Quantitative radioautographic light and electron microscopic analysis of the localization of monoamines in the median eminence of the rat

Summary By means of light and electron microscopic radioautography a quantitative study of the regional distribution of catecholamines in the median eminence of the rat was carried out. One hour after intraventricular injection of ³H-dopamine the highest radioautographic reaction was recorded in the external zone, especially in the lateral palisade zone where many neurosecretory terminals are separated from the basal lamina of the portal pericapillary space by a glial cuff. This area showed the highest percentage (52%) of labelled catecholamine containing neurosecretory terminals as well as the maximal silver grain density per one terminal. In the medial palisade zone where direct neurovascular contacts with the capillary loops prevail, only 27 per cent of neurosecretory terminals were found to harbour tritiated dopamine. On the average 35 per cent of neurosecretory terminals in the median eminence of the rat contain catecholamines (both dopamine and noradrenaline). Pretreatment of animals with reserpine strongly reduced the binding of the label. Per cent of labelled neurosecretory terminals as well as grain density over terminals were decreased in both the medial and lateral palisade zones, although to a lesser degree in the latter. The site of origin of catecholamine fibers as well as the mode of catecholamine action at the level of the median eminence are discussed.This work was presented at the joint session of the Society of Anatomists, Histologists and Embryologists, the Society of Physiologists, and the Society of Neuroendocrinologists dedicated to the memory of Professor Wolfgang Bargmann, held in Leningrad, January 17, 1979It is a pleasure to express our deep gratitude to Prof. P.P. Rumyantzev and Dr. N.V. Seina of the Institute of Cytology of the USSR Academy of Sciences, Leningrad, for their valuable advice on electron microscopic radioautography