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Background & objectives: Syzygium aromaticum (Clove) is a medicinal plant usually used in traditional medicine to reduce toothache. The aim of the present study was to evaluate the analgesic effect of topical Clove oil on acute and chronic pain in male mice using formalin test.
Methods: In this study, 24 mice were divided into 4 groups: control, morphine (as positive control), Clove oil, and Clove oil plus morphine groups. Before the formalin test, the animals were treated topically with clove oil for 6 hours.  A single dose of morphine (10 mg/kg) was prescribed subcutaneously. Pain scores were obtained using the formalin test through an injection of 20 microliter of formalin 2.5% into the palm of the animal's right hand.
Results: Topical administration of Clove oil significantly decreased acute pain (the initial phase of the formalin test) and chronic pain (the second phase of the formalin test). Furthermore, topical Clove oil increased the analgesic effect of morphine in acute pain phase.
Conclusions: This study showed that the analgesic effect of topical Clove oil was comparable to morphine.

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CT
 
Background & objectives: So far, various reports have been presented on the relationship between sex hormones and gender-related differences in pain and analgesia in humans and laboratory animals. The purpose of this study was to investigate the effect of testosterone hormone and spironolactone anti-androgen drug on morphine-induced analgesia in male mice using formalin test.
Methods: In this study, 80 male mice were divided into 10 groups (N=8); normal saline (control), sesame seed oil (as testosterone solvent), testosterone (5 and 10 mg/kg body weight), spironolactone, morphine, sesame seed oil + morphine, testosterone (5 and 10 mg/ kg body weight) + morphine and spironolactone + morphine. Formalin test was performed in all the mice, and data were analyzed by one-way ANOVA.
Results: The results showed that sesame seed oil + morphine (p<0.001), morphine (p<0.001), testosterone (5 mg/kg) + morphine (p<0.01) and testosterone (10 mg/kg) + morphine (p<0.001) significantly reduced acute  pain, and testosterone (5 mg/kg) (p<0.05), testosterone (10 mg/kg) (p<0.01), sesame seed oil + morphine (p<0.001), morphine (p<0.001), testosterone (5 mg/kg) + morphine (p<0.001) and testosterone (10 mg/kg) + morphine (p<0.001) significantly reduced chronic pain compared with control group. Spironolactone had no effect on pain relief in the presence and absence of morphine compared to control group.
Conclusions: It can be concluded that testosterone has analgesic effects on the chronic phase of the pain. On the other hand, spironolactone may have hyperalgesic effects due to its anti-androgenic properties.