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

- Gonadectomy decreased %OAT and %OAE.
- I.p. injection of testosterone and morphine in GDX male rats increased %OAT and %OAE.
- I.p. injection of naloxone in GDX male rats decreased %OAT and %OAE.
- I.p. injection of testosterone 1 h before infusion of morphine in GDX male rats did not significantly alter %OAT and %OAE.
- I.p. injection of testosterone 1 h before administration of naloxone in GDX male rats decreased %OAT and %OAE.

Background and aimRemoval 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.MethodsAdult 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.ResultsThe 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 × 100) and OAE (the ratio of entries into open arms to total entries × 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.ConclusionThe results show the involvement of testosterone and opioidergic system in anxiogenic-like behaviors induced by gonadectomy.