Quantitative morphological analysis of the cerebellar nuclei in normal and lurcher mutant mice. I. Morphology and cell number.

The present study indicates that the cerebellar nuclei of the mouse are essentially identical in structure with those described in the rat, and that the atrophic cerebellar nuclei in lurcher mutant mice exhibit a comparable anatomical organization. A quantitative estimate of the atrophy observed in the cerebellar nuclei of the adult lurcher mutant mouse reveals an overall 60% decrease in volume. Cell counts in the wild-type cerebellar nuclei reveal a total of 8,528 principal neurons and 10,203 small neurons. The ratio of small/principal neurons is 0.5 in the fastigial nucleus and between 1 and 1.5 in other subdivisions. In lurcher, the principal neurons are slightly reduced in number (-20%) in the nuclear complex, while the population of small neurons is reduced by 37% in the interposed and dentate nuclei, but is unchanged in the fastigial nucleus. These results suggest that the massive deafferentation of the cerebellar nuclei that occurs between 10 and 30 days of age in lurcher mutants has a relatively mild effect on the principal cerebellar nuclear neurons. In the population of small neurons, however, the effect of deafferentation may be exacerbated by a secondary retrograde transneuronal degeneration brought on by the severe degeneration of inferior olivary neurons and cerebellar cortex in this mutant.