Catecholamine, Serotonin, and Substance P-like Peptide Containing Intrinsic Neurons in the Mudpuppy Parasympathetic Cardiac Ganglion

The mudpuppy cardiac ganglion contains 2 neuron types: large parasympathetic postganglionic projection neurons and smaller intrinsic neurons originally described by McMahan and Purves (1976) as intensely fluorescent (SIF) cells. The function of these SIF cells, present in the mudpuppy cardiac ganglion, is unknown. Further, direct application of catecholamines, which are thought to be contained in SIF cells, to the parasympathetic postganglionic cells has no effect (Hartzell et al., 1977). As SIF cells in other ganglion preparations recently have been shown to contain putative transmitter substances in addition to catecholamines, immunocytochemical experiments were conducted to test for the presence of additional transmitter substances in the SIF cells within the cardiac ganglion. Whole-mount septal preparations were dissected from Necturus maculosus and processed for indirect immunocytochemistry. The results indicated that many of these intrinsic neurons contained 5-HT or a substance P-like peptide, or both. Many small intrinsic neurons which contain either substance P or 5-HT were also positive for aqueous-aldehyde-induced fluorescence, indicating the presence of a catecholamine. Finally, some of these cells appeared to contain all 3: a catecholamine, 5-HT, and a substance P-like peptide.