Radial columns in autoradiographs generated from tracer methods for measuring cerebral cortical blood flow

Radial columns in the cerebral cortex, sometimes seen in autoradiographic methods for measuring cerebral blood flow, were studied. Radioactively labeled tracers were injected into the internal carotid artery in pentobarbital sodium-anesthetized rats. The cortical patterns of tracer uptake were determined using autoradiography. When tracers for measuring cerebral blood flow were administered, cortical columns were apparent in the autoradiograph. The darker columns (higher tracer concentration) in the image aligned with penetrating arterioles, suggesting that the tracer was being removed from the penetrating arterioles. In another experiment, [14C]glucose was used as a qualitative blood flow tracer. Modeling of glucose uptake predicts that 26-29% more glucose should be extracted in the dark columns than the light columns if the columns represent capillary blood flow. [14C]glucose did not produce the cortical columns consistent with the model prediction. We conclude that capillary blood flow in the cortex is not organized in radial columns of higher and lower flow. The results support the idea that the flow tracers are removed from blood primarily in the penetrating arterioles.