Minami Akira, Sakurada Naomi, Fuke Sayuri, Kikuchi Kazuya, Nagano Tetsuo, Oku Naoto, Takeda Atsushi
Department of Medical Biochemistry, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
J Neurosci Res. 2006 Jan;83(1):167-76. doi: 10.1002/jnr.20714.
Zinc exists in high densities in the giant boutons of hippocampal mossy fibers. On the basis of the evidence that zinc decreases extracellular glutamate concentration in the hippocampus, the presynaptic action of zinc released from mossy fibers during high-frequency (tetanic) stimulation was examined using hippocampal slices. The increase in zinc-specific fluorescent signals was observed in both extracellular and intracellular compartments in the mossy fiber terminals during the delivery of tetanic stimuli (100 Hz, 1 sec) to the dentate granule cell layer, suggesting that zinc released from mossy fibers is immediately retaken up by mossy fibers. When mossy fiber terminals were preferentially double-stained with zinc and calcium indicators and tetanic stimuli (100 Hz, 1 sec) were delivered to the dentate granule cell layer, the increase in calcium orange signal during the stimulation was enhanced in mossy fiber terminals by addition of CaEDTA, a membrane-impermeable zinc chelator, and was suppressed by addition of zinc. The decrease in FM4-64 signal (vesicular exocytosis) during tetanic stimulation (10 Hz, 180 sec), which induced mossy fiber long-term potentiation, was also enhanced in mossy fiber terminals by addition of CaEDTA and was suppressed by addition of zinc. The present study demonstrates that zinc released from mossy fibers may be a negative-feedback factor against presynaptic activity during tetanic stimulation.
锌以高密度存在于海马苔藓纤维的巨大终扣中。基于锌可降低海马细胞外谷氨酸浓度这一证据，利用海马脑片研究了高频（强直）刺激期间从苔藓纤维释放的锌的突触前作用。当向齿状颗粒细胞层施加强直刺激（100Hz，1秒）时，在苔藓纤维终末的细胞外和细胞内区室均观察到锌特异性荧光信号增加，这表明从苔藓纤维释放的锌会立即被苔藓纤维重新摄取。当用锌和钙指示剂对苔藓纤维终末进行优先双重染色，并向齿状颗粒细胞层施加强直刺激（100Hz，1秒）时，通过添加膜不可渗透的锌螯合剂CaEDTA，刺激期间苔藓纤维终末中钙橙信号的增加增强，而添加锌则可抑制该增加。在诱导苔藓纤维长时程增强的强直刺激（10Hz，180秒）期间，FM4-64信号（囊泡胞吐作用）的降低在苔藓纤维终末中也因添加CaEDTA而增强，并因添加锌而受到抑制。本研究表明，从苔藓纤维释放的锌可能是强直刺激期间对突触前活动的一种负反馈因子。
