Electron microscopic studies of the innervation of the human spleen

The innervation of four normal human spleens was investigated by electron microscopy. Unmyelinated nerve fibers accompanied the arterial vascular system up to the arterioles of the red pulp. Neither myelinated nerve fibers nor ganglion cells were seen in the splenic hilum or in the splenic tissue itself. The nerve fibers terminated against the smooth muscle cells of the blood vessels in a manner that is typical of the autonomic nervous system. The terminal axons contained small and large granular vesicles and thus were adrenergic nerve fibers. In contrast to the results of previous studies using silver impregnation methods innervation of the red or white pulp could not be demonstrated. The findings on human spleens agree with those on mammalian spleens obtained by other authors using ultrastructural and fluorescence histochemical methods.