Toshio Watanuki

Characterization of the vulnerability to repeated stress in Fischer 344 rats: possible involvement of microRNA-mediated down-regulation of the glucocorticoid receptor.

In the present study, we established and characterized an animal model of vulnerability to repeated stress. We found that control Sprague–Dawley (SD) rats showed a gradual decrease in the HPA axis response following 14 days of repeated restraint stress, whereas Fischer 344 (F344) rats did not show such HPA axis habituation. Similar habituation was observed in the expression of c‐fos mRNA, corticotropin‐releasing hormone hnRNA, and phospho‐CREB and phospho‐ERK proteins in the hypothalamic paraventricular nucleus (PVN) of SD rats, but not in the F344 rats. In addition, repeatedly restrained F344 rats exhibited decreased cell proliferation in the dentate gyrus of the hippocampus and increased anxiety‐related behaviours, while repeatedly restrained SD rats exhibited a selective enhancement of hippocampal cell proliferation in the ventral area. Moreover, we found a lower expression of glucocorticoid receptor (GR) protein, but not mRNA, in the PVN of F344 rats compared to SD rats. We also identified that microRNA (miR)‐18a inhibited translation of GR mRNA in cultured neuronal cells and that increased expression of miR‐18a in the PVN was observed in F344 rats compared with SD rats. These strain differences in GR protein levels were not found in the hippocampus and prefrontal cortex, and the expression of miR‐18a was much lower in these brain regions than in the PVN. Our results suggest that F344 rats could be a useful animal model for studying vulnerability to repeated stress, and that miR‐18a‐mediated down‐regulation of GR translation may be an important factor to be considered in susceptibility to stress‐related disorders.

Altered expression of neurotrophic factors in patients with major depression.

There is an abundance of evidence suggesting the involvement of altered levels of expression of neurotrophic factors in the pathophysiology of neuropsychiatric disorders. Although postmortem brain studies have indicated the alterations in the expression levels of neurotrophic factors in mood disorder patients, it is unclear whether these changes are state- or trait-dependent. In this study, we examined the expression levels of the members of the glial cell line-derived neurotrophic factor (GDNF) family (GDNF, artemin (ARTN), neurturin, and persephin), brain-derived neurotrophic factor, nerve growth factor, neurotrophin-3 (NT-3), and neurotrophin-4 mRNAs by using quantitative real-time PCR method in peripheral blood cells of patients with major depressive and bipolar disorders in both a current depressive and a remissive states. Reduced expression levels of GDNF, ARTN, and NT-3 mRNAs were found in patients with major depressive disorder in a current depressive state, but not in a remissive state. Altered expressions of these mRNAs were not found in patients with bipolar disorder. Our results suggest that the changes in the expression levels of GDNF, ARTN, and NT-3 mRNAs might be state-dependent and associated with the pathophysiology of major depression.

Reduced expression of glyoxalase-1 mRNA in mood disorder patients.

Glyoxalase-1 (Glo1) is an antioxidant enzyme which detoxifies alpha-ketoaldehydes to prevent the accumulation of pro-oxidant compounds, such as methylglyoxal, in all cell types. Glo1 has been suggested to be involved in anxiety disorders, autism, and Alzheimers disease. Mood disorders have a high rate of comorbidity with anxiety disorders although, to date, little is known of the involvement of Glo1 in the pathophysiology of these conditions. In the present study, we examined the expression levels of Glo1 mRNA in peripheral white blood cells of mood disorder patients to understand the role of Glo1 in mood disorders. Quantitative real-time polymerase chain reaction experiments revealed that reduced expression of Glo1 mRNA was observed in major depressive and bipolar disorder patients in a current depressive state, as compared with healthy control subjects. In contrast, the expression of Glo1 mRNA in major depressive and bipolar patients, in a remissive state, showed no significant alteration when compared with healthy control subjects. These results suggest that the aberrant expression of Glo1 might be involved in the pathophysiology of mood disorders.

Prefrontal activation in response to emotional words in patients with bipolar disorder and major depressive disorder.

