Article

Daniels, R.W. et al. Increased expression of the Drosophila vesicular glutamate transporter leads to excess glutamate release and a compensatory decrease in quantal content. J. Neurosci. 24, 10466-10474

Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 12/2004; 24(46):10466-74. DOI: 10.1523/JNEUROSCI.3001-04.2004
Source: PubMed

ABSTRACT Quantal size is a fundamental parameter controlling the strength of synaptic transmission. The transmitter content of synaptic vesicles is one mechanism that can affect the physiological response to the release of a single vesicle. At glutamatergic synapses, vesicular glutamate transporters (VGLUTs) are responsible for filling synaptic vesicles with glutamate. To investigate how VGLUT expression can regulate synaptic strength in vivo, we have identified the Drosophila vesicular glutamate transporter, which we name DVGLUT. DVGLUT mRNA is expressed in glutamatergic motoneurons and a large number of interneurons in the Drosophila CNS. DVGLUT protein resides on synaptic vesicles and localizes to the presynaptic terminals of all known glutamatergic neuromuscular junctions as well as to synapses throughout the CNS neuropil. Increasing the expression of DVGLUT in motoneurons leads to an increase in quantal size that is accompanied by an increase in synaptic vesicle volume. At synapses confronted with increased glutamate release from each vesicle, there is a compensatory decrease in the number of synaptic vesicles released that maintains normal levels of synaptic excitation. These results demonstrate that (1) expression of DVGLUT determines the size and glutamate content of synaptic vesicles and (2) homeostatic mechanisms exist to attenuate the excitatory effects of excess glutamate release.

