Electron microscopy of the neurohypophysis in normal and histamine-treated rats

Summary The fine structure of the neurohypophysis has been studied in normal and histamine-treated rats with particular reference to capillary relationships and to the neurosecretory vesicles. Certain new information on the pericapillary space has been developed and is discussed with reference to the existing literature on the posterior hypophysis and other endocrine organs. The membrane-bounded pericapillary space penetrates deeply between surrounding nerve terminals and pituicyte processes, seemingly forming a pervasive metabolic lake which undoubtedly is of physiological significance for metabolic and secretory exchange.Following histamine treatment, the neurosecretory vesicles lose their electrondense centers, the mitochondria in the nerve terminals become swollen, and the capillary endothelium shows evidence of increased pinocytosis. In one rat subjected to painful stimuli, only the first and last of the above alterations are prominent. The experimental results are interpreted in the light of previous work done by other authors, as additional evidence for the identity of the stainable neurosecretion of light microscopy and the neurosecretory vesicles of electron microscopy.The author is greatly indebted to Prof. Dr. med. W. Bargmann for the use of electron microscope facilities and for other invaluable help during the course of the work. To Frau Dr. A. Knoop of the Anatomical Institute in Kiel, and to Frl. Dr. Weichan of Siemens & Halske AG in Berlin, for aid in obtaining the micrographs, a grateful acknowledgement is extended.Presented in part at the 55th meeting of the Anatomische Gesellschaft in Frankfurt/Main, April 9–12, 1958.United States Public Health Service Special Research Fellow, on leave from Department of Anatomy, University of Minnesota Medical School, Minneapolis, Minnesota, USA.