Baclofen and the Release of Neuropeptides in the Cat Spinal Cord

The antibody microprobe technique was used to study the effect of baclofen on the release of immunoreactive substance P and immunoreactive calcitonin gene-related peptide within the lower lumbar spinal cord of pentobarbitone-anaesthetized spinalized cats. Both peptides were released in the region of the substantia gelatinosa during ipsilateral noxious cutaneous stimulation or high-intensity electrical stimulation of a hind limb nerve. Intravenous administration of baclofen suppressed the excitation of lumbar dorsal horn neurons, but did not produce detectable alterations of the evoked release of immunoreactive substance P or immunoreactive calcitonin gene-related peptide in the superficial grey matter dorsal to these neurons. The results suggest that the antinociceptive action of baclofen does not involve a reduction of the intraspinal release of substance P or calcitonin gene-related peptide from the central terminals of nociceptive sensory fibres.