SIGNAL-AVERAGED LASER-DOPPLER MEASUREMENTS OF ACTIVATION-FLOW COUPLING IN THE RAT FOREPAW SOMATOSENSORY CORTEX

Regional alterations in cerebral blood flow (CBF) are widely used as a surrogate for neuronal function based on an intact coupling between c hanges in regional CBF and metabolism, activation-flow coupling (AFC). To further investigate parameters affecting AFC, we have implemented a rat model with electrical forepaw stimulation under alpha-chloralose anesthesia using laser Doppler (LD) measurements of flow parameters t hrough thinned skull over contralateral somatosensory cortex. Signal a veraging of the LD response was used to improve reproducibility. A cha racteristic flow response to electrical forepaw stimulation was reliab ly recorded from the somatosensory cortex using signal averaging. Stim ulation at 5 Hz maximized the LD response, and constant current stimul ation up to 1 mA did not induce changes in systemic blood pressure. Th e shape of the flow response consisted of an initial peak followed by a steady state plateau phase which was observed for stimulation durati ons longer than 4 s. When individual LD parameters of velocity, red bl ood cell concentration (CRBC), and cerebral blood flow (CBF) were comp ared, changes in LDCBF were primarily attributable to changes in LDvel ocity rather than LDCRBC. This finding was also observed during hyperc apnia. Characterization of AFC in the model provides a background for future studies of the effects of pharmacological manipulation or patho physiological states. (C) 1998 Elsevier Science B.V. All rights reserv ed.