Distribution of signaling neurotransmitters and interaction in the sphenopalatine ganglion

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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 the trigeminovascular system. Our work was performed to examine the expression of the parasympathetic signaling transmitters and their receptors in human and rat sphenopalatine ganglion (SPG), and if CGRP and CGRP receptor components are present in the human SPG in order to reveal an interaction between the sensory and parasympathetic systems. Indirect immunofluorescence technique was used for immunohistochemical demonstration of vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), nitric oxide synthase (NOS), glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), VIP and PACAP common receptors (VPAC1, VPAC2), PACAP receptor (PAC1), CGRP, the CGRP receptor components as the calcitonin receptor-like receptor (CLR) and the receptor activity modifying protein 1 (RAMP1) in human and rat SPG. In addition, double labeling was carried out to reveal the co-localization of neurotransmitters. 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 VIP/PACAP receptors and CGRP receptor components in rat SPG. In human SPG VIP immunoreactive neurons as well as fibers were frequently found.Many, homogenously stained NOS immunoreactive cells were found, but no positive fibers. In addition, PACAP immunoreactivity was observed in some of the neurons and in fibers. Co-localization was found between VIP/NOS and PACAP/NOS in human. In rat VIP, NOS and PACAP immunoreactivity were found in many neurons and fibers. Co-localization of PACAP and NOS was observed in rat neurons. PACAP and GS double staining revealed that the PACAP immunoreactivity was localized in/close to the cell membrane, but not in the satellite glial cells (SGCs). PAC1 and VPAC1 immunoreactivity was found in the SGCs, in addition, VPAC1 and VPAC2 in fibers of both human and rat. Western blot revealed protein expression of PAC1, VPAC1 and VPAC2 in rat SPG. CGRP immunoreactive fibers were frequently found intraganglionic in both human and rat SPG in the vicinity of neurons, and in neurons in rat SPG. CLR immunoreactivity was observed in 7 SGCs as well as in nerve fibers, but not in neurons in both human and rat. RAMP1 immunoreactivity was localized in many neurons (in both human and rat), SGCs (in human) and nerve fibers (in rat). Thus, the two CGRP receptor components together were found in the SGCs in human and in the nerve fibers in rat. Western blot confirmed the presence of RAMP1 and CLR in rat SPG. We hypothesized that VIP, PACAP, NOS, PAC1, VPAC1, and VPAC2 play a role in the activation of parasympathetic cranial outflow during trigeminal-autonomic reflex. We have revealed that the trigeminal CGRP-containing fibers project to the SPG and act on CGRP receptors on SGCs in human. Therefore, our results suggest a functional coupling between the trigeminal (sensory) and the sphenopalatinal (parasympathetic) system.

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