Ducret Eric, Le Feuvre Yves, Meyrand Pierre, Fénelon Valérie S
Laboratoire de Neurobiologie des Réseaux, Université Bordeaux I and Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5816, 33405 Talence, France.
J Neurosci. 2007 Apr 4;27(14):3626-38. doi: 10.1523/JNEUROSCI.4406-06.2007.
The maturation and operation of neural networks are known to depend on modulatory neurons. However, whether similar mechanisms may control both adult and developmental plasticity remains poorly investigated. To examine this issue, we have used the lobster stomatogastric nervous system (STNS) to investigate the ontogeny and role of GABAergic modulatory neurons projecting to small pattern generating networks. Using immunocytochemistry, we found that modulatory input neurons to the stomatogastric ganglion (STG) express GABA only after metamorphosis, a time that coincides with the developmental switch from a single to multiple pattern generating networks within the STNS. We demonstrate that blocking GABA synthesis with 3-mercapto-propionic acid within the adult modulatory neurons results in the reconfiguration of the distinct STG networks into a single network that generates a unified embryonic-like motor pattern. Using dye-coupling experiments, we also found that gap-junctional coupling is greater in embryos and GABA-deprived adults exhibiting the unified motor pattern compared with control adults. Furthermore, GABA was found to diminish directly the extent and strength of electrical coupling within adult STG networks. Together, these observations suggest the acquisition of a GABAergic phenotype by modulatory neurons after metamorphosis may induce the reconfiguration of the single embryonic network into multiple adult networks by directly decreasing electrical coupling. The findings also suggest that adult neural networks retain the ability to express typical embryonic characteristics, indicating that network ontogeny can be reversed and that changes in electrical coupling during development may allow the segregation of multiple distinct functional networks from a single large embryonic network.
已知神经网络的成熟和运作依赖于调节性神经元。然而，类似的机制是否可能同时控制成年期和发育期的可塑性，这一问题仍鲜有研究。为了探究这个问题，我们利用龙虾的口胃神经系统（STNS）来研究投射到小型模式生成网络的GABA能调节性神经元的个体发育及其作用。通过免疫细胞化学方法，我们发现，口胃神经节（STG）的调节性输入神经元仅在变态后才表达GABA，这一时期与STNS内从单一模式生成网络向多个模式生成网络的发育转变相吻合。我们证明，在成年调节性神经元内用3-巯基丙酸阻断GABA合成，会导致不同的STG网络重新配置成一个单一网络，该网络会产生一种统一的、类似胚胎的运动模式。通过染料偶联实验，我们还发现，与对照成年龙虾相比，胚胎以及表现出统一运动模式的GABA缺乏成年龙虾中的缝隙连接偶联更强。此外，我们发现GABA会直接降低成年STG网络内电偶联的程度和强度。这些观察结果共同表明，变态后调节性神经元获得GABA能表型可能通过直接降低电偶联，诱导单一胚胎网络重新配置成多个成年网络。这些发现还表明，成年神经网络保留了表达典型胚胎特征的能力，这表明网络个体发育可以逆转，并且发育过程中电偶联的变化可能允许从一个单一的大型胚胎网络中分离出多个不同的功能网络。
