谷氨酸是大脑中主要的兴奋性神经递质,在生理和病理神经元功能中起着至关重要的作用。在哺乳动物中,在缺氧条件下,谷氨酸会引起有害的兴奋毒性作用。相比之下,Trachemysscripta,淡水龟,是最耐缺氧的动物之一,能够在没有氧气的情况下存活几个月。因此,已经研究了海龟,以评估它们在缺氧条件下使用的神经保护策略的分子机制,比如保持低水平的谷氨酸,增加腺苷和GABA,上调热休克蛋白,并下调KATP通道。这些海龟脑的缺氧耐受机制可用于寻找人类谷氨酸能神经系统疾病的治疗剂,例如由于缺血引起的脑损伤或脑中风。尽管谷氨酸作为神经递质和乌龟作为理想的研究模型的重要性,乌龟大脑中的谷氨酸能回路仍未被描述,而在哺乳动物和鸟类大脑中对它们进行了充分的研究。在爬行动物中,特别是在乌龟的大脑中,已经通过检查囊泡谷氨酸转运蛋白(VGLUTs)的表达来鉴定谷氨酸能神经元。在大脑的某些区域,一些离子型谷氨酸受体(GluRs)已经进行了免疫组织化学研究,暗示有谷氨酸能目标区域。根据文献中提供的这些谷氨酸相关分子的表达模式和乌龟大脑的纤维连接数据,可以澄清许多候选谷氨酸能回路,比如嗅觉电路,海马-间隔通路,皮质纹状体通路,视觉通路,听觉通路,和颗粒细胞-浦肯野细胞途径。这篇综述总结了龟脑皮层中可能的谷氨酸能途径和谷氨酸能神经元的分布,并将其与鸟类和哺乳动物的大脑进行了比较。谷氨酸能途径的综合知识是乌龟大脑进一步功能研究的基础,这将提供对不同物种谷氨酸调节的生理和病理机制以及神经回路的见解。
Glutamate acts as the main excitatory neurotransmitter in the brain and plays a vital role in physiological and pathological neuronal functions. In mammals, glutamate can cause detrimental excitotoxic effects under anoxic conditions. In contrast, Trachemys scripta, a freshwater turtle, is one of the most anoxia-tolerant animals, being able to survive up to months without oxygen. Therefore, turtles have been investigated to assess the molecular mechanisms of neuroprotective strategies used by them in anoxic conditions, such as maintaining low levels of glutamate, increasing adenosine and GABA, upregulating heat shock proteins, and downregulating K ATP channels. These mechanisms of anoxia tolerance of the turtle brain may be applied to finding therapeutics for human glutamatergic neurological disorders such as brain injury or cerebral stroke due to ischemia. Despite the importance of glutamate as a neurotransmitter and of the turtle as an ideal research model, the glutamatergic circuits in the turtle brain remain less described whereas they have been well studied in mammalian and avian brains. In reptiles, particularly in the turtle brain, glutamatergic neurons have been identified by examining the expression of vesicular glutamate transporters (VGLUTs). In certain areas of the brain, some ionotropic glutamate receptors (GluRs) have been immunohistochemically studied, implying that there are glutamatergic target areas. Based on the expression patterns of these glutamate-related molecules and fiber connection data of the turtle brain that is available in the literature, many candidate glutamatergic circuits could be clarified, such as the olfactory circuit, hippocampal-septal pathway, corticostriatal pathway, visual pathway, auditory pathway, and granule cell-Purkinje cell pathway. This review summarizes the probable glutamatergic pathways and the distribution of glutamatergic neurons in the pallium of the turtle brain and compares them with those of avian and mammalian brains. The integrated knowledge of glutamatergic pathways serves as the fundamental basis for further functional studies in the turtle brain, which would provide insights on physiological and pathological mechanisms of glutamate regulation as well as neural circuits in different species.