Limits...
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.

Show MeSH

Related in: MedlinePlus

Glycinergic IPSCs are phasic compared to GABAergic IPSCs in response to sustained illumination. (A) IPSC responses evoked by different durations of light (2, 50, and 100 ms) in a bushy neuron. Notice that the glycinergic IPSCs peak shortly after the onset of the light pulse and decay rapidly even though the illumination is still on, whereas GABAergic IPSCs show little decay in amplitude. (B) Light evoked IPSC responses in a multipolar neuron. Traces in both (A) and (B) are averages of 10 trials. (C) Summary of the IPSC peak amplitudes (peak) and steady state amplitudes (SS) in bushy neurons. In (C-F): Gly: glycinergic IPSCs; GABA: GABAergic IPSCs. (D) Summary of the sustained current ratio in bushy neurons. (E) Summary of the IPSC peak amplitudes and steady state amplitudes in multipolar neurons. (F) Summary of the sustained current ratio in multipolar neurons. In (D) and (F): each connected pair represents a single neuron; black bar marks the average of the group. * p < 0.05; ** p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4109614&req=5

Figure 4: Glycinergic IPSCs are phasic compared to GABAergic IPSCs in response to sustained illumination. (A) IPSC responses evoked by different durations of light (2, 50, and 100 ms) in a bushy neuron. Notice that the glycinergic IPSCs peak shortly after the onset of the light pulse and decay rapidly even though the illumination is still on, whereas GABAergic IPSCs show little decay in amplitude. (B) Light evoked IPSC responses in a multipolar neuron. Traces in both (A) and (B) are averages of 10 trials. (C) Summary of the IPSC peak amplitudes (peak) and steady state amplitudes (SS) in bushy neurons. In (C-F): Gly: glycinergic IPSCs; GABA: GABAergic IPSCs. (D) Summary of the sustained current ratio in bushy neurons. (E) Summary of the IPSC peak amplitudes and steady state amplitudes in multipolar neurons. (F) Summary of the sustained current ratio in multipolar neurons. In (D) and (F): each connected pair represents a single neuron; black bar marks the average of the group. * p < 0.05; ** p < 0.01.

Mentions: The amplitudes of light evoked IPSCs in bushy and multipolar neurons were not different under control conditions, similar to the results for IPSPs. The peak IPSC amplitude was 2.65 ± 1.15 nA (n = 7) in bushy neurons and 2.10 ± 2.02 nA (n = 5) in multipolar neurons (Figure 3C; unpaired t-test: t10 = 0.60, p = 0.56). As shown in Figures 3A,B, strychnine blocked most of the IPSC in both bushy and multipolar neurons. We measured the amplitude of the GABAergic IPSCs (in the presence of strychnine) and of the glycinergic IPSCs (computed as the difference between control IPSCs and strychnine-resistant IPSCs). There was no significant difference in the glycinergic IPSC amplitudes (bushy: 2.60 ± 1.13 nA, n = 7; multipolar: 1.96 ± 1.98 nA, n = 5; Figure 3C; unpaired t-test: t10 = 0.71, p = 0.49) between two cell types. However, the GABAergic IPSCs were significantly smaller in bushy neurons (50 ± 24 pA, n = 7) than in multipolar neurons (137 ± 61 pA, n = 5) (Figure 3C; unpaired t-test: t10 = 3.50, p = 0.0057), consistent with the IPSP data (Figure 2I). The small percentage of GABAergic IPSC components measured here with short light pulses (compare to IPSP components in Figure 2I) suggests that GABAergic inhibition is more effectively activated with long light stimulation, which is also demonstrated in Figure 4.


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)

Glycinergic IPSCs are phasic compared to GABAergic IPSCs in response to sustained illumination. (A) IPSC responses evoked by different durations of light (2, 50, and 100 ms) in a bushy neuron. Notice that the glycinergic IPSCs peak shortly after the onset of the light pulse and decay rapidly even though the illumination is still on, whereas GABAergic IPSCs show little decay in amplitude. (B) Light evoked IPSC responses in a multipolar neuron. Traces in both (A) and (B) are averages of 10 trials. (C) Summary of the IPSC peak amplitudes (peak) and steady state amplitudes (SS) in bushy neurons. In (C-F): Gly: glycinergic IPSCs; GABA: GABAergic IPSCs. (D) Summary of the sustained current ratio in bushy neurons. (E) Summary of the IPSC peak amplitudes and steady state amplitudes in multipolar neurons. (F) Summary of the sustained current ratio in multipolar neurons. In (D) and (F): each connected pair represents a single neuron; black bar marks the average of the group. * p < 0.05; ** p < 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Glycinergic IPSCs are phasic compared to GABAergic IPSCs in response to sustained illumination. (A) IPSC responses evoked by different durations of light (2, 50, and 100 ms) in a bushy neuron. Notice that the glycinergic IPSCs peak shortly after the onset of the light pulse and decay rapidly even though the illumination is still on, whereas GABAergic IPSCs show little decay in amplitude. (B) Light evoked IPSC responses in a multipolar neuron. Traces in both (A) and (B) are averages of 10 trials. (C) Summary of the IPSC peak amplitudes (peak) and steady state amplitudes (SS) in bushy neurons. In (C-F): Gly: glycinergic IPSCs; GABA: GABAergic IPSCs. (D) Summary of the sustained current ratio in bushy neurons. (E) Summary of the IPSC peak amplitudes and steady state amplitudes in multipolar neurons. (F) Summary of the sustained current ratio in multipolar neurons. In (D) and (F): each connected pair represents a single neuron; black bar marks the average of the group. * p < 0.05; ** p < 0.01.
Mentions: The amplitudes of light evoked IPSCs in bushy and multipolar neurons were not different under control conditions, similar to the results for IPSPs. The peak IPSC amplitude was 2.65 ± 1.15 nA (n = 7) in bushy neurons and 2.10 ± 2.02 nA (n = 5) in multipolar neurons (Figure 3C; unpaired t-test: t10 = 0.60, p = 0.56). As shown in Figures 3A,B, strychnine blocked most of the IPSC in both bushy and multipolar neurons. We measured the amplitude of the GABAergic IPSCs (in the presence of strychnine) and of the glycinergic IPSCs (computed as the difference between control IPSCs and strychnine-resistant IPSCs). There was no significant difference in the glycinergic IPSC amplitudes (bushy: 2.60 ± 1.13 nA, n = 7; multipolar: 1.96 ± 1.98 nA, n = 5; Figure 3C; unpaired t-test: t10 = 0.71, p = 0.49) between two cell types. However, the GABAergic IPSCs were significantly smaller in bushy neurons (50 ± 24 pA, n = 7) than in multipolar neurons (137 ± 61 pA, n = 5) (Figure 3C; unpaired t-test: t10 = 3.50, p = 0.0057), consistent with the IPSP data (Figure 2I). The small percentage of GABAergic IPSC components measured here with short light pulses (compare to IPSP components in Figure 2I) suggests that GABAergic inhibition is more effectively activated with long light stimulation, which is also demonstrated in Figure 4.

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