Hippocampal laminar glucose utilization and theta rhythm following unilateral fimbria-fornix lesions in rats

Laminar profiles of glucose utilization were related to the presence or absence of movement-related hippocampal theta rhythm in CA1 and dentate gyrus of rats after aspirative unilateral combined lesions of the fimbria-fornix and cingulum. Three groups were studied: (1) sham-operated rats, (2a) lesioned rats with an ipsilateral loss of theta activity at 4 weeks post-lesion that persisted at 12 weeks post-lesion, and (2b) lesioned rats with a loss of theta activity at 4 weeks post-lesion, but a recovery of theta rhythm at 12 weeks post-lesion. Fimbria-fornix/ cingulum lesions served both to abolish ipsilateral theta rhythm and to decrease ipsilateral glucose metabolism in all cell layers of CA1 and the dentate gyrus, when normalized to the contralateral hemisphere. Although glucose metabolism in lesioned animals with a recovery of theta rhythm was not as high as control levels, in several laminae it was significantly higher than that of lesioned animals with persistent loss of theta rhythm. These laminae included the dentate hilus and strata oriens, pyramidale and lucunosum-moleculare of CA1. The increased glucose metabolism associated with the return of theta rhythm suggests a functional reinnervation of these layers of the hippocampus in such animals.