Wafford K A, van Niel M B, Ma Q P, Horridge E, Herd M B, Peden D R, Belelli D, Lambert J J
Department of Molecular and Cellular Neuroscience, Merck Sharp & Dohme Research Laboratories, The Neuroscience Research Centre, Harlow, United Kingdom.
Neuropharmacology. 2009 Jan;56(1):182-9. doi: 10.1016/j.neuropharm.2008.08.004. Epub 2008 Aug 13.
Inhibition in the brain is dominated by the neurotransmitter gamma-aminobutyric acid (GABA); operating through GABA(A) receptors. This form of neural inhibition was presumed to be mediated by synaptic receptors, however recent evidence has highlighted a previously unappreciated role for extrasynaptic GABA(A) receptors in controlling neuronal activity. Synaptic and extrasynaptic GABA(A) receptors exhibit distinct pharmacological and biophysical properties that differentially influence brain physiology and behavior. Here we used a fluorescence-based assay and cell lines expressing recombinant GABA(A) receptors to identify a novel series of benzamide compounds that selectively enhance, or activate alpha4beta3delta GABA(A) receptors (cf. alpha4beta3gamma2 and alpha1beta3gamma2). Utilising electrophysiological methods, we illustrate that one of these compounds, 4-chloro-N-[6,8-dibromo-2-(2-thienyl)imidazo[1,2-a]pyridine-3-yl benzamide (DS1) potently (low nM) enhances GABA-evoked currents mediated by alpha4beta3delta receptors. At similar concentrations DS1 directly activates this receptor and is the most potent known agonist of alpha4beta3delta receptors. 4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridine-3-yl benzamide (DS2) selectively potentiated GABA responses mediated by alpha4beta3delta receptors, but was not an agonist. Recent studies have revealed a tonic form of inhibition in thalamus mediated by the alpha4beta2delta extrasynaptic GABA(A) receptors that may contribute to the regulation of thalamocortical rhythmic activity associated with sleep, wakefulness, vigilance and seizure disorders. In mouse thalamic relay cells DS2 enhanced the tonic current mediated by alpha4beta2delta receptors with no effect on their synaptic GABA(A) receptors. Similarly, in mouse cerebellar granule cells DS2 potentiated the tonic current mediated by alpha6betadelta receptors. DS2 is the first selective positive allosteric modulator of delta-GABA(A) receptors and such compounds potentially offer novel therapeutic opportunities as analgesics and in the treatment of sleep disorders. Furthermore, these drugs may be valuable in elucidating the physiological and pathophysiological roles played by these extrasynaptic GABA(A) receptors.
大脑中的抑制作用主要由神经递质γ-氨基丁酸（GABA）介导，通过GABA(A)受体发挥作用。这种神经抑制形式曾被认为是由突触受体介导的，然而最近的证据突出了突触外GABA(A)受体在控制神经元活动方面以前未被认识到的作用。突触和突触外GABA(A)受体表现出不同的药理学和生物物理学特性，对大脑生理和行为有不同的影响。在这里，我们使用基于荧光的检测方法和表达重组GABA(A)受体的细胞系，鉴定出一系列新型苯甲酰胺化合物，它们能选择性增强或激活α4β3δ GABA(A)受体（与α4β3γ2和α1β3γ2相比）。利用电生理方法，我们表明这些化合物之一，4-氯-N-[6,8-二溴-2-(2-噻吩基)咪唑并[1,2-a]吡啶-3-基]苯甲酰胺（DS1）能有效（低纳摩尔）增强由α4β3δ受体介导的GABA诱发电流。在相似浓度下，DS1直接激活该受体，是已知最有效的α4β3δ受体激动剂。4-氯-N-[2-(2-噻吩基)咪唑并[1,2-a]吡啶-3-基]苯甲酰胺（DS2）选择性增强由α4β3δ受体介导的GABA反应，但不是激动剂。最近的研究揭示了丘脑由α4β2δ突触外GABA(A)受体介导的一种紧张性抑制形式，这可能有助于调节与睡眠、觉醒、警觉和癫痫疾病相关的丘脑皮质节律活动。在小鼠丘脑中继细胞中，DS2增强了由α4β2δ受体介导的紧张性电流，对其突触GABA(A)受体没有影响。同样，在小鼠小脑颗粒细胞中，DS2增强了由α6βδ受体介导的紧张性电流。DS2是首个δ-GABA(A)受体的选择性正变构调节剂，这类化合物可能作为镇痛药和用于治疗睡眠障碍提供新的治疗机会。此外，这些药物对于阐明这些突触外GABA(A)受体所起的生理和病理生理作用可能很有价值。
