Morphological changes of large layer V pyramidal neurons in cortical motor-related areas after spinal cord injury in macaque monkeys

Abstract

Abstract In primates, neurons giving rise to the corticospinal tract (CST) are distributed in several motor-related areas of the frontal lobe, such as the primary motor cortex (M1), the supplementary motor area (SMA), and the dorsal and ventral divisions of the premotor cortex (PMd, PMv). Recently, we have analyzed the morphology of basal dendrites of CST neurons, i.e., large layer V pyramidal neurons in macaque monkeys and shown that the complexity and spine density of the dendrites vary across the motor-related areas. Here, we investigated the alterations in basal dendrite morphology of CST neurons after spinal cord injury (SCI). In our SCI model, both the intersection number and the spine density of basal dendrites were highly decreased throughout the motor-related areas. Notably, these events were less prominent for the PMd than for the M1, SMA, and PMv. When we further compared the density changes post-SCI of the filopodia-, thin-, stubby-, and mushroom-type spines in individual areas, it was found that the density of filopodia-type (immature) spines was increased for all the areas, whereas the other types of spines exhibited their density reductions. Again, such spine density reductions were so limited for the PMd as compared to the M1, SMA, and PMv.