THE ACTION OF ELECTRICAL STIMULATION AND OF CERTAIN DRUGS ON CARDIAC NERVES OF THE CRAB, CANCER IRRORATUS

Abstract

Cardiac inhibitory and ex-citatory nerves of the rock crab Cancer irroratus were stimulated electrically while the heart was perfused in situ by per-fusion fluid with or without drugs. Strychnine 1:2500 blocked reyersibly the action of excitatory and inhibitory nerves. Nicotine in concn. of approx. 1:1,000,000 augmented the effect of excitatory nerves, and in higher concn. blocked the excitatory nerve and/or the heart ganglion, but even in concn. as high as 1:1000 had no effect upon the inhibitory nerves. Atropine, eserine, and eserine plus acetyl-choline had no effect upon either inhibition or excitation, although the lack of effect of eserine upon excitation is open to restudy by other methods. It is probable that excitatory nerves are cholinergic, exerting a somewhat "nicotine-like" effect upon the cardiac ganglion, which is believed to be pharmacologically similar. The pharmacologic nature of the inhibitory nerves is still obscure. Excitatory nerves were effective when stimulated at frequencies from 200-300 to less than 10/sec. Inhibitory nerves produced total inhibition at frequencies from 15-20 to 100-200/sec, while higher or lower frequencies bordering this range produced only partial inhibition or were without effect.