Effects of beta-funaltrexamine and naloxonazine on single-trial morphine-conditioned place preference and locomotor activity.
The current study assessed the ability of the selective irreversible mu-opioid receptor antagonists beta-funaltrexamine (betaFNA) and naloxonazine (NALZ) to alter the locomotor and rewarding effects of a single intravenous injection of morphine using the conditioned place preference (CPP) model. In the first experiment, rats were conditioned with a single injection of morphine (10 mg/kg iv) paired with one compartment of a CPP apparatus and then were tested for CPP at either 1 or 7 days after conditioning. Rats showed hypoactivity following acute morphine on the conditioning trial and showed CPP when tested either 1 or 7 days later. In the next experiments, rats were pretreated with betaFNA (20 mg/kg sc, 20 h before conditioning), NALZ (15 or 30 mg/kg sc, 24 h before conditioning) or saline and then were conditioned with a single injection of morphine (10 mg/kg iv) or saline. Pretreatment with NALZ alone, but not betaFNA, significantly decreased locomotor activity; neither antagonist alone produced a significant shift in preference for either compartment of the CPP apparatus. Pretreatment with either betaFNA or NALZ blocked completely morphine-induced hypoactivity, but neither antagonist had a significant effect on morphine CPP. These results indicate that mu-opioid receptors are more critically involved in acute morphine-induced hypoactivity than in acute morphine reward.
Bardo
M T
MT
Department of Psychology, University of Kentucky, Lexington, KY 40506-0044, USA. mbardo@uky.edu
Gehrke
B J
BJ
Shortridge
B E
BE
Rauhut
A S
AS
D000818:Animals; D003213:Conditioning, Psychological / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D009270:Naloxone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000502:physiology
D017450:Receptors, Opioid, mu; D009270:Naloxone; D009271:Naltrexone; C024524:beta-funaltrexamine; D009020:Morphine; C034643:naloxonazine