Serotonin Synthesis Inhibition by Para-Chlorophenylalanine Impairs Defensive Reactions of Aversive Learning and Long-term Sensitization in Terrestrial Snails

In this paper, we present a study of the effects of reducing serotonin levels by para-chlorophenylalanine (PCPA), an inhibitor of tryptophan hydroxylase, the limiting enzyme in serotonin biosynthesis, on two forms of behavioral plasticity in the terrestrial snail, Helix lucorum: the conditioned defensive reflex food aversion and long-term sensitization. We found that the snails injected with PCPA did not learn the conditioned reflex food aversion, while saline solution injection did not affect the learning process. The latency of consuming one kind of food in these snails was significantly reduced compared to the active control. We also found that PCPA injection prevents the formation of long-term sensitization.