Distribution of monoamines within the central nervous system of the juvenile pulmonate snail, Achatina fulica.

The distributions of serotonin and catecholamines were examined within the central ganglia of juvenile Achatina through the histological localization of serotonin-like immunoreactivity and of glyoxylic acid-induced fluorescence. Somata containing these amines were widely distributed throughout all central ganglia except the two pleural ganglia and the left parietal ganglion. Most catecholaminergic neurons were very small (5-10 microns in diameter) and located in clusters in the cerebral and pedal ganglia, although a few, somewhat larger catecholaminergic neurons were also scattered throughout other locations. Catecholamines also appeared to be heavily concentrated in certain neuropilar regions of the central ganglia. Serotonergic neurons were generally much larger than the catecholaminergic neurons, and some of these somata reached relatively large sizes (up to 50-70 microns in diameter). The majority of serotonergic cells were located in the pedal ganglia but major populations were also located in the paired cerebral, the right parietal and the visceral ganglia. Several of the serotonergic cells could be reliably recognized as distinct individuals which appear to be identical to those described in previous studies. Among the previously identified cells which appear to contain serotonin are v-RCDN ad v-LCDN (the right and left metacerebral giant cells) of the cerebral ganglia, d-LPeLN of the left pedal ganglion, and TAN, TAN-2, and TAN-3 of the right parietal ganglion. Comparisons are drawn with general distribution patterns of monoamines and with identified monoaminergic cells and cell populations found in other gastropod species.