Antidromic discharges in dorsal roots of decerebrate cats: I. Studies at rest and during fictive locomotion

Spontaneous rhythmic antidromic discharges have previously been recorded in proximal stumps of cut dorsal roots during locomotion (real and fictive). The goals of the present study were to elucidate (1) whether both orthodromic and antidromic discharges occur in the same dorsal root filament and (2) whether orthodromic discharges have an influence upon antidromic discharges of units in the same filament. Unitary activity was recorded in 70 uncut dorsal root filaments (L6-S1) in 15 decerebrate cats using bipolar Ag/AgCl electrodes. Spikes with similar wave shapes were considered to represent the activity of single units. Spike-triggered averaging (STA), local anaesthesia and transection of filaments were used to determine the direction of propagation of spikes. Spikes with different initial electrical polarities were found in most of the filaments and shown to propagate in opposite directions at rest and during fictive locomotion. On average, there were 38%±S.D. 23% antidromically discharging units per filament and their mean conduction velocity was 55 m/s±S.D. 25 m/s. After blocking orthodromic activity of the whole filament by a transection or local anesthesia applied distally to the recording site, changes were seen in the antidromic discharges of some units suggesting that spontaneous orthodromic discharges normally seen in the filament may influence the antidromic discharges of some units. Moreover, out of 27 antidromic units recorded during fictive locomotion, 12 were rhythmically modulated with peak discharges occurring in various parts of the locomotor cycle. We conclude that, in uncut dorsal roots, there is a normal coexistence of spontaneous orthodromic and antidromic discharges revealed by STA and that there is an interaction between spontaneous orthodromic and antidromic discharges.     

Treadmill training enhances the recovery of normal stepping patterns in spinal cord contused rats

Treadmill training is known to improve stepping in complete spinal cord injured animals. Few studies have examined whether treadmill training also enhances locomotor recovery in animals following incomplete spinal cord injuries. In the present study, we compared locomotor recovery in trained and untrained rats that received a severe mid-thoracic contusion of the spinal cord. A robotic device was used to train and to test bipedal hindlimb stepping on a treadmill. Training was imposed for 8 weeks. The robotic device supported the weight of the rats and recorded ankle movements in the hindlimbs for movement analyses. Both the trained and untrained rats generated partial weight bearing hindlimb steps after the spinal cord contusion. Dragging during swing was more prevalent in the untrained rats than the trained rats. In addition, only the trained rats performed step cycle trajectories that were similar to normal step cycle trajectories in terms of the trajectory shape and movement velocity characteristics. In contrast, untrained rats executed step cycles that consisted of fast, kick-like movements during forward swing. These findings indicate that spinal cord contused rats can generate partial weight bearing stepping in the absence of treadmill training. The findings also suggest that the effect of treadmill training is to restore normal patterns of hindlimb movements following severe incomplete spinal cord injury in rats.     

Dopamine receptors in the ventral tegmental area affect motor, but not motivational or reflexive, components of copulation in male rats

Microinjection of apomorphine into the ventral tegmental area (VTA) of male rats was previously shown to delay the onset of copulation and slow its rate, presumably by stimulating impulse-regulating autoreceptors on cell bodies of the A10 mesocorticolimbic dopamine tract. Such stimulation would be expected to slow the firing rate of these neurons and, thereby, to impair locomotion and/or motivational processes. The present experiments tested whether the delayed onset and slowed rate of copulation were related to deficits in motor performance, sexual motivation, and/or genital reflexes. In X-maze tests the speed of running to all 4 goal boxes was slowed; however, the percentage of trials on which the male chose the female's goal box was not decreased. Examination of videotaped copulation tests revealed that the male showed fewer complete copulatory behaviors (mounts, intromissions, and ejaculations), but more misdirected or incomplete copulatory attempts after apomorphine in the VTA. There were also fewer scores of active, as opposed to inactive, behaviors, and the onset and rate of copulation were slowed. The total number of female directed behaviors was not different in apomorphine tests, compared to vehicle. Finally, tests of ex copula genital reflexes revealed no significant effects of apomorphine in the VTA on erections, penile movements, or seminal emissions. These data suggest a role of the VTA in the motor aspects and/or sensorimotor integration of copulation. Sexual motivation and ex copula genital reflexes appeared to be unaffected by apomorphine in the VTA.     

