COMPARISON OF SEROTONIN AND DOPAMINE NEUR AL SYSTEMS IN ADULT AND JUVENILE TERRESTRIAL SNAILS HELIX AND EOBANIA

The distribution of serotonin- (5-HT) and dopamine- (DA) containing ne urons 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 clus ters 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 ce rebral ganglia, visceral and right parietal ganglia. DA-containing neu rons were found in the buccal ganglia, cerebral ganglia (there were 6- 8 large dorsal cells and about 80 small ventral cells) and pedal gangl ia (the median number of cells was 36 in Helix and 12 in Eobania). In juvenile animals of both species the number and distribution of cluste rs with monoaminergic cells resembled that of the adults. In the juven ile pedal ganglia the number of 5-HT-containing cells was about one fo urth of that in adult snails. The number of DA-containing cells in juv eniles was the same as in adults in both species. In juvenile snails o f 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 chan ge the transmitter phenotype or be transient.