Department of Pharmacology, UCL School of Pharmacy London, UK.
Front Neural Circuits. 2013 Jan 9;6:112. doi: 10.3389/fncir.2012.00112. eCollection 2012.
Dentate granule cells process information from the enthorinal cortex en route to the hippocampus proper. These neurons have a very negative resting membrane potential and are relatively silent in the slice preparation. They are also subject to strong feed-forward inhibition. Their unmyelinated axon or mossy fiber ramifies extensively in the hilus and projects to stratum lucidum where it makes giant en-passant boutons with CA3 pyramidal neurons. There is compelling evidence that mossy fiber boutons express presynaptic GABA(A) receptors, which are commonly found in granule cell dendrites. There is also suggestive evidence for the presence of other ionotropic receptors, including glycine, NMDA, and kainate receptors, in mossy fiber boutons. These presynaptic receptors have been proposed to lead to mossy fiber membrane depolarization. How this phenomenon alters the excitability of synaptic boutons, the shape of presynaptic action potentials, Ca(2+) influx and neurotransmitter release has remained elusive, but high-resolution live imaging of individual varicosities and direct patch-clamp recordings have begun to shed light on these phenomena. Presynaptic GABA(A) and kainate receptors have also been reported to facilitate the induction of long-term potentiation at mossy fiber-CA3 synapses. Although mossy fibers are highly specialized, some of the principles emerging at this connection may apply elsewhere in the CNS.
颗粒细胞的树突从内嗅皮层接收信息，然后将信息传递到海马体。这些神经元具有非常负的静息膜电位，在切片制备中相对沉默。它们还受到强烈的前馈抑制。它们的无髓轴突或苔藓纤维在门区广泛分枝，并投射到层状亮区，在那里与 CA3 锥体神经元形成巨大的经路性接触。有确凿的证据表明苔藓纤维末梢表达突触前 GABA(A)受体，这些受体通常存在于颗粒细胞树突中。也有迹象表明存在其他离子型受体，包括甘氨酸、NMDA 和海人酸受体，在苔藓纤维末梢。这些突触前受体被认为导致苔藓纤维膜去极化。这种现象如何改变突触末梢的兴奋性、突触前动作电位的形状、Ca(2+)内流和神经递质释放仍然难以捉摸，但对单个囊泡的高分辨率实时成像和直接膜片钳记录已开始揭示这些现象。也有报道称，突触前 GABA(A)和海人酸受体可促进苔藓纤维-CA3 突触的长时程增强诱导。尽管苔藓纤维具有高度特异性，但在这个连接中出现的一些原则可能适用于中枢神经系统的其他部位。
