Koksma Jan-Jurjen, Fritschy Jean-Marc, Mack Volker, Van Kesteren Ronald E, Brussaard Arjen B
Department of Experimental Neurophysiology, Centre for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands.
Mol Cell Neurosci. 2005 Jan;28(1):128-40. doi: 10.1016/j.mcn.2004.09.002.
Expression, functional properties, and clustering of alpha 1-, alpha 2-, and alpha 3-subunit containing GABA(A) receptors (GABA(A)Rs) were studied in dorsomedial SON neurons of the adult female rat supraoptic nucleus (SON) around parturition. We show that, although the decay time constant (tau(decay)) of GABAergic postsynaptic currents between and within individual recordings was very diverse, ranging from fast (i.e., alpha 1-like) to significantly slower (i.e., non-alpha 1-like), there was an overall shift towards slower decaying synaptic currents during the onset of lactation. This shift is not due to changes in mRNA expression levels, because real-time quantitative PCR assays indicated that the relative contribution of alpha 1, alpha 2, and alpha 3 remained the same before and after parturition. Also, changes in phosphorylation levels are not likely to affect the tau(decay) of postsynaptic currents. In alpha-latrotoxin (alpha-LTX)-induced bursts of synaptic currents from individual synapses, the tau(decay) of consecutive synaptic events within bursts was very similar, but between bursts there were large differences in tau(decay). This suggested that different synapses within individual SON neurons contain distinct GABA(A)R subtypes. Using multilabeling confocal microscopy, we examined the distribution of postsynaptic alpha 1-, alpha 2-, and alpha 3-GABA(A)Rs, based on colocalization with gephyrin. We show that the three GABA(A)R subtypes occurred either in segregated clusters of one subtype as well as in mixed clusters of two or possibly even three receptor subtypes. After parturition, the density and proportion of clusters containing alpha 2- (or alpha 3-), but not alpha1-GABA(A)Rs, was significantly increased. Thus, the functional synaptic diversity at the postsynaptic level in dorsomedial SON neurons is correlated with a differential clustering of distinct GABA(A)R subtypes at individual synapses.
在成年雌性大鼠视上核（SON）背内侧神经元分娩前后，研究了含α1、α2和α3亚基的γ-氨基丁酸A型受体（GABA(A)Rs）的表达、功能特性和聚集情况。我们发现，尽管在单个记录之间以及记录内部，GABA能突触后电流的衰减时间常数（tau(decay)）差异很大，从快速（即α1样）到显著减慢（即非α1样），但在泌乳开始时，突触电流衰减总体上有向较慢方向转变的趋势。这种转变并非由于mRNA表达水平的变化，因为实时定量PCR分析表明，α1、α2和α3的相对贡献在分娩前后保持不变。此外，磷酸化水平的变化也不太可能影响突触后电流的tau(decay)。在α-银环蛇毒素（α-LTX）诱导的单个突触的突触电流爆发中，爆发内连续突触事件的tau(decay)非常相似，但不同爆发之间tau(decay)存在很大差异。这表明单个SON神经元内的不同突触含有不同的GABA(A)R亚型。利用多标记共聚焦显微镜，我们基于与gephyrin的共定位，研究了突触后α1、α2和α3-GABA(A)Rs的分布。我们发现，这三种GABA(A)R亚型既可以出现在一种亚型的分离簇中，也可以出现在两种甚至可能三种受体亚型的混合簇中。分娩后，含有α2-（或α3-）但不含α1-GABA(A)Rs的簇的密度和比例显著增加。因此，SON背内侧神经元突触后水平的功能性突触多样性与单个突触处不同GABA(A)R亚型的差异聚集相关。
