Positive allosteric modulation of GABA-A receptors reduces capsaicin-induced primary and secondary hypersensitivity in rats

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Rikke Rie Hansen, Helle K Erichsen, David T Brown, Naheed R Mirza, Gordon Munro

GABA-A receptor positive allosteric modulators (PAMs) mediate robust analgesia in animal models of pathological pain, in part via enhancing injury-induced loss of GABA-A-α2 and -α3 receptor function within the spinal cord. As yet, a lack of clinically suitable tool compounds has prevented this concept being tested in humans. Prior to assessing the efficacy of GABA-A receptor PAMs in a human volunteer pain model we have compared compounds capable of variously modulating GABA-A receptor function in comparable rat models of capsaicin-induced acute nocifensive flinching behaviour and secondary mechanical hypersensitivity. The subtype-selective PAM NS11394 (0.3-10 mg/kg), and the non-selective PAM diazepam (1-5 mg/kg) variously reduced capsaicin-induced secondary mechanical hypersensitivity (180 min post-injection). However, the low efficacy subtype-selective PAM TPA023 (3-30 mg/kg) was completely ineffective. This was surprising as both NS11394 and TPA023 robustly attenuated late phase (6-30 min post-injection) capsaicin-induced flinching, a pain-like behaviour that is putatively driven by peripheral and central sensitizing mechanisms. Diazepam also attenuated capsaicin-induced nocifensive behaviours, albeit at doses previously shown to impair locomotor function. Our data indicate that GABA-A receptor PAMs with optimal selectivity and efficacy profiles reduce centrally-mediated mechanical hypersensitivity in capsaicin-injected rats, an observation that we expect can translate directly to human volunteer studies.
Original languageEnglish
JournalNeuropharmacology
Volume63
Issue number8
Pages (from-to)1360-7
Number of pages8
ISSN0028-3908
DOIs
Publication statusPublished - Dec 2012

    Research areas

  • Amines, Analgesics, Opioid, Animals, Behavior, Animal, Benzimidazoles, Capsaicin, Cyclohexanecarboxylic Acids, Diazepam, Endpoint Determination, GABA Antagonists, GABA Modulators, Hyperalgesia, Male, Pain, Physical Stimulation, Pyridazines, Rats, Rats, Sprague-Dawley, Receptors, GABA-A, Triazoles, gamma-Aminobutyric Acid

ID: 106020041