Zega Giuliana, Biggiogero Maira, Groppelli Silvia, Candiani Simona, Oliveri Diana, Parodi Manuela, Pestarino Mario, De Bernardi Fiorenza, Pennati Roberta
Dipartimento di Biologia, University of Milan, 20133, Milano, Italy.
J Comp Neurol. 2008 Jan 20;506(3):489-505. doi: 10.1002/cne.21565.
We describe Ciona intestinalis gamma-aminobutyric acid (GABA)-ergic neurons during development, studying the expression pattern of Ci-GAD (glutamic acid decarboxylase: GABA synthesizing enzyme) by in situ hybridization. Moreover, we cloned two GABA(B) receptor subunits (Ci-GABA(B)Rs), and a phylogenetic analysis (neighbor-joining method) suggested that they clustered with their vertebrate counterparts. We compared Ci-GAD and Ci-GABA(B)Rs expression patterns in C. intestinalis embryos and larvae. At the tailbud stage, Ci-GAD expression was widely detected in central and peripheral nervous system (CNS/PNS) precursors, whereas Ci-GABA(B)Rs expression was evident at the level of the precursors of the visceral ganglion. GABA was localized by immunohistochemistry at the same developmental stage. In the larva, Ci-GAD transcripts and GABA immunofluorescence were also detected throughout the CNS and in some neurons of the PNS, whereas transcripts of both GABA(B) receptor subunits were found mainly in the CNS. The expression pattern of Ci-GABA(B)Rs appeared restricted to Ci-GAD-positive territories in the sensory vesicle, whereas, in the visceral ganglion, Ci-GABA(B)Rs transcripts were found in ventral motoneurons that did not express Ci-GAD. Insofar as GABAergic neurons are widely distributed also in the CNS and PNS of vertebrates and other invertebrate chordates, it seems likely that GABA signaling was extensively present in the protochordate nervous system. Results from this work show that GABA is the most widespread inhibitory neurotransmitter in C. intestinalis nervous system and that it can signal through GABA(B) receptors both pre- and postsynaptically to modulate different sensory inputs and subsequent swimming activity.
我们描述了发育过程中的玻璃海鞘γ-氨基丁酸（GABA）能神经元，通过原位杂交研究Ci-GAD（谷氨酸脱羧酶：GABA合成酶）的表达模式。此外，我们克隆了两个GABA(B)受体亚基（Ci-GABA(B)Rs），系统发育分析（邻接法）表明它们与脊椎动物的对应亚基聚类。我们比较了玻璃海鞘胚胎和幼虫中Ci-GAD和Ci-GABA(B)Rs的表达模式。在尾芽期，Ci-GAD表达在中枢和外周神经系统（CNS/PNS）前体细胞中广泛检测到，而Ci-GABA(B)Rs表达在内脏神经节前体细胞水平上很明显。在相同发育阶段通过免疫组织化学对GABA进行了定位。在幼虫中，Ci-GAD转录本和GABA免疫荧光也在整个CNS和PNS的一些神经元中检测到，而两个GABA(B)受体亚基的转录本主要在CNS中发现。Ci-GABA(B)Rs的表达模式似乎局限于感觉泡中Ci-GAD阳性区域，而在内脏神经节中，Ci-GABA(B)Rs转录本在不表达Ci-GAD的腹侧运动神经元中发现。鉴于GABA能神经元在脊椎动物和其他无脊椎脊索动物的CNS和PNS中也广泛分布，GABA信号很可能在原索动物神经系统中广泛存在。这项工作的结果表明，GABA是玻璃海鞘神经系统中分布最广泛的抑制性神经递质，它可以通过GABA(B)受体在突触前和突触后发出信号，以调节不同的感觉输入和随后的游泳活动。
