Article

Basal GABA Regulates GABABR Conformation and Release Probability at Single Hippocampal Synapses

Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Neuron (Impact Factor: 15.98). 07/2010; 67(2):253-67. DOI: 10.1016/j.neuron.2010.06.022
Source: PubMed

ABSTRACT Presynaptic GABA(B) receptor (GABA(B)R) heterodimers are composed of GB(1a)/GB(2) subunits and critically influence synaptic and cognitive functions. Here, we explored local GABA(B)R activation by integrating optical tools for monitoring receptor conformation and synaptic vesicle release at individual presynaptic boutons of hippocampal neurons. Utilizing fluorescence resonance energy transfer (FRET) spectroscopy, we detected a wide range of FRET values for CFP/YFP-tagged GB(1a)/GB(2) receptors that negatively correlated with release probabilities at single synapses. High FRET of GABA(B)Rs associated with low release probability. Notably, pharmacological manipulations that either reduced or increased basal receptor activation decreased intersynapse variability of GB(1a)/GB(2) receptor conformation. Despite variability along axons, presynaptic GABA(B)R tone was dendrite specific, having a greater impact on synapses at highly innervated proximal branches. Prolonged neuronal inactivity reduced basal receptor activation, leading to homeostatic augmentation of release probability. Our findings suggest that local variations in basal GABA concentration are a major determinant of GB(1a)/GB(2) conformational variability, which contributes to heterogeneity of neurotransmitter release at hippocampal synapses.

Download full-text

Full-text

Available from: Inna Slutsky, May 22, 2014
0 Followers
 · 
121 Views
  • Source
    • "As a perturbation, we chose a suppression of synaptic activity via widely expressed GABA B receptors (GABA B Rs) using a selective GABA B R agonist, baclofen. GABA B Rs mediate presynaptic inhibition via inhibition of presynaptic calcium transients (Wu and Saggau, 1995; Laviv et al., 2010). Therefore, we first conducted experiments to determine the dose–response of baclofen at the level of presynaptic terminals utilizing FM1-43 dye in primary hippocampal cultures (Abramov et al., 2009). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Neuronal circuits' ability to maintain the delicate balance between stability and flexibility in changing environments is critical for normal neuronal functioning. However, to what extent individual neurons and neuronal populations maintain internal firing properties remains largely unknown. Here, we show that distributions of spontaneous population firing rates and synchrony are subject to accurate homeostatic control following increase of synaptic inhibition in cultured hippocampal networks. Reduction in firing rate triggered synaptic and intrinsic adaptive responses operating as global homeostatic mechanisms to maintain firing macro-stability, without achieving local homeostasis at the single-neuron level. Adaptive mechanisms, while stabilizing population firing properties, reduced short-term facilitation essential for synaptic discrimination of input patterns. Thus, invariant ongoing population dynamics emerge from intrinsically unstable activity patterns of individual neurons and synapses. The observed differences in the precision of homeostatic control at different spatial scales challenge cell-autonomous theory of network homeostasis and suggest existence of network-wide regulation rules.
    eLife Sciences 01/2015; 4. DOI:10.7554/eLife.04378 · 8.52 Impact Factor
  • Source
    • "In order to exclude potential contribution of donor/acceptor ratio to FRET efficiency measurements, all FRET experiments were performed under saturation conditions of acceptor over donor. Detection of Cer and Cit signals was done using custom-written scripts in MATLAB as described earlier (Laviv et al., 2010). "
  • Source
    • "APP-APP Interactions Correlate to Release Probability at Excitatory Synapses Because release probability is highly heterogeneous across hippocampal synapses (Laviv et al., 2010), we asked whether APP-APP interactions vary across individual synapses and correlate to synapse release probability. To directly address these questions, we monitored FM destaining kinetics, a reliable "
    [Show abstract] [Hide abstract]
    ABSTRACT: Accumulation of amyloid-β peptides (Aβ), the proteolytic products of the amyloid precursor protein (APP), induces a variety of synaptic dysfunctions ranging from hyperactivity to depression that are thought to cause cognitive decline in Alzheimer's disease. While depression of synaptic transmission has been extensively studied, the mechanisms underlying synaptic hyperactivity remain unknown. Here, we show that Aβ40 monomers and dimers augment release probability through local fine-tuning of APP-APP interactions at excitatory hippocampal boutons. Aβ40 binds to the APP, increases the APP homodimer fraction at the plasma membrane, and promotes APP-APP interactions. The APP activation induces structural rearrangements in the APP/Gi/o-protein complex, boosting presynaptic calcium flux and vesicle release. The APP growth-factor-like domain (GFLD) mediates APP-APP conformational changes and presynaptic enhancement. Thus, the APP homodimer constitutes a presynaptic receptor that transduces signal from Aβ40 to glutamate release. Excessive APP activation may initiate a positive feedback loop, contributing to hippocampal hyperactivity in Alzheimer's disease.
    Cell Reports 05/2014; 7(5). DOI:10.1016/j.celrep.2014.04.024 · 7.21 Impact Factor
Show more