Descending projections of the hypothalamic paraventricular nucleus to the parasympathetic preganglionic neurons

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The present study was undertaken to elucidate whether the descending fibers of the hypothalamic paraventricular nucleus have a direct connection with the parasympathetic pregaglionic neurons. At the first step of the experiment, we developed an operating technique to reach and expose the major pelvic gaglion of the male rat. After the major pelvic ganglion was exposed on the wall of the prostate gland, the retrograde labelling tracer, cholera toxin subunit B(CTB), was injected into the ganglion. This technique resulted in a retrograde labeling of many sympathetic and parasympathetic preganglionic neurons in the lumbar and sacral cords. In the sacral level, the primary sensory fibers that were labeled anterogradly were observed, in addition to the parasympathetic preganglionic neuros. At the lumbar cord level, many labeled sympathetic preganglionic neurons were obserbed in the midregion, just dorsal to the central canal. They formed a single cell column as the dorsal commissural nuclues. The nucleus appeared to be very similar with the Terni's nucleus of the chick in respects of cell location, forming single cell column. A signle cell column situated in the midline seens to be suitable to innervate unpaired pelvic organs. This results will be published in "The Experimental Brain Research" this year. Although the morphology of the dorsal commissural nucleus was shown, we were not able to clarify the neuronal connections between the hypothalamic paraventricular nuclues and the sacral parasympathetic preganglionic neurons.