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Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb.

Borin M, Fogli Iseppe A, Pignatelli A, Belluzzi O - Front Cell Neurosci (2014)

Bottom Line: The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP.We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors.These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy.

ABSTRACT
Dopaminergic (DA) periglomerular (PG) neurons are critically placed at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons; they are autorhythmic and are the target of numerous terminals releasing a variety of neurotransmitters. Despite the centrality of their position, suggesting a critical role in the sensory processing, their properties -and consequently their function- remain elusive. The current mediated by inward rectifier potassium (Kir) channels in DA-PG cells was recorded by adopting the perforated-patch configuration in thin slices; IKir could be distinguished from the hyperpolarization-activated current (I h ) by showing full activation in <10 ms, no inactivation, suppression by Ba(2+) in a typical voltage-dependent manner (IC50 208 μM) and reversal potential nearly coincident with EK. Ba(2+) (2 mM) induces a large depolarization of DA-PG cells, paralleled by an increase of the input resistance, leading to a block of the spontaneous activity, but the Kir current is not an essential component of the pacemaker machinery. The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP. We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

No MeSH data available.


Related in: MedlinePlus

Effects of Barium on DA-PG cells. (A) Effect of Ba2+ on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 2 mM Ba2+ into the bath; starting at the time indicated by the downward arrow, a 40 pA hyperpolarizing current was injected; (further explanation in the text). (B) Frequency analysis of action potentials (SPS, spike per second) for the experiment shown in panel A; the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the activity after the injection of a hyperpolarizing current, at the time marked by a yellow point in (A). (C) Illustration of the method used for the calculation of the prevailing membrane potential (further explanation in the text): 10 s frequency count histograms of the membrane potential were realized at 10 s intervals, and the distributions were fitted by an exponentially modified Gaussian function (equation 3 in the text); the point marked by the red dot indicates the prevailing membrane potential (xc in equation 3). (D) Depolarization induced by 2 mM Ba2+ in the experiment shown in (A) using the analysis of the prevailing membrane potential (blue dots); the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the membrane potential at the time marked by a yellow point in (A). (E) Depolarization induced by two different concentrations of [Ba2+]o: 13. 3 ± 2.2 mV for 300 μM (n = 14), and 38.1 ± 6.0 mV for 2 mM (n = 7).
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Figure 4: Effects of Barium on DA-PG cells. (A) Effect of Ba2+ on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 2 mM Ba2+ into the bath; starting at the time indicated by the downward arrow, a 40 pA hyperpolarizing current was injected; (further explanation in the text). (B) Frequency analysis of action potentials (SPS, spike per second) for the experiment shown in panel A; the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the activity after the injection of a hyperpolarizing current, at the time marked by a yellow point in (A). (C) Illustration of the method used for the calculation of the prevailing membrane potential (further explanation in the text): 10 s frequency count histograms of the membrane potential were realized at 10 s intervals, and the distributions were fitted by an exponentially modified Gaussian function (equation 3 in the text); the point marked by the red dot indicates the prevailing membrane potential (xc in equation 3). (D) Depolarization induced by 2 mM Ba2+ in the experiment shown in (A) using the analysis of the prevailing membrane potential (blue dots); the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the membrane potential at the time marked by a yellow point in (A). (E) Depolarization induced by two different concentrations of [Ba2+]o: 13. 3 ± 2.2 mV for 300 μM (n = 14), and 38.1 ± 6.0 mV for 2 mM (n = 7).

Mentions: If the IKir is active at rest, then it should be expected that the block of the current with Ba2+ should influence both input resistance and resting potential; in effect, Ba2+ (2 mM) induces a rapid and strong depolarization of DA-PG cells (Figures 4A,C), paralleled by an increase of the firing frequency before its block in depolarization (Figures 4A,B).


Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb.