Abnormal emotional processing is involved in the pathophysiology of bipolar disorder (BD) and major depressive disorder (MDD). However, whether the neural mechanism underlying this deficit is a trait characteristic of BD and MDD is unclear. The aim of this study was to elucidate the similarities and differences in processing of emotional stimuli between patients with BD and MDD in remission, using functional near-infrared spectroscopy (fNIRS). Thirty-two patients (16 with BD and 16 with MDD) and 20 healthy control subjects matched for age, sex, handedness, and years of education were included. An emotional Stroop task, including happy, sad, and threat words, was used. The relative oxygenated and deoxygenated hemoglobin concentration ([oxy-Hb] and [deoxy-Hb]) changes in the frontal region were measured using 52-channels of NIRS. During the threat task, compared to healthy control subjects, patients with BD showed significantly increased [oxy-Hb] in the left inferior frontal region whereas patients with MDD showed significantly increased [oxy-Hb] in the left middle frontal region. During the happy task, compared to healthy control subjects, patients with BD showed significantly decreased [oxy-Hb] in the middle frontal region in both hemispheres. Moreover, patients with BD exhibited decreased [oxy-Hb] and increased [deoxy-Hb] in the superior frontal and middle frontal regions compared to MDD in response to the happy stimulus. No significant differences in [oxy-Hb] or [deoxy-Hb] were seen between the groups during the sad task. These results suggest that abnormal neural responses to emotional stimuli in patients with mood disorders in remission may be a trait characteristic, that negative emotional stimuli are associated with similar prefrontal responses, and that positive emotional stimuli are associated with different prefrontal responses in patients with BD and MDD. These findings indicate that different neural circuits play a role in emotional processing in BD and MDD; this may aid the elucidation of the pathophysiology of these two disorders.

State-dependent changes in the expression levels of NCAM-140 and L1 in the peripheral blood cells of bipolar disorders, but not in the major depressive disorders.

Recent postmortem brain and imaging studies provide evidence for disturbances of structural and synaptic plasticity in patients with mood disorders. Several lines of evidence suggest that the cell adhesion molecules (CAMs), neural cell adhesion molecules (NCAM) and L1, play important roles in both structural and synaptic plasticity. Although postmortem brain studies have indicated altered expression levels of NCAM and L1, it is still unclear whether these changes are state- or trait-dependent. In this study, the mRNA levels for various CAMs, including NCAM and L1, were measured using quantitative real-time PCR in peripheral blood cells of major depressive disorder patients, bipolar disorder patients and normal healthy subjects. Reduced expression levels of NCAM-140 mRNA were observed in bipolar disorder patients in a current depressive state. In contrast, L1 mRNA levels were increased in bipolar disorder patients in a current depressive state. NCAM-140 and L1 mRNA levels were not changed in bipolar disorder patients in a remissive state, or in major depressive disorder patients. In addition, there were no significant changes in the expression levels of intercellular adhesion molecule -1, vascular cell adhesion molecule -1, E-cadherin, or integrin alphaD among healthy controls, major depressive or bipolar disorder patients. Our results suggest that the reciprocal alteration in the expression of NCAM-140 and L1 mRNAs could be state-dependent and associated with the pathophysiology of bipolar disorder.

Increased expression of splicing factor SRp20 mRNA in bipolar disorder patients.

BACKGROUND Variations and defects in alternative splicing are well known to be associated with a variety of human diseases and the stress response. We previously reported a decrease in glucocorticoid receptor (GR) alpha, but not GRbeta in mood disorder patients, suggesting an aberrant alternative splicing mechanism. To examine whether altered RNA splicing may underlie the pathophysiology of mood disorder, we evaluated the expression of a variety of SR protein splicing factors, a family of proteins indispensable for proper alternative splicing, in mood disorder patients. METHODS We used quantitative real-time PCR to measure expressions of SRp20, SRp30c, SC35, SRp40, SRp46, SRp54, SRp55, SRp75, ASF/SF2, and 9G8 mRNA in peripheral white blood cells of 33 mood disorder patients during a depressive episode. In addition, the expressions of SRp20 and SC35 mRNA were quantified for 78 mood disorder patients in a remissive state, and 32 the first-degree relatives of these mood disorder patients. RESULT A significant correlation was observed between SRp30c and the GRbeta/GRalpha ratio in control subjects, but not in mood disorder patients. Increased expression of SRp20 but not SRp30c mRNA was observed in bipolar disorder patients in both the depressive and remissive states. Major depressive disorder patients did not show any significant change in mRNA levels of SR proteins. LIMITATION Subjects were Japanese adults. Patient treatment was not standardized. CONCLUSIONS These results suggest that aberrant alternative splicing machinery caused by increased SRp20 mRNA expression would be associated with the pathophysiology of bipolar disorder.

Neural correlates of plasma acylated ghrelin level in individuals with major depressive disorder.

Anhedonic symptoms, which include loss of pleasure, appetite and motivation, are key symptoms of major depressive disorder (MDD) and are thought to depend on a neural circuit of the mesolimbic system. The neuropeptide ghrelin plays a crucial role in appetite and reward. Little is known, however, about the role of ghrelin in MDD. We examined the association between morphometric change and plasma ghrelin levels in patients with MDD. Twenty-four patients with MDD and 24 healthy control subjects were studied. Plasma concentration of acylated ghrelin was measured after a period of fasting. Using voxel-based morphometry, we found a main effect of ghrelin on the volume of several brain regions. We then compared these regional volumes in patients with MDD versus healthy subjects. We also compared brain volumes between the two groups, controlling for ghrelin level. There was no significant difference in plasma acylated ghrelin level between patients with MDD and healthy subjects. In the MDD group, ghrelin levels positively correlated with the severity of reduced appetite. Ghrelin levels negatively correlated with gray matter volume of the ventral tegmental area (VTA) in the total sample. The patients with MDD showed significantly smaller VTA gray matter volume compared to healthy subjects. Controlling for the plasma acylated ghrelin level, patients with MDD showed significantly smaller gray matter volume of right substantia nigra compared to healthy subjects. Our findings suggest that plasma acylated ghrelin is associated with neural abnormalities of the pleasure/reward system and may be involved in the pathophysiology of MDD.

