ANTAGONIST-PRECIPITATED OPIOID WITHDRAWAL IN RATS - EVIDENCE FOR DISSOCIATIONS BETWEEN PHYSICAL AND MOTIVATIONAL SIGNS

In rats made opioid dependant by the implantation of a single morphine 75 mg base pellet, an attempt was made to determine whether any corre lation existed between physical and motivational withdrawal signs by a djusting the dose of naloxone used to precipitate withdrawal. The mode ls used to study motivational signs were taste (one- and two-bottle) c onditioning and operant responding for food under an FR15 schedule of reinforcement. Naloxone at doses of 0.01 mg/kg and above produced both a conditioned taste aversion (two-bottle test only) and reduced food responding in morphine pellet, but not placebo pellet, implanted anima ls. No physical withdrawal signs, e.g., wet dog shakes, diarrhoea, wer e noted until naloxone doses of 0.05 mg/kg and above were used. It is concluded that the difference in naloxone doses required to elicit phy sical and motivational withdrawal components provides further support for their dissociation.