EFFECTS OF GABAERGIC DRUGS ON PHYSOSTIGMINE INDUCED YAWNING IN RATS

In the present work the effects of GABA agonists and antagonists on ya wning induced by physostigmine have been studied. Intraperitoneally (I P) injection of physostigmine (0.05-0.3 mg/kg) induced dose-related ya wning in rats. The maximum yawning response was observed with 0.2 mg/k g 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) do se dependently. Combination of both GABA agonists elicited greater inh ibition of yawning. The GABA-A antagonists bicuculline or picrotoxin b ut not the GABA-B antagonist phaclofen reduced the inhibitory response induced by muscimol, whereas phaclofen but not bicuculline or picroto xin reduced baclofen's inhibitory effect. Administration of bicucullin e, picrotoxin or phaclofen also decreased the yawning induced by physo stigmine. However, when the GABA-A and GABA-B antagonists were employe d in combination, the inhibitory responses of both drugs were lost. It is concluded that GABA-A and/or GABA-B receptor stimulation may inhib it physostigmine-induced yawning.