FACILITATORY AND INHIBITORY EFFECTS OF ‘y- AMINOBUTYRIC ACID ON GANGLIONIC TRANSMISSION IN THE SYMPATHETIC CARDIAC NERVES OF THE DOG

KIMURA, TOMOHIKO, HIR05HI IMAMURA AND KOROKU HASHIM0TO: Facilitatory and inhibitory effects of-y-aminobutyric acid on ganglionic transmission in the sympathetic cardiac nerves of the dog. J. Pharmacol. Exp. Ther. 202: 397-403, 1977. Effects of y-aminobutyric acid (GABA) on ganglionic transmission in the peripheral course of the sympathetic cardiac nerves were investigated in vagotomized and cardiac decentralized open-chest dogs. GABA (1-300 pg/kg) was given i.v. during electrical stimulation of pre-or postganglionic fibers which induced a sustained acceleration of sinus rate. GABA in small doses of 1 and 3 pg/kg augmented the sinus acceleration during electrical stimulation of the ansa subc!avia which largely consists of pregan-glionic fibers, but depressed the sinus acceleration in large doses over 30 pg/kg. With a dose of a 10 pg/kg, its effect was dual and varied from preparation to preparation. On the other hand, GABA did not modify basal heart rate or the increase in heart rate in response to stimulation of the stellate cardiac nerve postganglionic fibers. Thes