COMPARISON OF THE EFFECTS OF BETA-ENDORPHIN AND MORPHINE ON EXPLORATORY AND SOCIO-SEXUAL BEHAVIOR IN THE MALE-RAT

The socio-sexual and exploratory behavior profiles were studied in male rats after intracerebral administration of .beta.-endorphin and morphine. Two social test situations were used, 1 with a sexually receptive female and 1 with a castrated male as the stimulus subject. Time (10-60 min)-response and dose (0.25-5.0 .mu.g)-response relationships were investigated. A dose of 5 .mu. of .beta.-endorphin or morphine decreased exploratory activity and socio-sexual approaches. At lower doses (0.5-1.0 .mu.g) .beta.-endorphin produced a more selective inhibitory effect on copulatory behavior than morphine, which still caused a general depression of both social and sexual behaviors. In contrast to morphine, .beta.-endorphin increased amicable social contacts at a dose (1 .mu.g) which decreased sexual responses. The dissimilarities in morphine and .beta.-endorphin effects suggest involvement of different brain areas or opiate receptors. The particular behavior profiles observed after treatment with .beta.-endorphin indicate the possibility that .beta.-endorphin influences mechanisms implicated in perception or interpretation of environmental stimuli.