Masafumi Kodama

CNR1, central cannabinoid receptor gene, associated with susceptibility to hebephrenic schizophrenia.

To examine the cannabinoid hypothesis for pathogenesis of schizophrenia, we examined two kinds of polymorphisms of the CNR1 gene, which encodes human CB1 receptor, a subclass of central cannabinoid receptors, in schizophrenics and age-matched controls in the Japanese population. Allelic and genotypic distributions of polymorphism 1359G/A at codon 453 in the coding region and AAT triplet repeats in the 3′ flanking region in the Japanese population were quite different from those in Caucasians. Although the polymorphism 1359G/A was not associated with schizophrenia, the triplet repeat polymorphism of the CNR1 gene was significantly associated with schizophrenia, especially the hebephrenic subtype (P = 0.0028). Hebephrenic schizophrenia showed significantly increased rate of the 9 repeat allele (P = 0.032, OR = 2.30, 95% CI (1.91–2.69)), and decreased rate of the 17 repeat allele (P = 0.011, OR = 0.208, 95% CI (0.098–0.439)). The present findings indicated that certain alleles or genotypes of the CNR1 gene may confer a susceptibility of schizophrenia, especially of the hebephrenic type.

Gene Expression Related to Synaptogenesis, Neuritogenesis, and MAP Kinase in Behavioral Sensitization to Psychostimulants

Abstract: The most important characteristic of behavioral sensitization to psychostimulants, such as amphetamine and cocaine, is the very long‐lasting hypersensitivity to the drug after cessation of exposure. Rearrangement and structural modification of neural networks in CNS must be involved in behavioral sensitization. Previous microscopic studies have shown that the length of dendrites and density of dendritic spines increased in the nucleus accumbens and frontal cortex after repeated exposure to amphetamine and cocaine, but the molecular mechanisms responsible are not well understood. We investigated a set of genes related to synaptogenesis, neuritogenesis, and mitogen‐activated protein (MAP) kinase after exposure to methamphetamine. Synaptophysin mRNA, but not VAMP2 (synaptobrevin 2) mRNA, which are considered as synaptogenesis markers, increased in the accumbens, striatum, hippocampus, and several cortices, including the medial frontal cortex, after a single dose of 4 mg/kg methamphetamine. Stathmin mRNA, but not neuritin or narp mRNA, which are markers for neuritic sprouting, increased in the striatum, hippocampus, and cortices after a single dose of methamphetamine. The mRNA of arc, an activity‐regulated protein associated with cytoskeleton, but not of alpha‐tubulin, as markers for neuritic elongation, showed robust increases in the striatum, hippocampus, and cortices after a single dose of methamphetamine. The mRNAs of MAP kinase phosphatase‐1 (MKP‐1), MKP‐3, and rheb, a ras homologue abundant in brain, were investigated to assess the MAP kinase cascades. MKP‐1 and MKP‐3 mRNAs, but not rheb mRNA, increased in the striatum, thalamus, and cortices, and in the striatum, hippocampus, and cortices, respectively, after a single methamphetamine. Synaptophysin and stathmin mRNAs did not increase again after chronic methamphetamine administration, whereas the increases in arc, MKP‐1, and MKP‐3 mRNAs persisted in the brain regions after chronic methamphetamine administration. These findings indicate that the earlier induction process in behavioral sensitization may require various plastic modifications, such as synaptogenesis, neuritic sprouting, neuritic elongation, and activation of MAP kinase cascades, throughout almost the entire brain. In contrast, later maintenance process of sensitization may require only limited plastic modification in restricted regions.

Preliminary genome-wide association study of bipolar disorder in the Japanese population.

Recent progress in genotyping technology and the development of public databases has enabled large‐scale genome‐wide association tests with diseases. We performed a two‐stage genome‐wide association study (GWAS) of bipolar disorder (BD) in Japanese cohorts. First we used Affymetrix 100K GeneChip arrays in the analysis of 107 cases with bipolar I disorder and 107 controls, and selected markers that were nominally significant (P < 0.01) in at least one of the three models (1,577 markers in total). In the follow‐up stage, we analyzed these markers using an Illumina platform (1,526 markers; 51 markers were not designable for the platform) and an independent sample set, which consisted of 395 cases (bipolar I + II) and 409 controls. We also assessed the population stratification of current samples using principal components analysis. After the two‐stage analysis, 89 markers remained nominally significant (allelic P < 0.05) with the same allele being consistently over‐represented in both the first and the follow‐up stages. However, none of these were significant after correction for multiple‐testing by false discovery rates. Sample stratification was virtually negligible. Collectively, this is the first GWAS of BD in the Japanese population. But given the small sample size and the limited genomic coverage, these results should be taken as preliminary.

