The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 89-97
Copyright ©2001 by the American Physiological Society

Selective Expression of Electrical Correlates of Differential Appetitive Classical Conditioning in a Feeding Network

Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Brighton BN1 9QG, United Kingdom

Jones, Nick, György Kemenes, and Paul R. Benjamin. Selective Expression of Electrical Correlates of Differential Appetitive Classical Conditioning in a Feeding Network. J. Neurophysiol. 85: 89-97, 2001. Electrical correlates of differential appetitive classical conditioning were recorded in the neural network that underlies feeding in the snail Lymnaea stagnalis. In spaced training (15 trials over 3 days), the lips and the tentacle were used as CS+ (reinforced conditioned stimulus) or CS (nonreinforced conditioned stimulus) sites for behavioral tactile conditioning. In one group of experimental animals, touch to the lips (the CS+ site) was followed by sucrose (the unconditioned stimulus, US), but touch to the tentacle (the CS site) was not reinforced. In a second experimental group the CS+/CS sites were reversed. Semi-intact lip-tentacle-CNS preparations were made from both experimental groups and a naive control group. Intracellular recordings were made from the B3 motor neuron of the feeding network, which allowed the monitoring of activity in the feeding central pattern generator (CPG) interneurons as well as early synaptic inputs evoked by the touch stimulus. Following successful behavioral conditioning, the touch stimulus evoked CPG-driven fictive feeding activity at the CS+ but not the CS sites in both experimental groups. Naive snails/preparations showed no touch responses. A weak asymmetrical stimulus generalization of conditioned feeding was not retained at the electrophysiological level. An early excitatory postsynaptic potential (EPSP) response to touch was only enhanced following conditioning in the Lip CS+/tentacle CS group but not in the Tentacle CS+/lip CS group. The results show that the main features of differential appetitive classical conditioning can be recorded at the electrophysiological level, but some characteristics of the conditioned response are selectively expressed in the reduced preparation.