Dopamine modulation of network activity in the prefrontal cortex.

描述(申请人提供)：完整大脑中的皮质活动以间歇性持续性膜去极化为特征，称为“向上状态”。给定皮质区域的特定任务计算叠加在这种高度活跃的活动之上。在前额叶皮质(PFC)的情况下，深层神经元的反复兴奋被认为是工作记忆期间持续活动的基础。多巴胺(DA)调节工作记忆，然而，在清醒动物中研究其详细的生物物理效应是不可行的。相反，我们关于多巴胺对膜兴奋性或突触传递的影响的大部分知识都来自于“安静的”急性脑片准备的记录。然而，UP状态和持续活动是一种网络现象，跨神经元发生的异步放电是内在兴奋性和经常性突触传递之间相互作用的结果。本研究采用前额叶、海马区和腹侧被盖区(VTA)的有机共培养方法，研究DA对大脑活动皮质的调节作用。这些文化表现出持续的活动(向上状态)，并拥有工作记忆所需的关键输入，即来自VTA的海马体和DA输入。目前的提案测试了两个假设，这些假设来自于体外脑片准备和计算模型研究。第一种假说认为，DA可以剂量依赖的方式调节处于上行状态的持续活动。在特定目标1的实验中，将使用全细胞电流钳记录来测试是否存在动作电位激发和上行状态持续时间增强的DA调制的“最佳”范围，而超出该最佳范围的持续活动将减少。对照实验将评估从VTA释放DA的强直性和相性的贡献，并将测试DA是否具有网络特异性效应。通过快速扫描循环伏安法同时监测切片中DA的浓度。第二种假说认为，DA作用于GABA和NMDA电流，以调节处于上行状态的持续活动。结合电压钳和钙离子成像实验，分别测量高剂量和低剂量DA对GABA和NMDA电流的调制作用。这些研究将对有源PFC网络的持续活动和DA调制的结构提供见解；这些信息对于我们理解PFC的正常和病理状态至关重要。

DESCRIPTION (provided by applicant): Cortical activity in the intact brain is characterized by intermittent sustained membrane depolarizations called "up-states". The task-specific computations of a given cortical region are superimposed on top of this heightened activity. In the case of the prefrontal cortex (PFC), recurrent excitation of deep layer neurons is thought to underlie sustained activity during working memory. Dopamine (DA) modulates working memory, however, it has not been feasible to investigate its detailed biophysical effects in the awake animal. Instead, most of our knowledge about dopamine's effects on membrane excitability or synaptic transmission derives from recordings in "quiet" acute brain slice preparations. However, up-states and sustained activity are a network phenomenon and the asynchronous firing that occurs across neurons results from the interplay between intrinsic excitability and recurrent synaptic transmission. The present proposal investigates DA modulation of active cortex using an organotypic co-culture preparation of the PFC, hippocampus and ventral tegmental area (VTA). These cultures exhibit sustained activity (up-states) and possess key inputs required for working memory, namely the hippocampus and the DA input from the VTA. The present proposal tests two hypotheses generated from in vitro brain slice preparations and computational modeling studies. The first hypothesis posits that sustained activity during up-states can be modulated by DA in a dose-dependent manner. Experiments in Specific Aim 1 will use whole-cell current clamp recordings to test whether there is an "optimal" range of DA modulation in which action-potential firing and up-state duration are enhanced, while outside of this optimal range sustained activity will be reduced. Control experiments will assess the contribution of tonic vs. phasic release of DA from the VTA, and will test whether DA has network specific effects. The concentration of DA in the slice will be monitored simultaneously via fast-scan cyclic voltammetry. The second hypothesis states that DA acts on GABA and NMDA currents to modulate persistent activity during up-states. Combined voltage-clamp and calcium imaging experiments will be used to measure the modulation of GABA and NMDA currents by a high dose or low dose of DA, respectively. These studies will provide insights into the architecture of sustained activity and DA modulation of active PFC networks; information critical for our understanding of the normal and pathological conditions of the PFC.