CBF change evoked by somatosensory activation measured by laser-Doppler flowmetry: Independent evaluation of RBC velocity and RBC concentration

The purpose of this study was to examine the timing and magnitude of cerebr al blood flow (CBF) responses to neuronal activation. We measured the chang es in local CBF (LCBF), red blood cell (RBC) velocity and RBC concentration by laser-Doppler flowmetry (LDF) as well as field potential recordings dur ing activation of the somatosensory cortex of the rat in response to electr ical stimulation of the hind paw. Electrical stimuli, 0.1 ms pulses of 1-1. 5 mA for 5 s, were applied at: 0.2, 0.5, 5, 10 and 50 Hz under alpha-chlora lose anesthesia. LCBF showed the maximum increase at 5 Hz, and rose approxi mately 0.5 s after the onset of stimulation regardless of the frequency The maximum frequency of the field potentials was also obtained at 5 Hz. Durin g activation of the somatosensory cortex, the onset of rise in RBC concentr ation did not precede that of RBC velocity, and the peak RBC concentration was noted earlier than that of both LCBF and RBC velocity, suggesting that both arteriolar diameter and active changes in the capillary contributed to the LCBF response.