Nerve fibers and terminals in the rat anterior pituitary gland as revealed by electron microscopy.

During the course of studies on the ultrastructural changes of the rat anterior pituitary due to various experimental procedures acting on the pituitary-adrenal axis, bundles of unmyelinated nerve fibers and nerve terminals were found either in the pericapillary connective tissue space or intercellular space among the glandular cells. The fine structure of the nerves was not altered by these experiments. Nerve fibers and endings contain vesicles and tubules of various sizes, more or less filled with a dark substance. Relatively large dense granules looking like neurosecretory granules were contained and released from the surface of nerve endings by exocytosis. Somatotrophs were most frequently attached by the nerve terminals and the corticotroph was next. The function of these nerve terminals was not fully elucidated, but probably related to the endocrine activity of the gland. They were not vasomotor nerves, though they were often associated with blood vessels.