An electrophysiological study of single vagal efferent units associated with gastric movements in sheep.

1. A method for obtaining reticulo-ruminal movements for up to 19 hr in halothane-anaesthetized sheep is described. The duration, wave form and frequency of the movements resembles those in the conscious animal except that ruminal movements have a lower amplitude.2. A method of recording for up to 5(1/2) hr single efferent unit discharges from fibres presumed to innervate the reticulo-rumen is described.3. At least seven distinguishable types of discharge pattern were recorded. By relating these temporally to movements of the reticulum and rumen it was concluded that Types I, II and III occurred in fibres innervating the reticulum or associated structures, Type IV the rumen and Types V, VI and VII other gastric structures not yet identified. Apart from Type VII units there was no ;resting discharge' in efferent fibres during the quiescent phase of the gastric cycle.4. We conclude that the co-ordination of the complex sequence of gastric movements in ruminant animals is a function of the ;gastric centres' in the hind-brain through their ability to determine the pattern, durations, spike frequencies and temporal interrelationships of discharges in gastric motoneurons innervating the different parts of the forestomach.