Neuropeptide S attenuates neuropathological, neurochemical and behavioral changes induced by the NMDA receptor antagonist MK-801.

Neuropeptide S (NPS) and its cognate receptor were reported to mediate anxiolytic-like and arousal effects. NPS receptors are predominantly expressed in the brain, especially in limbic structures, including amygdala, olfactory nucleus, subiculum and retrosplenial cortex. In contrast, the NPS precursor is expressed in only a few brainstem nuclei where it is co-expressed with various excitatory transmitters, including glutamate. The current study investigates interactions of the NPS system with glutamatergic neurotransmission. It has been suggested that dysfunctions in glutamatergic neurotransmission via N-methyl-D-aspartate (NMDA) receptors might be involved in the pathophysiology of schizophrenia since NMDA receptor antagonists, such as MK-801, have been shown to induce psychotic-like behavior in humans and animal models. Also, MK-801 is known to produce histological changes such as cytoplasmic vacuoles in retrosplenial cortex neurons where NPS receptors are highly expressed. In this study we show that NPS is able to alleviate neuropathological, neurochemical and behavioral changes produced by NMDA receptor antagonists. NPS treatment attenuated MK-801-induced vacuolization in the rat retrosplenial cortex in a dose-dependent manner that can be blocked by an NPS receptor-selective antagonist. NPS also suppressed MK-801-induced increases of extracellular acetylcholine levels in the retrosplenial cortex. In the prepulse inhibition (PPI) assay, animals pretreated with NPS recovered significantly from MK-801-induced disruption of PPI. Our study suggests that NPS may have protective effects against the neurotoxic and behavioral changes produced by NMDA receptor antagonists and that NPS receptor agonists may elicit antipsychotic effects.

Dopaminergic hypofunctions and prepulse inhibition deficits in mice lacking midkine.

Midkine is a 13-kDa retinoic acid-induced heparin-binding growth factor involved in various biological phenomena such as cell migration, neurogenesis, and tissue repair. We previously demonstrated that midkine-deficient (Mdk(-/-)) mice exhibited a delayed hippocampal development with impaired working memory and increased anxiety only at the age of 4 weeks. To assess whether midkine gene could play important roles in development and maintenance of central nervous system, we investigated biochemical and behavioral parameters in dopamine and glutamate neurotransmission of Mdk(-/-) mice. The Mdk(-/-) mice exhibited a hypodopaminergic state (i.e., decreased levels of dopamine and its receptors in the striatum) with no alterations of glutamatergic system (i.e., normal level of glutamate, glutamine, glycine, d-serine, l-serine, and NMDA receptors in the frontal cortex and hippocampus). We also found prepulse inhibition deficits reversed by clozapine and haloperidol in the Mdk(-/-) mice. Our results suggested that midkine deficiency may be related to neurochemical and behavioral dysfunctions in dopaminergic system.

Glycine and D: -serine, but not D: -cycloserine, attenuate prepulse inhibition deficits induced by NMDA receptor antagonist MK-801.

RATIONALE: Several agents that stimulate the glycine site of N-methyl-D: -aspartate (NMDA) receptors have been reported to moderately improve both negative symptoms and cognitive dysfunctions in patients with schizophrenia. However, differences in efficacy have also been reported, and further comparative pharmacological studies are still needed. OBJECTIVES: We aimed to explore the effects of two glycine site agonists of the NMDA receptor, glycine and D: -serine, and a partial agonist, D: -cycloserine, on prepulse inhibition (PPI) deficits induced by a NMDA receptor antagonist, MK-801, in mice. Furthermore, we performed in vivo microdialysis and additional PPI measurements using a selective glycine site antagonist to verify if the beneficial effects observed after the systemic administration of glycine were due to glycine itself via its activity at the glycine site. RESULTS: High doses of glycine (1.6 g/kg) and D: -serine (1.8 and 2.7 g/kg) significantly attenuated MK-801-induced PPI deficits. In contrast, D: -cycloserine did not show any amelioration of MK-801-induced PPI deficits at doses ranging from 7.5 mg/kg to 60 mg/kg. The selective glycine site antagonist, L-701,324 (10 mg/kg), antagonized the effect of glycine on MK-801-induced PPI deficits. Furthermore, in vivo microdialysis demonstrated that intraperitoneal injection of glycine significantly increased glycine and L: -serine levels, but decreased D: -serine levels in the prefrontal cortex. CONCLUSIONS: The findings of the present study suggest that glycine and D: -serine but not D: -cycloserine could attenuate PPI deficits associated with NMDA receptor hypofunction via NMDA glycine sites in the brain.

