Postnatal development of central neural mechanisms controlling food ingestive movements-analysis in in vitropreparations

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The purpose of this study is (1) to develop the methods for induction of sucking and mastictory activities in an in vitro isolated brainstem of mice ranging from newborn to adult stages, and (2) using these rhythmical acitivies as the model for food ingestive movements, to analyze the postnatal development of central neural mechanisms of generation of patterns of food ingestive movements. In the first year of this study, we succeeded to induce rhythmical masticatory-like activities in jaw-opening and -closing muscles by repettive stimulation of the pontine pyramidal tract of the in vitro brainstem isolated from adult animals, which was kept alive by oxygen supply via the vascular system and by diffusion from a perfusing artificial cerebrospinal fluid, but bath application of NMDA induced no masticatory-like activities. In the second year, we succeeded to induce rhythmic sucking-like activities in the trigeminal (V), facial (VII) and hypoglossal (XII) nerves with cycle times diferent from one another in in vitro brainstem isolated from newborn mice by bath application of NMDA, but repetiive stimulation of the pontine pyramidal tract was not effective for induction of the sucking-like activities. The NMDA-induced rhythmical activities in the V, VII and XlI nerves persisted still after transection of the brainstem between the V and VII nerves, and between VII and Xll nerves. The results inndicate that there are separte rhythm generators for the V, VII and XII motoneuronal activities comprizing sucking movements, which are located segmentally in the brainstem at respective motor nuclei of these nerves. Taking into consideration of the report that the main portion of the masticatory rhythm gnenerator for the V moneurons in adult animals is lcated in the bulbar reticular formation, it is suggested that the central neuronal mechanisms underlying food ingestive movements is reorgnaized duing postnatal dvelopment of food ingestion from sucking to mastication.