毛利 彰宏

Tryptophan (TRP) is metabolized via the kynurenine (KYN) pathway, which is related to the pathogenesis of major depressive disorder (MDD). Kynurenine 3-monooxygenase (KMO) is a pivotal enzyme in the metabolism of KYN to 3-hydroxykynurenine. In rodents, KMO deficiency induces a depression-like behavior and increases the levels of kynurenic acid (KA), a KYN metabolite formed by kynurenine aminotransferases (KATs). We will introduce the involvement of TRP metabolism in the depression-like behavior induced by chronic unpredictable mild stress (CUMS). Corticosterone level in the serum and corticosterone-releasing hormone (CRH) mRNA level in the hypothalamus (HT) were elevated immediately after CUMS. Associated with the dysregulation of hypothalamic-pituitary-adrenal (HPA) axis, KMO mRNA level was decreased, and KA content was increased in the prefrontal cortex (PFC). Microglia marker Iba-1 was decreased immediately after CUMS. Because KMO is mainly found in microglia in the central nervous system, these results suggests that CUMS increased KA contents via alternation of kynurenine metabolic enzyme from KMO to KATs due to the reduction of microglia. Because KA is α7 nicotinic acetylcholine receptor (α7nAChR) antagonist, we investigated the effect of nicotine and galantamine (allosteric potentiating ligand for α7nAChR ) on the depression-like behavior and dysregulation of HPA axis induced by CUMS. When nicotine and galantamine were administrated before exposure to each stressor, they attenuated CUMS-induced depression-like behaviors. Although nicotine didn't affect elevated corticosterone level in the serum immediately after CUMS, it suppressed the sustained elevation 1 week after CUMS. Increase of KA associative with downregulation of KMO in microglia was involved in the depressive-like behavior and the sustained elevation of serum corticosterone after CUMS. The ameliorating effects of nicotine and galantamine on depression-like behaviors induced by CUMS are associated with the activation of α7nAChR.

Major depressive disorder (MDD) is a common mental disorder characterized by reduced motivation, diminished interest and pleasure, and anhedonia. We have proposed melanoma-associated antigen D1 (MAGE-D1) knock out (KO) mouse is a MDD model, and which involves the serotonergic hypofunction. However, not only serotonergic but also noradrenergic neuronal malfunctions are involved in depressive behaviors. Here, we investigate the involvement of noradrenergic neuronal system in depression-like behaviors of MAGE-D1 KO mice. MAGE-D1 KO mice showed decreases in locomotor activity, social interaction time and sucrose preference, but increases in immobility time in the forced swimming test (FST), and feeding latency in the novelty suppression feeding test. Noradrenaline (NA) tissue contents in the prefrontal cortex, hippocampus, and amygdala, and potassium-evoked noradrenaline releases in the prefrontal cortex and hippocampus were decreased in MAGE-D1 KO mice. The protein expression of noradrenaline transporter (NAT) was increased in the prefrontal cortex of the MAGE-D1 KO mice. Phosphorylation of NAT at threonine and protein expression of its kinase, protein kinase C (PKC) were decreased, but not changed in ubiquitination or expression of NAT mRNA. Acute administration of NA reuptake inhibitors (desipramine and atomoxetine) attenuated increase in immobility time in the FST and decrease in sucrose preference, but not other behavior changes in MAGE-D1 KO mice. These results suggested that depression-like behaviors in MAGE-D1 KO mice might be associated with hypofunction of noradrenergic neuronal system due to NAT overexpression through decrease in PKC-dependent phosphorylation of NAT.

