Page 45 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEndEffect of exercise on locomotor system 167
repetitive firing in spinal motoneurons, 36 interneurons, 76 hippo- prediction was verified experimentally in mouse spinal moto-
campal neurons, 77 and brainstem 5-HT neurons. 78 In addition, neurons using the KCNQ/Kv7 channel antagonist XE-991. 31
persistent sodium channels are critical in regulating pacemakers Simulation results further show downregulation of K(DR) chan-
and locomotion speed. 79 Recent studies have discovered that 3 nels increases the FI slope in a manner consistent with experi-
weeks of treadmill training increases neuronal excitability mental observations during locomotion. 23 These results in sum
through the enhancement of persistent sodium channels in spinal demonstrate that K(DR) channels are one of the major modula-
interneurons 15 and midbrain 5-HT neurons in mice. 16 Three tors of the locomotor system’s adaptability to exercise.TaggedAPTARAEnd
weeks of treadmill training significantly hyperpolarizes the acti-
vation voltage of persistent sodium channels, suggesting they TaggedAPTARAH24.5. K(Ca) channelsTaggedAPTARAEnd
play a key role in regulating spike initiation and excitability.
TaggedAPTARAPTwo types of K(Ca) channels mediate AHP, small conduc-
Modeling studies further confirm that PICs generated by persis-
tance K(Ca) and big conductance K(Ca). Small conductance
tent sodium channels are involved in the recruitment of spinal K(Ca) channels are activated by cytosolic calcium in response to
motoneuron pools and force generation by skeletal muscle. 48,66
calcium influx via voltage-gated calcium channels during AP
Studies of their FI relationship suggest persistent sodium chan- 62,88,89
generation. K(Ca) channels control many physiological
nels also play a role in regulating output from spinal neurons processes, from the firing properties of neurons to the control of
during locomotion. 23,78,80 More recent studies suggest persistent 90
neurotransmitter release. During repetitive firing, the inter-
sodium channels may contribute to the hour-long effects of trans-
spike interval is dependent on the amplitude and duration of the
spinal stimulation combined with epidural polarization, 60,91
81,82 AHP. Modeling studies have shown that reducing K(Ca)
suggesting they also play a role in promoting rehabilitation.
channel conductance by 30%50% leads to increases in the FI
Overall, persistent sodium channels help to facilitate the adapta- 23 48
slope, the number of recruited motoneurons, and the force
tion of the locomotor system in response to exercise.TaggedAPTARAEnd 66
production of skeletal muscles. Therefore, modulation of K(Ca)
channels regulates discharge rate and neuronal excitability.
TaggedAPTARAH24.3. L-type calcium channelsTaggedAPTARAEnd
The effect of exercise intervention on the amplitude of AHP
TaggedAPTARAPL-type calcium channels, mediated by voltage-gated mediated by K(Ca) channels is inconsistent. Experimental
calcium channel 1.3 (Cav1.3) are another generators of results show the amplitude of AHP is reduced in cat and rat
PICs, 33,7173 and they play an important role in spinal loco- spinal motoneurons during fictive locomotion, 9,22,25 while
motor network rhythm generation. 61,83 In studies of human results from genetic studies show gene expression of K(Ca)
MU recruitment, PICs mediated by L-type calcium channels channels decreases in rat spinal motoneurons after chronic
have been shown to reduce recruitment. 84 Modeling studies exercise. 92 However, the amplitude of AHP significantly
also emphasize the role of L-type calcium channels in regu- increases in fast motoneurons of rats subjected to chronic
lating motoneuron excitability, recruitment, and motor output compensatory muscle overload for 5 weeks or 12 weeks 45
during locomotion. 23 L-type calcium channels have also been and in motoneurons of rats subjected to spontaneous exercise
shown to amplify synaptic excitatory input, enhance firing wheels for 12 weeks. 11 Increased AHP is also observed in
frequency, 73 and maintain continuous firing in spinal cerebral artery smooth muscle cells after chronic exercise. 93
neurons. 75,78,80 Recent studies have revealed that 3 weeks of Furthermore, the amplitude of AHP does not undergo signifi-
treadmill exercise enhances L-type calcium channel activity in cant changes following 3 weeks of exercise. 15,16 The mecha-
laminar X interneurons and 5-HT neurons of the dorsal raphe nism underlying this paradoxical increase in AHP amplitude
nucleus. 12,16 Further studies have confirmed L-type calcium remains an open question. A possible interpretation of this
channels mainly contribute to the regulation of repetitive firing, paradox is that an increase in AHP amplitude following
the facilitation of spike initiation (along with persistent sodium training is used by the motor system to reduce PIC activa-
channels), and exercise-prolonged hysteresis of firing after tion and thus firing rates to offset fatigue. A further study
chronic exercise (along with persistent sodium channels). 12,16 is required to test this hypothesis. Overall, K(Ca) channels
Taken together, L-type calcium channels are crucial modulators play a certain role in regulating neuronal excitability and
of neuronal function, motor control, and the adaptive responses motor output during exercise; however, additional research
is needed to elucidate the mechanisms and factors contrib-
of the locomotor system to exercise intervention.TaggedAPTARAEnd
uting to the contradictory increases in AHP amplitude
TaggedAPTARAH24.4. K(DR) channelsTaggedAPTARAEnd observed under different exercise conditions.TaggedAPTARAEnd
TaggedAPTARAPK(DR) channels play a major role in modulating Vth in spinal
30
motoneurons. They also regulate diverse membrane properties, TaggedAPTARAH15. Exercise facilitates morphological and functional
plasticity of neuronsTaggedAPTARAEnd
including AP amplitude and duration, firing frequency, RMP,
and neurotransmitter release. 8587 Modeling studies suggest K TaggedAPTARAPA key feature of the central nervous system is the ability of
(DR) channels contribute mainly to hyperpolarization of Vth its neurons to alter their morphology and connectivity in
during fictive locomotion. 30,48 Modeling a 70% reduction of response to sensory experience and other changes in the envi-
conductance of K(DR) channels in the initial segment of moto- ronment. Neurons with distinct dendritic morphologies have
neurons results in a 3- to 5-mV hyperpolarization of Vth, compa- different functions in neural circuits, as they will make unique
rable to the amount observed during locomotion. 30 This connections with other neurons. 94 Voluntary physical exercise