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GABAergic and glycinergic inhibitory synaptic transmission in the ventral cochlear nucleus studied in VGAT channelrhodopsin-2 mice.

Xie R, Manis PB - Front Neural Circuits (2014)

Bottom Line: During prolonged stimulation, the ratio of steady state vs. peak IPSC amplitude was significantly lower for glycinergic IPSCs.In the absence of receptor blockers, repetitive light stimulation was only able to effectively evoke IPSCs up to 20 Hz in both bushy and multipolar neurons.We conclude that local GABAergic release within the VCN can differentially influence bushy and multipolar cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill Chapel Hill, NC, USA.

ABSTRACT
Both glycine and GABA mediate inhibitory synaptic transmission in the ventral cochlear nucleus (VCN). In mice, the time course of glycinergic inhibition is slow in bushy cells and fast in multipolar (stellate) cells, and is proposed to contribute to the processing of temporal cues in both cell types. Much less is known about GABAergic synaptic transmission in this circuit. Electrical stimulation of the auditory nerve or the tuberculoventral pathway evokes little GABAergic synaptic current in brain slice preparations, and spontaneous GABAergic miniature synaptic currents occur infrequently. To investigate synaptic currents carried by GABA receptors in bushy and multipolar cells, we used transgenic mice in which channelrhodopsin-2 and EYFP is driven by the vesicular GABA transporter (VGAT-ChR2-EYFP) and is expressed in both GABAergic and glycinergic neurons. Light stimulation evoked action potentials in EYFP-expressing presynaptic cells, and evoked inhibitory postsynaptic potentials (IPSPs) in non-expressing bushy and planar multipolar cells. Less than 10% of the IPSP amplitude in bushy cells arose from GABAergic synapses, whereas 40% of the IPSP in multipolar neurons was GABAergic. In voltage clamp, glycinergic IPSCs were significantly slower in bushy neurons than in multipolar neurons, whereas there was little difference in the kinetics of the GABAergic IPSCs between two cell types. During prolonged stimulation, the ratio of steady state vs. peak IPSC amplitude was significantly lower for glycinergic IPSCs. Surprisingly, the reversal potentials of GABAergic IPSCs were negative to those of glycinergic IPSCs in both bushy and multipolar neurons. In the absence of receptor blockers, repetitive light stimulation was only able to effectively evoke IPSCs up to 20 Hz in both bushy and multipolar neurons. We conclude that local GABAergic release within the VCN can differentially influence bushy and multipolar cells.

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Related in: MedlinePlus

GABAergic IPSCs are blocked by tetrodotoxin. Cells were tested in control conditions (red traces), in the presence of 2 µM strychnine to isolate the GABAergic IPSC (green trace), and in the presence of both strychnine and 1 µM tetrodotoxin to block action potential evoked release. No IPSC was evident in the presence of tetrodotoxin in any of the three cells tested, indicating that voltage-gated sodium channel activation is required for GABA release in response to ChR2 activation.
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Figure 6: GABAergic IPSCs are blocked by tetrodotoxin. Cells were tested in control conditions (red traces), in the presence of 2 µM strychnine to isolate the GABAergic IPSC (green trace), and in the presence of both strychnine and 1 µM tetrodotoxin to block action potential evoked release. No IPSC was evident in the presence of tetrodotoxin in any of the three cells tested, indicating that voltage-gated sodium channel activation is required for GABA release in response to ChR2 activation.

Mentions: The GABAergic IPSCs did not often show large rapidly-decaying current events typically seen with the glycinergic IPSCs, which raised a question regarding whether the IPSCs arose from action-potential evoked release, or simply from ChR2 mediated depolarization of presynaptic terminals, and subsequent asynchronous release. To address this, we tested three cells (all multipolar cells). Recordings were made in control solutions, followed by the addition of 2 µM strychnine to isolate the GABAergic component. Examples of traces for a cell held at +13 and −107 mV are shown in Figure 6. The isolated GABAergic component (green traces) was completely blocked by the addition of 1 µM TTX to the bath (black trace). The same result was obtained in the other two cells. These experiments indicate that the light evoked GABAergic IPSC requires presynaptic action potentials that initiate transmitter release, and is that ChR2-mediated depolarization of presynaptic terminals alone is not sufficient to drive release.


