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Impairment of hippocampal mossy fiber LTD in mice lacking mGluR2
M Yokoi1, K Kobayashi, T Manabe
1Department of Biological Sciences, Kyoto University Faculty of Medicine, Kyoto 606, Japan.
Abstract:
Subtype 2 of the metabotropic glutamate receptor (mGluR2) is expressed in the presynaptic elements of hippocampal mossy fiber-CA3 synapses. Knockout mice deficient in mGluR2 showed no histological changes and no alterations in basal synaptic transmission, paired-pulse facilitation, or tetanus-induced long-term potentiation (LTP) at the mossy fiber-CA3 synapses. Long-term depression (LTD) induced by low-frequency stimulation, however, was almost fully abolished. The mutant mice performed normally in water maze learning tasks. Thus, the presynaptic mGluR2 is essential for inducing LTD at the mossy fiber-CA3 synapses, but this hippocampal LTD does not seem to be required for spatial learning.
Insights
Presynaptic metabotropic glutamate receptor 2 (mGluR2) is crucial for hippocampal long-term depression (LTD) at mossy fiber-CA3 synapses. However, this LTD is not essential for spatial learning in mice.
Area of Science:
- Neuroscience
- Synaptic Plasticity
- Molecular Biology
Background:
- Metabotropic glutamate receptor 2 (mGluR2) is localized to presynaptic terminals of hippocampal mossy fiber-CA3 synapses.
- Understanding the precise role of presynaptic mGluR2 in synaptic function and learning is essential.
Purpose of the Study:
- To investigate the role of presynaptic mGluR2 in synaptic plasticity at the hippocampal mossy fiber-CA3 synapses.
- To determine the necessity of mGluR2-dependent long-term depression (LTD) for spatial learning.
Main Methods:
- Utilized mGluR2 knockout mice.
- Electrophysiological recordings were performed to assess basal synaptic transmission, paired-pulse facilitation, long-term potentiation (LTP), and LTD at mossy fiber-CA3 synapses.
- Spatial learning was evaluated using water maze tasks.
Main Results:
- mGluR2 deficiency did not affect histology, basal synaptic transmission, paired-pulse facilitation, or LTP.
- Low-frequency stimulation-induced LTD at mossy fiber-CA3 synapses was significantly impaired in mGluR2 knockout mice.
- Mutant mice exhibited normal performance in water maze learning tasks.
Conclusions:
- Presynaptic mGluR2 is indispensable for the induction of LTD at hippocampal mossy fiber-CA3 synapses.
- Hippocampal LTD mediated by mGluR2 is not required for successful spatial learning.