IMMUNOHISTOCHEMISTRY OF SMALL INTENSELY FLUORESCENT (SIF) CELLS AND OF SIF CELL-ASSOCIATED NERVE-FIBERS IN THE RAT SUPERIOR CERVICAL-GANGLION

Double-labelling immunofluorescence was applied on single sections of the rat superior cervical ganglion to evaluate neurochemistry and conn ectivity of intraganglionic SIF cells. The synaptic vesicle membrane p rotein synaptophysin and secretoneurin, a newly discovered neuropeptid e derived from secretogranin II, proved reliable molecular markers of this cell type, whereas serotonin and tyrosine hydroxylase immunoreact ivities were observed in slightly incongruent SIF cell subpopulations. Immunolabelling for vasoactive intestinal polypeptide and neuropeptid e Y occurred in few SIF cells. None of the above immunoreactivities we re visibly altered by preganglionic or postganglionic denervation, whi le some SIF cells were immunolabelled for galanin or for the neuronal microtubule-associated protein MAP2 after postganglionic denervation. SIF cells were nonreactive for the pan-neuronal marker protein gene pr oduct (PGP) 9.5 or neurofilament 160 kD. Intense staining of NADPH-dia phorase in some SIF cells, suggesting catalytic activity of nitric oxi de synthase, could not be substantiated by immunoreactivity for this e nzyme. SIF cells were approached by nonidentical fiber populations imm unoreactive for PGP 9.5, neurofilament, or neuropeptide Y, whereas imm unoreactivities for galanin and vasoactive intestinal polypeptide were colocalized in fiber meshes around SIF cells. The findings indicate ( 1) neurochemical SIF cell heterogeneity, (2) SIF cell plasticity in re sponse to ganglionic perturbation, and (3) a differentiated innervatio n of SIF cells in the rat superior cervical ganglion. (C) 1994 Wiley-L iss, Inc.