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.