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.


Five patterns of discharge recorded in response to current ramp stimulation in postnatal lumbar motoneurons (n = 38). The four classical types (A–D) as described in adult motoneurons (Bennett et al., 2001) are present and a fifth type called transient, since no discharge firing, or only a few spikes (<5), could be evoked during the descending phase (E). (A) type 1: linear F-I relationship where the firing frequency curves overlapped on the ascending and descending phases. (B) type 2: clockwise hysteresis pattern where the instantaneous frequency is lower in the descending phase for the same current intensity. (C) type 3: Linear F-I relationship with sustained firing in the descending phase. (D) type 4: Counter clockwise hysteresis where the frequency is higher during the descending phase; (E) type 5: transient discharge during the ascending phase with usually no discharge or only a few spikes in the descending phase. In this case which is frequent before P5 (40%), it was not possible to plot an F-I curve during the descending ramp. (F) distribution of the five discharge patterns according to the postnatal ages. Note that types 1 and 2 are the predominant types before P8 (n = 15/26) whereas the types 3 and 4 are most frequent at P8–P9 (n = 6/12) but rare before P8 (n = 3/26).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Five patterns of discharge recorded in response to current ramp stimulation in postnatal lumbar motoneurons (n = 38). The four classical types (A–D) as described in adult motoneurons (Bennett et al., 2001) are present and a fifth type called transient, since no discharge firing, or only a few spikes (<5), could be evoked during the descending phase (E). (A) type 1: linear F-I relationship where the firing frequency curves overlapped on the ascending and descending phases. (B) type 2: clockwise hysteresis pattern where the instantaneous frequency is lower in the descending phase for the same current intensity. (C) type 3: Linear F-I relationship with sustained firing in the descending phase. (D) type 4: Counter clockwise hysteresis where the frequency is higher during the descending phase; (E) type 5: transient discharge during the ascending phase with usually no discharge or only a few spikes in the descending phase. In this case which is frequent before P5 (40%), it was not possible to plot an F-I curve during the descending ramp. (F) distribution of the five discharge patterns according to the postnatal ages. Note that types 1 and 2 are the predominant types before P8 (n = 15/26) whereas the types 3 and 4 are most frequent at P8–P9 (n = 6/12) but rare before P8 (n = 3/26).

Mentions: Firing pattern was further characterized using increasing and decreasing (triangular) slow current ramps as described previously (Hounsgaard et al., 1988; Amendola et al., 2007; Pambo-Pambo et al., 2009). The F-I plots revealed differences in discharge patterns which could be classified in five types according to the frequency response on up and down going ramps. The four classical types already described in motoneurons from adult (Bennett et al., 2001) or neonate (Amendola et al., 2007) rodents are illustrated as followed: linear (Figure 5A), clockwise hysteresis (Figure 5B), prolonged sustained (Figure 5C) and counterclockwise hysteresis (Figure 5D). A fifth type was defined by the lack or the quasi-absence of discharge firing during the descending phase of the ramp at early postnatal ages (Figure 5E). This fifth type was present in 40% of motoneurons at P3–P5, in 25% of motoneurons at P6–P7 and in less than 10% at P8–P9 (Figure 5F). At an early postnatal age, type 1 (linear) and type 2 (clockwise) were predominant whereas the number of motoneurons exhibiting type 3 and type 4 markedly increases at P8–P9. Type 3 and type 4 discharge patterns, displaying a sustained firing during the down going ramp and a counter-clockwise hysteresis, respectively, was observed in 50% of motoneurons in older animals whereas the number of motoneurons exhibiting a non-linear electrical behavior during ramp current injection was <20% before P8. The emergence of types 3 and 4 discharge patterns correspond with the period of maturation of L-type calcium channels in mouse motoneurons (Carlin et al., 2000).


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)

Five patterns of discharge recorded in response to current ramp stimulation in postnatal lumbar motoneurons (n = 38). The four classical types (A–D) as described in adult motoneurons (Bennett et al., 2001) are present and a fifth type called transient, since no discharge firing, or only a few spikes (<5), could be evoked during the descending phase (E). (A) type 1: linear F-I relationship where the firing frequency curves overlapped on the ascending and descending phases. (B) type 2: clockwise hysteresis pattern where the instantaneous frequency is lower in the descending phase for the same current intensity. (C) type 3: Linear F-I relationship with sustained firing in the descending phase. (D) type 4: Counter clockwise hysteresis where the frequency is higher during the descending phase; (E) type 5: transient discharge during the ascending phase with usually no discharge or only a few spikes in the descending phase. In this case which is frequent before P5 (40%), it was not possible to plot an F-I curve during the descending ramp. (F) distribution of the five discharge patterns according to the postnatal ages. Note that types 1 and 2 are the predominant types before P8 (n = 15/26) whereas the types 3 and 4 are most frequent at P8–P9 (n = 6/12) but rare before P8 (n = 3/26).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Five patterns of discharge recorded in response to current ramp stimulation in postnatal lumbar motoneurons (n = 38). The four classical types (A–D) as described in adult motoneurons (Bennett et al., 2001) are present and a fifth type called transient, since no discharge firing, or only a few spikes (<5), could be evoked during the descending phase (E). (A) type 1: linear F-I relationship where the firing frequency curves overlapped on the ascending and descending phases. (B) type 2: clockwise hysteresis pattern where the instantaneous frequency is lower in the descending phase for the same current intensity. (C) type 3: Linear F-I relationship with sustained firing in the descending phase. (D) type 4: Counter clockwise hysteresis where the frequency is higher during the descending phase; (E) type 5: transient discharge during the ascending phase with usually no discharge or only a few spikes in the descending phase. In this case which is frequent before P5 (40%), it was not possible to plot an F-I curve during the descending ramp. (F) distribution of the five discharge patterns according to the postnatal ages. Note that types 1 and 2 are the predominant types before P8 (n = 15/26) whereas the types 3 and 4 are most frequent at P8–P9 (n = 6/12) but rare before P8 (n = 3/26).
Mentions: Firing pattern was further characterized using increasing and decreasing (triangular) slow current ramps as described previously (Hounsgaard et al., 1988; Amendola et al., 2007; Pambo-Pambo et al., 2009). The F-I plots revealed differences in discharge patterns which could be classified in five types according to the frequency response on up and down going ramps. The four classical types already described in motoneurons from adult (Bennett et al., 2001) or neonate (Amendola et al., 2007) rodents are illustrated as followed: linear (Figure 5A), clockwise hysteresis (Figure 5B), prolonged sustained (Figure 5C) and counterclockwise hysteresis (Figure 5D). A fifth type was defined by the lack or the quasi-absence of discharge firing during the descending phase of the ramp at early postnatal ages (Figure 5E). This fifth type was present in 40% of motoneurons at P3–P5, in 25% of motoneurons at P6–P7 and in less than 10% at P8–P9 (Figure 5F). At an early postnatal age, type 1 (linear) and type 2 (clockwise) were predominant whereas the number of motoneurons exhibiting type 3 and type 4 markedly increases at P8–P9. Type 3 and type 4 discharge patterns, displaying a sustained firing during the down going ramp and a counter-clockwise hysteresis, respectively, was observed in 50% of motoneurons in older animals whereas the number of motoneurons exhibiting a non-linear electrical behavior during ramp current injection was <20% before P8. The emergence of types 3 and 4 discharge patterns correspond with the period of maturation of L-type calcium channels in mouse motoneurons (Carlin et al., 2000).

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.