Corticosterone-induced Hippocampal 5-HT Responses were Muted in Depressive-like State

SERT and OCT mediate 5-HT1B receptor regulation of immobility behavior and uptake of 5-HT and HIS

5-HT clearance, commonly mediated by transporters in the uptake-1 and uptake-2 families, has been linked to 5-HT1B receptor's action on behaviors. Since no specific transporters identified yet, effects of serotonin transporter (SERT) and organic cation transporter (OCTs) on 5-HT1B-elicited immobility phenotype, and 5-HT and HIS uptake were then investigated. Intraperitoneal injections of SERT inhibitor fluoxetine (FLX) and/or OCTs inhibitor decynium (D22) were used prior to local perfusion of 5-HT1B agonist CP93129 into the ventral hippocampus to measure immobility times in the FST and TST, to measure 5-HT uptake efficiencies and HIS uptake efficiencies derived from linear regressions using the transient no-net-flux quantitative microdialysis in C57BL/6 mice. Exogenous 5-HT and HIS uptake were measured following incubation of FLX and/or D22 with CP93129 in the RBL-2H3 cells. Moreover, surface membrane levels of SERT and OCT were detected in response to CP93129. Local CP93129 prolonged immobility times, which were attenuated following pretreatment of either inhibitor. Local CP93129 lowered the slopes obtained from the lineal regressions for 5-HT and HIS (slope is reciprocal to uptake efficiency), which were then weakened following pretreatment of either inhibitor. Similar findings were obtained following CP93129 incubation, and co-incubation of CP93129 with either inhibitor in the RBL-2H3. Moreover, CP93129 dose-dependently moved SERT and OCT3 in the cytosol to the surface membrane. Both SERT and OCT are the target effectors mediating 5-HT1B regulation of immobility time and 5-HT uptake, OCT mediates 5-HT1B regulation of HIS uptake. Their underlying signal transductions need to be further explored.

Alpha-glycosyl isoquercitrin alleviates subchronic social defeat stress-induced depression symptoms by modulating the microbiota-gut-brain axis in mice

AIMS

Increasing evidence suggests a link between gut microbial dysbiosis and the pathogenesis of depression. Alpha-glycosyl isoquercitrin (AGIQ), consisting of isoquercitrin and its glycosylated quercetin, has beneficial effects on the gut microbiome and brain function. Here, we detected the potential antidepressant impact of a four-week administration of AGIQ and its underlying mechanisms using a mouse model of depression.

MAIN METHODS

Male C57BL/6 mice were orally administered AGIQ (0.05 % or 0.5 % in drinking water) for 28 days; subchronic social defeat stress was performed in the last 10 days. Behavior tests were conducted to assess anxiety and depressive-like behaviors. Additionally, evaluations encompassed 5-hydroxytryptamine (5-HT) levels, the gut microbiota composition, lipopolysaccharide (LPS) concentrations, short-chain fatty acids levels, and intestinal barrier integrity changes.

KEY FINDINGS

AGIQ significantly alleviated depression-like behaviors and increased hippocampal 5-HT levels. Further, AGIQ mitigated stress-induced gut microbial abnormalities and reduced the levels of LPS in the serum, which affected the relative gene expression levels of 5-HT biosynthesis enzymes in vitro. Furthermore, AGIQ reversed the reduced butyrate levels in cecal contents and improved the impaired intestinal barrier by increasing the expression of colonic zonula occluden-1 (ZO-1) and occludin, thereby decreasing LPS leakage.

SIGNIFICANCE

Our results suggest that AGIQ could improve stress-induced depression by regulating the gut microbiome, which inhibits LPS production and maintains the gut barrier. This is the first report on the potential effect of AGIQ on depression via the gut microbiota-brain axis, shedding new light on treatment options.

Sex differences in a corticosterone-induced depression model in mice: Behavioral, neurochemical, and molecular insights

Depression is characterized by a significant sex disparity, with higher rates observed in women compared to men. This study aimed to investigate the impact of sex on depressive behaviors and explore the underlying mechanisms using a corticosterone (CORT)-induced depression model in mice. Behavioral tests, Nissl staining, UPLC-MS/MS, and Western blot analysis were performed to assess behavioral changes, as well as neuronal alterations, neurotransmitter levels, and protein expressions in the hippocampus. The mice in the model group exhibited sex-specific anxiety- and depression-like behaviors. Nissl staining revealed structural abnormalities in the CA3 region of the hippocampus in females. Neurotransmitter analysis indicated decreased serotonin and norepinephrine levels in both sexes, while glutamate levels were elevated in females. Furthermore, female mice demonstrated elevated serum CORT levels. Western blot analysis revealed sex-specific alterations in specific protein expression. Female mice exhibited downregulated glucocorticoid receptor and brain-derived neurotrophic factor expression, whereas male mice showed minimal changes. Additionally, female mice displayed reduced phosphorylated AKT, phosphorylated PI3K, and phosphorylated mTOR levels. These findings enhance our understanding of sex-specific differences in the CORT-induced depression model and provide insights into the underlying mechanisms of depression. This research emphasizes sex in depression studies and supports tailored interventions.

