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.

Deficits in auditory P50 inhibition in obsessive-compulsive disorder.

Obsessive-compulsive disorder (OCD) is considered to involve abnormalities in inhibitory processes including gating systems. Auditory P50 inhibition, which is assessed by using a paired auditory stimulus paradigm to record P50 mid-latency evoked potential, is assumed to reflect sensory gating. In the present study, we investigated auditory P50 inhibition in subjects with OCD, and examined the relationship between P50 and clinical variables or neuropsychological performance. Twenty-six subjects with OCD and 26 age- and sex-matched healthy controls received P50 recording and neuropsychological tests. In the OCD subjects, we also evaluated clinical features including OC symptoms and subtypes of the disorder. P50 T/C ratios were significantly higher in OCD subjects than in control subjects (t=2.9, df=50, p=0.006). Compared to the controls, the OCD subjects performed significantly worse on the Symbol Digit Modalities Test (SDMT) and the Trail Making Test (TMT). There were no correlations between P50 T/C ratios and clinical variables or the results of neuropsychological tests. Our findings suggest that sensory gating deficits may be involved in the pathophysiology of OCD in a different way from clinical symptoms and executive attention dysfunction.

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.

Tropisetron improves deficits in auditory P50 suppression in schizophrenia.

Physiological deficits in inhibition of the P50 auditory evoked potential in schizophrenia have been related to diminished expression of alpha7 nicotinic acetylcholine receptors. Diminished P50 inhibition is correlated with neuropsychological deficits in attention, one of the principal neurocognitive disturbances in schizophrenia. Nicotine administration improves P50 inhibition, presumably by achieving additional activation of these diminished receptors, but its toxicity and marked tachyphylaxis make it an ineffective therapeutic. Nicotine also has weak positive effects on several neurocognitive deficits in schizophrenia, which raises the possibility that the alpha7 nicotinic receptor is a clinically relevant therapeutic target that should be addressed by less toxic agents. Tropisetron, a drug already approved for clinical use outside the United States as an anti-emetic, is a partial agonist at alpha7 nicotinic receptors and an antagonist at 5-HT(3) receptors. As an initial proof-of-principle study, we determined that a single administration of tropisetron significantly improves P50 inhibition in schizophrenia. These data are consistent with biological activity at a pathophysiological mechanism in schizophrenia and support further trials of this drug as a possible therapeutic for neurocognitive deficits in schizophrenia.

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.

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.

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.

Effect of antioxidant N-acetyl-L-cysteine on behavioral changes and neurotoxicity in rats after administration of methamphetamine.

Several lines of evidence suggest that oxidative stress may play a role in the behavioral changes and neurotoxicity in rats after administration of methamphetamine (MAP). N-acetyl-L-cysteine (NAC) is a precursor of glutathione, and it also exerts as an antioxidant. In this study, we investigated the effects of NAC on the behavioral changes (hyperlocomotion and development of sensitization) and neurotoxicity in male Wistar rats after administration of MAP. Pretreatment with NAC (30, 100 or 300 mg/kg, i.p.) attenuated significantly hyperlocomotion in rats induced by a single administration of MAP (2 mg/kg, i.p.), in a dose-dependent manner. Furthermore, pretreatment with NAC (100 mg/kg, i.p., 15 min before MAP injection, once daily for 5 consecutive days) blocked significantly the development of behavioral sensitization in rats after repeated administration of MAP (2 mg/kg, once daily for 5 consecutive days), whereas the behaviors in rats after repeated administration of NAC plus saline groups were not different from those of control (vehicle plus saline) groups. One week after administration of MAP (7.5 mg/kg x 4, 2-h intervals), levels of dopamine (DA) in rat striatum were significantly decreased as compared with control groups. Pretreatment with NAC (1, 3, 10 or 30 mg/kg, i.p., 30 min before each MAP injection) attenuated significantly the MAP-induced reduction of DA in rat striatum, in a dose-dependent manner. These results suggest that NAC could prevent the behavioral changes (acute hyperlocomotion and development of behavioral sensitization) in rats and neurotoxicity in rat striatum after administration of MAP, and that NAC would be a useful drug for treatment of several symptoms associated with MAP abuse.

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.

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.

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.

