Short‐day aggression is independent of changes in cortisol or glucocorticoid receptors in male Siberian hamsters (Phodopus sungorus)

Abstract

Testosterone mediates aggression in many vertebrates. In some species, aggression remains high during the non-breeding season (e.g., winter), when testosterone levels are low. In Siberian hamsters (Phodopus sungorus), we have demonstrated photoperiodic changes in aggression with hamsters housed in short, "winter-like" days displaying significantly more territorial aggression than long-day animals, despite low levels of testosterone. The mechanisms by which photoperiod regulates aggression, however, remain largely unknown. Adrenocortical hormones (e.g., glucocorticoids) have been implicated in mediating seasonal aggression; circulating concentrations of these hormones have been correlated with aggression in some species. The goal of this study was to examine the role of cortisol and glucocorticoid receptors in mediating photoperiodic changes in aggression in male Siberian hamsters. Males were housed in long or short days and treated with either exogenous cortisol or vehicle. Circulating levels of cortisol, adrenal cortisol content, and aggression were quantified. Lastly, photoperiodic effects on glucocorticoid receptor (GR) protein levels were quantified in limbic brain regions associated with aggression, including medial prefrontal cortex, amygdala, and hippocampus. Short-day hamsters were more aggressive than long-day hamsters, however cortisol treatment did not affect aggression. Photoperiod had no effect on serum or adrenal cortisol or GR levels in the brain regions examined. Taken together, these data suggest that increases in cortisol levels do not cause increases associated with short-day aggression, and further that GR protein levels are not associated with photoperiodic changes in aggression. The results of this study contribute to our understanding of the role of adrenocortical steroids in mediating seasonal aggression.

Bi‐directional actions of dehydroepiandrosterone and aggression in female Siberian hamsters

“…One alternative hypothesis is that that marked ACTH‐induced increases in CORT concentrations attenuated the actions of elevated DHEA concentrations on aggression (Rendon et al, ). Prior studies have shown that elevated glucocorticoid levels can inhibit aggression in this and other species (Nock and Leshner, ; Leshner et al, ; Wingfield and Silverin, ; Scotti et al, ). Studies that block hormone‐specific enzymatic cascades allowing for differential release of DHEA and CORT concentrations in response to an ACTH challenge could distinguish these likely effects.…”

“…Increased aggression in short‐day‐like animals is blocked by bilateral adrenalectomy (which eliminates both adrenal steroids and catecholamines), but not demedullation (which eliminates catecholamines, leaving adrenal steroids intact) (Demas et al, ). Although these findings suggest a role for adrenal steroids, short‐day aggression is independent of both cortisol (CORT) levels and glucocorticoid receptor expression in hamsters (Scotti et al, ). In contrast, the adrenal androgen DHEA, a steroid that serves as a prohormone and can be converted to biologically active hormones (e.g., T and 17β–estradiol (E 2 )), appears to be a critical regulator of aggression in this and other species (Soma and Wingfield, ; Pradhan et al, ; Scotti et al, ; Rendon et al, ).…”

Dissociation of Puberty and Adolescent Social Development in a Seasonally Breeding Species

“…These include pounces (lunges toward the playmates face or nape), pins (one animal on top, holding its playmate in the supine position), and boxing (both animals standing on their hind legs pushing or batting each other with their forepaws). Offensive aggressive behaviors in Siberian hamsters were typified by rapid strikes/bites typically directed toward the rump and genitals and vigorous chases that usually ended with the subordinate animal in the supine defensive posture [as in 10,11]. Unlike during playful pins, the dominant aggressor did not sustain contact during this supine posture.…”

Abstinence from prolonged ethanol exposure affects plasma corticosterone, glucocorticoid receptor signaling and stress-related behaviors

“…GR expression is 4-fold greater than MR expression in the mPFC, a disproportionately greater ratio than in many other regions associated with the stress response (Cintra et al, 1994; Diorio et al, 1993), and, thus, the mPFC may play a differential role in stress-induced regulation of CORT or behavior, since the GR preferentially responds to elevated glucocorticoid levels. Yet, few studies have investigated the relation between mPFC GR and anxiety- and aggression-like behaviors (Lin et al, 2016; Scotti et al, 2015). Firstly, mPFC GR can modulate physiological stress through negative feedback on the HPA response (Akana et al, 2001; Diorio et al, 1993).…”