Page 39 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAFigure TaggedAPTARAEndEffect of exercise on locomotor system 161

Fig. 1. Exercise-induced adaptation of neurons in the locomotor system. The treadmill exercise affects neurons in the CPG and MLR. The plasticity of neurons
includes (A) modulated ion channels, (B) promoted dendritic plasticity, (C) increased number of excitatory synapses, and (D) increased neurotrophic expression.
CPG = central pattern generator; DRG = dorsal root ganglion; MLR = mesencephalic locomotor region.TaggedAPTARAEnd
potential (RMP), input resistance (Rin, calculated by motoneurons. 8,1820 Specifically, their lumbar motoneurons
membrane potential deflection divided by negatively injected undergo a reduction in Rin 20,21 followed by a decrease in ampli-
current), frequency and current relationship (FI relationship, tude of AHP during similar interspike intervals. 22 Additional
established by firing frequency vs. step current), action poten- studies of fictive locomotor outputs in cat motoneurons have also
tial (AP), and afterhyperpolarization (AHP, hyperpolarization revealed significant changes in their FI relationship, a pattern
of membrane potential after an AP). The ion channels focused of nonlinear voltage-dependent excitation, and perhaps most
on in this review included: (a) transient sodium channels, significantly, a hyperpolarization of their Vth required for AP
which determine the threshold of AP generation, (b) persistent generation. 8,9,2227 The varying changes in FI relationship
sodium channels, which generate persistent inward currents during fictive locomotion are shown as the left-shift of FI rela-
(PICs) important for motoneuron excitability, (c) L-type calcium tionship with alteration of FI slopes during the excitatory phase
channels, which generate PICs regulating rhythm generation in of the locomotor drive potentials and the right-shift of FI rela-
the locomotor system, (d) delayed-rectifier potassium (K(DR)) tionship with changes in FI slopes in the inhibitory phase of the
channels, which modulate Vth, and (e) calcium-activated potas- locomotor drive potentials. In addition, the disappearance of FI
relationships in the excitatory phase of the locomotor drive poten-
sium channels (K(Ca)), which mediate AHP.TaggedAPTARAEnd
tials is also observed in some cells, where the motoneuron
TaggedAPTARAH12. Acute exercise increases neuronal excitabilityTaggedAPTARAEnd discharge rates are saturated without changing with the injected
TaggedAPTARAPOur present understanding of the relationship between acute currents. 22,24 Similar alterations in neuronal membrane properties
exercise and neuronal excitability has emerged from comprehen- indicating acute exercise-enhanced neuronal excitability have
sive studies of fictive locomotion in different animal models. also been reported in other species. Studies of fictive locomotion
Fictive locomotion refers to the generation of neural activity in decerebrated neonatal rats likewise demonstrate that their
patterns in the nervous system resembling those patterns spinal motoneurons undergo decreases in amplitude of AHP and
observed during actual locomotion, but without actual movement a hyperpolarization of their Vth during locomotor-like
9,26,28
of the limbs or body; hence, the resulting locomotion is consid- activity. Increases in neuronal excitability experienced
ered not real but fictive. 17 Studies of fictive locomotion in cats during acute exercise ultimately dissipate back into a steady state
have demonstrated that acute exercise leads to enhanced neuronal once the locomotor state terminates such that the cycle may
excitability. For instance, electrical stimulation of mesencephalic repeat again. Mechanism studies suggest that ion channels are
locomotor regions of decerebrated cats generates locomotion 17 responsible for regulating this cycle. Experimental and modeling
via the increase of the excitability of their spinal studies indicate that the hyperpolarization of Vth can be mediated