Enhancement of c-fos Expression in Neurons of the Rat Spinal Cord after Partial Denervation: Evidence for Functional Plasticity

Abstract

c-fos immunocytochemistry was used to test a functional correlate of neuroplasticity involving nociceptive primary afferent fibers in the partially denervated adult rat spinal cord. Unilateral dorsal root ganglionectomies were made at L1-L4 (chronic side). After 3 weeks, contralateral L1-L4 ganglionectomies (acute side) were made 1 week prior to sacrifice. Two hours prior to perfusion, the animals were anesthetized and their hindlimbs were immersed in a 52°C water bath for 20 s. The spinal cords were then processed for c-fos immunocytochemistry and the numbers of c-fos-immunoreactive cells determined. Following bilateral noxious thermal stimulation of the hindlimbs, the numbers of c-fos-immunoreactive cells in laminae I-II from L3 to L5 were increased by nearly twofold on the chronically deafferented side of the spinal cord ( P < 0.05). This finding suggests augmented functional plasticity of nociceptive primary afferent fibers on the chronically denervated side of spinal cord. These observations are discussed with relation to recent demonstrations of enhanced calcitonin gene-related peptide immunoreactivity and possible primary afferent fiber sprouting in similar denervation models.