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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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Intracellular mechanism inherent to D1- and D2-like receptors.Bars indicate the percent INa inhibition produced by 100 μM DA and compared with its effect when 500 μM GDP-β-S (P < 0.001) were added intracellularly. The perfusion of 100 nM okadaic acid decreased the INa amplitude in a similar percentage as 100 μM DA (P = 0.3 unpaired t-test). While 100 nM okadaic acid added intracellularly occluded the DA action (P = 0.01). Insets above bars show representative recordings in control conditions and after drug application. Asterisks denote a significant difference (P < 0.05 unpaired t-test). Calibration bars are 1 ms and 0.5 nA for all recordings.
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pone.0120808.g003: Intracellular mechanism inherent to D1- and D2-like receptors.Bars indicate the percent INa inhibition produced by 100 μM DA and compared with its effect when 500 μM GDP-β-S (P < 0.001) were added intracellularly. The perfusion of 100 nM okadaic acid decreased the INa amplitude in a similar percentage as 100 μM DA (P = 0.3 unpaired t-test). While 100 nM okadaic acid added intracellularly occluded the DA action (P = 0.01). Insets above bars show representative recordings in control conditions and after drug application. Asterisks denote a significant difference (P < 0.05 unpaired t-test). Calibration bars are 1 ms and 0.5 nA for all recordings.

Mentions: To determine the participation of G-proteins in the DA action, GDP-β-S (500 μM), which is a non-hydrolyzable GDP analog was used to block G proteins (GDP-β-S was dissolved in the intracellular solution, n = 5). In this condition, DA (100 μM) perfusion did not produce any significant effect on the INa amplitude (current increased 8 ± 5%, P = 0.265), nor significant changes in the activation or inactivation curves or voltage sensitivity of the INa, indicating that DA receptor activation implies the activation of a G-protein coupled receptor (Fig. 3).


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)

Intracellular mechanism inherent to D1- and D2-like receptors.Bars indicate the percent INa inhibition produced by 100 μM DA and compared with its effect when 500 μM GDP-β-S (P < 0.001) were added intracellularly. The perfusion of 100 nM okadaic acid decreased the INa amplitude in a similar percentage as 100 μM DA (P = 0.3 unpaired t-test). While 100 nM okadaic acid added intracellularly occluded the DA action (P = 0.01). Insets above bars show representative recordings in control conditions and after drug application. Asterisks denote a significant difference (P < 0.05 unpaired t-test). Calibration bars are 1 ms and 0.5 nA for all recordings.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0120808.g003: Intracellular mechanism inherent to D1- and D2-like receptors.Bars indicate the percent INa inhibition produced by 100 μM DA and compared with its effect when 500 μM GDP-β-S (P < 0.001) were added intracellularly. The perfusion of 100 nM okadaic acid decreased the INa amplitude in a similar percentage as 100 μM DA (P = 0.3 unpaired t-test). While 100 nM okadaic acid added intracellularly occluded the DA action (P = 0.01). Insets above bars show representative recordings in control conditions and after drug application. Asterisks denote a significant difference (P < 0.05 unpaired t-test). Calibration bars are 1 ms and 0.5 nA for all recordings.
Mentions: To determine the participation of G-proteins in the DA action, GDP-β-S (500 μM), which is a non-hydrolyzable GDP analog was used to block G proteins (GDP-β-S was dissolved in the intracellular solution, n = 5). In this condition, DA (100 μM) perfusion did not produce any significant effect on the INa amplitude (current increased 8 ± 5%, P = 0.265), nor significant changes in the activation or inactivation curves or voltage sensitivity of the INa, indicating that DA receptor activation implies the activation of a G-protein coupled receptor (Fig. 3).

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