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Morphine influences on classical aversive conditioned heart rate in rats
1Department of Anatomy, University of Colorado Health Sciences Center, Denver.
Behavioral Neuroscience
|April 1, 1988
Summary
Morphine impaired the learning of a conditioned heart rate response in rats, possibly by reducing the shock
Area of Science:
- Behavioral neuroscience
- Pharmacology
- Psychopharmacology
Background:
- Classical conditioning involves associative learning between stimuli.
- Heart rate conditioned responses (CRs) are used to study learning and drug effects.
- Opioids like morphine can influence learning and physiological responses.
Purpose of the Study:
- To investigate the effects of morphine and naloxone on aversive heart rate conditioning.
- To determine if morphine interferes with the acquisition or performance of a conditioned response.
- To examine the role of opioid receptors in mediating these effects.
Main Methods:
- Rats received preconditioning injections of morphine or naloxone.
- A tone conditioned stimulus (CS) was paired with an electric shock unconditioned stimulus (US).
- Heart rate responses were measured during conditioning and testing phases.
Main Results:
- Morphine attenuated heart rate responses to the CS before conditioning.
- High-dose morphine (10 mg/kg) markedly reduced both the bradycardia CR and tachycardia UR.
- Naloxone did not affect heart rate conditioning but reversed morphine-induced analgesia.
Conclusions:
- Morphine, particularly at higher doses, interferes with the learning of aversive heart rate conditioning.
- This interference may be due to reduced aversion to the shock US.
- Morphine's cardiovascular effects impacted performance of the unconditioned response, not the conditioned response itself.