Hemodynamics of local cerebral blood flow induced by somatosensory stimulation under normoxia and hyperoxia in rats

We observed changes in the local cerebral blood how (LCBF), red blood cell (RBC) concentration and RBC velocity in a-chloralose anesthetized rats usin g laser-Doppler flowmetry during activation of the somatosensory cortex fol lowing electrical stimulation of the hind paw under hyperoxia (PaO2 = 513.5 +/- 48.4 mmHg; mean +/- S.D.) and normoxia (PaO2 = 106.4 +/- 8.4 mmHg). El ectrical stimuli of 5 and 10 Hz (pulse width 0.1 ms) with an intensity of 1 .5 mA were applied for 5 s (n = 13 at 5 Hz, n = 9 at 10 Hz). Baseline level s of LCBF and RBC concentration under hyperoxia were, respectively, 5.6 +/- 3.3 and 8.8 +/- 3.0% lower than those under normoxia (P < 0.05), and that of RBC velocity under hyperoxia was slightly higher than that under normoxi a (NS), suggesting mild vasoconstriction at rest under hyperoxia. At 5 Hz s timulation, after normalization to each baseline level, normalized response magnitudes of LCBF, RBC concentration and RBC velocity under hyperoxia wer e, respectively, 68.2 <plus/minus> 48.0, 71.1 +/- 65.5 and 66.0 +/- 56.3% g reater than those under normoxia (P < 0.05). At 10-Hz stimulation, normaliz ed response magnitudes of LCBF and RBC concentration under hyperoxia were, respectively, 44.6 <plus/minus> 32.0 and 55.9 +/- 43.5% greater than those under normoxia (P < 0.05), although a significant difference in the normali zed response magnitude of RBC velocity was not detected between both condit ions. The evoked LCBF under hyperoxia increased earlier, by approximately 0 .15 s, than that under normoxia regardless of the stimulus frequency (P < 0 .05). These results suggest the involvement of oxygen interaction on the re gulation of LCBF during neuronal activation. (C) 2001 Elsevier Science Inc. All rights: reserved.