Phosphorylation of proteins involved in activity-dependent forms of synaptic plasticity is altered in hippocampal slices maintained in vitro

Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
Journal of Neurochemistry (Impact Factor: 4.28). 01/2005; 91(6):1344-57. DOI: 10.1111/j.1471-4159.2004.02815.x
Source: PubMed


The acute hippocampal slice preparation has been widely used to study the cellular mechanisms underlying activity-dependent forms of synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD). Although protein phosphorylation has a key role in LTP and LTD, little is known about how protein phosphorylation might be altered in hippocampal slices maintained in vitro. To begin to address this issue, we examined the effects of slicing and in vitro maintenance on phosphorylation of six proteins involved in LTP and/or LTD. We found that AMPA receptor (AMPAR) glutamate receptor 1 (GluR1) subunits are persistently dephosphorylated in slices maintained in vitro for up to 8 h. alpha calcium/calmodulin-dependent kinase II (alphaCamKII) was also strongly dephosphorylated during the first 3 h in vitro but thereafter recovered to near control levels. In contrast, phosphorylation of the extracellular signal-regulated kinase ERK2, the ERK kinase MEK, proline-rich tyrosine kinase 2 (Pyk2), and Src family kinases was significantly, but transiently, increased. Electrophysiological experiments revealed that the induction of LTD by low-frequency synaptic stimulation was sensitive to time in vitro. These findings indicate that phosphorylation of proteins involved in N-methyl-D-aspartate (NMDA) receptor-dependent forms of synaptic plasticity is altered in hippocampal slices and suggest that some of these changes can significantly influence the induction of LTD.

Download full-text


Available from: Oanh Ho, Mar 06, 2015
  • Source
    • "Authenticated | author's copy Download Date | 5/22/15 2:14 PM 2014). Hoyt and Coffino (2004) supposed that uncoupling degradation from ubiquitin modification may reflect the evolutionary conservation of mechanisms optimized for highly specialized regulatory functions. Despite the ambiguity of this model and its inability to answer several serious questions, it may provide some tentative answers for the variability of LTP response to the protein synthesis inhibitors. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Long-term potentiation (LTP) remains the most widely accepted model for learning and memory. In accordance with this belief, the temporal differentiation of LTP into early and late phases is accepted as reflecting the differentiation of short-term and long-term memory. Moreover, during the past 30 years, protein synthesis inhibitors have been used to separate the early, protein synthesis-independent (E-LTP) phase and the late, protein synthesis-dependent (L-LTP) phase. However, the role of these proteins has not been formally identified. Additionally, several reports failed to show an effect of protein synthesis inhibitors on LTP. In this review, a detailed analysis of extensive behavioral and electrophysiological data reveals that the presumed correspondence of LTP temporal phases to memory phases is neither experimentally nor theoretically consistent. Moreover, an overview of the time courses of E-LTP in hippocampal slices reveals a wide variability ranging from <1 h to more than 5 h. The existence of all these conflictual findings should lead to a new vision of LTP. We believe that the E-LTP vs. L-LTP distinction, established with protein synthesis inhibitor studies, reflects a false dichotomy. We suggest that the duration of LTP and its dependency on protein synthesis are related to the availability of a set of proteins at synapses and not to the de novo synthesis of plasticity-related proteins. This availability is determined by protein turnover kinetics, which is regulated by previous and ongoing electrical activities and by energy store availability.
    Full-text · Article · May 2015 · Reviews in the neurosciences
  • Source
    • "Incubation time determines the effect of protein synthesis inhibitors Why should incubation time have such a dramatic effect on the efficacy of synthesis inhibitors? One possibility is suggested by evidence that the preparation of the slice causes transient increases in the activity of kinases involved in synaptic plasticity (Ho et al., 2004 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Although sometimes disputed, it has been assumed for several decades that new proteins synthesized following a learning event are required for consolidation of subsequent memory. Published findings and new results described here challenge this idea. Protein synthesis inhibitors did not prevent Theta Bust Stimulation (TBS) from producing extremely stable long-term potentiation (LTP) in experiments using standard hippocampal slice protocols. However, the inhibitors were effective under conditions that likely depleted protein levels prior to attempts to induce the potentiation effect. Experiments showed that induction of LTP at one input, and thus a prior episode of protein synthesis, eliminated the effects of inhibitors on potentiation of a second input even in depleted slices. These observations suggest that a primary role of translation and transcription processes initiated by learning events is to prepare neurons to support future learning. Other work has provided support for an alternative theory of consolidation. Specifically, if the synaptic changes that support memory are to endure, learning events/TBS must engage a complex set of signaling processes that reorganize and re-stabilize the spine actin cytoskeleton. This is accomplished in fast (10min) and slow (50min) stages with the first requiring integrin activation and the second a recovery of integrin functioning. These results align with, and provide mechanisms for, the long-held view that memories are established and consolidated over a set of temporally distinct phases. Copyright © 2014. Published by Elsevier B.V.
    Full-text · Article · Dec 2014 · Brain Research
  • Source
    • "While electrochemical signaling allows neurons to rapidly communicate between compartments, soluble signaling molecules have also been shown to translocate from synapse to nucleus to trigger changes in gene expression (Otis et al., 2006; Cohen and Greenberg, 2008). We, and others, have described a role for importin nuclear transporters in relaying signals from distal processes to the nucleus (Hanz, 2003; Thompson, 2004; Dieterich, 2008; Lai, 2008; Jordan and Kreutz, 2009). In this study, we present data showing that importin α binds to a bipartite NLS in the NR1-1a subunit of the NMDA receptor. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Synaptic plasticity, the capacity of neurons to change the strength of their connections with experience, provides a mechanism for learning and memory in the brain. Long-term plasticity requires new transcription, indicating that synaptically generated signals must be transported to the nucleus. Previous studies have described a role for importin nuclear transport adaptors in mediating the retrograde transport of signals from synapse to nucleus during plasticity. Here, we investigated the possibility that stimulus-induced translocation of importins from synapse to nucleus involves activity-dependent anchoring of importins at the synapse. We show that importin alpha binds to a nuclear localization signal (NLS) present in the cytoplasmic tail of NR1-1a. This interaction is disrupted by activation of NMDA receptors in cultured neurons and by stimuli that trigger late-phase, but not early-phase, long-term potentiation of CA3-CA1 synapses in acute hippocampal slices. In vitro PKC phosphorylation of GST-NR1-1a abolishes its ability to bind importin alpha in brain lysates, and the interaction of importin alpha and NR1 in neurons is modulated by PKC activity. Together, our results indicate that importin alpha is tethered at the postsynaptic density by binding to the NLS present in NR1-1a. This interaction is activity dependent, with importin alpha being released following NMDA receptor activation and phosphorylation rendering it available to bind soluble cargoes and transport them to the nucleus during transcription-dependent forms of neuronal plasticity.
    Full-text · Article · Dec 2009 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
Show more