Changes of environment and darkness enhance the NADPH-diaphorase staining in the rat paraventricular nucleus.

Nitric oxide (NO) plays an important role in the maintenance of autonomic homeostasis of the body. NO-producing neurons are activated in the brain during exposure to different levels of environmentally produced stimulations. These facts prompted the authors to investigate the levels of activation of NO-producing neurons of the paraventricular nucleus of the hypothalamus (PVN) following change of environment and darkness. Cryostat sections were cut and processed for the histochemical detection of the NADPH-diaphorase (ND)-activity. Following change of the environment and darkness for 12 and 24 h, statistical analysis displayed a significant increase in the number of ND-neurons, especially in the posterior magnocellular and the lateral parvicellular subdivisions of the PVN. These data indicate that the ND-neurons of the PVN are influenced by changes of the environment and darkness.