Summary
A morphometric evaluation of electron micrographs has been carried out from neurosecretory terminals in the neurohypophysis and from the supraoptic and paraventricular nuclei in normal male and female rats as well as in pregnant and water deprived rats. The task of this investigation was to find out whether frequency distribution diagrams of the mean diameter of the neurosecretory granules, plotted versus the number of axons, reveal a grossly bimodal distribution. In normal rats the nerve cells of the nucleus supraopticus (S.O.N.) show more numerous and larger granules than the cells of the nucleus paraventricularis (P.V.N), this difference with respect to the diameter being more pronounced in female than in male animals. In the posterior pituitary lobes the neurosecretory granules exhibit a bimodal distribution, the second peak being situated more closely to the first one in male controls. In pregnant animals both nuclei appear to be activated, and the granules of P.V.N. are distinctly larger as compared to those of female control animals. In early pregnancy larger, i.e. presumably vasopressin-containing granules are stored in the neurohypophysis, while in the last phase before delivery oxytocin-containing neurons and vasopressin-containing ones cannot be differentiated any more. After 48 hrs of thirst both hypothalamic nuclei exhibit signs of increased activation, the diameters of the granules in the S.O.N. being distinctly smaller than in normals. In the neurohypophysis granules with large diameters are lacking, while axons with small granules are more frequent. In the S.O.N. of animals, water deprived for 10 days the diameters of the granules are smaller than normal and in the neurohypophysis the number of granule-containing fibres is strongly reduced. In the frequency distribution diagram granules with larger diameters are lacking whereas the peak, attributed to oxytocin, is not essentially altered. However, from the observed alteration on the distribution patterns of the six experimental groups and in connection with the electron microscopic results the granules with smaller diameters can be attributed to oxytocin-containing axons and the larger ones to vasopressin-containing terminals. Analogous morphometric data have been obtained from the neurosecretory nuclei as well. The electron-microscopic and morphometric observations are discussed with regard to hormone-shifts between the reserve pool and the easily-releasable pool.
Zusammenfassung
Die Neurohypophyse und die neurosekretorischen hypothalamischen Kerngebiete von normalen männlichen und weiblichen Ratten, von trächtigen und durstenden Tieren wurden elektronenmikroskopisch und morphometrisch mit der Fragestellung untersucht, ob sich in den Häufigkeitsverteilungen der mittleren Granula-Durchmesser, bezogen auf die Anzahl der Axone, eine zweigipflige Verteilung ergibt. Bei Kontrolltieren zeigen die Perikarya des Nucleus supraopticus zahlreichere und größere Granula als die Zellen des Nucleus paraventricularis, wobei der Unterschied in den Durchmessern der Granula bei den weiblichen Tieren ausgeprägter ist als bei den männlichen. Beide Kontrollgruppen zeigen in der Neurohypophyse ein zweigipfliges Verteilungsmuster der Granula, wobei die beiden Gipfel bei den männlichen Kontrollen dichter beieinander liegen als bei den weiblichen. Bei den trächtigen Tieren weisen beide Kerngebiete Zeichen gesteigerter Aktivität auf und die Granula in den Zellen des Nucleus paraventricularis sind deutlich größer als bei Kontrolltieren. Zu Beginn der Tragzeit werden relativ große, wahrscheinlich vasopressinhaltige Granula in der Neurohypophyse gespeichert, während sich im letzten Drittel der Tragezeit die beiden Populationen dort nicht mehr unterscheiden lassen. Nach 48 Std. Wasserentzug erscheinen beide hypothalamischen Kerne aktiviert. Auffallend ist, daß die Granula im Nucleus supraopticus deutlich kleiner sind als bei Kontrolltieren. Entsprechend fehlen in der Neurohypophyse große Granula, während Axone mit kleinen Granula vermehrt sind. Nach zehntägiger Durstperiode lassen sich im Nucleus supraopticus, neben sehr typischen morphologischen Veränderungen, morphometrisch ebenfalls deutlich kleinere Granula nachweisen. Im Hypophysenhinterlappen dieser Versuchsgruppe sind die granulahaltigen Axone sehr stark vermindert, und in der Häufigkeitsverteilung fehlen die Granula mit großem Durchmesser während der dem Oxytocin zugeordnete Gipfel unverändert erscheint. In Verbindung mit den elektronenmikroskopischen Befunden lassen sich also aus den Verschiebungen der Verteilungsmuster zwischen den sechs Versuchsgruppen die Granula mit kleinerem Durchmesser oxytocinhaltigen Axonen zuordnen und Granula mit größerem Durchmesser zu den Endigungen, die Vasopressin enthalten. Die morphometrischen Befunde in den neurosekretorischen hypothalamischen Kerngebieten bestätigen diese Zuordnung. Die elektronenmikroskopischen und morphometrischen Befunde werden besonders im Hinblick auf die Hormonverschiebungen zwischen dem “reserve pool” und den “easily releasable pool” diskutiert.
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This work was supported by the Stiftung Volkswagen-Werk and Deutsche Forschungsgemeinschaft.
(Head: Prof. Dr. Drs. h.c. W. Bargmann)
The excellent technical assistence of Mrs. Helga Prien is gratefully acknowledged. The author is indebted to Dr. L. Sachs (Inst. f. Med. Statistik u. Dokumentation, University Kiel) for his mathematical advice and, in particular, to Dr. Udo Rempe (Inst. f. Haustierkunde, University Kiel), who performed the mathematical operations at the PDP 10 computer.
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Krisch, B. Different populations of granules and their distribution in the hypothalamo-neurohypophysial tract of the rat under various experimental conditions. Cell Tissue Res. 151, 117–140 (1974). https://doi.org/10.1007/BF00222039
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DOI: https://doi.org/10.1007/BF00222039