Aim. To study subcellular nitrergic response in the rat brain regions following chronic stress-induced depression-like behavior. Methods. An animal model of depression induced by chronic circadian stress (CCS) established in our laboratory was used. The L-arginine, L-citrulline and reactive nitrogen species (RNS) levels were determined spectrophotometrically. Results. Immediately after CCS and four days later, a depression-like behavior of rats was observed and accompanied by a substantial persistent elevation of the L-arginine, L-citrulline and RNS levels with a simultaneous up-regulation of the inducible nitric oxide synthase (iNOS) in both cytosolic and mitochondrial compartments of the rat prefrontal cortex, striatum, hippocampus, and hypothalamus, and a down-regulation of their cytosolic constitutive NOS isoforms (cNOS), mitochondrial cNOS was not significantly changed, with the exception for hypothalamus, in which the latter dropped. Conclusions. Compromised balance of the L-arginine levels and NO synthesis in both mitochondria and cytosol in the limbic brain appears to be implicated in the pathogenesis of depression and pathological anxiety.

Keywords: L-arginine, brain, chronic stress, depression-like behavior, mitochondria, nitric oxide synthase