meanwhile, the prenatal exposure reduced the phosphorylation of NR1, although it increased the expression of NR1 itself. Furthermore, these behavioural changes were attenuated by atypical antipsychotic treatment. Taken together, prenatal exposure to PCP produced long-lasting behavioural deficits, accompanied by the abnormal expression and dysfunction of NMDA receptors in postpubertal mice. It is worth investigating the influences of disrupted NMDA receptors during the prenatal period on behaviour in later life.

Protective Potential of the Glutathione Peroxidase-1 Gene in Abnormal Behaviors Induced by Phencyclidine in Mice

Escalating evidence suggests that the impairment of glutathione (GSH)-dependent systems is one of the etiologic factors of schizophrenia. GSH is an important substrate of glutathione peroxidase (GPx). Among GPx isozymes, selenium-dependent GPx (GPx-1) is recognized as a major type, and therefore, this study investigates the role of the GPx-1 gene in abnormal behaviors induced by repeated phencyclidine (PCP) treatment using GPx-1 knockout (KO) and overexpressing transgenic (GPx-1 TG) mice. PCP-induced abnormal behaviors were more pronounced in GPx-1 KO mice than abnormal behaviors in wild-type (WT) mice, and the abnormal behaviors were less pronounced in GPx-1 TG mice than abnormal behaviors in non-TG mice. PCP treatment significantly reduced GSH levels and enhanced oxidative burdens in the prefrontal cortex of the test animals. In addition, PCP treatment significantly upregulated the nuclear translocations of nuclear factor erythroid-2-related factor 2 (Nrf2) and nuclear factor kappa-B (NF-κB) p65, as well as their DNA binding activities and γ-glutamylcysteine (GCL) mRNA expression in WT and non-TG mice. However, GPx-1 KO abolished this upregulation system. In contrast, genetic overexpression of GPx-1 further upregulated Nrf2-dependent GSH synthetic system, but downregulated NF-κB p65 activity in the presence of PCP. Clozapine, an antipsychotic, significantly upregulated GPx-1 and Nrf2-dependent GSH synthetic systems in the presence of PCP, but failed to affect NF-κB p65 activity. Our results suggest that interactive modulations between the GPx-1 gene and Nrf2-dependent GSH induction are critical for attenuating PCP-induced abnormal behaviors in mice.

SHATI/NAT8L regulates neurite outgrowth via microtubule stabilization

We previously identified a new molecule, “SHATI/NAT8L,” which has an inhibitory effect on methamphetamine (METH)‐induced hyperlocomotion, sensitization, and conditioned place preference. Nevertheless, the extent of SHATI localization and its functions are only partially understood. In this study, we used the FLAG‐tag method to investigate SHATI localization. We found that SHATI was localized to microtubules when expressed in COS7 cells and cortical primary neurons. This distribution of SHATI was less apparent after cells were treated with colchicine, a tubulin polymerization inhibitor that disrupts the microtubule structure. This finding suggests that SHATI is associated with microtubule structure. Interestingly, overexpression of SHATI in COS7 cells could attenuate the colchicine‐induced decrease in acetylated microtubules, indicating that SHATI plays a role in stabilizing microtubules. Furthermore, we showed that Shati deletion impaired neurite elongation. In cortical primary neurons, neurite length and complexity in Shati‐knockout (KO) mice were significantly decreased. In pyramidal neurons in the prefrontal cortex, dendrite length and complexity were also significantly decreased in Shati‐KO mice compared with wild‐type mice. These results suggest a novel function for SHATI, which may be a new member of the microtubule‐associated protein family.