PHRENIC RESPONSES TO CONTRALATERAL SPINAL STIMULATION IN RATS - EFFECTS OF OLD-AGE OR CHRONIC SPINAL HEMISECTION

Serotonin reveals ineffective spinal pathways from the C2-lateral funi culus to contralateral phrenic motoneurons in young adult rats with ac ute spinal hemisection. We tested the hypothesis that old age (1.5-2 y ears) or chronic hemisection (3-5 days) strengthens these pre-existing crossed spinal pathways. There were no consistent differences between young adult rats with acute hemisection versus young adult rats with chronic hemisection or old rat with acute hemisection except that one long-latency phrenic excitation could not be elicited in old rats. The results indicate that neither old age nor chronic hemisection strengt hens crossed-spinal pathways, but that old age may selectively diminis h spinal pathways involved in the neural control of breathing.