Summary
Axo-dendritic and axo-somatic synapses and complex axo-dendritic junctions from the nucleus infundibularis and nucleus supraopticus of Passer domesticus were studied in the electron microscope. A morphological asymmetry, represented by clustering of synaptic vesicles (of about 500 Å diameter) at the presynaptic membrane and a thickening of and subsynaptic web formation at the postsynaptic membrane, was observed in the axo-dendritic and axo-somatic synapses, and to a smaller extent in the complex axo-dendritic junctions. In the hypothalamic synaptic axon terminals, as in the perikarya of nucleus infundibularis, dense-core vesicles of 800–1,000 Å mean diameter were observed in addition to the synaptic vesicles, but the 800–1,000 Å vesicles were not concentrated at the presynaptic membrane. Granules of 2,000 Å mean diameter, observed in the neurons of nucleus supraopticus, were not seen in any hypothalamic synaptic terminals. Intersynaptic filaments and an intrasynaptic band lying in the intersynaptic cleft were frequently observed. The significance of the synaptic structures was discussed in relation to neurotransmission and to possible mechanisms by which perikarya of the nucleus infundibularis and nucleus supraopticus receive nervous information.
Zusammenfassung
Mit dem Elektronenmikroskop wurden im Nucleus infundibularis und Nucleus supraopticus von Passer domesticus axo-dendritische und axo-somatische Synapsen sowie komplexe axo-dendritische Kontaktstellen untersucht. Vor allem zeichnen sich die axodendritischen und axo-somatischen Synapsen durch eine Polarität ihrer Feinstruktur aus. Diese wird in erster Linie durch eine Anhäufung von etwa 500 Å großen synaptischen Bläschen an der präsynaptischen Membran sowie durch eine Verdichtung und ein subsynaptisches Geflechtwerk an der postsynaptischen Membran gekennzeichnet. Die hypothalamischen synaptischen Axonendigungen enthalten neben den charakteristischen synaptischen Bläschen elektronendichte Granula mit einem Durchmesser von etwa 800–1000 Å; die letzteren, die u.a. auch für Perikaryen des Nucleus infundibularis charakteristisch sind, lassen sich jedoch nicht in unmittelbarer Nähe der präsynaptischen Membran nachweisen. Granula mit einem Durchmesser von etwa 2000 Å, die in den Neuronen des Nucleus supraopticus zu beobachten sind, fehlen in den hypothalamischen synaptischen Nervenendigungen. Intersynaptische Filamente und ein den Synapsenspalt füllendes intrasynaptisches Band konnten in zahlreichen Synapsen dargestellt werden. Die Bedeutung der Synapsenstrukturen wird im Hinblick auf die nervöse Übertragung und auf die Mechanismen, die der Zuleitung nervöser Informationen an den Nucleus infundibularis und Nucleus supraopticus dienen, diskutiert.
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Dedicated to Professor Ernst Horstmann.
The investigation was supported by a scholarship of the Alexander von Humboldt-Stiftung to Dr. J. Priedkalns (on leave from the Department of Veterinary Anatomy, University of Minnesota, St. Paul, U. S. A.) and by a research grant of the Deutsche Forschungsgemeinschaft to Professor A. Oksche.
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Priedkalns, J., Oksche, A. Ultrastructure of synaptic terminals in nucleus infundibularis and nucleus supraopticus of Passer domesticus . Z. Zellforsch. 98, 135–147 (1969). https://doi.org/10.1007/BF00344513
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DOI: https://doi.org/10.1007/BF00344513