Effects of thiopental(TPL) on swallowing-related unit (SRU) activities in the rabbit.

Abstract

We have been reported that barbiturates and other central nervous system(CNS) depressants have a potent inhibitory effect on muscle activities during the buccopharyngeal phase of swallowing. Thus, the duration of the phase was shortened. Swallowing-relevant muscle activities are probably formed in the brainstem swallowing center and are mediated by their respective innervations. However, no detailed information of neuronal organisation forming the temporal sequence of muscle activities has been reported. We systematically explored for bulbar SRUs in vagotomized, immobilized, artificially respirated rabbits which have been awake from ether anesthesia. The superior laryngeal nerve was stimulated, and the evoked swallowing-related neural activities were identified in both phrenic and inferior pharyngeal nerves. The elapse between the onset of phrenic degluticatory small activity and the termination of pharyngeal nerve activity means the buccopharyngeal phase. Thus, the discharge phase of a SRU could be precisely determined in these immobilized animals. 1) Most SRUs were found in the solitary tract, ambiguous, retrofacial and hypoglossal nuclei as well as in the respective portions of the reticular formation around these nuclei. They had different discharge phases during the buccopharyngeal or the esophageal phase of swallowing. Therefore, it might be assumed that the temporal sequence of motor activities as well as their respective patterns are formed by a network of these reticular SRUs. 2) TPL(0.25-0.5mg/kg, i.v.) inhibited all SRUs with different discharge phases(seven active during the pharyngeal and five during the esophageal phase). Their discharge phase was without exception shortened. The effect of TPL and other CNSdepressants on the pharyngeal phase could be explained by a non-selective inhibition of all SRUs, assuming that both excitatory and inhibitory SRUs have been in fact studied.