Synaptic scaffolding molecule alpha is a scaffold to mediate N-methyl-D-aspartate receptor-dependent RhoA activation in dendrites.

Synaptic scaffolding molecule (S-SCAM) interacts with a wide variety of molecules at excitatory and inhibitory synapses. It comprises three alternative splicing variants, S-SCAMalpha, -beta, and -gamma. We generated mutant mice lacking specifically S-SCAMalpha. S-SCAMalpha-deficient mice breathe and feed normally but die within 24 h after birth. Primary cultured hippocampal neurons from mutant mice have abnormally elongated dendritic spines. Exogenously expressed S-SCAMalpha corrects this abnormal morphology, while S-SCAMbeta and -gamma have no effect. Active RhoA decreases in cortical neurons from mutant mice. Constitutively active RhoA and ROCKII shift the length of dendritic spines toward the normal level, whereas ROCK inhibitor (Y27632) blocks the effect by S-SCAMalpha. S-SCAMalpha fails to correct the abnormal spine morphology under the treatment of N-methyl-d-aspartate (NMDA) receptor inhibitor (AP-5), Ca(2+)/calmodulin kinase inhibitor (KN-62), or tyrosine kinase inhibitor (PP2). NMDA treatment increases active RhoA in dendrites in wild-type hippocampal neurons, but not in mutant neurons. The ectopic expression of S-SCAMalpha, but not -beta, recovers the NMDA-responsive accumulation of active RhoA in dendrites. Phosphorylation of extracellular signal-regulated kinase 1/2 and Akt and calcium influx in response to NMDA are not impaired in mutant neurons. These data indicate that S-SCAMalpha is a scaffold required to activate RhoA protein in response to NMDA receptor signaling in dendrites.

Posterior cingulate gyrus metabolic changes in chronic schizophrenia with generalized cognitive deficits.

N-Methyl-d-aspartate (NMDA) receptor antagonists are known to induce schizophrenia-like psychotic symptoms and cognitive deficits in humans, and have been shown to cause neuronal damage in the posterior cingulate gyrus (PCG) of rodents. Patients with chronic schizophrenia exhibit generalized cognitive deficits, but it remains unclear whether or not the PCG is related to their cognitive dysfunction. To determine what biochemical changes may occur in the PCG of patients with chronic schizophrenia, and to ascertain whether or not such abnormalities may be related to the incidence of cognitive deficits, we obtained cognitive scores and proton magnetic resonance spectra (MRS) from the PCG and the left and right medial temporal lobes (MTL) of 19 patients with schizophrenia and 18 age- and sex-matched normal healthy controls. Compared to the normal controls, the patients with chronic schizophrenia showed significantly worse cognitive performance on verbal and visual memory tests, verbal fluency tests, and the Trail Making Test. The ratio of N-acetylaspartate to creatine and phosphocreatine (NAA/Cr) in the PCG of the patients was significantly lower than that of the controls. Moreover, the NAA/Cr in the PCG of the healthy controls exhibited age-related decline, whereas in the patients with schizophrenia, the corresponding values were consistently low, regardless of age. These findings are thus in accord with current speculation about neuronal dysfunction in the PCG based on the NMDA hypofunction hypothesis regarding the pathophysiology of chronic schizophrenia.

Association between angiotensin I-converting enzyme insertion/deletion gene functional polymorphism and novelty seeking personality in healthy females.

