A NEURONAL NETWORK FROM THE MOLLUSK LYMNAEA-STAGNALIS

The morphology, electrophysiology, and synaptic inputs of a ventrally located neuronal network from the CNS of the pond snail Lymnaea stagna lis was investigated. Three large, previously identified neurons [55] known as right parietal ventral one, two, and three (RPV1,2,&3) were f ound to be electrically coupled to one another. Coupling between eithe r RPV1&2 or RPV1&3 was weak while coupling between RPV2&3 was strong. Consistent bursting activity was observed in neuron RPV1 while neurons RPV2&3 were either silent or fired tonically. When isolated in vitro, similar patterns of activity could be elicited in neurons RPV1-3. Luc ifer yellow staining revealed that these cells send axons through nerv es innervating musculature involved in locomotion, whole-body withdraw al, and cardio-respiratory function. Neurons RPV1-3 were found to be i nhibited by an identified interneuron, visceral dorsal four, known to be directly involved in cardio-respiratory behavior [43]. Furthermore, neurons RPV1-3 were also inhibited by a wide-acting synaptic input, k nown as Input three [9], which is associated with respiratory pattern generation [43]. An interneuron, identified as right pedal dorsal elev en (RPeD11), which coordinates locomotory and withdrawal behavior [44] , was found to excite neuron RPV1. When neurons RPeD11 and RPV1 were i solated in vitro and allowed to extend neurites, they formed a synapti c connection similar to that observed in the isolated brain. In vitro work on these neurons may make them attractive model to study synapse formation and bursting activity.