SYNAPTIC VARIABILITY--DEVELOPMENTAL & STRUCTURAL SOURCES

本研究的目的是双重的：解释的关系 突触结构到突触强度，并发现发育 决定神经元上不同突触的相对强度的机制 普通的突触后神经元。小龙虾的每一个感觉SR神经元 腹部，总共20个神经元，与一对确定的目标突触 最后一个腹神经节的神经元。这些突触的力量在于 在成年动物中分级;后部SR神经元产生更强的突触， 前面的。本提案的具体目的是描述 定量地分析了这些生理差异的结构基础， 突触强度，并发现何时以及通过何种机制，这些 突触强度的梯度首先出现在动物 发展 每对靶神经元的突触后反应（PSP） 将测量每个SR轴突的刺激，然后选择 突触前SR轴突和两个靶神经元将被填充有 细胞内标记物HRP。SR轴突和 每个靶神经元将在光学显微镜中计数和映射，并且 在电子显微镜下检查每个触点的结构。通过 比较强突触和弱突触的结构和位置， 突触，我们将测试三个假设，既考虑突触前， 突触后因子： --具有强突触的SR轴突产生更多的突触接触 与 而不是弱突触。 --PSP的差异突触后衰减产生于 不同 靶神经元上的位点导致测量的 突触差异 实力 我们不知道这些突触强度的梯度是什么时候开始出现的。到 发现这是否发生在胚胎发生期间或胚后期间 生长，来自相同靶神经元的SR PSP将在新的 孵化的小龙虾 --如果梯度出现在胚后生长期间， 的 SR轴突之间的突触竞争， 率 增加新的突触接触， 目标 在正常发育过程中， 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.