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

1. Records were made from axons in the dorsal columns and cells in the cuneate nucleus which responded to stimulation of the wrist joint nerve. 2. A sample of twenty-five axons activated by the wrist joint nerve was recorded in the dorsal columns at the level of the third cervical segment. All twenty-five were post-synaptic fibres as judged by response latency, burst length, and maximum frequency of following. Nineteen of the twenty-five had convergent inputs from the wrist joint nerve and the cutaneous superficial radial nerve. 3. While no primary wrist joint afferent fibres 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. 4. The majority of cells recorded in the cuneate nucleus were activated not only by stimulation of joint afferents, but also by skin and muscle afferent fibres. 5. About half 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 phasic responses, which were weak and irregular in comparison with the responses of primary wrist joint afferents to the same movements. 6. Only two of thirty-four cells tested could be shown to project directly to the ventrobasal thalamus, using collision of antidromic and peripherally activated impulses as the criterion.