Sui dispositivi sinaptici delle cellule dei nuclei ottavo-motori (tangenziali) di lampreda (Lampetra pianeri)

Stefanelli, Alberto ; Caravita, Silvia

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 44 (1968) no. 3, pp. 455-462

Résumé

The ultrastructure of the synaptical apparatus of the cells of the «nuclei ottavomotori» of ammocoetes of Lampetra pianeri, considered to be homologous to the tangential nuclei of Sauropsida, was examined. This apparatus is formed by the contact between the club-shaped expansion of the vestibular root fibres and the cells of the nuclei, that wrap them; furthermore numerous synaptical bags are present on the external surface of the cells and on their axon hillock. On the extended surface of contact between the fiber and the cell there are numerous synaptical points or discs, intermingled with asynaptical zones. The club is loaded by a great amount of presynaptic vescicles in its middle part, while many mitochondria are disposed on its periphery. Presynaptic vescicles are associated to many of the synaptical points, but not all of them are of this type, which could be termed as «chemically active». In fact most of them show a desmosomoid appearance, since the membranes thickenings are symmetrical and no presynaptic vescicles are present. These contacts are interpreted as inactive points. There are other synaptical discs whose cleft is reduced, even if a complete obliteration of it, by fusion of the outer layers of the membranes, was never observed. This type of synaptical contact might be supposed to function by electrical transmission. Among the peripherical synaptic bags were observed the following conditions: there are boutons presynaptic to the cell but postsynaptic to another fiber ending on them, and other ones, which are presynaptic to the cell and to another ending that makes itself a contact with the cell. These morphological features can be interpreted as examples of presynaptic inhibition and sommation, though electrophysiological data are not available at present to prove or disprove this hypothesis.