Atsushi Ishige

Chronic stress attenuates glucocorticoid negative feedback: involvement of the prefrontal cortex and hippocampus.

Disruption of the glucocorticoid negative feedback system is observed in approximate one half of human depressives, and a similar condition is induced in animals by chronic stress. This disruption is thought to involve down-regulation of glucocorticoid receptors (GRs) in the feedback sites of the brain. However, the responsible site of the brain has not been well elucidated. Here we examined the effects of chronic stress induced by water immersion and restraint (2 h/day) for 4 weeks followed by recovery for 10 days on the GR levels in the prefrontal cortex (PFC), hippocampus, and hypothalamus of rats using a Western immunoblot technique. In the PFC, the cytosolic GR levels were decreased, but the nuclear GR levels were not changed. In the hippocampus, the levels of cytosolic and nuclear GRs were increased. However, there were no marked changes in the GR levels in the hypothalamus. The changes in the cytosolic GR levels were confirmed at the mRNA level by an in situ hybridization technique. We next examined the suppressive effects of dexamethasone (DEX) infusions into these regions on the circulating corticosterone levels. When DEX was infused into the PFC or hippocampus of the chronically stressed rats, the suppressive response to DEX was abolished, but the response was normal in the hypothalamus. In addition, when DEX was injected systemically to the chronically stressed rats, the suppressive response to DEX was significantly attenuated. These results suggest that the abnormal changes in GRs in the higher centers of the hypothalamo-pituitary-adrenal axis are involved in the chronic stress-induced attenuation of the feedback. Since dysfunction of the PFC or hippocampus is implicated in the pathogenesis of depression, the present findings would help to understand the mechanisms underlying the disrupted feedback system and its relation to brain dysfunction in depression.

EFFECTS OF CYCLOHEXIMIDE ON DELAYED NEURONAL DEATH IN RAT HIPPOCAMPUS

The effect of cycloheximide, a protein synthesis inhibitor, on hippocampal selective neuronal death was morphologically studied in rats subjected to 10 min forebrain ischemia using a 4-vessel occlusion model. Neuronal damage in the hippocampal CA1 subfield 72 h after ischemic insult was dramatically decreased by the lasting inhibition of protein synthesis through consecutive administration of cycloheximide. Cycloheximide, which was administered once within the first 24 h of recirculation, showed protective action on ischemic cell necrosis and its most potent effect was observed when injected at 12 h of post-ischemia. After 36 h of recirculation, however, treatment with cycloheximide could no longer prevent cell death. The possibility is considered that hippocampal delayed neuronal death following transient ischemia is caused by abnormal protein(s).

Endogenous Glucocorticoids Are Essential for Maintaining Prefrontal Cortical Cognitive Function

Glucocorticoid hormones are important in the maintenance of many brain functions. Although their receptors are distributed abundantly throughout the brain, including the prefrontal cortex (PFC), it is not clear how glucocorticoid functions, particularly with regard to cognitive processing in the PFC. There is evidence of PFC cognitive deficits such as working memory impairment in several stress-related neuropsychiatric disorders, including depression, schizophrenia, and Parkinsons disease. Disruption of the hypothalamo-pituitary-adrenal (HPA) system, which is characterized by attenuated glucocorticoid negative feedback, is also observed. In rats, chronic stress induces working memory impairment as a result of decreased dopaminergic transmission in the PFC. These chronically stressed rats also show HPA disruption; this is caused in part by a reduced glucocorticoid response in the PFC. These findings implicate reduced glucocorticoid actions in working memory impairment. In the present study, we examined the effects of the suppression of endogenous glucocorticoids by adrenalectomy (ADX) on working memory in rats and explored the involvement of PFC dopaminergic activities in memory. The ADX impaired working memory, decreased dopamine release, and upregulated D1 receptors in the PFC. These dysfunctions were prevented by corticosterone replacement that reproduced normal physiological plasma levels, indicating that suppression of glucocorticoids causes these dysfunctions. Moreover, the ADX-induced working memory impairment was ameliorated by intra-PFC infusions of a D1 receptor agonist, SKF 81297. Thus, suppression of glucocorticoids impaired working memory through a D1 receptor-mediated hypodopaminergic mechanism in the PFC. This finding indicates that endogenous glucocorticoids are essential for maintaining PFC cognitive function and suggests that HPA disruption contributes to PFC cognitive deficits.

