ACTH-like immunoreactivity in two electronically coupled giant neurons in the pond snail Lymnaea stagnalis.

Two giant neurons (diameter 130 micron) were identified immunocytochemically by means of the unlabeled antibody enzyme technique with anti-ACTH 1-39 and 1-24 in the pond snail Lymnaea stagnalis. The cells are located in the visceral and the right parietal ganglion, respectively. They contain moderately electron dense elementary granules (diameter 150-160 nm). By means of the intracellular horseradish peroxidase injection technique it was shown that the cells send fibres into the neuropiles of various ganglia and into nerves. Synapses occur on the fine fibre branches in the neuropile. Synapse-like structures were found on the cell bodies and on the major fibres. The giant neurons are electrotonically coupled. With toluidine blue staining for small peptides it was demonstrated that in the central nervous system of the pond snail numerous peptidergic neurons occur in addition to those identified with the classical staining methods for neurosecretion.