Nociceptive cortical responses during capsaicin-induced tactile allodynia in mice with spinal dorsal column lesioning.

We investigated nociceptive cortical responses using transcranial flavoprotein fluorescence imaging in anesthetized mice with capsaicin-induced allodynia. Tactile stimuli applied to the hindpaw produced fluorescence increases in the contralateral somatosensory cortex of naïve mice. Lesioning of the ipsilateral dorsal column in the spinal cord abolished most of the cortical responses. However, the responses to the same tactile stimuli appeared again after capsaicin was injected into the hindpaw. The capsaicin treatment reduced the thresholds of the hindpaw withdrawal responses. These findings strongly suggest that the responses to tactile stimuli in the lesioned mice after capsaicin injection represented nociceptive cortical responses.