Presynaptic NMDA receptors facilitate short-term plasticity and BDNF release at hippocampal mossy fiber synapses
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Curated by eLife
Evaluation Summary:
This paper will be of interest to a larger neuroscience community as this is the first functional demonstration of presynaptic NMDA receptors at mossy fiber terminals in the hippocampus. NMDA receptors are generally known for being critically involved in learning & memory as coincidence detectors in Hebbian plasticity. Some studies, however, find NMDA receptors that function in more unconventional manners. The present paper provides strong evidence for the existence of such unconventional NMDA receptors at a specific subset of hippocampal mossy-fibre boutons. The combined use of electron microscopy, electrophysiological, optogenetic, calcium imaging, and genetic manipulation approaches expertly employed by the authors yields high quality compelling evidence in full support of the study's main conclusions. Overall, the investigation is well designed with a clear hypothesis, appropriate methodological considerations, and logical flow resulting in a well written manuscript that is sure to be of broad scientific interest.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #2 and Reviewer #3 agreed to share their names with the authors.)
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Abstract
Neurotransmitter release is a highly controlled process by which synapses can critically regulate information transfer within neural circuits. While presynaptic receptors – typically activated by neurotransmitters and modulated by neuromodulators – provide a powerful way of fine-tuning synaptic function, their contribution to activity-dependent changes in transmitter release remains poorly understood. Here, we report that presynaptic NMDA receptors (preNMDARs) at mossy fiber boutons in the rodent hippocampus can be activated by physiologically relevant patterns of activity and selectively enhance short-term synaptic plasticity at mossy fiber inputs onto CA3 pyramidal cells and mossy cells, but not onto inhibitory interneurons. Moreover, preNMDARs facilitate brain-derived neurotrophic factor release and contribute to presynaptic calcium rise. Taken together, our results indicate that by increasing presynaptic calcium, preNMDARs fine-tune mossy fiber neurotransmission and can control information transfer during dentate granule cell burst activity that normally occur in vivo.
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Author Response:
Reviewer #1:
In this manuscript Lituma et al. provides compelling evidence demonstrating the physiological role of presynaptic NMDA receptors at mossy fiber synapses. The existence of these receptors on the presynaptic site at this synapse was suggested more than 20 years ago based on morphological data, but their functional role was only shown in a single abstract since then (Alle, H., and Geiger, J. R. (2005)). The current manuscript uses a wide variety of complementary technical approaches to show how presynaptic NMDA receptors contribute to shaping neurotransmitter release at this synapse. They show that presynaptic NMDA receptors enhance short-term plasticity and contribute to presynaptic calcium rise in the terminal. The authors use immunocytochemistry, electrophysiology, two-photon calcium imaging, and …
Author Response:
Reviewer #1:
In this manuscript Lituma et al. provides compelling evidence demonstrating the physiological role of presynaptic NMDA receptors at mossy fiber synapses. The existence of these receptors on the presynaptic site at this synapse was suggested more than 20 years ago based on morphological data, but their functional role was only shown in a single abstract since then (Alle, H., and Geiger, J. R. (2005)). The current manuscript uses a wide variety of complementary technical approaches to show how presynaptic NMDA receptors contribute to shaping neurotransmitter release at this synapse. They show that presynaptic NMDA receptors enhance short-term plasticity and contribute to presynaptic calcium rise in the terminal. The authors use immunocytochemistry, electrophysiology, two-photon calcium imaging, and uncaging to build a very solid case to show that these receptors play a role at synaptic communication at mossy fiber synapses. The authors conclusions are supported by the experimental data provided.
The study is built on a solid and logical experimental plan, the data is high quality. However, the authors would need to provide stronger evidence to demonstrate the physiological function of these receptors. It is hard to reconcile these experimental conditions with the authors' claim in the abstract: 'Here, we report that presynaptic NMDA receptors (preNMDARs) at hippocampal mossy fiber boutons can be activated by physiologically relevant patterns of activity'. We know that extracellular calcium can have a very significant impact of neurotransmitter release and how short-term plasticity is shaped. For this reason, it would be important to explore how the activity of these receptors at more physiological calcium concentrations contribute to calcium entry and short-term plasticity at these synapses.
