Modification of place preference conditioning in mice by systemically administered [Leu]enkephalin.
[Leu]enkephalin (300 micrograms/kg, i.p.) induced either a positive or negative conditioned place preference response in mice depending on whether the animals were trained against or towards their initial preference. Induction of a positive preference (300 micrograms/kg) was partially blocked by simultaneous addition of methylnaloxonium (10 mg/kg, i.p.), an opioid antagonist that does not readily cross the blood-brain barrier; methylnaloxonium alone (3 or 10 mg/kg) had no effect on the place preference response. The results indicate that [Leu]enkephalin treatment reverses the initial preference of the animal regardless of training, and that some aspect of the [Leu]enkephalin effect on place preference conditioning is mediated by peripheral opioid receptors. These findings challenge the notion that place preference conditioning is a simple measure of opioid reward.
D000818:Animals; D002755:Choice Behavior / Q000187:drug effects*; D003213:Conditioning, Psychological / Q000187:drug effects*; D004743:Enkephalin, Leucine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D007274:Injections, Intraperitoneal; D008297:Male; D051379:Mice; D009270:Naloxone / Q000031:analogs & derivatives / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds
D000644:Quaternary Ammonium Compounds; D009270:Naloxone; D004743:Enkephalin, Leucine; C041269:N-methylnaloxone