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Developing electrical properties of postnatal mouse lumbar motoneurons.

Durand J, Filipchuk A, Pambo-Pambo A, Amendola J, Borisovna Kulagina I, Guéritaud JP - Front Cell Neurosci (2015)

Bottom Line: Both parameters are significantly correlated with the total dendritic surface area of motoneurons, the largest motoneurons having the lowest Rin and the highest rheobase.We found 32 and 10% of motoneurons with a transient firing at P3-P5 and P8, respectively.No correlation was found between groups defined by step or triangular ramp of currents with the exception of transient firing patterns.

View Article: PubMed Central - PubMed

Affiliation: Institut de Neurosciences de la Timone, Aix Marseille Université - CNRS, UMR 7289 Marseille, France.

ABSTRACT
We studied the rapid changes in electrical properties of lumbar motoneurons between postnatal days 3 and 9 just before mice weight-bear and walk. The input conductance and rheobase significantly increased up to P8. A negative correlation exists between the input resistance (Rin) and rheobase. Both parameters are significantly correlated with the total dendritic surface area of motoneurons, the largest motoneurons having the lowest Rin and the highest rheobase. We classified the motoneurons into three groups according to their discharge firing patterns during current pulse injection (transient, delayed onset, sustained). The delayed onset firing type has the highest rheobase and the fastest action potential (AP) whereas the transient firing group has the lowest rheobase and the less mature AP. We found 32 and 10% of motoneurons with a transient firing at P3-P5 and P8, respectively. About 20% of motoneurons with delayed onset firing were detected at P8. At P9, all motoneurons exhibit a sustained firing. We defined five groups of motoneurons according to their discharge firing patterns in response to ascending and descending current ramps. In addition to the four classical types, we defined a fifth type called transient for the quasi-absence of discharge during the descending phase of the ramp. This transient type represents about 40% between P3-P5 and tends to disappear with age. Types 1 and 2 (linear and clockwise hysteresis) are the most preponderant at P6-P7. Types 3 and 4 (prolonged sustained and counter clockwise hysteresis) emerge at P8-P9. The emergence of types 3 and 4 probably depends on the maturation of L type calcium channels in the dendrites of motoneurons. No correlation was found between groups defined by step or triangular ramp of currents with the exception of transient firing patterns. Our data support the idea that a switch in the electrical properties of lumbar motoneurons might exist in the second postnatal week of life in mice.

No MeSH data available.


Related in: MedlinePlus

Electrophysiological identification and intracellular staining of lumbar motoneurons in the developing mouse spinal cord. (A) Electrical stimulation of the fifth lumbar (L5) ventral root evoked an anti AP. Asterisk indicates the stimulus artifact. (B) Direct intracellular stimulation of L5 motoneuron giving rise to a train of action potentials (APs; sustained discharge) recorded intracellularly (upper trace) and the propagated spikes in the ventral root (lower trace); rectangular injected current: 1.2 nA (middle trace). (C,D), two fully reconstructed lumbar motoneurons recorded from P8–P9 mice. Depending on the location of the soma in the ventro-lateral part of the spinal cord, dendritic arborisations extended either in all rostro-caudal directions and medially near the central canal (C) or confined in a restricted area into the latero-ventral part of the spinal cord (D). (E,F) Digitized full reconstructions of two motoneurons at postnatal days 3 and 8 (P3 and P8) in the transverse plane. During this period, the total dendritic length increases by 22%, only. Each dendrite is represented by a specific color.
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Figure 1: Electrophysiological identification and intracellular staining of lumbar motoneurons in the developing mouse spinal cord. (A) Electrical stimulation of the fifth lumbar (L5) ventral root evoked an anti AP. Asterisk indicates the stimulus artifact. (B) Direct intracellular stimulation of L5 motoneuron giving rise to a train of action potentials (APs; sustained discharge) recorded intracellularly (upper trace) and the propagated spikes in the ventral root (lower trace); rectangular injected current: 1.2 nA (middle trace). (C,D), two fully reconstructed lumbar motoneurons recorded from P8–P9 mice. Depending on the location of the soma in the ventro-lateral part of the spinal cord, dendritic arborisations extended either in all rostro-caudal directions and medially near the central canal (C) or confined in a restricted area into the latero-ventral part of the spinal cord (D). (E,F) Digitized full reconstructions of two motoneurons at postnatal days 3 and 8 (P3 and P8) in the transverse plane. During this period, the total dendritic length increases by 22%, only. Each dendrite is represented by a specific color.

Mentions: The data base for the electrophysiological study comprises 103 motoneurons from mice aged between P3 and P9. Only neurons displaying a stable membrane potential more negative than −50 mV with overshooting APs during the whole test procedure were kept for analysis. All the motoneurons were identified by recording either the anti AP evoked by the ventral root stimulation (Figure 1A, two superposed traces) or the orthodromic AP in the ventral root (Figure 1B, VR lower trace) evoked by direct intracellular stimulation (Figure 1B, upper trace). Among them, 12 motoneurons intracellularly recorded and stained were taken from our library of 3D reconstructed lumbar mouse motoneurons to link the electrical parameters (rheobase, Rin) and the morphology of individual lumbar motoneurons (see below and graphs; Figures 2E,F).


