title: The role of beta-endorphin in the acute motor stimulatory and rewarding actions of cocaine in mice.
abstract: BACKGROUND
  Opioid receptor antagonists have been shown to attenuate the rewarding and addictive effects of cocaine. Furthermore, cocaine has been shown to cause the release of beta-endorphin, an endogenous opioid peptide.
  
  
  OBJECTIVE
  We assessed whether this neuropeptide would play a functional role in cocaine-induced motor stimulation and conditioned place preference (CPP).
  
  
  METHODS
  Mice lacking beta-endorphin and their wild-type littermates were habituated to motor activity chambers for 1 h, then injected with cocaine (0, 15, 30, or 60 mg/kg, intraperitoneally) or morphine (0, 5, or 10 mg/kg, subcutaneously), and motor activity was recorded for 1 h. In the CPP paradigm, mice were tested for baseline place preference on day 1. On days 2 and 3, mice received an alternate-day saline/cocaine (15, 30, or 60 mg/kg) or saline/morphine (10 mg/kg) conditioning session and then tested for postconditioning place preference on day 4.
  
  
  RESULTS
  Cocaine-induced motor stimulation and CPP were both reduced in mice lacking beta-endorphin. On the other hand, motor stimulation and CPP induced by morphine were not altered in mutant mice.
  
  
  CONCLUSIONS
  The present results demonstrate that the endogenous opioid peptide beta-endorphin plays a modulatory role in the motor stimulatory and rewarding actions of acute cocaine.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, CA 91766, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Marquez
authors.forename: Ramkumarie
authors.initials: R
authors.lastname: Baliram
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Dabaja
authors.forename: Nagaraju
authors.initials: N
authors.lastname: Gajawada
authors.forename: Kabirullah
authors.initials: K
authors.lastname: Lutfy
mesh_terms: D000818:Animals; D001245:Association Learning / Q000187:drug effects; D003042:Cocaine / Q000494:pharmacology*; D019970:Cocaine-Related Disorders / Q000503:physiopathology*; D003216:Conditioning, Operant / Q000187:drug effects* / Q000502:physiology; D003433:Crosses, Genetic; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006580:Genetic Carrier Screening; D005838:Genotype; D007274:Injections, Intraperitoneal; D007279:Injections, Subcutaneous; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009020:Morphine / Q000494:pharmacology; D009042:Motivation; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D011333:Pro-Opiomelanocortin / Q000235:genetics; D012201:Reward; D012931:Social Environment; D001615:beta-Endorphin / Q000235:genetics / Q000502:physiology*
chemical_list: D018765:Dopamine Uptake Inhibitors; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D009020:Morphine; D003042:Cocaine