Experience-dependent development of spinal motor neurons

Locomotor activity in many species undergoes pronounced alterations in earl y postnatal life, and environmental cues may be responsible for modifying t his process. To determine how these events are reflected in the nervous sys tem, we studied rats reared under two different conditions-the presence or absence of gravity-in which the performance of motor operations differed. W e found a significant effect of rearing environment on the size and complex ity of dendritic architecture of spinal motor neurons, particularly those t hat are likely to participate in postural control. These results provide ev idence that neurons subserving motor function undergo activity-dependent ma turation in early postnatal life in a manner analogous to sensory systems.