White matter abnormalities have been implicated in psychiatric diseases such as major depressive disorder (MDD) ; however, the underlying mechanisms remain poorly understood. The structure and function of the corpus callosum are particularly vulnerable to stress, which may lead to MDD. In the present study, we investigated whether chronic social defeat stress (CSDS) induces myelin abnormalities of the corpus callosum through inflammation that contributes to the pathogenesis of MDD. To produce CSDS, the adult C57BL/6J mouse was exposed to an aggressor ICR mouse for 10 consecutive days. CSDS decreased mature oligodendrocytes in the corpus callosum, and persistently developed depression-like behaviors such as increased immobility in the forced swimming test and impaired social interaction. On transmission electron microscopy, myelin abnormalities and axonal degeneration were observed with necrosis-like cell death of oligodendrocytes in the corpus callosum. Interestingly, CSDS significantly increased the Gasdermin D (Gsdmd), a marker of pyroptosis, concomitantly with enhanced IL-1β production in the corpus callosum. Administration of IL-1β inhibitor prevented the decrease of oligodendrocytes and CSDS-induced depression-like behaviors. These findings suggest that IL-1β acts as a crucial mediator of oligodendroglial pyroptosis induced by the CSDS, which may be responsible for the development of MDD.

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder characterized by social deficit and stereotyped, repetitive patterns of behaviors and interests. Maternal use of valproic acid (VPA) during pregnancy is associated with an increased risk of ASD in the offspring. In the pathophysiological hypothesis of ASD, excitation/inhibition (E/I) imbalance is attracted. In this study, we investigated how VPA (500 mg/kg) at embryonic day 12.5 changes the emotional, cognitive and glutamatergic functions in the offspring of mice. Prenatal VPA exposure induced excessive repetitive self-grooming behavior, impairments of social behavior and object recognition memory, increased glutamatergic signaling [i.e. phospho-Ca²+/calmodulin-dependent protein kinase II (CaMKⅡ)and phospho-protein kinase C (PKC) levels] and decreased serotonin contents in the prefrontal cortex. These results suggested that VPA-exposure induced ASD-like behaviors associated with hyper-excitation of glutamatergic and hypo-serotonergic functions in the prefrontal cortex. Activation of serotonergic system by fluoxetine (20mg/kg) attenuated the VPA-induced ASD-like behaviors and hyper-glutamatergic signaling in the prefrontal cortex. These results suggest that hypo-serotonergic function is involved in the prenatal VPA-induced ASD-like behaviors and hyper-excitation in the prefrontal cortex.

Major depressive disorder (MDD) is a worldwide serious psychiatric disease, and more than 300 million people suffer from MDD. Chronic stress contributes to the pathogenesis of MDD. Cigarette smoking is strongly associated with MDD. Epidemiological and clinical studies claim that the smoking is assumed as self-medication for stress and depression. In this study, we investigated the effect of nicotine on the depression-like behavior induced by chronic unpredictable mild stress (CUMS). At the age of 6 weeks, C57BL6J mice were randomly exposed to 9 kinds of mild stressors for 4 weeks. Nicotine (0.2mg/kg), galantamine (1mg/kg) and varenicline (1mg/kg) were administrated 30 min before exposure to each stressor during CUMS. After CUMS, mice were subjected social interaction test and measured serum corticosterone levels and mRNA levels of  nicotinic acetylcholine receptor (nAChR) subunits in the prefrontal cortex (PFC). Nicotine attenuated decrease in social interaction time of CUMS mice. Nicotine did not affect elevated serum corticosterone levels immediately after CUMS but reversed the sustained elevation after behavioral test. CUMS did not affect mRNA levels of α7, α4 or β2 nAChR subunit in the PFC. Finally, we evaluated the efficacies of galantamine, α7 nAChR allosteric modulator and varenicline, α4β2 nAChR partial agonist on CUMS mice. Administration of galantamine, but not varenicline attenuated decrease in social interaction time of CUMS mice. These data suggested that α7 nAChR is an important target for stress resilience and development of antidepressant.

