As a result, 6-hydroxydopamine could lead to PD-like lesions, including tremor, stiffness, attenuated spontaneous activity, and bradykinesia in mice, and the expression of tyrosine hydroxylase in the striatum was decreased.
In aged rats, increased TH expression and DA in SN alone increases movement frequency, suggesting aging-related TH and DA loss in the SN contributes to aging-related bradykinesia or decreased physical activity.
Aging studies report little to moderate loss of striatal dopamine (DA) or tyrosine hydroxylase (TH) in nigrostriatal terminals, in contrast to ~70%-80% loss associated with bradykinesia onset in Parkinson's disease.