Perineuronal nets in cognition and behaviour

周围神经网络(PNNS)是哺乳动物中枢神经系统中围绕神经元的细胞外基质结构1。PNN在关键发育期以外限制了神经元的可塑性，在一些大脑区域，成年后去除PNN有助于神经元的可塑性和相关的记忆功能。另一方面，几个大脑区域的PNN中断是一些神经精神障碍的特征，包括精神分裂症1，4，5，而啮齿动物特定大脑区域的PNN移除也会损害一些认知和行为功能6-8。在大脑皮层和海马区，PNN主要围绕GABA能抑制中间神经元，参与GABA能抑制的维持和调节，提示PNN干扰可能破坏GABA能抑制1，3，4，9，10。这具有临床意义，因为GABA能抑制受损，包括前额皮质和海马区，是精神分裂症的主要特征，而这些脑区GABA能抑制的破坏，即所谓的神经去抑制，会导致临床相关的认知和行为障碍11。然而，PNN在前额叶皮质和海马区的破坏是否会导致类似于神经去抑制的缺陷，这在很大程度上仍有待研究。此外，许多基于精神分裂症病理生理学因素的啮齿动物模型，包括NMDA受体功能低下，显示出PNNS和GABA能中间神经元的破坏，特别是在前额叶皮质和海马6，12-15。然而，尽管包括亚慢性注射NMDA受体拮抗剂苯环利定在内的NMDA受体功能低下模型被广泛应用于基础研究和药物发现14，但该模型中的PNN破坏尚未确定；此外，NMDA受体功能低下、PNN和GABA能神经元间质破坏之间的关系以及临床相关的认知和行为损害在很大程度上仍有待确定。目标和研究计划学生将研究前额叶皮质和海马区的PNN如何对大鼠的认知和行为做出贡献。该项目将使用PNNS的大脑部位特定操作(AIM 1)和NMDA受体功能低下的亚慢性苯环利定模型(AIM 2)，并结合行为测试、体内电生理学和体外组织学方法。目的1：我们将研究PNNS是否是一些神经、行为和认知功能所必需的，我们已经证明需要前额叶和海马GABA能抑制11，16-19。为此，我们将通过局部注射软骨素酶ABC2，3，6-8，结合体内电生理测量和大鼠行为测试来移除前额皮质或海马区的PNN，类似于我们之前的研究16-19。使用体外组织学方法20，21，我们还将检查去除PNN是否扰乱GABA能神经元间标记(包括GAD67和钙结合蛋白小白蛋白、钙结合蛋白和钙维A蛋白)。目的：采用体外组织学方法，研究亚慢性苯环利定NMDA受体功能低下模型前额叶皮质和海马区PNN的破坏，并探讨PNN的改变是否与GABA能中间神经元标志物的破坏有关。我们还将在模型中将组织学测量与认知和行为损害联系起来，并通过预定的运动来挽救这些损害。

Perineuronal nets (PNNs) are extracellular matrix structures surrounding neurons in the mammalian central nervous system1. PNNs have been implicated in limiting neuronal plasticity outside critical developmental periods and, in some brain regions, PNN removal in adulthood facilitates neuronal plasticity and associated memory functions1-3. On the other hand, PNN disruptions in several brain regions characterise some neuropsychiatric disorders, including schizophrenia1,4,5, and PNN removal in selected brain regions in rodents also impairs some cognitive and behavioural functions 6-8. In neocortex and hippocampus, PNNs mainly surround GABAergic inhibitory interneurons and have been implicated in maintenance and regulation of GABAergic inhibition, suggesting that PNN disruption may disrupt GABAergic inhibition1,3,4,9,10. This is of clinical relevance, because impaired GABAergic inhibition, including in prefrontal cortex and hippocampus, is a key feature of schizophrenia, and disruption of GABAergic inhibition, so-called neural disinhibition, in these brain regions causes clinically relevant cognitive and behavioural deficits in rats11. However, it largely remains to be examined if PNN disruption in prefrontal cortex and hippocampus causes similar deficits to neural disinhibition. Moreover, many rodent models based on factors implicated in schizophrenia pathophysiology, including NMDA receptor hypofunction, show disruption of both PNNs and GABAergic interneurons, particularly in prefrontal cortex and hippocampus6,12-15. However, although the NMDA receptor hypofunction model involving subchronic injections of the NMDA receptor antagonist phencyclidine is widely used in basic and drug discovery research14, PNN disruption in this model has not been characterised; in addition, the relationship between NMDA receptor hypofunction, PNN and GABAergic interneuron disruption, and clinically relevant cognitive and behavioural impairments largely remains to be determined. AIMS AND RESEARCH PLAN The student will study how PNNs in prefrontal cortex and hippocampus contribute to cognition and behaviour in rats. The project will use brain site-specific manipulations of PNNs (Aim 1) and the subchronic phencyclidine model of NMDA receptor hypofunction (Aim 2) in combination with behavioural tests, in vivo electrophysiology and ex vivo histological methods. Aim 1: We will study if PNNs are required for some of the neural, behavioural and cognitive functions we have shown to require prefrontal and hippocampal GABAergic inhibition11,16-19. To this end, we will use removal of PNNs in prefrontal cortex or hippocampus by local injection of the enzyme chondroitinase ABC2,3,6-8, in combination with in vivo electrophysiological measurements and behavioural testing in rats, similar to our previous studies16-19. Using ex vivo histological methods20,21, we will also examine if PNN removal disrupts GABAergic interneuron markers (including GAD67 and calcium-binding proteins parvalbumin, calbindin and calretinin). Aim 2: Using ex vivo histological methods20,21, we will characterise PNN disruption in prefrontal cortex and hippocampus of the subchronic phencyclidine model of NMDA receptor hypofunction14 and examine if PNN changes are associated with the disruption of GABAergic interneuron markers in this model. We will also correlate histological measures with cognitive and behavioural impairments in the model, as well as to the rescue of such impairments by scheduled exercise.