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Local dentate circuits support spatial working memory regardless of position along the longitudinal hippocampal axis /

Abstract

The dentate gyrus (DG) is the initial site of information processing in the hippocampus. Previous studies have shown that the rostral-dorsal DG (rdDG) is essential in the rat's ability to discriminate similar spatial locations. In addition, the DG has been shown to support spatial working memory(WM). However, the question of how the DG supports spatial WM remains unclear. We demonstrated that spatial WM performance in rats is not selectively supported by a specific region along the longitudinal axis of the DG. Rats with 20 -40% volume reduction specific to the rdDG or the caudal-ventral DG (cvDG) did not impair spatial WM, suggesting a mechanism independent of the anatomical location of the DG could support WM. To further elucidate the mechanism responsible for WM in the DG, we investigated whether a compensatory activity of neurons existed in the remaining DG of the rdDG or cvDG lesion rats. Using immediate early gene c-fos to label active neurons in the DG granule cell layer, we quantified the number of active neurons for each group (control, rdDG lesion, and cvDG lesion) through stereological methods. The fraction of c-fos labeled granule neurons in the lesion groups did not change compared to control. Thus, WM is supported in rats with cvDG or rdDG lesions without compensatory activity of granule neurons.The result implies that local dentate circuits with a network in which sparsity is retained can support dentate-dependent memory

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