Electromyographic activity of m. longissimus and the kinematics of the vertebral column during level and downslope treadmill walking in cats.

A series of kinematic and electromyographic (EMG) studies were conducted to characterize the neural control of underground movement in the Japanese mole, Mogera wogura For the purposes of the present study, the locomotion of moles was classified into two modes: crawling, which comprises alternate movements of the left and right forelimbs; and burrowing, in which both forelimbs move synchronously In crawling, moles exhibit both symmetrical and asymmetrical locomotion independent of cycle duration and speed of travel In burrowing, the movements of fore- and hindlimbs, and of the left and right hindlimb are loosely coordinated We divided cycles of limb movement into recovery stroke phase and power stroke phases and observed that control of cycle duration in forelimbs and hindlimbs was achieved through changes to both recovery and power stroke phases Our results showed phasic EMG bursts in various muscles in moles, whose timing differed from that seen in terrestrial four-legged mammals such as cats and dogs The difference was especially apparent in the m longissimus, in which EMG bursts recorded at the level of the thoracic and lumbar vertebrae corresponded to movements of the forelimbs and hindlimbs, respectively Thus, we conclude that moles have evolved a distinctive mechanism of neural control to perform their specialized forms of underground locomotion

Underground locomotion in moles: kinematic and electromyographic studies of locomotion in the Japanese mole (Mogera wogura).

Previous studies (Wada and Kanda 2001, Exp Brain Res 136:263–263; Wada et al. 1999, Exp Brain Res 128:543–549) demonstrated that input patterns from hindlimb muscles and cutaneous afferents vary among individual trunk muscle motoneurons. The purpose of the present study was to examine the relationship between the synaptic pattern from hindlimb afferents and the area innervated by motoneurons. Histologic study of m. longissimus lumborum (Long) indicated that the distribution of different fiber types (slow-twitch oxidative, SO; fast-twitch oxidative glycolytic, FOG; fast-twitch glycolytic, FG) depends on the area of the Long cross-section. The ventromedial area and dorsolateral area of the cross-section possess a high content of SO and FG, respectively. The motoneurons innervating the dorsolateral area receive muscle afferent inputs mainly from the ipsilateral side, while the motoneurons innervating the ventromedial area often receive bilateral afferent inputs. The motoneurons innervating the dorsolateral area receive excitatory post-synaptic potentials from cutaneous nerves on both sides. These findings indicate that the effects of afferent inputs from the hindlimbs are related to motoneuron type or the area innervated by the motoneurons.

Differential effects of hindlimb peripheral afferents on motoneurons innervating different parts of longissimus muscle in cats.

The trunk plays a pivotal role in limbed locomotion. Yet, little is known about how the brain stem controls trunk activity during walking. In this study, we assessed the spatiotemporal activity patterns of axial and hindlimb motoneurons (MNs) during drug-induced fictive locomotor-like activity (LLA) in an isolated brain stem-spinal cord preparation of the neonatal mouse. We also evaluated the extent to which these activity patterns are affected by removal of brain stem. Recordings were made in the segments T7, L2, and L5 using calcium imaging from individual axial MNs in the medial motor column (MMC) and hindlimb MNs in lateral motor column (LMC). The MN activities were analyzed during both the rhythmic and the tonic components of LLA of LLA, the tonic component being used as a readout of generalized increase in excitability in spinal locomotor networks. The most salient effect of brain stem removal was an increase in locomotor rhythm frequency and a concomitant reduction in burst durations in both MMC and LMC MNs. The lack of effect on the tonic component of LLA indicated specificity of action during the rhythmic component. Cooling-induced silencing of the brain stem reproduced the increase in rhythm frequency and accompanying decrease in burst durations in L2 MMC and LMC, suggesting a dependency on brain stem neuron activity. The work supports the idea that the brain stem locomotor circuits are operational already at birth and further suggests an important role in modulating trunk activity. The brain stem may influence the axial and hindlimb spinal locomotor rhythm generating circuits by extending their range of operation. This may represent a critical step of locomotor development when learning how to walk in different conditions and environments is a major endeavor.

/pdf/influence-of-brain-stem-on-axial-and-hindlimb-spinal-58ciswwkrv.pdf

Influence of Brain Stem on Axial and Hindlimb Spinal Locomotor Rhythm Generating Circuits of the Neonatal Mouse.

This chapter addresses the neural control of spinal-column behavior during locomotion. Kinematic and EMG measurements were obtained from the adult cat during its level and upslope treadmill walking. Increasing the grade of upslope walking augmented horizontal movements of the spinal column and decreased its lateral movements. In conjunction, there were significant increases in the amplitude, duration, and pattern of EMG bursts in relevant spinal column musculature. During even steeper upslope walking, three EMG bursts were evident. They were phase-locked to the outward, downward and backward movements of the spinal column, respectively. Our results suggest that the component of the locomotor pattern generator that produces rhythmical spinal column movements must generate a wide variety of EMG bursts in spinal column muscles, as dependent in part on sensory input from the spinal column and its musculature.

Trunk movements and EMG activity in the cat: level versus upslope walking

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Trunk movements and EMG activity in the cat: level versus upslope walking