Contact Heat Evoked Potentials Are Responsive to Peripheral Sensitization: Requisite Stimulation Parameters

Area of Science:

• Neuroscience
• Pain Research
• Sensory Physiology

Background:

• Capsaicin induces peripheral sensitization, a key factor in hyperalgesia.
• Contact heat evoked potentials (CHEPs) show promise in measuring peripheral sensitization, but optimal parameters are unclear.
• Laser evoked potentials (LEPs) are less sensitive to peripheral sensitization compared to CHEPs.

Purpose of the Study:

• To determine the optimal contact heat stimulation parameters for detecting capsaicin-induced peripheral sensitization.
• To refine the CHEP method for improved measurement of peripheral sensitization.
• To investigate the relationship between baseline temperature and the detection of altered nerve conduction.

Main Methods:

• Rapid contact heat stimulation (70°C/s) was applied to the hand dorsum.
• Stimulation was performed from three baseline temperatures (35°C, 38.5°C, 42°C) to a 52°C peak.
• CHEPs (N2 latency) and pain ratings were recorded before and after topical capsaicin application.

Main Results:

• Topical capsaicin application increased pain ratings and reduced N2 latency.
• Significant reductions in N2 latency were observed only when stimulation started from 35°C and 38.5°C baseline temperatures.
• Stimulation from a 42°C baseline showed no significant changes in N2 latency after capsaicin application.

Conclusions:

• Contact heat stimulation with a baseline temperature below 42°C is effective for detecting peripheral sensitization.
• The findings suggest earlier recruitment of sensitized afferents within the 35-42°C range.
• Optimized CHEP protocols can objectively measure peripheral sensitization, potentially aiding in pain assessment.