NOS2 and major depressive disorder: The nitrergic system has previously been shown to mediate the effects of stress on anxiety and depression.(7) Nitric oxide (NO) is a gaseous modulator that influences several behaviors such as sleep, memory, learning, and reproductive behavior.(8) Nitric oxide is synthesized via L-arginine oxidation by nitric oxide synthase (NOS).(9)N(G)-Nitro-L-arginine methyl ester (L-NAME) is a nonspecific NOS inhibitor.