Change in number and activation of androgen receptor-immunoreactive cells in the medial amygdala in response to chemosensory input

Abstract

In many species social behaviors are dependent on integration of chemosensory and hormonal cues. Many chemosensory stimuli are detected by the vomeronasal organ, which projects to many regions that contain steroid receptors, including the medial amygdala. In male hamsters, testosterone is known to acutely increase in response to chemosensory stimulation; and can facilitate sexual behavior by direct action within the medial amygdala. Conspecific stimuli activate the anterior (MeA) and posterior (MeP) medial amygdala, while heterospecific stimuli activate only MeA. Chemosensory stimuli with different social significance differentially activate the dorsal and ventral subdivisions of MeA and MeP. Therefore, it is likely that steroids differentially facilitate stimulation of the medial amygdala by various chemosensory stimuli. We used Fos expression to examine activation of androgen receptor (AR)-containing cells in the medial amygdala by heterospecific and conspecific stimuli in intact male hamsters and castrated males with testosterone (T)-replacement. The number of AR-immunoreactive (-ir) cells was significantly different from control and between stimuli in intact males, but not in T-replaced castrates. Fos activation was similar in all animals. The results are consistent with a change in number of AR-ir cells in intact animals due to acute increases in testosterone caused by chemosignals.

Winning agonistic encounters increases testosterone and androgen receptor expression in Syrian hamsters

“…Androgen receptors are abundant in the MeA (Wood and Newman, 1993), and it is well established that they regulate reproduction, aggression, and processing of chemosensory information, but less is known about their role in stress-related behavior (Blake and Meredith, 2011). We have shown the maintenance of dominant social status for two weeks leads to an up-regulation of androgen receptors in the dMeA with a similar trend found in vMeA.…”

Maintenance of dominance status is necessary for resistance to social defeat stress in Syrian hamsters

“…One possible mechanism by which social dominance might modulate neural signaling in the MeA is via androgen receptors. The MeA contains an abundance of androgen receptors [59], and winning agonistic encounters can increase plasma testosterone levels and androgen receptor expression [60, 61]. Altogether, neural activation in the MeA is associated with both increased and decreased defensive behavior, which is likely modulated by neuropeptides and steroid feedback.…”

Morphological and Functional Features of the Sex Steroid-Responsive Posterodorsal Medial Amygdala of Adult Rats

“…This rim was formerly called the ventromedial "molecular" layer [20]. Among other functions, the MeA subnuclei are important for the interpretation of the social relevance of both olfactory and vomeronasal stimuli [21][22][23][24][25]; the response to genitosensorial stimulation, modulation of sexual behavior in males and females, and sexual satiety [9,[26][27][28][29][30][31]; maternal behavior or avoidance of the offspring [32,33]; anxiety and conditioned or innate fear [34,35]; and, emotional processing or neuroendocrine responses to stressful stimuli [36][37][38][39]. The finding that various social behaviors can be modulated by the same MeA subnuclei suggests that local cells integrate different demands from specific pathways.…”

“…The MePD is located within this area. In male hamsters, the number of androgen receptorimmunoreactive cells increases in the MePD after exposure to chemosensory stimuli [51]. Fos-immuno reactivity (Fosir), suggestive of neuronal activation, completely overlaps androgen receptor-immunoreactivity in MePD neurons of male rats that mated to ejaculation [52].…”