Stimulation of dural vessels excites the SI somatosensory cortex of the cat via a relay in the thalamus.

Aim We carried out experiments in cats to determine the thalamo-cortical projection sites of trigeminovascular sensory neurons. Methods 1) We stimulated the middle meningeal artery (MMA) with C-fibre intensity electrical shocks and made field potential recordings over the somatosensory cortical surface. 2) We then recorded neurons in the ventroposteromedial (VPM) nucleus of the thalamus in search of neurons which could be activated from the skin, MMA and superior sagittal sinus. 3) Finally, we attempted to antidromically activate the neurons found in stage 2 by stimulating the responsive cortical areas revealed in stage 1. Results VPM neurons received trigeminovascular input, input from the V1 facial skin and could also be activated by electrical stimulation of the somatosensory cortex. VPM neurons activated from the cortex responded with short and invariant latencies (6.7 +/- 7.7 msec mean and SD). They could follow high rates of stimulation and sometimes showed collision with orthodromic action potentials. Conclusions We conclude that somatosensory (SI) cortical stimulation excites trigeminovascular VPM neurons antidromically. In consequence, these VPM neurons project to the somatosensory cortex. These findings may help to explain the ability of migraineurs with headache in the trigeminal distribution to localise their pain to a particular region in this distribution.