Parkinson's disease (PD) is characterized by rigidity, tremor, bradykinesia, and postural instability. The proximate cause of these symptoms is striatal dopamine (DA) insufficiency. The motor symptoms of PD can be alleviated by DA replacement therapy. However, late in the course of the disease patients appear to become less responsive to DA replacement. This therapeutic change suggests the possibility of structural and/or functional defects in striatal medium spiny neurons, which receive convergent DA and cortical (glutamate) inputs.

To understand the neuronal reorganization occurring in Parkinson's disease, we used ultrastructural methods to examine the striatum of rats with striatal dopaminergic deafferentation induced by unilateral intranigral injection of 6-hydroxydopamine. After a six month survival, rats were deeply anesthetized with pentobarbital and perfused with 4% paraformaldehyde-1 % glutaraldehdyde solution in 0.1M Sorenson's phosphate buffer (pH 7.4). The brains were removed, post-fixed for 12 hours, embedded in paraffin, and coronal sections cut through the striatum and midbrain.