Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK.
Department of Neuroscience, Physiology & Pharmacology, UCL, Gower Street, London, WC1E 6BT, UK.
Neuropharmacology. 2023 Aug 1;233:109530. doi: 10.1016/j.neuropharm.2023.109530. Epub 2023 Apr 8.
Neurosteroids are important endogenous modulators of GABA receptor-mediated neurotransmission within the CNS and play a vital role in maintaining normal healthy brain function. Research has mainly focussed on neurosteroids such as allopregnanolone and tetrahydro-deoxycorticosterone (THDOC) which are allosteric potentiators of GABA receptors, whilst the sulphated steroids, including pregnenolone sulphate (PS), which inhibit GABA receptor function, have been relatively neglected. Importantly, a full description of PS effects on inhibitory synaptic transmission, at concentrations that are expected to inhibit postsynaptic GABA receptors, is lacking. Here, we address this deficit by recording inhibitory postsynaptic currents (IPSCs) from rat hippocampal neurons both in culture and in acute brain slices and explore the impact of PS at micromolar concentrations. We reveal that PS inhibits postsynaptic GABA receptors, evident from reductions in IPSC amplitude and decay time. Concurrently, PS also causes an increase in synaptic GABA release which we discover is due to the activation of presynaptic TRPM3 receptors located close to presynaptic GABA release sites. Pharmacological blockade of TRPM3 receptors uncovers a PS-evoked reduction in IPSC frequency. This second presynaptic effect is caused by PS activation of inwardly-rectifying Kir2.3 channels on interneurons, which act to depress synaptic GABA release. Overall, we provide a comprehensive characterisation of pre- and postsynaptic modulation by PS of inhibitory synaptic transmission onto hippocampal neurons which elucidates the diverse mechanisms by which this understudied neurosteroid can modulate brain function.
神经甾体是中枢神经系统内 GABA 受体介导的神经传递的重要内源性调节剂，在维持正常健康的大脑功能方面发挥着至关重要的作用。研究主要集中在神经甾体上，如别孕烯醇酮和四氢去氧皮质酮 (THDOC)，它们是 GABA 受体的别构增强剂，而硫酸化甾体，包括硫酸孕烯醇酮 (PS)，抑制 GABA 受体功能，相对被忽视。重要的是，缺乏 PS 对抑制性突触传递的影响的完整描述，在预期抑制突触后 GABA 受体的浓度下。在这里，我们通过在培养物和急性脑切片中从大鼠海马神经元记录抑制性突触后电流 (IPSCs) 来解决这一缺陷，并探索 PS 在微摩尔浓度下的影响。我们发现 PS 抑制突触后 GABA 受体，这从 IPSC 幅度和衰减时间的减少中可以明显看出。同时，PS 还导致突触 GABA 释放增加，我们发现这是由于靠近突触前 GABA 释放位点的 TRPM3 受体的激活。TRPM3 受体的药理学阻断揭示了 PS 诱导的 IPSC 频率降低。这种第二个突触前效应是由 PS 对中间神经元上的内向整流 Kir2.3 通道的激活引起的，该通道作用是抑制突触 GABA 释放。总体而言，我们全面描述了 PS 对海马神经元抑制性突触传递的前突触和后突触调制，阐明了这种研究较少的神经甾体调节大脑功能的多种机制。
