Systemic and regional haemodynamic responses elicited by microinjection of N-methyl-D-aspartate into the lateral periaqueductal gray matter in anaesthetized rats.
The haemodynamic defence responses were studied by chemically stimulating the lateral periaqueductal gray matter in 27 anaesthetized, artificially ventilated, and paralysed rats. Blood flow was measured by the radiolabelled microsphere method. Microinjection of N-methyl-D-aspartate (1 nmol as 100 nl of a 10-mM solution, delivered over 10 s) into the brain region elicited a distinctive pattern of haemodynamic defence responses. Vasodilation of the hindlimb skeletal muscle tended to be provoked from the caudal third of the periaqueductal gray, whereas vasoconstriction was elicited from the intermediate third. Whichever stimulation was made, however, increases in arterial pressure, heart rate, cardiac output, and total peripheral resistance were consistently provoked. The blood flow was redistributed away from the abdominal viscera. One new finding was that the brain and heart also had their blood flow increased consistently, the former with and the latter without a significant decrease in vascular resistance. As suggested for the classic pattern of haemodynamic defence responses, we consider that the cerebral and coronary circulations may also be involved in coping with the emergency that threatens the animal. The increased cerebral blood flow should be beneficial for ensuring adequate achievement of central processing and organization of the well-coordinated defence reactions. The increased coronary blood flow should help to ensure maintenance of an increased cardiac output striving against the increased total peripheral resistance.
Nakai
M
M
National Cardiovascular Center Research Institute, Osaka, Japan.
Maeda
M
M
D000758:Anesthesia; D000818:Animals; D001933:Brain Stem / Q000033:anatomy & histology / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects*; D008297:Male; D008845:Microinjections; D008863:Microspheres; D016202:N-Methylaspartate / Q000008:administration & dosage / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000033:anatomy & histology / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012039:Regional Blood Flow / Q000187:drug effects; D013238:Stereotaxic Techniques; D013268:Stimulation, Chemical
D016202:N-Methylaspartate