Stress-induced changes in the function of the parasympathetic nervous system are mimicked by blocking GABA in the CNS of the cat.

The purpose of this study was to determine the effect of blockade of receptors for gamma-aminobutyric acid (GABA) in the forebrain, on vagal activity to the stomach and heart. This was done by injecting bicuculline (50 micrograms) into the lateral ventricle of the brain and restricting the drug to the forebrain ventricles by cannulating the cerebral aqueduct. Studies were performed in chloralose-anesthetized cats and gastric motility was monitored using extraluminal force transducers, sutured to the antrum and pylorus. Cardiac vagal activity was determined by noting the sinus bradycardia that developed from activation of the baroreceptor reflex induced by phenylephrine. Administration of bicuculline into the lateral ventricle of 7 animals produced increases in the minute motility index of 5.3 +/- 0.8 (antrum) and 13.9 +/- 2.1 (pylorus). This was associated with inhibition of baroreceptor-induced vagal bradycardia (i.e. -38 +/- 6.4 beats/min before bicuculline and -7.7 +/- 5.7 beats/min after bicuculline). These data indicate that a GABAergic mechanism in the forebrain may be important for controlling vagal outflow to both the stomach and the heart.