A certain type of personality is at risk for developing psychiatric diseases. Several lines of evidence support the interaction between brain angiotensins and central catecholamine systems, and suggest that angiotensin I-converting enzyme (ACE) may be a reasonable candidate gene for psychiatric disorders. The present study examined the possibility that ACE insertion (I)/deletion (D) functional polymorphism might be associated with particular personality traits. Healthy Japanese subjects (N=184) were administered the Temperament and Character Inventory (TCI) and the NEO Personality Inventory Revised version (NEO-PI-R), and their ACE I/D polymorphisms were determined. There was an ethnic difference in the genetic distribution of ACE I/D between Japanese (D=34.5%) and Caucasians (D=55.2%). We found that the scores of novelty seeking (NS) in the Low-ACE group (II genotype) of healthy female subjects were significantly lower than those in the High-ACE group (ID or DD genotype) (p=0.018). Our findings suggested that the ACE I/D polymorphism might be associated with the NS personality trait in females, but not males. Taking into account the effects of multiple comparisons, this result should be interpreted with caution, and needs confirmation in a larger sample.

Functional polymorphism of the NQO2 gene is associated with methamphetamine psychosis.

Several lines of evidence suggest that genetic factors contribute to the vulnerability of drug abuse such as methamphetamine (MAP), and that dopamine-quinones produced by administration of MAP may be involved in the mechanism of MAP-related symptoms. The detoxification of quinones is catalyzed by a family of proteins designated as quinone oxidoreductases (NQOs). We analysed the polymorphisms of NQO1 and NQO2 genes to elucidate the association with genetic vulnerability to MAP abuse in Japan. The genotype and allele frequencies for the polymorphism (Pro187Ser) of the NQO1 gene did not differ between each subgroup of patients and controls. In contrast, the genotype frequency for the insertion/deletion (I/D) polymorphism in the promoter region of the NQO2 gene was a significant (p = 0.038) difference between patients with prolonged-type MAP psychosis and controls. This study suggests that the NQO2 gene polymorphism contributes to the aetiology of MAP-related psychosis in Japanese.

Increased midkine levels in sera from patients with Alzheimer's disease.

Midkine (MK) is a heparin binding growth factor and promotes growth, survival and migration of various cells including neurons. It is also known to accumulate in senile plaques of patients with Alzheimer's disease (AD). To investigate the involvement of serum MK in the pathophysiology of AD, serum MK levels were determined in patients with AD (n=36) and age- and sex-matched healthy controls (n=32), using an enzyme-linked immunosorbent assay (ELISA). The serum MK values of the patients with AD (median 560 and interquartile range (500-755) pg/ml) were significantly (U=278.5, P=0.0003, Mann-Whitney U-test) higher than those of the controls (median 500 and interquartile range (385-520) pg/ml). Moreover, 17 patients (47.2%) had abnormally high values of more than 600 pg/ml, but no controls (0%) did. There was no correlation between serum MK level and the mini mental state examination (MMSE) score in the patients. The demonstration of elevated MK levels in sera of patients with AD may contribute toward an understanding the pathophysiology of this disease, and provide a novel potential therapeutic strategy for decreasing neuronal damages in patients with AD. We found that serum MK levels in patients with AD were increased in comparison with those of normal controls.

Serum brain-derived neurotrophic factor (BDNF) levels in patients with panic disorder: as a biological predictor of response to group cognitive behavioral therapy.