We thank the reviewer for noting our study is “built on a solid and logical experimental plan, the data is of high quality”. We agree with the reviewer that exploring the role of preNMDAR under more physiological conditions is extremely important. In response, we have performed new experiments at 35 ºC and at a more physiological 1.2 mM Ca+2 and 1.2 mM Mg+2 concentrations. Our new results, now included in Figure 4-figure supplement 1, demonstrate that our conclusion that preNMDARs at mossy fiber boutons can be activated by physiologically relevant patterns of activity is also true under more physiological recording conditions.
Reviewer 2:
Lituma et al. examined the presence and functions of preNMDARs in dentate gyrus granule cells (GCs) in the hippocampus. The authors found that GluN1+ preNMDARs are indeed present at mossy fiber (mf) terminals with electron microscopy. With pharmacological and genetic approaches, the authors showed that preNMDARs are important in low frequency facilitation (LFF), burst-induced facilitation and information transfer at the mf-CA3 synapse. The authors further demonstrated that this preNMDAR contribution is independent of the somatodendritic compartment of the GCs. With 2-photon calcium imaging, the authors found that preNMDARs contribute to presynaptic Ca2+ transients and can be activated by local glutamate uncaging. Separately, the authors showed that GluN1+ preNMDARs might also contribute to BDNF release at mossy fiber terminals during repetitive stimulation. Lastly, non-postsynaptic NMDARs specifically mediates mf transmission onto mossy cells, similar to mf-CA3 synapses, but not interneurons. The authors concluded that preNMDARs mediate synapse-specific transmission originating from the GCs/mf inputs.
Overall, the study provides compelling evidence from a battery of techniques, ranging from EM, pharmacology, genetic deletion, electrophysiology to 2-photon imaging/uncaging. The data supports a coherent story on the presence of preNMDARs at mf terminals and that preNMDARs play important roles in LFF.
In conclusion, this study reveals how NMDA receptors can be found in unexpected locations and how they may have unconventional functions, i.e. outside the narrow textbook view that they primarily serve as coincidence detectors in Hebbian learning. This study thus helps to change the way we think about NMDA receptor functioning, so should be of broad interest.
We appreciate the reviewer’s comments that our study provides compelling evidence for the presence and role of preNMDARs at mossy fiber terminals. We also agree with the reviewer that our study challenges the way we think about NMDA receptor function.
Reviewer #3:
In this manuscript Lituma and colleagues investigate a potential role for presynaptic NMDARs at hippocampal mossy fiber (MF) synapses in regulating synaptic transmission. The combined use of electron microscopy, electrophysiology, optogenetics, calcium imaging, and genetic manipulations expertly employed by the authors yields high quality compelling evidence that presynaptic NMDARs can participate in activity dependent short term facilitation of release onto postsynaptic CA3 pyramid and mossy cell targets but not onto inhibitory interneurons. Moreover, presynaptic NMDAR activation is demonstrated to be particularly effective in promoting BDNF release from MF boutons. The investigation is well designed with a clear hypothesis, appropriate methodological considerations, and logical flow yielding results that fully support he authors conclusions. The manuscript fills an important gap in our understanding of MF regulation by unambiguously confirming a functional role for presynaptic NMDARs that were first described anatomically at MF terminals nearly 30 years ago. Combined with a handful of other studies describing presynaptic NMDARs at various central synapses this study expands the role of NMDARs as critical players in synaptic plasticity on both sides of the cleft.
We very much appreciate the reviewer’s positive remarks of our study as “well designed with a clear hypothesis, appropriate methodological considerations, and logical flow”. We concur that the manuscript fills an important gap in understanding MF regulation by preNMDARs and expanding the role of NMDARs in synaptic plasticity on both sides of the cleft.
