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Updated: Jul 6, 2026
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Absence and rescue of morphine withdrawal in GIRK/Kir3 knock-out mice
Hans G Cruz1, Frédérique Berton, Monica Sollini
1Department of Basic Neurosciences , University of Geneva, CH-1211 Geneva, Switzerland.
Abstract:
Although morphine induces both analgesia and dependence through mu-opioid receptors (MORs), the respective contributions of the intracellular effectors engaged by MORs remain unknown. To examine the contribution of G-protein-gated inwardly rectifying K(+) (GIRK, Kir3) channels to morphine dependence and analgesia, we quantified naloxone-precipitated withdrawal behavior and morphine analgesia using GIRK knock-out ((-/-)) mice. The morphine withdrawal syndrome was strongly attenuated, whereas morphine analgesia was mostly preserved in mice lacking both GIRK2 and GIRK3 (GIRK2/3(-/-) mice). In acute slices containing the locus ceruleus (LC) from GIRK2/3(-/-) mice, the increase in spontaneous firing typically associated with morphine withdrawal was absent. Moreover, although morphine elicited normal presynaptic inhibition in the LC, postsynaptic GIRK currents were completely abolished in GIRK2/3(-/-) mice. Altogether, these data suggested that morphine-evoked postsynaptic inhibition of the LC was required for the induction of dependence. Consistent with this hypothesis, morphine withdrawal behavior was rescued in GIRK2/3(-/-) mice by ablation of adrenergic fibers using the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine. Our data suggest that inhibition of adrenergic tone is required for the induction of dependence, and that channels containing GIRK2 and GIRK3 serve as an inhibitory gate.
Insights
G-protein-gated inwardly rectifying potassium (GIRK) channels are crucial for morphine dependence but not analgesia. Inhibiting these channels in the locus ceruleus prevents withdrawal symptoms, suggesting a new therapeutic target.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- Morphine, a potent analgesic, induces both pain relief and dependence via mu-opioid receptors (MORs).
- The specific intracellular pathways mediating these distinct MOR effects are not fully understood.
- G-protein-gated inwardly rectifying K(+) (GIRK, Kir3) channels are potential MOR effectors.
Purpose of the Study:
- To investigate the role of GIRK channels in morphine analgesia and dependence.
- To determine if GIRK channels are essential for the development of morphine withdrawal syndrome.
Main Methods:
- Utilized GIRK2 and GIRK3 double knockout (GIRK2/3(-/-)) mice to assess naloxone-precipitated withdrawal behavior and morphine analgesia.
- Performed electrophysiological recordings in acute brain slices of the locus ceruleus (LC).
- Investigated the effect of adrenergic fiber ablation on withdrawal behavior in knockout mice.
Main Results:
- Morphine withdrawal syndrome was significantly attenuated in GIRK2/3(-/-) mice.
- Morphine analgesia was largely preserved in the absence of GIRK2 and GIRK3 channels.
- Postsynaptic GIRK currents in the LC were abolished in knockout mice, and morphine-induced inhibition of LC firing was prevented.
- Ablation of adrenergic fibers rescued morphine withdrawal behavior in GIRK2/3(-/-) mice.
Conclusions:
- GIRK2 and GIRK3 channels are critical for the induction of morphine dependence.
- Inhibition of postsynaptic GIRK currents in the locus ceruleus is a key mechanism for morphine dependence.
- Targeting GIRK channels may offer a strategy to mitigate opioid dependence without compromising analgesia.
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