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The M-current contributes to high threshold membrane potential oscillations in a cell type-specific way in the pedunculopontine nucleus of mice.

Bordas C, Kovacs A, Pal B - Front Cell Neurosci (2015)

Bottom Line: Blockade of the M-current abolished the oscillatory activity at 20 Hz, and largely diminished it at other frequencies.Taken together, the M-current seems to be characteristic for PPN cholinergic neurons.It provides a possibility for modulating gamma band activity of these cells, thus contributing to neuromodulatory regulation of the reticular activating system.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Medicine, Department of Physiology, University of Debrecen Debrecen, Hungary.

ABSTRACT
The pedunculopontine nucleus is known as a cholinergic nucleus of the reticular activating system, participating in regulation of sleep and wakefulness. Besides cholinergic neurons, it consists of GABAergic and glutamatergic neurons as well. According to classical and recent studies, more subgroups of neurons were defined. Groups based on the neurotransmitter released by a neuron are not homogenous, but can be further subdivided. The PPN neurons do not only provide cholinergic and non-cholinergic inputs to several subcortical brain areas but they are also targets of cholinergic and other different neuromodulatory actions. Although cholinergic neuromodulation has been already investigated in the nucleus, one of its characteristic targets, the M-type potassium current has not been described yet. Using slice electrophysiology, we provide evidence in the present work that cholinergic neurons possess M-current, whereas GABAergic neurons lack it. The M-current contributes to certain functional differences of cholinergic and GABAergic neurons, as spike frequency adaptation, action potential firing frequency or the amplitude difference of medium afterhyperpolarizations (AHPs). Furthermore, we showed that high threshold membrane potential oscillation with high power, around 20 Hz frequency is a functional property of almost all cholinergic cells, whereas GABAergic neurons have only low amplitude oscillations. Blockade of the M-current abolished the oscillatory activity at 20 Hz, and largely diminished it at other frequencies. Taken together, the M-current seems to be characteristic for PPN cholinergic neurons. It provides a possibility for modulating gamma band activity of these cells, thus contributing to neuromodulatory regulation of the reticular activating system.

No MeSH data available.


Related in: MedlinePlus

Cholinergic neurons possess M-current, whereas GABAergic neurons lack it. (A–C) Identification of a cholinergic neuron. Scale bar = 50 μm. (A) ChAT-dependent tdTomato expression (red). (B) Biocytin labeling of a recorded neuron (green). (C) Merged image. (D) Current traces from a cholinergic neuron elicited by the voltage protocol at the top of the panel. (E) Current trace at −40 mV repolarizing step. Dotted lines indicate the instantaneous (upper dotted line) and the steady state (lower dotted line) current components. The M-current was determined as the difference of these current components. The red trace indicates the fitting of the declining phase of the current (see text). (F) Voltage-dependence of the M-current amplitude (X axis: amplitudes of repolarizing current steps). (G) Pharmacological identification of the M-current (black = control; red = 20 μM XE991). (H) The XE991-sensitive current; calculated by the digital subtraction of the control and XE991-resistant current traces. The clear difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV also represent the presence of M-current. (I–K) Identification of a GABAergic neuron. (I) GAD2-dependent tdTomato expression (red). (J) Biocytin labeling of a recorded neuron (green). (K) Merged image. (L) Current traces from a GABAergic neuron elicited by the same voltage protocol as on panel (D). (M) Current trace at −40 mV repolarizing step. Note that there is almost no difference between the instantaneous and steady state currents. (N) None of the repolarizing steps elicited M-current. (O) Currents from GABAergic neurons did not show XE991-sensitivity. (P) Digital subtraction of current traces under control conditions and in the presence of XE991. The lack of difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV indicates that M-current was not recorded.
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Figure 1: Cholinergic neurons possess M-current, whereas GABAergic neurons lack it. (A–C) Identification of a cholinergic neuron. Scale bar = 50 μm. (A) ChAT-dependent tdTomato expression (red). (B) Biocytin labeling of a recorded neuron (green). (C) Merged image. (D) Current traces from a cholinergic neuron elicited by the voltage protocol at the top of the panel. (E) Current trace at −40 mV repolarizing step. Dotted lines indicate the instantaneous (upper dotted line) and the steady state (lower dotted line) current components. The M-current was determined as the difference of these current components. The red trace indicates the fitting of the declining phase of the current (see text). (F) Voltage-dependence of the M-current amplitude (X axis: amplitudes of repolarizing current steps). (G) Pharmacological identification of the M-current (black = control; red = 20 μM XE991). (H) The XE991-sensitive current; calculated by the digital subtraction of the control and XE991-resistant current traces. The clear difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV also represent the presence of M-current. (I–K) Identification of a GABAergic neuron. (I) GAD2-dependent tdTomato expression (red). (J) Biocytin labeling of a recorded neuron (green). (K) Merged image. (L) Current traces from a GABAergic neuron elicited by the same voltage protocol as on panel (D). (M) Current trace at −40 mV repolarizing step. Note that there is almost no difference between the instantaneous and steady state currents. (N) None of the repolarizing steps elicited M-current. (O) Currents from GABAergic neurons did not show XE991-sensitivity. (P) Digital subtraction of current traces under control conditions and in the presence of XE991. The lack of difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV indicates that M-current was not recorded.

Mentions: In order to detect M-current of different types of PPN neurons, mice expressing tdTomato fluorescent protein in a GAD2- or ChAT-promoter-dependent way were used. The identified tdTomato-expressing neurons were filled with biocytin, and later recovered; and confocal images were taken in order to assess their location and document their GAD2- or ChAT-positivity (Figures 1A–C,I–K).


