Bonin RP, Labrakakis C, Eng DG, Whissell PD, De Koninck Y, Orser BA. (2011) Pain. 152(6):1317-26.
The development of new strategies for the treatment of acute pain requires the identification of novel nonopioid receptor targets. This study explored whether δ-subunit-containing GABAARs (δGABAARs) in neurons of the spinal cord dorsal horn generate a tonic inhibitory conductance in vitro and whether δGABAAR activity regulates acute nociception. Whole-cell recordings revealed that δGABAARs generate a tonic inhibitory conductance in cultured spinal neurons and lamina II neurons in spinal cord slices. Increasing δGABAAR function by applying the δGABAAR-preferring agonist 4,5,6,7-tetrahydroisoxazolo [5,4-c]pyridine-3-ol (THIP) increased the tonic current and inhibited neuronal excitability in spinal neurons from wild-type (WT) but not δ subunit null-mutant (Gabrd-/-) mice. In behavioral studies, baseline δGABAAR activity did not regulate acute nociception; however, THIP administered intraperitoneally or intrathecally attenuated acute nociception in WT but not Gabrd-/- mice. In the formalin nociception assay, the phase 1 response was similar for WT and Gabrd-/- mice. In contrast, the phase 2 response, which models central sensitization, was greater in Gabrd-/- mice than WT. THIP administered intraperitoneally or intrathecally inhibited phase 1 responses of WT but not Gabrd-/- mice and had no effect on phase 2 responses of WT mice. Surprisingly, THIP reduced the enhanced phase 2 response in Gabrd-/- mice. Together, these results suggest that δGABAARs in spinal neurons play a major physiological and pharmacological role in the regulation of acute nociception and central sensitization. Spinal δ-subunit-containing GABAA receptors were identified with electrophysiological methods and behavioral models as novel targets for the treatment of acute pain.
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