DRD2 and neurodegenerative disease: Thirdly, although the mechanism by which MZA inhibited PMA-stimulated O2-generation in vitro remains undetermined, MZA was more potent than propentofylline, a selective phosphodiesterase inhibitor, cabergoline, a potent and selective agonist of D2-dopamine receptors and nicergoline, an ergoline derivative used for cerebrovascular diseases, compounds which have been proposed to confer protective effects against neurodegenerative diseases by affecting O2- release by activated rat microglia.