Download full-text

Full-text

Available from: Richard W Daniels, Jun 20, 2014
0 Followers
 · 
93 Views
 · 
20 Downloads
    • "Because of its key role in the regulation of neurotransmitter release, the CB 1 R represents an interesting candidate for the control of emotional and stress-related behavioral states (Lutz, 2009; Hill and Gorzalka, 2009; Moreira and Wotjak, 2010). The expression of VGluT1 or VGAT affects vesicular quantal size (Daniels et al., 2004; Wilson et al., 2005), which, in turn, influences synaptic plasticity (Takamori, 2006). Therefore, we used putative changes in VGluT1 and VGAT protein expression as an indirect measure of the putative effects of the abnormal constitutive increase of 2-AG levels in MAGL-/-mice on CB 1 R-mediated neurotransmission in emotion-and stress-related brain areas. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Endocannabinoids (eCB) are key regulators of excitatory/inhibitory neurotransmission at cannabinoid-1-receptor (CB1R)-expressing axon terminals. The most abundant eCB in the brain, that is 2-arachidonoylglycerol (2-AG), is hydrolyzed by the enzyme monoacylglycerol lipase (MAGL), whose chronic inhibition in the brain was reported to cause CB1R desensitization. We employed the MAGL knock-out mice (MAGL-/-), a genetic model of congenital and sustained elevation of 2-AG levels in the brain, to provide morphological and biochemical evidence for β-arrestin2-mediated CB1R desensitization in brain regions involved in the control of emotional states, that is, the prefrontal cortex (PFC), amygdala, hippocampus and cerebellar cortex. We found a widespread CB1R/β-arrestin2 co-expression in the mPFC, amygdala and hippocampus accompanied by impairment of ERK signaling and elevation of vesicular glutamate transporter (VGluT1) at CB1R-positive excitatory terminals in the mPFC, or vesicular GABA transporter (VGAT) at CB1R-positive inhibitory terminals in the amygdala and hippocampus. The impairment of CB1R signaling in MAGL-/- mice was also accompanied by enhanced excitatory drive in the BLA-mPFC circuit, with subsequent elevation of glutamate release to the mPFC and anxiety-like behavior, as assessed by the marble burying test. Collectively, these data provide evidence for a β-arrestin2-mediated desensitization of CB1R in MAGL-/- mice, with impact on the synaptic plasticity of brain circuits involved in emotional functions. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Journal of Neurochemistry 07/2015; DOI:10.1111/jnc.13267 · 4.24 Impact Factor
  • Source
    • "These studies also indicate that the VGLUT2− mediated glutamate signaling by the central endings of nociceptive afferents may be enhanced following inflammation, thus contributing to central sensitization and inflammatory hyperalgesia. The increase in the VGLUT2, but not VGLUT1, expression in the pulpal axons and TG somata following pulpal inflammation in our study provides a morphological evidence supporting the notion that the peripheral glutamate signaling by the pulpal axons may be also enhanced following pulpal inflammation, and that it may be mediated by VGLUT2: It was shown that expression level of VGLUT is closely related with the amount of glutamate release [25], [26]. It corroborates previous studies showing increased glutamate release in peripheral tissues following inflammation [6], [27], [28], but is at variance with a recent study showing that the number of neurons that express mRNA for VGLUT1 and VGLUT2 in the mouse DRG does not change following CFA-induced inflammation [29]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Background There is increasing evidence that peripheral glutamate signaling mechanism is involved in the nociceptive transmission during pathological conditions. However, little is known about the glutamate signaling mechanism and related specific type of vesicular glutamate transporter (VGLUT) in the dental pulp following inflammation. To address this issue, we investigated expression and protein levels of VGLUT1 and VGLUT2 in the dental pulp and trigeminal ganglion (TG) following complete Freund’s adjuvant (CFA) application to the rat dental pulp by light microscopic immunohistochemistry and Western blot analysis. Results The density of VGLUT2− immunopositive (+) axons in the dental pulp and the number of VGLUT2+ soma in the TG increased significantly in the CFA-treated group, compared to control group. The protein levels of VGLUT2 in the dental pulp and TG were also significantly higher in the CFA-treated group than control group by Western blot analysis. The density of VGLUT1+ axons in the dental pulp and soma in the TG remained unchanged in the CFA-treated group. Conclusions These findings suggest that glutamate signaling that is mediated by VGLUT2 in the pulpal axons may be enhanced in the inflamed dental pulp, which may contribute to pulpal axon sensitization leading to hyperalgesia following inflammation.
    PLoS ONE 10/2014; 9(10):e109723. DOI:10.1371/journal.pone.0109723 · 3.23 Impact Factor
  • Source
    • "The neurotransmitter content of SV is in dynamic equilibrium between transporter-mediated accumulation and leakage (Williams, 1997; Takamori, 2006). Genetic ablation of ClC-3 might enhance the osmotic gradient across the vesicular membrane via stimulating neurotransmitter accumulation and thus cause water influx and vesicular growth (Colliver et al., 2000; Pothos et al., 2000; Daniels et al., 2004). Increased glutamate accumulation and water influx into SV will reach a new equilibrium at higher values for both parameters and thus account for the observed difference in vesicle volume between WT and Clcn3-/- neurons. "
    [Show abstract] [Hide abstract]
    ABSTRACT: ClC-3 is a member of the CLC family of anion channels and transporters that localizes to early and late endosomes as well as to synaptic vesicles (SV). Its genetic disruption in mouse models results in pronounced hippocampal and retinal neurodegeneration, suggesting that ClC-3 might be important for normal excitatory and/or inhibitory neurotransmission in central neurons. To characterize the role of ClC-3 in glutamate accumulation in SV we compared glutamatergic synaptic transmission in cultured hippocampal neurons from WT and Clcn3-/- mice. In Clcn3-/- neurons the amplitude and frequency of miniature as well as the amplitudes of action-potential evoked EPSCs were significantly increased as compared to WT neurons. The low-affinity competitive AMPA receptor antagonist γ-DGG reduced the quantal size of synaptic events more effectively in WT than in Clcn3-/- neurons, whereas no difference was observed for the high-affinity competitive non-NMDA antagonist NBQX. Paired pulse ratios of evoked EPSCs were significantly reduced, whereas the size of the readily releasable pool was not affected by the genetic ablation of ClC-3. Electron microscopy revealed increased volumes of SV in hippocampi of Clcn3-/- mice. Our findings demonstrate that ClC-3 controls fast excitatory synaptic transmission by regulating the amount of neurotransmitter as well as the release probability of SV. These results provide novel insights into the role of ClC-3 in synaptic transmission and identify excessive glutamate release as a likely basis of neurodegeneration in Clcn3-/-.
    Frontiers in Cellular Neuroscience 05/2014; 8:143. DOI:10.3389/fncel.2014.00143 · 4.18 Impact Factor
Show more