Single high-concentration capsaicin application prevents c-Fos expression in spinothalamic and postsynaptic dorsal column neurons after surgical incision.

BACKGROUND: Allodynia and hyperalgesia present after surgical interventions are often a major complain of surgical patients. It is thought that both peripheral and central mechanisms contribute to these symptoms. In this study, the role of peripheral nerve fibres that express transient receptor potential vanilloid 1 (TRPV1) receptors in the activation of spinothalamic tract (STT) and postsynaptic dorsal column (PSDC) neurons was assessed in a model of surgical pain.

METHODS: Spinothalamic tract and PSDC neurons retrogradely labelled from the thalamus and nucleus gracilis were used. Activation of these projection neurons was evaluated after plantar incision as expression of the early gene product, c-Fos protein, in the nuclei of these neurons.

RESULTS: There was a robust increase in c-Fos immunopositivity in the STT and PSDC neurons, in the control animals after a plantar incision. This increase in c-Fos expression was significantly attenuated in animals in which a single high-concentration capsaicin injection was made intradermally at the incision site 24 h before the surgery.

CONCLUSIONS: Our results suggest that activation of both STT and PSDC neurons is involved in development of pain states present after surgical incision and that TRPV1-containing peripheral nerve fibres are needed for c-Fos expression in these dorsal horn neurons after plantar incision.