Granule cell heterotopia in normal and nervous mutant mice of the BALB/c strain

Aberrant granule cells are present in the cerebellar molecular layer of ‘nervous’ (nr/nr) mutant mice of the Balb/cGr strain. These heterotopic cells produce dendrites which form glomerulus-like synaptic complexes in the molecular layer with both mossy and climbing fibers. Similar heterotopic cells are also present in normal mice of the Balb/cGr and C3Heb/FeJ strains, although to a much lesser degree, while they are rare in C57BL/6J mice. The relevance of these findings to mechanisms of normal granule cell migration and synaptogenesis during development are discussed.