INHIBITION OF THE TURTLE'S ATRIA BY SINGLE INDUCTION SHOCKS APPLIED DIRECTLY

Abstract

Inhibition of the turtle''s atria produced by direct application of single brief electrical shocks is demonstrated. The threshold intensity for such inhibition is comparatively high, lying much above that necessary for excitation. The depression is both inotropic and chronotropic. It requires a short time to reach its maximum and slowly disappears. Prevention of the inhibition by atropine and its prolongation by eserine are interpreted as evidence that acetylcholine is liberated at vagus terminals in sufficient quantity to inhibit. The ventricle which receives no vagus terminals is not inhibited. The similarity of time-depression curves to curves constructed from effects of single vagal volleys is noted.