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The Journal of Neurophysiology Vol. 80 No. 4 October 1998, pp. 2038-2045
Copyright ©1998 by the American Physiological Society
Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, Copenhagen N, Denmark
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ABSTRACT |
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 Abstract
 Introduction
Methods
Results
Discussion
References
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Bennett, David J., Hans Hultborn, Brent Fedirchuk, and Monica Gorassini. Short-term plasticity in hindlimb motoneurons of decerebrate cats. J. Neurophysiol. 80: 2038-2045, 1998. Cat hindlimb motoneurons possess noninactivating voltage-gated inward currents that can, under appropriate conditions, regeneratively produce sustained increments in depolarization and firing of the cell (i.e., plateau potentials). Recent studies in turtle dorsal horn neurons and motoneurons indicate that facilitation of plateaus occurs with repeated plateau activation (decreased threshold and increased duration; this phenomenon is referred to as warm-up). The purpose of the present study was to study warm-up in cat motoneurons. Initially, cells were studied by injecting a slow triangular current ramp intracellularly to determine the threshold for activation of the plateau. In cells where the sodium spikes were blocked with intracellular QX314, plateau activation was readily seen as a sudden jump in membrane potential, which was not directly reversed as the current was decreased (cf. hysteresis). With normal spiking, the plateau activation (the noninactivating inward current) was reflected by a steep and sustained jump in firing rate, which was not directly reversed as the current was decreased (hysteresis). Repetitive plateau activation significantly lowered the plateau activation threshold in 83% of cells (by on average 5 mV and 11 Hz with and without QX314, respectively). This interaction between successive plateaus (warm-up) occurred when tested with 3- to 6-s intervals; no interaction occurred at times >20 s. Plateaus initiated by synaptic activation from muscle stretch were also facilitated by repetition. Repeated slow muscle stretches that produced small phasic responses when a cell was hyperpolarized with intracellular current bias produced a larger and more prolonged responses (plateau) when the bias was removed, and the amplitude and duration of this response grew with repetition. The effects of warm-up seen with intracellular recordings during muscle stretch could also be recorded extracellularly with gross electromyographic (EMG) recordings. That is, the same repetitive stretch as above produced a progressively larger and more prolonged EMG response. Warm-up may be a functionally important form of short-term plasticity in motoneurons that secures efficient motor output once a threshold level is reached for a significant period. Finally, the finding that warm-up can be readily observed with gross EMG recordings will be useful in future studies of plateaus in awake animals and humans.
When identical stimuli are repeatedly delivered to dorsal horn neurons, there is an increase in the duration and rate of discharge with each repetition (related to the wind-up phenomenon in the central sensitization to pain), and this can in part be attributed to a facilitation of the postsynaptic L-type Ca2+ channels (in rat: Morisset and Nagy 1996 Intracellular recordings were made in hindlimb motoneurons of 14 decerebrate cats with approval from the local ethical committee. The detailed methods are described in a companion paper (Bennett et al. 1998
Terminology
As a point of terminology, the term "plateau" is used rather broadly to indicate that the noninactivating voltage-gated inward currents are activated (see review Hultborn and Kiehn 1992 Effects of repeated intracellular current injection
In the results described below, we only discuss the properties of hindlimb motoneurons that were capable of exhibiting plateaus during intracellular current injection, as described by Bennett et al. (1998)
Stretch reflex activated plateaus and warm-up
To examine the functional relevance of the warm-up phenomenon, we investigated repeated plateau activation in motoneurons of the triceps surae muscle during repeated stretch of this muscle. As we have shown in the companion paper (Bennett et al. 1998 Warm-up reflected in the EMG responses to muscle stretch
Because warm-up was seen in a high percentage of motoneurons during stretch activation, its combined effect over many motor units should be reflected in the activation of the whole muscle. We thus measured gross EMG during stretch after making intracellular recordings as above. To do this we waited 60 min for the muscle paralysis (pancuronium bromide) to wear off, during which time we inserted EMG wires. Figure 5 illustrates the results, with the same continuous sinusoidal stretch as before. Initially, many units were typically seen in the EMG recordings; some fired phasically and others in a sustained manner between the stretches (left of Fig. 5). To study warm-up, we silenced the entire motoneuron pool with a stimulation train applied to the CP nerve during the sinusoidal stretching, as shown in Fig. 5 (thick bar). This stimulation typically produced a gap in firing of most motor units for ~6-8 s, thus long