Capsaicin-sensitive A delta fibers in cat tooth pulp

Area of Science:

• Neuroscience
• Dental Research
• Pharmacology

Background:

• The relationship between nerve fiber conduction velocity and receptive properties in dental pulp is not fully understood.
• Investigating the effects of capsaicin on different types of pulpal nerve fibers is crucial for understanding pain mechanisms.

Purpose of the Study:

• To determine if capsaicin affects both polymodal C fibers and A delta fibers.
• To investigate the existence of A alpha polymodal nociceptors in the tooth pulp.

Main Methods:

• Analysis of 139 functional single cat tooth pulp nerve fibers (A beta, C, and A delta).
• Topical application of capsaicin (1 nM, 100 nM, 10 muM) through thin dentin to record neural responses.
• Categorization of A delta fibers based on intra- and extrapulpal conduction velocities.

Main Results:

• Low-concentration capsaicin (100 nM) activated slow-conducting A delta and C fibers, but not A beta or fast A delta fibers.
• High-concentration capsaicin (10 muM) reversibly or irreversibly blocked conduction in slow A delta and C fibers.
• Fast A delta fibers showed decreased antidromic action potential amplitude, and some experienced conduction block at high capsaicin concentrations.

Conclusions:

• Low concentrations of capsaicin excite slow pulpal A delta and C fibers.
• High concentrations of capsaicin inhibit nerve fiber conduction in the dental pulp, impacting various fiber types.
• The study provides insights into the differential effects of capsaicin on pulpal sensory nerve fibers.