Role of glial glutamate transporters in V1 plasticity and development

描述(申请人提供)：视觉皮质中的神经元网络整合突触输入，以产生构成视觉基础的复杂输出。大多数关于视觉皮质功能和发育的研究都集中在神经元上。星形胶质细胞是大脑中的一种非神经细胞类型，其数量至少与神经元一样多，并执行多种代谢和支持功能。星形胶质细胞发挥着多种功能作用，可以影响感觉信息的处理，证据可以在躯体感觉皮质、嗅球和脊髓中找到。在初级视觉皮质中，定向调节和反应增益的调节是视觉的重要特征。这些特征背后的机制包括兴奋和抑制之间的相互作用，以建立给定神经元的反应属性。我假设星形胶质细胞对这种相互作用起到了重要作用。它们的功能之一是在活动过程中从突触中移除神经递质。星形胶质细胞表达的最具影响力的转运蛋白系统之一是谷氨酸转运蛋白系统，它将突触释放的谷氨酸从突触间隙移除，以缩短传递的时间进程，并减少突触外受体或相邻突触的激活。这是一种减少兴奋的机制，这种兴奋可能在视觉皮质功能中很重要。初步证据表明，谷氨酸转运蛋白是维持视觉处理的关键成分，因为抑制转运蛋白可以延长神经反应并扩大在体视皮层神经元的定向调节。谷氨酸转运体对大脑回路的发育也是至关重要的，有证据表明，当谷氨酸转运体增加或减少时，皮质发育异常。谷氨酸转运体的失调与精神分裂症和自闭症等神经发育障碍有关。因此，研究星形胶质细胞对细胞外谷氨酸的调控可以为了解神经元网络的发育和谷氨酸转运体的功能提供有价值的见解。这项建议详细介绍了一种实验方法，该方法利用电生理学和最先进的活体成像技术来确定星形胶质细胞谷氨酸转运体在视觉皮质功能和发育中的作用。首先，将通过切片电生理学实验评估谷氨酸转运体抑制对小鼠初级视皮层神经元传递的影响。其次，将使用公认的单眼剥夺范例和星形胶质细胞转运基因突变的小鼠来研究谷氨酸转运体在皮质发育和经验依赖性可塑性中的作用。最后，体内成像和电生理学将被用来研究谷氨酸转运体活性的抑制如何改变视皮层神经元的定向调节和反应增益。这些方法的结合将允许对星形胶质细胞如何通过谷氨酸转运体调节神经活动并影响视觉皮质的发育和处理进行关键评估。 公共卫生相关性：星形胶质细胞谷氨酸转运体功能障碍与许多神经退行性和神经精神疾病有关，如精神分裂症和自闭症。通过研究和了解星形胶质细胞谷氨酸转运体在皮质发育和调节视皮层网络活动中的作用，可能成为治疗谷氨酸能信号障碍的药物靶点。

DESCRIPTION (provided by applicant): Neuronal networks in the visual cortex integrate synaptic inputs to make complex outputs that underlie vision. Most studies of visual cortical function and development have focused exclusively on neurons. Astrocytes are a non-neuronal cell type in the brain that are at least as numerous as neurons and perform multiple metabolic and support functions. Astrocytes perform several functional roles that can affect the processing of sensory information, evidence for which can be found in the somatosensory cortex, olfactory bulb, and spinal cord. In the primary visual cortex, orientation tuning and regulation of response gain are critical features of vision. The mechanisms underlying these features involve interplay between excitation and inhibition to establish the response properties of a given neuron. I hypothesize that astrocytes contribute importantly to this interplay. Among their functions is the removal of neurotransmitters from the synapse during activity. One of the most influential transporter systems expressed by astrocytes is the glutamate transporter system, which removes synaptically released glutamate from the synaptic cleft to curtail the time course of transmission and reduce the activation of extrasynaptic receptors or adjacent synapses. This serves as a mechanism to reduce excitation that may be important in visual cortex function. Preliminary evidence suggests that glutamate transporters are a critical component in the maintenance of visual processing, as inhibition of transporters prolongs neural responses and broadens the orientation tuning of visual cortex neurons in vivo. Glutamate transporters are also critical to the development of brain circuits, with evidence existing for abnormal cortical development when there is either increased or decreased glutamate transport. Dysregulation of glutamate transporters has been implicated in neurodevelopmental disorders such as schizophrenia and autism. Therefore, studies into astrocytic regulation of extracellular glutamate could provide valuable insight into neuronal network development and function through glutamate transporters. This proposal details an experimental approach that utilizes electrophysiology and state of the art in vivo imaging techniques to determine the role of astrocyte glutamate transporters in visual cortex function and development. First, the effects of glutamate transporter inhibition on neuronal transmission in primary visual cortex of mice will be assessed using slice electrophysiology experiments. Second, the role of glutamate transporters in cortical development and experience-dependent plasticity will be investigated using the well- established paradigm of monocular deprivation and mice that are mutant for astrocyte transporter genes. Finally, in vivo imaging and electrophysiology will be used to examine how inhibition of glutamate transporter activity alters orientation tuning and response gain of visual cortex neurons. The combination of these methods will allow for a critical assessment of how astrocytes modulate neural activity through glutamate transporters and influence visual cortex development and processing. PUBLIC HEALTH RELEVANCE: Astrocyte glutamate transporter dysfunction has been implicated in a number of neurodegenerative and neuropsychiatric disorders, such as schizophrenia and autism. By studying and understanding the role of astrocyte glutamate transporters during cortical development and in modulating network activity in the visual cortex, potential drug targets for treatment of glutamatergic signaling disorders.