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The relationships of immunoreactive neuropeptide Y, enkephalin and tyrosine hydroxylase, on the one hand, and acetylcholinesterase histochemical activity, on the other, were studied in human lumbar sympathetic ganglia. Two thirds of the ganglion cells contained immunoreactive neuropeptide Y. Electron microscopically the immunoreaction was localized in the Golgi apparatus and in large dense-cored vesicles in the nerve endings. Most of the neuropeptide-containing neurons and nerve fibres were also reactive for tyrosine hydroxylase. Nerve fibres reactive for neuropeptide Y were found around ganglion cells regardless of their transmitter contents, whereas enkephalin-reactive nerve terminals surrounded only acetylcholinesterase-containing neurons. The results demonstrate that neuropeptide Y is colocalized with noradrenaline in most of the human sympathetic neurons and that the nerve fibres may innervate selectively the noradrenergic and cholinergic subpopulations of ganglion cells depending on the transmitters of the nerves.

The localization of bombesin- (BOMB) and enkephalin- (ENK) immunoreactive (IR) nerves was studied in rat coeliac-superior mesenteric ganglion complex in relation to neuropeptide Y (NPY)- and tyrosine hydroxylase (TH)-immunoreactive neurons with an immunofluorescence double-staining method. Very dense networks of BOMB-IR nerve terminals surrounded the majority of the principal ganglion cells, whether or not they were TH-IR. BOMB-IR nerves were specifically related to the non-NPY-IR neurons. Moderately dense networks of ENK-IR fibers were unevenly distributed among the ganglion cells. Majority of these neurons exhibited TH-IR and some of them also contained NPY-IR. In sections double stained with antibodies to ENK and BOMB some nerve fibers contained both peptides. The findings suggest that BOMB-IR nerves, which have been previously demonstrated to originate from gut, control the function of non-NPY-IR ganglion cells. ENK-IR nerves apparently control the adrenergic neurons which project to gut and also some NPY-IR vasomotoric neurons. The finding that ENK- and BOMB-IR coexist in some nerves suggests that some ENK-IR nerves may originate from gut, although the major part probably represents preganglionic fibers originating from spinal cord.

Vasoactive intestinal peptide immunoreactive (VIP-IR) nerve fibres and terminals, neurons and small granule containing cells were observed in human lumbal sympathetic ganglia. Electron-microscopically VIP-IR was localized in the large dense-cored vesicles in nerve terminals and on the membranes of the Golgi complexes in the neurons. A small population of principal ganglion cells was surrounded by VIP-IR nerve terminals. Most of these neurons contained acetylcholinesterase (AChE) enzyme but were not tyrosine hydroxylase-immunoreactive (TH-IR). All VIP-IR ganglion cells and most of the nerve fibres contained AChE but not TH-IR. It appears that in human sympathetic ganglia VIP is localized in the cholinergic neurons and nerve fibres and that the VIP-IR nerve terminals innervate mainly the cholinergic subpopulation of the sympathetic neurons.

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The localization of somatostatin-like immunoreactivity (SOM-LI) was examined in human lumbar sympathetic ganglia using the peroxidase-antiperoxidase method. Few of the principal neurons showed immunolabelling for somatostatin and sparse networks of nerve terminals were unevenly associated with ganglion cells. Using light microscopy, the most intense SOM-LI was seen in the perinuclear zone of the neurons. Electron-microscopically, the staining was localized on the membranes of the Golgi apparatuses. In the nerve terminals, SOM-LI was seen inside the small vesicles (40-60 nm diameter). All neurons with SOM-LI were also found to be tyrosine-hydroxylase immunoreactive when examined with a double-staining technique. These results provide evidence that somatostatin and noradrenaline co-exist in human sympathetic neurons.

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