Functional Development of the Central Emetic Mechanism in the Puppy Dog 1

Abstract

Summary

Ninety dogs at different ages (from days 2 to 60) were tested for their emetic responses to graded doses of apomorphine injected intravenously and to copper sulfate administered orally. None of the 2-day-old puppies vomited in response to apomorphine, up to a dose of 1 mg/kg. However, some did vomit when given 20 or 40 mg of copper sulfate. The reactivity to copper sulfate increased remarkably from days 2 to 5, and thereafter it remained almost unchanged up to day 60. The reactivity to apomorphine first appeared at day 5 and increased remarkably up to day 10. Thereafter, it continued to increase at a much slower rate up to day 30, at which time the ED₅₀ was very close to that of adults. These results suggest that the emetic response mediated by the chemoceptive emetic trigger zone (CTZ) did not function at the second day after birth, but that the vomiting center could be excited by impulses from the gastrointestinal tract, and that the vomiting center and CTZ matured at different rates in puppies.