A hypertensive response to baclofen in the nucleus tractus solitarii in rats.

The hypertension and tachycardia after intraperitoneal administration of baclofen, 5 mg kg-1, to conscious rats was prevented by a midcollicular decerebration but not by a brain transection rostral to the hypothalamus. In conscious rats, local application of baclofen (50 ng) into the region of the nucleus tractus solitarii (NTS) caused a consistent pressor response while injections into the hypothalamus, n. fastiguus, nn. amygdala, nn. dorsalis raphe or n. locus coeruleus did not. The cardiovascular effects of NTS injections of baclofen in anaesthetized animals were variable. The reflex heart rate reduction to noradrenaline (0.5 microgram i.v.) was prevented by administration of baclofen i.v. as well as locally into the NTS. It is concluded that baclofen causes elevation of blood pressure in the NTS, and that this structure is a possible locus of action for systemically administered baclofen in producing hypertension.