Switching ability of over trained movements in a Parkinson’s disease rat model

"Patients with Parkinson’s disease show unbalanced capability to manage self-paced vs externally driven. movements, or automatic-associated movements with respect to the intended voluntary movements.. We studied the effect of a selective loss of dopaminergic terminals within the striatum and the. execution of a well-learned set-shifting task as revealed using tyrosine hydroxylase immunoreactivity. and magnetic resonance imaging in the rat. We found that, both in the externally cued condition,. and in the externally-internally driven switching task, the cue-dependent constraints interfered with. motor readiness in over training condition. The unilateral dopaminergic striatal depletion enhanced the. switch-induced performance differences in favour of the internally-externally cued transition. Dopamine. depleted rats, in fact, were impaired to produce an alternative motion when task switching required to. change from an over trained behaviour, towards an alternative self-paced response.. The comparative analysis of behavioural, tyrosine hydroxylase immunoreactivity and magnetic resonance. imaging data, revealed a shrinkage of the lesioned striatum, and an enlargement of the ipsilateral. ventricle that could provide useful markers for monitoring pathological changes occurring during early. stages of Parkinson’s disease in vivo."