AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 5 1052-R1059, Copyright © 1993 by American Physiological Society
Role of periaqueductal gray in the pressor response produced by central injections of angiotensin II
L. R. Portis, S. J. Lewis and M. J. Brody
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242.
The present studies were undertaken to determine the role of rostral
periaqueductal gray (PAG) in mediating the pressor effect produced by
intracerebroventricular (icv) injection of angiotensin II (ANG II, 200 ng).
Two functionally and anatomically distinct sites were identified in rostral
PAG: a dorsomedial site involved in the hemodynamic responses produced by
electrical stimulation of the anteroventral third ventricle (AV3V) region
and a ventromedial site required for the pressor response elicited by icv
administration of ANG II. In Saffan-anesthetized rats, injection of
lidocaine (LIDO, 4%) in dorsomedial PAG, but not in ventromedial PAG,
significantly attenuated the decrease in hindquarter resistance (HQR)
produced by electrical stimulation of the AV3V region, and the
poststimulatory increase in mean arterial pressure (MAP) and HQR. The
injection of LIDO in ventromedial PAG had no effect on the hemodynamic
responses produced by electrical stimulation of the AV3V region in
anesthetized rats but significantly attenuated the pressor response
produced by icv administration of ANG II in conscious rats. The hypothesis
that these two sites receive separate projections was addressed by
microinjecting two retrogradely transported fluorescent dyes, Fluoro-Gold
and Fast Blue. The anatomic findings suggest that separation of the
pathways activated by electrical and chemical stimulation of the AV3V
region occurs at the level of rostral PAG.
