Analysis of memory formation and readout in the slug

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Slugs perform odor-taste associative learning, and the present work was aimed at clarifying the mechanisms of odor learning using physiological and molecular biological methods. A high frequency stimulation of the lip nerve, which is an in vitro analog of the unconditioned stimulus, caused an increased frequency in the local Meld potential oscillation in the procerebrum (PC), as well as excitation of the bursting PC neurons and inhibition of the nonbursting PC neurons. As the nonbursting neurons are thought to be the principal neurons of the PC and may mediate output of information from the PC to other brain regions, these results suggest that output of information from the PC is decreased during conditioning. A high frequency stimulation of the tentacle nerve resulted in a potentiation of the evoked potential in the PC, which lasted for more than 2 h. Such plastic changes in the efficacy of synaptic transmission in the PC may be involved in odor learning.Injection of the protein synthesis inhibitors anisomycin or cycloheximide impaired memory retention after 2-7 days alter conditioning, indicating that protein synthesis is necessary for the retention of long-term memory. We further explored genes induced by the odor-taste associative conditioning using the PCR-differential display method in the brains from paired and unpaired conditioned animals. Using 100 pairs of random primers, 12 bands showed a reproducible induction pattern, and partial sequences of 8 genes were cloned.