Substance P microinjections into the nucleus tractus solitarius elicit a pressor response in capsaicin-treated rats

The role of Substance P in the nucleus tractus solitarius was investigated by observing the effect of local injections of the peptide on blood pressure, heart rate and vasopressin secretion in both normal and neonatally capsaicin-treated rats. Substance P did not modify and of these parameters in control rats, but elicited a marked pressor response, not associated with changes in heart rate or plasma vasopressin levels, in capsaicin-treated animals. The study demonstrates that neonatal capsaicin treatment modifies the sensitivity of this area of the brainstem to exogenous substance P and provides evidence for a modulatory action of substance P on the cardiovascular system at the site of the nucleus tractus solitarius.