enough for the effects of previous warm-up to be reduced. Following the stimulation, the first cycle only activated a few motor units phasically. Subsequent stretch cycles activated more motor units, and the firing lasted for longer with each stretch, until by the fourth stretch cycle sustained firing occurred in some units. Eventually, a steady state was reached similar to that before the CP nerve stimulation. These findings are consistent with the effects of warm-up with stretch seen with intracellular recordings. One concern was that the CP stimulation itself caused inhibition that lasted for many seconds after it was turned off. However, this is unlikely, because we used a similar CP stimulation during intracellular recordings and found no hyperpolarization beyond the stimulation period (e.g., see Fig. 6C in Bennett et al. 1998
We have shown that plateau potentials in cat motoneurons are facilitated by a preceding activation, a phenomenon referred to as warm-up. The effects of warm-up on plateaus are short term, lasting several seconds after a plateau activation, and thus constitute an example of short-term plasticity in the postsynaptic membrane, similar to that described in turtle dorsal horn neurons and motoneurons (Russo and Hounsgaard 1994 Mechanisms of warm-up
As referred to in the introduction, plateau potentials in cat motoneurons are assumed to depend on L-type Ca2+ currents or similar noninactivating inward currents. Thus the observed warm-up likely involves a direct or indirect facilitation of these inward currents. Similar warm-up effects have been analyzed both in turtle motoneurons (Svirskis and Hounsgaard 1997) and turtle dorsal horn neurons (Russo and Hounsgaard 1994 Synaptic activation of plateaus
The finding that depolarization from intracellular or synaptic input can cause warm-up and thus lower the plateau threshold leads to the possibility that warm-up might, in part, underlie the lowered plateau threshold seen with tonic synaptic excitation (tonic EPSPs) in the companion paper (Fig. 2 of Bennett et al. 1998 Functional implications
Because we have demonstrated that warm-up can occur in individual motoneurons during repeated muscle stretch (e.g., Fig. 4), it is logical to suppose that this should be reflected in the behavior of the entire motoneuron pool, as measured with EMG and muscle force. Measurements of EMG, such as in Fig. 5, support this important conclusion. It should be kept in mind, however, that the fusimotor system was blocked during the intracellular recordings where we initially studied warm-up, and not during the EMG recordings (cf. muscle paralysis). However, the relevant point in either situation is that the afferent input does not change from stretch cycle to cycle, so the changes can be attributed to warm-up. During intracellular recording, this condition was met, because at hyperpolarized levels the responses to stretch were identical with each stretch cycle (Fig. 4, left). During EMG recording this condition was also likely to be met, particularly because previous studies indicate that in decerebrate cats Ia afferents respond similarly on each stretch cycle, suggesting that fusimotor drive does not change during repeated muscle stretch (e.g., Fig. 8 of Bennett et al. 1996
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
; in turtle: Russo and Hounsgaard 1994, 1996a). This facilitation is short lasting (5 s) and results in a facilitation of plateau potentials and bursting associated with these calcium channels. The facilitation of L-type Ca2+ channels can be evoked either by synaptic excitation or intracellular pulses; thus the depolarization per se seems to be an essential factor, although a number of neurotransmitters and intracellular messengers may modulate the plateau properties (Russo et al. 1997).
). In cat motoneurons a similar noninactivating (possibly calcium) inward current is likely involved in plateau potentials (Hounsgaard et al. 1988; Hultborn and Kiehn 1992; Schwindt and Crill 1980a-c, 1982, 1984).
). Initially, we saw this warm-up phenomenon as a nuisance and waited long enough between trials (>20 s) to avoid it. However, we later realized that the effects of warm-up were so strong that they must be functionally important. The objective of the present paper is thus to describe warm-up in cat motoneurons, first as it occurs with intracellular current injection and second, with more natural activation produced from repeated (sinusoidal) muscle stretches. Although the main part of this study involved intracellular recordings, we also found that the effects of warm-up were easily seen in gross EMG recordings. This finding may open new possibilities for investigating the question of whether plateaus are present in awake animals and humans (Eken and Kiehn 1989, 1992; Gorassini et al. 1998).
METHODS
Abstract
Introduction
Methods
Results
Discussion
References
). Plateaus were studied both by activation with intracellular current injection (triangular ramps; Figs. 1 and 2), and by stretch reflex activation (Fig. 4; sinusoidal stretching of the triceps surae muscle). After activation, the plateaus were often deactivated by hyperpolarization from intracellular current or nerve stimulation [e.g., common peroneal (CP) nerve stimulation]. The threshold for the first activation of a plateau was compared with the threshold for subsequent activations.
