Hisayoshi Kubota

Maternal use of valproic acid (VPA) during pregnancy is associated with an increased risk of autism spectrum disorder (ASD) in the offspring. In the pathophysiological hypothesis of ASD, excitation/inhibition (E/I) imbalance is attracted. Dysfunction of serotonergic system is also suggested to be involved in ASD. In this study, we investigated glutamatergic-serotonergic neuronal interaction in the ASD-like behavior induced by prenatal VPA exposure in mice. Prenatal VPA exposure induced not only excessive repetitive self-grooming behavior, impairments of social behavior and object recognition memory, but also increased glutamatergic signaling (CaMKII phosphorylation) and decreased serotonin contents in the prefrontal cortex. Memantine (low-affinity NMDA antagonist) suppressed both the increase of CaMKII phosphorylation and ASD-like behaviors. Activation of serotonergic signaling via 5-HT_1A receptor by fluoxetine, tandospirone (5-HT_1A receptor agonist) and optogenetics attenuated the ASD-like behaviors in prenatal VPA-exposed mice. WAY-100635 (5-HT_1A receptor antagonist) antagonized the effect of fluoxetine on the ASD-like behaviors. These results suggest that the hyper-NMDA receptor signaling and ASD-like behaviors are associated with hypo-signaling of 5-HT_1A receptor in the prenatal VPA-exposed mice.

Chronic stress contributes to the pathogenesis of major depressive disorder (MDD). In the kynurenine pathway (KP), kynurenine is metabolized to 3-hydroxykynurenine (3-HK) by kynurenine 3-monooxygenase (KMO) and to kynurenic acid (KA) by kynurenine aminotransferase. KP alternation has been reported to be associated with the pathogenesis of MDD. We investigated the involvement of KP in the depressive-like behavior induced by chronic unpredictable mild stress (CUMS). Mice were randomly exposed to 9 kinds of mild stressors for 4 weeks. Corticosterone level in the serum and corticotropin-releasing hormone (CRH) mRNA level in the hypothalamus (HT) elevated immediately after CUMS. Further, KMO mRNA level was decreased, but KA content was increased in the prefrontal cortex (PFC). Because KA is α7 nicotinic acetylcholine receptor (α7nAChR) antagonist, we investigated the effects of nicotine (Nic) and galantamine (Gal :α7nAChR agonist) on the depressive-like behavior and dysregulation of HPA axis induced by CUMS. When Nic and Gal were administrated before exposure to each stressor during CUMS, they attenuated CUMS-induced decreased sociability. Although Nic failed to inhibit elevated corticosterone level in the serum immediately after CUMS, but suppressed that sustained elevation 1 week after CUMS. Alternation of KP from 3-HK to KA through downregulation of KMO may be involved in the depressive-like behavior and the sustained elevation of serum corticosterone 1 week after CUMS.

High salt (HS) intake is known as a risk factor for hypertension and dementia. Prostaglandin E2 (PGE2) has various effects on vascular function and central nervous system via four types of PGE2 receptors (EP1-EP4). However, an involvement of PGE2/EP1 signaling in the HS intake-induced hypertension and emotional and cognitive dysfunctions is still unclear. In this study, we confirmed the effect of HS intake on the blood pressure and emotional and cognitive functions in mice. Mice showed hypertension and impairments of social behavior in social interaction test and object recognition memory in novel object recognition test 12 weeks after HS intake. HS intake increased phosphorylation of tau, but decreased phosphorylation of Ca2+ / calmodulin-dependent protein kinase II and expression of PSD95 in the prefrontal cortex. HS intake increased expressions of mRNA of EP1 receptor in the kidney and prefrontal cortex. The HS intake-induced hypertension, abnormal behaviors and increased phosphorylation of tau were not observed in the EP1 heterozygous knockout mice. These findings suggest that PGE2/EP1-tau phosphorylation signaling is involved in the HS intake-induced hypertension and emotional and cognitive dysfunctions.

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.

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.

High salt (HS) intake is known as a risk factor for hypertension and dementia. However, an involvement of the brain-peripheral interaction in the HS-induced hypertension and cognitive dysfunction is still unclear. In this study, we confirmed the effect of HS intake on the blood pressure and cognitive and emotional functions in mice. Mice showed hypertension and impairments of object recognition memory in novel object recognition test and social behavior in social interaction test 12 weeks after HS intake. We investigated the mechanism of HS intake-induced hypertension and abnormal behaviors. HS intake increased phosphorylation of tau and decreased phosphorylation of Ca2+ / calmodulin-dependent protein kinase II (CaMKII) and expression of PSD95 in the prefrontal cortex and hippocampus, suggesting HS intake induces neuronal dysfunction. On the other hand, HS intake increased mRNA levels of inducible nitric oxide synthase (iNOS) and serum amyloid A (SAA) in the small intestine and picolinic acid levels in the serum, suggesting HS intake induces peripheral inflammatory response. The present findings suggest that HS intake induces hypertension and abnormal behaviors with peripheral inflammatory response.

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.

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.