EXPRESSION OF TYROSINE-HYDROXYLASE IN CEREBELLAR PURKINJE NEURONS OF THE MUTANT TOTTERING AND LEANER MOUSE

In situ hybridization histochemistry, Northern blot analysis and immunohistochemistry were used to examine tyrosine hydroxylase (TH) mRNA concentrations and immunoreactivity in the locus coeruleus and cerebellum of the tottering (tg/tg), leaner (tg(la)/tg(la)), compound heterozygous (tg/tg(la)) and wild type control (+/+) mice, bred on a C57BL/6J background. Cerebellar Purkinje neurons, long considered to be GABAergic, showed high levels of TH mRNA in the caudal vermis and the lateral hemispheres of the cerebellum of tg/tg, tg/tg(la), and tg(la)/tg(la) mice. Analysis of grain density over individual Purkinje cells showed significantly greater concentrations of TH mRNA in tg/tg, tg/tg(la), and tg(la)/tg(la) mice as compared to +/+ wild type control mice. Comparison of adult (greater-than-or-equal-to 2 months) and young, pre-seizure (less-than-or-equal-to 3 weeks) mutant mice showed Purkinje cells densely labelled for TH mRNA at both ages, suggesting that TH gene expression in Purkinje cells is independent of the onset of seizures. Northern blot analysis confirmed the findings from the in situ hybridization studies, demonstrating a single band identical to TH mRNA. Immunohistochemistry confirmed the presence of TH protein in Purkinje cells of the caudal vermis and the lateral hemispheres of the cerebellum in both control and mutant mice. Quantitation of mRNA for TH and the coexisting neuropeptide, galanin, in the locus coeruleus detected no significant differences between adult tg/tg, tg/tg(la) and +/+ control mice. The present findings demonstrate that the classically GABAergic Purkinje cells in the cerebellum express low levels of TH, and that the mutant tottering and leaner strains of mice express extremely high levels of mRNA and protein for TH.