Neurons with different immunoreactivity form clusters in the CNS of Helix pomatia

The distribution of serotonin (5HT-ir), FMRF amide (FMRF a-ir), catch-relaxing-peptide (CARP-ir), dopamine (DA-ir), gamma-amino-butyric-acid (GABA-ir), and leucokinin (LK-ir) immunoreactive neurons were compared in the ganglia of Helix CNS. These neurons are not distributed randomly, but their location outlines distinct groups in the ganglia. In a few groups only DA-ir, GABA-ir and LK-ir neurons can be seen, whereas in the majority of groups FMRFa-ir, CARP-ir and 5HT-ir neurons are localized together. In the latter groups of immunoreactive neurons either FMRFa- and CARP- or 5HT- and FMRFa-immunoreactivities coexist in numerous neurons. Immunoreactive groups composed of DA-ir, GABA-ir and LK-ir neurons are localized exclusively in the areas of the origin of skin nerves, suggesting that these neurons are related to the processing of cutaneous afferent information. Other groups constituted by 5HT-ir, FMRFa-ir and CARP-ir neurons are localized first of all in ganglia the neurons of which innervate large masses of muscle fibers. The primary role of these neurons in motor/efferent processes is assumed.