Smail_2017_Brain.Res.Bull_137_23

Central cholinergic systems regulate the hypothalamic-pituitary-adrenal (HPA) axis differentially in males and females (sexual diergism). We previously investigated the role of muscarinic receptors in this regulation by administering physostigmine (PHYSO), an acetylcholinesterase inhibitor, to male and female rats pretreated with scopolamine (SCOP), a nonselective muscarinic antagonist. SCOP pretreatment enhanced adrenocorticotropic hormone (ACTH) and corticosterone (CORT) responses in both sexes; males had greater ACTH responses while females had greater CORT responses. In the present study, we further explored the role of muscarinic receptor subtypes in HPA axis regulation by administering PHYSO to male and female rats following SCOP or various doses of either the M1 or the M2 selective muscarinic receptor antagonists, pirenzepine (PIREN) or methoctramine (METHO), respectively. Blood sampling occurred before and at multiple times after PHYSO. ACTH and CORT were determined by highly specific immunoassays. PIREN+PHYSO resulted in sustained, dose-dependent increases in ACTH and CORT: ACTH responses were similar in both sexes, CORT responses were greater in females, and percent changes from baseline for both hormones were greater in males. METHO+PHYSO resulted in overall decreases in ACTH and CORT: ACTH and CORT responses were higher in females but lower than those caused by PIREN or SCOP in both sexes, and percent changes from baseline were lower in males. Area under the curve analyses further supported these sexually diergic effects. These results suggest that specific muscarinic receptor subtypes differentially influence the HPA axis in a sexually diergic manner.