Role of the adrenergic system in physostigmine-induced yawning

In this study the effect of adrenergic receptor agonists and antagonists on physostigmine induced yawning was investigated. Intraperitoneal injection of different doses of physostigmine (0.03, 0.05, 0.1 and 0.2 mg/kg) caused yawning in white rats. The greatest response was seen at a dose of 0.2 mg/kg physostigmine. Phenylephrine, an α1 agonist, and clonidine, an α2 agonist, led to a decrease in physostigmine-induced yawning. Prazosine and high-dose phenoxybenzamine decreased the inhibitory effect of phenylephrine. Also, high doses of yohimbine decreased the effect of clonidine. Adrenergic receptor antagonists phenoxybenzamine, prazosine and propranolol had no significant effect on the physostigmine-induced response, while the α2 antagonist (yohimbine) and low-dose prazosine decreased physostigmine's effect. Based on these results, we may conclude that activation of α1 and α2 receptors leads to a decrease in physostigmine-induced yawning in rats.