Food-aversive classical conditioning increases a persistent sodium current in molluscan withdrawal interneurons in a transcription dependent manner

Abstract

In this study we examined changes in a persistent sodium current ( I NaP) after behavioral aversive classical conditioning in the snail Helix pomatia. We trained animals by pairing food with a mild electric shock that triggered the whole-body withdrawal reflex. This aversive training resulted in transcription dependent long-term associative memory. Isolated central nervous system preparations were set up from trained, random control and naive animals and using two-electrode voltage clamp methods, I NaP was activated and measured in identified body withdrawal interneurons RPa3 and LPa3. We show here that in preparations from conditioned animals I NaP is increased, suggesting that modifications in intrinsic cellular properties contribute to the formation of the memory trace. Blocking RNA synthesis by systemic injection of actinomycin D (0.12 μM) suppressed both memory consolidation in intact animals and the learning-induced increase of I NaP in withdrawal interneurons, suggesting that aversive classical conditioning affects sodium channel expression at the transcriptional level.