The granule cells of the dentate gyrus (DG), origin of the mossy fibers (MFs), have been considered to be glutamatergic. However, data obtained with different experimental approaches in recent years may be calling for a redefinition of their phenotype. Although they indeed release glutamate for fast neurotransmission, immunohistological and molecular biology evidence has revealed that these glutamatergic cells also express GABAergic markers. The granule cell expression of a GABAergic phenotype is developmentally regulated. Electrophysiological studies reveal that during the first 3 weeks of age, mossy fiber stimulation provokes monosynaptic fast inhibitory transmission mediated by GABA, besides the monosynaptic excitatory glutamatergic transmission, onto their targets in CA3. After this age, mossy fiber GABAergic transmission abruptly disappears and the GABAergic markers are undetected. In the adult, the GABAergic markers are upregulated and GABA-mediated transmission emerges after induction of hyperexcitability. The simultaneous glutamate- and GABA-mediated signals share the same plastic and pharmacological characteristics that correspond to neurotransmission of mossy fiber origin. This intriguing evidence gives rise to two fundamental points of discussion. The first is the plausible fact that glutamate and GABA, two neurotransmitters of opposing actions, are coreleased from the mossy fibers. The second relates to its functional implications that can be immediately inferred, as the dentate gyrus can exert direct GABA-mediated excitatory actions early in life and inhibitory actions in young and adult hippocampus. This evidence poses the need to reevaluate and reinterpret some aspects of the physiology of the mossy fiber pathway under normal and pathological conditions. This work reviews the recent evidence that supports the assumption that glutamate and GABA can be coreleased from a single pathway, the mossy fibers, and makes some considerations about its functional implications.

中文翻译：

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齿状回的“谷氨酸能”颗粒细胞的GABA能表型。

苔藓纤维（MFs）起源的齿状回（DG）的颗粒细胞被认为是谷氨酸能的。然而，近年来通过不同实验方法获得的数据可能要求重新定义其表型。尽管它们确实释放谷氨酸以快速传递神经，但免疫组织学和分子生物学证据表明，这些谷氨酸能细胞也表达GABA能标记。GABA能表型的颗粒细胞表达受到发育调节。电生理研究表明，在最初的3周内，苔藓纤维刺激除了由单突触兴奋性谷氨酸能传递外，还由GABA介导了单突触快速抑制传递到其在CA3中的靶标上。这个年龄以后 苔藓纤维的GABA能传递突然消失，并且未检测到GABA能标志。在成年人中，诱导过度兴奋后，GABA能标记被上调，并出现GABA介导的传递。同时发生的谷氨酸和GABA介导的信号具有相同的塑性和药理学特征，与苔藓纤维起源的神经传递相对应。有趣的证据引起了两个基本的讨论点。首先是可能的事实，即苔藓纤维中共释放出两种相反作用的神经递质谷氨酸和GABA。第二个原因是可以立即推断出其功能含义，因为齿状回可以在生命早期发挥直接的GABA介导的兴奋作用，并在年轻和成年海马中起抑制作用。该证据提出需要重新评估和重新解释正常和病理条件下苔藓纤维途径的某些生理生理学方面。这项工作回顾了最近的证据，这些证据支持谷氨酸和GABA可以从一条路径（苔藓纤维）中共释放的假设，并对它的功能含义进行了一些考虑。