Presynaptic receptors and analog signaling in the CNS

描述（由申请人提供）：递质从突触前释放位点释放的可能性受到几个因素的调节，包括动作电位的频率和突触前受体的活性。除了这些机制外，最近已经证明，体树突隔室的阈下去极化可以改变轴突远端动作电位驱动的释放。这种形式的释放调节本质上是类似的，即，虽然它将释放的概率改变为动作电位，但其改变释放的潜力既不需要动作电位，也不需要局部受体激活。相反，这些阈下去极化通过轴突被动传播，据报道通过钙依赖性和钙非依赖性机制影响释放。模拟信号为神经元回路功能的控制增加了另一个维度，它不仅依赖于动作电位频率的历史，还依赖于给定动作电位之前膜电位的阈下变化。突触前受体也可以调节释放概率和改变轴突膜电位。轴突膜电位的变化可以被动地反向传播，改变轴突初始段的兴奋性，直到最近才被认为是躯体树突膜上突触的专属功能。本提案的目的是确定正反模拟信号的机制，并确定这些机制是否在中枢神经系统中普遍使用。研究了小脑分子层中间神经元、齿状回颗粒细胞和皮层第5层锥体细胞三种不同神经元的正交信号。在这三种细胞类型中提出的正交信号传导机制是相互矛盾的，但包括钙依赖性和钙非依赖性过程。反调信号只在一种神经元类型中被证实，即小脑颗粒细胞。尽管许多轴突受体类型可能影响初始节段兴奋性，但由于其使用依赖性，NMDA受体是特别有趣的候选者。大量证据表明，视觉和桶状皮层的皮质层4棘星状神经元表达突触前NMDA受体，该受体改变释放特性，是诱导长期抑郁所必需的。我们将使用双光子激光扫描显微镜、双光子激光解封和电生理学来确定正交模拟信号的机制和突触前NMDA受体的表达程度、其激活所需的生理条件及其对轴突初始兴奋性的影响

DESCRIPTION (provided by applicant): The likelihood of transmitter release from presynaptic release sites is regulated by several factors including the frequency of action potentials and the activity of presynaptic receptors. In addition to these mechanisms, subthreshold depolarizations of the somatodendritic compartment recently have been shown to alter action potential-driven release at distant locations of the axon. This form of regulation of release is analog in nature, i.e., though it alters the probability of release to an action potential, its potential to alter reease requires neither action potentials nor local receptor activation. Rather, these subthreshold depolarizations passive spread through the axon and are reported to affect release by calcium-dependent and calcium-independent mechanisms. Analog signaling adds another dimension to the control of neuronal circuit function which depends not only on the history of action potential frequency but also on the subthreshold changes in membrane potential that preceded a given action potential. Presynaptic receptors can also regulate release probability and alter the axonal membrane potential. The changes in axonal membrane potential can passively propagate antidromically and alter the excitability of the axon initial segment, a function which until recently was thought to be the exclusive domain of synapses on the somatodendritic membrane. The objective of this proposal is to determine the mechanisms underlying orthodromic and antidromic analog signaling and to determine if these mechanisms are used generally in the CNS. Orthodromic signaling will be studied in three dissimilar neurons, cerebellar molecular layer interneurons, dentate gyrus granule cells and cortical layer 5 pyramidal cells. The proposed mechanisms for orthodromic signaling in these three cells types are contradictory but include both calcium-dependent and calcium-independent processes. Antidromic signaling has only been demonstrated in one neuronal type, cerebellar granule cells. Though a number of axonal receptor types may affect initial segment excitability, NMDA receptors are particularly interesting candidates because of their use-dependence. Abundant evidence indicates that cortical layer 4 spiny stellate neurons in both visual and barrel cortex express presynaptic NMDA receptors that alter release properties and are required for the induction of long term depression. We will use two photon laser scanning microscopy, two photon laser uncaging and electrophysiology to determine the mechanisms of orthodromic analog signaling and the extent of presynaptic NMDA receptor expression, the physiological conditions necessary for their activation and their effects on the excitability of the axon initial segments of the layer 4 spiny stellate neurons.