Comparison of aversive and reward one-trial classical conditioning in the Lymnaea feeding system

We previously developed a one-trial reward classical conditioning paradigm using amyl-acetate as the conditioned stimulus (CS) and sucrose as the unconditioned stimulus (US), to study the electrical and molecular changes underlying long-term memory formation in the feeding system of the pond snail Lymnaea. Here, we compare the features of one-trial reward conditioning with an alternative aversive conditioning paradigm where quinine was used as the US while the CS was the same (amyl acetate) as in reward conditioning. Here, a single pairing of CS and US led to aversive conditioning. An electrophysiological correlate of both types of conditioning was measured in semi-intact preparations. The same CS caused excitation or inhibition depending on the type of the training. The source of the inhibition in case of aversive conditioning appears to be in non-feeding ganglia in the rest of the brain. Our results indicate that the same CS can trigger alternative responses depending on the type of training (US). These two types of responses involve different pathways within the CNS. The sensitivity of the aversive and appetitive memory trace to NO, dopamine and octopamine blockers was also studied. We established that while NO and dopamine are important in the development of a long-term appetitive memory trace at an early stage after conditioning they do not play a role in aversive memory formation. Octopamine, on the other hand is not needed for appetitive memory formation, but seems to be the key transmitter needed shortly after aversive training.