The D-2 Dopamine Receptor

Although there are five distinct types of dopamine receptors, they fall into two broad categories: excitatory and inhibitory. As the labels suggest, the former activates a process while the latter prevents it or regulates it in some way. The D2 receptor falls into the latter category. [inhibitory] When the dopamine process is interrupted, the result can be any one of a wide range of neuro-psychiatric and movement disorders that can include not only tardive dyskinesia, but Tourette's syndrome, Parkinson's disease and others.

http://www.tardivedyskinesia.com/tre...e-agonists.php


Exp Neurol. 2010 Aug;224(2):395-402. Epub 2010 May 7.
Dyskinetic potential of dopamine agonists is associated with different striatonigral/striatopallidal zif-268 expression.

Carta AR, Frau L, Pinna A, Morelli M.
Department of Toxicology, University of Cagliari, Cagliari, Italy; Centre of Excellence for Studies on Neurobiology of Addiction, Cagliari, Italy. acarta@unica.it
Exp Neurol. 2010 Nov;226(1):11-4.
Abstract

In the dopamine-depleted striatum, an altered post-synaptic signalling of efferent neurons might underline the onset of variable dyskinetic responses to dopaminergic agonists. We have previously shown that a subchronic treatment with the D1 agonist SKF-38393 and the D2 agonist ropinirole induces a dyskinetic response of high and low intensities respectively, in 6-hydroxydopamine-lesioned rats. Here, zif-268 mRNA expression was evaluated in striatonigral and striatopallidal neurons to assess a neurochemical marker of these different dyskinetic responses upon drug administration. Acute and subchronic SKF-38393 (3mg/kg) increased zif-268 expression per neuron in the striatonigral pathway, albeit the number of neurons displaying high early-gene levels was reduced by the subchronic treatment. Zif-268 mRNA in striatopallidal neurons was not affected by SKF-38393 treatments. In contrast, ropinirole (5mg/kg) did not alter zif-268 mRNA in striatonigral neurons acutely, whereas ropinirole decreased zif-268 mRNA subchronically. Both acute and subchronic ropinirole decreased zif-268 levels in the striatopallidal pathway. The differential expression of zif-268 in striatonigral and striatopallidal neurons might provide a biochemical correlate of the dyskinetic outcome displayed by SKF-38393 and ropinirole treatments, suggesting that evaluation of neuronal responses upon drug administration provides a tool for the preclinical characterization of dyskinetic potential beyond behavioural tests.


http://www.ncbi.nlm.nih.gov/pubmed/20452347