Limits...
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

Effect of different concentrations of Ba2+ on input resistance. (A,B) Sample tracings showing the response to the injection of 40 pA in current-clamp conditions for the indicated external Ba2+ concentrations. (C) Increase of input resistance at the indicated external Ba2+ concentrations: +17.8 ± 3.2%, n = 12, and 58.7 ± 14.2%, n = 10 in 0.3 and 2 mM external [Ba2+]o with respect to controls. ** and *** indicate significance levels of 0.01 and 0.001, respectively. (D) Family of tracings obtained in response to hyperpolarizing current pulses as indicated in (A); green and blue traces are taken at the beginning and at the end of a 5′ test; Ba2+ was applied after 2′. (E) Time course of the variation of input resistance for the experiment shown in (D); the dashed line marks the time of application of Ba2+ 2 mM; green and blue dots mark the resistance of the traces with the same color in (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4126183&req=5

Figure 5: Effect of different concentrations of Ba2+ on input resistance. (A,B) Sample tracings showing the response to the injection of 40 pA in current-clamp conditions for the indicated external Ba2+ concentrations. (C) Increase of input resistance at the indicated external Ba2+ concentrations: +17.8 ± 3.2%, n = 12, and 58.7 ± 14.2%, n = 10 in 0.3 and 2 mM external [Ba2+]o with respect to controls. ** and *** indicate significance levels of 0.01 and 0.001, respectively. (D) Family of tracings obtained in response to hyperpolarizing current pulses as indicated in (A); green and blue traces are taken at the beginning and at the end of a 5′ test; Ba2+ was applied after 2′. (E) Time course of the variation of input resistance for the experiment shown in (D); the dashed line marks the time of application of Ba2+ 2 mM; green and blue dots mark the resistance of the traces with the same color in (D).

Mentions: Next, we tested the variations of the input resistance in response to hyperpolarizing current pulses in presence of 0.3 and 2 mM Ba2+ (Figures 5A,B). In these conditions, for both concentrations we observed an increase of the membrane impedance (Figures 5D,E). In Ba2+ 0.3 mM the membrane impedance changes from 1079.6 ± 163.9 to 1260.0 ± 186.5 MΩ (Figure 5C; n = 12, p = 0.00033, t-test for paired data), and in Ba2+ 2 mM the mean value changes from 1061.6 ± 202.0 MΩ to 1621.2 ± 284.2 MΩ (n = 10; Figure 5C; p = 0.0018, t-test for paired data).


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)

Effect of different concentrations of Ba2+ on input resistance. (A,B) Sample tracings showing the response to the injection of 40 pA in current-clamp conditions for the indicated external Ba2+ concentrations. (C) Increase of input resistance at the indicated external Ba2+ concentrations: +17.8 ± 3.2%, n = 12, and 58.7 ± 14.2%, n = 10 in 0.3 and 2 mM external [Ba2+]o with respect to controls. ** and *** indicate significance levels of 0.01 and 0.001, respectively. (D) Family of tracings obtained in response to hyperpolarizing current pulses as indicated in (A); green and blue traces are taken at the beginning and at the end of a 5′ test; Ba2+ was applied after 2′. (E) Time course of the variation of input resistance for the experiment shown in (D); the dashed line marks the time of application of Ba2+ 2 mM; green and blue dots mark the resistance of the traces with the same color in (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126183&req=5

Figure 5: Effect of different concentrations of Ba2+ on input resistance. (A,B) Sample tracings showing the response to the injection of 40 pA in current-clamp conditions for the indicated external Ba2+ concentrations. (C) Increase of input resistance at the indicated external Ba2+ concentrations: +17.8 ± 3.2%, n = 12, and 58.7 ± 14.2%, n = 10 in 0.3 and 2 mM external [Ba2+]o with respect to controls. ** and *** indicate significance levels of 0.01 and 0.001, respectively. (D) Family of tracings obtained in response to hyperpolarizing current pulses as indicated in (A); green and blue traces are taken at the beginning and at the end of a 5′ test; Ba2+ was applied after 2′. (E) Time course of the variation of input resistance for the experiment shown in (D); the dashed line marks the time of application of Ba2+ 2 mM; green and blue dots mark the resistance of the traces with the same color in (D).
Mentions: Next, we tested the variations of the input resistance in response to hyperpolarizing current pulses in presence of 0.3 and 2 mM Ba2+ (Figures 5A,B). In these conditions, for both concentrations we observed an increase of the membrane impedance (Figures 5D,E). In Ba2+ 0.3 mM the membrane impedance changes from 1079.6 ± 163.9 to 1260.0 ± 186.5 MΩ (Figure 5C; n = 12, p = 0.00033, t-test for paired data), and in Ba2+ 2 mM the mean value changes from 1061.6 ± 202.0 MΩ to 1621.2 ± 284.2 MΩ (n = 10; Figure 5C; p = 0.0018, t-test for paired data).

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