7-Nitroindazole, or 7-NI, is a heterocyclic small molecule containing an indazole ring that has been nitrated at the 7 position. Nitroindazole acts as a selective inhibitor for neuronal nitric oxide synthase, a hemoprotein enzyme that, in neuronal tissue, converts arginine to citrulline and nitric oxide (NO). Nitric oxide can diffuse through the plasma membrane into neighbouring cells, allowing cell signalling, so nitroindazole indirectly inhibits this signalling process. Other inhibitors exist such as 3-bromo-7-nitroindazole, which is more potent but less specific, or NPA (N-propyl-L-arginine), which acts on a different site.