Corticotropin-releasing factor-like immunoreactive nerve fibers in the rat superior cervical ganglion and their fine structures.

The existence of nerve fibers containing corticotropin-releasing factor (CRF)-like immunoreactivity (CRFI) in the rat superior cervical ganglion (SCG) was demonstrated by using immunocytochemistry. They were found to be extrinsic in origin, because no CRFI neurons were seen in the SCG and decentralization resulted in the disappearance of CRFI fibers in the SCG on the operated side. These findings were also confirmed by immunoelectron microscopic analysis; CRFI fibers contained a number of small clear synaptic vesicles but were devoid of large granular and agranular vesicles. These morphological characteristics are identical to those of the preganglionic fibers. The present immunoelectron microscopic analysis revealed that most of the CRFI fibers in the SCG make synaptic contact predominantly with the dendrites of the principal cells, partly with their somas and rarely with a non-CRFI terminal. Thus, the present study provides direct morphological evidence that CRF directly influences the function of the principal cells of the SCG and that CRFI fibers are preganglionic.