Absence of tonic supraspinal control of substance P release in the substantia gelatinosa of the anaesthetized cat.

Antibody microprobes were used to measure immunoreactive substance P (irSP) release in the substantia gelatinosa of the lower lumbar spinal cord of barbiturate-anaesthetized cats. Release of irSP was produced by noxious peripheral stimuli. Such release was not altered by blocking spinal conduction at the first lumbar segment by cooling or transecting the spinal cord. The results suggest that the release of irSP from the central terminals of nociceptors is not subject to tonic supraspinal inhibition.