CORTICOSPINAL PROJECTION PATTERNS FOLLOWING UNILATERAL SECTION OF THECERVICAL SPINAL-CORD IN THE NEWBORN AND JUVENILE MACAQUE MONKEY

Immediately following a unilateral section of the midcervical spinal c ord that interrupts the dorsolateral, lateral, and ventral columns, th e macaque monkey has a severe flaccid paralysis on the side of the les ion. Recovery of hand function is rapid, and, although it is incomplet e, within a few months, the monkey uses the initially disabled hand an d fingers with considerable skill. We examined the accompanying change s in the pattern of projection of corticospinal neurons to the cervica l spinal cord that occurred following such a lesion. Spinal section wa s done both in newborn and juvenile macaques, and the postlesion perio d was followed for up to 150 weeks. Corticospinal neuron populations w ere visualized by using both anterogradely and retrogradely transporte d labels, and their origins, spinal pathways, and terminations were ex amined at intervals during the period of recovery of hand function. Im mediately following unilateral section of the spinal cord at C3, sampl ed counts of soma profiles of retrogradely labeled neurons indicated t hat there was a profound reduction in the corticospinal projection to the hemicord caudal to the lesion. The few labeled corticospinal axons spared by the lesion bypassed the spinal lesion by descending in the contralateral cord and then crossing the midline caudal to the lesion. A few corticospinal axons may also have bypassed the lesion in the ip silateral ventromedial column when this was not fully interrupted by t he lesion. In every monkey, we observed a similar, profound reduction in the corticospinal (and rubrospinal) projections to the hemicord cau dal to the lesion: This pattern did not alter significantly over an ex tended recovery period. An unchanging corticospinal projection to the cervical spinal cord contralateral to the lesion was also visualized i n each monkey and resembled that seen in the normal macaque. Although the resolution of the labeling and counting procedures used precluded the identification of small increases in the numbers of corticospinal neurons projecting to the hemicord caudal to the lesion, we concluded that there was no substantial reconstruction of this projection over a recovery period of more than 2 years. (C) 1997 Wiley-Liss, Inc.