Study of curcumin mechanism by using yawning induced by physostigmine and pilocarpine in rats

Curcumin is the active substance of Turmeric (Curcuma longa), that many therapeutic uses is reported for it. The previous studies reported its improving effect effect on cholinergic nerves. In order to better describing its its cholinergic effects, we investigated the effect of curcumin on yawning induced by physostigmine and pilocarpine in male rats. In this study, yawning was induced by physostigmine, as a cholinesterase inhibitor, (
0.1, 0.2 and 0.4 mg/kg, s.c.) and pilocarpine, as a muscarinic receptor agonist, (
1, 2 and 4 mg/kg, s.c.) in male rats, and the number of yawns was counted for 45 min. The result showed that physostigmine in doses (
0.1, 0.2 and 0.4 mg/kg, s.c.) and pilocarpine in doses (
1, 2 and 4 mg/kg, s.c.) were able to induce yawning in male rats (P<0.05). The s.c. injection of atropine in doses (1 and 2 mg/kg) was significantly (P<0.05) decreased physostigmine (0.2 mg/kg) and pilocarpine (2 mg/kg) induced yawning, respectively. Yawning induced by physostigmine and pilocarpine was significantly (P<0.05) increased by curcumin (80 mg/kg, i.p.). In the presence of atropine, curcumin (40 and 80 mg/kg, i.p.) did not produce yawning. The results of the our study indicated that physostigmine and pilocarpine via muscarinic cholinergic receptors produced yawning and curcumin induce yawning through affecting on muscarinic receptor. Therefore, the improving effect of curcumin on function of cholinergic nerves is further confirmed by our study.