Limits...
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.

Show MeSH

Related in: MedlinePlus

Transducer mechanisms activated by D1-like receptors.Bars show the effect of A-68930 in control condition in comparison with its action while other drugs were used. The use of H89 in the intracellular solution decreased the inhibitory effect of A-68930 from 29 ± 4% to 16 ± 5% at −10 mV (P = 0.08). When cells were preincubated with 50 μM Rp-cAMP, A-68930 effect was completely blocked (P < 0.001). Coapplication of 8-Br-cAMP and IBMX mixture caused a decrease in the INa current which mimicked the effect of A-68930 (P = 0.114). Forskolin also mimicked the effect of D1-like agonist decreasing the INa 18 ± 11% (P = 0.27). The NPC-15437 in the intracellular solution did not significantly modify the A-68930 effect (P = 0.92). Insets above bars show typical recordings of the INa under control conditions and after drug application. Calibration bars are 2 ms and 0.5 nA for all recordings.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4359166&req=5

pone.0120808.g005: Transducer mechanisms activated by D1-like receptors.Bars show the effect of A-68930 in control condition in comparison with its action while other drugs were used. The use of H89 in the intracellular solution decreased the inhibitory effect of A-68930 from 29 ± 4% to 16 ± 5% at −10 mV (P = 0.08). When cells were preincubated with 50 μM Rp-cAMP, A-68930 effect was completely blocked (P < 0.001). Coapplication of 8-Br-cAMP and IBMX mixture caused a decrease in the INa current which mimicked the effect of A-68930 (P = 0.114). Forskolin also mimicked the effect of D1-like agonist decreasing the INa 18 ± 11% (P = 0.27). The NPC-15437 in the intracellular solution did not significantly modify the A-68930 effect (P = 0.92). Insets above bars show typical recordings of the INa under control conditions and after drug application. Calibration bars are 2 ms and 0.5 nA for all recordings.

Mentions: Inclusion of a selective inhibitor of PKA, H89 (1 μM), in the intracellular solution (n = 6) produced a decrease in the effect of 300 nM of A-68930 on the INa from 29 ± 4% in control condition to 16 ± 5% (at −10 mV) (P = 0.027). No changes in the V½ or the slope of activation or inactivation curves were found (Fig. 5).


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)

Transducer mechanisms activated by D1-like receptors.Bars show the effect of A-68930 in control condition in comparison with its action while other drugs were used. The use of H89 in the intracellular solution decreased the inhibitory effect of A-68930 from 29 ± 4% to 16 ± 5% at −10 mV (P = 0.08). When cells were preincubated with 50 μM Rp-cAMP, A-68930 effect was completely blocked (P < 0.001). Coapplication of 8-Br-cAMP and IBMX mixture caused a decrease in the INa current which mimicked the effect of A-68930 (P = 0.114). Forskolin also mimicked the effect of D1-like agonist decreasing the INa 18 ± 11% (P = 0.27). The NPC-15437 in the intracellular solution did not significantly modify the A-68930 effect (P = 0.92). Insets above bars show typical recordings of the INa under control conditions and after drug application. Calibration bars are 2 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.g005: Transducer mechanisms activated by D1-like receptors.Bars show the effect of A-68930 in control condition in comparison with its action while other drugs were used. The use of H89 in the intracellular solution decreased the inhibitory effect of A-68930 from 29 ± 4% to 16 ± 5% at −10 mV (P = 0.08). When cells were preincubated with 50 μM Rp-cAMP, A-68930 effect was completely blocked (P < 0.001). Coapplication of 8-Br-cAMP and IBMX mixture caused a decrease in the INa current which mimicked the effect of A-68930 (P = 0.114). Forskolin also mimicked the effect of D1-like agonist decreasing the INa 18 ± 11% (P = 0.27). The NPC-15437 in the intracellular solution did not significantly modify the A-68930 effect (P = 0.92). Insets above bars show typical recordings of the INa under control conditions and after drug application. Calibration bars are 2 ms and 0.5 nA for all recordings.
Mentions: Inclusion of a selective inhibitor of PKA, H89 (1 μM), in the intracellular solution (n = 6) produced a decrease in the effect of 300 nM of A-68930 on the INa from 29 ± 4% in control condition to 16 ± 5% (at −10 mV) (P = 0.027). No changes in the V½ or the slope of activation or inactivation curves were found (Fig. 5).

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