Pituitary Adrenal Axis Activity in the Male Libyan Jird, Meriones libycus: Seasonal Effects and Androgen Mediated Regulation

Many wild species exhibit seasonal cycles of testicular and adrenal functions suggesting important interrelationships between the two. However, data on desert rodents are very scarce. We investigated the pituitary adrenal (PA) axis activity of the Libyan jird from the Sahara desert, during the breeding and the non-breeding seasons. We explored, during the breeding season, the effects induced by orchidectomy and testosterone replacement (75 μg/40 μl sesame oil/100g BW). We found that the PA axis is more active during the non-breeding season and after orchidectomy with high ACTH and cortisol plasma concentrations (P<0.05). In the quiescent period, adrenal cells were hypertrophied in all cortical zonae (P<0.05), while orchidectomized jirds had thin zona fasciculata and thick zona reticularis with hypertrophied cells. Testosterone reduces the activity of the PA axis, probably by acting in the brain and/or pituitary. Here, we found that testosterone treatment led to a significant decrease in adrenocorticotropin levels together with structural remodeling of the adrenal cortex; analysis of androgen receptor (AR) densities in the adrenal cortex suggests that the AR mediates the direct effect of testosterone on adrenocortical morphology. This action may allow for homeostatic adjustments to occur, increasing individual fitness under extreme conditions in which this Saharan rodent species lives.