Effects of chronic social defeat stress on peripheral leptin and its hypothalamic actions.

BACKGROUND: Suppression of body weight and symptom of anorexia are major symptoms of depression. Recently, we reported that chronic social defeat stress (CSDS) induced suppression of body weight gain and anorexic feeding behavior in rats. These abnormalities were the result of disrupted malonyl-coenzyme A (CoA) signaling pathway in the hypothalamus. However, the condition of peripheral leptin and its hypothalamic downstream signal molecules which regulate hypothalamic malonyl-CoA level in the CSDS-exposed rats (CSDS rats) is still unknown. RESULTS: CSDS rats showed suppressed body weight gain and food intake. The weight of the CSDS rats' epididymal white adipose tissues was decreased when compared to the control rats. The plasma cholesterol concentration was decreased significantly in the CSDS rats compared to the control rats (P < 0.05). The plasma glucose concentration was slightly decreased in the CSDS rats compared to the control rats (P < 0.1). The expression of leptin mRNA in epididymal white adipose tissues and the plasma leptin concentration were decreased in CSDS rats. Furthermore, the phosphorylation of the hypothalamic downstream signals of leptin, including extracellular signal-regulated kinase 1/2 (ERK1/2) and signal transducer and activator of transcription 3 (STAT3), was decreased in CSDS rats. CONCLUSIONS: Our results indicated that decreased peripheral leptin expression in CSDS rats could down-regulate the hypothalamic downstream signaling pathways of leptin while suppressed food intake. These data indicate that CSDS induces the down-regulation of hypothalamic AMPK following the elevation of hypothalamic malonyl-CoA levels and is independent of peripheral leptin and glucose.

Antidepressant-like effect of chronic taurine administration and its hippocampal signal transduction in rats.

Taurine is one of the most abundant amino acids in the central nervous system, and it has various important functions as a neuromodulator and antioxidant. Taurine is expected to be involved in the mental disorders such as depression; however, knowledge of its function in relation to depression is limited. In this research, we tried to elucidate the effects of taurine supplementation on antidepressant-like behaviors in rats and depression-related signal transduction in the hippocampus. In behavioral tests, rats fed a high taurine (HT: 45 mmol/kg taurine) diet for 4 weeks (HT4w) showed decreased immobility in the forced swim test (FS) compared to controls. On the other hand, rats fed a low taurine (LT: 22.5 mmol/kg taurine) diet for 4 weeks or an HT diet for 2 weeks (HT2w) did not show a significant difference in FS compared to controls. In western blot analyses, the expression of glutamic acid decarboxylase (GAD) 65 and GAD67 in the hippocampus was not affected by taurine supplementation. However, the phosphorylation levels of extracellular signal-regulated kinase1/2 (ERK1/2), protein kinase B (Akt), glycogen synthase kinase3 beta (GSK3ß), and cAMP response element-binding protein (CREB) were increased in the hippocampus of HT4w and HT2w rats. Phosphorylated calcium/calmodulin-dependent protein kinase II (CaMKII) was increased in the hippocampus of HT4w rats only. Moreover, no significant changes in these molecules were observed in the hippocampus of rats fed an HT diet for 1 day. In conclusion, our discoveries suggest that taurine supplementation has an antidepressant-like effect and an ability to change depression-related signaling cascades in the hippocampus.

Effects of a low-protein diet supplemented with essential amino acids on egg production performance and environmental gas emissions from layer-manure composting in laying hens in the later laying period.

