Haydon P G, Kater S B
Department of Zoology, Iowa State University, Ames 50011.
J Neurobiol. 1988 Oct;19(7):636-55. doi: 10.1002/neu.480190706.
Novel chemical and electrical connections form between neurons not normally connected in the buccal ganglia of the snail Helisoma. We examined the cellular and environmental conditions required for the formation of each type of connection. Previous work in situ showed that novel electrical connections could form in response to axotomy. We have now found that axotomy can evoke the formation of novel unidirectional chemical connections between neurons B5 and B4 in addition to a novel electrical connection. The novel chemical connections display all of the normal properties of chemical synapses in Helisoma ganglia. These connections, however, are transient in nature and break 4 days following axotomy. Previous work has shown that conjoint outgrowth is required for the formation of electrical connections. In cell culture we have investigated whether conjoint outgrowth is also required for chemical synaptogenesis. Using neurons B5 and B19 we have found that when neuron pairs make contact in cell culture, under conditions of synchronous neurite extension, both electrical and chemical synapses form. However, if one neuron has ceased extension prior to contact by a growing neuron, electrical synapses never form (Hadley et al., 1983, 1985) but chemical synapses do form. Furthermore, the addition of serotonin (10(-6) M) to culture medium to inhibit neurite extension of B19, but not that of B5, selectively prevents the formation of electrical connections while permitting the formation of chemical synapses. Thus, the timing of contact in relation to the state of neurite extension can specify the type of connection a given neuron can form.
在蜗牛日光螺的颊神经节中，通常不相连的神经元之间形成了新的化学和电连接。我们研究了每种类型连接形成所需的细胞和环境条件。先前的原位研究表明，新的电连接可因轴突切断而形成。我们现在发现，轴突切断除了能诱发新的电连接外，还能在神经元B5和B4之间诱发新的单向化学连接。这些新的化学连接具有日光螺神经节中化学突触的所有正常特性。然而，这些连接本质上是短暂的，在轴突切断后4天就会断开。先前的研究表明，联合生长是电连接形成所必需的。在细胞培养中，我们研究了联合生长是否也是化学突触形成所必需的。使用神经元B5和B19，我们发现当神经元对在细胞培养中接触时，在同步神经突延伸的条件下，电突触和化学突触都会形成。然而，如果一个神经元在生长中的神经元接触之前就停止了延伸，电突触就永远不会形成（哈德利等人，1983年，1985年），但化学突触会形成。此外，向培养基中添加血清素（10^(-6) M）以抑制B19的神经突延伸，但不抑制B5的神经突延伸，可选择性地阻止电连接的形成，同时允许化学突触的形成。因此，与神经突延伸状态相关的接触时机可以确定给定神经元能够形成的连接类型。
