Expression of the α and β subunits of Ca²⁺/calmodulin kinase II in the cerebellum of jaundiced Gunn rats during development: a quantitative light microscopic analysis

Abstract

The homozygous (jj) jaundiced Gunn rat model for hyperbilirubinemia displays pronounced cerebellar hypoplasia. To examine the cellular mechanisms involved in bilirubin toxicity, this study focused on the effect of hyperbilirubinemia on calcium/calmodulin-dependent kinase II (CaM kinase II). CaM kinase II is a neuronally enriched enzyme which performs several important functions. Immunohistochemical analysis of alternating serial sections were performed using monoclonal antibodies for the α and β subunits of CaM kinase II. Measurements were made of the total numbers of stained cells in each of the deep cerebellar nuclei and of Purkinje and granule cell densities in cerebellar lobules II, VI, and IX. The β subunit was present in Purkinje cells and deep cerebellar nuclei of both groups at all ages, but only granule cells which had migrated through the Purkinje cell layer showed staining for β subunit; external granule cells were completely negative. Many Purkinje cells had degenerated in the older animals, and the percent of granule cells stained for β subunit was significantly reduced. The α subunit was found exclusively in Purkinje cells, although its appearance was delayed in the jaundiced animals. Sulfadimethoxine was administered to some jj rats 24 h or ¶15 days prior to sacrifice to increase brain bilirubin concentration. Results showed that bilirubin exposure modulated both α and β CaM kinase II subunit expression in selective neuronal populations, but sulfadimethoxine had no acute effect on enzyme immunoreactivity. Thus, developmental expression of the α and β subunits of CaM kinase II was affected by chronic bilirubin exposure during early postnatal development of jaundiced Gunn rats.