We fed 330-545 day-old laying hens (later laying period) a low-protein diet supplemented with essential amino acids (LPS) and composted their manure. We then investigated the laying performance of the hens, the nitrogen balance and emission of nitrous oxide (N2 O), methane (CH4 ), and ammonia (NH3 ) from the composting, and several characteristics of the finished compost. There were no significant differences in the egg-laying rate, egg mass, egg weight, proximate compositions in egg yolk and egg white, or feed intake between the laying hens fed a Control diet (Cont) and those fed the LPS diet. However, the LPS-fed hens had lower excreta levels and nitrogen excretion. In addition, the environmental gas emissions per layer from composting of the manure from the LPS-fed laying hens were decreased by 9.7% for N2 O, 40.9% for CH4 , and 24.8% for NH3 compared to the Cont-fed laying hens. The concentrations of total nitrogen in the finished compost were similar between the LPS-fed and Cont-fed laying hens. In a vegetable-growth test, the weights of komatsuna plants grown with compost from LPS-fed and Cont-fed hens were also not significantly different. Feeding an LPS diet to 330-545 day-old laying hens was suggested to reduce environmental gas emissions from manure composting without affecting the egg production performance.

Anorexic behavior and elevation of hypothalamic malonyl-CoA in socially defeated rats.

Suppression of body weight and eating disorders, such as anorexia, are one of the major symptoms of psychiatric disorders such as depression. However, the mechanisms of weight loss and reduced appetite in depressive patients and in animal models of depression are largely unknown. In this study, we characterized the mechanism of anorexia resulting from depression using socially defeated rats as an animal model of depression. Socially defeated rats showed suppressed body weight gain, enlarged adrenal glands, decreased home cage activity, decreased food intake, and increased immobility in the forced swim test. These results are representative of some of the core symptoms of depression. Simultaneously, we observed decreased levels of phosphorylated AMP-activated protein kinase (AMPK) and acetyl-coenzyme A (CoA) carboxylase (ACC) and increased levels of malonyl-CoA in the hypothalamus of socially defeated rats. Hypothalamic malonyl-CoA controlled feeding behavior and elevation of malonyl-CoA in the hypothalamus induced inhibition of food intake. Our findings suggest that the suppression of body weight gain caused by social defeat stress is caused by anorexic feeding behavior via an increased concentration of malonyl-CoA in the hypothalamus.

Effect of diet composition on coenzyme A and its thioester pools in various rat tissues.

Three coenzyme A (CoA) molecular species, i.e., acetyl-CoA, malonyl-CoA, and nonesterified CoA (CoASH), in 13 types of fasted rat tissue were analyzed. A relatively larger pool size of total CoA, consisting of acetyl-CoA, malonyl-CoA, and CoASH, was observed in the medulla oblongata, liver, heart, and brown adipose tissue. Focusing on changes in the CoA pool size in response to the nutrient composition of the diet given, total CoA pools in rats continuously fed a high-fat diet for 4 weeks were significantly higher in the hypothalamus, cerebellum, and kidney, and significantly lower in the liver and skeletal muscle than those of rats fed a high-carbohydrate or high-protein diet. In particular, reductions in the liver were remarkable and were caused by decreased CoASH levels. Consequently, the total CoA pool size was reduced by approximately one-fifth of the hepatic contents of rats fed the other diets. In the hypothalamus, which monitors energy balance, all three CoA molecular species measured were at higher levels when rats were fed the high-fat diet. Thus, it was of interest that feeding rats a high-fat diet affected the behaviors of CoA pools in the hypothalamus, liver, and skeletal muscle, suggesting a significant relationship between CoA pools, especially malonyl-CoA and/or CoASH pools, and lipid metabolism in vivo.

The effects of oral taurine administration on behavior and hippocampal signal transduction in rats.

