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Dopaminergic modulation of the voltage-gated sodium current in the cochlear afferent neurons of the rat.

Valdés-Baizabal C, Soto E, Vega R - PLoS ONE (2015)

Bottom Line: Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability.The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively.These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México.

ABSTRACT
The cochlear inner hair cells synapse onto type I afferent terminal dendrites, constituting the main afferent pathway for auditory information flow. This pathway receives central control input from the lateral olivocochlear efferent neurons that release various neurotransmitters, among which dopamine (DA) plays a salient role. DA receptors activation exert a protective role in the over activation of the afferent glutamatergic synapses, which occurs when an animal is exposed to intense sound stimuli or during hypoxic events. However, the mechanism of action of DA at the cellular level is still not completely understood. In this work, we studied the actions of DA and its receptor agonists and antagonists on the voltage-gated sodium current (INa) in isolated cochlear afferent neurons of the rat to define the mechanisms of dopaminergic control of the afferent input in the cochlear pathway. Experiments were performed using the voltage and current clamp techniques in the whole-cell configuration in primary cultures of cochlear spiral ganglion neurons (SGNs). Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability. Inhibition of the INa was produced by a phosphorylation of the sodium channels as shown by the use of phosphatase inhibitor that produced an inhibition analogous to that caused by DA receptor activation. Use of specific agonists and antagonists showed that inhibitory action of DA was mediated both by activation of D1- and D2-like DA receptors. The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively. These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

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Effects of quinpirole on the INa.A) Typical recordings of the INa under control conditions and after 1 μM quinpirole perfusion. B) Current- voltage relationship of the INa in control conditions and after 1 μM quinpirole. The maximum inhibition was 28 ± 6% at −10 mV. C) Conductance activation and steady state inactivation curves of the INa in control conditions and after 1 μM quinpirole perfusion. Quinpirole caused a 5 mV hyperpolarizing shift in the V½ of the inactivation curve. D) Current-voltage relationship of the INa in control condition (with 1 μM eticlopride) and after coapplication of 1 μM quinpirole. E) Bar graph of the percent inhibition of the INa by quinpirole in control, with NPC-15437 in the intracellular solution (P = 0.004) and when the cells were preincubated with U-73122 (P = 0.02) or PTx (P = 0.82). Insets above bars show typical recordings of the INa in control and after drug application. Calibration bars 0.5 nA, 1 ms for all recordings.
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pone.0120808.g006: Effects of quinpirole on the INa.A) Typical recordings of the INa under control conditions and after 1 μM quinpirole perfusion. B) Current- voltage relationship of the INa in control conditions and after 1 μM quinpirole. The maximum inhibition was 28 ± 6% at −10 mV. C) Conductance activation and steady state inactivation curves of the INa in control conditions and after 1 μM quinpirole perfusion. Quinpirole caused a 5 mV hyperpolarizing shift in the V½ of the inactivation curve. D) Current-voltage relationship of the INa in control condition (with 1 μM eticlopride) and after coapplication of 1 μM quinpirole. E) Bar graph of the percent inhibition of the INa by quinpirole in control, with NPC-15437 in the intracellular solution (P = 0.004) and when the cells were preincubated with U-73122 (P = 0.02) or PTx (P = 0.82). Insets above bars show typical recordings of the INa in control and after drug application. Calibration bars 0.5 nA, 1 ms for all recordings.

Mentions: The application of the D2-like receptor agonist quinpirole (1 μM) significantly decreased the INa peak amplitude at all the voltages (n = 10) (Fig. 6A-B). At −10 mV, the INa peak amplitude was 28 ± 6% (P = 0.001). The V½ of the inactivation curve was shifted 5 mV leftward (P < 0.001), with no changes in the slope (Fig. 6C). The effects of quinpirole were blocked by 1 μM eticlopride (D2-like receptor antagonist), which reduced quinpirole action to 2 ± 6% (n = 4; P = 0.76, Fig. 6D).


Dopaminergic modulation of the voltage-gated sodium current in the cochlear afferent neurons of the rat.

