Differential expression of T-type calcium channels in P/Q-type calcium channel mutant mice with ataxia and absence epilepsy

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Abstract
Mutations in P/Q‐type calcium channels generate common phenotypes in mice and humans, which are characterized by ataxia, paroxysmal dyskinesia, and absence seizures. Subsequent functional changes of T‐type calcium channels in thalamus are observed in P/Q‐type calcium channel mutant mice and these changes play important roles in generation of absence seizures. However, the changes in T‐type calcium channel function and/or expression in the cerebellum, which may be related to movement disorders, are still unknown. The leaner mouse exhibits severe ataxia, paroxysmal dyskinesia, and absence epilepsy due to a P/Q‐type calcium channel mutation. We investigated changes in T‐type calcium channel expression in the leaner mouse thalamus and cerebellum using quantitative real‐time polymerase chain reaction (qRT‐PCR) and quantitative in situ hybridization histochemistry (ISHH). qRT‐PCR analysis showed no change in T‐type calcium channel α1G subunit (Cav3.1) expression in the leaner thalamus, but a significant decrease in α1G expression in the whole leaner mouse cerebellum. Interestingly, quantitative ISHH revealed differential changes in α1G expression in the leaner cerebellum, where the granule cell layer showed decreased α1G expression while Purkinje cells showed increased α1G expression. To confirm these observations, the granule cell layer and the Purkinje cell layer were laser capture microdissected separately, then analyzed with qRT‐PCR. Similar to the observation obtained by ISHH, the leaner granule cell layer showed decreased α1G expression and the leaner Purkinje cell layer showed increased α1G expression. These results suggest that differential expression of T‐type calcium channels in the leaner cerebellum may be involved in the observed movement disorders. © 2004 Wiley Periodicals, Inc. J Neurobiol, 2005