Locomotor deficits in the mutant mouse,Lurcher

Summary The effect of total Purkinje cell degeneration on treadmill locomotion was studied in the cerebellar mutant mouse Lurcher. Other movements such as swimming and scratchting were also studied in order to evaluate the cerebellar control of rhythmic actions. Cinematographic and electromyographic recordings were taken from normal and Lurcher mice that were subsequently perfused to obtain a Purkinje cell count. Walking deteriorated progressively and was clearly abnormal in 30 day old Lurchers with 90% Purkinje cell degeneration. In adult Lurcher mice in which Purkinje cells were totally absent, walking was characterized by short steps with exaggerated hindlimb flexion in the swing phase. Also, both the interlimb step ratio, defined as the step length of the reference limb divided by the step length of the opposite limb, and the interlimb coupling, defined as the temporal relation of one footfall with respect to the footfall of another limb, varied more than in normal mice. Furthermore, the locomotion of Lurcher mice displayed increased vertical displacement of the hip and an inability to produce continuous step cycles without stumbling. Both the EMG onset relative to foot contact and the EMG burst duration were highly variable, and a greater overlap in the activities of antagonist muscles at the transition from ankle extension to flexion was evident. Although both walking and swimming involve cyclical limb movements, the disorganization of the cycle and the irregular EMG pattern seen in the Lurcher during walking were not observed during swimming. Furthermore, scratching was well executed in the Lurcher mice. However, a consistently higher tonic extensor activity at the ankle appeared during walking, swimming and scratching. These results suggest that, in contrast to swimming and scratching, the requirements of walking depend to a greater degree on a functional cerebellar cortex for successful performance.     

Lateral pelvic displacement during gait: abnormalities after stroke and changes during the first month of rehabilitation

OBJECTIVES: To measure the amplitude and symmetry of lateral pelvic displacement (LPD) in patients with acute hemiparetic stroke; to assess the relationship between LPD and walking speed; and to quantify changes in LPD during 1- and 4-week intervals in the early stages of gait rehabilitation. DESIGN: LPD amplitude and symmetry were measured in stroke patients on admission to acute rehabilitation, 1 week later, and at 4-week follow-up. Performance was compared with sex-, height-, and age-matched control subjects. SETTING: Urban geriatric inpatient rehabilitation facility in Australia. PARTICIPANTS: Fifteen patients with a single-hemisphere stroke, confirmed by computed tomography, were compared with the data from 12 control subjects. Patients' FIM trade mark instrument scores ranged from 54 to 124. INTERVENTION: Gait rehabilitation involved twice-daily individual physical therapy sessions of 45 to 60 minutes, 5 days a week, incorporating whole and part practice, mental rehearsal, verbal feedback on performance, manual guidance, and strengthening techniques. MAIN OUTCOME MEASURES: Three-dimensional motion analysis of LPD amplitude and symmetry; and preferred walking speed over 10m. RESULTS: Compared with controls, stroke patients initially showed increased amplitude of LPD, with no difference in LPD symmetry. A statistically significant linear relationship existed between walking speed and amplitude of LPD (r=-.53; P=.04), yet not between walking speed and symmetry (r=-.41, P=.13). Amplitude and symmetry values remained consistent during the 4-week period of rehabilitation. CONCLUSIONS: These results provide baseline LPD values for patients with acute hemiparetic stroke and demonstrate the relationship between LPD and walking speed. Change in LPD during inpatient rehabilitation was not uniform or predictable, particularly during longer periods. This highlights the need for therapists to regularly reassess each patient during the early rehabilitation phase after stroke, especially given that individual differences can be marked.     

