Cannabinoids have a long history of medicinal uses and their analgesic properties are well documented, however, their mechanisms of action, especially in the periphery, are poorly understood. In light of these analgesic effects, coupled with the untoward side effects of many currently used analgesics including the NSAIDS and opioids, we believe that careful scrutiny of the action of cannabinoid compounds at peripheral nociceptive sites is warranted. The present proposal will test the hypothesis that cannabinoids inhibit calcitonin gene related peptide (CGRP) release through cannabinoid type one receptor (CBI) mediated decreases in calcium influx. The rational for this hypothesis is that cannabinoid activation of CB1 would stimulate the dissociation of beta-gamma subunits from GalphaO which interact directly with P/Q and N type calcium channels to inhibit calcium influx. This, in turn, would decrease the available voltage sensitive calcium pool causing a reduction in the release of secretary granules from primary sensory neurons under stimulatory states. To address this hypothesis, the specific aims of this research plan will be; 1) to co-localize CB1 receptors with CGRP in small and medium diameter trigeminal ganglion primary sensory neurons through combined in situ hybridization and immunohistochemistry, 2) to evaluate the G-protein coupling properties of the CB1 receptor utilizing selective immunoprecpitation with radiolabeled CB1 ligands and commercially available G-protein alpha subunit antibodies; and 3) to examine in cultured trigeminal ganglion the second messenger pathways through which the CB1 receptor modulates capsaicin-evoked CGRP release utilizing pharmacological methodologies and calcium imaging approaches.
