Langeloh Hendrik, Wasser Hannah, Richter Nicole, Bicker Gerd, Stern Michael
University of Veterinary Medicine Hannover, Division of Cell Biology, Bischofsholer Damm 15/102, D-30173 Hannover, Germany.
Front Zool. 2018 Aug 1;15:28. doi: 10.1186/s12983-018-0274-9. eCollection 2018.
The neuromuscular junction is the chemical synapse where motor neurons communicate with skeletal muscle fibers. Whereas vertebrates and many invertebrates use acetylcholine as transmitter at the neuromuscular junction, in those arthropods examined up to now, glutamate and GABA are used instead. With respect to taxon sampling in a phylogenetic context, there is, however, only a limited amount of data available, focusing mainly on crustaceans and hexapods, and neglecting other, arthropod groups. Here we investigate the neurotransmitter equipment of neuromuscular synapses of a myriapod, , using immunofluorescence and histochemical staining methods.
Glutamate and GABA could be found colocalised with synapsin in synaptic boutons of body wall and leg muscles of . Acetylcholinesterase activity as a marker for cholinergic synapses was found abundantly in the central nervous system and also in some peripheral nerves, but not at neuromuscular junctions. Furthermore, a large number of leg sensory neurons displayed GABA-immunofluorescence and was also labeled with an antiserum against the GABA-synthesizing enzyme, glutamate decarboxylase.
Our data indicate that glutamate and GABA are neurotransmitters at neuromuscular junctions, whereas acetylcholine is very unlikely to play a role here. This is in line with the concept of glutamate as excitatory and GABA as the main inhibitory neuromuscular transmitters in euarthropods. Furthermore, we have, to our knowledge for the first time, localized GABA in euarthropod leg sensory neurons, indicating the possibility that neurotransmitter panel in arthropod sensory systems may be far more extensive than hitherto assumed.
神经肌肉接头是运动神经元与骨骼肌纤维进行通信的化学突触。脊椎动物和许多无脊椎动物在神经肌肉接头处使用乙酰胆碱作为递质，而在目前已研究的节肢动物中，使用的是谷氨酸和γ-氨基丁酸（GABA）。然而，在系统发育背景下的分类群抽样方面，可用数据有限，主要集中在甲壳类动物和六足动物，而忽略了其他节肢动物类群。在这里，我们使用免疫荧光和组织化学染色方法研究了一种多足动物神经肌肉突触的神经递质情况。
在该多足动物体壁和腿部肌肉的突触小体中，发现谷氨酸和GABA与突触素共定位。作为胆碱能突触标志物的乙酰胆碱酯酶活性在中枢神经系统以及一些外周神经中大量存在，但在神经肌肉接头处未发现。此外，大量腿部感觉神经元显示出GABA免疫荧光，并且也用针对GABA合成酶谷氨酸脱羧酶的抗血清标记。
我们的数据表明，谷氨酸和GABA是该多足动物神经肌肉接头处的神经递质，而乙酰胆碱在此处不太可能发挥作用。这与真节肢动物中谷氨酸作为兴奋性神经递质以及GABA作为主要抑制性神经肌肉递质的概念一致。此外，据我们所知，我们首次在真节肢动物腿部感觉神经元中定位了GABA，这表明节肢动物感觉系统中的神经递质组合可能比迄今所认为的要广泛得多。
