Capsaicin-evoked neuropeptide release is not dependent on membrane potential changes

Area of Science:

• Neuroscience
• Neuropharmacology
• Spinal Cord Research

Background:

• Sensory afferents, particularly C-fibers, utilize neuropeptides like substance P and calcitonin gene-related peptide (CGRP) for neurotransmission.
• Capsaicin is a known activator of transient receptor potential vanilloid 1 (TRPV1) channels, which are expressed on sensory neurons.

Purpose of the Study:

• To investigate the mechanism of capsaicin-induced neuropeptide release from sensory afferents in the spinal cord.
• To determine if capsaicin-induced calcium influx relies on voltage-sensitive calcium channels (VSCCs).

Main Methods:

• Utilized high K(+)-depolarized rat spinal cord slices.
• Administered capsaicin to evoke neuropeptide release.
• Measured the release of substance P and CGRP from central terminals of C-fibre afferents.

Main Results:

• Capsaicin induced the release of substance P and CGRP from central C-fiber afferent terminals.
• This release occurred independently of membrane potential changes, suggesting it does not require VSCC activation.
• In the presence of capsaicin, high K+ evoked substance P release, likely from intrinsic spinal neurons, but not CGRP.

Conclusions:

• Capsaicin-evoked neuropeptide release from sensory afferents is independent of membrane depolarization and VSCCs.
• Capsaicin-induced calcium influx into nerve terminals does not necessitate the opening of voltage-sensitive calcium channels.
• Substance P release under combined capsaicin and high K+ conditions may involve distinct neuronal populations within the spinal cord.