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FIG. 1.
Warm-up with repeated intracellular plateau activation. Firing rates during ramp current injections into a tibial motoneuron plotted against current (triangular current ramps as in Fig. 2, but at 8.2 nA/s). Threshold for plateau onset indicated with an asterisk; arrows indicate direction of time. A-C: responses to 3 successive ramps, one following immediately after the other (3- to 4-s pause in firing between each ramp response). Note the drop in plateau threshold with each successive ramp (warm-up). D: superimposed responses from A-C, with only firing rate during upward current ramp shown. Note the overlap in firing in the 3 cases before the plateau was activated (at <25 Hz).
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FIG. 2.
Effect of repeated current injection with and without plateaus activation. Intracellular recording from soleus motoneuron during 4 ramp current injections, one following immediately after the other, with a 5-s pause in firing between each response (A-C). First and 2nd ramp responses were nearly identical (see Fig. 3A for comparison), so only the 1st is shown. All ramps at 5.8 nA/s. Spikes clipped to amplify signal. A, left column: 1st current ramp, up to 10 nA (subthreshold for plateau at this time). Right column: membrane potential replotted on same vertical scale, but as a function of current during up and down phases of ramp. Likewise, firing rate is plotted against current, with solid and open circles for up and down phases of ramp, respectively (rate computed from average number of spikes in 0.5-nA intervals). Arrows indicate direction of time. B: 3rd current ramp, but with a higher peak current, which activates a plateau, as seen by hysteresis in plots of potential and frequency against current [voltage-current (V-I) and frequency-current (F-I), right column]. C: 4th current ramp, which activated the plateau at a much lower threshold before firing began (cf. warm-up), as seen by steep rise in potential at arrow (compare with reference line drawn in band C), sustained firing and hysteresis in V-I plot.
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FIG. 4.
Warm-up with repeated muscle stretch. A: intracellular recording from relatively low recruitment threshold gastrocnemius-soleus (GS) motoneuron during sinusoidal stretching [5.5 nA rheobase, 81 ms afterhyperpolarization (AHP) half-amplitude duration]. Firing inactivated with intracellular QX314, and estimation of firing threshold before inactivation indicated by horizontal line. Cell initially held hyperpolarized by 
1-nA current bias. When this current was removed, the stretch caused progressively larger and more prolonged responses that ended in a tonic plateau activation (far right). B: same as A, but in high-threshold GS motoneuron (9 nA rheobase, 24 ms AHP half-amplitude duration). Initially, cell held depolarized with 8-nA bias current (subthreshold for plateau). When this current was increased by 1 nA, warm-up was seen, as in A, but the plateau did not remain tonically active between muscle stretches. Arrows indicate sustained responses following stretch.
). These currents can be activated regeneratively and produce a sustained depolarization or increment in firing rate, thus the term plateau. The term plateau is however misleading because it implies that the potential and firing rate is somehow fixed. This is not the case (see Bennett et al. 1998; Hounsgaard et al. 1988); plateau activation simply means that an additional depolarizing current is present, just as if a constant current were injected through a microelectrode. We could have used the phrase "noninactivating voltage-gated inward current" instead of "plateau," but for brevity and historic reasons we use the latter. Also, we will use the term "warm-up" to refer to the phenomena of facilitation of plateau potentials with repeated activation in general, without regard to the underlying mechanism.
RESULTS
Abstract
Introduction
Methods
Results
Discussion
References
. In Fig. 1 we illustrate the frequency-current (f-I) relations for a motoneuron with a relatively high initial threshold for plateau activation during triangular ramp current injections. In each ramp, the current was increased to activate the plateau (at steep rise in frequency; upward arrows), and then decreased to deactivate the plateau (to 5 nA; downward arrows; note counterclockwise hysteresis and self-sustained firing indicative of plateau) (see Bennett et al. 1998) (Fig. 2). The current ramps were repeated with 3- to 4-s intervals between each response to investigate their interactions. In this example, the first current ramp initiated the plateau at a threshold frequency of ~35 Hz (asterisk in Fig. 1A). On the second ramp, the plateau threshold was at only 25 Hz (Fig. 1B). Furthermore, firing was sustained for lower current levels on the descending phase of the triangular current ramp, compared with the first ramp. A third ramp (Fig. 1C) lowered the plateau threshold even more, to the point where it was initiated just after recruitment. That is, the firing rate increased steeply at recruitment, and the cell remained on the plateau for most of the up and downward swing of the injected current. Further ramps produced little change in the plateau threshold, i.e., a steady-state threshold was reached so the responses looked as in Fig. 1C, with repeated activation (see also Fig. 4, described below). This progressive facilitation of the plateaus with repeated activation we refer to as warm-up (see discussion for its relation to warm-up in other cells).
