Craniovascular application of capsaicin activates nociceptive thalamic neurones in the cat

In cats anaesthetized with alpha-chloralose and urethane, extracellular recordings were made in ventrobasal thalamus from cells responding to electrical stimulation of the superior sagittal sinus and middle meningeal artery. Capsaicin, but not vehicle, evoked an increase in the firing rate of nociceptive cells (5 of 6 wide dynamic range and the only nociceptive specific cell). Non-nociceptive cells did not respond to either capsaicin or vehicle. Cells with long latencies to electrical stimulation were excited by capsaicin but cells with short latencies were not. Capsaicin-responsive cells were found in the ventroposteromedial nucleus and the medial nucleus of the posterior complex and mostly had receptive fields involving the first trigeminal division.