Capsaicin acutely stimulates cutaneous small diameter afferent neurons by acting directly on the TRPV1. TRPV1 is a non-selective cation channel, present exclusively in small to medium sized neurons. Objectives: Current knowledge concerning capsaicin comes from studies performed on cutaneous tissues, very little is known about the effect of capsaicin on muscle nociceptors. In this study the role of TRPV1 in mediating nociceptive responses produced by capsaicin injections intramuscularly will be assessed and the presence of TRPV1 in muscle afferent neurons in the trigeminal ganglia (TG) will be investigated. Methods: A behavioral model of craniofacial muscle pain will be utilized to assess the involvement of TRPV1 in mediating nocifensive responses to capsaicin injection. Fluorogold (1%) and polyclonal antibody were used to identify TRPV1 positive muscle afferents in the TG. Results: Capsaicin (30mM, 10ml) injected into the masseter muscle (n=5) produced vigorous shaking of the ipsilateral hind paw that diminished over a few minutes, the mean peak counts (MPC) and the area under the curve (AUC) were significantly higher than those evoked by isotonic saline injection (P< 0.001). Pre-treatment with caspazepine (4 and 20 mM, n=10, i.m); a selective TRPV1 antagonist 5 min prior to capsaicin adminstration, reliably and dose dependently attenuated the hind paw shaking behavior. This attenuation was reflected in both the MPC and AUC (P<0.05). Anatomical studies indicated that TRPV1 is present in small to medium sized neurons in the TG. Muscle afferent neurons with TRPV1 immuno-like reactivity comprised 25% of all TRPV1 positive cells. Conclusion: This study provides an evidence for the involvement of TRPV1 in mediating nociceptive responses caused by craniofacial muscle pain. The knowledge of the actions and mechanisms behind the effects of capsaicin will contribute to the further progress in the biology of nociception and for the development of novel analgesic strategies. Supported by DE06027

Back to the Neuroscience / TMJ Program
Back to the IADR/AADR/CADR 82nd General Session (March 10-13, 2004)

Top Level Search