Basal GABA regulates GABA(B)R conformation and release probability at single hippocampal synapses.
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.
- SourceAvailable from: nyu.edu[show abstract] [hide abstract]
ABSTRACT: Previous studies of short-term plasticity in central nervous systems synapses have largely focused on average synaptic properties. In this study, we use recordings from putative single synaptic release sites in hippocampal slices to show that significant heterogeneity exists in facilitation and depletion among synapses. In particular, the amount of paired-pulse facilitation is inversely related to the initial release probability of the synapse. We also examined depletion at individual synapses using high frequency stimulation, and estimated the size of the readily releasable vesicle pool, which averaged 5.0 +/- 3.0 quanta (n = 13 synapses). In addition, these experiments demonstrate that the release probability at a synapse is directly correlated with the size of its readily releasable vesicle pool.Neuron 07/1997; 18(6):995-1008. · 15.77 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: The entorhinal cortex provides both direct and indirect inputs to hippocampal CA1 neurons through the perforant path and Schaffer collateral synapses, respectively. Using both two-photon imaging of synaptic vesicle cycling and electrophysiological recordings, we found that the efficacy of transmitter release at perforant path synapses is lower than at Schaffer collateral inputs. This difference is due to the greater contribution to release by presynaptic N-type voltage-gated Ca(2+) channels at the Schaffer collateral than perforant path synapses. Induction of long-term potentiation that depends on activation of NMDA receptors and L-type voltage-gated Ca(2+) channels enhances the low efficacy of release at perforant path synapses by increasing the contribution of N-type channels to exocytosis. This represents a previously uncharacterized presynaptic mechanism for fine-tuning release properties of distinct classes of synapses onto a common postsynaptic neuron and for regulating synaptic function during long-term synaptic plasticity.Neuron 09/2009; 63(3):372-85. · 15.77 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: After its release from interneurons in the CNS, the major inhibitory neurotransmitter GABA is taken up by GABA transporters (GATs). The predominant neuronal GABA transporter GAT1 is localized in GABAergic axons and nerve terminals, where it is thought to influence GABAergic synaptic transmission, but the details of this regulation are unclear. To address this issue, we have generated a strain of GAT1-deficient mice. We observed a large increase in a tonic postsynaptic hippocampal GABAA receptor-mediated conductance. There was little or no change in the waveform or amplitude of spontaneous inhibitory postsynaptic currents (IPSCs) or miniature IPSCs. In contrast, the frequency of quantal GABA release was one-third of wild type (WT), although the densities of GABAA receptors, GABAB receptors, glutamic acid decarboxylase 65 kDa, and vesicular GAT were unaltered. The GAT1-deficient mice lacked a presynaptic GABAB receptor tone, present in WT mice, which reduces the frequency of spontaneous IPSCs. We conclude that GAT1 deficiency leads to enhanced extracellular GABA levels resulting in an overactivation of GABAA receptors responsible for a postsynaptic tonic conductance. Chronically elevated GABA levels also downregulate phasic GABA release and reduce presynaptic signaling via GABAB receptors thus causing an enhanced tonic and a diminished phasic inhibition.Journal of Neurophysiology 11/2003; 90(4):2690-701. · 3.30 Impact Factor