Effects of Immobilization Stress on Nitric Oxide Active Neurons in Rat’s dlPAG; Histochemical Study

Abstract

Background: Exposure to stress-factors caused an array of biochemical, physiological and behavioral changes. According to literature data, specific stressors may elicit specific responses, and different stressors may activate different brain systems by using specific pathways within the central nervous system. Several brain structures, including the periaqueductal gray (PAG), have been implicated in the functional neuroanatomy of stress response. The dorsolateral column of the periaqueductal gray (dlPAG) integrates aversive emotional experiences and represents an important site responding to life threatening situations. It was reported that nitric oxide (NO) affects the neuronal activity of the PAG. The goal of the present study was to investigate the changes of NO activity in the dlPAG of immobilized rats using a histochemical examination of the distribution of NADPH-d reactivity neurons. Our results showed that NO activity in rats dlPAG was significantly increased by acute immobilization stress. This suggests a pivotal role of this part of the brain and NO-ergic system in stress response which main role is to attenuate the effect of stress and to restore the homeostasis. Methods: The experiments were carried out on male Wistar rats (180-200g), divided into two groups. The first group represented intact controls. The second group was subjected to acute immobilization stress. Results: The acute stressor 1 hour immobilization, showed statistically significant increase in the number of the NADPH-d positive neurons compared to the control group (p < 0.01). Conclusion: NO activity in rats dlPAG was significantly increased by acute immobilization stress.