Dorsal raphé nucleus glucocorticoid receptors inhibit tph2 gene expression in male C57BL/6J mice

Chronic jet lag-like conditions dysregulate molecular profiles of neurological disorders in nucleus accumbens and prefrontal cortex

Background

Patients with neurological disorders often display altered circadian rhythms. The disrupted circadian rhythms through chronic jetlag or shiftwork are thought to increase the risk and severity of human disease including, cancer, psychiatric, and related brain diseases.

Results

In this study, we investigated the impact of shiftwork or chronic jetlag (CJL) like conditions on mice's brain. Transcriptome profiling based on RNA sequencing revealed that genes associated with serious neurological disorders were differentially expressed in the nucleus accumbens (NAc) and prefrontal cortex (PFC). According to the quantitative PCR (qPCR) analysis, several key regulatory genes associated with neurological disorders were significantly altered in the NAc, PFC, hypothalamus, hippocampus, and striatum. Serotonin levels and the expression levels of serotonin transporters and receptors were significantly altered in mice treated with CJL.

Conclusion

Overall, these results indicate that CJL may increase the risk of neurological disorders by disrupting the key regulatory genes, biological functions, serotonin, and corticosterone. These molecular linkages can further be studied to investigate the mechanism underlying CJL or shiftwork-mediated neurological disorders in order to develop treatment strategies.

Venlafaxine reduces the striatal il6/il10 ratio and increases hippocampal GR expression in female mice subjected to chronic social instability stress

Women are twice as likely as men to develop depression and antidepressant treatment is more frequent in females. Moreover, neuroinflammatory changes related to affective disorders differ in accordance with sex. Despite this evidence, female populations have been largely omitted from preclinical experiments studying antidepressants. The aim of this work is to analyze the potential restorative effect of venlafaxine on an animal model of depression. Female CD1 mice were subjected to chronic social instability (CSI) stress for 7 weeks, and were administered venlafaxine during the last 3 weeks of the stress period. Behavioral and physiological parameters were then analyzed. Stressed mice showed a decreased sucrose preference and increased whisking behavior, and had a lower body weight, higher plasma corticosterone levels and increased hypothalamic GR expression. They also had lower levels of 5-HT, 5-HIAA and NA and a higher KYN/TRYP ratio in the hippocampus. Moreover, CSI increased striatal IL-6 mRNA expression levels. Venlafaxine treatment reduced the striatal IL-6/IL-10 ratio and increased hippocampal GR expression, although it did not reverse stress-induced behavioral changes. In conclusion, seven weeks of exposure to CSI produced depressive-like alterations in female mice. The venlafaxine treatment regimen was found to have a modest anti-inflammatory effect in the striatum and increased hippocampal GR mRNA, although it failed to redress stress-induced behavioral disturbances.

Maternal chewing improves prenatal stress-induced cognitive deficit and anxiety-like behavior associated with alterations of the apoptotic response and serotonin pathway in mouse offspring

OBJECTIVE

To examine whether maternal chewing affects prenatal stress-induced behavioral alternations associated with the changes in apoptosis-related proteins and serotonin pathway of the mouse offspring.

DESIGN

Pregnant mice were assigned to control, stress, and stress/chewing groups. Stress mice were placed in restraint tubes, from gestational day 12 until parturition. Stress/chewing mice were given a wooden stick for chewing during stress period. Morris water maze and hole-board tests were applied for behavioral alterations in one-month-old male pups. Hippocampal mRNA expression of B-cell lymphoma 2 (Bcl-2) and Bcl-2 associated X protein (Bax) was analyzed by quantitative real-time PCR. Serotonin and tryptophan hydroxylase expression level in the dorsal raphe nucleus was investigated immunohistochemically.

RESULTS

Prenatal stress impaired the spatial learning, induced anxiety-like behavior, increased the ratio of hippocampal Bax/Bcl-2 expression, and decreased the expression of serotonin and tryptophan hydroxylase in dorsal raphe nucleus of the offspring. Maternal chewing ameliorated prenatal stress-induced cognitive impairment, anxiety-like behavior, and attenuated the increased ratio of hippocampal Bax/Bcl-2 expression, and the downregulated serotonin signaling in dorsal raphe nucleus of the offspring.

