CARDIOREGULATION IN LIMULUS. II. GAMMA AMINOBUTYRIC ACID, ANTAGONISTS AND INHIBITOR NERVES

Abstract
Gamma aminobutyric acid (GABA) (5 x 10"" to 5 x 10"5 to) perfused through the isolated heart of L. polyphemus, the horseshoe crab, mimics stimulation of the cardioinhibitory nerves by decreasing the rate and strength of beating of the heart. GABA, unlike activity in the cardioinhibitory nerves, decreases neither the number of units discharging nor the total duration of each burst of electrical activity in the cardiac ganglion. Picro-toxin blocks the function of the cardioinhibitory nerves but does not block the effects of applied GABA. Since GABA does not mimic the action of the inhibitor nerves it appears probable that GABA is not a transmitter in the cardioinhibitory pathway in Lumulus.