Sex differences in the hypothalamic-pituitary-adrenal axis response following a single or multiple days of sleep restriction.

One in three adults reports experiencing inadequate or disrupted sleep throughout the night, with the incidence being higher in women than in men. Disturbances in nightly sleep result in physiological alterations that contribute to a number of disorders. Poor sleep quality is believed to contribute to the pathogenesis of these disorders through interactions with the hypothalamic-pituitary-adrenal (HPA) axis. The present study investigated the effect of one and three days of restricted sleep on HPA axis reactivity. Male and female C57BL/6J (n = 8/group) mice were sleep-deprived for a 20 h period for one day or three consecutive days using the modified multiple platform method, and then subjected to acute restraint stress. In response to sleep restriction, males showed blunted restraint-induced rises in CORT relative to controls. After three days of restricted sleep, females showed a similar attenuation in restraint-induced CORT. However, this effect was ablated after a single day of sleep restriction. Analyses of gene expression revealed significant elevations in the expression of pituitary HPA axis regulatory genes proopiomelanocortin and corticotropin releasing factor receptor 1 in both sexes following sleep restriction. In males, but not females, adrenal mRNA expression of 11ß-hydroxylase and melanocortin receptor 2 were also increased. Altogether, these data suggest several possible mechanisms are involved in the HPA axis dysregulation following sleep restriction, and that there are sex differences in how the HPA axis responds to sleep loss.Lay summarySleep restriction alters the stress response differently in males and females following varying nights of sleep restriction. These alterations are accompanied by changes in gene expression in the pituitary and adrenal glands.

Differential expression of the immediate early genes c-Fos, Arc, Egr-1, and Npas4 during long-term memory formation in the context preexposure facilitation effect (CPFE).

The context preexposure facilitation effect (CPFE) is a contextual fear conditioning paradigm in which learning about the context, acquiring the context-shock association, and retrieving/expressing contextual fear are temporally dissociated into three distinct phases (context preexposure, immediate-shock training, and retention). The current study examined changes in the expression of plasticity-associated immediate early genes (IEGs) during context and contextual fear memory formation on the preexposure and training days of the CPFE, respectively. Using adolescent Long-Evans rats, preexposure and training day expression of the IEGs c-Fos, Arc, Egr-1, and Npas4 in the medial prefrontal cortex (mPFC), dorsal hippocampus (dHPC), and basolateral amygdala (BLA) was analyzed using qPCR as an extension of previous studies from our lab examining Egr-1 via in situ hybridization (Asok, Schreiber, Jablonski, Rosen, & Stanton, 2013; Schreiber, Asok, Jablonski, Rosen, & Stanton, 2014). In Expt. 1, context preexposure induced expression of c-Fos, Arc, Egr-1 and Npas4 significantly above that of home-cage (HC) controls in all three regions. In Expt. 2, immediate-shock was followed by a post-shock freezing test, resulting in increased mPFC c-Fos expression in a group preexposed to the training context but not a control group preexposed to an alternate context, indicating expression related to associative learning. This was not seen with other IEGs in mPFC or with any IEG in dHPC or BLA. Finally, when the post-shock freezing test was omitted in Expt. 3, training-related increases were observed in prefrontal c-Fos, Arc, Egr-1, and Npas4, hippocampal c-Fos, and amygdalar Egr-1 expression. These results indicate that context exposure in a post-shock freezing test re-engages IEG expression that may obscure associatively-induced expression during contextual fear conditioning. Additionally, these studies suggest a key role for long-term synaptic plasticity in the mPFC in supporting the CPFE.

Alterations in the activation of corticotropin-releasing factor neurons in the paraventricular nucleus following a single or multiple days of sleep restriction.

