Experimental and Computational Analyses of a Central Pattern Generator Underlying Aspects of Feeding Behaviour of Aplysia

Abstract

Both experimental and computational approaches were used to examine how a circuit of identified neurons in the buccal ganglia of Aplysia functions as a central pattern generator (CPG) controlling aspects of feeding, the ways in which transmitters modulate the electrical activity of this circuit, and the features of consummatory behaviours that are mediated by the various patterns of electrical activity in this CPG. The biophysical properties of neurons B4, B31, B35, B51, B52 and B64, and their synaptic connections were mathematically modelled and simulated using the SNNAP computer program. In the model, brief depolarizations of B31 elicited single cycles of patterned activity in the circuit, and long depolarizations induced sustained patterned activity. The phase relationships, duration and frequency of simulated electrical activity in the network model were very similar to empirical observations and indicated that such a circuit could account for many features of patterned electrical activity in the isolated buccal ganglia. In addition, the possible involvement of catecholamines in regulating activity of this CPG was examined. Dopamine or its metabolic precursor L-3, 4-dihydroxyphenylalanine (DOPA) elicited sustained rhythmic neural activity in isolated buccal ganglia. A newly identified catecholaminergic interneuron, B65, was found to be rhythmically active in presence of DOPA, in response to radula nerve stimulation, as well as during its direct depolarization, which in turn elicited rhythmic activity in the CPG similar to that induced by DOPA. Finally, perfusion of semi-intact preparations with DOPA initiated rhythmic feeding movements indicative of ingestive behaviours.