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The Journal of Neuroscience, December 12, 2007, 27(50):13603-13613; doi:10.1523/JNEUROSCI.3985-07.2007

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Cellular/Molecular
Target Cell-Specific Involvement of Presynaptic Mitochondria in Post-Tetanic Potentiation at Hippocampal Mossy Fiber Synapses

Doyun Lee, Kyu-Hee Lee, Won-Kyung Ho, and Suk-Ho Lee

National Research Laboratory for Cell Physiology, Department of Physiology, Seoul National University College of Medicine and Neuroscience Research Institute, Seoul National University Medical Research Center, Seoul 110-799, Korea

Correspondence should be addressed to Dr. Suk-Ho Lee, Department of Physiology, Seoul National University College of Medicine, Chongno-Ku, Yongon-Dong 28, Seoul 110-799, Korea. Email: leesukho{at}snu.ac.kr

Previous studies indicate that boutons from the same axon exhibit distinct Ca²⁺ dynamics depending on the postsynaptic targets. Mossy fibers of hippocampal granule cells innervate synaptic targets via morphologically distinct boutons. We investigated mitochondrial involvement in the generation of post-tetanic residual Ca²⁺ (Ca_res) at large and small en passant mossy fiber boutons (MFBs). Mitochondria limited the [Ca²⁺]_i build-up during high-frequency stimulation (HFS) at large MFBs, but not at small MFBs. The amount of Ca_res, quantified as a time integral of residual [Ca²⁺]_i, was significantly larger at large MFBs than at small MFBs, and that at large MFBs was substantially attenuated by inhibitors of mitochondrial Ca²⁺ uniporter and mitochondrial Na⁺/Ca²⁺ exchanger (mitoNCX). In contrast, blockers of mitoNCX had no effect on the Ca_res at small MFBs. Post-tetanic Ca_res has been proposed as a mechanism for post-tetanic potentiation (PTP). We examined mitochondrial involvement in PTP at mossy fiber synapses on hilar mossy cells (MFMC synapse) and on hilar interneurons (MFHI synapse), which are presumably innervated via large and small MFBs, respectively. Consistent with the differential contribution of mitochondria to Ca_res at large and small MFBs, mitoNCX blockers significantly reduced the PTP at the MFMC synapse, but not at the MFHI synapse. In contrast, protein kinase C (PKC) inhibitors significantly reduced the PTP at MFHI synapse, but not at the MFMC synapse. These results indicate that mitochondria- and PKC-dependent PTP are expressed at distinct hilar mossy fiber synapses depending on postsynaptic targets.

Key words: post-tetanic potentiation; residual calcium; mitochondria; hippocampal mossy fiber; hilar mossy cell; hilar interneuron

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Received Feb. 10, 2007; revised Oct. 12, 2007; accepted Oct. 22, 2007.

Correspondence should be addressed to Dr. Suk-Ho Lee, Department of Physiology, Seoul National University College of Medicine, Chongno-Ku, Yongon-Dong 28, Seoul 110-799, Korea. Email: leesukho{at}snu.ac.kr

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				J. S. Lee, M.-H. Kim, W.-K. Ho, and S.-H. Lee Presynaptic Release Probability and Readily Releasable Pool Size Are Regulated by Two Independent Mechanisms during Posttetanic Potentiation at the Calyx of Held Synapse J. Neurosci., August 6, 2008; 28(32): 7945 - 7953. [Abstract] [Full Text] [PDF]

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