Rapid recruitment NMDA receptor transport packets to nascent synapses

Center for Neuroscience, University of California Davis, 1544 Newton Ct., Davis, California 95616, USA.
Nature Neuroscience (Impact Factor: 16.1). 09/2002; 5(8):751-9. DOI: 10.1038/nn883
Source: PubMed


Although many of the molecules involved in synaptogenesis have been identified, the sequence and kinetics of synapse assembly in the central nervous system (CNS) remain largely unknown. We used simultaneous time-lapse imaging of fluorescent glutamate receptor subunits and presynaptic proteins in rat cortical neurons in vitro to determine the dynamics and time course of N-methyl-D-aspartate receptor (NMDAR) recruitment to nascent synapses. We found that both NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunits are present in mobile transport packets in neurons before and during synaptogenesis. NMDAR transport packets are more mobile than AMPAR subunits, moving along microtubules at about 4 microm/min, and are recruited to sites of axodendritic contact within minutes. Whereas NMDAR recruitment to new synapses can be either concurrent with or independent of the protein PSD-95, AMPARs are recruited with a slower time course. Thus, glutamatergic synapses can form rapidly by the sequential delivery of modular transport packets containing glutamate receptors.

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Available from: A. Kimberley Mcallister, Oct 06, 2015
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    • "Trafficking of NMDAR puncta in axons and dendrites was also distinct . In axons , approximately one quarter of the NR1 – GFP puncta were mobile , moving at a mean velocity of 0 . 23 mm / s . In dendrites , a previous study found that a third of dendritic NR1 – GFP clusters are mobile , moving at a mean velocity of 0 . 07 mm / s ( Washbourne et al . , 2002 ) , although another study failed to detect mobile dendritic NR1 – GFP puncta ( Bresler et al . , 2004 ) . Most NR2A and NR2B clusters are mobile within developing dendrites ( Yin et al . , 2012 ; Yin et al . , 2011 ) . However , dendritic NR2A and NR2B move anterogradely at , 0 . 7 – 0 . 8 mm / s ( Yin et al . , 2012 ; Yin et al . , 20"
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    ABSTRACT: During cortical development, NMDA receptors (NMDARs) facilitate presynaptic terminal formation, enhance neurotransmitter release, and are required in presynaptic neurons for spike timing-dependent LTD. However, the extent to which NMDARs are found within cortical presynaptic terminals has remained controversial, and the sub-synaptic localization and dynamics of axonal NMDARs are unknown. Here, using live confocal imaging and biochemical purification of presynaptic membranes, we provide strong evidence that NMDARs localize to presynaptic terminals in vitro and in vivo, in a developmentally regulated manner. NR1 and NR2B subunits are found within the active zone membrane, where they could respond to synaptic glutamate release. Surprisingly, NR1 also appears in glutamatergic and GABAergic synaptic vesicles. During synaptogenesis, NR1 is mobile throughout axons - including growth cones and filopodia, structures that are involved in synaptogenesis. Upon synaptogenic contact, NMDA receptors are quickly recruited to terminals by neuroligin-1/neurexin signaling. Unlike dendrites, the trafficking and distribution of axonal NR1 are insensitive to activity changes, including NMDA exposure, local glutamate uncaging or action potential blockade. These results support the idea that presynaptic NMDARs play an early role in presynaptic development.
    Journal of Cell Science 12/2014; 128(4). DOI:10.1242/jcs.162362 · 5.43 Impact Factor
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    • "Primary neuronal cultures were prepared from rat or mouse cortices on 18 mm glass coverslips as described previously [38,41,98,99] and maintained in Neurobasal A media with B27 Supplement (Invitrogen, Carlsbad, CA, USA). At 6 to 9 days in vitro (DIV) and 24 to 48 hours prior to imaging, neurons were transfected using Lipofectamine 2000, essentially according to the manufacturer’s instructions (Invitrogen, Carlsbad, CA, USA). "
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    ABSTRACT: Background Synapse formation occurs when synaptogenic signals trigger coordinated development of pre and postsynaptic structures. One of the best-characterized synaptogenic signals is trans-synaptic adhesion. However, it remains unclear how synaptic proteins are recruited to sites of adhesion. In particular, it is unknown whether synaptogenic signals attract synaptic vesicle (SV) and active zone (AZ) proteins to nascent synapses or instead predominantly function to create sites that are capable of forming synapses. It is also unclear how labile synaptic proteins are at developing synapses after their initial recruitment. To address these issues, we used long-term, live confocal imaging of presynaptic terminal formation in cultured cortical neurons after contact with the synaptogenic postsynaptic adhesion proteins neuroligin-1 or SynCAM-1. Results Surprisingly, we find that trans-synaptic adhesion does not attract SV or AZ proteins nor alter their transport. In addition, although neurexin (the presynaptic partner of neuroligin) typically accumulates over the entire region of contact between axons and neuroligin-1-expressing cells, SV proteins selectively assemble at spots of enhanced neurexin clustering. The arrival and maintenance of SV proteins at these sites is highly variable over the course of minutes to hours, and this variability correlates with neurexin levels at individual synapses. Conclusions Together, our data support a model of synaptogenesis where presynaptic proteins are trapped at specific axonal sites, where they are stabilized by trans-synaptic adhesion signaling.
    Neural Development 05/2014; 9(1):13. DOI:10.1186/1749-8104-9-13 · 3.45 Impact Factor
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    • "It has been proposed that sAβ exert their neurotoxicity through interaction with NMDAR via a postsynaptic site [45], [46]. The NMDARs are mainly non-synaptic in immature neurons before and during synapse formation (≦ 7 DIV), and are rapidly recruited to nascent synapses after synaptic contact or terminal differentiation (≧ 13 DIV) [47]. Therefore, the immature neurons under basal conditions normally lack of synaptic NMDARs. "
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