Activity-induced changes in cerebellar blood flow M. Lauritzen a, * , K. Caesar b a Department of Clinical Neurophysiology, Glostrup Hospital, Denmark b Department of Medical Physiology, Panum Institute, University of Copenhagen, Copenhagen, Denmark Abstract Changes in brain cellular activity are accompanied almost invariably by changes in the local cerebral blood flow (CBF). In most functional imaging studies, the increase in local blood flow is assumed to correlate with an increase in the net spike activity of the neurons in the activated region. The question raised in this work is whether the increase in perfusion correlates to spike activity or synaptic transmission, or both. By utilizing measurements of neuronal activity, i.e., single-cell spike activity and synaptic activity of ensembles of neurons (i.e., field potentials), we were able to show that activity-dependent increases in CBF are independent of spiking activity; however, it can be explained by active and passive pre- and postsynaptic mechanisms distinct from spiking. Our work has primarily been focused on the cerebellar cortex where CBF was monitored by laser-Doppler flowmetry and neuronal activity was measured using a glass electrode positioned close to the Purkinje cell. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Cerebral blood flow; Electrophysiology; Cerebellum; Glutamate; GABA 1. Introduction Neurovascular coupling is a fundamental feature of the brain and is traditionally seen as an increase in spike activity in the principal target cells or interneurons of the active brain region, accompanied by an increase in metabolism and CBF [1]. The issue addressed in this study is whether the increase in perfusion correlates to spike activity, or rather to synaptic transmission, or both. Our working hypothesis is that events related to passive and active postsynaptic events trigger and determine the amplitude of the blood-flow increase. These events are the interaction of the neurotransmitter with the receptor, external and internal gating of ion conductance and the production of second messengers (including calcium), 0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII:S0531-5131(02)00197-8 * Corresponding author. E-mail address: mlauritz@mfi.ku.dk (M. Lauritzen). International Congress Series 1235 (2002) 251 – 257