Chronic stress contributes to the pathogenesis of major depressive disorder (MDD). The efficacy of ketamine on the treatment-resistant MDD implies the involvement of glutamatergic dysregulation in its pathophysiology. We recently demonstrated the abnormalities of ubiquitin-proteasome system (UPS) in the pathophysiology of MDD. In the present study, we investigated the involvement of glutamatergic dysregulation by UPS in chronic social defeat stress (CSDS)-induced depression-like behavior. To induce CSDS, the adult C57BL/6J mouse was exposed to aggressor ICR mouse for 10 consecutive days. CSDS reduced the duration of time spent at the interaction zone in the social interaction test. Increase in high potassium-induced release of glutamate was diminished in the prefrontal cortex (PFC) of the stressed mice. Interestingly, ubiquitinated but not total glutamate transporter 1 (GLT-1) was decreased in the PFC of the stressed mice. Protein levels of neural precursor cell expressed developmentally downregulated gene 4-like (Nedd4L) and ubiquitin-conjugating enzyme E2D2 (Ube2d2) were also reduced in the stressed mice. Injection of adeno-associated virus (AAV) expressing shRNA against Nedd4L into the PFC exacerbated the social impairments induced by CSDS. These results suggest that CSDS induces depressive-like behavior and glutamatergic dysfunction, through the decrease of GLT-1 ubiquitination by down-regulation of Ube2d2-Nedd4L pathway. Taken together, GLT-1 ubiquitination could play crucial roles in the pathophysiology of MDD.

It has been shown that adverse events during pregnancy have a negative impact on brain development and may increase the risk for neuropsychiatric disorders in later life in human. In this study, we explored the long-lasting influences of psychosocial stress during pregnancy in adult offspring of mice using a communication box method.    Pregnant C57BL/6J mice were exposed to a psychosocial stress by communication box daily from the gestational day 12 (G12) until delivery. We observed the behaviors of offspring at 7 weeks old in the social interaction and elevated plus-maze tests, and measured plasma corticosterone levels, GABAergic neuronal changes in the amygdala. We found anxiety-like behaviors and reduction of social interaction in offspring received prenatal stress. Those mice had decrease in parvalbumin-positive cells in the amygdala and a hyperactivity of stress-induced corticosterone release compared to control group. In addition, these anxiety-like behaviors in the both tests were blocked by intra-amygdala injection of diazepam.  These results suggest that this prenatal psychosocial stress may lead to GABAergic hypofunction in the amygdala accompanied with anxiety-like behaviors of offspring.

統合失調症は幻覚や妄想，意欲の低下，認知障害などを主訴とする精神疾患である。多くの患者では抗精神病薬に対する治療抵抗性を有することから新しい作用機序をもつ予防・治療薬の開発が急務となっている。統合失調症の発症・病態仮説には，炎症による神経発達障害仮説やグルタミン酸仮説などが提唱されている。キヌレニン代謝経路は炎症により活性化され，その代謝産物には神経毒性，およびグルタミン酸神経機能に影響を与えるものがある。本稿では，母親が妊娠期にインフルエンザに感染すると胎児に統合失調症に対する発症脆弱性が形成されるという疫学仮説に基づき，作成したウイルスRNA様の作用を示す合成二本鎖RNAポリイノシン‐ポリシチジン（poly I：C）を胎生期に曝露させた統合失調症様モデル動物についての概説とこのモデル動物におけるキヌレニン代謝経路の関与について紹介する。

Successful completion of daily activities relies on the ability to select the relevant features of the environment for memory and recall. Disruption to these processes can lead to various disorders, such as attention-deficit hyperactivity disorder (ADHD). Dopamine is a neurotransmitter implicated in the regulation of several processes, including attention. In addition to the higher-order brain function, dopamine is implicated in the regulation of adult neurogenesis. Previously, we generated mice lacking Shati, an N-acetyltransferase-8-like protein on a C57BL/6J genetic background (Shati/Nat8l-/- ). These mice showed a series of changes in the dopamine system and ADHD-like behavioral phenotypes. Therefore, we hypothesized that deficiency of Shati/Nat8l would affect neurogenesis and attentional behavior in mice. We found aberrant morphology of neurons and impaired neurogenesis in the dentate gyrus of Shati/Nat8l-/- mice. Additionally, research has suggested that impaired neurogenesis might be because of the reduction of dopamine in the hippocampus. Galantamine (GAL) attenuated the attentional impairment observed in the object-based attention test via increasing the dopamine release in the hippocampus of Shati/Nat8l-/- mice. The α7 nicotinic acetylcholine receptor antagonist, methyllycaconitine, and dopamine D1 receptor antagonist, SCH23390, blocked the ameliorating effect of GAL on attentional impairment in Shati/Nat8l-/- mice. These results suggest that the ameliorating effect of GAL on Shati/Nat8l-/- attentional impairment is associated with activation of D1 receptors following increased dopamine release in the hippocampus via α7 nicotinic acetylcholine receptor. In summary, Shati/Nat8l is important in both morphogenesis and neurogenesis in the dentate gyrus and attention, possible via modulation of dopaminergic transmission.

