Noxious heat-induced CGRP release from rat sciatic nerve axons in vitro

Area of Science:

• Neuroscience
• Molecular Biology
• Physiology

Background:

• Noxious heat is a known activator of the capsaicin receptor (VR1) and its homologue VRL1.
• Capsaicin induces calcium-dependent calcitonin gene-related peptide (CGRP) release from rat sciatic nerve axons.

Purpose of the Study:

• To investigate the mechanisms of heat-induced CGRP release from rat sciatic nerves.
• To determine if capsaicin receptors mediate heat responses.

Main Methods:

• Isolated rat sciatic nerves were stimulated with noxious heat.
• Calcitonin gene-related peptide (CGRP) release was measured.
• The effects of capsaicin receptor antagonists (capsazepine, Ruthenium Red) and capsaicin desensitization were examined.
• Calcium dependency of heat-induced release was assessed.

Main Results:

• Heat stimulation significantly increased CGRP release in a temperature-dependent manner (Q10 ≈ 15, threshold 40-42°C).
• Heat-induced CGRP release was largely dependent on extracellular calcium.
• Capsazepine and Ruthenium Red did not significantly inhibit heat-induced CGRP release.
• Heat-induced CGRP release persisted even after capsaicin-induced desensitization of capsaicin receptors.

Conclusions:

• Heat activates CGRP release through mechanisms distinct from VR1/VRL1 capsaicin receptors.
• Both capsaicin-sensitive and -insensitive nerve fibers contribute to heat-induced CGRP release.
• Other heat-activated ion channels likely mediate axonal calcium influx and neuropeptide release in response to noxious heat.