Sympathetic cardiac stimulation in Bufo marinus under MS-222 anesthesia.

SMITH, D. G. S’mpathetic cardiac stimulation in Bufo marinus under MS-222 anesthesia. Am. J. Physiol. 226(Z) : 367-370. 1974.-The cardiac stimulant effect of tricaine methanesulfonate (MS-222 Sandoz) was studied in unrestrained intact toads (Bufo marinus). During anesthesia in a 1 : 1000 solution of MS-222, the average heart rate rose from 26 to 46 beats/min, and the average systemic arterial pressure fell slightly from 40.4 to 35.8 cm of water. The increase in heart rate was prevented by both spinal and double pithing and by treatment-with bretylium. It was not prevented by brain pithing or treatment with hyoscine. Perfusion of the spinal canal with MS-222 dissolved in nutrient solution produced tachycardia similar to that observed in the whole animal in hearts attached to the body only via the vagosympathetic nerves. It was concluded that MS-222 produces tachycardia in the toad by activation of the spinal centers for the sympathetic outflow to the heart.