Dopamine receptors in Parkinson's disease

In vitro and in vivo studies of striatal dopamine receptor changes have been reviewed in this article. A background of receptor pharmacology methods has been included to assist the reader in assessing the merits of the published studies. Overall the literature is not consistent in the relevant observations in parkinsonian brains. D2 receptors are increased in the striatum of parkinsonian patients who have not been exposed to L-dopa therapy. This has been confirmed by both in vivo and in vitro experiments. This supersensitivity is reversed with L-dopa treatment, but it is unclear as to the time sequence of this reversal and the clinical correlation that this has. D1 receptors have also been shown to be up-regulated in postmortem tissues from nontreated patients. The density seems to be normal compared with controls after treatment is initiated. A single PET study, however, did not find any differences in D1 binding between untreated parkinsonian patients and controls, and we must await further studies before conclusions may be reached. There are a number of new receptor subtypes that were recently identified with molecular biology techniques. Their relevance to Parkinson's disease is currently unknown, and we await reports of potential changes in these sites in this condition. In addition to these new subtypes, there has been tremendous progress in molecular techniques to understand the regulation of receptor protein formation in different brain regions in response to dopaminergic denervation. In the near future, we may encounter reports of changes in receptor regulation that may help us in understanding the changes that occur in Parkinson's disease.