Occurrence, co-occurrence and topographic distribution of choline acetyl transferase, Met-enkephalin and neurotensin in the stellate ganglion of the cat.

The presence of the classical ganglionic transmitter acetylcholine (ACh), its occurrence and possible co-occurrence with the neuromodulator peptides methionine enkephalin (Met-ENK) and neurotensin (NT), as well as the possible coexistence of these peptides in the preganglionic axon terminals of the cat stellate ganglia were investigated with light and confocal microscopy using immunofluorescence. Choline acetyltransferase (ChAT), Met-ENK, and NT immunoreactivity was detected with light microscopy in axon terminals near tyrosine hydroxylase (TH) immunoreactive (IR) cells. Cell bodies immunopositive for ChAT or Met-ENK were also detected and were TH-negative or TH-positive. Denervation by sectioning preganglionic axons produced two effects: the almost complete elimination of IR fibers and an increase in the number of ChATIR and Met-ENKIR cell bodies, together with the appearance of NTIR cell bodies. Preganglionic ChATIR fibers and boutons form a dense network throughout the entire ganglion, with a homogeneous regional distribution. ChAT, Met-ENK, and NT are essentially stored in different nerve endings, although a low level of co-occurrence was detected. NTIR and Met-ENKIR networks of boutons were observed to have independent and somewhat complementary regional distributions. Further analysis with simultaneous triple labeling for NT, Met-ENK, and TH, and confocal microscopy showed fibers and boutons containing Met-ENK or NT reached distinct neurons separately, or both converge onto the same cells. This finding suggests that modulation (the facilitation-inhibition balance) of ganglionic transmission is achieved mainly by the selective and complementary innervation of boutons containing NT (facilitation) and Met-ENK (inhibition) and only rarely by terminals which coexpress both peptides.