Cells of origin innervating the liver and their axonal projections with synaptic terminals into the liver parenchyma in rats.

By utilizing a horseradish peroxidase (HRP) axonal flow technique for retrograde tracing, and electron microscopic techniques, attempts were made in adult Wistar rats to elucidate the central organization of the parasympathetic hepatic innervation. The results were as follows: 1) cells of origin directly innervating the liver were located mainly in the left dorsal motor nucleus of the vagus (DMV). Their mean number was 175 with a standard deviation of 14 (n = 14). 2) the hepatic branch of the vagus consisted mostly of unmyelinated nerve fibers. The mean number of unmyelinated fibers was 2072 with a standard of 137, while that of myelinated fibers was only 13 with a standard deviation of 4 (n = 10). 3) nerve terminals were found in two different regions; one adjacent to the vasculature in the portal area, and the other in the space of Disse among hepatic parenchymal cells. These nerve terminals contained several synaptic vesicles different both in their form and size.