Marin-Burgin Antonia, Eisenhart F James, Kristan William B, French Kathleen A
Section of Neurobiology, Division of Biological Sciences, University of California, 3119 Pacific Hall, San Diego, La Jolla, CA 92093-0357, USA.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2006 Feb;192(2):123-33. doi: 10.1007/s00359-005-0055-8. Epub 2005 Oct 5.
During development, many embryos show electrical coupling among neurons that is spatially and temporally regulated. For example, in vertebrate embryos extensive dye coupling is seen during the period of circuit formation, suggesting that electrical connections could pre-figure circuits, but it has been difficult to identify which neuronal types are coupled. We have used the leech Hirudo medicinalis to follow the development of electrical connections within the circuit that produces local bending. This circuit consists of three layers of neurons: four mechanosensory neurons (P cells), 17 identified interneurons, and approximately 24 excitatory and inhibitory motor neurons. These neurons can be identified in embryos, and we followed the spatial and temporal dynamics as specific connections developed. Injecting Neurobiotin into identified cells of the circuit revealed that electrical connections were established within this circuit in a precise manner from the beginning. Connections first appeared between motor neurons; mechanosensory neurons and interneurons started to connect at least a day later. This timing correlates with the development of behaviors, so the pattern of emerging connectivity could explain the appearance first of spontaneous behaviors (driven by a electrically coupled motor network) and then of evoked behaviors (when sensory neurons and interneurons are added to the circuit).
在发育过程中，许多胚胎的神经元之间表现出在空间和时间上受到调控的电耦合。例如，在脊椎动物胚胎中，在神经回路形成期间可观察到广泛的染料耦合，这表明电连接可能先于神经回路形成，但很难确定哪些神经元类型是耦合的。我们利用医用水蛭来追踪产生局部弯曲的神经回路内电连接的发育过程。这个神经回路由三层神经元组成：四个机械感觉神经元（P细胞）、17个已确定的中间神经元，以及大约24个兴奋性和抑制性运动神经元。这些神经元在胚胎中可以被识别出来，我们追踪了特定连接形成过程中的空间和时间动态。将神经生物素注入该神经回路中已确定的细胞，结果显示该神经回路内从一开始就以精确的方式建立了电连接。连接首先出现在运动神经元之间；机械感觉神经元和中间神经元至少在一天后才开始连接。这个时间与行为的发育相关，因此新出现的连接模式可以解释自发行为（由电耦合的运动网络驱动）先出现，然后是诱发行为（当感觉神经元和中间神经元加入到神经回路中时）的出现。
