Beta-endorphin-induced inhibition of rumen contractions in sheep. The effect of hypothalamic de-efferentiation.

In conscious sheep, beta-endorphin (1 and 2 micrograms/kg) administered into the third cerebral ventricle caused psychomotor excitability and a significant inhibition of the frequency of rumen contractions. The amplitude of the first rumen contractions, following immediately after the end of endorphin infusion, and the average amplitude of primary rumen contractions were also inhibited. De-efferentiation at the level of the hypothalamus prevented both the inhibitory effect of beta-endorphin on the frequency of rumen contractions and the drug-induced psychomotor excitability. However, de-efferentiation did not prevent beta-endorphin-induced inhibition of the mean amplitude of rumen contractions. The character of pathohistological changes induced by de-efferentiation showed descending degenerative changes of the nerve tracts connecting the hypothalamus with the pons and the medulla oblongata. These results, together with previously published evidence, do suggest that de-efferentiation at the level of the hypothalamus causes degeneration of inhibitory descending opioid-noradrenergic pathways connecting the hypothalamus with the gastric centres in the medulla oblongata.