Inset: Drawing of spinal gray matter divided into radial sectors for measure of quadriceps motoneuron dendritic distribution. Length per radial bin of quadriceps dendrites in untreated animals (black bars), saporin-injected animals that either received no further treatment (SAP, white bars) or were given ad lib exercise (SAP+EXERCISE, light gray bars), and intact animals given ad lib exercise (intact+EXERCISE, dark gray bars). For graphic purposes, dendritic length measures have been collapsed into 6 bins of 60° each. Quadriceps motoneuron dendritic arbors display a non-uniform distribution, with the majority of the arbor located between 300° and 120°. Following saporin-induced motoneuron death, surviving neighboring motoneurons had reduced dendritic length throughout the radial distribution. Exercise attenuated this reduction, but had no effect in intact animals. Bar heights represent means ± SEM. * indicates significantly different from untreated animals. † indicates significantly different from untreated saporin-injected animals.