ROSTROCAUDAL AND VENTRODORSAL CHANGE IN NEURONAL CELL-SIZE IN HUMAN MEDIAL VESTIBULAR NUCLEUS

Background: The present paper describes the cytoarchitectonic, morphom etric, and three-dimensional characteristics of the human medial vesti bular nucleus (MVN). We also studied the regional distribution, in siz e, of the different neurons and its possible relationship with a funct ional polarization of the different regions of the nucleus. Methods: N ine adult human brainstems (30-50 years of age) without neurological p roblems were used. Specimens were obtained from necropsy and fixed in 4% paraformaldehyde and 5% acetic acid in distilled water. After fixat ion, blocks were washed, dehydrated, and embedded in paraffin and seri al sectioned at 20 mu m. Sections were stained with formaldehyde-thion in, dehydrated, cleared in eucalyptol, and mounted with Eukitt. MVN ne urons were drawn with the aid of a camera lucida at 200-mu m intervals at 390 x magnification. Serial 50-mu m frozen sections were used to d etermine the volume of the MVN. The three-dimensional reconstruction o f MVN was accomplished with a drawing program in a Macinthosh II compu ter and an AVS on a Stardent workstation computer. Results: In the thr ee-dimensional reconstruction, the human MVN shows a pyramidal form. T he base of this pyramid constitutes the rostral limit, and its vertex forms the caudal border of the MVN. The estimated volume is 30.44 +/- 0.85 mm(3), with a neuronal population of 127,737 cells and 4,136 neur ons/mm(3) in density. The average neuronal cross-section changes from one minimum at caudal level (212.46 +/- 2.04 (mu m(2)) to one maximum at rostral level (491.47 +/- 5.08 mu m(2)). Four cell types, small (<2 00 mu m(2)), medium (200-500 mu m(2)), large (500-1000 mu m(2)), and g iant (>1,000 mu m(2)) cells, were observed. Medium cells constitute 66 %, small cells 18%, and large and giant cells 15% and 1% of the neuron al population. Conclusions: The MVN shows a variation in neuronal size , and it has the highest neuronal density of all the human vestibular nuclei. Large cells predominate in rostral regions of the MVN, with si gnificant differences in the area and diameter of the cells among rost ral, central, and caudal regions. Furthermore, the largest cells are g rouped in the ventrolateral part of the nucleus, close to its boundari es with the inferior and the lateral vestibular nuclei. The morphologi cal polarization, with respect to the neuronal size of the MVN, can be related to a functional polarization of rostral and caudal regions of this nucleus. (C) 1996 Wiley-Liss, Inc.