Abnormalities in the composition of the gut microbiota in mice after repeated administration of DREADD ligands

Chemogenetic activation of PVN CRH neurons disrupts the estrous cycle and LH dynamics in female mice

Introduction

The impact of stress on reproductive function is significant. Hypothalamic paraventricular nucleus (PVN) corticotrophin-releasing hormone (CRH) plays a major role in regulating the stress response. Understanding how the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-gonadal (HPG) axis interact is crucial for comprehending how stress can lead to reproductive dysfunction. However, whether stress influences reproductive function via modulating PVN CRH or HPA sequelae is not fully elucidated.

Methods

In this study, we investigated the impact of chemogenetic activation of PVN CRH neurons on reproductive function. We chronically and selectively stimulated PVN CRH neurons in female CRH-Cre mice using excitatory designer receptor exclusively activated by designer drugs (DREADDs) viral constructs, which were bilaterally injected into the PVN. The agonist compound-21 (C21) was delivered through the drinking water. We determined the effects of DREADDs activation of PVN CRH neurons on the estrous cycles, LH pulse frequency in diestrus and metestrus and LH surge in proestrus mice. The effect of long-term C21 administration on basal corticosterone secretion and the response to acute restraint stress during metestrus was also examined. Additionally, computer simulations of a mathematical model were used to determine the effects of DREADDs activation of PVN CRH neurons, simulating chronic stress, on the physiological parameters examined experimentally.

Results

As a result, and consistent with our mathematical model predictions, the length of the estrous cycle was extended, with an increase in the time spent in estrus and metestrus, and a decrease in proestrus and diestrus. Additionally, the frequency of LH pulses during metestrus was decreased, but unaffected during diestrus. The occurrence of the preovulatory LH surge during proestrus was disrupted. The basal level of corticosterone during metestrus was not affected, but the response to acute restraint stress was diminished after long-term C21 application.

Discussion

These data suggest that PVN CRH neurons play a functional role in disrupting ovarian cyclicity and the preovulatory LH surge, and that the activity of the GnRH pulse generator remains relatively robust during diestrus but not during metestrus under chronic stress exposure in accordance with our mathematical model predictions.

Associations between gastrointestinal symptoms, medication use, and spontaneous drug discontinuation in patients with major depressive disorder in China

BACKGROUND

The study was designed to investigate the associations between gastrointestinal (GI) symptoms, medication use, and spontaneous drug discontinuation (SDD) in patients with major depressive disorder (MDD).

METHODS

This cross-sectional study included 3256 MDD patients from the National Survey on Symptomatology of Depression (NSSD). Differences in the sociodemographic factors, clinical characteristics, medication use, and self-reported reasons for SDD were compared in patients with different frequencies of GI symptoms. A multiple logistic regression analysis was employed to assess the contribution of GI symptoms to the risk of spontaneous drug discontinuation.

RESULTS

MDD patients with a higher frequency of GI symptoms were prone to have higher proportions of mood stabilizer and benzodiazepine uses (p_{s for trend} < 0.001) but a lower proportion of SNRI use (p_{for trend} < 0.001). With the increase in GI symptoms, patients were prone to report worries about long-term side effects (p_{for trend} < 0.001), with the patients stating ineffective treatments (p_{for trend} = 0.002) and intolerance of adverse drug reactions (p_{for trend} = 0.022) as the reasons for SDD. Compared with those patients without GI symptoms, all of the MDD patients with GI symptom frequencies of several days (OR = 1.317; 95 % CI: 1.045-1.660), more than half of all days (OR = 1.305; 95 % CI: 1.005-1.695), and nearly every day (OR = 1.820; 95 %: 1.309-2.531) had an increased risk of SDD.

CONCLUSION

GI symptoms are highly associated with drug discontinuation in MDD patients. These findings may have important implications for clinical treatment options, as well as for drug adherence management, in MDD patients.

