The effect of opiodergic system and testosterone on anxiety behavior in gonadectomized rats

Background and aim: Removal of the testes (gonadectomy; GDX), the primary source of androgens, increases anxiety behavior in several tasks. Opioids are known to play a role in mediating the effects of androgen. In the present study, the effect of testosterone and opioidergic system on anxiety behavior was investigated. Methods: Adult male Wistar rats were bilaterally castrated. The elevated plus maze which is a useful test to investigate the effects of anxiogenic or anxiolytic drugs in rodents was used. Results: The data indicated that there is a decrease, 10 days after castration, in the percentage of OAT (the ratio of time spent in the open arms to total times spent in any arms x 100) and OAE (the ratio of entries into open arms to total entries x 100) but not locomotor activity, showing anxiogenic-like effects of gonadectomy. Intraperitoneal injection of testosterone (200,300 and 450 mg/kg) and morphine (2.5, 5 and 7.5 mg/kg), before testing 10 days after castration, showed an increase in OAT and OAE. Furthermore, injection of naloxone (5 and 7.5 mg/kg, i.p.), 5 min before testing 10 days after castration, decreased OAT and OAE. Also, injection of a significant dose of testosterone (300 mg/kg, i.p.), 1 h before the injection of different doses of morphine (1,2.5,5 and 7.5 mg/kg, i.p.), 10 days after castration, did not significantly alter OAT, OAE and locomotor activity. While, administration of a significant dose of testosterone (300 mg/kg, i.p.), 1 h before the infusion of different doses of naloxone (1, 2.5, 5 and 7.5 mg/kg, i.p.), 10 days after castration, decreased OAT and OAE. Conclusion: The results show the involvement of testosterone and opioidergic system in anxiogenic-like behaviors induced by gonadectomy. (C) 2014 Elsevier B.V. All rights reserved.