Little is known about biological predictors of treatment response in panic disorder. Our previous studies show that the brain-derived neurotrophic factor (BDNF) may play a role in the pathophysiology of major depressive disorders and eating disorders. Assuming that BDNF may be implicated in the putative common etiologies of depression and anxiety, the authors examined serum BDNF levels of the patients with panic disorder, and its correlation with therapeutic response to group cognitive behavioral therapy (CBT). Group CBT (10 consecutive 1 h weekly sessions) was administered to the patients with panic disorder after consulting the panic outpatient special service. Before treatment, serum concentrations of BDNF and total cholesterol were measured. After treatment, we defined response to therapy as a 40% reduction from baseline on Panic Disorder Severity Scale (PDSS) score as described by [Barlow, D.H., Gorman, J.M., Shear, M.K., Woods, S.W., 2000. Cognitive-behavioral therapy, imipramine, or their combination for panic disorder: A randomized controlled trial. JAMA. 283, 2529-2536]. There were 26 good responders and 16 poor responders. 31 age- and sex-matched healthy normal control subjects were also recruited in this study. The serum BDNF levels of the patients with poor response (25.9 ng/ml [S.D. 8.7]) were significantly lower than those of the patients with good response (33.7 ng/ml [S.D. 7.5]). However, there were no significant differences in both groups of the patients, compared to the normal controls (29.1 ng/ml [S.D. 7.1]). No significant differences of other variables including total cholesterol levels before treatment were detected between good responders and poor responders. These results suggested that BDNF might contribute to therapeutic response of panic disorder. A potential link between an increased risk of secondary depression and BDNF remains to be investigated in the future.

No association of the brain-derived neurotrophic factor (BDNF) gene polymorphisms with panic disorder.

Several lines of evidence suggest that genetic factors might contribute to susceptibility to panic disorder. Our previous studies show that the brain-derived neurotrophic factor (BDNF) may play a role in the pathophysiology of major depressive disorders and eating disorders. Assuming that BDNF may be implicated in the putative common pathophysiology of depression and anxiety, we analyzed the association of two BDNF gene single nucleotide polymorphisms (SNPs), 132C > T (formerly named C270T) in the noncoding region of exon V and 196G > A (val66met) in the coding region of exon XIIIA, with panic disorder. In this study, 109 patients with panic disorder diagnosed according to the DSM-IV criteria, and 178 control subjects were recruited. There were no significant differences in the frequency of the genotype or allele in these two SNPs between patients and controls [132C > T in exon V: genotype, p = 1.0, allele, p = 0.59; 196G > A (val66met) in exon XIIIA: genotype, p = 0.77, allele, p = 0.78]. Furthermore, no significant associations of agoraphobia with the two SNPs were detected. This study suggests that the BDNF gene polymorphisms are not associated with panic disorder in our Japanese population.

The immunophilin ligand FK506 protects against methamphetamine-induced dopaminergic neurotoxicity in mouse striatum.

Repeated use of methamphetamine (MAP) is known to cause neurotoxicity in the dopaminergic neurons of the striatum. Recently, we reported that FK506, a calcineurin inhibitor and immunosuppressive agent, could attenuate acute behavioral changes and the development of sensitization after administration of MAP. In this study, we investigated the effects of FK506 on the neurotoxicity in the dopaminergic neurons induced by repeated administration of MAP. BALB/c mice were injected subcutaneously (s.c.) with vehicle (10 ml/kg) or MAP (4 mg/kg) four times every 2h. Vehicle (10 ml/kg) or FK506 (0.1, 0.3, 1 or 3 mg/kg i.p.) was administered 15 min before the first MAP administration. Three days later, we assessed the contents of dopamine (DA) and its major metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), in the mouse striatum using high-performance liquid chromatography (HPLC). We also examined the immunohistochemistry of dopamine transporter (DAT) and tyrosine hydroxylase (TH) in the mouse brain. Repeated administration of MAP decreased significantly the contents of DA and DOPAC in the mouse striatum, and pretreatment with FK506 inhibited significantly the reduction of DA and DOPAC in the mouse brain by repeated administration of MAP. Furthermore, repeated administration of MAP decreased significantly the immunoreactivity of DAT and TH in the striatum as compared to controls. Pretreatment with FK506 (3 mg/kg) attenuated significantly the reduction of DAT and TH immunoreactivity after repeated administration of MAP. These results suggest that FK506 shows protective effects on the MAP-induced neurotoxicity in the dopaminergic neurons of the mouse striatum.

Lack of association between angiotensin I-converting enzyme insertion/deletion gene functional polymorphism and panic disorder in humans.

