Laminar analysis of 2 deoxyglucose uptake in olfactory bulb and olfactory cortex of rabbit and rat

A method for mapping active regions in the nervous system, based on the use of radioactively labeled 2-deoxyglucose to localize sites of glucose uptake by active cells, has been applied to a laminar analysis of the olfactory bulb and olfactory cortex of rabbit and rat. In anesthetized rabbits, laminar densities reflecting different levels of glucose uptake can be correlated with the histological layers of the olfactory bulb. The lowest levels are found in the superficial olfactory nerve layer and the deep bulbar core. The highest levels are found at or near the glomerular, mitral cell body, and granule layers. A similar pattern is seen in the olfactory bulbs of resting awake rats. In addition, small foci of glucose uptake are present, localized to the layer of olfactory glomeruli. In rats exposed to strong stimulation by the odor of amyl acetate, broad regions of glucose uptake are found bilaterally on the medial and lateral bulbar aspects. The peak is in the glomerular layer, with spread into the adjacent layers. These patterns appear to reflect high energy demands of active unmyelinated axons in the olfactory nerve layers and synaptic terminals in the glomerular and external plexiform layers. The results provide evidence for spatial patterns within the bulb related to the processing of odor information. Laminar patterns of glucose uptake are also seen in the rat olfactory cortex. The lowest levels are found in the superficial lateral olfactory tract and the deep cortical core. The highest levels are found in the molecular, pyramidal cell body, and polymorphic cell layers. The peak in the inner part of the molecular layer may reflect activity in synaptic terminals of lateral olfactory tract fibers and intrinsic axon collateral systems.