TABLE 2.Comparison of rat hindlimb motoneuron properties recorded in vitro and in vivo
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Property | In Vitro |
In Vivo |
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Fast | Slow | Fast | Slow | |||
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Resting potential, mV | –68 ± 11 | –63 ± 14 | –71 ± 6 | –64 ± 6 | ||
AP amplitude, mV | 79.9 ± 8.9 | 75.7 ± 8.6 | 76.0 ± 11.5 | 82.6 ± 12.2 | ||
Input resistance, mΩ | 4.0 ± 2.1** | 7.7 ± 4.8 | 1.8 ± 0.6 | 2.7 ± 1.2 | ||
AHP half-time, ms | 14 ± 3*** | 27 ± 4 | 14 ± 2 | 27 ± 7 | ||
AHP amplitude, mV | –2.4 ± 1.2* | –4.5 ± 2.8 | –1.5 ± 1.1 | –2.7 ± 1.2 | ||
Rheobase, nA | 4.9 ± 3.2* | 2.8 ± 1.5 | 9.8 ± 3.0 | 5.9 ± 4.7 | ||
Voltage threshold, mV | –51 ± 12 | –46 ± 9 | –52 ± 7 | –46 ± 12 | ||
Ramp onset firing rate, pps | 16.7 ± 6.6** | 9.2 ± 1.1 | 26.5 ± 7.7 | 16.7 ± 7.2 | ||
Ramp offset firing rate, pps | 12.5 ± 3.6* | 8.8 ± 2.6 | 24.7 ± 6.8 | 14.1 ± 5.6 | ||
Ramp onset firing current, nA | 7.9 ± 4.6** | 2.8 ± 1.8 | 26.5 ± 7.7 | 16.7 ± 7.2 | ||
Ramp offset firing current, nA | 8.2 ± 4.9** | 2.5 ± 1.6 | 10.9 ± 3.1 | 7 ± 4 | ||
Offset – onset current, nA | 0.3 ± 0.8*** | –0.3 ± 0.2 | –0.2 ± 0.6 | –0.4 ± 0.3 | ||
Number of motoneurons | 15–26 | 6–10 | 21 | 7 |
* P < 0.05,
** P < 0.01, and
*** P < 0.001. Slow motoneurons are defined by AHP half-time ≥20 ms. With respect to rheobase, the current threshold for AP initiation is during 40-ms depolarizing pulse. The instantaneous firing rate (ramp onset) from the first interspike interval (ISI) is that during the ascending current ramp. The instantaneous firing rate (ramp offset) from the last ISI is that during the descending current ramp. Ramp onset current is that during the ascending ramp at which firing begins. Ramp offset current is that during the descending ramp at which firing ends: Offset – onset current is the ramp current at firing offset minus the ramp current at firing onset.