SCANNING AND TRANSMISSION ELECTRON-MICROSCOPY OF INTRA-VENTRICULAR DENDRITE TERMINALS OF HYPOTHALAMIC CEREBROSPINAL-FLUID CONTACTING NEURONS IN TRITURUS-VULGARIS

  • 1 January 1979
    • journal article
    • research article
    • Vol. 93  (4) , 609-642
Abstract
A scanning-(SEM) and transmission electron microscopic (TEM) study of the ventricular wall of the hypothalamus of T. vulgaris was performed with special regard to the intraventricular dendrite terminals of the CSF contacting neurons of the preoptic area (magnocellular and parvocellular preoptic nuclei), the infundibular lobe (anterior periventricular nucleus, infundibular nucleus) and the paraventricular organ. In the preoptic area and infundibular lobe, the terminals were knob-like or club-shaped, of various sizes (diameter about 0.5-3.0 .mu.m) and located immediately above the ependyma. Ultrastructurally, they may contain dense-core vesicles of varying sizes. The CSF contacting dendrite endings of the paraventricular organ built up a supraependymal labyrinthic layer which could be divided into a rostral crest-like part and a caudal flat and broad division. In both parts, 3 main types of terminals of various size and shape could be distinguished: ramifying, elongated and bulb-like dendrite endings which differed by their TEM structure. The bulb-like terminals, 1st of all the small ones, originated from the distal part of the nucleus of the organ (nucleus organi paraventricularis) while the other 2 types took their origin from its intra- and subependymal part. In all areas investigated, each intraventricular dendrite ending gave rise to a solitary cilium (type 9 .times. 2 + 0). It differed from the ependymal kinocilia by both SEM and TEM characteristics. In the paraventricular organ, the neuronal cilia were hidden inside, or below the supraependymal layer of terminals. There were intraventricular axons which formed synapses on CSF contacting dendrite endings of both parts of the paraventricular organ. Free intraventricular neurons, further ependymal areas heavily or scarcely ciliated, were described. The CSF contacting dendrite terminals were predominantly present near ventricular recesses and in regions where the ependyma was scarcely ciliated. The special structure of the cilia of the intraventricular dendrite endings is discussed with regard to a possible receptor function. The differing CSF contacting dendrite terminals of the 3 main types of neurons of the paraventricular organ are considered to take different shares in the function of the organ. The relation of the CSF contacting neuronal regions to the differently ciliated ependymal areas suggests peculiar current conditions of the CSF around the intraventricular dendrite terminals.