Capsaicin‐evoked CGRP release from rat buccal mucosa: development of a model system for studying trigeminal mechanisms of neurogenic inflammation

Abstract

Many of the physiological hallmarks associated with neurogenic inflammatory processes in cutaneous tissues are similarly present within orofacial structures. Such attributes include the dependence upon capsaicin-sensitive sensory neurons and the involvement of certain inflammatory mediators derived therein, including calcitonin gene-related peptide (CGRP). However, there are also important differences between the trigeminal and spinal nervous systems, and the potential contributions of neurogenic processes to inflammatory disease within the trigeminal system have yet to be fully elucidated. We present here a model system that affords the ability to study mechanisms regulating the efferent functions of peptidergic terminals that may subserve neurogenic inflammation within the oral cavity. Freshly dissected buccal mucosa tissue from adult, male, Sprague-Dawley rats was placed into chambers and superfused with oxygenated, Krebs buffer. Serial aliquots of the egressing superfusate were acquired and analysed by radioimmunoassay for immunoreactive CGRP (iCGRP). Addition of the selective excitotoxin, capsaicin (10-300 microm), to the superfusion buffer resulted in a significant, concentration-dependent increase in superfusate levels of iCGRP. Similarly, release of iCGRP from the buccal mucosa could also be evoked by a depolarizing concentration of potassium chloride (50 mm) or by the calcium ionophore A23187 (1 microm). The specific, capsaicin receptor antagonist, capsazepine (300 microm), completely abolished the capsaicin-evoked release of iCGRP while having no effect whatsoever on the potassium-evoked release. Moreover, capsaicin-evoked release was dependent upon the presence of extracellular calcium ions and was significantly, though incompletely, attenuated by neonatal capsaicin denervation. Collectively, these data indicate that the evoked neurosecretion of iCGRP in response to capsaicin occurs via a vanilloid receptor-mediated, exocytotic mechanism. The model system described here should greatly facilitate future investigations designed to identify and characterize the stimuli that regulate the release of CGRP or other neurosecretory substances in isolated tissues. This system may also be used to elucidate the role of these mediators in the aetiology of inflammatory processes within the trigeminal field of innervation.

Anandamide Is Able to Inhibit Trigeminal Neurons Using an in Vivo Model of Trigeminovascular-Mediated Nociception

“…Anandamide was also able to inhibit capsaicin-induced dilation. Capsaicin evokes CGRP release from trigeminal sensory nerves (Flores et al, 2001) and more generally from sensory nerve terminals (Saito and Goto, 1986;Maggi et al, 1988;Martling et al, 1988). We have also previously shown (Akerman et al, 2003b) using this model Fig.…”

Neuropeptides and Neurogenic Mechanisms in Oral and Periodontal Inflammation

“…For example, ligation or constriction of the sciatic nerve increased sympathetic nerve sprouting in the affected dorsal root ganglia, but similar injuries to the inferior alveolar nerve did not produce similar sprouting in the affected trigeminal ganglion (Bongenhielm et al, 1999). It would appear that there are differences not only in the neurogenic responses between the trigeminal and spinal systems but also between various tissues within the oral cavity (Flores et al, 2001). …”

Differential distribution of vanilloid receptors in the primary sensory neurons projecting to the dorsal skin and muscles

“…Colocalization of TRPV1 with neuropeptides in the cutaneous sensory nerve fibers suggests that the neuropeptide release is mediated by the activation of TRPV1 in the same sensory nerve fibers. Experiments with the ischiadic nerve and buccal mucosa demonstrated that neuropeptide release after application of capsaicin is mediated by activation of TRPV1 (Fischer et al 2003;Flores et al 2001). On the other hand, because CGRP release by nociceptive thermal stimuli does not always require activation of TRPV1, another mechanism might be involved (Petho¨et al 2004).…”