Effects of the Serotonin Precursor 5-Hydroxytryptophan and the Neurotoxic Analog 5,7-Dihydroxytryptamine on the Formation of a Conditioned Defensive Reflex in the Common Snail

We report here our studies on the effects of the metabolic serotonin precursor 5-hydroxytryptophan and the neurotoxic analog 5,7-dihydroxytryptamine on the acquisition of a conditioned defensive reflex and post-training electrophysiological parameters of defensive behavior command neurons in snails. Injections of 5-hydroxytryptophan into snails via the sinus node led to acceleration of the acquisition of the conditioned defensive reflex. Snails injected with 5,7-dihydroxytryptamine did not form the conditioned reflex; subsequent injection of 5- hydroxytryptophan prevented this blockade. While 5-hydroxytryptophan prevented the action of 5,7-dihydroxytryptamine at the behavioral level, no such effect was seen at the level of the electrical properties of command neurons.