Chronic stress differentially regulates glucocorticoid negative feedback response in rats

Exposure to chronic stress is thought to play an important role in the etiology of depression. In this disorder, a disrupted negative feedback response to exogenous glucocorticoids on cortisol secretion has been indicated. However, the regulation of glucocorticoid negative feedback by chronic stress is not fully understood. In the present study, we investigated the effects of chronic stress administered by water immersion and restraint (2 h/day) for four weeks on the glucocorticoid feedback in rats. In the acutely (one-time) stressed rats, the basal plasma corticosterone (CORT) level was markedly elevated, remained at high levels for 5 h after the termination of stress, and then decreased. In the chronically stressed rats, the CORT level was initially elevated similarly, but rapidly decreased at 2 h. In the dexamethasone (DEX) suppression test, the peak CORT level in response to stress was not suppressed by DEX in the acutely stressed rats, but was significantly suppressed in the chronically stressed rats. In contrast, the suppressive effects of DEX on the basal CORT secretion in naive rats were attenuated in the chronically stressed rats. In the chronically stressed hippocampus, which plays an important role in the regulation of the glucocorticoid feedback response, the binding of [3H]DEX was decreased and the increased response of activator protein-1 induced by acute stress was abolished. These results suggest that chronic stress induces a hypersuppressive state for induced CORT secretion in response to acute stress, which is caused by partial habituation, coping, and adaptation to the stressor, whereas it induces a hyposuppressive state for the basal CORT secretion, which is caused by glucocorticoid receptor downregulation. These mechanisms may be involved in the stress-induced neural abnormalities observed in depression.

Genipin, a metabolite derived from the herbal medicine Inchin-ko-to, and suppression of Fas-induced lethal liver apoptosis in mice.

BACKGROUND & AIMS We showed previously that a Kampo (Chinese/Japanese herbal) medicine, Inchin-ko-to (ICKT), inhibits hepatocyte apoptosis induced by transforming growth factor beta1 in vitro. The present study investigated whether ICKT or its ingredients inhibit Fas-mediated liver apoptosis in vivo. METHODS Acute liver injury was induced by an intravenous injection of anti-Fas antibody, Jo2. The effects of ICKT and its ingredients on lethality, histology, apoptotic index, serum transaminase levels, caspase activation, mitochondrial membrane potential (Deltapsi(m)), and mitochondrial permeability transition (MPT) were analyzed. Apoptosis in mouse hepatocytes in vitro was also evaluated. RESULTS Pretreatment with ICKT rescued 75% of Jo2-treated mice and markedly suppressed liver apoptosis/injury. Genipin, an intestinal bacterial metabolite of geniposide that is a major ingredient of ICKT, was found to be an active principle of ICKT. Genipin also suppressed in vitro Fas-mediated apoptosis in primary-cultured murine hepatocytes. Activation of caspase 3 and 8 in the liver homogenate and rapid reduction of triangle uppsi(m) of hepatocytes isolated from Jo2-treated mice were inhibited by genipin preadministration. The resistance to Ca(2+)-induced MPT was enhanced in liver mitochondria of genipin-treated mice. CONCLUSIONS These results suggest that the antiapoptotic activity of genipin via the interference with MPT is a possible mechanism for therapeutic effects of ICKT.

The herbal medicine Dai-kenchu-to and one of its active components [6]-shogaol increase intestinal blood flow in rats.

The present study investigated the effects of the herbal medicine Dai-kenchu-to (DKCT) and its 4 individual ingredients on intestinal blood flow (IBF) in rats by laser Doppler flowmetry. Intraduodenal administration of DKCT (30, 100 and 300 mg/kg) increased IBF in a dose-dependent manner, whereas the mean arterial blood pressure was not affected. One of the ingredients in DKCT is dried ginger rhizome (150 mg/kg), whose main component is [6]-shogaol (2 mg/kg), both of which showed similar effects to those shown by DKCT, while the other ingredients in DKCT only slightly increased IBF or had no effect. The calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP (8-37), completely abolished the hyperemia induced by DKCT, dried ginger rhizome and [6]-shogaol. However, the vasoactive intestinal polypeptide (VIP) receptor antagonist, [4-Cl-DPhe6, Leul7]-VIP, and atropine were less inhibitory than CGRP (8-37), and the substance P (SP) receptor antagonist, spantide, had no effect. The present study demonstrated that DKCT and one of its active components, [6]-shogaol, produced an increase in IBF which was mainly mediated by CGRP and suggests that DKCT may be useful in the treatment of intestinal ischemia-related diseases.

