REDUCED RETROGRADE LABELING OF DIENCEPHALIC-PROJECTING NEURONS IN THE GRACILE NUCLEUS OF THE MONKEY FOLLOWING REMOVAL OF DORSAL COLUMN INPUT

As part of an anatomical investigation of neuronal responses to deafferentation of the dorsal column nuclei by transection of the dorsal spinal columns, the uptake and retrograde transport of HRP by thalamic projection cells in the dorsal column nuclei was studied. The ventrobasal thalamus of 13 macaque monkeys was injected bilaterally with HRP at periods ranging from 3 to 364 days following intended unilateral transection of fasciculus gracilis at a mid- to upper thoracic level. The density of labeled cells in the gracile nuclei ipsilateral to complete lesions of fasciculus gracilis was compared with the density of labeled cells in the contralateral gracile nuclei that were fully innervated or partially denervated by an incomplete lesion. Also, the density of labeled cells in the fully innervated cuneate nuclei was compared. In general, there was a reduction in density of labeled cells in the gracile nuclei ipsilateral to complete lesions, without a corresponding decrement in labeled cells in the cuneate nuclei on that side. This result confirms effects on spinal motoneurons and on thalamocortical projection cells in the lateral geniculate nucleus following deafferentation. However, attempts to define a time course for the reduction in transport by lemniscal projection cells revealed an effect that was dramatic in some animals, partial in others, and not demonstrable in the remainder, without a clear relationship to time after surgery. This result is related to a literature which describes a variety of morphological, biochemical, electrophysiological, and behavioral effects of deafferentation which appear to wax and wane with time after neuronal injury. © 1993 by Academic Press, Inc.