| Research Abstract |
We examined the functional organization of the rat trigeminal nuclear complex and its developmental dynamics, using a multiple-site optical recording technique. Brainstem preparations were dissected from E12-E16 rat embryos, and stimulation was applied individually to the three branches of the tngerninal nerve (V_1-V_3). The action potential activity of presynaptic fibers was detected from E13. The glutamate-mediated postsynaptic response was observed significantly from E15. At E14, the evoked signals usually consisted of only the action potential-related fast component. However, when extracellular Mg^<2+> removed, significant APV-sensitive slow component appeared. These results suggest that postsynaptic function mediated by NMDA (N-methyl-D-aspartate) receptors is latently generated as early as E14. The response area of the three branches of the trigemmal nerve showed some functional somatotopic organization, with the ophthalmic (V_1) nerve area located medially and the mandibular (V_3) nerve area laterally. The center of the trigeminal nuclear complex, in which the activity of neurons/synaptic function was greatest, shifted caudally with development, suggesting that the functional architecture of ~the. trigeminal nuclear complex is not fixed, but changes dynamically, during embryogenesis. In an electron microscopic study, we could not observe clear correlations between functional data and morphological information: as far as we surveyed in El 6 preparations, we could not identify typical synaptic structures between the DiI-labeled trigemmal nerve terminals and the neurons in the trigeminal nuclear complex. The result implies that postsynaptic function in the trigeminal nuclear complex is generated well before the appearance of the morphological structure of conventional synapses.
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