PROPRIOSPINAL NEURONS IN THE C1-C2 SPINAL SEGMENTS PROJECT TO THE L5-S1 SEGMENTS OF THE RAT SPINAL-CORD

Physiological studies indicate that neurons in the upper cervical spin al cord have descending projections to the lumbosacral spinal cord and mediate inhibition of dorsal horn neurons activated from afferent inp ut. In the present study, retrograde tracing techniques were used to e xamine the distribution of propriospinal neurons in C1-C2 spinal segme nts that project to lumbosacral spinal segments, Fluorogold or horsera dish peroxidase were injected unilaterally or bilaterally into the L5- S1 spinal segments. After 2-4 days, rats were perfused with fixative a nd C1-C2 spinal segments were processed for retrograde labeling. Numer ous neurons were found in the C1-C2 segments. In unilaterally and bila terally injected rats, retrogradely labeled neurons were located on bo th the ipsilateral and contralateral sides. Retrogradely labeled neuro ns were located in the following locations: lateral cervical and spina l nuclei, nucleus proprius, ventral horn and the central gray region ( area X), These studies demonstrate a descending projection from C1-C2 segments to the lower lumbar and sacral spinal cord. We hypothesize th at many of these C1-C2 propriospinal neurons are important in modulati ng responses of spinal neurons at lower segmental levels to various pe ripheral stimuli. (C) 1998 Elsevier Science Inc.