THE NEURAL CONTROL OF EGG-LAYING BEHAVIOR IN THE POND SNAIL LYMNAEA-STAGNALIS - MOTOR CONTROL OF SHELL TURNING

Behavioural and neurophysiological techniques were used to study the n euronal control of shell turning during egg-laying in the pond snail L ymnaea stagnalis. Egg-laying consists of three phases: resting, turnin g and oviposition, and is triggered by an electrical discharge in a gr oup of neuroendocrine cells, the caudodorsal cells. During the dischar ge, several peptides encoded on two CDCH genes are known to be release d. Behavioural experiments in which different combinations of nerves w ere lesioned indicated that the inferior cervical nerves are necessary for turning behaviour to occur. The right inferior cervical nerve inn ervates the right dorsal longitudinal muscle and contains axons of neu rones that are active just prior to, and during, shell movements in fr eely behaving animals. These axons are probably the axons of motor neu rones. The motor neurones of the dorsal longitudinal muscle were ident ified in the cerebral A and pedal N clusters. We have demonstrated tha t there is a correlation between the state of excitability of the caud odorsal cells and the electrical activity of the pedal N motor neurone s. Our results indicate that the pedal N motor neurones are involved i n executing the turning phase during egg-laying.