A robust increase in expression of arc gene, an effector immediate early gene, in the rat brain after acute and chronic methamphetamine administration

The effect of acute and chronic administration of methamphetamine (METH) on the levels of activity-regulated cytoskeleton-associated protein (arc), an effector-immediate early gene, mRNA has been investigated in rat brain using in situ hybridization. Levels of arc mRNAs in the brain regions examined increased significantly from 0.5-1 h after an acute METH (4 mg/kg) administration compared with basal levels. The increase in arc mRNA continued by 3 h, and then subsided to basal levels by 6 h. The degree of increase in arc mRNA and the peak time after METH administration varied according to brain area. Arc mRNA in cerebral cortices showed robust increase 1 h after METH administration. In the striatum and hippocampus, it showed earlier and later increase, respectively, and its degree of both was less than in the cortices. Microscopic examination revealed that the METH-induced arc mRNAs in the parietal cortex were enriched in layers IV and VI, and those in the striatum existed mainly in the medium-sized neuron. Pretreatment with either 0.5 mg/kg SCH23390 or 0.25 mg/kg MK-801 almost completely blocked the enhanced striatal arc mRNA levels induced by acute METH administration, whereas such pretreatments only partially reduced the effect of METH in the cerebral cortical regions. In the chronic treatment experiment, the arc mRNA levels of the group that received chronic treatment with METH followed by a METH challenge showed an increase like seen after acute METH administration. Since previous studies proposed that arc is one of cytoskeleton-associated proteins and is selectively localized in neural dendrites, the results of the present study suggested that arc may play an important role in the synaptic plasticity underlying METH-induced adaptational changes including behavioral sensitization.

Two kinds of mitogen-activated protein kinase phosphatases, MKP-1 and MKP-3, are differentially activated by acute and chronic methamphetamine treatment in the rat brain.

Two functionally different MAP kinase phosphatases (MKPs) were investigated to clarify their roles in behavioral sensitization to methamphetamine (METH). MKP‐1 mRNA levels increased substantially by about 60–300% in a range of brain regions, including several cortices, the striatum and thalamus 0.5–1 h after acute METH administration. After chronic METH administration its increase was less pronounced, but a more than 50% increase was still seen in the frontal cortex. MKP‐1 protein levels also increased 3 h after acute or chronic METH administration. MKP‐3 mRNA levels increased by about 30–50% in several cortices, the striatum and hippocampus 1 h after acute METH administration, but only in the hippocampus CA1 after chronic METH administration. Pre‐treatment with the D1 dopamine receptor antagonist, SCH23390, attenuated the METH‐induced increase of MKP‐1 and MKP‐3 mRNA in every brain region, while pre‐treatment with the NMDA receptor antagonist, MK‐801, attenuated it in some regions. These findings suggest that in METH‐induced sensitization, MKP‐1 and MKP‐3 play important roles in the neural plastic modification in widespread brain regions in the earlier induction process, but in the later maintenance process, they do so only in restricted brain regions such as MKP‐1 in the frontal cortices and MKP‐3 in the hippocampus.

Genetic variants of D2 but not D3 or D4 dopamine receptor gene are associated with rapid onset and poor prognosis of methamphetamine psychosis

D2-like receptors are key targets for methamphetamine in the CNS, and their activation is an initial and indispensable effect in the induction of dependence and psychosis. It is possible that genetic variants of D2-like receptors may affect individual susceptibility to methamphetamine dependence and psychosis. To test this hypothesis, 6 putatively functional polymorphisms of D2-like receptors, -141C Ins/Del, Ser311Cys and TaqIA of the DRD2 gene, Ser9Gly of the DRD3 gene, and -521C>T and a variable number of tandem repeats in exon 3 of the DRD4 gene, were analyzed in 202 patients with methamphetamine dependence and/or psychosis and 243 healthy controls in a Japanese population. No polymorphism examined showed significant association with methamphetamine dependence, but two polymorphisms of DRD2 were associated with the clinical course and prognosis of methamphetamine psychosis. The A1/A1 homozygote of DRD2 was a negative risk factor for a poorer prognosis of psychosis that continues for more than 1 month after the discontinuance of methamphetamine abuse and the beginning of treatment with neuroleptics (p=0.04, odds ratio (OR)=0.42, 95% CI; 0.27-0.65) and the complication of spontaneous relapse of methamphetamine psychosis after remission (p=0.014, OR=0.34, 95% CI; 0.22-0.54). The genotype of -141C Del positive (Del/Del and Del/Ins) was at risk for rapid onset of methamphetamine psychosis that develops into a psychotic state within 3 years after initiation of methamphetamine abuse (p=0.00037, OR=3.62, 95% CI 2.48-5.28). These findings revealed that genetic variants of DRD2, but not DRD3 or DRD4, confer individual risks for rapid onset, prolonged duration, and spontaneous relapse of methamphetamine psychosis.

