Properties of feline thalamic neurons activated by stimulation of the middle meningeal artery and sagittal sinus.

Previous studies have identified a population of neurons in the cat trigeminal brainstem complex that respond to stimulation of the middle meningeal artery (MMA) and/or superior sagittal sinus (SS). In the present study, neuronal responses to stimulation of the MMA and SS were sought in the thalamus of the cat. Sixty-one neurons excited by electrical stimulation of the MMA and/or SS were located in the ventroposteromedial (VPM) nucleus, and surrounding regions in lateral thalamus. Of these 61 neurons, 23% were excited only by MMA stimulation, 39% only by SS stimulation and 38% by both MMA and SS stimulation. The latencies to activation from MMA and/or SS stimulation suggest the involvement of small, myelinated primary afferent fibers. Most neurons (48/61) responded to electrical stimulation of the MMA or SS with a burst of 2-5 spikes. Mechanical stimulation of the MMA and SS was also an effective stimulus and in some cases evoked a burst response. Of the neurons tested for the existence of orofacial inputs, all were found to have an excitatory receptive field (RF) on the face and usually (22/26 neurons) involved the ophthalmic distribution. Twelve of these neurons were excited by a tap stimulus applied to the face, 6 by pinching (nociceptive specific), 6 by low-threshold mechanical stimuli (LTM), one by both pinch and low-threshold stimuli and one by mechanical stimulation of the cornea. The firing properties, RF and modalities of these thalamic neurons suggest that they may play a role in the appreciation of pain of cerebrovascular origin.