Sleep disturbances are common among disorders associated with hypothalamic pituitary-adrenal (HPA) axis dysfunction, such as depression and anxiety. This comorbidity may partly be the result of the intersection between the role of the HPA axis in mediating the stress response and its involvement in sleep-wake cyclicity. Our previous work has shown that following 20 h of sleep restriction, mice show a blunting of the HPA axis in response to an acute stressor. Furthermore, these responses differ in a sex-dependent manner. This study sought to examine the effect of sleep restriction on corticotropin-releasing factor (CRF)-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Male and female Crf-IRES-Cre: Ai14 (Tdtomato) reporter mice were sleep restricted for 20 h daily for either a single or three consecutive days using the modified multiple platform method. These mice allowed the visualization of CRF+ neurons throughout the brain. Animals were subjected to acute restraint stress, and their brains were collected to assess PVN neuronal activation via c-Fos immunohistochemistry. Analyses of cell counts revealed an ablation of the restraint-induced increase in both CRF/c-Fos colocalization and overall c-Fos expression in female mice following both a single day and three days of sleep restriction. Males showed an overall decrease in restraint-induced c-Fos levels following a single day of sleep restriction. However, male mice examined after three days of sleep restriction showed a recovery in PVN-CRF and overall PVN neuronal activation. These data suggest the sex dependent dysregulation in CRF function following sleep restriction.

Gut microbiota and metabolic marker alteration following dietary isoflavone-photoperiod interaction.

Introduction: The interaction between isoflavones and the gut microbiota has been highlighted as a potential regulator of obesity and diabetes. In this study, we examined the interaction between isoflavones and a shortened activity photoperiod on the gut microbiome. Methods: Male mice were exposed to a diet containing no isoflavones (NIF) or a regular diet (RD) containing the usual isoflavones level found in a standard vivarium chow. These groups were further divided into regular (12L:12D) or short active (16L:8D) photoperiod, which mimics seasonal changes observed at high latitudes. White adipose tissue and genes involved in lipid metabolism and adipogenesis processes were analysed. Bacterial genomic DNA was isolated from fecal boli, and 16S ribosomal RNA sequencing was performed. Results: NIF diet increased body weight and adipocyte size when compared to mice on RD. The lack of isoflavones and photoperiod alteration also caused dysregulation of lipoprotein lipase (Lpl), glucose transporter type 4 (Glut-4) and peroxisome proliferator-activated receptor gamma (Pparg) genes. Using 16S ribosomal RNA sequencing, we found that mice fed the NIF diet had a greater proportion of Firmicutes than Bacteroidetes when compared to animals on the RD. These alterations were accompanied by changes in the endocrine profile, with lower thyroid-stimulating hormone levels in the NIF group compared to the RD. Interestingly, the NIF group displayed increased locomotion as compared to the RD group. Conclusion: Together, these data show an interaction between the gut bacterial communities, photoperiod length and isoflavone compounds, which may be essential for understanding and improving metabolic health.

Isoflavones Alter Hypothalamic-Pituitary-Adrenal Axis Response Following Photoperiod Alteration.

Photoperiod and diet are factors known to modulate the hypothalamic-pituitary-adrenal (HPA) axis. Specifically, shifts in photoperiod have been previously linked with affective and anxiety disorders. Furthermore, isoflavones have been shown to mediate behavioral outcome in response to the environment of the animal. Here, we investigated the effect of photoperiod alteration on the HPA axis and how the addition of isoflavones might modulate the response to stress. Male C57BL/6J mice were maintained on either a 12:12 or a 16:8 light-dark (LD) cycle for 10 days, and fed a diet of either standard rodent chow or an isoflavone free (IF) chow beginning 3 weeks prior to light alteration. Consistent with previous work, mice in the shorter active period (16:8 LD cycle) showed increased basal corticosterone (CORT) secretion. In the absence of isoflavones, this response was attenuated. Increases in mineralcorticoid (MR) and glucocorticoid (GR) receptor mRNA expression were seen in the pituitary following photoperiod alteration. However, animals fed the standard isoflavone rich chow showed increases in the ratio of MR:GR mRNA in the anterior bed nucleus of the stria terminalis following photoperiod alteration. Decreases in corticotrophin-releasing factor receptor 1 (CRFR1) mRNA expression were seen in animals fed the IF chow in the amygdala, prefrontal cortex and ventral hippocampus. These data suggest that alterations in CORT secretion following photoperiod alteration may be mediated through differences in CRFR1 gene expression or changes in MR:GR mRNA ratios. These findings provide insight into the potential mechanisms by which the HPA axis adapts to photoperiod and diet.