Effects of intrahypothalamic testosterone implants on LHRH levels in the preoptic area and the medial basal hypothalamus.

Following castration LHRH levels in the MBH but not in the POA decreased. Testosterone implants in the medial POA following castration failed to alter the LHRH activity either locally in the POA or in remote sites in the MBH. On the contrary, similar T implants in the MBH blocked castration-induced depletion of MBH LHRH stores without affecting either the POA LHRH content or the post-castration hypersecretion of pituitary LH. These findings identify the MBH as the focal site of T action in the regulation of hypothalamic LHRH activity.