Effects of microinjection of a GABA antagonist into the periaqueductal gray upon electrically-induced vocalization in decerebrate cats

Abstract

The effects of the GABA antagonist bicuculline methiodide (BIC), microinjected into the ventrolateral periaqueductal gray (PAG) on the stimulus threshold of electrically-induced vocalization were examined in unanesthetized precollicular-postmamillary decerebrate cats. To induce vocalization, repetitive electrical stimulation (0.2 ms, 100 Hz, 5–10 s duration) was delivered to the caudal portion of the PAG (30 to 300 μA) or the pontine call site (PCS) (10 to 60 μA) in the ventrolateral pontine reticular formation. Injection of 0.1 μl of 2 mM BIC into the caudal portion of the PAG decreased the stimulus thresholds of the PCS and the injection site for about 1 h. Injection of BIC into the reticular formation near the PAG, where the electrical stimulation induced vocalization, did not decrease the stimulus thresholds of the PCS or the injection site. These results indicate that GABAergic inhibition regulates the excitability of the cells within the ventrolateral PAG, which exerts an excitatory effect on the lower brain structures that produce vocalization.