## 4 Discussion  
### Variability of the Oxidative Stress and Hormonal Response in Restraint Stress  
Several studies were completed for prolonged periods of restraint stress exposure (between 10 and 40 days) and some of these studies were developed with intravenous corticosterone administration in rats. Their results indicated a substantial decline in antioxidant defenses by actions of corticosterone evidenced by coordinate decreases in the activities in the brain, liver, and heart of the free-radical scavenging enzymes. These results were significantly changed after corticosterone injection when the blood concentration was -15-60 ug/dL, whereas endogenous hypercorticosteronenia was -10-16 ug/dL according to our previous results, as well as with [PERSON]'s available data [59]. Returning to our findings, short (2 days) and medium (6 days) time exposure to restraint stress for 3 h/day had gradually increased the corticosterone concentration, as well as SOD-CAT activity in the hippocampus and these data demonstrated that oxidative imbalance after restraining was started even after 2 days of repeated stress exposure. [PERSON] et al. [60] also mentioned that short-time exposure to psychiatric stress or physical stress was known to induce oxidative stress in the brain. Further, the same authors described the role of  
Figure 10: Electron micrographs of the CA3 neurons and oligodendrocytes after 6 days of repetitive exposure to restraint stress; (**a**) Small dark neuron (DN) with prominent mitochondrial lysis (asterisk); (**b**) Another aspect with one dark neuron and mitochondrial lysis (asterisk); (**c**) Dark neuron (DN) with dilated endoplasmic reticulum (ERdil, white arrow) in distal position to a neuron with normal aspect (black arrow). A satellite oligodendrocyte (OLG) marks the space between neurons; (**d**) Dark neuron (DN) with the dilated endoplasmic reticulum (ERdil, white arrow) with satellitosis of an oligodendrocyte (OLG) with indented nucleus (black arrows); Original magnification \(\times\)6000.  
sex hormones in stress coping reactions. Unlike estrogen, testosterone had not been well investigated in connection with its function on the brain exposed to restraint or psychological stress. Restraint stress significantly reduced testosterone levels in rats after 14 days of restraining (5 h/day). Our data were in accordance with other results and showed that even after 2 days of restraining, testosterone concentration was decreased in the hippocampus [60]. As mentioned by [PERSON] et al., the hippocampal neurons and glial cells contained high levels of corticosterone receptors, which exposed them to glucocorticoids signaling during stress periods [3]. High corticosterone levels induced oxidative stress by stimulating glutamate-mediated ROS production and mitochondrial oxidative stress in neurons and glycocytes. Similarly to our results, several authors have reported that short or long-term periods of restraint stress decreased the blood concentration of testosterone and determined a prominent redox imbalance [61, 62]. Based on both, in vitro and animal models, [PERSON] et al. [63] and [PERSON] et al. [64] showed that corticosterone and HPA activation inhibited the testosterone production by the testes Leydig cells. The authors noticed that the absence of testosterone generated free radicals in male rats. Our findings also showed that oxidative stress enzymes and corticosterone were augmented whereas testosterone was decreased after 2 and 6 days of repeated stress [65]. Excessive corticosterone levels in the hippocampus accelerate neuronal inflammatory reactions by releasing pro-inflammatory cytokines such as IL-1\(\beta\), IL-6, or TNF\(\alpha\)[66].