CONCLUSIONS

Our results indicate that maternal chewing could improve prenatal stress-related anxiety-like behavior and cognitive impairment in mouse offspring, at least in part by affecting hippocampal apoptotic response and central serotonin pathway.

The impact of glucocorticoids and statins on sleep quality

Glucocorticoids and statins are the foundation of lifelong therapies and as such, may generate a variety of side effects. Among these, sleep impairments are one of the least explored and, simultaneously, majorly underestimated in clinical practice. Based on the available evidence, we have concluded that glucocorticoid action on the suprachiasmatic nucleus (SCN) that drives sleep disturbances is dual in nature. It involves both serotonin depletion and reduced arginine vasopressin signalling in the SCN. The former seems to involve activation of glucocorticoid receptors in the dorsal raphe, whereas the latter likely results from changes in glucose serum levels affecting the SCN, among other blood-borne factors which are yet to be discovered. Literature remains inconclusive when it comes to statins. Their diverse potential to cross the blood-brain barrier is considered the key factor determining statins' capability to evoke sleep impairments. Concurrently, an effect similar to that produced by steroids occurs - alteration in serum levels of blood-borne factors, such as glucose, which is a likely cause of statin-induced sleep disturbances.

A single-cell transcriptomic and anatomic atlas of mouse dorsal raphe Pet1 neurons

Among the brainstem raphe nuclei, the dorsal raphe nucleus (DR) contains the greatest number of Pet1-lineage neurons, a predominantly serotonergic group distributed throughout DR subdomains. These neurons collectively regulate diverse physiology and behavior and are often therapeutically targeted to treat affective disorders. Characterizing Pet1 neuron molecular heterogeneity and relating it to anatomy is vital for understanding DR functional organization, with potential to inform therapeutic separability. Here we use high-throughput and DR subdomain-targeted single-cell transcriptomics and intersectional genetic tools to map molecular and anatomical diversity of DR-Pet1 neurons. We describe up to fourteen neuron subtypes, many showing biased cell body distributions across the DR. We further show that P2ry1-Pet1 DR neurons - the most molecularly distinct subtype - possess unique efferent projections and electrophysiological properties. These data complement and extend previous DR characterizations, combining intersectional genetics with multiple transcriptomic modalities to achieve fine-scale molecular and anatomic identification of Pet1 neuron subtypes.

Selective effects of dorsal raphé nucleus glucocorticoid receptor deletion on depression-like behavior in female C57BL/6J mice

We have shown differing effects of glucocorticoid receptor (GR) deletion from the dorsal raphé nucleus (DRN) and locus coeruleus (LC) on depression-relevant behavior in male mice, but DRN GR deletion has not been tested in female mice. Female floxed GR mice were given DRN injections of AAV2/9 pseudotype viral vectors transducing Cre recombinase to produce DRN GR gene deletion (Cre) and compared with mice receiving DRN injections of AAV2/9 transducing green fluorescent protein (GFP). Social interaction, a measure of depression-like withdrawal, was unaffected by DRN GR deletion, but forced swim immobility, a measure of despair-like passivity, was reduced in female Cre vs. GFP mice. Behavioral effects were not attributable to changes in basal corticosterone or LC GR deletion. Combined with our prior studies, the current findings suggest that DRN GR have sex-independent effects to promote forced swim immobility, but influence social interaction only in male mice. Differential effects of DRN GR deletion in female mice may provide insight into the greater incidence of depression and specific depression symptoms in women.

Effects of maternal separation on serotonergic systems in the dorsal and median raphe nuclei of adult male Tph2-deficient mice

