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Nitric oxide signaling modulates synaptic inhibition in the superior paraolivary nucleus (SPN) via cGMP-dependent suppression of KCC2.

Yassin L, Radtke-Schuller S, Asraf H, Grothe B, Hershfinkel M, Forsythe ID, Kopp-Scheinpflug C - Front Neural Circuits (2014)

Bottom Line: Here we show that nitric oxide (NO) signaling in the auditory brainstem (where activity-dependent generation of NO is documented) modulates the strength of inhibition by changing the chloride equilibrium potential.Recent evidence demonstrates that large inhibitory postsynaptic currents (IPSCs) in neurons of the superior paraolivary nucleus (SPN) are enhanced by a very low intracellular chloride concentration, generated by the neuronal potassium chloride co-transporter (KCC2) expressed in the postsynaptic neurons.Our data show that modulation by NO caused a 15 mV depolarizing shift of the IPSC reversal potential, reducing the strength of inhibition in SPN neurons, without changing the threshold for action potential firing.

View Article: PubMed Central - PubMed

Affiliation: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-University Munich Planegg-Martinsried, Germany.

ABSTRACT
Glycinergic inhibition plays a central role in the auditory brainstem circuitries involved in sound localization and in the encoding of temporal action potential firing patterns. Modulation of this inhibition has the potential to fine-tune information processing in these networks. Here we show that nitric oxide (NO) signaling in the auditory brainstem (where activity-dependent generation of NO is documented) modulates the strength of inhibition by changing the chloride equilibrium potential. Recent evidence demonstrates that large inhibitory postsynaptic currents (IPSCs) in neurons of the superior paraolivary nucleus (SPN) are enhanced by a very low intracellular chloride concentration, generated by the neuronal potassium chloride co-transporter (KCC2) expressed in the postsynaptic neurons. Our data show that modulation by NO caused a 15 mV depolarizing shift of the IPSC reversal potential, reducing the strength of inhibition in SPN neurons, without changing the threshold for action potential firing. Regulating inhibitory strength, through cGMP-dependent changes in the efficacy of KCC2 in the target neuron provides a postsynaptic mechanism for rapidly controlling the inhibitory drive, without altering the timing or pattern of the afferent spike train. Therefore, this NO-mediated suppression of KCC2 can modulate inhibition in one target nucleus (SPN), without influencing inhibitory strength of other target nuclei (MSO, LSO) even though they are each receiving collaterals from the same afferent nucleus (a projection from the medial nucleus of the trapezoid body, MNTB).

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Nitric oxide suppresses KCC2 activity. (A) Glycinergic IPSCs were evoked in a mouse SPN neuron by electrical stimulation of the MNTB. The command potentials ranged from −120 to −30 mV in steps of 10 mV. The IPSC reversal potential changed from −80 mV in control conditions to −50 mV after the modulation of KCC2 activity by NO signaling. (B) Current–voltage relationship for the SPN-IPSCs shown in (A). The parallel shift of the curves indicates a sole change in reversal potential without changing the conductance. (C) Average data show a significant depolarizing shift in IPSC reversal potential following NO application in the SPN, but not in LSO or MSO. (D) The overall glycinergic conductance in SPN neurons is unchanged by NO, indicating no change in the glycine receptor or the glycine release to be involved. **p ≤ 0.01.
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Figure 3: Nitric oxide suppresses KCC2 activity. (A) Glycinergic IPSCs were evoked in a mouse SPN neuron by electrical stimulation of the MNTB. The command potentials ranged from −120 to −30 mV in steps of 10 mV. The IPSC reversal potential changed from −80 mV in control conditions to −50 mV after the modulation of KCC2 activity by NO signaling. (B) Current–voltage relationship for the SPN-IPSCs shown in (A). The parallel shift of the curves indicates a sole change in reversal potential without changing the conductance. (C) Average data show a significant depolarizing shift in IPSC reversal potential following NO application in the SPN, but not in LSO or MSO. (D) The overall glycinergic conductance in SPN neurons is unchanged by NO, indicating no change in the glycine receptor or the glycine release to be involved. **p ≤ 0.01.

Mentions: Sustained synaptic stimulation causes generation of NO within the SOC (Steinert et al., 2008, 2011). Here, endogenous NO release was mimicked by bath application of the NO-donor (SNP; 100 μM) and its effect on KCC2 activity was measured. Strong KCC2 activity drives the negative Eglycine (Lohrke et al., 2005) in mature mammalian auditory brainstem neurons. Within the nuclei of the SOC in mouse and gerbil, mouse SPN neurons showed the largest deviation from calculated reversal potential for glycine (Figure 1C), suggesting that KCC2 activity is strongest in the SPN. Therefore, SPN neurons might support an activity-dependent mechanism that allows down-regulation of KCC2, but this seems to be less essential in the MSO and LSO. To test this hypothesis, the effect of NO on KCC2 activity in mouse LSO, MSO and SPN was measured before and during the application of NO. NO did not affect KCC2 activity in MSO or LSO neurons, but caused a depolarizing shift in Eglycine from −83.7 ± 5.4 mV to −67.3 ± 4.5 mV (n = 10, p = 0.002; Figures 3A–C), in the SPN consistent with suppression of KCC2. The IPSC current-voltage relationship showed a parallel shift (Figure 3B) and the glycinergic conductance did not change significantly during the NO application (IPSGcontrol: 39.1 ± 9.1 nS; IPSGNO: 36.7 ± 8.5 nS; n = 10; P = 0.57). These results indicate that there was no direct effect of NO signaling on the glycine receptors nor was there a major influence on presynaptic glycine release (Figure 3D).


