Electron microscopic observations of neurosecretory granules, nerve and glial fibers, and blood vessels in the median eminence of the rabbit

The median eminence of the rabbit has been studied electron microscopically and the neurosecretory granules in the nerve terminals of the external layer were shown to be smaller and have a denser central core than the granules composing Herring bodies which are generally larger and has a paler core which is finely granular or vesicular.

Abstract

Abstract The median eminence of the rabbit has been studied electron microscopically and the neurosecretory granules in the nerve terminals of the external layer were shown to be smaller and have a denser central core than the granules composing Herring bodies which are generally larger and have a paler core which is finely granular or vesicular. It was proposed that the small dense granules, which may represent neurosecretory substances destined to reach the pars distalis via portal veins, reach the nerve terminals in the external layer via certain dilated fibers described in this paper which contain identical granules. Some may also arise from the small dense granules occasionally seen in Herring bodies. The demonstration of neurotubules within Herring bodies and the continuity of nerve fibers into Herring bodies, as well as the demonstration of myelin around some aggregates of large pale granules such as those seen in Herring bodies are further evidence that Herring bodies are dilated axons. Wide perivascular connective tissue spaces and interfibrillary spaces were generally seen in the external but not the internal layers. The absence of neurosecretory granules from the perivascular connective tissue spaces suggests that neurosecretory granules go into solution before entering the connective tissue space. Some fibers containing neurosecretory granules, however, penetrated through the basement membrane into the perivascular spaces and certain unidentified electron dense granules were seen beneath the basement membrane of blood vessels.