An experimental model of deafferented pain in cats -an electrophysiological and neurochemical study-

Deafferentation hyperactivity, which was produced unilaterally in the neurons of the subnucleus caudalis of the spinal trigeminal nucleus (STNcd) in cats by a Gasserian ganglionectomy, was studied neurochemically and electrophysiologically. The distribution of STNcd neurons responsive to various stimulations of the face was first determined with the extracellular microelectrode recording technique in 10 cats. Unilateral sensory deafferentation was made by a left Gasserian ganglionectomy in 6 cats. Spontaneous hyperactivity, which became progressively intensive, was provoked in the neurons of the denervated STNcd for about 10 days after the ganglionectomy. In the principal experiment, another 18 adult cats were unilaterally devervated. The analysis of neuronal activities on both sides of the STNcd was done 11 to 63 days after the denervation. On the non-denervated side, as many as 44 of the 51 STNcd neurons identified were wide dynamic range neurons. On the denervated side, 37 neurons (57%) of the 65 neurons identified showed deafferentation hyperactivity. Continuous and spontaneous firings 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 non-denervated side, was remarkably inhibited both by the administration of the same drugs and by periaqueductal gray stimulation. After Gasserian ganglionectomy, the cats showed abnormal behavior never seen in those without the ganglionectomy: incessant rubbing of the face of the denervated side against the cage caused the vibrissae to break and the skin to ulcerate. These results are compatible with the clinical experiences that the facilitation of the opioid-mediated pain inhibiting system is effective in relieving pain in patients with excess pain, but not in patients with deafferented pain. Therefore, the deafferentation hyperactivity produced in this experiment in the STNcd of the denervated side may have a close physiological relationship to the deafferented pain of clinical patients.