Limits...
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

Discharge firing patterns and distributions with age. Three different types of discharge firing patterns were found in lumbar motoneurons (n = 70) at different postnatal ages in response to rectangular current injection. The transient discharge (A) is characterized by a short burst of spike. The sustained pattern (B) starts by an early spiking followed by a burst and discharge firing maintained during the whole pulse. The third pattern is called delayed onset discharge firing (C) the arrow indicating a late depolarization. At P3–P5, one third of motoneurons still present a transient discharge and the motoneuron is not able to fire APs up to the end of the pulse as illustrated in (A) (see pie chart). In older animals the number of motoneurons presenting this pattern decreases up to P9. At that age, there is no more transient firing but all motoneurons exhibit a sustained discharge firing pattern (B). Between P3 and P8 a fraction of motoneurons has a delayed onset firing pattern which disappears at P9.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4557103&req=5

Figure 3: Discharge firing patterns and distributions with age. Three different types of discharge firing patterns were found in lumbar motoneurons (n = 70) at different postnatal ages in response to rectangular current injection. The transient discharge (A) is characterized by a short burst of spike. The sustained pattern (B) starts by an early spiking followed by a burst and discharge firing maintained during the whole pulse. The third pattern is called delayed onset discharge firing (C) the arrow indicating a late depolarization. At P3–P5, one third of motoneurons still present a transient discharge and the motoneuron is not able to fire APs up to the end of the pulse as illustrated in (A) (see pie chart). In older animals the number of motoneurons presenting this pattern decreases up to P9. At that age, there is no more transient firing but all motoneurons exhibit a sustained discharge firing pattern (B). Between P3 and P8 a fraction of motoneurons has a delayed onset firing pattern which disappears at P9.

Mentions: During the development of spinal motoneurons, different patterns of discharge have been previously described (Vinay et al., 2000a; Mentis et al., 2007; Pambo-Pambo et al., 2009; Leroy et al., 2014). Only recently a delayed onset firing pattern was detected in lumbar motoneurons in slice preparation (Pambo-Pambo et al., 2009; Leroy et al., 2014). We then used intracellular injection of depolarizing constant current pulses (pulse protocols, see methods) to analyze in details the discharge firing pattern of the motoneurons in the whole brainstem-spinal cord preparation. Three different firing patterns were clearly identified during this period of maturation (P3–P9) according to the mode of discharge firing which was transient (Figure 3A), sustained (Figure 3B) or delayed (Figure 3C) in the different motoneurons. Figure 3A illustrates the typical pattern of discharge of transient firing cells. The motoneuron fired a single spike or a burst of spikes and the discharge firing did not last during the entire pulse but a few hundreds of ms, only. This transient firing was recorded in 32% of motoneurons at P3–P5 (pie chart in Figure 3). This ratio is in agreement with previous report on extensor motoneurons in the neonate rat (Vinay et al., 2000a). The transient firing pattern was not observed in motoneurons from animals older than P8 (see pie chart). The second group called sustained firing also displayed an early AP at rheobase and then several APs appeared with increasing current intensities (Figure 3B). The instantaneous discharge frequency progressively increased and the motoneuron was able to fire continuously up to the end of the pulse (Figure 3B; 1.2 nA). A third group is composed of motoneurons that display a delayed onset firing. The delayed onset firing (Figure 3C) corresponds to the late bursting motoneurons previously described in spinal motoneurons (Pambo-Pambo et al., 2009). As illustrated on Figure 3C, they were characterized by a delayed trigger of the AP. At potentials below spike threshold, an initial transient small overshoot in voltage response to the current pulse was observed (arrow on Figure 3C, upper traces). It was followed by a slow rising, late depolarization. This delayed onset firing was seen in 20% of motoneurons in our sample at P8 but was not detected at P9 (n = 12). The distribution of the different firing patterns is illustrated in pie charts in Figure 3. Most motoneurons exhibit an early and sustained discharge (as in 3B) at all postnatal ages.


