Calcitonin receptor‐like receptor (CLR), receptor activity‐modifying protein 1 (RAMP1), and calcitonin gene‐related peptide (CGRP) immunoreactivity in the rat trigeminovascular system: Differences between peripheral and central CGRP receptor distribution

Abstract

Calcitonin gene-related peptide (CGRP) is a key mediator in primary headaches including migraine. Animal models of meningeal nociception demonstrate both peripheral and central CGRP effects; however, the target structures remain unclear. To study the distribution of CGRP receptors in the rat trigeminovascular system we used antibodies recognizing two components of the CGRP receptor, the calcitonin receptor-like receptor (CLR) and the receptor activity-modifying protein 1 (RAMP1). In the cranial dura mater, CLR and RAMP1 immunoreactivity (-ir) was found within arterial blood vessels, mononuclear cells, and Schwann cells, but not sensory axons. In the trigeminal ganglion, besides Schwann and satellite cells, CLR- and RAMP1-ir was found in subpopulations of CGRP-ir neurons where colocalization of CGRP- and RAMP1-ir was very rare ( approximately 0.6%). CLR- and RAMP1-ir was present on central, but not peripheral, axons. In the spinal trigeminal nucleus, CLR- and RAMP1-ir was localized to "glomerular structures," partly colocalized with CGRP-ir. However, CLR- and RAMP1-ir was lacking in central glia and neuronal cell bodies. We conclude that CGRP receptors are associated with structural targets of known CGRP effects (vasodilation, mast cell degranulation) and targets of unknown function (Schwann cells). In the spinal trigeminal nucleus, CGRP receptors are probably located on neuronal processes, including primary afferent endings, suggesting involvement in presynaptic regulation of nociceptive transmission. Thus, in the trigeminovascular system CGRP receptor localization suggests multiple targets for CGRP in the pathogenesis of primary headaches.

Neuropeptide Effects in the Trigeminal System: Pathophysiology and Clinical Relevance in Migraine

“…30 Thus, localization of CGRP receptor components on mast cells may indicate that CGRP can act as a mild mast cell degranulator. 27 Together, the dural CGRP receptor distribution is in line with existing functional data and suggests targets important in our understanding of the pharmacologic effector sites of CGRP inhibitors. This forms the starting point in our understanding of the exact interplay of substructures in meningeal nociception and the relation to CGRP signaling and headache generation.…”

“…Instead, CLR was co-localized with glial fibrillary acidic protein (GFAP) as a marker for glia, indicating that CGRP receptor components may be expressed by Schwann cells. 27 While the functional significance of CGRP receptors on Schwann cells is currently unexplored, findings of CGRP receptors on arterial blood vessels are in line with CGRP functions (Fig. 1A).…”

“…27 Subpopulations of CGRP-immunoreactive neurons were also immunopositive for either CLR or RAMP1, but the co-existence of CGRP with CLR and RAMP1 was extremely rare (Fig. 1C, D).…”

“…27 Multiple-color immunofluorescence examinations demonstrated co-localization of CLR and RAMP1 immunoreactivity in meningeal nerves, indicating functional CGRP receptors; however, CLR was neither co-localized with protein gene product 9.5 (a pan-neuronal axonal marker) nor with CGRP. Instead, CLR was co-localized with glial fibrillary acidic protein (GFAP) as a marker for glia, indicating that CGRP receptor components may be expressed by Schwann cells.…”

Calcitonin gene-related peptide (CGRP) and its receptor components in human and rat spinal trigeminal nucleus and spinal cord at C1-level

“…In rat STN, it was suggested that CGRP and its receptor components are localized in terminals from primary afferents [29]. In contrast, CLR did not co-localize with neuropeptides of primary spinal afferents in the dorsal horn of rat [30].…”