踝关节外骨骼助行模式对下肢肌肉激活与协调模式的影响EI北大核心CSCD

踝关节外骨骼可用来提高人的行走效率,辅助老年人、运动功能障碍患者等进行日常活动或康复训练,但外骨骼的助行模式会对穿戴者的下肢肌肉激活与协调模式产生影响。本文利用一款绳驱动踝关节外骨骼,设计了不同助力时机与助力大小组合的助行模式,采集了7名穿戴者在跑步机上以1.25 m/s速度水平行走时的下肢表面肌电信号,研究不同助行模式对穿戴者下肢肌肉激活与协调模式的影响。实验结果表明,比目鱼肌激活程度在踝关节外骨骼助力时有明显降低,在助力时机为步态周期49%、助力大小为0.7 N·m/kg时,最高可降低(38.5±10.8)%。并且,相对于助力时机,助力大小对比目鱼肌激活程度影响更为显著。踝关节外骨骼不同模式助行时,所测量下肢肌肉可分解为5个基本协同模式,且合适的助力时机与助力大小条件下,下肢肌肉协调模式和正常行走相比改变较小。此外,比目鱼肌-胫骨前肌、股直肌-半腱肌的协同收缩度在外骨骼助力时比正常行走均有升高。本研究有助于理解健康穿戴者如何调整自身的神经肌肉控制机制来适应不同外骨骼助力,并为选择合适的助行模式以及合理利用外骨骼提高行走效率提供依据。     

Effectiveness of automated locomotor training in patients with chronic incomplete spinal cord injury: a multicenter trial

OBJECTIVE: To determine whether automated locomotor training with a driven-gait orthosis (DGO) can increase functional mobility in people with chronic, motor incomplete spinal cord injury (SCI). DESIGN: Repeated assessment of the same patients or single-case experimental A-B design. SETTING: Research units of rehabilitation hospitals in Chicago; Heidelberg, Germany; and Basel and Zurich, Switzerland. PARTICIPANTS: Twenty patients with a chronic (>2 y postinjury), motor incomplete SCI, classified by the American Spinal Injury Association (ASIA) Impairment Scale with ASIA grades C (n=9) and D (n=11) injury. Most patients (n=16) were ambulatory before locomotor training. INTERVENTION: Locomotor training was provided using robotic-assisted, body-weight-supported treadmill training 3 to 5 times a week over 8 weeks. Single training sessions lasted up to 45 minutes of total walking time, with gait speed between .42 and .69 m/s and body-weight unloading as low as possible (mean +/- standard deviation, 37%+/-17%). MAIN OUTCOME MEASURES: Primary outcome measures included the 10-meter walk test, the 6-minute walk test, the Timed Up & Go test, and the Walking Index for Spinal Cord Injury-II tests. Secondary measures included lower-extremity motor scores and spastic motor behaviors to assess their potential contribution to changes in locomotor function. All subjects were tested before, during, and after training. RESULTS: Locomotor training using the DGO resulted in significant improvements in the subjects' gait velocity, endurance, and performance of functional tasks. There were no significant changes in the requirement of walking aids, orthoses, or external physical assistance. There was no correlation between improvements in walking speed or changes in muscle strength or spastic motor behaviors. CONCLUSIONS: Intensive locomotor training on a treadmill with the assistance of a DGO results in improved overground walking.     

