ROLE OF NEUROPEPTIDES ENCODED ON CDCH-1 GENE IN THE ORGANIZATION OF EGG-LAYING BEHAVIOR IN THE POND SNAIL, LYMNAEA-STAGNALIS

Egg laying in the pond snail Lymnaea stagnalis is triggered by a disch arge of the neuroendocrine caudodorsal cells (CDCs). The CDCs expresse s three different caudorsal cell hormone (CDCH) genes. This gene famil y expresses, in total, 11 different peptides among which is the ovulat ion hormone. Besides the CDCs, the CDCH gene family is expressed in ot her central and peripheral neurons. In this study, we investigated the roles the different CDCH peptides play in the organization of egg-lay ing behavior. Egg-laying behavior is a sequence of stereotyped movemen ts in which three phases can be distinguished: resting, turning, and o viposition. We have used the excitation of right pedal N (RPeN) motor neurons as a simple analogue of shell-turning behavior, one of the ele ments of egg-laying behavior. RPeN motor neurons were inhibited during the resting phase of egg laying but were subsequently excited at the onset of and during the turning phase. The excitatory effect could be evoked by application of beta3-CDCP on RPeN motor neurons in the CNS a s well as in isolation but not by the ovulation hormone, alpha-CDCP or Calfluxin, the other CDCH-1 peptides tested. The ovulation hormone it self caused inhibition of RPeN motor neurons. Anti-CDCH-1 positive fib er tracts were found close to the cell bodies and axons of the RPeN mo tor neurons. Electrical stimulation of a nerve that contains these fib ers resulted in excitation of the RPeN motor neurons. The effects of i njection of CDCH-1 peptides into intact animals correlated well with t he effects of these peptides on RPeN motor neurons. Injection of beta3 -CDCP or alpha-CDCP into intact animals resulted in immediate turning behavior in the absence of egg laying itself. The ovulation hormone an d Calfluxin had no immediate effect on the behavior. Furthermore, our data indicate that the individual CDCH-1 peptides act on different tar gets.