بررسي نقش گيرنده هاي موسكاريني كولينرژيكي هسته پاراجيگانتو سلولاريس تنه مغزي بر شدت درد موشهاي صحرايي

ROLE OF BRAIN STEM PARAGIGANTOCELLULARIS NUCLEUS CHOLINERGIC MUSCARINIC RECEPTORS ON PAIN SCORE IN RATS

The paragigantocellularis nucleus (PGI) is a part of brain stem pontomedullary reticular formation that has an important role in pain processing . Investigations have shown that PGI neurons contain some neurotransmitters such as GABA ,neuropeptides ,Monoamines , substance P, enkephaline and serotonine. It has been Also suggested that PGl is a main cholinergic source in rat brain stern . There is a little evidence about presence and importance of cholinergic receptors on PGI neurons for nociception . In present study 38 NMRI young male rats , 200-300 gr were used . They were aneasthetized with Ketamine Hydrochloride (110 mg / kg / ip ) and a guide cannule were implanted in dorsal or lateral subdivisions of left PGI of both test and sham animals . One microlitter contain 781 micromoles of scopolamine ( 0.3 mg/ml ) was injected in dorsal or lateral PGI ( DPGI or LPGI ) after 7-10 days recovery period . Acute and chronic pain were evaluated by formalin test (50 microlitters formalin %2.5 injected in right hind paw subcutaneously) ten minutes after injection of scopolamine . Sham animals were received same volume of normal saline . Results showed that injection of scopolamine in DPGI or LPGI reduces pain score in both acute and chronic phases significantly. Also injection of scopolamine in LPGI has induced longer analgesic effect. These data suggest that:1)PGI neurons contain cholinergic muscarinic receptors,2)these receptors involve in pain processing , and 3) the injection of scopolamine has longer effect on chronic pain in LPGI than EPGI.