SEX STEROID REGULATION OF CHIN-MARKING BEHAVIOR IN MALE NEW-ZEALAND RABBITS

Chin-marking behavior (chinning) was evaluated daily in nine intact ad ult male rabbits. All subjects (Ss) displayed chinning (mean of means +/- SE = 61 +/- 7 marks/10 min) but the frequency of this behavior var ied largely across them (range of mean chinning frequency = 19-84 mark s/10 min). Chinning frequency showed abrupt variations at intervals of 2-3 days, but periodogram analysis did not reveal the existence of an endogenous rhythm in this behavior. Castration significantly decrease d (mean of means +/- SE = 29 +/- 9 marks/10 min; p < 0.01) but did not suppress chinning. Testosterone propionate (TP; 1 mg/day for 16 days) restored chinning in castrated Ss to slightly below precastration lev els (mean +/- S.E. = 53 +/- 13 marks/10 min). The daily administration of 1 mu g estradiol benzoate (EB) plus 1 mg dihydrotestosterone propi onate (DHTP) stimulated chinning within 2 days (mean increase = 147%; p < 0.005). DHTP (1 mg/day) given alone stimulated chinning only after 11 days of treatment (mean increase = 475%; p < 0.01). At higher dose s, both DHTP (10 mg/day) and EB (10 or 50 mu g/day) stimulated chinnin g by 450%, 80%, and 100%, respectively, over baseline values. Results indicate that chinning largely depends on testicular steroids. Androge n receptor occupation by T or DHT, which is enhanced by E, optimally a ctivates chinning.