EFFECTS OF MICROINJECTION OF A GABA ANTAGONIST INTO THE PERIAQUEDUCTAL GRAY UPON ELECTRICALLY-INDUCED VOCALIZATION IN DECEREBRATE CATS

The effects of the GABA antagonist bicuculline methiodide (BIC), micro injected into the ventrolateral periaqueductal gray (PAG) on the stimu lus threshold of electrically-induced vocalization were examined in un anesthetized precollicular-postmamillary decerebrate cats. To induce v ocalization, repetitive electrical stimulation (0.2 ms, 100 Hz, 5-10 s duration) was delivered to the caudal portion of the PAG (30 to 300 m u A) or the pontine call site (PCS) (10 to 60 mu A) in the ventrolater al pontine reticular formation. Injection of 0.1 mu l of 2 mM BIC into the caudal portion of the FAG decreased the stimulus thresholds of th e PCS and the injection site for about 1 h. Injection of BIC into the reticular formation near the FAG, where the electrical stimulation ind uced vocalization, did not decrease the stimulus thresholds of the PCS or the injection site. These results indicate that GABAergic inhibiti on regulates the excitability of the cells within the ventrolateral FA G, which exerts an excitatory effect on the lower brain structures tha t produce vocalization.