Changes in c-fos expression in the dorsal column-medial lemniscal system following dorsal column lesions

Transection of the hindlimb dorsal column fibers leads to a partial deafferentation of the neurons of the nucleus gracilis, the first relay of the ascending dorsal column-medial lemniscal (DC-ML) neural network. In response to the deafferentation, a synaptic renewal cycle is initiated and the neurons of the nucleus gracilis atrophy. The present study examines the molecular changes that occur in synaptic relays of the ascending DC-ML following a hindlimb dorsal column transection. Rats were sacrificed 0.5, 1, 24, or 72 hours postlesion. Steady-state levels of mRNA coding for c-fos were significantly elevated only at 24 hours postlesion in caudal dorsal medulla, which contains the nucleus gracilis. The increased c-fos is neuronal in origin since there is an increased level of c-fos immunoreactivity in both the cluster neurons and the interneurons of the nucleus gracilis. In the third relay of the DC-ML system, the somatomotor cortex, levels of c-fos mRNA were significantly decreased 72 hours postlesion. These data indicate that lesions of the hindlimb dorsal column fibers have transneuronal effects on gene expression that extend to at least the third synaptic relay in the DC-ML system.