Population analysis of single units in the cuneate nucleus of the cat

Abstract

Population analysis has been used to investigate the properties of cells in the cuneate nucleus of the chloralose-anesthetized cat. Postsynaptic units were grouped on the basis of the maximum frequency following to ipsilateral superficial radial nerve stimulation, the degree of convergence onto cells from central and peripheral sources, and the response to natural stimulation of the ipsilateral forelimb. The groups were analyzed further on the basis of depth in the brainstem, initial spike latency, and variability in the initial spike latency in response to stimulation of the ipsilateral forelimb. Maximum order to the data resulted when the cells were grouped on the basis of maximum frequency following ability. The possible role of the defined cell groups in production of primary afferent depolarization (PAD) was examined by constructing simulated PAD time course curves. Both a rapidly rising time course curve, typical of ipsilateral forelimb activation, and a slowly rising curve, typical of “off-focus” activation, could be obtained by linearly summing unit depolarizations in a temporal pattern defined by measured spike latencies to the appropriate input. This, and other evidence, suggest that the observed properties of cuneate inhibition can be accounted for by the activity of cells within the cuneate nucleus. A wiring diagram for cuneate inhibition circuitry is presented.