Perineuronal nets in cognition and behaviour

神经元周网（PNN）是哺乳动物中枢神经系统中神经元周围的细胞外基质结构1。PNN已被牵连在关键发育期之外限制神经元可塑性，并且在某些脑区域中，成年期PNN去除促进神经元可塑性和相关的记忆功能1 -3。另一方面，几个脑区的PNN中断导致一些神经精神疾病，包括精神分裂症1，4，5，啮齿动物选定脑区的PNN去除也会损害一些认知和行为功能6-8。在新皮层和海马中，PNN主要围绕GABA能抑制性中间神经元，并参与GABA能抑制的维持和调节，表明PNN破坏可能会破坏GABA能抑制1，3，4，9，10。这具有临床相关性，因为受损的GABA能抑制（包括前额叶皮层和海马）是精神分裂症的关键特征，并且这些脑区中GABA能抑制的破坏（所谓的神经去抑制）会导致大鼠临床相关的认知和行为缺陷11。然而，它在很大程度上仍有待研究，如果PNN破坏前额叶皮层和海马神经抑制引起类似的赤字。此外，许多基于精神分裂症病理生理学中涉及的因素（包括NMDA受体功能减退）的啮齿动物模型显示PNN和GABA能中间神经元的破坏，特别是在前额叶皮层和海马中6，12-15。然而，尽管涉及亚慢性注射NMDA受体拮抗剂苯环利定的NMDA受体功能减退模型广泛用于基础和药物发现研究14，但该模型中的PNN破坏尚未表征;此外，NMDA受体功能减退、PNN和GABA能中间神经元破坏以及临床相关认知和行为障碍之间的关系在很大程度上仍有待确定。目的和研究-学生将研究前额叶皮层和海马中的PNN如何有助于大鼠的认知和行为。该项目将结合行为测试、体内电生理学和离体组织学方法，使用PNN的脑部位特异性操作（目标1）和NMDA受体功能减退的亚慢性苯环利定模型（目标2）。目标1：我们将研究PNN是否需要一些神经，行为和认知功能，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ABC 2，3，6-8去除前额叶皮质或海马中的PNN，并结合大鼠体内电生理测量和行为测试，类似于我们之前的研究16 -19。使用离体组织学方法20，21，我们还将检查PNN去除是否破坏GABA能中间神经元标记物（包括GAD 67和钙结合蛋白小清蛋白、钙结合蛋白和钙视网膜蛋白）。目标二：使用离体组织学方法20，21，我们将观察NMDA受体功能减退的亚慢性苯环利定模型14的前额叶皮层和海马中的PNN破坏，并检查PNN变化是否与该模型中GABA能中间神经元标记物的破坏相关。我们还将组织学测量与模型中的认知和行为障碍相关联，以及通过定期运动来挽救这种障碍。

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.