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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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Scheme of the signaling pathways activated by D1- and D2-like receptors in the spiral ganglion neurons.Receptors are shown as homodimers. Phosphorylation and glycosylation sites are indicated (P and Y). The drugs used in this work are shown in red. Lines with transverse-endings indicate blockade and those with circle-endings stimulation. D1-like receptors are coupled to a Gαs protein leading to AC stimulation, thus increasing cAMP levels and subsequent PKA activation. PKA phosphorylates the Na+ channels thus decreasing the INa. D2-like receptors are coupled to a Gαq protein whose activation stimulates the PLC, which cleaves PIP2 into IP3 and DAG, the IP3 increases the Ca2+ concentration, and both Ca2+ and DAG activates PKC leading also to a Na+ channel phosphorylation thus decreasing the INa. In both cases, phosphorylation was prevented by okadaic acid.
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pone.0120808.g008: Scheme of the signaling pathways activated by D1- and D2-like receptors in the spiral ganglion neurons.Receptors are shown as homodimers. Phosphorylation and glycosylation sites are indicated (P and Y). The drugs used in this work are shown in red. Lines with transverse-endings indicate blockade and those with circle-endings stimulation. D1-like receptors are coupled to a Gαs protein leading to AC stimulation, thus increasing cAMP levels and subsequent PKA activation. PKA phosphorylates the Na+ channels thus decreasing the INa. D2-like receptors are coupled to a Gαq protein whose activation stimulates the PLC, which cleaves PIP2 into IP3 and DAG, the IP3 increases the Ca2+ concentration, and both Ca2+ and DAG activates PKC leading also to a Na+ channel phosphorylation thus decreasing the INa. In both cases, phosphorylation was prevented by okadaic acid.

Mentions: Our results show that increasing the cAMP levels (using a cAMP analog plus a phosphodiesterase inhibitor or an AC activator) mimics the DA effect. Thus indicating that increase in the cAMP secondary to adenylyl cyclase activation leads to PKA activation. Together these results showed that D1-like dopamine receptors activate a Gαs/AC/cAMP/PKA pathway (Fig. 8). However, we cannot rule out the involvement of additional signaling pathways. The D1-like receptors have been shown to be coupled to three different signaling mechanisms: SCH-23390 sensitive Gαs/olf/AC/PKA, adenosine A2A receptor-dependent Gαs/olf/AC/PKA and Gαq/PLC [32]. In our experiments no significant effect was produced by PKC inhibition on D1-like receptor actions, indicating that Gαq protein seems not to participate in the SGNs D1 receptors response. In neostriatal neurons, even a marginal activation of PKC potentiates the effects of PKA [32], and in striato-nigral neurons (P25 rats), D1-like receptors decrease the INa via PKA, but PKC is also involved in the INa modulation [34].


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)

Scheme of the signaling pathways activated by D1- and D2-like receptors in the spiral ganglion neurons.Receptors are shown as homodimers. Phosphorylation and glycosylation sites are indicated (P and Y). The drugs used in this work are shown in red. Lines with transverse-endings indicate blockade and those with circle-endings stimulation. D1-like receptors are coupled to a Gαs protein leading to AC stimulation, thus increasing cAMP levels and subsequent PKA activation. PKA phosphorylates the Na+ channels thus decreasing the INa. D2-like receptors are coupled to a Gαq protein whose activation stimulates the PLC, which cleaves PIP2 into IP3 and DAG, the IP3 increases the Ca2+ concentration, and both Ca2+ and DAG activates PKC leading also to a Na+ channel phosphorylation thus decreasing the INa. In both cases, phosphorylation was prevented by okadaic acid.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0120808.g008: Scheme of the signaling pathways activated by D1- and D2-like receptors in the spiral ganglion neurons.Receptors are shown as homodimers. Phosphorylation and glycosylation sites are indicated (P and Y). The drugs used in this work are shown in red. Lines with transverse-endings indicate blockade and those with circle-endings stimulation. D1-like receptors are coupled to a Gαs protein leading to AC stimulation, thus increasing cAMP levels and subsequent PKA activation. PKA phosphorylates the Na+ channels thus decreasing the INa. D2-like receptors are coupled to a Gαq protein whose activation stimulates the PLC, which cleaves PIP2 into IP3 and DAG, the IP3 increases the Ca2+ concentration, and both Ca2+ and DAG activates PKC leading also to a Na+ channel phosphorylation thus decreasing the INa. In both cases, phosphorylation was prevented by okadaic acid.
Mentions: Our results show that increasing the cAMP levels (using a cAMP analog plus a phosphodiesterase inhibitor or an AC activator) mimics the DA effect. Thus indicating that increase in the cAMP secondary to adenylyl cyclase activation leads to PKA activation. Together these results showed that D1-like dopamine receptors activate a Gαs/AC/cAMP/PKA pathway (Fig. 8). However, we cannot rule out the involvement of additional signaling pathways. The D1-like receptors have been shown to be coupled to three different signaling mechanisms: SCH-23390 sensitive Gαs/olf/AC/PKA, adenosine A2A receptor-dependent Gαs/olf/AC/PKA and Gαq/PLC [32]. In our experiments no significant effect was produced by PKC inhibition on D1-like receptor actions, indicating that Gαq protein seems not to participate in the SGNs D1 receptors response. In neostriatal neurons, even a marginal activation of PKC potentiates the effects of PKA [32], and in striato-nigral neurons (P25 rats), D1-like receptors decrease the INa via PKA, but PKC is also involved in the INa modulation [34].

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