Ventral hippocampus is more sensitive to fluoxetine-induced changes in extracellular 5-HT concentration, membrane 5-HT transporter level and immobility times

Hippocampal responses to selective 5-HT reuptake inhibitor (SSRI) have long been studied. However, its sub-regional involvements in mediating SSRI's pharmacological effects have not been fully addressed. The current study sought to investigate neurochemical, neurobiological and neurobehavioral changes in response to direct fluoxetine perfusion into the ventral and dorsal sub-regions of the hippocampus in C57BL/6 mice. Following fluoxetine perfusion, time courses of dialysate 5-HT, 5-HT transporter (5-HTT) protein (total, membrane and cytoplasmic fractions), locomotion, and immobility times in the forced swim test (FST) and tail suspension test (TST) were determined. At baseline, 5-HT uptake efficiency assessed by the no-net-flux microdialysis, and 5-HTT protein were measured as well. Results show that fluoxetine dose-dependently increased dialysate 5-HT, lowered membrane 5-HTT protein and increased cytoplasmic fraction without changing the total level, decreased immobility times in both the FST and TST, with greater responses all detected in the ventral sub-region compared to the dorsal sub-region. Fluoxetine didn't affect locomotor activity, ruling out the possibility that fluoxetine's effects on immobility maybe due to alteration in locomotion. Besides, lower 5-HT uptake efficiency and lower membrane 5-HTT protein level were found in the ventral sub-region at baseline. Together, the sub-regional differences at baseline and in responses to fluoxetine added powerful evidence to support the existence of two distinct 5-HT sub-systems in the hippocampus, with greater changes to fluoxetine detected in the ventral sub-system.

Sargassum horneri Extract Attenuates Depressive-like Behaviors in Mice Treated with Stress Hormone

Sargassum horneri, a brown seaweed, is known for its various health benefits; however, there are no reports on its effects on depression. This study aimed to investigate the antidepressant effects of S. horneri ethanol extract (SHE) in mice injected with corticosterone (CORT) and to elucidate the underlying molecular mechanisms. Behavioral tests were conducted, and corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), and CORT levels were measured. A fluorometric monoamine oxidase (MAO) enzyme inhibition assay was performed. Neurotransmitters like serotonin, dopamine, and norepinephrine levels were determined. Moreover, the ERK-CREB-BDNF signaling pathway in the prefrontal cortex and hippocampus was evaluated. Behavioral tests revealed that SHE has antidepressant effects by reducing immobility time and increasing time spent in open arms. Serum CRH, ACTH, and CORT levels decreased in the mice treated with SHE, as did the glucocorticoid-receptor expression in their brain tissues. SHE inhibited MAO-A and MAO-B activities. In addition, SHE increased levels of neurotransmitters. Furthermore, SHE activated the ERK-CREB-BDNF pathway in the prefrontal cortex and hippocampus. These findings suggest that SHE has antidepressant effects in CORT-injected mice, via the regulation of the hypothalamic-pituitary-adrenal axis and monoaminergic pathway, and through activation of the ERK-CREB-BDNF signaling pathway. Thus, our study suggests that SHE may act as a natural antidepressant.

Free-L-Cysteine improves corticosterone-induced behavioral deficits, oxidative stress and neurotransmission in rats

L-Cysteine (L-Cys) is a semi-essential amino acid. It serves as a substrate for enzyme cystathionine-β-synthase in the central nervous system (CNS). L-Cys showed various antioxidant characteristics. Though, studies on the effect of free L-Cys administration to evaluate the CNS functioning is very limited. Therefore, we assessed the effects of L-Cys on corticosterone (CORT) induced oxidative stress, behavioral deficits and memory impairment in male rats. L-Cys (150 mg/kg/ml) administered to vehicle and CORT (20 mg/kg/ml) treated rats orally for 28 days. Behavioral activities were conducted after treatment period. Subsequently, rats were sacrificed, blood and brain were removed. Hippocampus was isolated from brain and then hippocampus and plasma were collected for oxidative, biochemical and neurochemical analysis. Results showed that repeated treatment of L-Cys produced antidepressant, anxiolytic and memory-improving effects which may be ascribed to the enhanced antioxidant profile, normalized cholinergic, serotonergic neurotransmission in brain (hippocampus) following CORT administration. Increased plasma CORT by CORT administration was also normalized by L-Cys. The current study concluded that administration of free L-Cys improved the behavioral, biochemical, neurochemical and redox status of CNS. Hence, L-Cys could be protective therapeutic modulator against stress induced neurological ailments.

Jie-Yu-He-Huan Capsule Ameliorates Anxiety-Like Behaviours in Rats Exposed to Chronic Restraint Stress via the cAMP/PKA/CREB/BDNF Signalling Pathway

Chronic stress is a critical factor in the aetiology of anxiety disorders; however, in the clinic, enduring and preventive measures are not available, and therapeutic drugs are associated with inevitable side effects. Our study established an anxiety rat model using chronic restraint stress (CRS) and assessed these animals using the open-field test, elevated plus-maze test, and light-dark box test. Jie-Yu-He-Huan capsule (JYHH), a Chinese medicine formula, was used as a preventative drug. The HPA axis-mediated release of corticotropin-releasing hormone, adrenocorticotropic hormone, and corticosterone from the hypothalamus was tested. In the hippocampus and prefrontal cortex, concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid, as well as monoamine oxidase A, glucocorticoid receptor, and 5-HT1A receptor expression levels, were measured. Furthermore, we examined protein and mRNA expression of cAMP-PKA-CREB-BDNF pathway components. The results showed that JYHH had a significant preventative effect on the anxiety-like behaviour induced by CRS and prevented abnormal changes in the HPA axis and 5-HT system. Furthermore, CRS inhibited the cAMP-PKA-CREB-BDNF pathway, which returned to normal levels following JYHH treatment. This might be the underlying molecular mechanism of the antianxiety effect of JYHH, which could provide a new clinical target for preventative anxiolytic drugs for chronic stress.