An experimental model of deafferented pain in the cat.

Deafferentation hyperactivity, produced unilaterally in the neurons of the subnucleus caudalis of the spinal trigeminal nucleus (STNcd) in cats by left Gasserian ganglionectomy, was studied neurochemically and electrophysiologically. Analysis of neuronal activities on both sides of the STNcd was done 11-63 days after the denervation. On the denervated side, 37 (57%) of the 65 neurons identified showed deafferentation hyperactivity. Continuous and spontaneous firing of these hyperactive neurons were inhibited neither by the intraventricular administration of morphine or enkephalinamide nor by the electrical stimulation of periaqueductal gray. In contrast, the facilitation of the pain perceptive neuronal activities in the STNcd of the nondenervated side was remarkably inhibited, both by the administration of the same drugs and by periaqueductal gray stimulation. The deafferentation hyperactivity produced in this experiment in the STNcd of the denervated side might have a close physiological relationship to the deafferented pain of clinical patients.