Developing electrical properties of postnatal mouse lumbar motoneurons.

Durand J, Filipchuk A, Pambo-Pambo A, Amendola J, Borisovna Kulagina I, Guéritaud JP - Front Cell Neurosci (2015)

Electrophysiological identification and intracellular staining of lumbar motoneurons in the developing mouse spinal cord. (A) Electrical stimulation of the fifth lumbar (L5) ventral root evoked an anti AP. Asterisk indicates the stimulus artifact. (B) Direct intracellular stimulation of L5 motoneuron giving rise to a train of action potentials (APs; sustained discharge) recorded intracellularly (upper trace) and the propagated spikes in the ventral root (lower trace); rectangular injected current: 1.2 nA (middle trace). (C,D), two fully reconstructed lumbar motoneurons recorded from P8–P9 mice. Depending on the location of the soma in the ventro-lateral part of the spinal cord, dendritic arborisations extended either in all rostro-caudal directions and medially near the central canal (C) or confined in a restricted area into the latero-ventral part of the spinal cord (D). (E,F) Digitized full reconstructions of two motoneurons at postnatal days 3 and 8 (P3 and P8) in the transverse plane. During this period, the total dendritic length increases by 22%, only. Each dendrite is represented by a specific color.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4557103&req=5

Figure 1: Electrophysiological identification and intracellular staining of lumbar motoneurons in the developing mouse spinal cord. (A) Electrical stimulation of the fifth lumbar (L5) ventral root evoked an anti AP. Asterisk indicates the stimulus artifact. (B) Direct intracellular stimulation of L5 motoneuron giving rise to a train of action potentials (APs; sustained discharge) recorded intracellularly (upper trace) and the propagated spikes in the ventral root (lower trace); rectangular injected current: 1.2 nA (middle trace). (C,D), two fully reconstructed lumbar motoneurons recorded from P8–P9 mice. Depending on the location of the soma in the ventro-lateral part of the spinal cord, dendritic arborisations extended either in all rostro-caudal directions and medially near the central canal (C) or confined in a restricted area into the latero-ventral part of the spinal cord (D). (E,F) Digitized full reconstructions of two motoneurons at postnatal days 3 and 8 (P3 and P8) in the transverse plane. During this period, the total dendritic length increases by 22%, only. Each dendrite is represented by a specific color.
Mentions: The data base for the electrophysiological study comprises 103 motoneurons from mice aged between P3 and P9. Only neurons displaying a stable membrane potential more negative than −50 mV with overshooting APs during the whole test procedure were kept for analysis. All the motoneurons were identified by recording either the anti AP evoked by the ventral root stimulation (Figure 1A, two superposed traces) or the orthodromic AP in the ventral root (Figure 1B, VR lower trace) evoked by direct intracellular stimulation (Figure 1B, upper trace). Among them, 12 motoneurons intracellularly recorded and stained were taken from our library of 3D reconstructed lumbar mouse motoneurons to link the electrical parameters (rheobase, Rin) and the morphology of individual lumbar motoneurons (see below and graphs; Figures 2E,F).

Bottom Line: Both parameters are significantly correlated with the total dendritic surface area of motoneurons, the largest motoneurons having the lowest Rin and the highest rheobase.We found 32 and 10% of motoneurons with a transient firing at P3-P5 and P8, respectively.No correlation was found between groups defined by step or triangular ramp of currents with the exception of transient firing patterns.

View Article: PubMed Central - PubMed

Affiliation: Institut de Neurosciences de la Timone, Aix Marseille Université - CNRS, UMR 7289 Marseille, France.

ABSTRACT
We studied the rapid changes in electrical properties of lumbar motoneurons between postnatal days 3 and 9 just before mice weight-bear and walk. The input conductance and rheobase significantly increased up to P8. A negative correlation exists between the input resistance (Rin) and rheobase. Both parameters are significantly correlated with the total dendritic surface area of motoneurons, the largest motoneurons having the lowest Rin and the highest rheobase. We classified the motoneurons into three groups according to their discharge firing patterns during current pulse injection (transient, delayed onset, sustained). The delayed onset firing type has the highest rheobase and the fastest action potential (AP) whereas the transient firing group has the lowest rheobase and the less mature AP. We found 32 and 10% of motoneurons with a transient firing at P3-P5 and P8, respectively. About 20% of motoneurons with delayed onset firing were detected at P8. At P9, all motoneurons exhibit a sustained firing. We defined five groups of motoneurons according to their discharge firing patterns in response to ascending and descending current ramps. In addition to the four classical types, we defined a fifth type called transient for the quasi-absence of discharge during the descending phase of the ramp. This transient type represents about 40% between P3-P5 and tends to disappear with age. Types 1 and 2 (linear and clockwise hysteresis) are the most preponderant at P6-P7. Types 3 and 4 (prolonged sustained and counter clockwise hysteresis) emerge at P8-P9. The emergence of types 3 and 4 probably depends on the maturation of L type calcium channels in the dendrites of motoneurons. No correlation was found between groups defined by step or triangular ramp of currents with the exception of transient firing patterns. Our data support the idea that a switch in the electrical properties of lumbar motoneurons might exist in the second postnatal week of life in mice.

No MeSH data available.


Related in: MedlinePlus