The effect of blocking of dorsal and lateral paragigantocellularis muscarinic receptors on pain scores in rats

Previous studies have shown that paragigantocellularis nucleus (PGI) neurons contain some neurotransmitters such as GABA, neuropeptides, monoamines, substance P, enkephalin and serotonin. It has been suggested that PGI is a main cholinergic source in the rat’s brain stem. There are few evidences on the presence and importance of cholinergic receptors on PGI neurons with regard to nociception. In the present study, 38 NMRI young male rats (200-300 g) were used. They were aneasthetized with ketamine hydrochloride (110 mg/kg, i.p.) and a guide cannula was implanted into dorsal or lateral subdivisions of left PGI of both test and sham-operated animals. Then, 1 microliter of the solution containing 781 micromoles of scopolamine (0.3 mg/ml) was injected into dorsal or lateral (DPGI or LPGI). After the recovery period, acute and chronic pain was evaluated by formalin test (50 ?l of formalin, %2.5 injected into right hind paw subcutaneously) ten minutes after the injection of scopolamine. Sham animals 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 (P