Region-Specific Effects of Trigeminal Capsaicin Stimulation

Area of Science:

• Neuroscience
• Pain Research
• Sensory Science

Background:

• The trigeminal nerve innervates the face and oral cavity, mediating sensations like pain and temperature.
• Capsaicin, a vanilloid receptor agonist, is commonly used to induce experimental pain and study neurogenic inflammation.
• Understanding region-specific trigeminal nerve responses is crucial for diagnosing and managing craniofacial pain conditions.

Purpose of the Study:

• To investigate the differential effects of capsaicin stimulation on various branches of the trigeminal nerve.
• To assess changes in pain perception, thermal and mechanical sensitivity, and autonomic responses following capsaicin application.
• To determine if trigeminal nerve stimulation elicits region-specific autonomic activity.

Main Methods:

• Twenty healthy participants received topical capsaicin or placebo cream on supraorbital, nasal, or oral mucosa areas.
• Participants rated perceived sensations using a numeric rating scale (NRS).
• Thermal and mechanical sensitivities were tested, alongside lacrimation (Schirmer test) and systemic autonomic activity (Task Force Monitor).

Main Results:

• Capsaicin significantly increased NRS scores and heat sensitivity across all tested trigeminal nerve areas compared to placebo.
• Lacrimation levels significantly increased after capsaicin application specifically to the nasal mucosa.
• No significant differences in systemic autonomic activity were reported between capsaicin and placebo conditions.

Conclusions:

• Topical capsaicin application to trigeminal nerve branches increases pain perception and alters somatosensory sensitivity.
• Nasal mucosa stimulation with capsaicin induces a pronounced local and generalized parasympathetic activation.
• These findings highlight the region-specific autonomic effects of trigeminal nerve stimulation.