], and a steep jump in frequency did not occur (cf. no plateau activation). An identical response was obtained when the ramp was repeated 5 s later (ramp 2; shown in Fig. 3A). That is, no facilitation in the response occurred with repetition when firing was initially confined to these low rates, well below the plateau threshold.
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FIG. 3.
Superimposed F-I plots during repeated intracellular activation. A: F-I plot for 1st and 2nd current ramp responses for cell in Fig. 2, with direction of time indicated by arrows. Solid and open circles for up and down phases of ramp, respectively. Note responses identical in each case. B: F-I plot for 3rd ramp. The plateau was activated at point shown and continued for the rest of the up (solid symbols) and down (open symbols) phase of the triangular ramps. C: F-I plots for 1st (triangles) and 4th (squares) current ramps, which respectively caused firing with the plateau entirely activated (on plateau) and not activated (off plateau), as indicated by the superimposed F-I plot from the 3rd ramp (solid line).
). Again, we found that the plateau threshold dropped significantly with repeated activation; on average by 5.3 ± 4.0 mV [P < 0.05, 71% of cells studied (5/7) showed warm-up].
), the threshold for plateau activation is close to the recruitment level (i.e., the spike threshold), when the motoneurons are synaptically activated in this way (i.e., without additional current injection) (Bennett et al. 1998). Therefore it was most convenient to study the plateaus and warm-up in these motoneurons following QX314 injection to block spiking. When these cells were initially hyperpolarized, and the muscle was stretched, there were phasic depolarizations during stretch, and not during muscle shortening. We suppose that this depolarization reflected the synaptic excitation per se, from the Ia afferents (under curarizated conditions), relatively unaffected by nonlinear membrane properties (see Bennett et al. 1998), because the depolarizations were below the threshold for plateau activation. Also, note that the responses remained the same with repeated stretches (i.e., no signs of warm-up at this level of depolarization; see 5 stretch responses of left of Fig. 4A).
1-nA bias current produced a phasic response and a sustained depolarization during shortening (arrow). The second stretch produced an even larger and more sustained response and so on. Finally, after the fourth stretch the membrane potential remained depolarized (tonically; on a plateau; Fig. 4A, at right). The gradually increasing and more prolonged responses to the first four stretch cycles (described above) likely reflected transient activations of the plateau, and the effect of these activations appeared to accumulate to potentiate subsequent plateaus, as we have seen with the intracellular current injection (Figs. 1-3). Such warm-up during repeated stretch activation also occurred without QX314, an example of which is shown in Fig. 7 of Bennett et al. (1998). In total, 83% of cells tested (10/12) showed the effects of warm-up during stretch, similar to the incidence of warm-up with intracellular current injection.
).
). In this situation the current bias was initially held just below the level to activate plateaus during muscle stretch and then stepped up slightly to enable plateau activation by muscle stretch (Fig. 4B). In the example in Fig. 4B, a 1-nA step increase in current triggered a gradual increase and prolongation of the stretch responses, over three stretch cycles, i.e., a warm-up. The prolonged depolarization (seconds long) after each stretch cycle suggests that the plateau was being activated, as before. In this situation the steady-state response to stretch did not involve a tonic activation of the plateau. Instead the plateau dropped off over 2-3 s after each stretch (e.g., right half of Fig. 4B). This tendency for the plateaus to not last (tonically) was also seen in cells that did not exhibit warm-up and was associated with high recruitment threshold cells that required large depolarizing currents to activate the plateaus (Bennett et al. 1998).
15 nA) of the cell between stretch-evoked plateaus did not eliminate warm-up; thus the effect of warm-up was not simply the accumulation of depolarization mentioned above.
).
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FIG. 5.
Warm-up of electromyographic (EMG) response to muscle stretch. EMG recorded from soleus muscle during continuous sinusoidal stretching of the whole triceps surae, as in Fig. 4. Initially, motoneuron pool was silenced with a long inhibitory nerve stimulation [common peroneal (CP) nerve; 5T, 100 Hz, during bar]. Note that the motor-unit responses (EMG) to stretch only grew slowly after the pool was silenced, with a similar time course to warm-up seen in single motoneurons (Fig. 4).
