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Effects of neuropeptides proposed as neurotransmitters of mammals and invertebrates and those of natural toxins, etc., on the identifiable giant neurones of an African giant snail (Achatina fulica Férussac) were examined. Oxytocin had a tendency to show the excitatory effects; this substance was excitatory on five neurones and inhibitory on one neurone. A substance related to oxytocin, vasotocin, also showed excitatory effects on the three neurones. On the other hand, FMR Famide was inhibitory on six neurones. Proctolin had excitatory effects on only one neurone.

Following the previous works, we identified recently the twelve giant neurones in the ganglia of an African giant snail (Achatina fulica Férussac), by the pharmacological study of their sensitivities to putative neurotransmitters and derivatives, and by the morphological investigation of their axonal pathways due to the intracellular injection of Lucifer Yellow. The neurones studied were: TAN-2, TAN-3, BAPN, LPPN, LBPN and LAPN in the right parietal ganglion; RPeNLN and LPeNLN in the pedal ganglia; and d-LBAN, d-LBMN, d-LBCN and d-LBPN in the left buccal ganglion.