Summary
In stressed rats the tanycytes of the ventrolateral wall of the third ventricle exhibit by light microscopic immunohistochemistry a positive staining for neurohormones which is distinctly limited to the distal perivascular end of the tanycyte process. Since by electron microscopic immuncytochemistry the tanycyte cytoplasm does not show any reaction product, the light microscopic reaction most likely results from a labeling of the intercellular space in the direct vicinity of the subendothelial cleft. Whether this subendothelial space is permeable to neurohormones was tested by injection of HRP1. In the region of the arcuate nucleus 30 min after intravenous application, the marker is affixed to the membranes of the perivascular tanycyte processes in the subendothelial cleft of capillaries possessing non-fenestrated endothelia. Occasionally, HRP penetrates for a short distance between the tanycytes. Then the labeling of the intercellular cleft ends abruptly. Here, several parallel ridges of tight junctions between the perivascular distal tanycyte processes are found by the freezeetching technique. Since HRP cannot reach the subendothelial clefts of this region by passing through capillary walls due to the presence of a blood-brain barrier, it is suggested that the marker penetrates from the median eminence this far via the subendothelial extracellular space. It is prevented from spreading further by the tight junctions of the perivascular tanycyte endings. The same way may be taken by the neurohormones. Hence, a border area exists adjacent to the dorsolateral aspect of the neurohemal region of the median eminence where the tanycytes isolate the neuropil from the cerebrospinal fluid not only by their apical tight junctions, but also by basal tight junctions from the subendothelial cleft. This communicates with the perivascular space of the portal vessels.
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Akmayev, I.G., Fidelina, O.V.: Morphological aspects of the hypothalamic-hypophyseal system. VI. The tanycytes: Their relation to the sexual differentiation of the hypothalamus. An enzyme-histochemical study. Cell Tiss. Res. 173, 407–416 (1976)
Akmayev, I.G., Popov, A.P.: Morphological aspects of the hypothalamic-hypophyseal system. VII. The tanycytes: Their relation to the hypophyseal adrenocorticotropic function. An ultrastructural study. Cell Tiss. Res. 180, 263–282 (1977)
Ambach, G., Palkovits, M., Szentágothai, J.: Blood supply of the rat hypothalamus. IV. Retrochiasmatic area, median eminence, arcuate nucleus. Acta morph. Acad. Sci. hung. 24, 93–119 (1976)
Bern, H.A., Knowles, Sir F.G.W.: Neurosecretion. In: Neuroendocrinology (eds. L. Martini, W.F. Ganong), pp. 139–186. New York-London: Academic Press 1966
Brightman, M.W.: The intracerebral movement of proteins injected into blood and cerebral fluid of mice. Progr. Brain Res. 29, 34–37 (1967)
Brightman, M.W., Prescott, L., Reese, T.S.: Intercellular junctions of special ependyma. In: Brain-Endocrine Interaction II. The ventricular system in neuroendocrine mechanisms. 2nd Int. Symp. Shizuoka (K.M. Knigge, D.E. Scott, H. Kobayashi, S. Ishii, eds.), pp. 146–165. Basel: Karger 1975
Brightman, M.W., Reese, T.S.: Junctions between intimately apposed cell membranes in the vertebrate brain. J. Cell Biol. 40, 648–677 (1969)
Broadwell, R.D., Brightman, M.W.: Entry of peroxidase into neurons of the central and peripheral nervous system from extracerebral and cerebral blood. J. comp. Neurol. 166, 257–284 (1976)
Duvernoy, H.: The vascular architecture of the median eminence. In: Brain-Endocrine Interaction I. Median eminence: Structure and function. (K.M. Knigge, D.E. Scott, A. Weindl, eds.), pp. 79–108. Basel: Karger 1972
Fuxe, K., Hökfelt, T., Agnati, L., Löfström, A., Everitt, B.J., Johansson, O., Jonsson, G., Wuttke, W., Goldstein, M.: Role of monoamines in the control of gonadotropin secretion. Neuroendocrine regulation of fertility. Int. Symp., Simla 1974, pp. 124–140. Basel: Karger 1976
Krisch, B.: Immunohistochemical and electron microscopic study of the rat hypothalamic nuclei and cell clusters under various experimental conditions. Cell Tiss. Res. 174, 109–127 (1976)
Krisch, B.: Morphological equivalent of the bifunctional role of somatostatin. Cell Tiss. Res. 179, 211–224 (1977a)
Krisch, B.: Electron microscopic immunocytochemical study on the vasopressin-contaming neurons of the thirsting rat. Cell Tiss. Res. 184, 237–247 (1977b)
Krisch, B.: The distribution of LHRH in the hypothalamus of the thirsting rat. Cell Tiss. Res. 186, 135–148 (1978a)
Krisch, B.: Altered pattern of vasopressin distribution in the hypothalamus of rats subjected to immobilization stress. Cell Tiss. Res. 189, 267–275 (1978b)
Leonhardt, H.: Ependym, Erkenntnisse und Probleme. Nova Acta Leopoldina (G. Sterba, W. Bargmann, eds.), Suppl. Nr. 9, pp. 11–37. Halle 1977
McCann, S.M., Harms, P.G., Ojeda, S.R.: Neurotransmitters involved in the release of gonadotropin-releasing factors. Neuroendocrine regulation of fertility. Int. Symp., Simla 1974, pp. 169–179. Basel: Karger 1976
Nakai, Y., Naito, N.: Uptake and bidirectional transport of peroxidase injected into blood and cerebrospinal fluid by ependymal cells of the median eminence. In: Brain-Endocrine Interaction II. The ventricular system in neuroendocrine mechanisms. 2nd Int. Symp. Shizuoka (K.M. Knigge, D.E. Scott, H. Kobayashi, S. Ishii, eds.), pp. 94–108. Basel: Karger 1975
Sternberger, L.A.: Immunocytochemistry. Foundation of immunology series (A. Osler, L. Weis, eds.). Englewood Cliffs, New Jersey: Prentice Hall Inc. 1974
Tani, E., Ikeda, K., Nishiura, M, Highashi, N.: Specialized intercellular junctions and ciliary necklace in rat brain. Cell Tiss. Res. 151, 57–68 (1974)
Vandesande, F., Dierickx, K.: Identification of the vasopressin producing and of the oxytocin producing neurons in the hypothalamic magnocellular neurosecretory system in the rat. Cell Tiss. Res. 164, 153–162 (1975)
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Dedicated to Professor Dr. R. Ortmann on the occasion of his 65th birthday.
Supported by the Deutsche Forschungsgemeinschaft (Grant Nr. Kr. 569/2) and Stiftung Volkswagenwerk
The skilful technical assistance of Miss K. Bielenberg, Mrs. A. Hinz and Mrs. H. Prien is thankfully acknowledged
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Krisch, B., Leonhardt, H. & Buchheim, W. The functional and structural border of the neurohemal region of the median eminence. Cell Tissue Res. 192, 327–339 (1978). https://doi.org/10.1007/BF00220750
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DOI: https://doi.org/10.1007/BF00220750