Histological changes in monoaminergic neurons of Long-Evans Cinnamon rats

The Long-Evans Cinnamon rat, an animal model of Wilson's disease, is an inbred mutant strain with spontaneous hepatitis isolated from Long-Evans rats. The copper concentration in the brains of Long-Evans Cinnamon rats at 4 weeks of age was lower than that of controls, but higher than that of controls at 20 weeks of age. We investigated the tyrosine hydroxylase and 5-hydroxytryptamine immunoreactive fiber densities in the brains of Long-Evans Cinnamon rats aged 4, 10, and 20 weeks by immunohistochemistry, comparing them with Long-Evans Agouti rats used as controls. Tyrosine hydroxylase immunoreactive fiber densities in the cingulate cortex, hippocampus and cerebellum in Long-Evans Cinnamon rats were significantly lower than those of Long-Evans Agouti rats at 4 and 10 weeks of age. On the other hand, 5-hydroxytryptamine immunoreactive fiber densities in the cingulate cortex, caudate-putamen, hypothalamus, and hippocampus in Long-Evans Cinnamon rats were significantly higher than those of controls at 4, 10 and 20 weeks of age. In the cingulate cortex and caudate-putamen, 5-hydroxytryptamine immunoreactive fiber densities became gradually higher with age. The number of aberrant 5-hydroxytryptamine immunoreactive fibers in the cingulate cortex, caudate-putamen, hypothalamus and hippocampus in LEC rats was significantly higher than that of controls. The number of another type of aberrant 5-hydroxytryptamine immunoreactive fibers, which were detected only at 20 weeks of age in the caudate-putamen in LEC rats was significantly higher than that of controls. These results suggest that age-dependent changes in copper concentrations of Long-Evans Cinnamon rats were related to changes in monoaminergic neuron systems.