Gut-microbiota-brain axis in the vulnerability to psychosis in adulthood after repeated cannabis exposure during adolescence

Increasing epidemiological evidence shows that the use of cannabis during adolescence could increase the risk for psychosis in adulthood. However, the precise mechanisms underlying long-lasting cannabis-induced risk for psychosis remain unclear. Accumulating evidence suggests the role of gut microbiota in the pathogenesis of psychiatric disorders. Here, we examined whether gut microbiota plays a role in the risk for psychosis of adult after exposure of cannabinoid (CB) receptor agonist WIN55,212-2 during adolescence. Repeated administration of WIN55,212-2 (2 mg/kg/day) during adolescence (P35-P45) significantly increased the expression of Iba1 (ionized calcium-binding adapter molecule 1) in the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) of adult mice after administration of lipopolysaccharide (LPS: 0.5 mg/kg). In contrast, there were no changes in blood levels of pro-inflammatory cytokines between the two groups. Although alpha-diversity and beta-diversity of gut microbiota were no differences between the two groups, there were several microbes altered between the two groups. Interestingly, there were significant correlations between the relative abundance of microbiota and Iba1 expression in the mPFC and NAc. Furthermore, there were also significant correlations between the relative abundance of microbiota and several metabolites in the blood. These findings suggest that gut microbiota may play a role in the microglial activation in the mPFC and NAc of adult mice after repeated WIN55,212-2 exposure during adolescence. Therefore, it is likely that gut-microbiota-microglia crosstalk might play a role in increased risk for psychosis in adults with cannabis use during adolescence.

Effects of (R)-ketamine on reduced bone mineral density in ovariectomized mice: A role of gut microbiota

Depression is a high risk for osteoporosis, suggesting an association between depression and low bone mineral density (BMD). We reported that the novel antidepressant (R)-ketamine could ameliorate the reduced BMD in the ovariectomized (OVX) mice which is an animal model of postmenopausal osteoporosis. Given the role of gut microbiota in depression and bone homeostasis, we examined whether gut microbiota plays a role in the beneficial effects of (R)-ketamine in the reduced BMD of OVX mice. OVX or sham was operated for female mice. Subsequently, saline (10 ml/kg/day, twice weekly) or (R)-ketamine (10 mg/kg/day, twice weekly) was administered intraperitoneally into OVX or sham mice for the six weeks. The reduction of cortical BMD and total BMD in the OVX mice was significantly ameliorated after subsequent repeated intermittent administration of (R)-ketamine. Furthermore, there were significant changes in the α- and β-diversity between OVX + saline group and OVX + (R)-ketamine group. There were correlations between several OTUs and cortical (or total) BMD. There were also positive correlations between the genera Turicibacter and cortical (or total) BMD. Moreover, there were correlations between several metabolites in blood and cortical (or total) BMD. These data suggest that (R)-ketamine may ameliorate the reduced cortical BMD and total BMD in OVX mice through anti-inflammatory actions via gut microbiota. Therefore, it is likely that (R)-ketamine would be a therapeutic drug for depressed patients with low BMD or patients with osteoporosis.

Regulation of neurotoxicity in the striatum and colon of MPTP-induced Parkinson's disease mice by gut microbiome

Increasing evidence suggests the role of gut-microbiota-brain axis in the pathogenesis of Parkinson's disease (PD). The objective of this study was to examine whether repeated administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) can influence the neurotoxicity in the striatum and colon, and the composition of gut microbiota and short-chain fatty acids (SCFAs) in feces of adult mice. MPTP caused the reduction of dopamine transporter (DAT) and tyrosine hydroxylase (TH) in the striatum, and increases in phosphorylated α-synuclein (p-α-Syn) in the striatum and colon. There was a negative correlation between the expression of TH in the striatum and the expression of p-α-Syn in the colon, suggesting a role of gut-brain communication. MPTP caused abnormalities in the α- and β-diversity of gut microbiota in the mice. Furthermore, the relative abundance of the genus Faecalicatena in the MPTP-treated group was significantly lower than that of control group. Interestingly, there was a positive correlation between the genus Faecalicatena and the expression of TH in the striatum. Moreover, MPTP did not alter the levels of SCFAs in feces samples. However, there was a positive correlation between the relative abundance of the genus Faecalicatena and propionic acid. The data suggest that MPTP-induced increases in colonic p-α-Syn expression might be associated with dopaminergic neurotoxicity in the striatum via gut-microbiota-brain axis.