Investigation of Antinociceptive effect of the citronellyl acetate: Role of serotoninergic system

ERV Rios1, NFM Rocha1, ML Dias1, LF Vasconcelos1, AMR Carvalho1, DP de Sousa3, FCF de Sousa1, MMF Fonteles1,2. 1Federal University of Ceara, Physiology and Pharmacology, Brazil, 2Federal University of Ceara, Pharmacy, Brazil, 3Federal University of Sergipe, Pharmacy, Brazil

Many works show the antinociceptive activity of essential oils, thus, we tested whether the citronellyl acetate (CAT), a citronelol derivate, also has this effect. The aim of present work was show the antinociceptive activity of the CAT and verifies the involvement of the serotoninergic pathway in the antinociceptive mechanism. It was submitted in local Ethics Committee on Animal Research by protocol number: 44/12. The male Swiss mice with 25-32g were used in all experiments that were conducted with 7-9 animals per group. For statistical analysis, we used analysis of variance (ANOVA) and Student-Newman-Keuls as post hoc. Initially, CAT was administrated by gavage at doses of 50, 100 and 200 mg/kg and performed the model of visceral nociception induced by acetic acid 0.6% and nociception induced by the intraplantar administration of formalin 1%. In both the CAT was capable of decrease the pain behaviour by 85.74% and 82.28% at dose of 200 mg/kg, and 79.78% and 55.48% at dose of 100 mg/kg, respectively. In the formalin test, it was not observed difference between groups in the first phase. Another test was the hot plate (55°C ± 0.3°C). The animals were pretreated with 100 mg/kg or 200 mg/kg doses and no group showed significant difference against the vehicle group. Only the morphine group was antinociceptive, as expected. Finally, the inflammatory hypernociception test was conducted, using the VonFrey’s filament. We used 2 groups pretreated with CAT 100 mg/kg or 200 mg/kg and was made the reading after 30, 60 and 180 minutes of the injection of noxious stimulation. The results demonstrated that with dose of 100 mg/kg has reduced the withdrawal threshold by 71.45% and 79.78% after 60 and 180 minutes, respectively. With dose of 200 mg/kg has reduced the withdrawal threshold by 84.47%, 89.99% and 100.65% after 30, 60 and 180 minutes, respectively. For verifying the participation of serotoninergic system in the antinociceptive activity of CAT, we induced the depletion of serotonin by pretreatment of the animals with pCPA 100mg/kg/day for 4 days. Thirty minutes after the last treatment, animals received the CAT 200 mg/kg in the order to submit them for model of visceral nociception. The treatment pCPA plus CAT decrease the nociception promoted by acetic acid by 33.19%, while that the CAT group reduced the nociception by 96.73%. This result indicates that the modulation of pain caused by CAT may be mediated, at least in part, by inducing the release of serotonin. After the observation, the animals were sacrificed, and the peritoneal cavity was washed with 1mL of cold sterile saline. The peritoneal fluid was recovered for the analysis of neurotransmitters by HPLC, which showed decreasing only in HVA amount by 89.54%. It suggests a protection against metabolization of serotonin by CAT. We also investigated the participation of 5-HT1, 5-HT2a and 5-HT3 receptors in the antinociceptive activity of CAT. In this case, the various animals groups were pretreated with NAN-190 0.5mg/kg, Ritanserin 1 mg/kg, Ondasentron 0.5mg/kg. After 15 minutes, the animals received CAT 200mg/kg and were submitted at model of visceral nociception. The pre-treatment with Nan-190 and Ritanserin reduced the antinociceptive effect of CAT by 100% and 64.62%, respectively. The results showed that 5-HT1 and 5-HT2a receptors seem to be involved in the antinociceptive mechanism. In conclusion, our findings showed the antinociceptive effect of the CAT, suggesting that this effect may be mediated, at least in part, by modulation of serotoninergic pathway by inducing of the release of serotonin and binding in the 5-HT1 or 5-HT2a receptors.

Financial support: CNPq and CAPES