The effects of testosterone and naloxone treatments on fear behavior in gonadectomized rats

Introduction: Effective perception of fear signals is crucial for organism survival. When threated, the organism indicates defensive behaviors. Methods: Elevated plus–maze has high efficiency for measurement of fear behavior and is widly used for fear behavior determination. Increase in two parameters; percent of openarm entries (%OAE) and percent of time spent in the open-arm (%OAT) in the elevated plus- maze were considered as the indexes of fear reduction effect. In this study, the effect of testosterone and naloxone on fear behavior of gonadectomized rats (GDX) was investigated. Also, the interaction of testosterone with naloxone was investigated. Results: Subcutaneous (SC) injections of different doses of testosterone (100, 200, 300, 450 μg /rat) increased the %OAE and %OAT in a dose dependent manner. Maximum response was obtained by 450 μg/rat dose of testosterone (P<0.001). SC injections of opioid receptors antagonist, naloxone 1, 2.5, 5, 7.5 mg / kg reduced %OAE and %OAT (P<0.01) . Conclusion: It may be concluded that testosterone decreases fear behavior and naloxone increased fear behavior. Also the results indicate that there is an interaction between testosteone and naloxone (P<0.001).