Possible role of D-serine in the pathophysiology of Alzheimer's disease.

Several lines of evidence suggest that D-serine may function as an endogenous agonist of the glycine site on the N-methyl-D-aspartate (NMDA) receptor that has been implicated in the pathophysiology of Alzheimer's disease (AD). The purpose of the study was to determine whether serum levels of D- and L-serine in patients with AD are altered as compared with normal controls. Serum levels of D- and L-serine in patients of AD and age- and gender-matched normal controls were determined using a high-performance liquid chromatography (HPLC). Serum levels of D-serine in the patients with AD were slightly (z=-1.77, p=0.078) lower than those of normal controls. In contrast, serum levels of L-serine in the patients were slightly (z=-1.73, p=0.083) higher than those of controls. In addition, the percentage (%) of D-serine in the total (L+D) serine in the patients was significantly (z=-2.36, p=0.018) lower than that of controls. The present study suggests that the reduced activity of serine racemase, an enzyme catalyzing the formation of D-serine from L-serine may play a role in the pathophysiology of AD.

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.

Serum brain-derived neurotrophic factor (BDNF) levels in schizophrenia are indistinguishable from controls.

Our previous study showed that serum brain-derived neurotrophic factor (BDNF) was significantly decreased in the antidepressant-naive patients with major depressive disorders. However, it was still unclear whether serum BDNF level was altered in drug-naive patients with schizophrenia. Using ELISA, we measured serum BDNF levels in antipsychotic-naive (n=15) and medicated (n=25) patients with schizophrenia, and in age- and sex-matched normal controls (n=40). There were no significant differences in serum BDNF levels among antipsychotic-naive (n=15) and medicated (n=25) patients and normal controls (n=40). Possible factors such as duration of illness, age of onset, Brief Psychiatric Rating Scale scores, and chlorpromazine equivalent dosages of antipsychotics did not reveal any significant correlations with BDNF levels. Our results do not support the view that serum BDNF levels are associated with schizophrenia.

Alterations of serum levels of brain-derived neurotrophic factor (BDNF) in depressed patients with or without antidepressants.

BACKGROUND: Because researchers have reported that antidepressants increase the expression of brain-derived neurotrophic factor (BDNF) in the rat hippocampus, we investigated whether serum BDNF levels may be used as a putative biological marker for major depressive disorders (MDD). METHODS: We measured serum BDNF in the following three groups: antidepressant-naive patients with MDD (n = 16), antidepressant-treated patients with MDD (n = 17), and normal control subjects (n = 50). Patients were evaluated using the Hamilton Rating Scale for Depression (HAM-D). Serum BDNF was assayed with the sandwich ELISA method. RESULTS: We found that serum BDNF was significantly lower in the antidepressant-naive group (mean, 17.6 ng/mL; SD, 9.6) than in the treated (mean, 30.6 ng/mL; SD, 12.3; p =.001) or in the control group (mean, 27.7 ng/mL; SD, 11.4; p =.002). There was a significant negative correlation (r = -.350, z = -2.003, p =.045) between serum BDNF and HAM-D scores in all patients. In a preliminary examination, reduced BDNF values of three drug-naive patients recovered to basal levels after antidepressant treatment. CONCLUSIONS: Our study suggests that low BDNF levels may play a pivotal role in the pathophysiology of MDD and that antidepressants may increase BDNF in depressed patients.

Two clusters of serum midkine levels in drug-naive patients with schizophrenia.

Midkine (MK) is a heparin-binding growth factor implicated in various biological phenomena such as development of the hippocampus and anxiety. We evaluated serum MK levels of drug-naive (n=15) and medicated (n=25) patients with schizophrenia, and age- and sex-matched normal controls (n=38). The patients showed two clusters in the levels. Four drug-naive patients (26.7%) and two medicated patients (8.0%) had abnormally high values, but no controls did, there being a significant difference in the numbers (P=0.003, Fisher's exact test). Furthermore, in other patients, the mean MK levels in drug-naive schizophrenia (0.30+/-0.10 ng/ml) were significantly (P=0.018, Fisher's protected least significant difference test) decreased than those in the controls (0.40+/-0.12 ng/ml). These suggest that there are two clusters of serum MK abnormalities in drug-naive patients with schizophrenia.