DefinePK

Abstract

In order to investigate the role of cuneiformis (CnF) in pain modulation, we evaluated the effect of GABAA antagonist (bicuculline) on antinociceptive response of morphine in this nucleus. Eighty five male N-MRI rats, weighing 250-350 g were used, they were maintained on a 12 h light/dark cycle at 22-24°C. The animals were anesthetized with pentobarbital sodium (60 mg kg-1 ip) and were fixed on a stereotaxic apparatus. Then CnF was calculated and the animal was left to recovery for one week. The animals were divided into 4 groups; group I which received 0.5 μL of different doses of bicuculline dissolved in saline (12.5, 25, 50 and 100 ng), group II which received morphine (10 g/0.5 μL saline), group III which received a dose of bicuculline (50 ng/0.5 μL saline) plus morphine (10 g/0.5 μL saline) that followed with receive of naloxone (2 mg kg-1, i.p.) and group IV; which received 0.5 μL saline and served as control. Tail Flick Latency (TFL) was measured as an index of pain during 2, 7, 12, 17, 22 and 27 min post micro-injection in CnF in all groups. Micro-injection of bicuculline in CnF increased TFL dose dependently. Morphine + bicuculline significantly increased maximum possible effect (%MPE) of antinociceptive response compared with morphine or bicuculline alone. Naloxone decreased the response to morphine. The results of this study indicates that CnF has a significant role in pain modulation, gabaergic system and opioid analogs have also play an important role on its antinociception.