Nitric oxide signaling modulates synaptic inhibition in the superior paraolivary nucleus (SPN) via cGMP-dependent suppression of KCC2.

Yassin L, Radtke-Schuller S, Asraf H, Grothe B, Hershfinkel M, Forsythe ID, Kopp-Scheinpflug C - Front Neural Circuits (2014)

Nitric oxide suppresses KCC2 activity. (A) Glycinergic IPSCs were evoked in a mouse SPN neuron by electrical stimulation of the MNTB. The command potentials ranged from −120 to −30 mV in steps of 10 mV. The IPSC reversal potential changed from −80 mV in control conditions to −50 mV after the modulation of KCC2 activity by NO signaling. (B) Current–voltage relationship for the SPN-IPSCs shown in (A). The parallel shift of the curves indicates a sole change in reversal potential without changing the conductance. (C) Average data show a significant depolarizing shift in IPSC reversal potential following NO application in the SPN, but not in LSO or MSO. (D) The overall glycinergic conductance in SPN neurons is unchanged by NO, indicating no change in the glycine receptor or the glycine release to be involved. **p ≤ 0.01.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 3: Nitric oxide suppresses KCC2 activity. (A) Glycinergic IPSCs were evoked in a mouse SPN neuron by electrical stimulation of the MNTB. The command potentials ranged from −120 to −30 mV in steps of 10 mV. The IPSC reversal potential changed from −80 mV in control conditions to −50 mV after the modulation of KCC2 activity by NO signaling. (B) Current–voltage relationship for the SPN-IPSCs shown in (A). The parallel shift of the curves indicates a sole change in reversal potential without changing the conductance. (C) Average data show a significant depolarizing shift in IPSC reversal potential following NO application in the SPN, but not in LSO or MSO. (D) The overall glycinergic conductance in SPN neurons is unchanged by NO, indicating no change in the glycine receptor or the glycine release to be involved. **p ≤ 0.01.
Mentions: Sustained synaptic stimulation causes generation of NO within the SOC (Steinert et al., 2008, 2011). Here, endogenous NO release was mimicked by bath application of the NO-donor (SNP; 100 μM) and its effect on KCC2 activity was measured. Strong KCC2 activity drives the negative Eglycine (Lohrke et al., 2005) in mature mammalian auditory brainstem neurons. Within the nuclei of the SOC in mouse and gerbil, mouse SPN neurons showed the largest deviation from calculated reversal potential for glycine (Figure 1C), suggesting that KCC2 activity is strongest in the SPN. Therefore, SPN neurons might support an activity-dependent mechanism that allows down-regulation of KCC2, but this seems to be less essential in the MSO and LSO. To test this hypothesis, the effect of NO on KCC2 activity in mouse LSO, MSO and SPN was measured before and during the application of NO. NO did not affect KCC2 activity in MSO or LSO neurons, but caused a depolarizing shift in Eglycine from −83.7 ± 5.4 mV to −67.3 ± 4.5 mV (n = 10, p = 0.002; Figures 3A–C), in the SPN consistent with suppression of KCC2. The IPSC current-voltage relationship showed a parallel shift (Figure 3B) and the glycinergic conductance did not change significantly during the NO application (IPSGcontrol: 39.1 ± 9.1 nS; IPSGNO: 36.7 ± 8.5 nS; n = 10; P = 0.57). These results indicate that there was no direct effect of NO signaling on the glycine receptors nor was there a major influence on presynaptic glycine release (Figure 3D).

Bottom Line: Here we show that nitric oxide (NO) signaling in the auditory brainstem (where activity-dependent generation of NO is documented) modulates the strength of inhibition by changing the chloride equilibrium potential.Recent evidence demonstrates that large inhibitory postsynaptic currents (IPSCs) in neurons of the superior paraolivary nucleus (SPN) are enhanced by a very low intracellular chloride concentration, generated by the neuronal potassium chloride co-transporter (KCC2) expressed in the postsynaptic neurons.Our data show that modulation by NO caused a 15 mV depolarizing shift of the IPSC reversal potential, reducing the strength of inhibition in SPN neurons, without changing the threshold for action potential firing.

View Article: PubMed Central - PubMed

Affiliation: Division of Neurobiology, Department Biology II, Ludwig-Maximilians-University Munich Planegg-Martinsried, Germany.

ABSTRACT
Glycinergic inhibition plays a central role in the auditory brainstem circuitries involved in sound localization and in the encoding of temporal action potential firing patterns. Modulation of this inhibition has the potential to fine-tune information processing in these networks. Here we show that nitric oxide (NO) signaling in the auditory brainstem (where activity-dependent generation of NO is documented) modulates the strength of inhibition by changing the chloride equilibrium potential. Recent evidence demonstrates that large inhibitory postsynaptic currents (IPSCs) in neurons of the superior paraolivary nucleus (SPN) are enhanced by a very low intracellular chloride concentration, generated by the neuronal potassium chloride co-transporter (KCC2) expressed in the postsynaptic neurons. Our data show that modulation by NO caused a 15 mV depolarizing shift of the IPSC reversal potential, reducing the strength of inhibition in SPN neurons, without changing the threshold for action potential firing. Regulating inhibitory strength, through cGMP-dependent changes in the efficacy of KCC2 in the target neuron provides a postsynaptic mechanism for rapidly controlling the inhibitory drive, without altering the timing or pattern of the afferent spike train. Therefore, this NO-mediated suppression of KCC2 can modulate inhibition in one target nucleus (SPN), without influencing inhibitory strength of other target nuclei (MSO, LSO) even though they are each receiving collaterals from the same afferent nucleus (a projection from the medial nucleus of the trapezoid body, MNTB).

Show MeSH
Related in: MedlinePlus