Elsevier

Brain Research

Volume 646, Issue 2, 23 May 1994, Pages 235-241
Brain Research

Interactions between laudanosine, GABA, and opioid subtype receptors: implication for laudanosine seizure activity

https://doi.org/10.1016/0006-8993(94)90084-1Get rights and content

Abstract

We examined the interactions ofd,l-laudanosine, a potentially epileptogenic metabolite of the neuromuscular relaxant atracurium besylate, with γ-aminobutyric acid (GABA) and opioid binding sites, all of which have been implicated in seizure activity. Laudanosine was almost ineffective at [3H]muscimol binding to high-affinity GABA receptors (IC50 = 100 μM). However, laudanosine displayed an inhibitory effect at the low-affinity GABA receptors labeled by [3H]bicuculline methochloride, with an IC50 value of 10 μM. At the opioid receptor subtype, laudanosine lowered radiolabeled opioid binding at the μ1, μ2, δ, κ1, and κ3 receptors with Ki values of 2.7, 13, 5.5, 21, and 24 μM, respectively, concentrations seen clinically in blood and approaching those measured in cerebrospinal fluid. Saturation studies of μ1, μ2, δ, and κ3 sites in the presence of laudanosine revealed competitive interactions, with increases in the apparent Kd values but without significant changes in the maximal numbers of binding sites. In addition, we investigated whether the in vitro laudanosine-opioid receptor interaction would also be expressed by analgesic physiologic effects. We found that laudanosine elicited a dose-dependent analgesia in mouse tail-flick assay that was attenuated by coadministration of β-funaltrexamine (μ1- and μ2-sselective antagonist) and of naloxonazine (μ1 antagonist), but not by nor-binaltophimine (κ1-selective antagonist) or naltrindole (δ-selective antagonist), indicating a μ1 mechanism for analgesia-mediated properly of laudanosine. There is evidence suggesting μ2 activity as well, but this is due to the ability of laudanosine to elicit analgesia when given intrathecally. We also observed cross-tolerance between laudanosine and morphine, as well as a partial effect of laudanosine on gastrointestinal transit. These results suggest an interaction between laudanosine and the low-affinity GABA receptor, as well as opioid μ1 and μ2 receptors.

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  • Cited by (0)

    1

    Present address: Department of Anesthesiology, Rambam Medical Center, Haifa, Israel.

    2

    Present address: Department of Anatomy and Anthropology, Sackeler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

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