Ion channel analysis of neurons of the mesencephalic trigeminal nucleus in in vitro preparations

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In the trigeminal mesencephalic nucleus (MTN), there are two functional types of neurons : one supplying the muscle spindles in jaw-closing muscles and the other the periodontal mechanoreceptors, and also two anatomical types of neurons : pseudomonopolar and multipolar. The purpose of this study was to investigate the organization of ion-channels on each type of MTN neurons in in vitro preparations.To achieve this goal, I had developed two types of in vitro preparations : slice preparation and isolated brainstem-spinal cord preparation. Although the slice preparation is of use to an analysis of ion-channels, it will not achieve characterizations of individual cells and a system analysis. On the other hand, the isolated brainstem-spinal cord preparation involves intact circuits including MTN neurons and generates reflex responses and rhythmical activity.The in vitro brainster-spinal cord preparation were isolated from neonatal rats (from 0- to 3-day-old). Neural activities were monitored in trigeminal sensory (Vs), trigeminal motor (Vm), hypoglossal (Xll) nerves as well as ventral roots of the cervical spinal cord (C4-C5) with suction electrodes. The following results were obtained : (1) electrical stimulation of Vs evoked nerve volley in Vm and Xll ; (2) rhythmical nerve discharges distinct from spontaneously generated respiratory activities recorded in Vm, Xll and C4,5 nerves could be observed in the Xll nerve after application of N-menthyl-D-aspartate into the bath solution.I conclude that this isolated brainstem-spinal cord preparation will be useful for the investigation of cellular mechanisms (ion-channel) and neuronal organization (system) related to the function of MTN neurons. At present, I am trying to analyze ion-channel mechanisms of MTN neurons in these preparations.