Elsevier

Experimental Neurology

Volume 52, Issue 3, September 1976, Pages 480-495
Experimental Neurology

The immediate shift of afferent drive of dorsal column nucleus cells following deafferentation: A comparison of acute and chronic deafferentation in gracile nucleus and spinal cord

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Abstract

The somatotopic map of the gracile nucleus was determined using tungsten electrodes in anesthetized adult cats. Following deafferentation of the hind leg by cutting all dorsal roots caudal to L3, the nucleus was remapped. The total number of points in the map where abdomen responses were recorded doubled immediately following deafferentation. The latency of responses of cells responding to brush of the abdomen was not different after deafferentation. Some of the cells which began responding to abdominal stimulation had one or more of the following characteristics: (i) a rapid flick of the hair was required to fire the cell, (ii) habituation, and (iii) widespread inhibitory fields. To confirm that individual cells had switched the afferents which excite them, we examined the respone of single cells before, during, and after a reversible cold block of all the afferents from the hind leg. Of 40 single cells examined, 11 which had receptive fields on the leg switched their receptive fields to the abdomen as soon as the block of leg afferents was complete. Mapping the gracile nucleus 8 months following deafferentation still showed an increase in abdominal representation. Examination of the dorsal horn in the L6–7 segment of these chronically deafferented cats showed that abdominal afferents excited cells in a region normally responding to leg afferents. These results suggest that deafferentation results in the unmasking of normally ineffective connections. Unmasking could be a mechanism which explains many of the observed changes in the responses of central nervous system neurons following lesions.

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    Dorsal root entry zone lesions have been reported to immediately abolish trigger zones associated with nerve root avulsions [25], supporting a primary subcortical mechanism for referral after nerve injury. There is a large amount of literature demonstrating reorganization following deafferentation at the level of the thalamus [5,18] and the gracile and cuneate nuclei of the brainstem [5,9,13,34] in primates and cats. Davis and colleagues [6] found a large representation of the stump in patients with limb amputation, compatible with the expansion of somatotopically adjacent regions into deafferented regions in the thalamus.

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2

Dr. Dostrovsky is a postdoctoral fellow of the Medical Research Council of Canada.

3

The present address of Dr. Millar is the Physiology Department, The London Hospital Medical College, Turner St., London E1.

1

This work was supported by the Medical Research Council of Great Britain and by the U. S. National Institutes of Health.

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