Family and twin studies have indicated that genes influence susceptibility to panic disorder, but the genes involved remain unknown. The neuropeptide angiotensin II has been found to be involved in anxiety and regulation of respiration which are important in the pathophysiology of panic attacks. Assuming that angiotensins may be candidate genes in panic disorder, we analyzed the association between panic disorder and angiotensin I-converting enzyme (ACE) insertion (I)/deletion (D) gene functional polymorphism. We recruited 101 patients with panic disorder diagnosed according to DSM-IV criteria, and 184 control subjects in the study. No significant differences in the frequency of the genotype or allele in the polymorphism between patient and control groups were found (genotype, chi(2)=0.56, d.f.=2, P=0.77; allele, chi(2)=0.074, d.f.=1, P=0.78). This study suggests that the ACE I/D gene polymorphism is not directly associated with panic disorder in our Japanese patient group.

Decreased cell proliferation in the dentate gyrus of alpha 7 nicotinic acetylcholine receptor heterozygous mice.

It is suggested that deficits of alpha 7 nicotinic acetylcholine receptors (nAChRs) might be associated with the cognitive impairments of Alzheimer's disease and schizophrenia, and that agonists for alpha 7 nAChR could be useful for treatment of cognitive dysfunction in these diseases. This study was undertaken to examine the role of alpha 7 nAChRs on hippocampal cellular proliferation of adult mice. The number of 5-bromo-2'-deoxyuridine (BrdU)-immunoreactive cells in the granule cell layer (GCL) and hilus of alpha 7 nAChR heterozygous (+/-) mice was significantly decreased as compared with that of wild-type (+/+) mice. In contrast, the number of BrdU-immunoreactive cells in GCL and hilus of alpha 7 nAChR homozygous (-/-) mice was not different from that of wild-type mice. The results suggest that reduced levels of alpha 7 nAChRs may decrease cell proliferation of adult hippocampus.

Association between the brain-derived neurotrophic factor 196G/A polymorphism and eating disorders.

Several lines of evidence suggest that genetic factors might contribute to the pathogenesis of eating disorders and that brain-derived neurotrophic factor (BDNF) plays a role in the pathophysiology of eating disorders. To investigate the role of the BDNF gene in the susceptibility to eating disorders, we analyzed the BDNF 196G/A gene polymorphism in female patients with eating disorders and female normal controls. The difference in the genotype frequency between patients (n = 198) and normal controls (n = 222) was statistically significant (P = 0.029). Interestingly, a significant (P = 0.015) difference in the genotype frequency between normal controls and bulimia nervosa patients (n = 101) with binge-purging type was detected. This study suggests that the BDNF 196G/A gene polymorphism might be associated with a susceptibility to eating disorders.

Protective effect of LY379268, a selective group II metabotropic glutamate receptor agonist, on dizocilpine-induced neuropathological changes in rat retrosplenial cortex.

In the present study, we examined the effects of LY379268, the group II metabotropic glutamate receptor (mGluR) agonist, on the neuropathological changes in the rat retrosplenial cortex induced by noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine ((+)-MK-801). Administration of LY379268 (1, 3, 10 mg/kg, i.p.) reduced dizocilpine (0.5 mg/kg, i.p.)-induced neuropathological changes in the retrosplenial cortex, in a dose-dependent manner. Co-administration of LY379268 (10 mg/kg, i.p.) with group II mGluR antagonist LY341495 (5 mg/kg, i.p.) blocked the effects of LY379268. Furthermore, LY379268 (10 mg/kg, i.p.) significantly reduced the expression of heat shock protein HSP-70, a marker of reversible neuronal injury, in the rat retrosplenial cortex after administration of dizocilpine (0.5 mg/kg, i.p.). Moreover, pretreatment with LY379268 (10 mg/kg, i.p.) significantly suppressed the increase in extracellular acetylcholine (ACh) levels in the retrosplenial cortex induced by administration of dizocilpine (0.5 mg/kg, i.p.). These results suggest that LY379268 has a protective effect on the neurotoxicity in the rat retrosplenial cortex after administration of NMDA receptor antagonists such as dizocilpine.