Pain Modulation through Opioid and Monoaminergic Pathways in Aloe Vera Induced Analgesia in Rats

Objective: To study analgesic activity and to evaluate the involvement of opioid and monoaminergic pain mechanisms in the antinociceptive activity of aqueous extract of aloe vera (AEAV) Materials and Methods: Analgesic activity of AEAV alone (100, 200 and 400 mg/kg orally) and in combination with pentazocine or venlafaxine ( sub analgesic doses) were studied using tail immersion test and acetic acid induced writhing in rats. The effect of pre-treatment with opioid antagonist naltrexone 1 mg/kg was also studied. Results: AEAV produced a dose dependent significant antinociceptive activity in tail immersion test and acetic acid induced writhing in rats (P< 0.01) which is suggestive of possible central as well as peripheral action. Administration of sub analgesic dose of AEAV with pentazocine or venlafaxine resulted in significant (P< 0.01) antinociceptive activity in both the pain models. This demonstrated the involvement of opioid receptors and serotonergic and noradrenergic systems (descending pathway) leading to synergistic action between the drugs. The central pathway was further confirmed by pre-treatment with naltrexone which inhibited antinociceptive activity induced by AEAV alone and combination with pentazocine or venlafaxine in both experimental models. Conclusion: Aqueous extract of Aloe vera induced antinociception is mediated through both opioid and monoaminergic pain mechanisms suggesting its potential use in neuropathic and chronic pain conditions.