MEDIAL PREOPTIC AREA INNERVATING SACRAL SPINAL CORDPROJECTING NEURONS IN BARRINGTON NUCLEUS: LIGHT AND ELECTRON MICROSCOPE STUDY IN THE RAT

Direct projections from the medial preoptic area (MPO) to sacral spinal cordprojecting neurons of Barrington nucleus were revealed in the rat by a double labeling method with light and electron microscopy. Biotinylated dextran amine (BDA), an anterograde tracer, was injected into the MPO to label projection axon terminals originating from the MPO and horseradish peroxidase (HRP), a retrograde tracer, was injected into the lumbosacral cord segments to label neurons projecting to the lumbosacral spinal cord in Barrington nucleus. At light microscope level, a large number of BDAlabeled presumptive axon terminals and HRPlabeled neurons were seen in Barrington nucleus. Electron microscopic observation showed that some BDAlabeled axon terminals made symmetric synaptic contacts with dendrites and somata of HRPlabeled neurons in Barrington nucleus. The present results provided evidence for involvement of MPO in the neuronal mechanisms of the rat micturition reflex.