Taurine, 2-aminoethylsulfonic acid, is one of the most abundant amino acids in the brain. It has various important physiological functions as a neuromodulator and antioxidant. Taurine is expected to be involved in depression; however, knowledge regarding its function in relation to depression is limited. In this study, we attempted to elucidate the effects of oral taurine administration on antidepressant-like behaviors in rats and depression-related signal transduction in the hippocampus. In behavioral tests, rats fed a high taurine (HT: 45.0 mmol/kg taurine) diet for 4 weeks (HT4w) showed decreased immobility in the forced swim test (FS) compared to controls. However, rats fed a low taurine (LT: 22.5 mmol/kg taurine) diet for 4 weeks or an HT diet for 2 weeks (HT2w) did not show a significant difference in FS compared to controls. In biochemical analyses, the expression of glutamic acid decarboxylase (GAD) 65 and GAD67 in the hippocampus was not affected by taurine administration. However, the phosphorylation levels of extracellular signal-regulated kinase1/2 (ERK1/2), protein kinase B (Akt), glycogen synthase kinase3 beta (GSK3ß) and cAMP response element-binding protein (CREB) were increased in the hippocampus of HT4w and HT2w rats. Phospho-calcium/calmodulin-dependent protein kinase II (CaMKII) was increased in the hippocampus of HT4w rats only. Moreover, no significant changes in these molecules were observed in the hippocampus of rats fed an HT diet for 1 day. In conclusion, our findings suggest that taurine has an antidepressant-like effect and an ability to change depression-related signaling cascades in the hippocampus.

Isolation and identification of cellulose-binding proteins from sheep rumen contents.

To extend our understanding of the mechanisms of plant cell wall degradation in the rumen, cellulose-binding proteins (CBPs) from the contents of a sheep rumen were directly isolated and identified using a metaproteomics approach. The rumen CBPs were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and some CBPs revealed endoglucanase activities toward carboxymethyl cellulose. Using mass spectrometry analyses, four CBPs were identified and annotated as known proteins from the predominant rumen cellulolytic bacterium Fibrobacter succinogenes: tetratricopeptide repeat domain protein, OmpA family protein, fibro-slime domain protein, and cellulose-binding endoglucanase F (EGF). Another CBP was identified as the cellulosomal glycosyl hydrolase family 6 exoglucanase, Cel6A, of Piromyces equi. F. succinogenes cells expressing EGF were found to be major members of the bacterial community on the surface or at the inner surface of hay stems by immunohistochemical analyses using anti-EGF antibody. The finding that four of the five CBPs isolated and identified from sheep rumen contents were from F. succinogenes indicates that F. succinogenes is significantly involved in cellulose degradation in the rumen.

Influence of Chronic Social Defeat Stress on Digestive System Functioning in Rats.

Mental disorders are caused by chronic psychosocial stress, and can cause various symptoms related to the digestive system. We focused on the conjugation of intestinal absorptive and enzymatic mechanisms between chronic social defeat stress (CSDS) model rats and healthy controls to obtain general biochemical data about the intestine of the model in this study. The small intestine was divided into three regions: proximal (PI), middle (MI), and distal (DI); mRNA expression associated with a nutrient absorption, glucose absorption activity, and activities of the digestive enzymes such as maltase, sucrase and lactase was measured. Expression of both sodium-dependent glucose transporter 1 (Sglt1) and glucose transporter 2 gene tended to be higher in the stress group compared to the control group in PI. Glucose absorption was also higher in PI of the CSDS group. Sglt1 and peptide transporter 1 gene expressions in the CSDS group were significantly higher than those in the control group in DI. Furthermore, in PI, expression of the aquaporin 1 gene was significantly higher in the CSDS group compared to the control group. Thus, absorption of some nutrients might be higher in the small intestine of the CSDS rat.

Effects of chronic mild food restriction on behavior and the hypothalamic malonyl-CoA signaling pathway.

Depression induces anorexia, leading to suppressed feeding behaviors and energy intake. Previously, we revealed that chronic social defeat induced a mild suppression of feeding in rats with elevated levels of hypothalamic malonyl-CoA which regulates feeding. Therefore, we attempted to elucidate the effects of chronic mild food restriction on behavior and on hypothalamic malonyl-CoA. The chronic mild food restricted rats were fed a restricted diet approximately 80% to 90% amount of diet compared to the control for 5 weeks. Ratios of restriction were adjusted with feed consumption in the chronic social defeat stressed rats. Chronic mild food restricted rats exhibited a suppression of body weight gain similar to that of the chronic social defeat stressed rats. Also these rats showed increased time spent in the center area of an open field (OF), prolonged immobility time in forced swim, increased phosphorylation of hypothalamic adenosine monophosphate-activated protein kinase (AMPK) and acetyl-CoA carboxylase and a decreased concentration of hypothalamic malonyl-CoA. Weight of the adrenal glands, locomotion in an OF, mitogen-activated protein kinase cascade and calcium/calmodulin-dependent protein kinases II in the hippocampus were not affected by chronic mild food restriction. Our findings suggest that chronic mild food restriction activates AMPK following a decreased hypothalamic malonyl-CoA.

