Abstract: Objective There have been robust of reports about quantity changes of dopamine receptors but there has no report describing the distribution changes of dopamine receptors at ultrastructural level in Parkinson disease until now. As whether those receptors are functional and the magnitude of their function is closely related to their distribution, it is necessary to study their distribution changes at ultrastructural revel under the disease situation. Methods Changes of striatal dopamine D1 receptors (D1R) and D2 dopamine receptors (D2R) in rats 4 weeks and 16 weeks after 6-hydroxydopamine(6-OHDA) unilateral lesion nigro-striatal dopaminergic pathway were studied by immunohistochemical and pre-imbedding immunogold electron microscopic methods. Results Four weeks after lesion, striatal D1R ipsilateral to lesion side decreased as observed under light microscope. The decrease happened at spines but not dendrites or cell bodies under electron microscope. 16 weeks after lesion, although the degree of striatal D1R ipsilateral to lesion side returned to the degree contralateral to the lesion side at light microscopic level, the amount of D1R decreased at spines and dendrite but increased significantly at cell bodies at electron microscopic level. Both 4 and 16 weeks after lesion, striatal D2R increased ipsilateral to lesion side under light microscope, the increased D2R particles were found at spines and dendrites but not cell bodies. Moreover, more gold particles of the two receptors were found at the extrasynaptic site both 4 weeks and 16 weeks after lesion. Conclusion These changes might play important roles in the onset and development of Parkinson’s disease and mechanism of side effect of levodopa therapy.

Key words: Parkinson disease, Dopamine receptor, Ultrastructure, Immunogold, Immunohistochemistry, Rat