Hajime Mannen

Axonal branches and terminations in the cat abducens nucleus of secondary vestibular neurons in the horizontal canal system.

Single vestibular neurons functionally identified as secondary neurons receiving primary afferents from the horizontal canal in the cat were intracellularly stained with horseradish peroxidase (HRP). The vestibular neurons projecting to the ipsilateral abducens nucleus distributed terminal branches in a relatively narrow band in the nucleus. The stem axon of contralaterally projecting vestibular neurons bifurcated into ascending and descending branches in the contralateral medial longitudinal fasciculus. The collaterals emerging from these branches distributed terminals in a relatively wide area in the abducens nucleus. Collateral branches extended into the medial vestibular nucleus, prepositus hypoglossi nucleus and reticular formation.

Central course and terminal arborizations of single primary vestibular afferent fibers from the horizontal canal in the cat

Physiologically identified single primary vestibular afferents originating from the horizontal canal in the cat were intraaxonally stained with horseradish peroxidase. All afferents examined gave off one collateral to the interstitial nucleus of Cajal located in the vestibular root bundle in the brainstem. Then these fibers bifurcated into ascending and descending branches in the lateral vestibular nucleus. The ascending branch distributed terminals mainly in the middle part of the superior vestibular nucleus. The descending branch issued several collaterals in the ventrolateral regions of the lateral and inferior vestibular nuclei. These collaterals ran horizontally and reached the medial vestibular nucleus. Terminals were observed mainly in the boundaries between the medial nucleus and the lateral or inferior nucleus. Two types of primary vestibular afferents may be distinguished. Type A fibers had terminal arborizations with plenty of boutons en passage and boutons terminaux, while type B fibers those with a few boutons. The axonal diameter of the main trunk was smaller in type A fibers than in type B fibers.

Morphological analysis of single astrocytes of the adult cat central nervous system visualized by HRP microinjection

The morphology of individual astrocytes of the adult cat was analyzed by HRP microinjection and light microscopy. The astrocytes had generally two types of processes: (1) thread-like processes of relatively constant width with few ramifications and few lamellar appendages and (2) the sinuous processes with clusters of lamellar appendages. The former processes were morphologically characterized as follows: (1) Those of fibrous astrocytes were frequently remarkably long, ranging from 600 to 1500 microns. They were much longer than any astrocytic processes hitherto reported in the literature. In contrast, those of protoplasmic astrocytes were usually short (30-400 microns), and were sometimes decorated with lamellae. (2) The processes often terminated in endfeet on the subpial surface of the brain tissue or on blood vessel walls. The number of endfeet per cell varied from 1-11 with a tendency to split into two populations close to each extreme number. Another type of endfoot was also found, i.e. swellings along the trunk of the processes which made side-to-side contact with the vessel wall. The sinuous processes rich in lamellae were predominant in protoplasmic astrocytes, and clearly corresponded to the sheet- or veil-like processes of Golgi-impregnated astrocytes. They formed an ellipsoidal field (100 microns for the longer, and 50-60 microns for the shorter, diameter) around the nucleus.

Electron microscopic comparison of the terminals of two electrophysiologically distinct types of primary vestibular afferent fibers in the cat.

Two types of electrophysiologically distinct vestibular primary afferents (regular-type and irregular-type) were injected intraaxonally with HRP and their terminals were compared using the electron microscope. In general, regular-type terminals were small and two or more terminals contacted a single dendrite side by side, whereas irregular-type terminals were large and covered a wide surface of the dendrites. Both types of terminals contained spherical clear vesicles with almost the same diameter. Prominent postsynaptic membrane specializations were observed in both types. Mitochondria in both types had an elliptical profile with the same elongation index, but mitochondria in the regular-type terminals were thicker than those in the irregular-type ones.