Calbindin D-28k in the lateral vestibular nucleus of mutant mice as a tool to reveal Purkinje cell plasticity.

Antibodies against the calcium-binding protein Calbindin D-28k (CaBP) are specific markers of cerebellar Purkinje cells (PC). To identify the origin of CaBP-immunopositive (CaBP+) terminals and fibres in the dorsal part of the lateral vestibular nucleus (dLVN), brains of Purkinje cell degeneration mutants (PCD) were immunoreacted for CaBP using the avidin-biotin method (ABC). In PCD an almost complete loss of CaBP+ fibres and terminals in the dLVN compared to the wildtype and the Weaver mutant was present. Morphometric analysis of CaBP+ synaptic terminals in the dLVN of adult Weaver mutants showed that the maximum and mean terminal size exceeded those in wildtypes by almost twice, which is a far larger difference than in GABA-immunoreacted material. The results show that CaBP-immunoreactivity and terminal size expansion in Weaver are both mainly attributable to PCs. Moreover, it can be concluded that the colocalization of CaBP and GABA in fibres and terminals of the dLVN in normal animals is almost entirely restricted to the PC-innervation of this nucleus. Therefore CaBP-immunocytochemistry is an excellent tool to selectively investigate the direct PC-projections in the dLVN, as it sets off the GABAergic PC-innervation from the total GABAergic innervation of this area.