FUNCTIONAL-ROLE OF PEPTIDERGIC ANTERIOR LOBE NEURONS IN MALE SEXUAL-BEHAVIOR OF THE SNAIL LYMNAEA-STAGNALIS

A morphologically defined group of peptidergic neurons in the CNS of t he hermaphroditic snail, Lymnaea stagnalis, is concerned with the cont rol of a very specific element of male sexual behavior. These neurons are located in the anterior lobe of the right cerebral ganglion (rAL). By using chronically implanted electrodes, we show that the rAL neuro ns are selectively active during eversion of the penis-carrying struct ure, the preputium. The preputium is normally contained inside the bod y cavity and is everted during copulation in the male role. Electrical stimulation of the rAL neurons through the implanted electrodes, indu ced eversion of the preputium in vivo. Injection of APGWamide (Ala-Pro -Gly-Try-NH2), a small neuropeptide that is present in all rAL neurons , induced eversion of the preputium. Application of APGWamide to in vi tro preparations of the preputium caused relaxation of this organ. In contrast, injection of the neuropeptide conopressin, which is co-local ized with APGWamide in 60% of the rAL neurons, did not induce any beha vior associated with male sexual activities. These results show that t he neurons of the rAL can induce an eversion of the preputium as occur s during male copulation by release of APGWamide during a period of el ectrical activity.