Research reportSwitching ability of over trained movements in a Parkinson's disease rat model

- The impaired capability of lesioned rats to internalize rules was abolished by the external cues.
- After practice, the switch test revealed a cue-based interference on self-paced responses.
- The unilateral DA striatal lesion enhanced the cue-dependent bias in motor behavior.
- Lateral ventricular enlargement suggest MRI scans as a possible marker of disease progression.

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.