Cellular and molecular mechanisms of different memory phases after single-trial classical conditioning in Lymnaea

An in vitro conditioning paradigm was developed to investigate the different phases of memory leading to associative long-term memory formation in the feeding system of the pond snail, Lymnaea stagnails. Using a one-trial chemical conditioning paradigm, a paired application of the CS (amyl acetate) and US (sucrose) to the lips/oesophagus in a semi-intact preparation was carried out. The conditioned response was measured as an increase in the frequency of fictive feeding cycles in feeding motoneurons following application of the CS to the lips. The time course of expression of the memory trace from 10 min to 4 hr after conditioning was followed. Importantly, the expression of the in vitro memory trace was shown to be intermittent unlike the one observed in behavioural experiments that was continuous. The in vitro memory trace was detected at 10 min, 1 hr and up to 4hr but not at 30 min and 2 hr. Protein synthesis was required for the expression of a memory trace from 1 hr after raining and for later time points, but not at 10 min. This result suggests a correspondence between the inability to detect an in vitro memory trace at 30 min and the transition from a protein independent mechanism for memory expression to a protein-dependent one. Experiments using RNA-synthesis blockers have shown a requirement for de novo synthesis of RNA from 4 hr after training and onward. Based on in vitro and in vivo data, a model for associative conditioning is presented, suggesting the presence of a short-term memory trace at 10 min after conditioning (protein synthesis and RNA synthesis-independent), an intermediate-term memory trace at 1-3 hr after conditioning (protein synthesis-dependent, RNA synthesis-independent) and a long-term memory trace (protein synthesis-dependent, RNA synthesis-dependent) at 4 hr and up to 24 hr after conditioning.EThOS - Electronic Theses Online ServiceGBUnited Kingdo