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| Untersuchte Arbeit: Seite: 19, Zeilen: 7-23 |
Quelle: Sajikumar 2005 Seite(n): 19, Zeilen: 3-22 |
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| 1.5.1. Multiple Phases of LTP and LTD
Brief high-frequency stimulation of the CA3-CA1 synapses can result in LTP, which can be divided into several temporal phases characterized by different underlying mechanisms. In general, it is divided into induction, expression and maintenance. The initial induction phase of LTP i.e. so named ‘posttetanic potentiation’ (PTP) with a duration of several seconds to minutes is characterized by presynaptic mechanisms, i.e. transient increase in transmitter release. PTP is followed by a ‘short-term potentiation’ (STP) with a duration up to one hour. Postsynaptic events like activation of transmitter receptors by local protein kinases (e.g. CaMKII, tyrosine kinase) (Dobrunz et al., 1997;Huang, 1998) are responsible for the maintenance of that phase. STP can be followed by at least two further phases: early-and late-LTP (Matthies et al., 1990;Huang, 1998). Early-LTP is a transient form of LTP which lasts 2-3 h in vitro and 7-8 h in vivo, while late-LTP lasts for 8-10 h in vitro and days or even months in intact animals (Abraham and Bear, 1996;Abraham, 2003) (Fig. 2). The different forms of LTP can be specifically induced by distinct stimulus protocols in acute slices in vitro (Frey et al., 1993;Huang and Kandel, 1994). A single high-frequency stimulus train of distinct stimulation strength can induce early-LTP, but [such a protocol is normally not sufficient to induce late-LTP.] 1. Abraham WC (2003) How long will long-term potentiation last? Philos Trans R Soc Lond B Biol Sci 358: 735-744. 2. Abraham WC, Bear MF (1996) Metaplasticity: the plasticity of synaptic plasticity. Trends Neurosci 19: 126-130. 40. Dobrunz LE, Huang EP, Stevens CF (1997) Very short-term plasticity in hippocampal synapses. Proc Natl Acad Sci U S A 94: 14843-14847. 54. Frey U, Huang YY, Kandel ER (1993) Effects of cAMP simulate a late stage of LTP in hippocampal CA1 neurons. Science 260: 1661-1664. 71. Huang EP (1998) Synaptic plasticity: going through phases with LTP. Curr Biol 8: R350-R352. 72. Huang YY, Kandel ER (1994) Recruitment of long-lasting and protein kinase A-dependent long-term potentiation in the CA1 region of hippocampus requires repeated tetanization. Learn Mem 1: 74-82. 103. Matthies H, Frey U, Reymann K, Krug M, Jork R, Schroeder H (1990) Different mechanisms and multiple stages of LTP. Adv Exp Med Biol 268:359-68.: 359-368. |
1.3. Temporal phases of LTP and LTD
Brief high-frequency stimulation of the the [sic] CA3-CA1 synapses can result in LTP, which can be divided into several temporal phases characterized by different underlying mechanisms. In general, it is divided into induction, expression and maintenance. The initial induction phase of LTP i.e. so named ‘posttetanic potentiation’ (PTP) with a duration of several seconds to minutes is characterized by presynaptic mechanisms, i.e. transient increase in transmitter release (Huang, 1998;Dobrunz et al., 1997). PTP is followed by a ‘short-term potentiation’ (STP) with a duration up to one hour. Postsynaptic events like activation of receptors by local protein kinases (e.g. CaMKII, tyrosine kinase) (Huang, 1998;Dobrunz et al., 1997) are responsible for the maintenance of that phase. STP can be followed by at least two further phases: early-and late-LTP (Matthies et al., 1990;Huang, 1998). Early-LTP is a transient form of LTP which lasts 3-4 h in vitro and 7-8 h in vivo, while late-LTP lasts for 8-10 h in vitro and days or even months in intact animals The different forms of LTP can be specifically induced by distinct stimulus protocols in acute slices in vitro (Frey et al., 1993;Huang and Kandel, 1994). A single high-frequency stimulus train of distinct stimulation strength can induce early-LTP that lasts for up to 3-4 h, but such a protocol is normally not sufficient to induce late-LTP. Dobrunz LE, Huang EP, Stevens CF (1997) Very short-term plasticity in hippocampal synapses. Proc Natl Acad Sci U S A 94: 14843-14847. Frey U, Huang YY, Kandel ER (1993) Effects of cAMP simulate a late stage of LTP in hippocampal CA1 neurons. Science 260: 1661-1664. Huang EP (1998) Synaptic plasticity: going through phases with LTP. Curr Biol 8: R350-R352. Huang YY, Kandel ER (1994) Recruitment of long-lasting and protein kinase A-dependent long-term potentiation in the CA1 region of hippocampus requires repeated tetanization. Learn Mem 1: 74-82. Matthies H, Frey U, Reymann K, Krug M, Jork R, Schroeder H (1990) Different mechanisms and multiple stages of LTP. Adv Exp Med Biol 268:359-68.: 359-368. |
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