Morphological study about glutamate neural transmission in the micturitional center in central nervous system.

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Glutamate is a major excitatory neurotransmitter in the mammalian central nervous system. Physiological studies have shown that lower urinary tract function is regulated through the glutamate receptors at the level of spinal and supraspinal cord. To know the ontogenic change of NMDA receptor subunit mRNAs and function in developing spinal micturitional system, we employed double labeling technique of retrograde neuronal tracing and in situ hybridization for detecting NMDA subunit mRNAs in developing preganglionic neurons (PGNs) in the rat, which innervate bladder muscle. We also examined expression patterns of NMDA subunit mRNAs and glutamate transporter subtype mRNAs in lower urinary tract obstruction model and spinal cord injury model, which are both important human pathologies in micturition system.The PGNs showed strong signals for NR1 subunit mRNA at every stage during development to adult. Moderate signals for the NR2B and NR2D subunit mRNAs were found in PGNs at postnatal day 7. However, their expression levels decreased gradually during development, with minimal expressions in Adult. These results show that there are dynamic changes in the expression of the NR2 subunit mRNAs in the PGNs during development. PGNs seem to change their property through the NMDA receptor during development. This temporal expression of functional NMDA receptors during early development might contribute to the establishment of the adult-type micturitional neural circuit through activity-dependent synaptic plasticity and refinement. There were no significant changes in the expression of glutamate receptor and transporter molecules both in lower urinary tract obstruction and spinal cord injury models.