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Reviewer #3 (Public Review):
In this manuscript Lituma and colleagues investigate a potential role for presynaptic NMDARs at hippocampal mossy fiber (MF) synapses in regulating synaptic transmission. The combined use of electron microscopy, electrophysiology, optogenetics, calcium imaging, and genetic manipulations expertly employed by the authors yields high quality compelling evidence that presynaptic NMDARs can participate in activity dependent short term facilitation of release onto postsynaptic CA3 pyramid and mossy cell targets but not onto inhibitory interneurons. Moreover, presynaptic NMDAR activation is demonstrated to be particularly effective in promoting BDNF release from MF boutons. The investigation is well designed with a clear hypothesis, appropriate methodological considerations, and logical flow yielding results that …
Reviewer #3 (Public Review):
In this manuscript Lituma and colleagues investigate a potential role for presynaptic NMDARs at hippocampal mossy fiber (MF) synapses in regulating synaptic transmission. The combined use of electron microscopy, electrophysiology, optogenetics, calcium imaging, and genetic manipulations expertly employed by the authors yields high quality compelling evidence that presynaptic NMDARs can participate in activity dependent short term facilitation of release onto postsynaptic CA3 pyramid and mossy cell targets but not onto inhibitory interneurons. Moreover, presynaptic NMDAR activation is demonstrated to be particularly effective in promoting BDNF release from MF boutons. The investigation is well designed with a clear hypothesis, appropriate methodological considerations, and logical flow yielding results that fully support he authors conclusions. The manuscript fills an important gap in our understanding of MF regulation by unambiguously confirming a functional role for presynaptic NMDARs that were first described anatomically at MF terminals nearly 30 years ago. Combined with a handful of other studies describing presynaptic NMDARs at various central synapses this study expands the role of NMDARs as critical players in synaptic plasticity on both sides of the cleft.
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Reviewer #2 (Public Review):
Lituma et al. examined the presence and functions of preNMDARs in dentate gyrus granule cells (GCs) in the hippocampus. The authors found that GluN1+ preNMDARs are indeed present at mossy fiber (mf) terminals with electron microscopy. With pharmacological and genetic approaches, the authors showed that preNMDARs are important in low frequency facilitation (LFF), burst-induced facilitation and information transfer at the mf-CA3 synapse. The authors further demonstrated that this preNMDAR contribution is independent of the somatodendritic compartment of the GCs. With 2-photon calcium imaging, the authors found that preNMDARs contribute to presynaptic Ca2+ transients and can be activated by local glutamate uncaging. Separately, the authors showed that GluN1+ preNMDARs might also contribute to BDNF release at …
Reviewer #2 (Public Review):
Lituma et al. examined the presence and functions of preNMDARs in dentate gyrus granule cells (GCs) in the hippocampus. The authors found that GluN1+ preNMDARs are indeed present at mossy fiber (mf) terminals with electron microscopy. With pharmacological and genetic approaches, the authors showed that preNMDARs are important in low frequency facilitation (LFF), burst-induced facilitation and information transfer at the mf-CA3 synapse. The authors further demonstrated that this preNMDAR contribution is independent of the somatodendritic compartment of the GCs. With 2-photon calcium imaging, the authors found that preNMDARs contribute to presynaptic Ca2+ transients and can be activated by local glutamate uncaging. Separately, the authors showed that GluN1+ preNMDARs might also contribute to BDNF release at mossy fiber terminals during repetitive stimulation. Lastly, non-postsynaptic NMDARs specifically mediates mf transmission onto mossy cells, similar to mf-CA3 synapses, but not interneurons. The authors concluded that preNMDARs mediate synapse-specific transmission originating from the GCs/mf inputs.
Overall, the study provides compelling evidence from a battery of techniques, ranging from EM, pharmacology, genetic deletion, electrophysiology to 2-photon imaging/uncaging. The data supports a coherent story on the presence of preNMDARs at mf terminals and that preNMDARs play important roles in LFF.