Association study of CAG repeats in the KCNN3 gene in Japanese patients with schizophrenia, schizoaffective disorder and bipolar disorder

To investigate a possible involvement of expanded triplet repeats of genome in the genomes of patients with endogenous psychoses, we examined a CAG repeat polymorphism in the coding region of the KCNN3 gene in schizophrenia, schizoaffective disorder, bipolar disorder and controls of the Japanese population. There were no significant differences in the CAG repeat number of longer or shorter alleles among the four diagnostic groups or among the schizophrenia hebephrenic and paranoid subtypes.

Leukemia inhibitory factor gene is associated with schizophrenia and working memory function

Leukemia inhibitory factor (LIF), a member of the interleukin-6 cytokine family, regulates the neuronal phenotype and coordinates astrocyte, oligodendrocyte, microglia, and inflammatory cell responses. The LIF gene is located on 22q12.1-q12.2, a hot spot for schizophrenia. Three polymorphisms of the LIF gene (rs929271, rs737812, and rs929273) were examined in a case-control association study of 390 patients with schizophrenia and 410 age- and sex-matched controls. Effects of a risk genotype of LIF on cognitive domains were evaluated by the Wechsler Adult Intelligence Scale-Revised, Wechsler Memory Scale-Revised, and Wisconsin Card Sorting Test (WCST) in 355 healthy volunteers. The LIF gene showed significant associations with schizophrenia at rs929271 and a haplotype consisting of rs929271-rs737812. After stratification by subtype of schizophrenia, the hebephrenic, but not paranoid, type was associated with the LIF gene at rs929271 (allele, P=0.014) and the haplotype (permutation P=0.013). Having the T-allele and T-carrier genotypes (TT and TG) of rs929271 were risks for hebephrenic schizophrenia, and the odds ratios were 1.38 (95% CI: 1.21-1.56) and 1.54 (95%CI: 1.19-1.98), respectively. Subjects with T-carrier genotypes made significantly more errors on the WCST compared with those without (P=0.04). The present study indicated that the LIF gene variant may produce susceptibility to hebephrenic schizophrenia and deterioration of working memory function.

G72 gene is associated with susceptibility to methamphetamine psychosis

Methamphetamine psychosis is considered as one of the pharmacological models of schizophrenia, and a hyperdopaminergic one. However, many lines of experimental evidence indicate that glutamatergic signaling is also involved in development of methamphetamine psychosis. Several genes related to glutamate function, e.g. the DTNBP1, G72, and GRM3 genes, were shown to be associated with schizophrenia susceptibility. Recently, we found significant association of the DTNBP1 gene with methamphetamine psychosis. This finding prompted us to examine the G72 gene encoding the d-amino acid oxidase activator (DAOA), which metabolizes d-serine, an NMDA co-agonist, in methamphetamine psychosis. Six SNPs of the G72 gene, which previously showed significant association with schizophrenia, were analyzed in 209 patients with methamphetamine psychosis and 291 age- and sex-matched normal controls. One SNP of M22 (rs778293) showed a significant association with methamphetamine psychosis (genotype: p=0.00016, allele: p=0.0015). Two haplotypes G-A of M12 (rs3916965)-M15 (rs2391191) (p=0.00024) and T-T of M23 (rs947267)-M24 (rs1421292) (p=0.00085) also showed associations with methamphetamine psychosis. The present findings suggest that the G72 gene may contribute to a predisposition to not only schizophrenia but also to methamphetamine psychosis.

Association between neuropeptide Y gene and its receptor Y1 gene and methamphetamine dependence

Aims:  Neuropeptide Y (NPY) is a 36‐amino acid peptide that is widely distributed in the brain, adrenal medulla, and sympathetic nervous system. Several lines of evidence suggest a possible involvement of the NPY system in the physiological effects of several classes of abused substances including alcohol, phencyclidine, cocaine, and marijuana and in endogenous psychosis. Accordingly, it was hypothesized that the NPY system may also be involved in methamphetamine dependence or psychosis.