Prakash N, Cohen-Cory SC, Frostig RD (2000) NGF-induced rapid functional plasticity in the adult rat somatosensory cortex is mediated by fibers originating in the basal forebrain cholinergic system. Neuroscience 2000 Abstracts 722.6. Society for Neuroscience, New Orleans, LA.
Summary: We have previously demonstrated, by using intrinsic signal optical imaging in vivo, that topical application of nerve growth factor (NGF) to the somatosensory cortex of an adult rat augments the functional representation of a whisker, within minutes after NGF application (Prakash et al. Nature 381:702-6, 1996). In addition, we have shown that the NGF receptor, TrkA is found on fibers projecting to the cortex. We have now tested the hypothesis that these TrkA-positive fibers originate in basal forebrain cholinergic system (BFCS) and that NGF augments the size and amplitude of a cortical representation by enhancing the release of ACh from these fibers. To this end we demonstrate: 1) that BFCS fibers indeed express TrkA receptors by co-localizing TrkA and ChAT immunostaining to single cortical fibers; 2) that removal of these cortical BFCS-fibers by injection of a specific cytotoxin, 192 IgG-saporin, prevented the NGF-induced augmentation; and 3) that topical application of the ACh agonist carbachol induced a rapid augmentation of the whisker functional representation similar to the one observed with NGF. Thus, these results firmly support our hypothesis that NGF-induced effects on cortical functional representations are mediated by the BFCS projection fibers and provide a mechanism for NGF-induced rapid plasticity in vivo.
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