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)

Discharge firing patterns and distributions with age. Three different types of discharge firing patterns were found in lumbar motoneurons (n = 70) at different postnatal ages in response to rectangular current injection. The transient discharge (A) is characterized by a short burst of spike. The sustained pattern (B) starts by an early spiking followed by a burst and discharge firing maintained during the whole pulse. The third pattern is called delayed onset discharge firing (C) the arrow indicating a late depolarization. At P3–P5, one third of motoneurons still present a transient discharge and the motoneuron is not able to fire APs up to the end of the pulse as illustrated in (A) (see pie chart). In older animals the number of motoneurons presenting this pattern decreases up to P9. At that age, there is no more transient firing but all motoneurons exhibit a sustained discharge firing pattern (B). Between P3 and P8 a fraction of motoneurons has a delayed onset firing pattern which disappears at P9.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4557103&req=5

Figure 3: Discharge firing patterns and distributions with age. Three different types of discharge firing patterns were found in lumbar motoneurons (n = 70) at different postnatal ages in response to rectangular current injection. The transient discharge (A) is characterized by a short burst of spike. The sustained pattern (B) starts by an early spiking followed by a burst and discharge firing maintained during the whole pulse. The third pattern is called delayed onset discharge firing (C) the arrow indicating a late depolarization. At P3–P5, one third of motoneurons still present a transient discharge and the motoneuron is not able to fire APs up to the end of the pulse as illustrated in (A) (see pie chart). In older animals the number of motoneurons presenting this pattern decreases up to P9. At that age, there is no more transient firing but all motoneurons exhibit a sustained discharge firing pattern (B). Between P3 and P8 a fraction of motoneurons has a delayed onset firing pattern which disappears at P9.
Mentions: During the development of spinal motoneurons, different patterns of discharge have been previously described (Vinay et al., 2000a; Mentis et al., 2007; Pambo-Pambo et al., 2009; Leroy et al., 2014). Only recently a delayed onset firing pattern was detected in lumbar motoneurons in slice preparation (Pambo-Pambo et al., 2009; Leroy et al., 2014). We then used intracellular injection of depolarizing constant current pulses (pulse protocols, see methods) to analyze in details the discharge firing pattern of the motoneurons in the whole brainstem-spinal cord preparation. Three different firing patterns were clearly identified during this period of maturation (P3–P9) according to the mode of discharge firing which was transient (Figure 3A), sustained (Figure 3B) or delayed (Figure 3C) in the different motoneurons. Figure 3A illustrates the typical pattern of discharge of transient firing cells. The motoneuron fired a single spike or a burst of spikes and the discharge firing did not last during the entire pulse but a few hundreds of ms, only. This transient firing was recorded in 32% of motoneurons at P3–P5 (pie chart in Figure 3). This ratio is in agreement with previous report on extensor motoneurons in the neonate rat (Vinay et al., 2000a). The transient firing pattern was not observed in motoneurons from animals older than P8 (see pie chart). The second group called sustained firing also displayed an early AP at rheobase and then several APs appeared with increasing current intensities (Figure 3B). The instantaneous discharge frequency progressively increased and the motoneuron was able to fire continuously up to the end of the pulse (Figure 3B; 1.2 nA). A third group is composed of motoneurons that display a delayed onset firing. The delayed onset firing (Figure 3C) corresponds to the late bursting motoneurons previously described in spinal motoneurons (Pambo-Pambo et al., 2009). As illustrated on Figure 3C, they were characterized by a delayed trigger of the AP. At potentials below spike threshold, an initial transient small overshoot in voltage response to the current pulse was observed (arrow on Figure 3C, upper traces). It was followed by a slow rising, late depolarization. This delayed onset firing was seen in 20% of motoneurons in our sample at P8 but was not detected at P9 (n = 12). The distribution of the different firing patterns is illustrated in pie charts in Figure 3. Most motoneurons exhibit an early and sustained discharge (as in 3B) at all postnatal ages.

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