Related Experiment Video
Updated: Jul 19, 2026

Operant Protocols for Assessing the Cost-benefit Analysis During Reinforced Decision Making by Rodents
Published on: September 10, 2018
Morphine and methadone dependence in the rat: withdrawal and brain met-enkephalin levels
T L Pierce1, G K Tiong, J E Olley
1Department of Pharmacology, Monash University, Clayton, Victoria, Australia.
Abstract:
Opioids were administered to female Long Evans rats in their drinking water. Maintenance doses of 0.8 and 0.4 mg/ml for morphine and methadone, respectively, were achieved using an ascending dosage schedule. Rats were decapitated 0, 20, or 60 min after naloxone (10 mg/kg, IP) or saline. Brain met-enkephalin-like immunoreactivity (ME-LI) was determined by radioimmunoassay (RIA). In morphine-drinking animals, ME-LI in all regions of the brain was unaltered following saline administration; however, 20 min after naloxone injection ME-LI had increased in the striatum, hypothalamus, midbrain, and pituitary. By 60 min, ME-LI was no longer elevated. In both methadone- and water-drinking rats, ME-LI did not deviate from normal. These elevated levels of ME-LI, 20 min after naloxone-precipitated withdrawal in morphine-dependent rats, coincided with the peak of behavioural signs in the precipitated withdrawal syndrome. The milder behavioural disturbances observed in the withdrawal of methadone-drinking rats were consistent with the unaltered ME-LI in these animals.
More Related Videos
04:11A Conditioned Place Preference Protocol for Measuring Incubation of Craving in Rats
Published on: November 6, 2018
09:54Combining Laser Capture Microdissection and Microfluidic qPCR to Analyze Transcriptional Profiles of Single Cells: A Systems Biology Approach to Opioid Dependence
Published on: March 8, 2020
Related Concept Videos
Drug Dependence
Drug Abuse and Addiction: Pharmacological Phenomena
Opioid Receptors: Overview
Analgesia and Pain Management
Opioid Analgesics: Morphine and Other Natural Cogeners
Opioid Analgesics: Synthetic and Semisynthetic Opioids