Differential expression of genes encoding neurotrophic factors and their receptors along the septal-temporal axis of the rat hippocampus.

The hippocampus plays a key role in learning and emotional regulation. The hippocampus' function varies along its septotemporal axis, with the septal pole being more frequently involved in spatial learning and memory, and the temporal pole playing a greater role in emotional behaviors. In this study, we present findings aimed at checking the expression level of the genes encoding neurotrophins and their receptors, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and their receptors (TrkA, TrkB and TrkC) in the hippocampus along the septotemporal axis. Using real-time PCR, several different expression patterns were observed. Remarkably, the expression of both NT-3 and TrkA genes in the septal hippocampus was higher than in the middle and temporal hippocampus. Higher expression of NT-3 and TrkA may implicate active neurogenesis in the dentate gyrus (DG) of the septal hippocampus because more neurogenesis occurs in the septal than the temporal DG of rats. Finally, the results obtained in this study emphasize the importance of choosing the hippocampal portion along its septotemporal axis for any hippocampal molecular and biochemical experimental studies.

Subchronic and mild social defeat stress accelerates food intake and body weight gain with polydipsia-like features in mice.

Development and characterization of animal models of depression are essential for fully understanding the pathogenesis of depression in humans. We made and analyzed a mouse model exhibiting social deficit and hyperphagia-like behavior using a subchronic and mild social defeat stress (sCSDS) paradigm. The body weight, food and water intake of mice were monitored during a test period, and their behaviors and serum components were analyzed at two stages: immediately after the sCSDS period and 1 month after the sCSDS. The body weight and food intake of defeated mice were significantly higher than control mice at the sCSDS period, and these differences were sustained until 1 month after the sCSDS, whereas the water intake of defeated mice was significantly higher than control mice for the period of sCSDS only. Behavioral analyses revealed that the defeated mice exhibit significant social aversion to unfamiliar mice in a social interaction test and a trend of anxiety-like behavior in an elevated-plus maze test. Possibly due to polydipsia-like symptoms, defeated mice had significantly lower levels of albumin and blood urea nitrogen than control mice immediately after the sCSDS period but not at 1 month after sCSDS. The present study revealed that our sCSDS mice keep much more water in their body than control mice. This study reports the first step toward an understanding of the mechanisms of stress-induced overhydration, over-eating and resultant weight gain.

Effects of chronic social defeat stress on MAP kinase cascade.

Chronic psychological and social stress can cause psychiatric disorders in humans. In this study, we analyzed the mitogen-activated protein kinase (MAPK) cascade in the hippocampus of chronically socially defeated rats. The rats that were subjected to social defeat every day for 5 weeks showed physiological and behavioral changes, including a reduced rate of weight gain, enlarged adrenal glands, and increased immobility in the forced swim test without concomitant changes in locomotor activity in the open field test. Altered body weight and enlarged adrenal glands are typical symptoms of human depression. Prolonged immobility in the forced swim test indicates behavioral despair, a well-established index of depression. Because the MAPK cascade plays a pivotal role in depression, we quantified the expression of these molecules in the hippocampus of chronically defeated rats using western blot analysis. We found that phospho-MAPK kinases 1/2 (MEK1/2) and phospho-extracellular signal-regulated kinases 1/2 (ERK1/2) were decreased, whereas MAPK phosphatase-1 (MKP-1) was increased in the hippocampus of chronically defeated rats compared to the control group. These results were consistent with findings in depressed patients and other animal models of depression. In conclusion, our findings suggest that chronic psychosocial stress in Wistar rats induced depression-like behavior and downregulated the MAPK cascade in the hippocampus.