DISCUSSION
Abstract
Introduction
Methods
Results
Discussion
References
, 1996a,b; Russo et al. 1997; Svirskis and Hounsgaard 1997). Warm-up can be seen from synaptic input as well as current injected into the cell body. Importantly, its effects are also reflected in the extracellular records recorded with conventional gross EMG. In the following we wish to address 1) the mechanism underlying warm-up, 2) the relation between the reduction in plateau thresholds by warm-up (present study) and synaptic excitation (Bennett et al. 1998), and finally 3) the possible functional implications.
, 1996a,b; Russo et al. 1997) and rat dorsal horn neurons (Morisset and Nagy 1996). Rosso and Hounsgaard found that facilitation of plateaus occurred with and without a buildup of residual depolarization between each plateau activation, and argued that the latter situation would indicate that there was a direct facilitation of the L-type Ca2+ channels. In cat motoneurons we also saw evidence for a similar facilitation with (Fig. 4) and without (Fig. 1 and see text) a residual depolarization (or increase in firing rate) between plateau activations. In comparison with facilitation of L-type Ca2+ channels in other systems (Dolphin 1996), it is noteworthy that the warm-up in dorsal horn neurons and motoneurons occurs at a relatively low level of depolarization and has a longer duration (several seconds). This would imply that it is of importance in the physiological range of membrane potentials and would influence synaptic integration over a period of several seconds.
), although the mechanism behind this was unclear. It is therefore interesting to consider the possibility that the slow plateau onset may result from the same mechanism as warm-up (i.e., slow kinetics intrinsic to the channels may be involved) as described by Svirskis and Hounsgaard (1995, 1997). That is, a depolarizing pulse may initially only influence a fraction of the Ca2+ channels associated with the plateau, and when these channels have sufficient time to be facilitated (warm-up), they will depolarize the cell further, activate further Ca2+ channels, and thus set up a slow regenerative depolarization, limited in speed, as warm-up is. This mechanism would also explain why stronger stimuli produce more rapid plateau activations (more channels initially affected). Also, when the stimulus is sufficiently weak, it may only cause a partial activation of the plateau, and only on subsequent activations will the plateau be fully activated, as we have seen.
). Two situations need to be considered to rule out this possibility. First, the effect of the repeated plateau activation in the companion paper probably did not in itself cause a lowering of the plateau threshold, for as we have already stated, there were long intervals (>20 s) between plateau activations, and warm-up has only short-term effects (~5 s). Second, the tonic EPSPs could have caused warm-up, even though they did not by themselves cause plateau activation (or firing). Such a subthreshold warm-up is certainly conceivable, because Russo and Hounsgaard (1996a) have reported that the warm-up can occur "just subthreshold" to the plateau. In our case we have not found that subthreshold activations cause warm-up (Figs. 3 and 4), although this issue clearly warrants more specific investigation.
).
; Gorassini et al. 1998). The phenomenon of warm-up, seen in extracellular recordings (EMG) in the present study, should provide a useful new tool for studying plateaus in humans (and awake animals). Indeed, Gorassini et al. (1997, 1998) have recently shown that the duration of sustained motor-unit firing following phasic muscle vibration progressively increases on repeated activation of the motor unit (with vibration), as for the cat motoneurons in Figs. 4 and 5. Warm-up may also explain the lowering of recruitment thresholds seen in human motor units during repetitive activation (Gorassini et al. 1997, 1998; Suzuki et al. 1990). In summary, together the effects of repeated depolarization (warm-up) and synaptic activation (companion paper; Bennett et al. 1998) seen in cat motoneurons provide powerful mechanisms of changing the threshold and gain of the motoneuron. These effects, if present in humans, are likely to influence the effectiveness of recruitment and force production in many motor tasks, especially those that involve repetitive movements.
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ACKNOWLEDGEMENTS |
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We thank L. Grondahl and I. Kjær for expert technical assistance.
Funding was provided by the Danish Medical Research Council, the Michaelsen Foundation, the Alberta Heritage Foundation for Medical Research (for D. Bennett), the Canadian Medical Research Council (for B. Fedirchuk), and a grant from the Danish Research Academy (for M. Gorassini).
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FOOTNOTES |
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Address for reprint requests: D. Bennett, 513 HMRC, Division of Neuroscience, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Received 26 September 1997; accepted in final form 17 June 1998.
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REFERENCES |
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References
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|
|
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|
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|
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|
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