Interacting Premotor Networks Mediating Behavioral Selection in the Predatory Marine Snail Pleurobranchaea Californica

148 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1998.The role of premotor neurons in behavioral selection was examined in the mollusc, Pleurobranchea californica, by identifying elements mediating escape swimming and avoidance turning, and by documenting interactions among these and other neurons.Escape swimming in Pleurobranchaea is a rhythmic series of alternating dorsal and ventral body flexions driven by a central pattern generator (CPG) in the cerebropleural ganglion. The CPG is composed of at least eight interneurons whose activities are both phase-locked to and affect CPG output. The dorsal flexion phase is mediated by a coupled ensemble of four serotonin-immunoreactive neurons, the As1, As2, As3, and As4, and an electrically coupled pair, the A1 and A10 cells. Ventral flexion is mediated by at least two cells, the A3 cell and the yet unlocated ventral swim interneuron, $\rm I\sb{vs}.$ As1-4 also act as intrinsic neuromodulatory excitors in the swim CPG. A10 acts as a command element with the ability to drive swimming motor output. CPG output pattern is sustained by recurrent excitation among As1-4 and between them and A1/A10, recurrent inhibition from A1/A10 to $\rm A3/I\sb{vs},$ and reciprocal inhibition between As1-4 and $\rm I\sb{vs}.$ Similarity in CPGs of Pleurobranchaea and the mollusc Tritonia suggests strong conservation in CPG structure and function.Avoidance turning, mediated by longitudinal muscle bands, depends on at least two premotor neuron types. The activity of A4, which only responds to ipsilateral stimuli, is necessary for turning. The ensemble As1-4, sensitive to bilateral stimuli, supports prolonged bursting in A4 during turning.The swim network acts upon the feeding network. A1 activity suppresses feeding motor output both in whole animals and the isolated CNS by inhibiting the feeding command neurons, the phasic paracerebral neurons $\rm(PC\sb{P}s).$ Other non-serotonergic swim CPG interneurons and a commissural interneuron, A-ci1, also inhibit the $\rm PC\sb{P}s$ and other feeding network neurons. The As1-4 may contribute to general behavioral arousal by monosynaptically exciting other serotonergic neurons of feeding (e.g., the MCG) and locomotor networks.These results suggest that premotor neurons may have distinct multifunctional or dedicated roles in behavioral selection. Multifunctional neurons like As1-4 may excite multiple networks, whereas one role for dedicated network neurons is to exclude incompatible behavior by inhibiting other appropriate premotor neurons.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD