TRANSIENT EXPRESSION OF CHOLINERGIC MARKERS IN THE PVCN

描述(申请人提供)：大脑中的通路和突触连接是由一系列精心策划的神经化学事件建立的。虽然中枢听觉系统的突触在听力开始后会根据经验进行修改，但突触连接是在第八神经对外部环境做出反应之前建立的。一项新兴的文献表明，在发育过程中，一些在成人大脑的神经传递中起次要作用的酶和蛋白质在引导轴突和建立突触方面发挥了重要作用。乙酰胆碱(ACh)、乙酰胆碱酯酶(AChE)和A7烟碱型乙酰胆碱受体(NAChR)是调节突触活动的神经化学物质，包括靶神经元中成熟突触形成所必需的基因的表达。在我们的实验室中，我们发现了一条投射到啮齿动物耳蜗后腹核(PVCN)章鱼细胞区的通路，它瞬时表达AChE和a？NAChR在出生后第二周。超微结构研究表明，出生后第3天，突触连接很少，到出生后第5天，突触连接丰富。胆碱能标记物表达的时间序列，以及来自其他实验室的电生理数据，表明ACh和相关的酶和蛋白质对突触的成熟是必不可少的。它们的功能之一可能是调节谷氨酸受体基因的表达。特定影响胆碱能受体的毒素，如尼古丁，在胎儿和出生后的大脑中以生理上相关的浓度集中。虽然这不会导致耳聋，但它可能会导致长期的语言缺陷。本研究的目的是阐明啮齿动物PVCN中与突触成熟和NMDA受体基因表达调控相关的胆碱能分子机制。总体假设是ACh的弥漫释放通过聚集在PVCN章鱼细胞突触后部位的A7烟碱型乙酰胆碱受体来调节细胞内钙离子，从而调节NMDA谷氨酸受体的表达。具体的假设是：(1)ACh的释放是非囊性的；(2)nAChRs在章鱼细胞突触后聚集；(3)章鱼细胞上的A7nAChRs在听力开始之前但不是在听力开始后调节细胞内钙；(4)尼古丁的使用将上调NMDA受体基因的表达，但不会上调AMPA受体基因的表达；以及(5)ACh通过A7 nAChRs调节NMDA谷氨酸受体的表达。

DESCRIPTION (provided by applicant): The pathways and synaptic connections in the brain are established by a finely orchestrated series of neurochemical events. Although central auditory system synapses are modified by experience after the onset of hearing, synaptic connectivity is established before the eighth nerve is responsive to the external environment. There is an emerging literature indicating that some enzymes and proteins with minor roles in neurotransmission in the adult brain have major roles in guiding axons and establishing synapses during development. Acetylcholine (ACh), acetylcholinesterase (AChE) and the a7 nicotinic acetylcholine receptor (nAChR) are among the neurochemicals that regulate synaptic events, including the expression of genes obligatory for mature synapse formation in target neurons. In our laboratory, we have discovered a pathway projecting to the rodent octopus cell region of the posterior ventral cochlear nucleus (PVCN) that transiently expresses AChE and the a? nAChR during the second postnatal week. Ultrastructural studies indicate that few synaptic junctions are present by postnatal day 3, and are abundant by P5. The temporal sequence of the expression of the cholinergic markers, together with electrophysiological data from other laboratories, suggests that ACh and related enzymes and proteins are essential for the maturation of synapses. One of their functions may be to modulate glutamatergic receptor gene expression. Toxins that specifically affect cholinergic receptors, such as nicotine, concentrate in the fetal and postnatal brain in physiologically relevant concentrations. While this would not cause deafness, it could contribute to long-term language deficits. The goal of the proposed studies is to elucidate the cholinergic molecular mechanisms related to the maturation of synapses and regulation of NMDA receptor gene expression in the rodent PVCN. The overall hypothesis is that the diffuse release of ACh regulates NMDA glutamate receptor expression by regulating intracellular calcium through a7 nicotinic acetylcholine receptors clustered on postsynaptic sites of PVCN octopus cells. The specific hypotheses are: (1) ACh release is nonvesicular; (2) nAChRs are clustered postsynaptically on octopus cells; ACh (3) a7 nAChRs on octopus cells regulate intracellular calcium before, but not after, the onset of hearing; (4) nicotine administration will upregulate NMDA, but not AMPA, receptor gene expression; and (5) ACh, through a7 nAChRs, regulates NMDA glutamate receptor expression.