Role of dorsal medullary reticular formation in maintenance of vasomotor tone in rats

Abstract

Recent investigations of central nervous system structures involved in the generation of vasomotor tone have focused on the rostral ventrolateral portion of the medulla, whereas other medullary areas have not been considered to have primary importance. The present study was designed to determine the role of the medullary reticular formation, dorsal to the ventrolateral medulla, in the maintenance of vasomotor tone. The effects of microinjections of the inhibitory amino acid glycine into this medullary region on systemic arterial pressure, heart rate and renal nerve activity were determined in male rats anaesthetized with propofol and treated with atropine to block vagal influences on the heart. Unilateral injections (24 of 57 sites) of glycine into the dorsal medulla caused significant decreases in arterial pressure (−10 ± 1.0 mmHg) and renal sympathetic nerve activity (−12 ± 1%) whereas heart rate was not significantly affected. Bilateral injections (12 of 20) of glycine caused significantly greater decreases in heart rate (−10 ± 1 bpm) and renal nerve activity (−25 ± 4%) than were elicited by unilateral injections. In contrast, although arterial pressure decreased significantly from control values (−10 ± 1 mmHg), these responses were not different from the arterial pressure changes caused by unilateral injections. These results demonstrate that, in the propofol anaesthetized rat, neurons in the dorsal medullary reticular formation contribute to the maintenance of vasomotor tone.