Previous studies have highlighted interactions between serotonergic systems and adverse early life experience as important gene x environment determinants of risk of stress-related psychiatric disorders. Evidence suggests that mice deficient in Tph2, the rate-limiting enzyme for brain serotonin synthesis, display disruptions in behavioral phenotypes relevant to stress-related psychiatric disorders. The aim of this study was to determine how maternal separation in wild-type, heterozygous, and Tph2 knockout mice affects mRNA expression of serotonin-related genes. Serotonergic genes studied included Tph2, the high-affinity, low-capacity, sodium-dependent serotonin transporter (Slc6a4), the serotonin type 1a receptor (Htr1a), and the corticosterone-sensitive, low-affinity, high-capacity sodium-independent serotonin transporter, organic cation transporter 3 (Slc22a3). Furthermore, we studied corticotropin-releasing hormone receptors 1 (Crhr1) and 2 (Crhr2), which play important roles in controlling serotonergic neuronal activity. For this study, offspring of Tph2 heterozygous dams were exposed to daily maternal separation for the first two weeks of life. Adult, male wild-type, heterozygous, and homozygous offspring were subsequently used for molecular analysis. Maternal separation differentially altered serotonergic gene expression in a genotype- and topographically-specific manner. For example, maternal separation increased Slc6a4 mRNA expression in the dorsal part of the dorsal raphe nucleus in Tph2 heterozygous mice, but not in wild-type or knockout mice. Overall, these data are consistent with the hypothesis that gene x environment interactions, including serotonergic genes and adverse early life experience, play an important role in vulnerability to stress-related psychiatric disorders.

Circadian regulation of depression: A role for serotonin

Synchronizing circadian (24 h) rhythms in physiology and behavior with the environmental light-dark cycle is critical for maintaining optimal health. Dysregulation of the circadian system increases susceptibility to numerous pathological conditions including major depressive disorder. Stress is a common etiological factor in the development of depression and the circadian system is highly interconnected to stress-sensitive neurotransmitter systems such as the serotonin (5-hydroxytryptamine, 5-HT) system. Thus, here we propose that stress-induced perturbation of the 5-HT system disrupts circadian processes and increases susceptibility to depression. In this review, we first provide an overview of the basic components of the circadian system. Next, we discuss evidence that circadian dysfunction is associated with changes in mood in humans and rodent models. Finally, we provide evidence that 5-HT is a critical factor linking dysregulation of the circadian system and mood. Determining how these two systems interact may provide novel therapeutic targets for depression.

Effects of chronic caffeine exposure during adolescence and subsequent acute caffeine challenge during adulthood on rat brain serotonergic systems

Caffeine is the most commonly used drug in the world. However, animal studies suggest that chronic consumption of caffeine during adolescence can result in enhanced anxiety-like behavioral responses during adulthood. One mechanism through which chronic caffeine administration may influence subsequent anxiety-like responses is through actions on brainstem serotonergic systems. In order to explore potential effects of chronic caffeine consumption on brainstem serotonergic systems, we evaluated the effects of a 28-day exposure to chronic caffeine (0.3 g/L; postnatal day 28-56) or vehicle administration in the drinking water, followed by 24 h caffeine withdrawal, and subsequent challenge with caffeine (30 mg/kg; s.c.) or vehicle in adolescent male rats. In Experiment 1, acute caffeine challenge induced a widespread activation of serotonergic neurons throughout the dorsal raphe nucleus (DR); this effect was attenuated in rats that had been exposed to chronic caffeine consumption. In Experiment 2, acute caffeine administration profoundly decreased tph2 and slc22a3 mRNA expression throughout the DR, with no effects on htr1a or slc6a4 mRNA expression. Chronic caffeine exposure for four weeks during adolescence was sufficient to decrease tph2 mRNA expression in the DR measured 28 h after caffeine withdrawal. Chronic caffeine administration during adolescence did not impact the ability of acute caffeine to decrease tph2 or slc22a3 mRNA expression. Together, these data suggest that both chronic caffeine administration during adolescence and acute caffeine challenge during adulthood are important determinants of serotonergic function and serotonergic gene expression, effects that may contribute to chronic effects of caffeine on anxiety-like responses.

Pathophysiological mechanisms implicated in postpartum depression

This review aims to summarize the diverse proposed pathophysiological mechanisms contributing to postpartum depression, highlighting both clinical and basic science research findings. The risk factors for developing postpartum depression are discussed, which may provide insight into potential neurobiological underpinnings. The evidence supporting a role for neuroendocrine changes, neuroinflammation, neurotransmitter alterations, circuit dysfunction, and the involvement of genetics and epigenetics in the pathophysiology of postpartum depression are discussed. This review integrates clinical and preclinical findings and highlights the diversity in the patient population, in which numerous pathophysiological changes may contribute to this disorder. Finally, we attempt to integrate these findings to understand how diverse neurobiological changes may contribute to a common pathological phenotype. This review is meant to serve as a comprehensive resource reviewing the proposed pathophysiological mechanisms underlying postpartum depression.