Serotonin-immunoreactive cells in the superior cervical ganglion of the rat. Evidence for the existence of separate serotonin- and catecholamine-containing small ganglionic cells.

Superior cervical ganglia of 8 adult male rats were examined by indirect immunofluorescence microscopy, using an antibody to a conjugate of bovine serum albumin and serotonin, and an antibody to a conjugate of bovine serum albumin and noradrenaline. The fixative used was 4% paraformaldehyde in 0.1 M phosphate buffer, pH 7.3. Consecutive cryostat sections of whole ganglia were alternately stained with these antibodies. Serotonin- as well as catecholamine-immunoreactive, small ganglionic cells were demonstrated, both arranged in clusters. Serotonin-immunoreactive cells were mostly located at the cranial or caudal side of the ganglia. Serotonin-immunoreactive cells provided with processes were easily observed. Only a few mast cells were seen. Catecholamine-immunoreactive cells were rounded without processes. This cell type did not seem to have a preferential position within the ganglia. Intermingling of both immunoreactive, small ganglionic cells was not observed. A considerable variety in the number of both immunoreactive cell types was established. Catecholamine-immunoreactive cells were absent in 3 our of 8 animals. Evidence is provided that the catecholamine-immunoreactive cells are storing noradrenaline. The presented data seem to indicate the presence of 3 different types of small, intensely fluorescent (SIF) cells in the superior cervical ganglion of the rat, viz. a dopamine-storing, a noradrenaline-storing, and a serotonin-storing SIF cell type.