The Effects of Testosterone and Gonadectomy Conditions on Nociception and Their Effect on Morphine-Induced Analgesia in Male Mice, Using the formalin test

Introduction & There are too many disagreements about the effects of gender and sex hormones on the behavioral responses to noxious stimuli and morphine analgesia. The purpose of this study was to determine the different effects of testosterone and gonadectomy conditions on pain and morphine-induced analgesia, using the formalin test. The present study was conducted at Razi University, in Kermanshah. Sixty three male NMRI mice were divided into nine groups (n=7). The effects of gonadectomy and testosterone on responses to noxious stimuli were evaluated in five groups (G1 to G5). The effects of these factors on morphine-induced analgesia were investigated in other groups (G6 to G9). According to grouping, each group received normal saline, testosterone, testosterone solvent or morphine and some groups were also gonadectomized and separately received these agents. Finally, the formalin test was taken from all groups. Data were statistically analyzed by one-way ANOVA. The results showed that the response to the painful stimuli had no significant difference in 5 minutes (acute pain) in all groups. Testosterone increased the response to the noxious stimuli in sub acute pain (10-30 minutes) and chronic phase (15-60 minutes) stages. This increase was significant in the group receiving testosterone compared with the gonadectomized group in both stages. In the presence of morphine, there were no significant differences in response to painful stimulus in 5 minutes (acute pain) in all groups. But testosterone in the presence of morphine caused an increased in pain score in sub acute pain (10-30 minutes) and chronic phase (15-60 minutes) stages. Testosterone increased the response to the painful stimuli in sub acute and chronic pain stages. Testosterone also reduced morphine-induced analgesia in peripheral and chronic pain stages in mice.