The projection of joint receptors to the cuneate nucleus in the cat.

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Abstract
Axons in the dorsal columns and cells in the cuneate nucleus responding to stimulation of the wrist joint nerve were recorded. A sample of 25 axons activated by the wrist joint nerve was recorded in the dorsal columns at the level of the 3rd cervical segment. All 25 were judged post-synaptic fibers by response latecny, burst length and maximum frequency of following. Of the 25, 19 had convergent inputs from the wrist joint nerve and the cutaneous superficial radial nerve. Although no primary wrist joint afferent fibers were recorded in the dorsal columns, their presence was demonstrated by recording single units in the wrist joint nerve which were antidromically activated by microstimulation in the cuneate fasciculus. The majority of cells recorded in the cuneate nucleus were activated not only by stimulation of joint afferents, but by skin and muscle afferent fibers. About 1/2 of the cells in the cuneate nucleus responded to wrist movement in animals with partially denervated forelimbs, where the intact wrist joint nerve was the only afferent channel providing information about natural, imposed wrist movements. The majority of the cells had weak and irregular phastic responses compared with the responses of primary wrist joint afferents to the same movements. Only 2 of 34 cells tested projected directly to the ventrobasal thalamus, using collision of antidromic and peripherally activated impulses.