NERVE GROWTH-FACTOR PREVENTS APOPTOTIC CELL-DEATH IN INJURED CENTRAL CHOLINERGIC NEURONS

Experimental lesions have been widely used to induce neuronal degenera tion and to test the ability of trophic molecules to prevent lesion-in duced alterations, but these studies have not demonstrated unequivocal ly that afflicted neurons die as a result of these manipulations. The documentation of neuronal death in the above-described models and the time when it occurs after injury are crucial for the interpretation of trophic effects. In the present study, we combined multiple approache s to investigate the nature of retrograde neuronal changes in choliner gic neurons of the medial septal nucleus (MSN) after complete, unilate ral transection of the fimbria-fornix (F-F). Projection neurons of the MSN were prelabeled with the fluorescent tracer Fluoro-gold (FG) 1 we ek prior to lesion. By counting both FG-labeled and choline acetyltran sferase (ChAT)-immunoreactive neurons in the MSN at multiple time poin ts postaxotomy, we differentiated the phenotypic response to injury fr om the degenerative process and established a critical time between th e third and fourth weeks postaxotomy, during which similar to 50% of f luorescent perikarya disappear. Working in the previous time window, w e identified dying cells by electron microscopy (EM) and terminal tran sferase-mediated (TdT) deoxyuridine triphosphate (d-UTP)-biotin nick e nd labeling (TUNEL) and showed that MSN neurons die via apoptosis, beg inning at 16 days postaxotomy. An additional group of animals was allo wed to survive for 1 month (i.e., 10 days after cell death has been co mpleted); during this period, animals were treated with intraventricul ar nerve growth factor (NGF). Quantitative analysis of surviving choli nergic perikarya showed that NGF prevented retrograde degeneration of the majority of neurons. In concert, the results of the present study establish that NGF does not merely protect the phenotype but also prev ents cell death in lesioned central cholinergic neurons. (C) 1995 Wile y-Liss, Inc.