Functional recruitment of red blood cells to rat brain microcirculation accompanying increased neuronal activity in cerebellar cortex

SCANNING laser-Doppler flowmetry (SLDF) combines laser-Doppler flowmetry an d laser scanning to provide images of cerebral blood flow (CBF) with high s patial and temporal resolution. We investigated the contribution of single vascular elements to the local increase of CBF accompanying increased neuro nal activity in halothane-anesthetized rats. CBF was examined in the cerebe llar cortex under control conditions and in response to electrical stimulat ion of parallel and climbing fibers. At rest, arterioles contributed 9%, ve nules 11-13% and small vessels (< 20 mu m) 8-14%, while the background cons tituted 64-72% of the total SLDF signal. During activation the background s ignal decreased to 55-60% while the signal from arterioles increased to 11- 12%, from venules to 14-15% and from small vessels to 14-19%. The signal in crease in small vessels that did not give any laser-Doppler signal at rest was due to functional recruitment of red blood cells to the capillary bed. We conclude that functional recruitment may be an integral part of the hemo dynamic response accompanying neuronal activity. NeuroReport 10:3257-3263 ( C) 1999 Lippincott Williams & Wilkins.