AUTORADIOGRAPHIC EVIDENCE FOR FLOW-METABOLISM UNCOUPLING DURING STIMULATION OF THE NUCLEUS BASALIS OF MEYNERT IN THE CONSCIOUS RAT

We earlier reported that electrical stimulation of the rat nucleus bas alis of Meynert (NBM) induces large cerebral blood flow increases, par ticularly in frontal cortical areas but also in some subcortical regio ns. The present study was designed to address the issue of blood flow control exerted by NBM projections. To this aim, we have determined wh ether these flow increases were associated with proportionate changes in metabolic activity as evaluated by cerebral glucose utilization (CG U) strictly under the same experimental conditions in the conscious ra t. An electrode was chronically implanted in a reactive site of the NB M as determined by laser-Doppler flowmetry (LDF) of the cortical circu lation. one to two weeks later, while the cortical blood flow was moni tored by LDF, we measured CGU using the [C-14]2-deoxyglucose autoradio graphic technique during unilateral electrical stimulation of the NBM, and analyzed the local flow-metabolism relationship. The large increa ses in cortical blood flow induced by NBM stimulation, exceeding 300% in various frontal areas, were associated with at most 24% increases i n CGU (as compared with the control group) in one frontal area. By con trast, strong increases in CGU exceeding 150% were observed in subcort ical regions ipsilateral to the stimulation, especially in extrapyrami dal structures, associated with proportionate CBF changes. Thus, none of the blood flow changes observed in the cortex can be ascribed to an increased metabolic activity, whereas CBF and CGU were coupled in man y subcortical areas. This result indicates that different mechanisms, which do not necessarily involve any metabolic factor, contribute to t he regulation of the cerebral circulation at the cortical and subcorti cal level. Because the distribution of the uncoupling is coincident wi th that of cholinergic NBM projections directly reaching cortical micr ovessels, these data strongly support the hypothesis that NBM neurons are capable of exerting a neurogenic control of the cortical microcirc ulation.