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Naloxone in ultralow concentration restores endomorphin-1-evoked Ca(2+) signaling in lipopolysaccharide pretreated astrocytes.

Journal article
Authors Linda Block
Johan Forshammar
Anna Westerlund
Ulrika Björklund
Christopher Lundborg
Björn Biber
Elisabeth Hansson
Published in Neuroscience
Volume 205
Pages 1-9
ISSN 1873-7544
Publication year 2012
Published at Institute of Neuroscience and Physiology, Department of Clinical Neuroscience and Rehabilitation
Institute of Clinical Sciences, Department of Anesthesiology and Intensive care
Institute of Biomedicine, Department of Microbiology and Immunology
Pages 1-9
Language en
Subject categories Neurology, Anesthesiology and Intensive Care


Long-term pain is a disabling condition that affects thousands of people. Pain may be sustained for a long time even after the physiological trigger has resolved. Possible mechanisms for this phenomenon include low-grade inflammation in the CNS. Astrocytes respond to inflammatory stimuli and may play an important role as modulators of the inflammatory response in the nervous system. This study aimed first to assess how astrocytes in a primary culture behave when exposed to the endogenous μ-opioid receptor agonist endomorphin-1 (EM-1), in a concentration-dependent manner, concerning intracellular Ca(2+) responses. EM-1 stimulated the μ-opioid receptor from 10(-15) M up to 10(-4) M with increasing intensity, usually reflected as one peak at low concentrations and two peaks at higher concentrations. Naloxone, pertussis toxin (PTX), or the μ-opioid receptor antagonists CTOP did not totally block the EM-1-evoked Ca(2+) responses. However, a combination of ultralow concentration naloxone (10(-12) M) and PTX (100 ng/ml) totally blocked the EM-1-evoked Ca(2+) responses. This suggests that ultralow (picomolar) concentrations of naloxone should block the μ-opioid receptor coupled G(s) protein, and that PTX should block the μ-opioid receptor coupled G(i/o) protein. The second aim was to investigate exposure of astrocytes with the inflammatory agent lipopolysaccharide (LPS). After 4 h of LPS incubation, the EM-1-evoked Ca(2+) transients were attenuated, and after 24 h of LPS incubation, the EM-1-evoked Ca(2+) transients were oscillated. To restore the EM-1-evoked Ca(2+) transients, naloxone was assessed as a proposed anti-inflammatory substance. In ultralow picomolar concentration, naloxone demonstrated the ability to restore the Ca(2+) transients.

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