Department of Functional Biology, CIBUS, Faculty of Biology, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain.
Department of Anatomy, Neuroscience Center, University of Helsinki, Haartmaninkatu 8, 00014, Helsinki, Finland.
Cell Death Dis. 2018 Jun 28;9(6):663. doi: 10.1038/s41419-018-0704-9.
The poor regenerative capacity of descending neurons is one of the main causes of the lack of recovery after spinal cord injury (SCI). Thus, it is of crucial importance to find ways to promote axonal regeneration. In addition, the prevention of retrograde degeneration leading to the atrophy/death of descending neurons is an obvious prerequisite to activate axonal regeneration. Lampreys show an amazing regenerative capacity after SCI. Recent histological work in lampreys suggested that GABA, which is massively released after a SCI, could promote the survival of descending neurons. Here, we aimed to study if GABA, acting through GABAB receptors, promotes the survival and axonal regeneration of descending neurons of larval sea lampreys after a complete SCI. First, we used in situ hybridization to confirm that identifiable descending neurons of late-stage larvae express the gabab1 subunit of the GABAB receptor. We also observed an acute increase in the expression of this subunit in descending neurons after SCI, which further supported the possible role of GABA and GABAB receptors in promoting the survival and regeneration of these neurons. So, we performed gain and loss of function experiments to confirm this hypothesis. Treatments with GABA and baclofen (GABAB agonist) significantly reduced caspase activation in descending neurons 2 weeks after a complete SCI. Long-term treatments with GABOB (a GABA analogue) and baclofen significantly promoted axonal regeneration of descending neurons after SCI. These data indicate that GABAergic signalling through GABAB receptors promotes the survival and regeneration of descending neurons after SCI. Finally, we used morpholinos against the gabab1 subunit to knockdown the expression of the GABAB receptor in descending neurons. Long-term morpholino treatments caused a significant inhibition of axonal regeneration. This shows that endogenous GABA promotes axonal regeneration after a complete SCI in lampreys by activating GABAB receptors.
下行神经元的再生能力差是脊髓损伤 (SCI) 后缺乏恢复的主要原因之一。因此，找到促进轴突再生的方法至关重要。此外，防止逆行变性导致下行神经元萎缩/死亡是激活轴突再生的明显前提。文昌鱼在 SCI 后表现出惊人的再生能力。文昌鱼的最近组织学研究表明，SCI 后大量释放的 GABA 可以促进下行神经元的存活。在这里，我们旨在研究 GABA 是否通过 GABAB 受体促进完全 SCI 后幼鱼的下行神经元的存活和轴突再生。首先，我们使用原位杂交来确认晚期幼虫的可识别下行神经元表达 GABAB 受体的 gabab1 亚基。我们还观察到 SCI 后下行神经元中该亚基的表达急性增加，这进一步支持 GABA 和 GABAB 受体在促进这些神经元的存活和再生中的可能作用。因此，我们进行了增益和失能实验来证实这一假设。用 GABA 和巴氯芬（GABAB 激动剂）处理可显着减少 SCI 后 2 周下行神经元中的 Caspase 激活。用 GABOB（GABA 类似物）和巴氯芬长期处理可显着促进 SCI 后下行神经元的轴突再生。这些数据表明，通过 GABAB 受体的 GABA 能信号传导促进 SCI 后下行神经元的存活和再生。最后，我们使用针对 gabab1 亚基的 morpholino 来敲低下行神经元中 GABAB 受体的表达。长期 morpholino 处理会显着抑制轴突再生。这表明内源性 GABA 通过激活 GABAB 受体促进文昌鱼完全 SCI 后的轴突再生。
