title: Opposite effects of typical and atypical anti-psychotic drugs on sensitized dopamine receptors: sub-chronic low dose Olanzapine exposure reverses sensitization but a similar regimen of low dose haloperidol potentiates sensitization effects.
abstract: BACKGROUND
  Both typical and atypical antipsychotic drugs are D2 receptor antagonists but yet appear to have markedly different effects upon the induction of dopamine sensitization.
  
  
  OBJECTIVE
  This study aims to compare the effects of subchronic regimens of low-dose olanzapine and haloperidol administered to rats previously sensitized to apomorphine.
  
  
  METHODS
  Initially, rats received apomorphine (2.0 mg/kg) or vehicle treatments for five consecutive days followed by a conditioning test and an apomorphine challenge test. Next, there was an antipsychotic exposure phase in which three vehicle groups and three apomorphine groups received 10 daily injections of either vehicle, haloperidol (0.03 mg/kg) or olanzapine (0.01 mg/kg). In the final phase, all groups were given a second conditioning test and apomorphine challenge test.
  
  
  RESULTS
  Apomorphine induced sensitization and conditioning effects. Following haloperidol exposure, apomorphine conditioned and sensitization effects were potentiated but, in contrast, olanzapine exposure eliminated apomorphine sensitization effects. In addition, the sensitization induced by apomorphine transformed the low-dose haloperidol treatment into a potent locomotor stimulant treatment. In the vehicle groups, haloperidol and olanzapine exposure effects were equivalent and not different from vehicle treatment.
  
  
  CONCLUSIONS
  The profound differences observed between typical and atypical antipsychotic exposure in animals with an upregulated dopamine system are consistent with clinical evidence for lower risk of psychomotor disturbances with chronic treatment with atypical antipsychotic. Importantly, the finding that a very low dose of olanzapine reversed sensitization effects suggests that low-dose olanzapine may have clinical utility in a variety of disorders linked to sensitization of the dopamine system.
authors.affiliation: Behavioral Pharmacology Group, Laboratory of Animal Morphology and Pathology Animal, State University of North Fluminense Darcy Ribeiro, Avenida Alberto Lamego, 2000, Campos dos Goytacazes, 28013-602, RJ, Brazil.
authors.forename: Flávia Regina Cruz
authors.initials: FR
authors.lastname: Dias
authors.forename: João Marcos
authors.initials: JM
authors.lastname: de Mello Bastos
authors.forename: Maria
authors.initials: M
authors.lastname: de Fátima Dos Santos Sampaio
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Carey
authors.forename: Marinete Pinheiro
authors.initials: MP
authors.lastname: Carrera
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D001058:Apomorphine / Q000494:pharmacology; D001569:Benzodiazepines / Q000008:administration & dosage / Q000494:pharmacology*; D003213:Conditioning, Psychological / Q000187:drug effects; D004298:Dopamine / Q000378:metabolism; D018492:Dopamine Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D006220:Haloperidol / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D000077152:Olanzapine; D051381:Rats; D017208:Rats, Wistar
chemical_list: D014150:Antipsychotic Agents; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D001569:Benzodiazepines; D006220:Haloperidol; D001058:Apomorphine; D000077152:Olanzapine; D004298:Dopamine