Localization of central rhythm generator for tongue movements in sucking--analysis of isolated brainstem-spinal cord preparation from newborn rats

Abstract

Localization of the central rhythm generator (CRG) for tongue movements in sucking was studied in in vitro brainstem-spinal cord preparations from newborn rats, using the rhythmical sucking-like activity (RSA) of the hypoglossal nerve (XII) induced by perfusion of N-methyl-D-aspartate (NMDA) as the index of sucking. Sulforhodamine 101 (S 101), a fluorescent dye taken up by neurons in an activity dependent manner, was applied to the preparations which showed only spontaneous inspiratory activity in XII without NMDA application and to those which showed NMDA-induced RSA in XII. In both preparations, the neurons labelled with S 101 were found in the hypoglossal nucleus, facial nucleus, ambiguous nucleus, solitary tract nucleus, trigeminal spinal nucleus, inferior olivary nucleus, gigantocellular, lateral and ventral reticular nuclei. More neurons were labelled more intensely in the latter preparations. The difference was particularly conspicuous in the gigantocellular reticular nucleus, suggesting that it plays an especially important role in central rhythm generation of sucking. The NMDA-induced RSA in XII persisted after removal of the dorsal medulla oblongata, the caudal pons constituting a part of the CRG for mastication, and the trigeminal spinal nucleus relaying afferents in sucking reflex. It was concluded that the CRG for tongue movements in sucking is localized in the ventromedial medulla oblongata.