Toth K, Suares G, Lawrence J J, Philips-Tansey E, McBain C J
Laboratory of Cellular and Molecular Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4495, USA.
J Neurosci. 2000 Nov 15;20(22):8279-89. doi: 10.1523/JNEUROSCI.20-22-08279.2000.
The axons of the dentate gyrus granule cells, the so-called mossy fibers, innervate their inhibitory interneuron and pyramidal neuron targets via both anatomically and functionally specialized synapses. Mossy fiber synapses onto inhibitory interneurons were comprised of either calcium-permeable (CP) or calcium-impermeable (CI) AMPA receptors, whereas only calcium-impermeable AMPA receptors existed at CA3 principal neuron synapses. In response to brief trains of high-frequency stimuli (20 Hz), pyramidal neuron synapses invariably demonstrated short-term facilitation, whereas interneuron EPSCs demonstrated either short-term facilitation or depression. Facilitation at all CI AMPA synapses was voltage independent, whereas EPSCs at CP AMPA synapses showed greater facilitation at -20 than at -80 mV, consistent with a role for the postsynaptic unblock of polyamines. At pyramidal cell synapses, mossy fiber EPSCs possessed marked frequency-dependent facilitation (commencing at stimulation frequencies >0.1 Hz), whereas EPSCs at either type of interneuron synapse showed only moderate frequency-dependent facilitation or underwent depression. Presynaptic metabotropic glutamate receptors (mGluRs) decreased transmission at all three synapse types in a frequency-dependent manner. However, after block of presynaptic mGluRs, transmission at interneuron synapses still did not match the dynamic range of EPSCs at pyramidal neuron synapses. High-frequency stimulation of mossy fibers induced long-term potentiation (LTP), long-term depression (LTD), or no change at pyramidal neuron synapses, interneuron CP AMPA synapses, and CI AMPA synapses, respectively. Induction of LTP or LTD altered the short-term plasticity of transmission onto both pyramidal cells and interneuron CP AMPA synapses by a mechanism consistent with changes in release probability. These data reveal differential mechanisms of transmission at three classes of mossy fiber synapse made onto distinct targets.
齿状回颗粒细胞的轴突，即所谓的苔藓纤维，通过解剖学和功能上专门化的突触支配其抑制性中间神经元和锥体神经元靶点。苔藓纤维与抑制性中间神经元的突触由钙通透性（CP）或钙非通透性（CI）AMPA受体组成，而在CA3主神经元突触处仅存在钙非通透性AMPA受体。在对短串高频刺激（20 Hz）的反应中，锥体神经元突触总是表现出短期易化，而中间神经元的兴奋性突触后电流（EPSC）则表现出短期易化或抑制。所有CI AMPA突触处的易化与电压无关，而CP AMPA突触处的EPSC在-20 mV时比在-80 mV时表现出更大的易化，这与多胺的突触后去阻断作用一致。在锥体细胞突触处，苔藓纤维EPSC具有明显的频率依赖性易化（在刺激频率>0.1 Hz时开始），而在任何一种类型的中间神经元突触处，EPSC仅表现出中等程度的频率依赖性易化或发生抑制。突触前代谢型谷氨酸受体（mGluR）以频率依赖性方式降低所有三种突触类型的传递。然而，在阻断突触前mGluR后，中间神经元突触处的传递仍与锥体神经元突触处EPSC的动态范围不匹配。苔藓纤维的高频刺激分别在锥体神经元突触、中间神经元CP AMPA突触和CI AMPA突触处诱导长时程增强（LTP）、长时程抑制（LTD）或无变化。LTP或LTD的诱导通过与释放概率变化一致的机制改变了向锥体细胞和中间神经元CP AMPA突触传递的短期可塑性。这些数据揭示了在投射到不同靶点的三类苔藓纤维突触处传递的不同机制。
