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Updated: Jul 29, 2026
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Published on: July 29, 2014
Two distinct unit activity responses to morphine in the rostral ventromedial medulla of awake rats
S McGaraughty1, S Reinis, J Tsoukatos
1Department of Psychology, University of Waterloo, Ont., Canada.
Abstract:
Past research investigating the rostral ventromedial medulla (RVM) in anesthetized animals has found two distinct classes of cells, ON and OFF, noted for their distinct responses to noxious stimuli and to morphine. However, only one class (ON) has been found in the awake animal paradigm. We report in this paper that we have found both the ON and OFF cell responses to morphine in the awake rat.
Insights
Researchers discovered both ON and OFF cell responses to morphine in awake rats, challenging previous findings in anesthetized models. This study advances our understanding of pain modulation and opioid effects in the rostral ventromedial medulla (RVM).
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- The rostral ventromedial medulla (RVM) is crucial for pain modulation.
- Previous studies in anesthetized animals identified ON and OFF cells in the RVM with distinct morphine responses.
- Only ON cells were previously observed in awake animal models.
Purpose of the Study:
- To investigate RVM cell activity in awake rats.
- To determine if both ON and OFF cells respond to morphine in awake rats.
Main Methods:
- Electrophysiological recordings in awake, behaving rats.
- Administration of morphine.
- Analysis of neuronal responses in the RVM.
Main Results:
- Both ON and OFF cells in the RVM of awake rats exhibited distinct responses to morphine.
- This finding contrasts with previous observations in awake animal paradigms.
Conclusions:
- The RVM contains both ON and OFF cells responsive to morphine in awake rats.
- These findings reconcile previous discrepancies between anesthetized and awake models.
- This research provides a more complete picture of RVM circuitry in pain and opioid action.
