CENTRAL GENERATION AND COORDINATION OF A COMPLEX BEHAVIORAL SEQUENCE IN APLYSIA CALIFORNICA: LOCOMOTION AND RESPIRATORY PUMPING.

摘要

Early work on the cellular mechanisms of behavior in Aplysia focussed primarily on simple reflex behaviors. To explore neuronal generation of more complex behaviors, I examined two interrelated behaviors, locomotion and respiratory pumping.;I next developed a semi-intact preparation which exhibited locomotion and respiratory pumping and permitted simultaneous intracellular recording from central neurons. In the symmetric pedal ganglia, I identified two groups of motorneurons and a unique parapodial motorneuron. These neurons receive cyclic input during locomotion and synchronous input during respiratory pumping.;To examine whether locomotion is generated by a central program, I cut all peripheral nerves while maintaining intracellular penetrations: in the isolated ganglia motorneurons maintained cyclical activity comparable only to that of locomotion. I next examined respiratory pumping to elucidate its interganglionic integration. Respiratory pumping is generated by an electrically coupled group of abdominal ganglion neurons, known as Interneuron II. Preventing the output of Interneuron II from reaching pedal ganglion neurons abolishes all synaptic input to the pedal ganglion neurons during respiratory pumping. I identified a major contributor to this input, Interneuron XXI, and traced its projection to the pedal ganglia. I also found that during locomotion phasic signals descend the connectives to entrain the burst generator of respiratory pumping.;In summary, I report a behaviorally relevant identification of neurons in the Aplysia pedal ganglia. These neurons participate in locomotion and respiratory pumping, two complex interrelated behaviors. Using these neurons, I have demonstrated that locomotion is based on a central program and established some of the mechanisms by which locomotion and respiratory pumping are combined into an integrated behavioral sequence.;Videotape analysis of intact animals demonstrated alternating waves of circumferential constriction and longitudinal contraction during pedal locomotion with coordinated parapodia, gill, and siphon activity, and forceful synchronous contraction of gill, siphon, and parapodia during respiratory pumping. Sectioning the pleuroabdominal connectives disrupted these behaviors: post-operative animals locomoted without coordinated gill and siphon activity and produced respiratory pumping without associated parapodial activity. This result demonstrated that locomotion is controlled by the circumesophageal ganglia and respiratory pumping by the abdominal ganglion: their integration requires intact connectives.