Dendritic alteration of rat spinal motoneurons after dorsal horn mince: computer reconstruction of dendritic fields

Mammalian spinal motoneuron dendrites respond with cyclic degeneration and regeneration after ventral root crush. In the following experiments, the cross-sectional dendritic profile of rat lamina IX, medial, motoneurons under the T2 vertebra were analyzed after mincing the dorsal horn (normals, 14, 30, 60, 90 days postoperative (DPO); N = 6 animals/DPO). 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 were computerized, and the dendrites were reconstructed by computer. Interanimal statistical comparisons were made by ANOVA a priori and Newman-Keuls test a posteriori. At 14 DPO, there was a statistically significant (P less than 0.05) increase in the number of dendritic segments, dendritic and serpentine length, and number of segments emanating from the soma compared with normal intact rats and with all other postoperative days. At 30 and 60 DPO, these parameters returned to normal values; however, there were many long, unbranched dendrites. At 90 DPO, there was a statistically significant (P less than 0.05) decrease in motoneuron dendritic serpentine length and segments. These data show that partially deafferented rat spinal motoneurons undergo a biphasic response; an initial growth phase followed by a degenerative phase.