The behavioural effects of intrathecally administered [D-PRO2, D-TRP7,9]-substance P, an analogue with presumed antagonist actions, in the rat.

[D-Pro2, D-Trp7,9]-substance P, an analogue of the putative nociceptive primary afferent neurotransmitter substance P, was administered to rats via chronically implanted intrathecal catheters (0.5-2.5 nmol per rat). Several animals showed large elevations of thermal and mechanical nociceptive thresholds, but these effects were always accompanied by profound, often long-lasting, impairments of motor function and thus cannot be regarded as a specific antinociceptive effect of the drug. These behavioural effects are considered to be probably due to direct spinal actions of the drug rather than antagonism of spinal substance P systems.