Spinal projections to the parabrachial nucleus are substance P-immunoreactive.

Substance P plays an important role in nociceptive processing in the spinal cord. Substance P is also present in several supraspinal regions, such as the pontine parabrachial nucleus, a major relay for autonomic regulation. In this study we examined in the cat with an immunogold method the presence of substance P-like immunoreactivity in spinoparabrachial terminals that were labelled by anterograde transport of unconjugated and lectin-conjugated horseradish peroxidase. We found that dense core vesicles in anterogradely labelled terminals were substance P-immunoreactive. Taken together with previous observations that noxious stimuli increase preprotachykinin expression in ascending nociceptive pathways from the spinal dorsal horn, the present finding provides evidence that substance P is involved in nociceptive processing also in the brain stem.