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

In this study we examined changes in a persistent sodium current (INaP) 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, INaP was activated and measured in identified body withdrawal interneurons RPa3 and LPa3. We show here that in preparations from conditioned animals INaP 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 INaP in withdrawal interneurons, suggesting that aversive classical conditioning affects sodium channel expression at the transcriptional level.