Direct intranigral administration of an ubiquitin proteasome system inhibitor in rat: Behavior, positron emission tomography, immunohistochemistry

- 0.5, 1, 2, 10 or 20 μg of lactacystin was injected in right substantia nigra in rat.
- High but not low doses produced a significant contralateral motor deficit.
- High but not low doses severely diminished striatal dopamine storage.
- Lactacystin produced dose dependent lesions of nigral dopamine neurons.
- Lesion size correlated with the behavioral deficit and striatal dopamine storage.

Several independent lines of research suggest that disruption of the ubiquitin proteasome system (UPS) may play a role in the pathophysiology of Parkinson's disease. Direct intracerebral injection of UPS inhibitors (e.g. lactacystin) in animals has consistently produced important features of the disease. In this study, a range of lactacystin doses (0.5, 1, 2, 10 and 20 μg) were injected into the right substantia nigra in rats to determine the ideal dose required to produce a robust and specific lesion of the dopamine nigro-striatal system and motor deficits. Motor behavior, assessed with the tapered ledged beam task, was severely affected in animals that received high doses (10 and 20 μg) but only mild, impairments were observed in animals that received low doses (0.5, 1, and 2 μg). Positron emission tomography was performed with a dedicated small animal scanner on the rats following the injection of the radio-labeled tracer (±)[11C]dihydrotetrabenazine (DTBZ) which labels vesicular monoamine transporter type 2. Severe loss of [11C]DTBZ binding in the ipsilateral striatum was observed in the higher dose groups and mild loss was observed in the low dose groups. Stereological cell counting of tyrosine hydroxylase immunoreactive cells in the substantia nigra and the ventral tegmental area indicated a dose dependent loss of dopaminergic neurons. Significant correlations were found between the behavioral motor deficits, striatal [11C]DTBZ binding and cell counts of tyrosine hydroxylase immunoreactive cells. Taken together these results indicate that intranigral injection of lactacystin produces dose dependent effects on the dopamine nigro-striatal system and a dose of 10 μg will produce a consistent severe lesion.