Short-term, D2 receptor blockade induces synaptic degeneration, reduces levels of tyrosine hydroxylase and brain-derived neurotrophic factor, and enhances D2-mediated firing in the ventral pallidum.
Repeated treatments with neuroleptics are associated with biochemical and morphological alterations in forebrain neurons as well as an upregulation of D2-mediated changes in neuronal function. The present study evaluated the histological and physiological effects of three once-daily treatments with two chemically divergent neuroleptics, haloperidol (1 mg/kg i.p./day) and eticlopride (3 mg/kg i.p./day), measured in rats 24 h after the last injection. It was determined that this short-term antagonism of D2-like receptors induced fiber and terminal degeneration and significantly decreased tyrosine hydroxylase (TH) and brain-derived neurotrophic factor (BDNF) immunoreactivity in the ventral pallidum (VP), as determined by optical density measurements. While other forebrain regions demonstrated changes in TH and BDNF, the neurodegeneration profile was unique to the VP. This was accompanied by an enhancement in the efficacy of the D2 agonist quinpirole to increase spiking rate of VP neurons recorded in chloral hydrate-anesthetized rats. These data indicate that short-term treatments with D2 antagonists are sufficient to induce changes in the biochemical and morphological profiles uniquely within the VP. Moreover, the functional ramifications of these changes appear to include profound alterations in the way dopamine regulates neuronal activity in this region.
Meredith
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GE
Department of Cellular and Molecular Pharmacology, The Chicago Medical School, Finch University of Health Sciences, 3333 Green Bay Rd., North Chicago, IL 60064-3095, USA. Gloria.Meredith@finchcms.edu
Switzer
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RC
Napier
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TC
D000818:Animals; D014150:Antipsychotic Agents / Q000633:toxicity*; D019208:Brain-Derived Neurotrophic Factor / Q000187:drug effects / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004298:Dopamine / Q000096:biosynthesis; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000633:toxicity; D065127:Dopamine D2 Receptor Antagonists; D004334:Drug Administration Schedule; D004409:Dyskinesia, Drug-Induced / Q000378:metabolism / Q000473:pathology; D006220:Haloperidol / Q000633:toxicity; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D009410:Nerve Degeneration / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000473:pathology / Q000648:ultrastructure; D016548:Prosencephalon / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D019257:Quinpirole / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000378:metabolism; D012457:Salicylamides / Q000633:toxicity; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D014150:Antipsychotic Agents; D019208:Brain-Derived Neurotrophic Factor; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D017448:Receptors, Dopamine D2; D012457:Salicylamides; D019257:Quinpirole; D014446:Tyrosine 3-Monooxygenase; D006220:Haloperidol; C045989:eticlopride; D004298:Dopamine