Effects of synthetic peptides on giant neurones identified in the ganglia of an African giant snail (Achatina fulica Férussac). IV.

1. The previous papers (Ku et al., 1986; Kim et al., 1987; Yongsiri et al., 1987) reported the effects of the synthetic peptides, i.e. Met-enkephalin, substance P, neurotensin, oxytocin, Arg-vasopressin, proctolin, FMRFamide, ranatensin C etc., on about 20 identifiable giant neurones of an African giant snail (Achatina fulica Férussac). 2. In the present study, the effects of the same peptides on the following Achatina neurones, other than those of the previous papers, were investigated: v-RPLN, v-LPSN, v-VNAN, v-VLN, r-VMN, l-VMN, v-l-VOrN and d-RCDN. 3. Of the neurones tested here, v-RPLN (ventral-right parietal large neurone) was excited slightly by Met-enkephalin, excited markedly by oxytocin, and inhibited by FMRFamide, at 10(-4) M. 4. Of these effects, those of oxytocin and FMRFamide were undoubtedly the direct effects on the neurone tested, whereas those of Met-enkephalin were probably due to the synaptic activations. 5. Another neurone, v-LPSN (ventral-left parietal large neurone), was affected by oxytocin and ranatensin C at 10(-4) M. The two substances sometimes showed similar simple excitatory effects, in other cases biphasic (excitation followed by inhibition) effects, and in a few cases almost no effect. 6. The rest of the neurones tested were not sensitive at all to any of the peptides examined.