NOS1 and Alzheimer disease: Among them, two of the isoforms (i.e., neuronal NOS [nNOS or NOS1] and endothelial NOS [eNOS or NOS3]) synthesize NO in a calcium-dependent manner, whereas the third isoform, inducible NOS (iNOS or NOS2) is transcriptionally controlled and predominantly located in microglia and astrocytes, particularly during neuroinflammatory changes as observed in AD.