Postsynaptic mechanism of withdrawal reflex sensitization in the snail.

Repeated tactile stimulation of the skin evoked sensitization and subsequent habituation of a behavioral avoidance reaction of pneumostome closure in the land snail, Helix lucorum L. Spike responses in putative command neurons for avoidance behavior increased and subsequently decreased parallel to behavioral events. Decrease of spike responses in command neurons was due to decreased synaptic input evoked by repeated tactile stimulation. Intracellular investigation of the increase in the spike response in command neurons for pneumostome closure, which underlies behavioral sensitization, revealed a synpatically-evoked, long-lasting depolarization. No conductance changes during this depolarization were found, but neuronal excitability was altered.