REDUCED BINDING OF OXYTOCIN IN THE RAT-BRAIN DURING AGING

Central oxytocin (OT) receptors were labelled in 3-month-old and 20-mo nth-old rats with an iodinated OT antagonist. Comparison of the autora diograms by quantitative image analysis revealed in the old animals a significant reduction of binding in three regions; the number of label led OT receptors was decreased by 90% in the head of the caudate putam en, by 68% in the olfactory tubercle, and by 41% in the ventromedial h ypothalamic nucleus. Previous studies had shown that the expression of OT receptors in the olfactory tubercle and in the ventromedial hypoth alamic nucleus was dependant upon gonadal steroids. Therefore we hypot hesize that the reduced number of OT receptors in the latter two struc tures of aged rats was the consequence of the 4-fold decrease of plasm a testosterone that we found in this age. Another mechanism may be res ponsible for the marked reduction of OT receptors in the caudate putam en.