Social Isolation Modulates CLOCK Protein and Beta-Catenin Expression Pattern in Gonadotropin-Inhibitory Hormone Neurons in Male Rats

Abstract

Postweaning social isolation reduces the amplitude of the daily variation of CLOCK protein in the brain and induces lower reproductive activity. Gonadotropin-inhibitory hormone (GnIH) acts as an inhibitor in the reproductive system and has been linked to stress. Social isolation has been shown to lower neuronal activity of GnIH-expressing neurons in the dorsomedial hypothalamus (DMH). The exact mechanism by which social isolation may affect GnIH is still unclear. We investigated the impact of social isolation on regulatory cellular mechanisms in GnIH neurons. We examined via immunohistochemistry the expression of CLOCK protein at four different times throughout the day in GnIH cells tagged with enhanced fluorescent green protein (EGFP-GnIH) in 9-week-old adult male rats that have been raised for 6 weeks under postweaning social isolation and compared them with group-raised control rats of the same age. We also studied the expression of β-catenin—which has been shown to be affected by circadian proteins such as Bmal1—in EGFP-GnIH neurons to determine whether it could play a role in linking CLOCK in GnIH neurons. We found that social isolation modifies the pattern of CLOCK expression in GnIH neurons in the DMH. Socially isolated rats displayed greater CLOCK expression in the dark phase, while control rats displayed increased CLOCK expression in the light phase. Furthermore, β-catenin expression pattern in GnIH cells was disrupted by social isolation. This suggests that social isolation triggers changes in CLOCK and GnIH expression, which may be associated with an increase in nuclear β-catenin during the dark phase.

The Effects of Alcohol and Social Isolation on Yawning Behavior in Adult Male Rats, Treated with Opioid Receptor Agonist and Antagonist

“…GnIH neuronal activity may point toward a circadian component in the maintenance of regular neuronal activity under chronically stressful conditions, such as that induced by social isolation. Our findings continue to support the long-held consensus on the negative effects of social isolation and provide new insights into circadian regulation of GnIH neuronal activity [23].…”

The Role of GnIH in Biological Rhythms and Social Behaviors

“…Stress exposure increases c-Fos expression in GnIH neurons of the DMH, and direct administration of RFRP-3 induces anxiety-like behavior in rats (120). More recently, social isolation in rats has been shown to disrupt the expression of circadian locomotor output cycles kaput (CLOCK) protein and beta-catenin, a protein known to control the circadian system and implicated in social isolation-induced depression (124). Furthermore, responsiveness of GnIH neurons to serotonin differs in relation to beta-catenin expression levels (125).…”

“…Thus, chronic stress-induced RFRP-3 expression may disrupt circadian rhythmicity via beta-catenin and the serotonergic system (Figure 3). Under chronic stress, clock genes may experience disruption (124), inducing an increase in beta-catenin while lowering neuronal activity (125). Beta-catenin is a vital part of the Wnt signaling pathway-activation of this pathway elevates phospholipase-D1 (126), which is connected with elevated inositol trisphosphate and calcium release (127,128).…”

Influence of mental stress and environmental toxins on circadian clocks: Implications for redox regulation of the heart and cardioprotection

“…There are first hints that social isolation in mice may influence the circadian clocks. For instance, post‐weaning social isolation (for 6 weeks starting at the age of 3 weeks), changed the pattern of CLOCK expression in gonadotropin‐inhibitory hormone neurons in the dorsomedial hypothalamus (Teo, Soga, & Parhar, 2017). Social isolation in adult mice led to decrease of mouse activities, phase advance of rhythm and down‐regulation of clock gene expression (Yu et al, 2018).…”