Swim stress enhances the NADPH-diaphorase histochemical staining in the paraventricular nucleus of the hypothalamus.

Regulatory control of the hypothalamic-pituitary-adrenocortical axis (HPA) originates principally from the paraventricular nucleus (PVN), which contains an important population of nitric oxide synthesizing (NOS) neurons. In the present study, the effect of swim stress upon these neurons was investigated by means of the NADPH-diaphorase (ND) histochemical technique. A significant increase in the number of ND-neurons was observed following forced swim, especially after 30 min. These data confirm the involvement of NOS-neurons of the PVN in the response to different types of acute stressors.