1. Electromyographic (EMG) activity of the reticulum, reticulo-omasal orifice (ROO) and abomasum was recorded from conscious lambs. 2. In fasted lambs diphasic reticular EMG bursts occurred at intervals of 60 +/- 13 s. In association with the second phase of the reticular EMG burst there was consistently a period of inactivity of the EMG of the ROO of 2.4-11.0 s (5.5 +/- 2.0 s, mean +/- S.D.). This period of quiescence ended with the onset of a burst of EMG activity of the ROO of 4.1 +/- 0.8 s termed here a long burst of activity. Preceding the following reticular EMG burst there were further long bursts of EMG activity of the ROO at intervals of 11.1 +/- 1.3 s or intermixing or replacement of long burst activity with short bursts which were of duration 1.1 +/- 0.3 s and which occurred at intervals of 2.4 +/- 0.5 s. 3. When the lambs were shown milk and at times when they could be expected to anticipate milk being provided, a period of inactivity of the EMG of the ROO developed for up to 60 s. In association with this there was commonly an increase in the frequency of reticular EMG bursts which at times became monophasic. 4. With the start of sucking there was quiescence of the EMG of the ROO which persisted throughout periods of sucking for up to 90 s. Simultaneously with the disappearance of activity of the ROO there was a monophasic burst of the reticular EMG, which was followed by either quiescence or disorganized low voltage activity. Inactivity of the EMG of the ROO still developed when lambs sucked milk after administration (I.V.) of atropine, phentolamine or propranolol, but not after hexamethonium. 5. In lambs observed over a period 30-60 min after feeding the diphasic reticular bursts occurred every 85 +/- 24 s and the duration of the period of inactivity of the EMG of the ROO associated with each reticular burst (3.7 +/- 1.2 s) was significantly less (P less than 0.001) than in fasted lambs. Short bursts of EMG activity of the ROO occurred more frequently than in fasted lambs. 6. In fasted lambs bursts of EMG activity of the body of the abomasum occurred at frequencies of 6-12 min-1 and those of the antrum and pylorus at ca. 6 min-1 but episodes of such activity were intermittent.(ABSTRACT TRUNCATED AT 400 WORDS)
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