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

Many of the physiological hallmarks associated with neurogenic inflammatory processes in cutaneous tissues are similarly present within orofacial stru ctures. Such attributes include the dependence upon capsalcin-sensitive sen sory neurons and the involvement of certain inflammatory mediators derived therein, including calcitonin gene-related peptide (CGRP). However, there a re also important differences between the trigeminal and spinal nervous sys tems, and the potential contributions of neurogenic processes to inflammato ry disease within the trigeminal system have yet to be fully elucidated. We present here a model system that affords the ability to study mechanisms r egulating the efferent functions of peptidergic terminals that may subserve neurogenic inflammation within the oral cavity. Freshly dissected buccal m ucosa tissue from adult, male, Sprague-Dawley rats was placed into chambers and superfused with oxygenated, Krebs buffer. Serial aliquots of the egres sing superfusate were acquired and analysed by radioimmunoassay for immunor eactive CGRP (iCGRP). Addition of the selective excitotoxin, capsaicin (10- 300 muM), to the superfusion buffer resulted in a significant, concentratio n-dependent increase in superfusater levels of iCGRP. Similarly, release of iCGRP from the buccal mucosa could also be evoked by a depolarizing concen tration of potassium chloride (50 mm) or by the calcium ionophore A23187 (1 muM). The specific, capsaicin receptor antagonist, capsazepine (300 muM), completely abolished the capsaicin-evoked release of ICGRP while having no effect whatsoever on the potassium-evoked release. Moreover, capsaicin-evok ed release was dependent upon the presence of extracellular calcium ions an d was significantly, though incompletely, attenuated by neonatal capsaicin denervation. Collectively, these data indicate that the evoked neurosecreti on of iCGRP in response to capsaicin occurs via a vanilloid receptor-mediat ed, exocytotic mechanism. The model system described here should greatly fa cilitate future investigations designed to identify and characterize the st imuli 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 trige minal field of innervation.