In conclusion, this study reveals how NMDA receptors can be found in unexpected locations and how they may have unconventional functions, i.e. outside the narrow textbook view that they primarily serve as coincidence detectors in Hebbian learning. This study thus helps to change the way we think about NMDA receptor functioning, so should be of broad interest.
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Reviewer #1 (Public Review):
In this manuscript Lituma et al. provides compelling evidence demonstrating the physiological role of presynaptic NMDA receptors at mossy fiber synapses. The existence of these receptors on the presynaptic site at this synapse was suggested more than 20 years ago based on morphological data, but their functional role was only shown in a single abstract since then (Alle, H., and Geiger, J. R. (2005)). The current manuscript uses a wide variety of complementary technical approaches to show how presynaptic NMDA receptors contribute to shaping neurotransmitter release at this synapse. They show that presynaptic NMDA receptors enhance short-term plasticity and contribute to presynaptic calcium rise in the terminal. The authors use immunocytochemistry, electrophysiology, two-photon calcium imaging, and uncaging to …
Reviewer #1 (Public Review):
In this manuscript Lituma et al. provides compelling evidence demonstrating the physiological role of presynaptic NMDA receptors at mossy fiber synapses. The existence of these receptors on the presynaptic site at this synapse was suggested more than 20 years ago based on morphological data, but their functional role was only shown in a single abstract since then (Alle, H., and Geiger, J. R. (2005)). The current manuscript uses a wide variety of complementary technical approaches to show how presynaptic NMDA receptors contribute to shaping neurotransmitter release at this synapse. They show that presynaptic NMDA receptors enhance short-term plasticity and contribute to presynaptic calcium rise in the terminal. The authors use immunocytochemistry, electrophysiology, two-photon calcium imaging, and uncaging to build a very solid case to show that these receptors play a role at synaptic communication at mossy fiber synapses. The authors conclusions are supported by the experimental data provided.
The study is built on a solid and logical experimental plan, the data is high quality. However, the authors would need to provide stronger evidence to demonstrate the physiological function of these receptors. It is hard to reconcile these experimental conditions with the authors' claim in the abstract: 'Here, we report that presynaptic NMDA receptors (preNMDARs) at hippocampal mossy fiber boutons can be activated by physiologically relevant patterns of activity'. We know that extracellular calcium can have a very significant impact of neurotransmitter release and how short-term plasticity is shaped. For this reason, it would be important to explore how the activity of these receptors at more physiological calcium concentrations contribute to calcium entry and short-term plasticity at these synapses.
-
Evaluation Summary:
This paper will be of interest to a larger neuroscience community as this is the first functional demonstration of presynaptic NMDA receptors at mossy fiber terminals in the hippocampus. NMDA receptors are generally known for being critically involved in learning & memory as coincidence detectors in Hebbian plasticity. Some studies, however, find NMDA receptors that function in more unconventional manners. The present paper provides strong evidence for the existence of such unconventional NMDA receptors at a specific subset of hippocampal mossy-fibre boutons. The combined use of electron microscopy, electrophysiological, optogenetic, calcium imaging, and genetic manipulation approaches expertly employed by the authors yields high quality compelling evidence in full support of the study's main conclusions. Overall, …
Evaluation Summary:
This paper will be of interest to a larger neuroscience community as this is the first functional demonstration of presynaptic NMDA receptors at mossy fiber terminals in the hippocampus. NMDA receptors are generally known for being critically involved in learning & memory as coincidence detectors in Hebbian plasticity. Some studies, however, find NMDA receptors that function in more unconventional manners. The present paper provides strong evidence for the existence of such unconventional NMDA receptors at a specific subset of hippocampal mossy-fibre boutons. The combined use of electron microscopy, electrophysiological, optogenetic, calcium imaging, and genetic manipulation approaches expertly employed by the authors yields high quality compelling evidence in full support of the study's main conclusions. Overall, the investigation is well designed with a clear hypothesis, appropriate methodological considerations, and logical flow resulting in a well written manuscript that is sure to be of broad scientific interest.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #2 and Reviewer #3 agreed to share their names with the authors.)
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