Differences in the Molecular Mechanisms of Long-Term Synaptic Facilitation in Associative Learning and Sensitization

Abstract

Studies on defensive behavior command neurons Lpl1 and Rpl1 in common snails addressed the involvement of translation and transcription processes in the mechanisms of synaptic plasticity during acquisition of conditioned taste aversion. In control snails, combinations of the taste stimulus (carrot juice) and the reinforcing stimulus (concentrated quinine solution) led to changes in neuron responses characteristic for both conditioning and concomitant sensitization. Facilitation of responses to a sensory chemical stimulus (dilute quinine solution) occurred 1 h after training started, with facilitation of reactions to the conditioned food stimulus occurring at 1.5 h. Application of the protein synthesis inhibitor cycloheximide during conditioning suppressed facilitation of responses to both dilute quinine solution and the conditioned food stimulus. However, application of the RNA synthesis inhibitor actinomycin D to neurons produced selective suppression of synaptic facilitation in responses to sensory stimulation with dilute quinine solution, but had no effect on synaptic facilitation in responses to the conditioned stimulus. It is suggested that the acquisition of conditioned taste aversion in snails induces long-term synaptic facilitation in nerve cells Lpl1 and Rpl1 typical of conditioning and sensitization processes, whose induction requires different molecular-genetic mechanisms.