Effects of GABAergic drugs on physostigmine-induced yawning in rats.

In the present work the effects of GABA agonists and antagonists on yawning induced by physostigmine have been studied. Intraperitoneally (IP) injection of physostigmine (0.05-0.3 mg/kg) induced dose-related yawning in rats. The maximum yawning response was observed with 0.2 mg/kg of the drug. The GABA agonists muscimol (1-4 mg/kg) and baclofen (0.125-1 mg/kg) decreased yawning induced by physostigmine (0.2 mg/kg) dose dependently. Combination of both GABA agonists elicited greater inhibition of yawning. The GABA-A antagonists bicuculline or picrotoxin but not the GABA-B antagonist phaclofen reduced the inhibitory response induced by muscimol, whereas phaclofen but not bicuculline or picrotoxin reduced baclofen's inhibitory effect. Administration of bicuculline, picrotoxin or phaclofen also decreased the yawning induced by physostigmine. However, when the GABA-A and GABA-B antagonists were employed in combination, the inhibitory responses of both drugs were lost. It is concluded that GABA-A and/or GABA-B receptor stimulation may inhibit physostigmine-induced yawning.