Alzheimer's disease: A contextual link with nitric oxide synthase.

Nitric oxide (NO) is a gasotransmitter with pleotropic effects which has made a great impact in biology and medicine. A multidimensional neuromodulatory role of NO has been shown in the brain with specific reference to neurodegerative disorders like Alzheimer's disease (AD) and cognitive dysfunction. It is found that NO/cGMP signalling pathway has an important role in learning and memory. Initially it was considered that indirectly NO exerted neurotoxicity in AD via glutamatergic excitotoxicity. However, considering the early development of cognitive functions involved in learning memory process including long term potentiation and synaptic plasticity, NO has crucial role. Increasing evidences uncovered the above facts that isoforms of NOS viz endothelial NO synthase (eNOS), neuronal NO synthase (nNOS) and inducible NO synthase (iNOS) having variable expression in AD is mainly responsible for learning and memory activities. In this review, we focus the role of NOS isoforms in AD parallel to NO. Further, this review provide convergent evidence that NO could provide a therapeutic avenue in AD via modulation of the relevant NOS expression.