Spinal cord blood flow decreases following chemical stimulation of the rostral ventrolateral medullary pressor area in anesthetized rats

Abstract In urethane-anesthetized, paralyzed and artificially ventilated rats, the neurons in the rostral ventrolateral medullary pressore area (VLPA) were chemically stimulated by microinjections of l -glutamate (1.7–5.0 nmol in 100 nl of 0.9% sodium chloride solution) and the spinal cord blood flow (SCBF) was determined using a combination of labeled microspheres ( 57 Co, 113 Sn and 46 Sc). In order to measure SCBF at normotension, moderate hypotension within the lower limit of spinal cord autoregulation was induced by controlled hemorrhage ( n = 12). Unilateral chemical stimulation of the VLPA in these rats increased arterial blood pressure (ABP) but it remained within normotensive range. The SCBFs of cervical, thoracic and lumbar cord decreased significantly from 27 ± 3 (mean ± S.E.M.) to 20 ± 2 ( P P P −1 · (100 g) −1 , respectively. The spinal cord vascular resistances (SCVRs) of cervical, thoracic and lumbar cord increased significantly from 3.7 ± 0.4 to 5.0 ± 0.6 ( P P P −1 · (100 g) −1 ], respectively. During the chemical stimulation of the VLPA, SCBF increased in response to the changes in arterial PaCO 2 indicating that the reactivity of spinal cord vasculature was intact ( n = 5). Microinjections of l -glutamate into an area adjacent to the VLPA had no effect on spinal cord circulation ( n = 5). These results suggest that the neurons within the VLPA may play a role in the control of spinal cord circulation.