The endogenous neuropeptide Phe-Met-Arg-Phe-NH2 directly gates a sodium channel (FaNaC) in Helix aspersa neurones (Green et al 1994). This response is also seen in an identified neurone (Giant Dopamine Neurone) of the pond snail Helisoma trivolvis. The fast response is observed in the isolated GDN as well as in intact ganglia. In situ hybridisation studies have shown the presence of FaNaC mRNA in this neurone (Davey et al 2001).To learn more about the physiological role of FaNaC, antibodies were raised in chickens against different regions of the FaNaC sequences of Helix aspersa and Helisoma trivolvis.Of the five antibodies raised, only one, directed against a region close to the carboxy terminus of the Helisoma trivolvis channel, was suitable for histochemical studies. This antibody was used on wax sections of ganglia and on isolated GDNs maintained in culture.Stained neurones were viewed with a Zeiss Axioclamp, and a Deltavision microscope, with de-convolution software. Specific staining with a FITC-labelled antibody, not observed with pre-immune antibody, peptide-bound antibody, or secondary antibody alone, was clearly observed with neurones in isolation, but less readily in histological sections. The reason for this difference is not clear, but could relate to stimulated expression in isolated neurones, or to more readily observed staining on the exposed membrane surface of isolated neurones. A punctate pattern of staining was observed on the neurone perikaryon, and on neuritic processes where some clustering was seen. The dimensions of the spots of immunofluoresence suggested each comprised a large number of channels. This observation is consistent with patch clamp recordings, where FMRFamideresponsive patches usually contained many active channels (Green at al, 2002). The role of the channels on the perikaryon is not known; few if any synapses are made on the perikarya of snail neurones. Those observed on neurites could represent channels normally involved in pre- or post-synaptic transmission. Further studies are planned to investigate the influence of co-culturing neurones, which may make pre- or post-synaptic junctions with the GDN, on the distribution of channels.