Quantitative analysis of anatomical changes in the cuneate nucleus following forelimb denervation: a stereological morphometric study in adult cats.

Abstract

The consequences on the cuneate nucleus of the transection of the major nerves of the forelimb in adult cats were studied quantitatively with stereological procedures on celloidin-embedded material. The cell cluster region of the normal cuneate was 2.93 +/- 0.41 (mean +/- SD) mm3. This volume decreased significantly 4.5 weeks after the injury. The decrease amounted to 11-23%, and persisted until the longest survival studied (36 weeks). Despite this reduction in nuclear volume, there was no significant loss of neurons. The normal cell cluster region contained 48.8 +/- 7.3 (mean +/- SD) x 1000 neurons. Neuronal density showed a significant 16.8% mean increase between 4 weeks and 36 weeks of deafferentation. Perikaryal volume decreased by an average of 15.2%, between 1 and 36 weeks, but since cell bodies make only a small fraction of the total volume, much of the overall volume reduction observed must be attributed to a concomitant reduction of the neuropil. The distribution of cell size suggested that there are two populations of neurons, presumably corresponding to interneurons and projection neurons. This bimodal distribution was maintained after deafferentation, but after 4 weeks it shifted to the left, showing an increase in small cells and a decrease of large cells. These findings demonstrate that peripheral deafferentation causes a substantial and persistent decrease of cytoplasmic mass in the cuneate nucleus, involving both neuropil and neuronal cell bodies, but does not lead to neuron loss, at least up to 36 weeks after injury. These effects suggest that the altered synaptic input and trophic support subsequent to deafferentation leave the cuneate nucleus in a permanently compromised, albeit seemingly stable, state.