Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. II. Role of the ventral white cell, anterior ventral, and B3 buccal neurons.

Identified buccal neurons in the mollusc Pleurobranchaea were stimulated and recorded intracellularly while recording the resultant identified motor program from buccal muscles (reduced preparation) or nerves (isolated central nervous system). Neurons studied included the ventral white cell (VWC), members of the anterior ventral (AV) population, and interneuron B3. Each of these neurons elicited the egestion motor program or its characteristic components when stimulated intracellularly. The characteristic prolonged plateau potential of the VWC was frequently associated with the egestion motor program but never with the ingestion motor program or its characteristic components. Intracellular recordings from these same neurons during spontaneous or induced buccal motor programs were consistent with the view that these neurons participate in production of the egestion motor program. The VWC discharged also during the neutral buccal rhythm, although in a different pattern from that seen during the egestion motor program, suggesting that it is multifunctional. Synaptic targets of the VWC are unknown, but synaptic influences of the AV and B3 neurons were found and are appropriate to their proposed role in egestion. This study therefore indicates that an interrelated cluster of buccal neurons is specialized to command the egestion motor program.