EUS and hindlimb motoneuron properties from adult rats in vitro
| Property | All EUS | Hindlimb | Quiescent EUS | Spontaneous EUS |
|---|---|---|---|---|
| Action potential amplitude, mV | 74.2 ± 7.2** | 77.9 ± 9.0 | 74.9 ± 1.4 | 71.5 ± 2.7 |
| Resting potential, mV | −55.0 ± 8.0*** | −66.0 ± 12.0 | −56.0 ± 2.0 | −53.0 ± 2.0 |
| Input resistance, MΩ | 11.1 ± 4.6*** | 5.1 ± 3.4 | 9.9 ± 0.8 | 15.6 ± 1.2†† |
| Sag, % | 4.0 ± 5.9 | 3.2 ± 4.4 | 4.8 ± 1.2 | 0.7 ± 0.5†† |
| Time constant, ms | 4.9 ± 1.5** | 3.6 ± 2.3 | 4.7 ± 0.3 | 5.8 ± 0.7 |
| AHP amplitude, mV | −6.7 ± 3.3*** | −3.0 ± 2.0 | −6.1 ± 0.6 | −8.9 ± 1.3 |
| AHP half-decay time, ms | 24.3 ± 10.1** | 17.3 ± 7.0 | 20.4 ± 1.4 | 34.4 ± 3.2††† |
| Number of motoneurons | 32–36 | 32–38 | 25–27 | 7–10 |
| Depolarization threshold, mV | 11.9 ± 4.6*** | 17.4 ± 7.4 | 12.5 ± 1.0 | 9.5 ± 1.4 |
| Firing threshold, mV | −45.0 ± 7.0 | −50.0 ± 12.0 | −45.0 ± 2.0 | −46.0 ± 2.0 |
| Rheobase, nA | 0.6 ± 0.6*** | 4.3 ± 3.0 | 0.7 ± 0.1 | 0.1 ± 0.0†† |
| Number of motoneurons | 23–28 | 32–33 | 19–22 | 4–6 |
| Recruitment current, nA | 0.8 ± 3.1*** | 6.6 ± 4.3 | 2.2 ± 1.0 | −0.8 ± 0.2†† |
| Derecruitment current, nA | 0.9 ± 3.1*** | 6.7 ± 4.6 | 2.4 ± 1.0 | −0.7 ± 0.2†† |
| ΔI, nA | 0.2 ± 0.2 | 0.1 ± 0.5 | 0.2 ± 0.1 | 0.1 ± 0.0 |
| Recruitment rate, pps | 9.3 ± 3.4*** | 15.5 ± 7.4 | 11.1 ± 1.0 | 7.4 ± 0.3†† |
| Derecruitment rate, pps | 9.9 ± 3.6* | 13.2 ± 6.6 | 12.1 ± 0.9 | 7.5 ± 0.5††† |
| ΔF, pps | 0.5 ± 1.8*** | −2.5 ± 3.2 | 1.0 ± 0.6 | 0.1 ± 0.3 |
| Ramp F–I slope, pps/nA | 6.4 ± 3.9 | 8.8 ± 7.3 | 7.7 ± 1.2 | 4.8 ± 0.6† |
| Number of motoneurons | 29 | 23–25 | 15 | 14 |
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Values are means ± SD for motoneurons innervating the external urethral sphincter (All EUS; present study) or hindlimb (Carp et al. 2008 and unpublished data) muscles recorded in vitro. Values are means ± SE for EUS motorneurons that never fired spontaneously (Quiescent EUS) and those that fired spontaneously upon impalement (Spontaneous EUS). Action potential amplitude, peak minus resting potential for action potentials elicited by 0.6-ms duration current pulses; sag, % decrease in slope of current–voltage relationship (i.e., input resistance) calculated for final 10 ms of 40-ms hyperpolarizing current pulses with respect to the slope calculated using the peak hyperpolarization; rheobase, current threshold for action potential initiation during 40-ms depolarizing pulse; ramp recruitment rate, average instantaneous firing rate from the first two interspike intervals during the ascending limb of current ramp; ramp derecruitment rate, average instantaneous firing rate from the last two interspike intervals during the descending limb of current ramp; ramp F–I slope, slope of frequency–current relationship on ascending limb of current ramp.
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↵* P < 0.05,
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↵** P < 0.01, and
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↵*** P < 0.001, EUS different from hindlimb motoneurons;
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↵† P < 0.05,
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↵†† P < 0.01,
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↵††† P < 0.001, spontaneous EUS motoneurons from quiescent EUS motoneurons.