Changes in number and size of Clarke's column neurons after cord transection.

The number of large neurons in Clarke's column of the L-1 segment of the spinal cord of the rat decreases five or more weeks after a T-9 spinal cord transection. Analysis of cells at 1, 2, 3, 5, 7, 9, 12, and 15 weeks (wk) postoperatively demonstrates a loss of large neurons at each time interval beyond five wk postoperatively. Comparison of cell sizes found in the anatomic region of Clarke's column at two or three wk postoperatively with the cells found at 15 wk after transection and their respective control groups, shows a decrease in total cells found in operated rats 15 wk postoperative with a profound decrease in larger neurons in these rats. We did not detect a significant offsetting increase in smaller neurons. We believe the observed changes are due to death of large neurons and can find no evidence to support the contention that axotomized cells persist in a shrunken, atrophic state.