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Morphine and self-stimulation: evidence for action on a common neural substrate
Pharmacology, Biochemistry, and Behavior
|February 1, 1978
Summary
Morphine enhances self-stimulation behavior at low intensities when presented in ascending order. However, this effect is blocked in descending sequences, suggesting neural adaptation can impede morphine
Area of Science:
- Neuroscience
- Pharmacology
- Behavioral Science
Background:
- Self-stimulation is a key technique for studying drug reward.
- Morphine's impact on reward pathways is not fully understood.
- Understanding drug effects on neural excitability is crucial.
Purpose of the Study:
- To investigate morphine's effect on the rate-intensity functions of self-stimulation.
- To explore how sequential presentation of stimulation intensity influences morphine's effects.
- To examine the role of neural adaptation in modulating morphine's rewarding properties.
Main Methods:
- Rats were trained to self-stimulate via lever pressing.
- Morphine was administered to the subjects.
- Bar pressing rates were measured across different stimulation intensity sequences (ascending and descending).
Main Results:
- Morphine significantly increased self-stimulation rates for low intensities in an ascending sequence.
- Morphine showed minimal effect on self-stimulation rates in a descending sequence.
- This suggests adaptation in the self-stimulation system can counteract morphine's effects.
Conclusions:
- Morphine's facilitatory effects on self-stimulation are dependent on the sequence of stimulation intensity.
- Neural adaptation within the self-stimulation system can block morphine's rewarding effects.
- Findings support the hypothesis that morphine modulates the excitability of neural systems mediating reward.