We investigated the possibility of prostaglandin E₂ (PGE₂) as one of common molecules associated with vulnerability to neurodevelopmental disruptions induced by environmental factors. PGE₂ levels in whole brain were significantly increased after exposure to viral infection [injection of polyinosinic-polycytidylic acid (polyI:C)], hypoxia (exposure to CO₂), and neglect (separation from the dams) in postnatal day (PD) 2, compared to those after non-exposure. The mice administered polyI:C during PD 2-6 exhibited the impairment of sociality, object recognition memory, and pre-pulse inhibition (PPI) in adult at PD 70, and further, significant decreased spine density of the mPFC in adult mice. Exposure to CO₂ at PD 2 and separation from dams during PD 2-21 exhibited the impairment of PPI and decrease of spine density in adult mice. These behavioral impairments induced by administration of polyI:C were recovered by an inhibition of PGE₂-EP1 (PGE₂ receptor subtype) and of cyclooxygenase (COX).  Our findings suggest that PGE₂ is one of potential common molecules associated with vulnerability to neurodevelopmental disruptions induced by environmental factors, and PGE₂ plays a crucial role in the development of behavioral and neuronal impairments, which are associated with activation of PGE₂-EP1.

Quinolinic acid phosphoribosyltransferase (QPRT) metabolizes quinolinic acid (QA) to nicotinamide adenine nucleotide (NAD⁺) via kynurenine pathway. QA is a excitotoxic substance that activate N-methyl-D-aspertate (NMDA) receptors and NAD⁺ is essential for cell survival. In this study, we evaluated QPRT knock out (KO) mice to explore the physiological role of QPRT in central nervous system. QPRT KO mice demonstrated motor deficits (decrease of locomotor activity, decrease of duration time to maintain balance on the rotarod, wide stance in footprint pattern test) and cognitive deficits (decrease of spontaneous alternation behavior in Y-maze test, and prolongation of latency to enter the target hole in the Barnes-maze test). But emotional change was not observed except for decrease in number of buried marbles in marble burying test. Dopaminergic dysfunction was observed in prefrontal cortex, nucleus accumbens and striatum of QPRT KO mice. Dopamine D₁ receptor agonist (SKF81297)-induced hyperactivity is not observed in QPRT KO mice. Dopamine D₂ receptor antagonist (raclopride)-induced catalepsy is more sensitive in QPRT KO mice. The activation of dopaminergic function by methylphenidate attenuated the impairment of short-term memory and hypoactivity of QPRT KO mice. QPRT KO mice showed increased level of QA in serum but normal level of NAD+ in brain. QA-mediated NMDA receptor signaling (phosphorylation of CaMK2 and activation of calpain) and oxidative stress were enhanced in prefrontal cortex, nucleus accumbens and striatum of QPRT KO mice. These results suggested that deficiency of QPRT lead motor and cognitive deficits associated with dopaminergic dysfunction via QA-induced calpain activation and oxidative stress.

