A Golgi study on the inferior olivary nucleus in the red sting ray, dasyatis akajei

$32 PROJECTION PATTERN OF VESTIBULOCEREBELLAR FIBERS IN THE ANTERIOR VERMIS OF THE CAT: AN ANTEROGRADE WGA-HRP STUDY blATSUO bIATSUSHITA and CHAN LI WANG , Department of Anatomy, Institute of Basic Medical Sciences, University of Tsukuba, Niihari, Ibaraki 305, Japan The distribution of mossy fiber terminals of vestibuloeerebellar fibers was studied in the anterior ]obe following the unilateral injection of wheat germ agglutinin-horseradish peroxidase into the medial and descending vestibular nuclei in the cat. The labeled mossy fiber terminals appeared bilaterally in the cerebellar cortex. In the transverse plane the labeled terminals appeared mainly in sections through the middle to basal parts of the lobules. Few labeled terminals were seen in sections through the apical parts. In transverse sections through the basal parts, three groups of labeled terminals were seen: group i located in the midline region, group 2 located at around 0.5 mm lateral to the midline~ and group 3 located between 0.75 and 1.5 mm from the midline. The distribution of labeled terminals in the horizontal plane was reconstructed from a series of transverse sections. The three groups of labeled terminals formed longitudinal areas of projection: area 1 extending in the midline region (zone AI), area 2 located from zones A1 to A2, and area 3 located from zone A2 to the medial part of zone B of Voozd. They were confined in the basal part of the lobules. The present findings suggest that vestibuloeerebellar fibers arising from the medial and descending vestibular nuclei terminate in specific longitudinal areas of the anterior lobe.

A GOLGI

STUDY

ON

THE

INFERIOR

OLIVARY

NUCLEUS

IN THE

RED

STING

RAY,

DASYATIS

AKAJEI

NOBUHARU Nagasaki

IWAHORI, Department 852, J a p a n

of Anatomy,

Faculty

of Medicine,

Nagasaki

University,

The intranuclear organization of the inferior olivary nucleus (ION) w a s s t u d i e d in the red sting ray using the rapid Golgi method. The ION was situated in the ventral region of the medulla oblongata on either side of the midsagittal plane. Over its rostral half the ION was a single cell mass, whereas over its caudal half the ION was divided into a large ventromedial and a small dorsolateral part. Except for its ventral surface the ION was surrounded by large reticular cells, and some dendrites of the reticular neurons extended i n t o t h e ION. T h e I O N w a s s e e n to b e t r a v ersed by numerous fiber bundles which ran in a transverse or longitudinal direction and among these fiber bundles were located the ION neurons. The ION neurons had polygonal or triangular cell bodies which generated three to five primary dendrites The primary dendrites extended in a radial fashion and branched out into several short branchlets. The dendrites were sparsely spinous and were distributed almost exclusively within the nuclear confine of the ION. The axons of the ION neurons arose from the somata or from the proximal portion of a primary dendrite and travelled in a medial direction to j o i n t h e f i b e r b u n d l e s w h i c h r a n t r a n s v e r s e l y in the n u c l e a r t e r r i t o r y o f t h e ION. F u r t h e r c o u r s e o f t h e a x o n s c o u l d n o t b e f o l l o w e d i n the present study. The afferent fibers to the ION were divided into three groups. The first group of the afferents ran ventrally in the paramedian tegmental region, entered the ION from the dorsal aspect and travelled ventrally or ventrolaterally within the ION emitting numerous fine terminal collaterals. At least some of these afferents were the collaterals of fibers which ran in a longitudinal direction in the paramedian tegmental region. The second group of afferents were derived from the fiber bundles which ran longitudinally in and around the ION and travelled dorsally or ventrally to terminate mainly in the lateral portion of the ION. The third group of afferents were collaterals of fibers which ran transversely in the ION and travelled medially or laterally in the nucleus branching out into many fine collaterals. Some fibers of these three groups of the afferents converged to f o r m p e r i cellular baskets.