Altered nucleolar morphology in substantia nigra dopamine neurons following 6-hydroxydopamine lesion in rats

The nucleolus, the site of ribosomal ribonucleic acid (rRNA) transcription and assembly, is an important player in the cellular response to stress. Altered nucleolar function and morphology, including decreased nucleolar volume, has been observed in Parkinson's disease; thus the nucleolus represents a potential indicator of neurodegeneration in the disease. This study determined the effects of a partial unilateral intrastriatal 6-hydroxydopamine (6-OHDA) lesion, which models the dopaminergic loss found in Parkinson's disease, on the nucleoli of dopaminergic cells in the substantia nigra pars compacta (SNpc). Adult male Long-Evans rats underwent unilateral intrastriatal infusion of 6-OHDA (12.5μg). Lesions were verified by amphetamine-stimulated rotation 7 days later, and rats were euthanized 14 days after infusion. Coronal sections (50μm) were stained for tyrosine hydroxylase-silver nucleolar (TH-AgNOR) stain using MultiBrain Technology (NeuroScience Associates), which resulted in clearly defined nucleoli and neuronal outlines. Stereological methods were used to compare dopaminergic morphology between lesioned and intact hemispheres in each rat. In cells exhibiting a definable nucleolus, nucleolar volume was decreased by 16% on the ipsilateral side. The ipsilateral SNpc also exhibited an 18% decrease in SNpc planimetric volume, a 46% decrease in total TH-positive neuron number, and an 11% decrease in neuronal body volume (all P<0.05 by paired t-test). These findings suggest that the 6-OHDA lesion alters nucleolar morphology and that these changes are similar to those occurring in Parkinson's disease.