THE EFFECTS OF MIDLUMBAR SPINAL-CORD SECTION ON OPIOIDERGIC MODULATION OF THE SURAL GASTROCNEMIUS REFLEX OF THE RABBIT

In decerebrated rabbits spinalized at the thoraco-lumbar junction, crushing the spinal cord between segments L4 and L5 resulted in enhancement of the sural-gastrocnemius reflex. After midlumbar crush, naloxone increased the reflex response to significantly greater levels than observed in earlier experiments in rabbits with only a low thoracic spinal section. Naloxone-reversible, stimulus-evoked inhibition of the reflex response was not affected by midlumbar crush. These findings show that neurones in midlumbar segments of the spinal cord do not contribute to opioidergic modulation of the sural-gastrocnemius reflex.