Departments of Psychiatry.
Anesthesiology, and.
J Neurosci. 2018 Sep 19;38(38):8128-8145. doi: 10.1523/JNEUROSCI.0799-18.2018. Epub 2018 Aug 3.
Two major GABA receptor classes mediate ionotropic GABA signaling, those containing a δ subunit and those with a γ2 subunit. The classical viewpoint equates γ2-containing receptors with IPSCs and δ-containing receptors with tonic inhibition because of differences in receptor localization, but significant questions remain because the populations cannot be pharmacologically separated. We removed this barrier using gene editing to confer a point mutation on the δ subunit in mice, rendering receptors containing the subunit picrotoxin resistant. By pharmacologically isolating δ-containing receptors, our results demonstrate their contribution to IPSCs in dentate granule neurons and weaker contributions to thalamocortical IPSCs. Despite documented extrasynaptic localization, we found that receptor localization does not preclude participation in isolated IPSCs, including mIPSCs. Further, phasic inhibition from δ subunit-containing receptors strongly inhibited summation of EPSPs, whereas tonic activity had little impact. In addition to any role that δ-containing receptors may play in canonical tonic inhibition, our results highlight a previously underestimated contribution of δ-containing receptors to phasic inhibition. GABA receptors play key roles in transient and tonic inhibition. The prevailing view suggests that synaptic γ2-containing GABA receptors drive phasic inhibition, whereas extrasynaptic δ-containing receptors mediate tonic inhibition. To re-evaluate the impact of δ receptors, we took a chemogenetic approach that offers a sensitive method to probe the synaptic contribution of δ-containing receptors. Our results reveal that localization does not strongly limit the contribution of δ receptors to IPSCs and that δ receptors make an unanticipated robust contribution to phasic inhibition.
两种主要的 GABA 受体介导离子型 GABA 信号转导，一种含有 δ 亚基，另一种含有 γ2 亚基。由于受体定位的差异，经典观点将含有 γ2 的受体与 IPSCs 等同，将含有 δ 的受体与紧张性抑制等同，但由于存在一些尚未解决的问题，这种观点仍存在争议，因为这两种受体不能通过药理学方法分离。我们使用基因编辑技术在小鼠中对 δ 亚基进行点突变，使含有该亚基的受体对 picrotoxin具有抗性，从而消除了这种障碍。通过药理学分离含有 δ 的受体，我们的结果表明它们对齿状回颗粒神经元中的 IPSCs 有贡献，对丘脑皮质 IPSCs 的贡献较弱。尽管有文献报道这些受体存在突触外定位，但我们发现受体定位并不排除其参与孤立的 IPSCs，包括 mIPSCs。此外，来自含有 δ 亚基的受体的相位抑制强烈抑制 EPSP 的总和，而紧张性活动的影响较小。除了含有 δ 的受体在经典的紧张性抑制中可能发挥的任何作用外，我们的结果还强调了含有 δ 的受体对相位抑制的作用被低估。GABA 受体在瞬时和紧张性抑制中发挥关键作用。流行的观点认为，突触 γ2 含有 GABA 受体驱动相位抑制，而突触外 δ 含有 GABA 受体介导紧张性抑制。为了重新评估 δ 受体的作用，我们采用了一种化学遗传方法，该方法提供了一种敏感的方法来探测含有 δ 受体的突触贡献。我们的结果表明，定位并不能强烈限制 δ 受体对 IPSCs 的贡献，而且 δ 受体对相位抑制有出乎意料的强大贡献。