Precentral and inferior prefrontal hypoactivation during facial emotion recognition in patients with schizophrenia: A functional near-infrared spectroscopy study

Although patients with schizophrenia demonstrate abnormal processing of emotional face recognition, the neural substrates underlying this process remain unclear. We previously showed abnormal fronto-temporal function during facial expression of emotions, and cognitive inhibition in patients with schizophrenia using functional near-infrared spectroscopy (fNIRS). The aim of the current study was to use fNIRS to identify which brain regions involved in recognizing emotional faces are impaired in patients with schizophrenia, and to determine the neural substrates underlying the response to emotional facial expressions per se, and to facial expressions with cognitive inhibition. We recruited 19 patients with schizophrenia and 19 healthy controls, statistically matched on age, sex, and premorbid IQ. Brain function was measured by fNIRS during emotional face assessment and face identification tasks. Patients with schizophrenia showed lower activation of the right precentral and inferior frontal areas during the emotional face task compared to controls. Further, patients with schizophrenia were slower and less accurate in completing tasks compared to healthy participants. Decreasing performance was associated with increasing severity of the disease. Our present and prior studies suggest that the impaired behavioral performance in schizophrenia is associated with different mechanisms for processing emotional facial expressions versus facial expressions combined with cognitive inhibition.

Distinct and Shared Endophenotypes of Neural Substrates in Bipolar and Major Depressive Disorders.

Little is known about disorder-specific biomarkers of bipolar disorder (BD) and major depressive disorder (MDD). Our aim was to determine a neural substrate that could be used to distinguish BD from MDD. Our study included a BD group (10 patients with BD, 10 first-degree relatives (FDRs) of individuals with BD), MDD group (17 patients with MDD, 17 FDRs of individuals with MDD), and 27 healthy individuals. Structural and functional brain abnormalities were evaluated by voxel-based morphometry and a trail making test (TMT), respectively. The BD group showed a significant main effect of diagnosis in the gray matter (GM) volume of the anterior cingulate cortex (ACC; p = 0.01) and left insula (p < 0.01). FDRs of individuals with BD showed significantly smaller left ACC GM volume than healthy subjects (p < 0.01), and patients with BD showed significantly smaller ACC (p < 0.01) and left insular GM volume (p < 0.01) than healthy subjects. The MDD group showed a tendency toward a main effect of diagnosis in the right and left insular GM volume. The BD group showed a significantly inverse correlation between the left insular GM volume and TMT-A scores (p < 0.05). Our results suggest that the ACC volume could be a distinct endophenotype of BD, while the insular volume could be a shared BD and MDD endophenotype. Moreover, the insula could be associated with cognitive decline and poor outcome in BD.

Blunted brain activation in patients with schizophrenia in response to emotional cognitive inhibition: a functional near-infrared spectroscopy study.

INTRODUCTION Patients with schizophrenia (SZ) have deficits of facial emotion processing and cognitive inhibition, but the brain pathophysiology underlying these deficits and their interaction are not clearly understood. We tested brain activity during an emotional face go/no-go task that requires rapid executive control affected by emotional stimuli in patients with SZ using functional near-infrared spectroscopy (fNIRS). METHODS Twenty-five patients with SZ and 28 healthy control subjects were studied. We evaluated behavioral performance and used fNIRS to measure oxygenated hemoglobin concentration changes in fronto-temporal areas during the emotional go/no-go task with emotional and non-emotional blocks. RESULTS Patients with SZ made more errors and had longer reaction times in both test blocks compared with healthy subjects. Significantly greater activation in the inferior, superior, middle, and orbital frontal regions were observed in healthy subjects during the emotional go/no-go block compared to the non-emotional go/no-go block, but this difference was not observed in patients with SZ. Relative to healthy subjects, patients with SZ showed less activation in the superior and orbital frontal and middle temporal regions during the emotional go/no-go block. DISCUSSION Our results suggest that fronto-temporal dysfunction in patients with SZ is due to an interaction between abnormal processing of emotional facial expressions with negative valence and cognitive inhibition, especially during the rapid selection of rule-based associations that override automatic emotional response tendencies. They indicate that fronto-temporal dysfunction is involved in the pathophysiology of emotional-cognitive deficits in patients with SZ.