Comparison of activity in pontine versus medullary neurones during swallowing

1. On decerebellectomized sheep lightly anaesthetized with fluothane, the activity of 49 neurones in the pontine relay (see Car et al., 1975) was recorded with microelectrodes following stimulation of afferents in the superior laryngeal nerve (SLN), 2. These pontine neurones (PN) exhibited an "initial activity" (one or a few spikes) for stimulation either of the homolateral SLN (35 PN) or glossopharyngeal nerve (14 PN). This initial activity had a latency between 1.5 and 4 msec. When swallowing was induced by SLN stimulation, a later discharge appeared. This "swallowing activity" consisted of a variable burst of spikes. 3. The effect of curarization was tested for 13 PN. It always eliminated the "swallowing activity". 4. A clear antidromic response of 16 PN (26 tested PN) was induced by stimulating the thalamic VPM nucleus. This stimulation failed to elicit an antidromic response in medullary neurones (14 tested) located in the nucleus of the tractus solitarius. 5. It is concluded that PN are probably sensory relay neurones which inform higher nervous centres of the state of oropharyngeal receptors; whereas medullary swallowing neurones are really interneurones involved in the programming of the wallowing motor sequence.