Mechanisms for Contractile Effect of Dai-kenchu-to in Isolated Guinea Pig Ileum

The mechanisms by which Dai-kenchu-to (TJ-100), a kampo medicine, enhances gastrointestinal motility was investigated using isolated guinea pig ileum. TJ-100 induced contractions accompanied by autonomous contraction at a concentration of more than 3 × 10−4 g/ml in a dose-related manner. The TJ-100-induced ileal contraction was suppressed by atropine and tetrodotoxin, but not by hexamethonium. This effect was partially suppressed in the presence of high concentrations of ICS 205-930, a serotonin 4 (5-HT4) receptor antagonist. In addition, TJ-100 showed an acetylcholine (ACh) -releasing action in the smooth muscle tissues of ileum. These results suggest that contractile response induced by TJ-100 is partially mediated by ACh released from the cholinergic nerve endings and that 5-HT4 receptors would be involved in the effect of TJ-100.

Chronic stress impairs rotarod performance in rats: implications for depressive state

Exposure to chronic stress is thought to precipitate or exacerbate several neuropsychiatric disorders such as depression. Here, we examined the effects of chronic stress administered by water immersion and restraint (2 h/day) for 4 weeks followed by a 10-day recovery period on rotarod performance. The time course study revealed that the riding time on a rotating rod was not affected at Day 1 or Week 1 of the stress period, but was significantly decreased at Week 4 and after the 10-day recovery period. However, traction performance and locomotor activity were not changed by chronic stress. We next examined the involvement of a serotonergic mechanism in the impairment of rotarod performance. The post-stress administration of a serotonergic antidepressant, trazodone (10 mg/kg, daily for 10 days) significantly ameliorated the impairment of rotarod performance. A microdialysis study also revealed a decrease in the extracellular concentration of serotonin in the prefrontal cortex. These results indicate that chronic stress impairs the rotarod performance in a manner that is not due to muscle relaxation or motor dysfunction, and this impairment may imply a behaviorally depressive state mediated by a serotonergic mechanism. These findings provide insight into the underlying mechanisms of stress-induced neuropsychiatric disorders.

LKM512 yogurt consumption improves the intestinal environment and induces the T‐helper type 1 cytokine in adult patients with intractable atopic dermatitis

Background In atopic dermatitis (AD) patients, the intestinal mucosal barrier function is weakened, permiting frequent invasion by antigens. Polyamines and short‐chain fatty acids (SCFA) produced by intestinal bacteria are involved in the promotion of intestinal mucosal barrier functions.

Suppressive effect of the herbal medicine Oren-gedoku-to on cyclooxygenase-2 activity and azoxymethane-induced aberrant crypt foci development in rats

The present study is part of a program to obtain effective chemopreventive agents with low toxicity from medicinal herbs and traditional herbal medicines. We previously reported that Oren (Coptidis rhizoma) and Ogon (Scutellariae radix) inhibit azoxymethane (AOM)-induced aberrant crypt foci (ACF) formation. In the present investigation, we found Sanshishi (Gardeniae fructus) and the traditional herbal medicine Oren-gedoku-to (OGT), composed of Ogon, Oren, Sanshishi and Obaku, also have preventive potential. Sanshishi and OGT decreased the numbers of ACF to 25.2 and 59.4% of the control value at 2% in the diet, respectively. Adverse effects, evidenced by body weight loss, were weaker with OGT than component herbs. To investigate their mechanisms of action, the influence on cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) activities was studied. Both OGT and Sanshishi inhibited COX-2 but not COX-1, this presumably contributing to their suppressive effects on ACF development. The results suggest that OGT may be useful for colon cancer chemoprevention in terms of efficacy and toxicity.