Borin M, Fogli Iseppe A, Pignatelli A, Belluzzi O - Front Cell Neurosci (2014)

Effects of Barium on DA-PG cells. (A) Effect of Ba2+ on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 2 mM Ba2+ into the bath; starting at the time indicated by the downward arrow, a 40 pA hyperpolarizing current was injected; (further explanation in the text). (B) Frequency analysis of action potentials (SPS, spike per second) for the experiment shown in panel A; the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the activity after the injection of a hyperpolarizing current, at the time marked by a yellow point in (A). (C) Illustration of the method used for the calculation of the prevailing membrane potential (further explanation in the text): 10 s frequency count histograms of the membrane potential were realized at 10 s intervals, and the distributions were fitted by an exponentially modified Gaussian function (equation 3 in the text); the point marked by the red dot indicates the prevailing membrane potential (xc in equation 3). (D) Depolarization induced by 2 mM Ba2+ in the experiment shown in (A) using the analysis of the prevailing membrane potential (blue dots); the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the membrane potential at the time marked by a yellow point in (A). (E) Depolarization induced by two different concentrations of [Ba2+]o: 13. 3 ± 2.2 mV for 300 μM (n = 14), and 38.1 ± 6.0 mV for 2 mM (n = 7).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 4: Effects of Barium on DA-PG cells. (A) Effect of Ba2+ on membrane potential. Perforated patch recording in standard saline (EC1 solution). The blue bar indicates the time of application of 2 mM Ba2+ into the bath; starting at the time indicated by the downward arrow, a 40 pA hyperpolarizing current was injected; (further explanation in the text). (B) Frequency analysis of action potentials (SPS, spike per second) for the experiment shown in panel A; the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the activity after the injection of a hyperpolarizing current, at the time marked by a yellow point in (A). (C) Illustration of the method used for the calculation of the prevailing membrane potential (further explanation in the text): 10 s frequency count histograms of the membrane potential were realized at 10 s intervals, and the distributions were fitted by an exponentially modified Gaussian function (equation 3 in the text); the point marked by the red dot indicates the prevailing membrane potential (xc in equation 3). (D) Depolarization induced by 2 mM Ba2+ in the experiment shown in (A) using the analysis of the prevailing membrane potential (blue dots); the dashed line marks the time at which Ba2+ has been applied and the yellow point after the x-axis interruption is a measure of the membrane potential at the time marked by a yellow point in (A). (E) Depolarization induced by two different concentrations of [Ba2+]o: 13. 3 ± 2.2 mV for 300 μM (n = 14), and 38.1 ± 6.0 mV for 2 mM (n = 7).
Mentions: If the IKir is active at rest, then it should be expected that the block of the current with Ba2+ should influence both input resistance and resting potential; in effect, Ba2+ (2 mM) induces a rapid and strong depolarization of DA-PG cells (Figures 4A,C), paralleled by an increase of the firing frequency before its block in depolarization (Figures 4A,B).

Bottom Line: The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP.We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors.These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Sciences and Biotechnology, University of Ferrara Ferrara, Italy.

ABSTRACT
Dopaminergic (DA) periglomerular (PG) neurons are critically placed at the entry of the bulbar circuitry, directly in contact with both the terminals of olfactory sensory neurons and the apical dendrites of projection neurons; they are autorhythmic and are the target of numerous terminals releasing a variety of neurotransmitters. Despite the centrality of their position, suggesting a critical role in the sensory processing, their properties -and consequently their function- remain elusive. The current mediated by inward rectifier potassium (Kir) channels in DA-PG cells was recorded by adopting the perforated-patch configuration in thin slices; IKir could be distinguished from the hyperpolarization-activated current (I h ) by showing full activation in <10 ms, no inactivation, suppression by Ba(2+) in a typical voltage-dependent manner (IC50 208 μM) and reversal potential nearly coincident with EK. Ba(2+) (2 mM) induces a large depolarization of DA-PG cells, paralleled by an increase of the input resistance, leading to a block of the spontaneous activity, but the Kir current is not an essential component of the pacemaker machinery. The Kir current is negatively modulated by intracellular cAMP, as shown by a decrease of its amplitude induced by forskolin or 8Br-cAMP. We have also tested the neuromodulatory effects of the activation of several metabotropic receptors known to be present on these cells, showing that the current can be modulated by a multiplicity of pathways, whose activation in some case increases the amplitude of the current, as can be observed with agonists of D2, muscarinic, and GABAA receptors, whereas in other cases has the opposite effect, as it can be observed with agonists of α1 noradrenergic, 5-HT and histamine receptors. These characteristics of the Kir currents provide the basis for an unexpected plasticity of DA-PG cell function, making them potentially capable to reconfigure the bulbar network to allow a better flexibility.

No MeSH data available.


Related in: MedlinePlus