OPIOIDERGIC AND CHOLINERGIC BUT NOT NITRIC OXIDE PATHWAYS ARE INVOLVED IN ANTINOCICEPTIVE ACTIVITY OF VITEX AGNUS-CASTUS ESSENTIAL OIL IN THE ACUTE TRIGEMINAL MODEL OF PAIN IN RAT

 Objective: Vitex agnus-castus (VAC) and its essential oil traditionally used to treat many conditions and symptoms such as premenstrual problems,mastalgia, inflammation, sexual dysfunction and pain. This study was conducted to investigate the analgesic effect of essential oil extracted from VAC(EOVAC) leaves in acute trigeminal model of nociception in adult male Wistar rats. Furthermore, possible involvements of opioidergic, cholinergic andL-arginine/NO/cyclic GMP pathway in analgesic activity of EOVAC were investigated.Methods: The EOVAC was extracted from powdered plant material by hydro-distillation in a Clevenger type apparatus. Acute trigeminal pain wasinduced by putting a drop of NaCl 5 M solution (40 μl) on the corneal surface of the eye and the numbers of eye wipes counted during the first 30 seconds.Results: EOVAC at doses of 100 and 200 mg/kg subcutaneous and morphine 2.5 and 5 mg/kg i.p. produced a significant anti-nociceptive effect inthis model of corneal pain. Naloxone (1 mg/kg i.p.) and atropine (1 mg/kg i.p.), L-arginine (100 and 200 mg/kg i.p.) and methylene blue (5 and10 mg/kg i.p.) alone had no any effect in the acute corneal pain. Pretreatment with naloxone or atropine significantly reversed the EOVAC‑inducedanalgesia, but L-arginine (300 mg/kg) and methylene blue (5 mg/kg) did not change the suppressive effect of EOVAC on pain response.Conclusion: The present results suggest that the EOVAC produced anti-nociception in the acute corneal pain through mechanisms that involved bothopioidergic system and/or the cholinergic system, but not via L-arginine/NO/cyclic GMP pathway, supporting the folkloric usage of the plant to treatvarious painful processes.Keywords: Acute trigeminal pain, Vitex agnus-castus essential oil, Opioidergic system, Cholinergic system, Rat

Evaluation of Cold allodynia by Thermal Place Preference Test Following A Short Term of Treadmill Exercise in Neuropathic Rats

Introduction: In this study, we investigated the hypothesis of whether short term and moderate intense treadmill exercise could lead to a sustained reversal of peripheral neuropathy induced cold aversion by activation of endogenous opioidergic systems. &nbsp; Materials & Methods: The tibial nerve transection (TNT) was performed in the anesthetized rats. 28 days after TNT surgery, the animals were randomized to three sedentary and four treadmill exercise (14 days, 30 min/day with max speed of 1.2 Km/h) groups. Animal activity and thermal preference behavior were determined by double plate technique (thermo-neutral plate: 24 &ordm;C and cold plate: 14 &ordm;C), equipped with a video tracking software. For determination of opioidergic system involvement, intraperitoneal injection of naltroxone (2 mg/kg) was done before exercise. Morphine (2.5 mg/kg) and naloxone (1 mg/kg) were also used exactly after the end of the last session of exercise. &nbsp; Findings: Tibial nerve transection significantly decreased the animals&rsquo; activities (P<0.001), the time spent in cold plate (P<0.002) and increased escape index from the cold plate (E.I), (P<0.0001), in comparison with intact animals. Treadmill exercise significantly prevented cold allodynia (P<0.002), increased animal activity (P<0.01) and decreased E.I (P<0.0001) 42 days after TNT surgery. Administration of morphine in the both exercised and none-exercised groups significantly reduced E.I., (P<0.0001). Injection of naltrexone before exercise training or naloxone immediately after exercise prevented anti-allodynia effect of exercise on the exercise trained animals. &nbsp; Discussion & Conclusion: Our investigation came to the conclusion that a short period of moderate aerobic exercise could reduce cold aversion and improve animal locomotor activity after peripheral neuropathy via activation of opioidergic system