Structural and immunohistological modifications in olfactory bulb of the staggerer mutant mouse

In the present study, we describe the structural and cytological changes ob served in staggerer mutant olfactory bulbs, as compared to normal mice. On the basis of photonic and ultrastructural observations we tried to define t he alterations induced by the mutation: ie a reduction of bulb size, a redu ction in the volume of three out of the six architectonic layers (glomerula r, external and internal plexiform), a reduction of glomeruli size, a loss of half the mitral cells and a slight decrease in juxtaglomerular interneur on number. In staggerer, an hypertrophy of glial ensheathing cell processes was especially evident at the level of each glomerulus, whereas the densit y of the astrocyte network was weaker in the granular layer and the nerve l ayer not apparently impaired. An immunofluorescent labelling study combined with confocal scanning microscopy was performed in order to identify the c ellular type and the differentiation degree of the various elements. Antibo dies anti-GFAP, a protein present in both ensheathing cells and astrocytes, and anti-OMP, the specific maturation protein of the nerve layer, were use d for that purpose. Data confirmed the reality of the gliosis and the persi stence of the sensory component in the mutant. All the structural alteratio ns described in staggerer olfactory bulb were in close agreement with the f unctional troubles previously recorded. Our results are discussed. in conne ction with the present knowledge on embryonal origin, fetal development and adult cellular renewal of the olfactory bulb. (C) Elsevier, Paris.