Regulation of mu binding sites after chronic administration of antibodies directed against specific anti-opiate peptides

There is some indication that anti-opiate peptides (AOP) modulate opioid re ceptor systems by altering mu-receptor density. To further characterize thi s phenomenon, we investigated the effects of continuous infusion of anti-AO P IgG on mu binding sites in the brains of rats. Specifically, male Sprague -Dawley rats received intracerebroventricular (ICV) infusions for 13 days o f either control (rabbit) IgG or test IgGs: anti-dynorphin A IgG, anti-dyno rphin A(1-8) IgG, anti-alpha-MSH IgG, or the monoclonal anti-NPFF IgG. Admi nistration of anti-NPFF IgG or the anti-dynorphin(1-8) IgG significantly in creased mu labeling by 40-70% in several brain regions at the caudate level . Contrary to these findings, anti-alpha-MSH IgG decreased (19-32%) [I-125] -DAMGO labeling in several thalamic nuclei. The results suggest that the de nsity of mu-opioid receptors is regulated in part by anti-opiate peptides i n the extracellular fluid of the brain. (C) 1998 Elsevier Science Inc.