HIPPOCAMPAL AND ENTORHINAL GLUCOSE-METABOLISM IN RELATION TO CHOLINERGIC THETA RHYTHM

Hippocampal and entorhinal cortex glucose metabolism were studied by C -14-2-deoxyglucose (2-DG) autoradiography in anesthetized rats with an d without continuous theta rhythm (theta). 2-Deoxyglucose changes in s pecific cytoarchitectonic regions were precisely assessed by an innova tive approach. In the absence of theta there were areas with a higher glucose metabolism corresponding to neuropile regions at CA3, dentate gyrus, and subiculum, while the cellular layers always showed lower va lues. In the presence of theta, provoked by intraventricular injection s of anticholinesterases (i.e., physostigmine) or curarimimetics (i.e. , d-tubocurarine), 2-DG uptake showed two opposite significant changes in relation to controls: a) it increased in the outer zone of the mol ecular layer (inner blade) of the dentate gyrus, and in the stratum la cunosum-moleculare of CA3, suggesting an increase in perforant path in put during theta rhythm; b) it decreased in the hilar dentate region. This noteworthy decrease in metabolic activity probably reflects an hi lar inhibition by local circuits during theta rhythm generation.