Role of the nucleus tractus solitarii and the rostral depressive area in the sympatholytic effect of 8-hydroxy-2-(di-n-propylamino)tetralin in the cat.

Bilateral microinjections of kainic acid (500 ng/site) into the nucleus tractus solitarii produced hypertension, tachycardia and sympatho-excitation in anesthetized cats. The cardiac-related component of renal sympathetic nerve activity was abolished as well as the sympatho-inhibitory effects that accompany the phenylephrine (5-10 micrograms/kg i.v.)-induced hypertension. About 60 min after kainic acid microinjections into the nucleus tractus solitarii, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) administered in cumulative doses (1-100 micrograms/kg i.v.) failed to alter mean blood pressure, heart rate or renal sympathetic nerve activity. In addition, bilateral microinjections of 8-OH-DPAT (2 nmol in 40 nl) into the nucleus tractus solitarii did not change mean blood pressure, heart rate or renal sympathetic nerve activity. Microinjections of kainic acid into the rostral vasodepressive area produced hypotension, bradycardia and renal sympatho-inhibition followed by persistent increases in blood pressure, heart rate and renal sympathetic nerve activity. These effects were also associated with an inhibition of the baroreceptor reflex elicited by phenylephrine and by the disappearance of the synchronism between the renal sympathetic bursts and cardiac rhythm. Subsequent i.v. 8-OH-DPAT (1-100 micrograms/kg) elicited decreases in mean blood pressure, heart rate and in renal sympathetic nerve activity. Central baroreceptor denervation by kainic acid lesions of the lateral tegmental field largely attenuated the hypotensive, bradycardiac and sympatho-inhibitory effects elicited by 8-OH-DPAT applied to the ventral surface of the rostral ventrolateral medulla.(ABSTRACT TRUNCATED AT 250 WORDS)