Lesion-specific pattern of immunocytochemical distribution of growth-associated protein B-50 (GAP-43) in the cerebellum of Weaver and PCD-mutant mice: lack of B-50 involvement in neuroplasticity of Purkinje cell terminals?

The growth-associated protein B-50 (GAP-43) is thought to play a major role in the development and regeneration of neurons. The participation of B-50 in neuronal plasticity is well documented, especially for monoaminergic systems. However, such an important role for B-50 in GABAergic systems has not been substantiated to date. This study was performed to obtain detailed information about the identity of B-50 immunopositive axons and terminals in the cerebellum and to test the involvement of this protein during plastic changes as observed in the projections of GABAergic Purkinje cells to the lateral vestibular nucleus (LVN). For this purpose mutant mice with specific cerebellar cell loss were used. Weaver mutants (B6CBA wv/wv), PCD-mutants (B6C3Fe pcd/pcd), and their corresponding wild-type mice were investigated with immunocytochemical and immunoblot procedures at the age of 8-23 days and 5-6 months using polyclonal and monoclonal antibodies to B-50. Substantial differences in B-50 distribution were detected between normals and mutants and between young and adult animals. These results demonstrate that the labeling of B-50 is mainly related to the out-growth of parallel fibers and to a minor degree on the ingrowth of non-GABAergic cerebellar afferents. There was no immunocytochemical indication that B-50 is related to Purkinje cells or accompanies the plasticity of the GABAergic innervation of the LVN.