Morphological studies for neurotransmission in the trigeminal nervous system -Roles of neuropeptides and amino acid-.

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Changes in the levels of transcription factor mRNA and neuropeptide precursor mRNA in the trigeminal nucleus caudalis (TNC) in response to orofacial pain induced by the injection of formalin into the facial skin of anesthetized rats were investigated. After the injection of formalin, the number of neurons expressing c-fos, NGFI-A and NGFI-B mRNA was increased, followed by increases in the number of neurons expressing preprogalanin (PPG), preproenkephalin A (PPEA), preprodynorphin (PPD) and preprotachykinin (PPT) mRNA in the superficial layers (laminae I and II) of the ipsilateral TNC in accordance with the projection system previously described. The increases in the number and intensity of the labeled neurons for PPG, PPEA, PPD and PPT mRNA were most marked 6 hrs after the injection of formalin. The increases in the number and intensity of the labeled neurons for c-fos, NGFI-A and NGFI-B mRNA were most marked at 2 hrs.Furthermore, the numbers of PPD and PPT mRNA containing neurons were … More increased in the contralateral TNC after the injection. The number of Fos-like immunoreactivity positive neurons was also increased in the contralateral TNC.These findings suggested that the modulation of pain is associated with the increased production of PPG, PPE, PPD and PPT, and the transcription of these genes are regulated by immediate early genes, such as c-fos, NGFI-A and NGFI-B. Noxious information seems to affect neurons in the contralateral TNC, as well.The distribution study of glutamate-like (GLU-LI) and glutaminase-like (GLNase-LI) immunoreactivity (IR) combined with tracer method showed that trigeminal neurons projecting to the thalamus and cerebellum constitute distinct subpopulations, and that some of these neurons are glutamatergic.Furthermore, NMDAR_1, GluR_2 and GluR_5 subunit mRNAs of glutamate receptor and beta_2,gamma_1 and gamma_2 subunit mRNAs of GABA_A receptor were found in the trigeminal ganglion. These findings indicate that primary sensory neurons are presynapticaly regulated by glutamate and GABA in the TNC. Less