SYNAPTIC VARIABILITY--DEVELOPMENTAL & STRUCTURAL SOURCES

这项研究的目的有两个：解释 突触结构对突触强度的影响，并发现发育 决定脑内不同突触相对强度的机制 常见的突触后神经元。小龙虾中的每一个感觉SR神经元 腹部，总共20个神经元，与一对已识别的靶点突触 最后一个腹部神经节的神经元。这些突触的优势在于 成年动物的分级；后部SR神经元产生更强的突触 前面的。这项提案的具体目的是描述 从数量上讲，这些生理差异的结构基础 突触强度，并发现何时以及通过什么机制 突触强度的梯度首先出现在动物的 发展。 靶神经元对的突触后反应(PSP) 对刺激的每个SR轴突进行测量，然后选择 突触前SR轴突和两个靶神经元都将充满 细胞内标记物HRP。SR轴突与神经元之间的突触联系 在光学显微镜中对每个靶神经元进行计数和标测，并 在电子显微镜下检查每个触点的结构。通过 强突触与弱突触的结构和位置比较 突触，我们将测试三个假设，这三个假设同时考虑了突触前和突触 突触后因素： --具有强大突触的SR轴突与 而不是弱突触。 --不同脑区PSP突触后衰减的差异 靶神经元上的位置导致测量到的突触差异 力量。 还不知道这些突触强度的梯度是什么时候开始出现的。至 了解这是发生在胚胎发生期间还是发生在胚胎发育后 生长，来自相同目标神经元的SR PSP将在新的 孵化的小龙虾。 -如果在胚胎后生长过程中出现梯度，则 SR轴突之间的突触竞争，其比率的差异 增加新的突触接触，以及靶点的生长 在正常发育过程中将对自己进行测试。

The objectives of this research are twofold: to explain the relation of synaptic structure to synaptic strength, and to discover the developmental mechanisms that determine the relative strength of different synapses on a common postsynaptic neuron. Each of the sensory SR neurons in the crayfish abdomen, twenty neurons in all, synapse with an identified pair of target neurons in the last abdominal ganglion. The strengths of these synapses are graded in adult animals; posterior SR neurons make stronger synapses that anterior ones. The Specific Aims of this proposal are to describe quantitatively the structural basic of these physiological differences in synaptic strength, and to discover when and by what mechanisms these gradients of synaptic strength first appear during the animal's development. The postsynaptic response (PSP) of each of the pair of the target neurons to stimulation of each SR axon will be measured, and then a selected presynaptic SR axon and both target neurons will be filled with an intracellular marker, HRP. The synaptic contacts between the SR axon and each target neuron will be counted and mapped in the light microscope, and the structure of each contact examined in the electron microscope. By comparing the structures and locations of strong synapse with those of weak synapses, we will test three hypotheses that consider both presynaptic and postsynaptic factors: --that SR axons with strong synapses make more synaptic contacts with the target than do weak synapses. --that differential postsynaptic attenuation of PSPs arising at different sites on the target neurons causes the measured differences in synaptic strength. It is not known when these gradients of synaptic strength first arise. To discover whether this occurs during embryogenesis or during postembryonic growth, SR PSPs from the same target neurons will be measured in newly hatched crayfish. --If the gradients arise during postembryonic growth, the roles of synaptic competition among SR axons, of differences in their rates of addition of new synaptic contacts, and of growth of the targets themselves during normal development will be tested.