[A comparison of serotonin- and dopaminergic neuronal systems in sexually mature and juvenile terrestrial mollusks of the genera Helix and Eobania].

The distribution of serotonin- (5-HT) and dopamine- (DA) containing neurons was studied in the brain of adult and juvenile (the first month of life) terrestrial molluscs Helix lucorum and Eobania vermiculata by means of glyoxylic acid fluorescent technique and neurotoxin 5,7-DiHT labelling. The majority of 5-HT-containing cells were grouped in clusters in the pedal ganglia (the median number of cells in a cluster was 213 in Eobania and 155 in Helix). Some cells were described in the cerebral ganglia, visceral and right parietal ganglia. DA-containing neurons were found in the buccal ganglia, cerebral ganglia (there were 6-8 large dorsal cells and about 80 small ventral cells) and pedal ganglia (the median number of cells was 36 in Helix and 12 in Eobania). In juvenile animals of both species the number and distribution of clusters with monoaminergic cells resembled that of the adults. In the juvenile pedal ganglia the number of 5-HT-containing cells was about one fourth of that in adult snails. The number of DA-containing cells in juveniles was the same as in adults in both species. In juvenile snails of both species one big and two medium-sized 5-HT-containing cells were found at the dorsal surface of the cerebral ganglia. Such cells were not revealed in adults. The finding suggests that these cells can change the transmitter phenotype or be transient.