Augmenting evidences disclose that stressful events evoke molecular alteration in brain, considered as a pathology in major depressive disorder (MDD). Chronic unpredictable mild stress (CUMS) induced hyperactivity in novel environment, decrease of social interaction time in social interaction test, prolongation of feeding latency in novelty suppressed feeding test, and enhancement of immobility in forced swimming test. The contents of dopamine and its metabolites, Dopamine (DA) turnover and protein level of tyrosine hydroxylase (TH) were increased by CUMS in the nucleus accumbens. The contents of serotonin, and protein levels of tryptophan hydroxylase (TPH) and TH were decreased by CUMS in the hippocampus and prefrontal cortex. Accompanies with activation of dopaminergic function, phosphorylation levels of ERK, Akt, and CREB were increased by CUMS in the nucleus accumbens. Administration of fluoxetine and aripiprazole during CUMS prevented the abnormal behavioral changes. These data suggest that CUMS induced depressive behaviors are associated with dopaminergic hyperfunction and ERK/Akt/CREB pathway in the nuclues accumbens, and serotonergic hypofunction in the prefrontal cortex and hippocampus.

Quinolinic acid (QA) is a neurotoxic and implicated in the neurological disorders. QA is metabolized by quinolinic acid phosphoribosyltransferase (QPRT). However, the physiological roles of QPRT in central nervous system are still unclear. To investigate the roles of QPRT in emotional and cognitive functions, QPRT KO mice were subjected to several types of neurobehavioral tests. The KO mice decreased locomotor activity in novel environment, prolonged escape latency in Barns maze test, and decreased alternation behavior in Y-maze test. In the KO mice, the contents of homovanillic acid (HVA) and 3,4-Dihydroxyphenylacetic acid (DOPAC), and the ratios of HVA/ dopamine (DA) in the nucleus accumbens and DOPAC/DA in the prefrontal cortex were decrease. In the immunohistochemistry, the number of tyrosine hydroxylase (TH)-positive neuron was less compared with wild mice. Taken together, the present findings suggest a novel role of QPRT in hypolocomotion and cognitive impairment in relation to impairment of dopaminergic functions in the nucleus accumbens and prefrontal cortex, respectively.

Glutamatergic systems play a critical role in the pathophysiology and treatment of stress-related disorders. In the present study, we conducted behavioral and neurochemical experiments to reveal involvement of glutamate receptors in the impairment of social behaviors induced by stress exposure as juveniles. Acute administration of ketamine, a non-competitive NMDA receptor antagonist and subsequent AMPA receptor stimulation attenuated the impairment of social behaviors in adolescent mice exposed to social defeat stress as juveniles. NBQX, a selective AMPA receptor antagonist prevented the attenuating effect of ketamine on the impairment of social behaviors. Although there were no significant changes in the ratios of phosphorylated protein of some NMDA subunits, that of AMPA receptor GluA1 subunit was significantly increased in the hippocampus of non-tested, defeated mice. In non-tested, defeated mice, ketamine increased the hippocampal total protein level, but not the ratio of phosphorylated protein of GluA1. These results suggest that exposure to social defeat stress as juveniles induces the impairment of social behaviors in adolescents through the functional changes in AMPA receptors.

High cortisol level in serum is one of the clinical features in depression. Exogenous administration of corticosterone (CORT) in rodents has been used as animal model of depression. Red resin of Dracaena cochinchinensis S.C. Chen, known as Chinese dragon's blood, has been used as a famous and precious traditional medicine since ancient times by many cultures. XJ-Et-8 is a compound extracted from Chinese dragon's blood. It has favorable effects on mouse models of Alzheimer' Diseases through the up regulating the BDNF level in the brain. The present study aimed to evaluate the XJ-Et-8 as antidepressant using a mouse model of CORT administration. CORT (20 mg/kg/day) was administered subcutaneously for 3 weeks, and XJ-Et-8 was given orally during the last 2 weeks. After corticosterone administration, mice were sequentially subjected behavioral tests: open field test, social interaction test, novelty suppressed feeding test, and forced swimming test. Corticosterone administration induced depressive and anxious behaviors and decrease of phosphorylation in AKT/mTOR/CREB signaling pathway and of BDNF contents in the prefrontal cortex. XJ-Et-8 reversed these behavioral changes, increased phosphorylation level in AKT/mTOR/CREB pathway and BDNF expression. These results suggest that the XJ-Et-8 could be a potential compound as an antidepressant via activating the AKT/mTOR/CREB pathway and BDNF expression.