The ultrastructure of the developing neural lobe

Summary The ultrastructure of the developing neural lobe of rats was studied. The results revealed three periods in its development. The first period lasts till the 17th day of fetal life. At its beginning the anlage of the neural lobe is formed as a mass of cells very similar in appearance and in connection with the subependymal cells of the future median eminence. During the first period the cells of the anlage differentiate into pituicytes, and the penetration of the first nerve fibres and blood vessels among them is seen. The second period is from the 18th day of fetal life till one month after birth. At its beginning the first signs of neurosecretory activity were detected. During the period increasing numbers of neurosecretory fibres penetrate into the neural lobe, and the pituicytes show morphological signs characteristic of active cells. An increase in the functional activity of the neural lobe is also detected. The third period is from the end of the 1st till the end of the third month. During this period the development of the neural lobe proceeds and at the end it has the appearance of the adult gland. During this period the pituicytes gradually lose the signs of activity and at the end of the period they look like those observed in adult animals. Considering the results from the study, together with some data from previous investigations it is suggested that the pituicytes exert some stimulating and regulative influences on the process of neurosecretion in the neural lobe.Research fellow of the Alexander von Humboldt Foundation.     

Nervenfasern mit ultrastrukturell verschiedenen Elementargranula im Hypophysenhinterlappen des Rhesusaffen

Zusammenfassung Im Hypophysenhinterlappen des Affen lassen sich elektronenmikroskopisch zwei Arten markarmer, neurosekrethaltiger Nervenfasern beobachten. Sie unterscheiden sich voneinander durch den Typ der Elementargranula, die sie enthalten.In Nervenfasern des Typs I haben die Elementargranula einen Durchmesser von 1500 bis 3500 Å. Sie besitzen eine geringe Elektronendichte und enthalten oft kreisförmig angeordnete Proteinkörnchen. Vereinzelt sind kristallähnliche Formationen des Granulainhalts zu erkennen.Die Elementargranula in Nervenfasern des Typs II messen 1200–2200 Å im Durchmesser. Ihr Inhalt besitzt infolge eng aneinander gelagerter granulärer Teilchen eine weitaus größere Elektronendichte als die Granula des Typs I. Kristallähnliche Granulaeinschlüsse waren nicht zu sehen.Die ultrastrukturelle Differenzierung zweier Nervenfasergruppen im Hypophysenhinterlappen wirft die Frage auf, ob es sich bei dem einen Typ um vasopressin-bei dem anderen Typ um oxytocinhaltige hypothalamische Nervenfasern handelt.Die Pituizyten im Hypophysenhinterlappen des Rhesusaffen besitzen Granula (1500 bis 3000 Å) mit einer Innenstruktur ähnlich den Neurosekretgranula vom Typ II. Sie enthalten außerdem größere, fein granulierte osmiophile Grana.

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Neurosecretory nerve fibres containing ultrastructurally different elementary granules in the hypophysial posterior lobe of the rhesus monkey

Summary In the posterior lobe of the neurohypophysis of the rhesus monkey, two kinds of unmyelinated nerve fibres containing neurosecretory substance can be discerned with the electron microscope. They differ with respect to the type of elementary granules they contain.In type I nerve fibres the elementary granules have a diameter of 1,500–3,500 Å. They are of little electron-density and often contain circularly arranged protein grains. Crystal-like formations of the content of the granules are sometimes observed.In type II nerve fibres the elementary granules measure 1,200–2,200 Å in diameter. Due to close packing of their granular content they are much more electron-dense than type I granules. Crystal-like inclusions were not seen.The ultrastructural differentiation of two groups of nerve fibres in the posterior lobe raises the question of whether the one type consists of vasopressin-containing and the other of oxytocin-containing hypothalamic nerve fibres.The pituicytes in the hypophysial posterior lobe of the rhesus monkey contain granules (1,500–3,000 Å) with an inner structure similar to type II neurosecretory granules. In addition, they contain larger, finely granulated osmiophilic grains.

Mit dankenswerter Unterstützung durch den Herrn Bundesminister für Bildung und Wissenschaft.     

The juxtaligamental cells of Ophiocomina nigra (Abildgaard) (Echinodermata: Ophiuroidea) and their possible role in mechano-effector function of collagenous tissue

Summary The intervertebral ligament of the brittlestar Ophiocomina nigra contains numerous cellular processes which belong to perikarya located on the outer surfaces of the ligament. These are described as the juxtaligamental cells and have been studied by light and electron microscopy. The cells are mainly concentrated in four pairs of ganglion-like nodes associated with the intervertebral ligament and in similar nodes adjacent to every other major connective tissue component of the arm. Although their histochemistry and ultrastructure indicate a neurosecretory function, they are anomalous in containing unusually large electron-dense granules probably associated with calcium. The ganglion-like nodes are innervated by hyponeural nerves, though synaptic contacts with the juxtaligamental cells have yet to be demonstrated.The function of the cells is discussed and it is suggested that they may be involved in the rapid loss of tensile strength which the intervertebral ligament sustains during arm autotomy. They may achieve this by controlling the availability of Ca²⁺ ions to the extracellular compartment of the ligament.A version of this paper was read at the U.K.-Eire Echinoderms Colloquium, Bedford College, London, in July 1978This work was conducted mainly at University Marine Biological Station, Millport, during tenure of a N.E.R.C. research studentship. I am grateful to Professor N. Millott for his keen supervision, to Professor D.R. Newth for permission to use the electron microscope in the Department of Zoology, University of Glasgow, where Maureen Gardner provided expert assistance, and to Professor R.M. Kenedi for Facilities in the University of Strathclyde. I have benefited from discussion with J.L.S. Cobb, V.W. Pentreath, and especially A.M. Raymond, University of St. Andrews, who allowed me to mention his unpublished observations.