Peripherally evoked single unit responses in ventroposterolateral nucleus in the absence of the dorsal column nuclei in rat

Summary

The present experiments were designed to determine the effects of removing the dorsal column nuclei on the evoked responses of the ventroposterolateral nucleus (VPL) neurons in the rat. Previously, we have observed inhibitory interactions between forelimb and hindlimb inputs to VPL (Roberts and Wells 1990), and have also observed a synaptic recovery process within VPL following dorsal column nuclei (DCN) lesions (Wells and Tripp 1987). In an attempt to describe any changes in VPL responses that correlate with the synaptic recovery in VPL following lesions to the DCN, we have studied the incidence of the inhibition process in VPL, the latency of activation of single unit VPL responses to peripheral nerve stimulation, the number of evoked unit responses observed per track studied and the somatotopy of responses in VPL. Dorsal column nuclei lesions did not alter the incidence or duration of the inhibitory interaction between forelimb and hindlimb inputs to VPL. Following DCN lesions, there was a significant increase in the latency to activation of VPL neurons by both forelimb and hindlimb inputs. This increase in latency returned to a non-significant difference from control over the same interval of time that is required for the structural recovery in VPL. There was a significant reduction in the number of evoked unit responses observed per track studied in the deafferented group at the twenty day post-lesion time course. This difference was no longer statistically significant in the sixty-four day post-lesion group. Finally, we have observed little change in the overall anatomic distribution of responses to forelimb or hindlimb stimulation in VPL following DCN lesions. This distribution is not discretely somatotopic when evoked by electrical stimulation of peripheral nerves either prior to or following DCN lesioning.