Beta-amyloid-induced cholinergic denervation correlates with enhanced nitric oxide synthase activity in rat cerebral cortex: reversal by NMDA receptor blockade.

Ample experimental evidence indicates that acute beta-amyloid infusion into the nucleus basalis of rats elicits abrupt degeneration of the magnocellular cholinergic neurons projecting to the cerebral cortex. In fact, involvement of a permanent Ca2+ overload, partially via N-methyl-D-aspartate (NMDA) receptors, was proposed as a pivotal mechanism in beta-amyloid-induced neurodegeneration. A definite measure of NMDA receptor-mediated processes and subsequent Ca2+ entry is the induction of Ca2+/calmodulin-activated neuronal nitric oxide synthase (nNOS) in nerve cells. In the present account we therefore assessed activation of nNOS in correlation with cholinergic decline after beta-amyloid(1-42) or beta-amyloid(25-35) infusion into the rat nucleus basalis. The results demonstrate the beta-amyloid conformation-dependent enhancement of cortical nitric oxide synthase (NOS) activity. Furthermore, chronic application of the polyamine site NMDA receptor blocker ifenprodil effectively attenuated beta-amyloid neurotoxicity. We propose that nNOS activation reflects the degree of beta-amyloid-induced excitotoxic injury in a proportional manner. Moreover, Ca2+-mediated processes via NMDA receptors, or direct binding of beta-amyloid to this receptor may be a critical step in the neurotoxic mechanisms in vivo.