Rumination in sheep: Effects of morphine, deslanoside and ablation of area postrema

Abstract

Abstract Continuous long-term recording of masticatory movements was obtained in four sheep housed in individual stalls. Total rumination time occupied about 33 per cent, and feeding activity an additional 25 per cent of the whole day. Intravenous injection of morphine sulfate, 1.0 mg/kg, did not produce a significant alteration in feeding or rumination behavior. By contrast, intracerebroventricular administration of morphine, 0.4 to 2.0 mg total, elicited compulsive and uninterrupted chewing activity for up to 15 hr. Apomorphine produced an effect similar to that of morphine, but of short duration. Intravenous injection of deslanoside, 0.04–0.08 mg/kg, resulted in complete inhibition of rumination for as long as 18 hr with little or no reduction in feeding activity. Forestomach (reticular) movements were also inhibited by the deslanoside. Vomiting was not elicited by any form of drug treatment. Chronic ablation of area postrema in the lower brain stem did not notably influence the character of spontaneous feeding and rumination behavior; it did not modify the compulsive chewing response to morphine; it abolished the inhibition of rumination as well as of reticular movements caused by deslanoside.