SEX-DEPENDENT EFFECTS OF RESTRAINT ON NOCICEPTION AND PITUITARY-ADRENAL HORMONES IN THE RAT

The sex-dependent effects of acute restraint (RT) on nociceptive and p ituitary-adrenal responses were investigated in the rat. In a first ex periment, the effect of 30 min RT on pain sensitivity was evaluated th rough repeated use of the tail withdrawal test during and after treatm ent. RT induced an increase in the nociceptive threshold, i.e., analge sia, in males and females, but the duration and time-course of this ef fect varied between sexes. The latencies returned to approximately con trol values in females in the second half of RT, but in males they rem ained higher for the whole period of RT and immediately afterwards. Tw enty-four hours later, males displayed longer latencies than controls in response to simple reexposure to the environment. In a second exper iment, ACTH and corticosterone plasma levels were measured immediately after 15 or 30 min of RT. ACTH and corticosterone were higher in rest rained animals than in controls after both periods of treatment, and i n both sexes; however, females showed higher basal and stress corticos terone levels than males. The role played by corticosteroids in the no ciceptive responses of the two sexes is discussed.