Dendritic alteration of spinal motoneurons after ablation of somatomotor cortex.

After peripheral axotomy, mammalian spinal motoneuron dendrites have been shown to cyclically degenerate and regenerate and after spinal dorsal horn mince to initially increase in length and then atrophy with time. In our experiment the dendritic profile of rat lamina IX motoneurons in the spinal segment under the T2 vertebra was studied for 90 postoperative days after bilateral somatomotor cortex ablation. The spinal cords were impregnated by the tungstate modification of the Golgi technique. Individual lengths along dendritic segments between branching points were measured from coded slides, the data computerized, and the dendrites reconstructed by computer. Interanimal statistical comparisons were made a priori (ANOVA) and a posteriori (Neuman-Keuls). There were no statistical differences in dendritic length or in the number of dendritic segments with DPO. However, there were shifts in the internal branching of all dendrites. The lack of statistical significance between control and experimental animals in numbers of dendritic branches with shifting internal dendritic branching was evidence that the motoneuron dendrites were actively growing but internal dendritic branch losses and gains were indistinguishable and approximately equally along the dendrite. These shifts in internal dendritic branching may be due to loss of information from the descending tracts.