GABAergic and glycinergic inhibitory synaptic transmission in the ventral cochlear nucleus studied in VGAT channelrhodopsin-2 mice.

Xie R, Manis PB - Front Neural Circuits (2014)

GABAergic IPSCs are blocked by tetrodotoxin. Cells were tested in control conditions (red traces), in the presence of 2 µM strychnine to isolate the GABAergic IPSC (green trace), and in the presence of both strychnine and 1 µM tetrodotoxin to block action potential evoked release. No IPSC was evident in the presence of tetrodotoxin in any of the three cells tested, indicating that voltage-gated sodium channel activation is required for GABA release in response to ChR2 activation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4109614&req=5

Figure 6: GABAergic IPSCs are blocked by tetrodotoxin. Cells were tested in control conditions (red traces), in the presence of 2 µM strychnine to isolate the GABAergic IPSC (green trace), and in the presence of both strychnine and 1 µM tetrodotoxin to block action potential evoked release. No IPSC was evident in the presence of tetrodotoxin in any of the three cells tested, indicating that voltage-gated sodium channel activation is required for GABA release in response to ChR2 activation.
Mentions: The GABAergic IPSCs did not often show large rapidly-decaying current events typically seen with the glycinergic IPSCs, which raised a question regarding whether the IPSCs arose from action-potential evoked release, or simply from ChR2 mediated depolarization of presynaptic terminals, and subsequent asynchronous release. To address this, we tested three cells (all multipolar cells). Recordings were made in control solutions, followed by the addition of 2 µM strychnine to isolate the GABAergic component. Examples of traces for a cell held at +13 and −107 mV are shown in Figure 6. The isolated GABAergic component (green traces) was completely blocked by the addition of 1 µM TTX to the bath (black trace). The same result was obtained in the other two cells. These experiments indicate that the light evoked GABAergic IPSC requires presynaptic action potentials that initiate transmitter release, and is that ChR2-mediated depolarization of presynaptic terminals alone is not sufficient to drive release.

Bottom Line: During prolonged stimulation, the ratio of steady state vs. peak IPSC amplitude was significantly lower for glycinergic IPSCs.In the absence of receptor blockers, repetitive light stimulation was only able to effectively evoke IPSCs up to 20 Hz in both bushy and multipolar neurons.We conclude that local GABAergic release within the VCN can differentially influence bushy and multipolar cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill Chapel Hill, NC, USA.

ABSTRACT
Both glycine and GABA mediate inhibitory synaptic transmission in the ventral cochlear nucleus (VCN). In mice, the time course of glycinergic inhibition is slow in bushy cells and fast in multipolar (stellate) cells, and is proposed to contribute to the processing of temporal cues in both cell types. Much less is known about GABAergic synaptic transmission in this circuit. Electrical stimulation of the auditory nerve or the tuberculoventral pathway evokes little GABAergic synaptic current in brain slice preparations, and spontaneous GABAergic miniature synaptic currents occur infrequently. To investigate synaptic currents carried by GABA receptors in bushy and multipolar cells, we used transgenic mice in which channelrhodopsin-2 and EYFP is driven by the vesicular GABA transporter (VGAT-ChR2-EYFP) and is expressed in both GABAergic and glycinergic neurons. Light stimulation evoked action potentials in EYFP-expressing presynaptic cells, and evoked inhibitory postsynaptic potentials (IPSPs) in non-expressing bushy and planar multipolar cells. Less than 10% of the IPSP amplitude in bushy cells arose from GABAergic synapses, whereas 40% of the IPSP in multipolar neurons was GABAergic. In voltage clamp, glycinergic IPSCs were significantly slower in bushy neurons than in multipolar neurons, whereas there was little difference in the kinetics of the GABAergic IPSCs between two cell types. During prolonged stimulation, the ratio of steady state vs. peak IPSC amplitude was significantly lower for glycinergic IPSCs. Surprisingly, the reversal potentials of GABAergic IPSCs were negative to those of glycinergic IPSCs in both bushy and multipolar neurons. In the absence of receptor blockers, repetitive light stimulation was only able to effectively evoke IPSCs up to 20 Hz in both bushy and multipolar neurons. We conclude that local GABAergic release within the VCN can differentially influence bushy and multipolar cells.

Show MeSH
Related in: MedlinePlus