Calcitonin gene-related peptide and its receptor components in the human sphenopalatine ganglion -- interaction with the sensory system

Clinical studies have suggested a link between the sensory trigeminal system and the parasympathetic ganglia. Calcitonin gene-related peptide (CGRP) is a sensory neuropeptide which plays an important role in vasodilatation and pain transmission in craniocervical structures. The present study was designed to examine if CGRP and CGRP receptor components are present in the human sphenopalatine ganglion (SPG) in order to reveal an interaction between the sensory and parasympathetic systems. Indirect immunofluorescence technique was used for immunohistochemical demonstration of CGRP, the calcitonin receptor-like receptor (CLR) and the receptor activity modifying protein 1 (RAMP1) in human and rat SPG. Cryostat sections were examined and images were obtained using a light- and epifluorescence microscope coupled to a camera to visualize co-labeling by superimposing the digital images. In addition, Western blot technique was used to demonstrate the existence of CGRP receptor components in rat SPG. CGRP immunoreactive fibers were frequently found intraganglionic in the SPG in the vicinity of neurons. CLR immunoreactivity was observed in satellite glial cells (SGCs) as well as in nerve fibers, but not in neurons. RAMP1 immunoreactivity was localized in many neurons and SGCs. Thus, the two CGRP receptor components together were found in the SGCs. In addition, Western blot revealed the presence of RAMP1 and CLR in rat SPG. Our results suggest a possible sensory influence in the parasympathetic cranial ganglia. The sensory CGRP-containing fibers probably originate in the trigeminal ganglion, project to the SPG and act on CGRP receptors on SGCs.