Region-Specific Effects of Trigeminal Capsaicin Stimulation

Aims: To investigate the region-specific effects of painful trigeminal capsaicin stimulation in healthy participants. Methods: Twenty healthy participants (10 men and 10 women) participated in four sessions in which they received application of 0.05 mL Vaseline (placebo) or capsaicin cream (0.1%) to a different area innervated by the three branches of the trigeminal nerve: the supraorbital area (V1), the nasal mucosa (V1/V2), and the maxillary (V2) and mandibular (V3) oral mucosa. The participants rated their perceived sensations on a 0-50-100 numeric rating scale (NRS). Thermal (5°C, 23°C, and 50°C) and mechanical (32 mN and 256 mN) sensitivities were assessed. The Schirmer tearing test was used to monitor the lacrimation level as a local measure of autonomic activity, and the Task Force Monitor was used to record systemic autonomic activity. Data were analyzed using repeated measures analysis of variance. Results: Capsaicin application evoked significantly higher overall NRS scores (P .001) and induced significantly higher ratings to the heat stimuli (P .009) in all sessions compared to control. For lacrimation level, capsaicin stimulation resulted in a significant increase compared to control (P .0002) only in the nasal mucosa session. Conclusion: Topical application of capsaicin cream to the different branches of the trigeminal nerve caused higher NRS scores along with an altered somatosensory sensitivity. Furthermore, in the nasal mucosa session, a robust local and generalized parasympathetic activation appeared following capsaicin application. Keywords: autonomic nervous system, capsaicin, experimental pain model, trigeminal nociception, trigeminal parasympathetic reflex