The M-current contributes to high threshold membrane potential oscillations in a cell type-specific way in the pedunculopontine nucleus of mice.

Bordas C, Kovacs A, Pal B - Front Cell Neurosci (2015)

Cholinergic neurons possess M-current, whereas GABAergic neurons lack it. (A–C) Identification of a cholinergic neuron. Scale bar = 50 μm. (A) ChAT-dependent tdTomato expression (red). (B) Biocytin labeling of a recorded neuron (green). (C) Merged image. (D) Current traces from a cholinergic neuron elicited by the voltage protocol at the top of the panel. (E) Current trace at −40 mV repolarizing step. Dotted lines indicate the instantaneous (upper dotted line) and the steady state (lower dotted line) current components. The M-current was determined as the difference of these current components. The red trace indicates the fitting of the declining phase of the current (see text). (F) Voltage-dependence of the M-current amplitude (X axis: amplitudes of repolarizing current steps). (G) Pharmacological identification of the M-current (black = control; red = 20 μM XE991). (H) The XE991-sensitive current; calculated by the digital subtraction of the control and XE991-resistant current traces. The clear difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV also represent the presence of M-current. (I–K) Identification of a GABAergic neuron. (I) GAD2-dependent tdTomato expression (red). (J) Biocytin labeling of a recorded neuron (green). (K) Merged image. (L) Current traces from a GABAergic neuron elicited by the same voltage protocol as on panel (D). (M) Current trace at −40 mV repolarizing step. Note that there is almost no difference between the instantaneous and steady state currents. (N) None of the repolarizing steps elicited M-current. (O) Currents from GABAergic neurons did not show XE991-sensitivity. (P) Digital subtraction of current traces under control conditions and in the presence of XE991. The lack of difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV indicates that M-current was not recorded.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4388076&req=5

Figure 1: Cholinergic neurons possess M-current, whereas GABAergic neurons lack it. (A–C) Identification of a cholinergic neuron. Scale bar = 50 μm. (A) ChAT-dependent tdTomato expression (red). (B) Biocytin labeling of a recorded neuron (green). (C) Merged image. (D) Current traces from a cholinergic neuron elicited by the voltage protocol at the top of the panel. (E) Current trace at −40 mV repolarizing step. Dotted lines indicate the instantaneous (upper dotted line) and the steady state (lower dotted line) current components. The M-current was determined as the difference of these current components. The red trace indicates the fitting of the declining phase of the current (see text). (F) Voltage-dependence of the M-current amplitude (X axis: amplitudes of repolarizing current steps). (G) Pharmacological identification of the M-current (black = control; red = 20 μM XE991). (H) The XE991-sensitive current; calculated by the digital subtraction of the control and XE991-resistant current traces. The clear difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV also represent the presence of M-current. (I–K) Identification of a GABAergic neuron. (I) GAD2-dependent tdTomato expression (red). (J) Biocytin labeling of a recorded neuron (green). (K) Merged image. (L) Current traces from a GABAergic neuron elicited by the same voltage protocol as on panel (D). (M) Current trace at −40 mV repolarizing step. Note that there is almost no difference between the instantaneous and steady state currents. (N) None of the repolarizing steps elicited M-current. (O) Currents from GABAergic neurons did not show XE991-sensitivity. (P) Digital subtraction of current traces under control conditions and in the presence of XE991. The lack of difference of XE991-sensitive current amplitudes recorded on −20 and −40 mV indicates that M-current was not recorded.
Mentions: In order to detect M-current of different types of PPN neurons, mice expressing tdTomato fluorescent protein in a GAD2- or ChAT-promoter-dependent way were used. The identified tdTomato-expressing neurons were filled with biocytin, and later recovered; and confocal images were taken in order to assess their location and document their GAD2- or ChAT-positivity (Figures 1A–C,I–K).

Bottom Line: Blockade of the M-current abolished the oscillatory activity at 20 Hz, and largely diminished it at other frequencies.Taken together, the M-current seems to be characteristic for PPN cholinergic neurons.It provides a possibility for modulating gamma band activity of these cells, thus contributing to neuromodulatory regulation of the reticular activating system.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Medicine, Department of Physiology, University of Debrecen Debrecen, Hungary.

ABSTRACT
The pedunculopontine nucleus is known as a cholinergic nucleus of the reticular activating system, participating in regulation of sleep and wakefulness. Besides cholinergic neurons, it consists of GABAergic and glutamatergic neurons as well. According to classical and recent studies, more subgroups of neurons were defined. Groups based on the neurotransmitter released by a neuron are not homogenous, but can be further subdivided. The PPN neurons do not only provide cholinergic and non-cholinergic inputs to several subcortical brain areas but they are also targets of cholinergic and other different neuromodulatory actions. Although cholinergic neuromodulation has been already investigated in the nucleus, one of its characteristic targets, the M-type potassium current has not been described yet. Using slice electrophysiology, we provide evidence in the present work that cholinergic neurons possess M-current, whereas GABAergic neurons lack it. The M-current contributes to certain functional differences of cholinergic and GABAergic neurons, as spike frequency adaptation, action potential firing frequency or the amplitude difference of medium afterhyperpolarizations (AHPs). Furthermore, we showed that high threshold membrane potential oscillation with high power, around 20 Hz frequency is a functional property of almost all cholinergic cells, whereas GABAergic neurons have only low amplitude oscillations. Blockade of the M-current abolished the oscillatory activity at 20 Hz, and largely diminished it at other frequencies. Taken together, the M-current seems to be characteristic for PPN cholinergic neurons. It provides a possibility for modulating gamma band activity of these cells, thus contributing to neuromodulatory regulation of the reticular activating system.

No MeSH data available.


Related in: MedlinePlus