TESTICULAR HORMONES DO NOT REGULATE SEXUALLY DIMORPHIC PAVLOVIAN FEARCONDITIONING OR PERFORANT-PATH LONG-TERM POTENTIATION IN ADULT MALE RATS

We recently reported that Pavlovian fear conditioning and hippocampal perforant-path long-ten potentiation (LTP) are sexually dimorphic in r ats. Males show greater contextual fear conditioning, which depends on the hippocampus, as well as greater hippocampal LTP. In order to exam ine the role of circulating gonadal hormones in adult male rats, anima ls were castrated in two experiments, and Pavlovian fear conditioning and in vivo perforant-path LTP were examined. It was found that sexual ly-dimorphic LTP and fear conditioning are not regulated by the activa tional effects of testicular hormones in adult male rats. That is, in every respect, castrated male rats were similar to intact male rats in Pavlovian fear conditioning and hippocampal LTP. It is likely that se xual dimorphism in this system is established earlier in development b y the organizational effects of gonadal hormones. (C) 1998 Elsevier Sc ience B.V. All rights reserved.