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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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GABAergic inhibition is weak in bushy but strong in multipolar neurons. (A) Discharge pattern of a bushy neuron to direct current injection. The bushy neuron fires only one or a few spikes with depolarizing current injections. (B) Light pulses at different durations evoke brief IPSP responses in bushy neurons. Each trace is an average of six trials. Blue bars on top mark the timing of the light pulses with duration of 1, 5 and 20 ms. (C) Strychnine (stry) blocks the majority of the IPSP evoked by 20 ms light pulses in bushy neurons. Addition of SR95531 (stry+SR) fully blocks light evoked IPSPs. Traces are averages of 10 trials. Data in (A–C) are from the same bushy neuron. (D) Discharge pattern of an example multipolar neuron to direct current injections. Multipolar neurons fire a regular train of spikes throughout the current injection. (E) Light pulses at durations of 1, 5 and 20 ms evoke IPSPs in multipolar neurons. Note that the IPSPs have a wider half-width than those of bushy neurons in (B). (F) Strychnine only blocks about half of light evoked IPSP. The remainder of the current is fully blocked by the further addition of SR95531. Data in (D–F) are from the same multipolar neuron. (G–I) Summary data of the eIPSP half-width (G), eIPSP amplitude (H) and percentage of GABAergic IPSP (I). * p < 0.05; ** p < 0.01. Data is plotted as mean ± S.D.
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Figure 2: GABAergic inhibition is weak in bushy but strong in multipolar neurons. (A) Discharge pattern of a bushy neuron to direct current injection. The bushy neuron fires only one or a few spikes with depolarizing current injections. (B) Light pulses at different durations evoke brief IPSP responses in bushy neurons. Each trace is an average of six trials. Blue bars on top mark the timing of the light pulses with duration of 1, 5 and 20 ms. (C) Strychnine (stry) blocks the majority of the IPSP evoked by 20 ms light pulses in bushy neurons. Addition of SR95531 (stry+SR) fully blocks light evoked IPSPs. Traces are averages of 10 trials. Data in (A–C) are from the same bushy neuron. (D) Discharge pattern of an example multipolar neuron to direct current injections. Multipolar neurons fire a regular train of spikes throughout the current injection. (E) Light pulses at durations of 1, 5 and 20 ms evoke IPSPs in multipolar neurons. Note that the IPSPs have a wider half-width than those of bushy neurons in (B). (F) Strychnine only blocks about half of light evoked IPSP. The remainder of the current is fully blocked by the further addition of SR95531. Data in (D–F) are from the same multipolar neuron. (G–I) Summary data of the eIPSP half-width (G), eIPSP amplitude (H) and percentage of GABAergic IPSP (I). * p < 0.05; ** p < 0.01. Data is plotted as mean ± S.D.

Mentions: We next characterized the light evoked inhibitory responses using current clamp recordings from non-expressing neurons in AVCN. All non-expressing neurons were classified into two cell types based on their characteristic firing patterns to depolarizing current injections. Bushy neurons fire only one or a few transient spikes after the onset of the depolarizing current injection (Figure 2A), while multipolar (stellate) neurons fire tonically throughout the duration of the current injection (Figure 2D). The multipolar neurons are primarily planar multipolar (T-stellate) neurons, because these are excitatory neurons that do not express ChR2 in this mouse.


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 inhibition is weak in bushy but strong in multipolar neurons. (A) Discharge pattern of a bushy neuron to direct current injection. The bushy neuron fires only one or a few spikes with depolarizing current injections. (B) Light pulses at different durations evoke brief IPSP responses in bushy neurons. Each trace is an average of six trials. Blue bars on top mark the timing of the light pulses with duration of 1, 5 and 20 ms. (C) Strychnine (stry) blocks the majority of the IPSP evoked by 20 ms light pulses in bushy neurons. Addition of SR95531 (stry+SR) fully blocks light evoked IPSPs. Traces are averages of 10 trials. Data in (A–C) are from the same bushy neuron. (D) Discharge pattern of an example multipolar neuron to direct current injections. Multipolar neurons fire a regular train of spikes throughout the current injection. (E) Light pulses at durations of 1, 5 and 20 ms evoke IPSPs in multipolar neurons. Note that the IPSPs have a wider half-width than those of bushy neurons in (B). (F) Strychnine only blocks about half of light evoked IPSP. The remainder of the current is fully blocked by the further addition of SR95531. Data in (D–F) are from the same multipolar neuron. (G–I) Summary data of the eIPSP half-width (G), eIPSP amplitude (H) and percentage of GABAergic IPSP (I). * p < 0.05; ** p < 0.01. Data is plotted as mean ± S.D.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 2: GABAergic inhibition is weak in bushy but strong in multipolar neurons. (A) Discharge pattern of a bushy neuron to direct current injection. The bushy neuron fires only one or a few spikes with depolarizing current injections. (B) Light pulses at different durations evoke brief IPSP responses in bushy neurons. Each trace is an average of six trials. Blue bars on top mark the timing of the light pulses with duration of 1, 5 and 20 ms. (C) Strychnine (stry) blocks the majority of the IPSP evoked by 20 ms light pulses in bushy neurons. Addition of SR95531 (stry+SR) fully blocks light evoked IPSPs. Traces are averages of 10 trials. Data in (A–C) are from the same bushy neuron. (D) Discharge pattern of an example multipolar neuron to direct current injections. Multipolar neurons fire a regular train of spikes throughout the current injection. (E) Light pulses at durations of 1, 5 and 20 ms evoke IPSPs in multipolar neurons. Note that the IPSPs have a wider half-width than those of bushy neurons in (B). (F) Strychnine only blocks about half of light evoked IPSP. The remainder of the current is fully blocked by the further addition of SR95531. Data in (D–F) are from the same multipolar neuron. (G–I) Summary data of the eIPSP half-width (G), eIPSP amplitude (H) and percentage of GABAergic IPSP (I). * p < 0.05; ** p < 0.01. Data is plotted as mean ± S.D.
Mentions: We next characterized the light evoked inhibitory responses using current clamp recordings from non-expressing neurons in AVCN. All non-expressing neurons were classified into two cell types based on their characteristic firing patterns to depolarizing current injections. Bushy neurons fire only one or a few transient spikes after the onset of the depolarizing current injection (Figure 2A), while multipolar (stellate) neurons fire tonically throughout the duration of the current injection (Figure 2D). The multipolar neurons are primarily planar multipolar (T-stellate) neurons, because these are excitatory neurons that do not express ChR2 in this mouse.

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