Respiratory stimulant effects of ethamivan and picrotoxin

The respiratory stimulant effects of ethamivan and picrotoxin were studied in unanesthetized decerebrate cats. It was found that neither compound exhibited selective stimulant action on the respiratory neurons. Ethamivan evoked increases in respiratory rate but not in tidal volume, whereas picrotoxin profoundly altered both of these variables. The increases in respiratory rate evoked by ethamivan required intact vagus nerves since midcervical vagotomy abolished this effect. It is conceivable that ethamivan stimulated pulmonary chemoreflexes which then led to increased respiratory rate. Picrotoxin had no discernible effect on peripheral chemoreflexes. It altered, however, the central respiratory rhythmicity, or rate, depth and rhythm of respiration. There was a marked effect on central respiratory control which led to cycling between slow and deep, and rapid and shallow breathing. These were interspersed with periods of rapid and deep respiration.