Effects of temporary deafferentation on raccoon post-synaptic dorsal column neurons

The effects of temporary deafferentation were studied in 54 post-synaptic dorsal column (PSDC) neurons in the cervical spinal cord of the raccoon. Deafferentation was induced by the injection of lidocaine into the base of the digit containing the receptive field of the neuron. These neurons all had receptive fields on a single digit of the forepaw and in no case did a new receptive field appear following lidocaine injection. High intensity electrical stimulation of an off-focus digit (adjacent to the one with the receptive field) produced responses in 92% of the neurons prior to lidocaine injection. The strength of these off-focus responses was not increased by deafferentation of the on-focus digit, as might be expected if they were being suppressed by the major input; rather it was decreased. These results argue against a convergence of multi-digit inputs onto these PSDC neurons that is masked under normal circumstances. As previously described for neurons in the cuneate nucleus, deafferentation produced a significant decrease in the spontaneous activity of PSDC neurons, indicating that they receive a tonic excitatory input from the periphery. The importance of these results in understanding the starting point for injury-induced reorganization is discussed.