Szabadics János, Soltesz Ivan
Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, California 92697-1280, USA.
J Neurosci. 2009 Apr 1;29(13):4239-51. doi: 10.1523/JNEUROSCI.5390-08.2009.
One million mossy fibers in the rat provide individually sparse but functionally important synaptic connections between the dentate gyrus and hippocampus. Although the majority of mossy fiber targets are GABAergic cells, the functional organization of the feedforward GABAergic machinery modulating the interactions of granule cells and CA3 pyramidal cells are not yet understood. We used mossy fiber bouton to GABA neuron paired recordings in the CA3 to demonstrate that mossy fibers provide cell type-specific innervation to distinct GABAergic neurons with specialized intra- and extrahippocampal outputs. Our results show that mossy fibers contact the perisomatically projecting fast-spiking and regular-spiking basket cells, in addition to the dendritically projecting ivy cells, and the septum-projecting spiny stratum lucidum cells. Monosynaptic mossy fiber inputs to fast-spiking basket cells and spiny stratum lucidum cells were found to be numerous, but they were small in amplitude and displayed low transmission probabilities. In contrast, regular-spiking basket cells and ivy cells were less likely to be innervated by mossy fibers, but the amplitudes of mossy fiber EPSCs were large and the transmission probabilities were high. The dependence of the numbers and strengths of the mossy fiber inputs to CA3 GABAergic cells on the postsynaptic cell type was correlated with the frequency of the background synaptic events, so that cells with weak but numerous mossy fiber inputs received high rates of spontaneous synaptic events. Together, these results reveal the diverse components and high degree of functional specificity of the GABAergic cellular machinery underlying the dentate gyrus-CA3 interface.
大鼠体内的一百万个苔藓纤维在齿状回和海马体之间提供了各自稀疏但功能重要的突触连接。尽管大多数苔藓纤维的靶点是γ-氨基丁酸能（GABAergic）细胞，但调节颗粒细胞和CA3锥体细胞相互作用的前馈GABA能机制的功能组织仍不清楚。我们在CA3区使用苔藓纤维终扣与GABA神经元配对记录，以证明苔藓纤维为具有特殊海马内和海马外输出的不同GABA能神经元提供细胞类型特异性支配。我们的结果表明，苔藓纤维除了接触树突投射的常春藤细胞和投射到隔膜的透明层棘状细胞外，还接触胞体周围投射的快速放电和规则放电的篮状细胞。发现苔藓纤维对快速放电篮状细胞和透明层棘状细胞的单突触输入数量众多，但幅度较小且传递概率较低。相比之下，规则放电篮状细胞和常春藤细胞受苔藓纤维支配的可能性较小，但苔藓纤维兴奋性突触后电流（EPSCs）的幅度较大且传递概率较高。苔藓纤维对CA3区GABA能细胞输入的数量和强度对突触后细胞类型的依赖性与背景突触事件的频率相关，因此具有微弱但大量苔藓纤维输入的细胞会接收到高频率的自发突触事件。总之，这些结果揭示了齿状回-CA3界面下GABA能细胞机制的多种成分和高度的功能特异性。
