Nerve cell atrophy and loss in the inferior olivary complex of “Purkinje cell degeneration” mutant mice

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Abstract
The genetically determined loss of cerebellar Purkinje cells (PCs) in “Purkinje cell degeneration” (pcd) mutant mice deprives inferior olivary (IO) neurons of their major postsynaptic target. The degeneration of PCs starts on postnatal day (P) 17 and loss of these neurons is virtually complete by P45. We examined the inferior olivary complex (IOC) of normal and pcd mutant mice by quantitative light microscopy to determine whether the degeneration of PCs is associated with atrophy and loss of their presynaptic neurons in the IOC. The number of IO neurons in 17‐day‐old mutants did not differ significantly from controls (P ≥.1). IO neurons in 23‐day‐old mutants were 23% (95% confidence limits: 12–34%) fewer than in age‐matched controls, and in 300‐day‐old mutants they were 48% (95% confidence limits: 37–58%) fewer than in their controls (P ≤.001 in both cases). The decline of the number of IO neurons in pcd mice between days 17 and 300 was 49% (P <.0001; 95% confidence limits: 38–57%). The medial accessory olive (MAO) appeared less affected than the principal (PO) and the dorsal accessory olive (DAO). The mean neuronal diameter in control mice was 11.6 μm at 23 days and 10.8 μm at 300 days of age. The respective values in pcd mutants were 11.5 μm and 8.7 μm. Diameters in old mutants were significantly smaller than those in both age‐matched controls and young mutants (P ≤.001). These findings suggest that in the mature olivocerebellar system the stability of IO neurons depends on the state of their postsynaptic PCs.

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