A proposed GABAergic pathway in the feeding neural network is associated with learning performance in conditioned taste aversion in Lymnaea

Conditioned taste aversion (CTA) provides a useful model for investigating the neural mechanisms underlying long-term memory (LTM). In Lymnaea stagnalis, CTA can be induced by pairing sucrose, which initially elicits feeding responses, with KCl, which suppresses feeding responses. Following such conditioning, snails exhibit a long-lasting reduction in feeding responses to sucrose, reflecting the formation of CTA-LTM. In the present study, however, individual snails exhibited marked variability in CTA-LTM performance. We therefore analyzed behavioral differences among learner phenotypes and examined how pharmacological manipulation of GABAergic signaling during CTA training influences learning performance. Behavioral analyses revealed that learner phenotypes were associated with differences in feeding responses to sucrose before training. External application of the GABAA receptor antagonist bicuculline significantly increased the proportion of good learners. Based on the present findings together with previous results, we propose a working model incorporating a putative GABAergic pathway within the feeding neural network, possibly involving the cerebral giant cell (CGC), and suggest that this pathway may be associated with individual differences in learning performance. Although the precise neural mechanisms remain to be determined, the present study provides a framework for understanding how GABAergic signaling contributes to CTA-LTM formation and individual variation in learning performance.