| Abstract: | In the present experiment we examined the circadian neural luteinizing hormone releasing hormone (LHRH) and serum luteinizing hormone (LH) response of prepubertal male and female rats under varying steroidal manipulations (Intact, Castrate, Castrate + estradiol 17 beta E2] + oil and Castrate + E2 + progesteroneP]). Prepubertal males demonstrated greater and acyclic LHRH concentrations in both the medial basal hypothalamus (MBH) and preoptic-suprachiasmatic regions (POA-Sch) irrespective of steroid treatment. In steroid-treatment castrated male rats only the negative feedback action on serum LH levels were observed with maximal effect in animals injected with the combination E2 + P. In contrasts, prepuberal castrated females exhibited both inhibitory and stimulatory feedback actions on LH release following steroid treatment. Moreover, a distinctive, significant, progesterone-dependent increase in AM POA-Sch, but not MBH-LHRH concentrations was detected. These results demonstrate the existence of a functional sexual dimorphism in the positive feedback response of the POA-Sch-pituitary axis of prepubertal rats to progesterone treatment. |
