Evaluation of the Effects of Chronic Administration of Citrus aurantium Essential Oil on the Development of Tolerance and Dependence to Morphine

Background: Long-term exposure to opioids may lead to physical dependence and tolerance. The purpose of this study was to investigate the effects of Citrus aurantium essential oil (CEO) on the morphine-induced tolerance and dependence. Methods: To evaluate morphine tolerance, the experiments were carried out in 6 rat groups (n=8) in the weight range of 225-275 g. The control group received morphine (10 mg/kg/day) and the test groups received morphine with the different doses of essential oil (CEO 20, 40 and 80 mg/kg/day) or 4 mL/kg of essential oil vehicle (KolliphorÒ HS15 30% in normal saline that adjusted in pH=7.4 with phosphate buffer) intraperitoneally. The hot-plate test was carried out every other day, 90 minutes after the injections. To examine morphine withdrawal, male Wistar rats were divided into seven groups (n=8) randomly, including: morphine sulphate, CEO (20, 40 and 80 mg/kg) + morphine, vehicle of CEO + morphine. The rats were rendered morphine-dependent by injection of additive doses of morphine subcutaneously for 9 days. The procedure of the morphine administration was as following protocol: day1: 5 mg/kg/12h, day 2 and 3: 10 mg/kg/12h, day 4 and 5: 15 mg/kg/12h, day 6 and 7: 20 mg/kg/12h and day 8 and 9: 25 mg/kg/12h. In the 9th day, 2 hours after the last dose of morphine, naloxone (4 mg/kg) was injected intraperitoneally. Some withdrawal behaviors were counted for 60 minutes. Results: Morphine tolerance was completed after 5 days in the control group. The vehicle group showed tolerance on the 9th day (p-value=0.991), 20mg group in the 13th day (p-value to control=0.010, to vehicle=0.049), 40 mg group on the 15th day (p-value to control and vehicle<0.001) and 80 mg group on the 13th day (p-value to control= 0.001, to vehicle= 0.007). The results showed that CEO could reduce the morphine withdrawal syndrome and total withdrawal score (TWS). Intraperitoneally injection of CEO in two doses (40 mg/kg with p<0.001 and 80 mg/kg with p<0.01) significantly reduced the TWS in comparison to the morphine+vehicle treated group. Conclusion: The results indicated that chronic administration of C. aurantium essential oil extracted had beneficial effects in reducing morphine withdrawal syndrome and could significantly delay tolerance to morphine.