Valdés-Baizabal C, Soto E, Vega R - PLoS ONE (2015)

Effects of quinpirole on the INa.A) Typical recordings of the INa under control conditions and after 1 μM quinpirole perfusion. B) Current- voltage relationship of the INa in control conditions and after 1 μM quinpirole. The maximum inhibition was 28 ± 6% at −10 mV. C) Conductance activation and steady state inactivation curves of the INa in control conditions and after 1 μM quinpirole perfusion. Quinpirole caused a 5 mV hyperpolarizing shift in the V½ of the inactivation curve. D) Current-voltage relationship of the INa in control condition (with 1 μM eticlopride) and after coapplication of 1 μM quinpirole. E) Bar graph of the percent inhibition of the INa by quinpirole in control, with NPC-15437 in the intracellular solution (P = 0.004) and when the cells were preincubated with U-73122 (P = 0.02) or PTx (P = 0.82). Insets above bars show typical recordings of the INa in control and after drug application. Calibration bars 0.5 nA, 1 ms for all recordings.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4359166&req=5

pone.0120808.g006: Effects of quinpirole on the INa.A) Typical recordings of the INa under control conditions and after 1 μM quinpirole perfusion. B) Current- voltage relationship of the INa in control conditions and after 1 μM quinpirole. The maximum inhibition was 28 ± 6% at −10 mV. C) Conductance activation and steady state inactivation curves of the INa in control conditions and after 1 μM quinpirole perfusion. Quinpirole caused a 5 mV hyperpolarizing shift in the V½ of the inactivation curve. D) Current-voltage relationship of the INa in control condition (with 1 μM eticlopride) and after coapplication of 1 μM quinpirole. E) Bar graph of the percent inhibition of the INa by quinpirole in control, with NPC-15437 in the intracellular solution (P = 0.004) and when the cells were preincubated with U-73122 (P = 0.02) or PTx (P = 0.82). Insets above bars show typical recordings of the INa in control and after drug application. Calibration bars 0.5 nA, 1 ms for all recordings.
Mentions: The application of the D2-like receptor agonist quinpirole (1 μM) significantly decreased the INa peak amplitude at all the voltages (n = 10) (Fig. 6A-B). At −10 mV, the INa peak amplitude was 28 ± 6% (P = 0.001). The V½ of the inactivation curve was shifted 5 mV leftward (P < 0.001), with no changes in the slope (Fig. 6C). The effects of quinpirole were blocked by 1 μM eticlopride (D2-like receptor antagonist), which reduced quinpirole action to 2 ± 6% (n = 4; P = 0.76, Fig. 6D).

Bottom Line: Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability.The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively.These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

View Article: PubMed Central - PubMed

Affiliation: Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, México.

ABSTRACT
The cochlear inner hair cells synapse onto type I afferent terminal dendrites, constituting the main afferent pathway for auditory information flow. This pathway receives central control input from the lateral olivocochlear efferent neurons that release various neurotransmitters, among which dopamine (DA) plays a salient role. DA receptors activation exert a protective role in the over activation of the afferent glutamatergic synapses, which occurs when an animal is exposed to intense sound stimuli or during hypoxic events. However, the mechanism of action of DA at the cellular level is still not completely understood. In this work, we studied the actions of DA and its receptor agonists and antagonists on the voltage-gated sodium current (INa) in isolated cochlear afferent neurons of the rat to define the mechanisms of dopaminergic control of the afferent input in the cochlear pathway. Experiments were performed using the voltage and current clamp techniques in the whole-cell configuration in primary cultures of cochlear spiral ganglion neurons (SGNs). Recordings of the INa showed that DA receptor activation induced a significant inhibition of the peak current amplitude, leading to a significant decrease in cell excitability. Inhibition of the INa was produced by a phosphorylation of the sodium channels as shown by the use of phosphatase inhibitor that produced an inhibition analogous to that caused by DA receptor activation. Use of specific agonists and antagonists showed that inhibitory action of DA was mediated both by activation of D1- and D2-like DA receptors. The action of the D1- and D2-like receptors was shown to be mediated by a Gαs/AC/cAMP/PKA and Gαq/PLC/PKC pathways respectively. These results showed that DA receptor activation constitutes a significant modulatory input to SGNs, effectively modulating their excitability and information flow in the auditory pathway.

Show MeSH
Related in: MedlinePlus