Dopaminergic synapses mediate neuronal changes in an analogue of operant conditioning

Feeding behavior in Aplysia can be modified by operant conditioning in whic h contingent reinforcement is conveyed by the esophageal nerve (E n.). A ne uronal analogue of this conditioning in the isolated buccal ganglia was dev eloped by using stimulation of E n. as an analogue of contingent reinforcem ent. Previous studies indicated that E n. may release dopamine. We used a d opamine antagonist (methylergonovine) to investigate whether dopamine media ted the enhancement of motor patterns in the analogue of operant conditioni ng. Methylergonovine blocked synaptic connections from the reinforcement pa thway and the contingent-dependent enhancement of the reinforced pattern. T hese results suggest that dopamine mediates at least part of the neuronal m odifications induced by contingent reinforcement.