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Capsaicin-induced secondary hyperalgesia differences between the trigeminal and spinal innervation
Isabela C Novaes1, Soraya S Ardestani1, Allen Matheus S Nascimento1
1Department of Biosciences, Universidade Estadual de Campinas (UNICAMP), Faculdade de Odontologia de Piracicaba (FOP), Piracicaba, Brazil.
Scientific Reports
|January 3, 2025
Summary
Topical capsaicin induced greater secondary hyperalgesia in the forearm (spinal innervation) compared to the masseter (trigeminal innervation). Capsaicin application to the masseter also reduced somatosensory function, unlike the forearm.
Area of Science:
- Neuroscience
- Pain Research
- Clinical Trials
Background:
- Secondary hyperalgesia and somatosensory changes are key indicators of pain processing.
- Understanding differences in these responses between spinal and trigeminal systems is crucial for pain management.
Purpose of the Study:
- To compare secondary hyperalgesia and somatosensory threshold alterations induced by capsaicin in spinal (forearm) versus trigeminal (masseter) innervated skin.
- To investigate potential differences in central sensitization between these two neural systems.
Main Methods:
- A randomized, crossover clinical trial involving 40 healthy participants.
- Topical application of 1% capsaicin cream to forearm and masseter skin areas.
- Assessment of allodynia, pinprick hyperalgesia, and electrical/mechanical pain thresholds.
Main Results:
- Higher incidence and larger areas of allodynia and pinprick hyperalgesia were observed on the forearm compared to the masseter.
- Capsaicin application to the masseter resulted in reduced electrical and mechanical pain thresholds, indicating somatosensory loss.
- No significant somatosensory threshold changes were noted on the forearm post-capsaicin.
Conclusions:
- Findings suggest distinct responses to capsaicin-induced hyperalgesia between trigeminal and spinal innervation.
- Differences observed are compatible with varying degrees of central sensitization in secondary hyperalgesia between the two systems.
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