, 2005), indicating that this test is also sensitive to peripheral acting opioids. In line with this idea, it is possible that M. lemniscatus venom exerts its antinociceptive effect both by central and peripheral mechanisms. The fact that M. lemniscatus venom produced antinociception
in the tail flick test suggests that it blocks the neural transmission of pain, like opioids do. Based signaling pathway on this possibility, the effects of the pharmacological blocked of opioid receptors on the antinociceptive activity of M. lemniscatus venom was evaluated. The maximal antinociception produced by MlV (1600 μg/kg) was completely prevented in mice pre-treated with naloxone (5 mg/kg i.p.; 15 min before), a non-selective opioid receptor antagonist ( Fig. 5). The inhibitory effect of naloxone was maintained for 2 h, in line with literature data showing the naloxone half-life ( Ngai et al., 1976). The demonstration that naloxone antagonizes the MlV-induced antinociception suggests an opioid-like activity for the venom. Similarly, administration of the μ-opioid receptor antagonist CTOP (1 mg/kg i.p.) 30 min after the MlV administration, blocked the antinociceptive effect of venom ( Fig. 6A). On the other hand, the pre-treatment click here with the k-opioid receptor antagonist nor-BNI (0.5 mg/kg s.c.; 15 min before) partially inhibited the venom-induced antinociception ( Fig. 6B). The pre-treatment with naltrindole
(3.0 mg/kg s.c.; 5 min before), a δ-opioid receptor antagonist, also reduced the venom-induced antinociception ( Fig. 6C). These results suggest that opioid receptors, particularly μ-opioid receptors, play a major role in the antinociceptive mechanisms of MlV. This idea is reinforced by literature data showing that opioid receptors are frequently involved in the antinociceptive effects of snake venoms ( Chen et al., 2006; Giorgi et al., 1993; Picolo et al., 2000; Pu et al., 1995). In conclusion, the
present study has demonstrated, for the first time, that oral administration Progesterone of M. lemniscatus venom, at doses that did not induce any apparent toxicity or motor performance alterations, produced potent antinociceptive effects. The antinociceptive effect due to M. lemniscatus venom is mediated by the opioid system, mainly by the μ-opioid receptor. However, a more in-depth evaluation of the mechanisms involved should be performed. This work was supported by CNPq, FAPESB, PRONEX, RENORBIO, FINEP, and FIOCRUZ. “
“Snake bites represent an important health problem in Peru, especially to the east of the Andes in the High Forest (600–3500 m altitude) and Tropical Rain Forest (<600 m altitude) (Ministério de Salúd Peru, 2004). These regions are known for containing the major Peruvian snake species and most diversified ophidian population. The Instituto Nacional de Salud (INS), located in Lima, Peru has been producing commercial anti-venoms since 1978 (Ministério de Salúd Peru, 2004).