title: Prevention and reversal of dopamine receptor supersensitivity by cyclo(leucyl-glycyl) (CLG): biphasic dose-response curves.
abstract: Chronic administration (21 days) of haloperidol (HAL) (IP, 1.0 mg/kg/day) induced a behavioral supersensitivity (stereotypic sniffing) to dopamine (DA) agonists (apomorphine) and upregulation (increased Bmax for sulpiride-inhibitable [3H]spiroperidol binding) of striatal and limbic D2 DA receptors (DAr). Coadministration of cyclo(leucyl-glycyl) (CLG; 8mg/kg, SC; every third day, every other day, but not every day) with HAL attenuated the behavioral supersensitivity. D2-DAr binding assays showed 1) that CLG-induced changes in Bmax parallel these behavioral changes and 2) that the biphasic CLG dose-response curve may involve CLG failure at high cumulative doses to lower Bmax. CLG also reversed an already established D2 DAr supersensitivity/upregulation (i.e., when CLG was injected daily for four days after the withdrawal of HAL). CLG alone did not alter behavior or binding. CLG's ability to both prevent and reverse D2 DAr upregulation/supersensitivity in animal models suggests that CLG may be useful, within a therapeutic window, in clinical disorders that are thought to involve upregulated DAr (e.g., tardive dyskinesia, L-DOPA-induced dyskinesias, and schizophrenia).
authors.affiliation: Department of Medicine, Loyola University, Stritch School of Medicine, Maywood IL 60153.
authors.forename: G E
authors.initials: GE
authors.lastname: Drucker
authors.forename: R F
authors.initials: RF
authors.lastname: Ritzmann
authors.forename: L J
authors.initials: LJ
authors.lastname: Wichlinski
authors.forename: K
authors.initials: K
authors.lastname: Engh
authors.forename: J H
authors.initials: JH
authors.lastname: Gordon
authors.forename: J Z
authors.initials: JZ
authors.lastname: Fields
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006220:Haloperidol / Q000494:pharmacology; D008297:Male; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011954:Receptors, Dopamine / Q000187:drug effects*; D013239:Stereotyped Behavior / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D009479:Neuropeptides; D010456:Peptides, Cyclic; D011954:Receptors, Dopamine; C021166:cyclo(leucylglycine); D006220:Haloperidol