Effect of oligopeptides containing L-Phe, L-Tyr, L-Trp, L-His or L-Met on the excitability of the 2 giant neurons of the African giant snail (Achatina fulica Ferussac)]

Effects of about ninety oligopeptides, containing L-Phe, L-Tyr, L-Trp, L-His and L-Met, on the excitability of two identifiable giant neurones (the PON, periodically oscillating neurone ; and the TAN, tonically autoactive neurone) of Achatine fulica Férussac were examined. Three oligopeptides, L-Lys-L-Phe-L-Tyr, L-Phe-L-Tyr and L-Phe-L-Trp, showed an inhibitory effect on the PON. However, this effect on the PON was weaker than that of the same three peptides on the TAN. [The latter has been reported in previous papers (1 to 3)]. Besides the three oligopeptides mentioned, four peptides, L-Phe-L-Phe, L-Phe-L-Phe-L-Phe, L-Tyr-L-Tyr and L-Tyr-L-Tyr-LTyr, still showed a weak inhibitory effect on the TAN in a high concentration.