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Opiate antagonists and self-stimulation: extinction-like response patterns suggest selective reward deficit
K A Trujillo1, J D Belluzzi, L Stein
1Department of Pharmacology, College of Medicine, University of California, Irvine 92717.
Brain Research
|July 17, 1989
Summary
Opiate antagonists, like naloxone and naltrexone, suppress brain stimulation reward by reducing its reinforcement value, not by impairing response ability. This occurs in an extinction-like pattern, suggesting a role for endogenous opioids.
Area of Science:
- Neuroscience
- Behavioral Pharmacology
Background:
- Intracranial self-stimulation (ICSS) is a key model for studying reward pathways in the brain.
- Opiate antagonists are used to investigate the role of endogenous opioid systems in reward processes.
Purpose of the Study:
- To investigate how opiate antagonists affect intracranial self-stimulation (ICSS) behavior.
- To determine if these drugs diminish the reinforcement value of stimulation or impair motor response capabilities.
Main Methods:
- Male rats were trained to lever-press forICSS of the nucleus accumbens on a continuous reinforcement schedule.
- Rats received injections of naloxone or naltrexone at different doses (2.0 and 20 mg/kg).
- Response decrement patterns and session duration effects were analyzed.
Main Results:
- Naloxone and naltrexone suppressed self-stimulation after a delay, exhibiting an extinction-like response decrement pattern.
- This pattern mimicked the effects of reduced stimulation intensity.
- Suppression was observed even as drug concentrations declined, and initial responding remained normal.
Conclusions:
- Opiate antagonists appear to reduce the reinforcement value of brain stimulation, rather than motor function.
- The findings support a role for endogenous opioid peptides in mediating brain stimulation reward.
- The delayed, extinction-like effect explains the need for extended sessions to observe antagonist-induced suppression.