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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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Current clamp response to sinusoidal stimulation and DA receptor activation.A) The use of 100 nM dihydrexidine (blue traces) shifted the maximum repolarization rate and increased the action potential duration. B) Phase plane plot of action potentials under control conditions and after dihydrexidine application. C) Action potentials produced by a current pulse injection of 150 pA were reduced from 13 under control conditions to 4 after dihydrexidine (100 nM). D) Typical response to sinusoidal current injection (10 Hz, 150 pA). Before the stimuli, the cells were held at −80 mV. E) In a cell discharging in a 2:1 phase lock to sinusoidal stimuli, the use of DA reduced action potential discharges per cycle to a phase lock of 1:1 F) Bar graph showing the percent change in the number of action potentials in the control, after 100 μM DA application and after washout of the drug.
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pone.0120808.g007: Current clamp response to sinusoidal stimulation and DA receptor activation.A) The use of 100 nM dihydrexidine (blue traces) shifted the maximum repolarization rate and increased the action potential duration. B) Phase plane plot of action potentials under control conditions and after dihydrexidine application. C) Action potentials produced by a current pulse injection of 150 pA were reduced from 13 under control conditions to 4 after dihydrexidine (100 nM). D) Typical response to sinusoidal current injection (10 Hz, 150 pA). Before the stimuli, the cells were held at −80 mV. E) In a cell discharging in a 2:1 phase lock to sinusoidal stimuli, the use of DA reduced action potential discharges per cycle to a phase lock of 1:1 F) Bar graph showing the percent change in the number of action potentials in the control, after 100 μM DA application and after washout of the drug.

Mentions: Current clamp recordings of SGNs were also performed to examine voltage responses to current pulse injection. The cell voltage was fixed at −80 mV, and at more depolarized membrane voltages, no action potential discharge was produced even by highly depolarizing (> 50 mV) current pulse injection. Action potential waveform parameters under control conditions were (n = 24): amplitude = 117 ± 5 mV, duration = 1 ± 0.2 ms, latency = 4 ± 1 ms, threshold = -38 ± 2 mV, MDR = 144 ± 11 mV/ms, MRR-150 ± 9 mV/ms. The use of DA agonists in current clamp experiments revealed that action potential parameters showed various modifications, summarized in Table 1. DA 100 μM decreased the action potential amplitude 10 ± 3%, (n = 4, P = 0.04) with non-significant changes in other action potential parameters. Under 100 ms current injection, 90% (n = 46) of the cells produced a single action potential when stimulated with suprathreshold depolarizing current pulses. The other 8% slowly adapted producing between 3–7 action potentials, and only 2% of the cells produced sustained, non-adapting, repetitive spiking. In neurons with repetitive spike activity under square current pulse injection, the D1 agonist dihydrexidine (100 nM, n = 10) produced a significant decrease of the MRR from −154 to −140 mV/ms (P = 0.005). The duration at 50% of the action potential was increased by 7 ± 0.1% (P = 0.005), and in two cells that showed repetitive spike activity, a reversible (44%) reduction in the number of action potentials produced by the current pulse injection was induced (Fig. 7A-C).


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)

Current clamp response to sinusoidal stimulation and DA receptor activation.A) The use of 100 nM dihydrexidine (blue traces) shifted the maximum repolarization rate and increased the action potential duration. B) Phase plane plot of action potentials under control conditions and after dihydrexidine application. C) Action potentials produced by a current pulse injection of 150 pA were reduced from 13 under control conditions to 4 after dihydrexidine (100 nM). D) Typical response to sinusoidal current injection (10 Hz, 150 pA). Before the stimuli, the cells were held at −80 mV. E) In a cell discharging in a 2:1 phase lock to sinusoidal stimuli, the use of DA reduced action potential discharges per cycle to a phase lock of 1:1 F) Bar graph showing the percent change in the number of action potentials in the control, after 100 μM DA application and after washout of the drug.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0120808.g007: Current clamp response to sinusoidal stimulation and DA receptor activation.A) The use of 100 nM dihydrexidine (blue traces) shifted the maximum repolarization rate and increased the action potential duration. B) Phase plane plot of action potentials under control conditions and after dihydrexidine application. C) Action potentials produced by a current pulse injection of 150 pA were reduced from 13 under control conditions to 4 after dihydrexidine (100 nM). D) Typical response to sinusoidal current injection (10 Hz, 150 pA). Before the stimuli, the cells were held at −80 mV. E) In a cell discharging in a 2:1 phase lock to sinusoidal stimuli, the use of DA reduced action potential discharges per cycle to a phase lock of 1:1 F) Bar graph showing the percent change in the number of action potentials in the control, after 100 μM DA application and after washout of the drug.
Mentions: Current clamp recordings of SGNs were also performed to examine voltage responses to current pulse injection. The cell voltage was fixed at −80 mV, and at more depolarized membrane voltages, no action potential discharge was produced even by highly depolarizing (> 50 mV) current pulse injection. Action potential waveform parameters under control conditions were (n = 24): amplitude = 117 ± 5 mV, duration = 1 ± 0.2 ms, latency = 4 ± 1 ms, threshold = -38 ± 2 mV, MDR = 144 ± 11 mV/ms, MRR-150 ± 9 mV/ms. The use of DA agonists in current clamp experiments revealed that action potential parameters showed various modifications, summarized in Table 1. DA 100 μM decreased the action potential amplitude 10 ± 3%, (n = 4, P = 0.04) with non-significant changes in other action potential parameters. Under 100 ms current injection, 90% (n = 46) of the cells produced a single action potential when stimulated with suprathreshold depolarizing current pulses. The other 8% slowly adapted producing between 3–7 action potentials, and only 2% of the cells produced sustained, non-adapting, repetitive spiking. In neurons with repetitive spike activity under square current pulse injection, the D1 agonist dihydrexidine (100 nM, n = 10) produced a significant decrease of the MRR from −154 to −140 mV/ms (P = 0.005). The duration at 50% of the action potential was increased by 7 ± 0.1% (P = 0.005), and in two cells that showed repetitive spike activity, a reversible (44%) reduction in the number of action potentials produced by the current pulse injection was induced (Fig. 7A-C).

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