Altered dopaminergic profiles: Implications for the regulation of voluntary physical activity

The biological regulating factors of physical activity in animals are not well understood. This study investigated differences in the central mRNA expression of seven dopamine genes (Drd1, Drd2, Drd3, Drd4, Drd5, TH, and DAT) between high active C57/LJ (n = 17) male mice and low active C3H/HeJ (n = 20) male mice, and between mice with access to a running wheel and without running wheel access within strain. Mice were housed with running wheels interfaced with a computer for 21 days with distance and duration recorded every 24 h. On day 21, the striatum and nucleus accumbens were removed during the active period (9 pm) for dopaminergic analysis. On average, the C57L/J mice with wheels ran significantly farther (10.25 ± 1.37 km/day vs. 0.01 ± 0.09 km/day, p < 0.001), longer (329.73 ± 30.52 min/day vs. 7.81 ± 6.32 min/day, p < 0.001), and faster (31.27 ± 3.13 m/min vs. 11.81 ± 1.08 m/min, p < 0.001) than the C3H/HeJ mice with wheels over the 21 day period. No differences in gene expression were found between mice in either strain with wheels and those without wheels suggesting that access to running wheels did not alter dopaminergic expression. In contrast, relative expression for two dopamine genes was significantly lower in the C57L/J mice compared to the C3H/HeJ mice. These results indicate that decreased dopaminergic functioning is correlated with increased activity levels in C57L/J mice and suggests that D1-like receptors as well as tyrosine hydroxylase (an indicator of dopamine production), but not D2-like receptors may be associated with the regulation of physical activity in inbred mice.     

Behavioral sensitization to cocaine: cooperation between glucocorticoids and epinephrine

Rationale  Stressful life experiences facilitate responsiveness to psychostimulant drugs. While there is ample evidence that adrenal glucocorticoids mediate these effects of stress, the role of the sympatho-adrenal system in the effects of psychostimulants is poorly understood. Objectives  The present study investigated the role of the two adrenal stress hormones, corticosterone and epinephrine, in sensitization to the locomotor stimulant effects of cocaine. Materials and methods  The DBA/2 mouse strain was used, as behavioral sensitization in this strain critically depends on adrenal hormones. Animals were subjected to adrenalectomy (“ADX”, surgical removal of the adrenals) or SHAM surgery, and ADX mice were given replacement of epinephrine (5 × 10⁻³ mg/kg subcutaneously (s.c.) just prior to each drug administration), corticosterone (20%, s.c., pellet), or both. Mice were subjected to a cocaine sensitization regimen (15.0 mg/kg cocaine on nine consecutive days followed by a 7.5 mg/kg cocaine challenge after a 5-day withdrawal). Results  In agreement with our previous observations, ADX prevented initiation and expression of cocaine-induced locomotor sensitization. Whereas neither corticosterone nor epinephrine alone were sufficient to reverse the ADX effect, both hormones were necessary to fully restore initiation and retention of sensitization to levels observed in SHAM animals. Conclusions  The present findings indicate that corticosterone and epinephrine cooperate to facilitate behavioral responsiveness to cocaine. These data emphasize that in addition to the hypothalamic–pituitary–adrenal axis, the sympathetic nervous system plays a critical role in psychostimulant sensitivity.     

An analytical formulation of the law of intersegmental coordination during human locomotion

The law of intersegmental coordination is a kinematic law that describes the coordination patterns among the elevation angles of the lower limb segments during locomotion (Borghese et al. in J Physiol 494:863–879, 1996). This coordination pattern reduces the number of degrees of freedom of the lower limb to two, i.e. the elevation angles covary along a plane in angular space. The properties of the plane that constrains the time course of the elevation angles have been extensively studied, and its orientation was found to be correlated with gait velocity and energy expenditure (Bianchi et al. in J Neurophysiol 79:2155–2170, 1998). Here, we present a mathematical model that represents the rotations of the elevation angles in terms of simple oscillators with appropriate phase shifts between them. The model explains what requirements the time courses of the elevation angles must fulfill in order for the angular covariation relationship to be planar. Moreover, an analytical formulation is proposed for both the orientation of the plane and for the eccentricity of the nearly elliptical shape that is generated within this plane, in terms of the amplitudes and relative phases of the first harmonics of the segments elevation angles. The model presented here sheds some new light on the possible interactions among the Central Pattern Generators possibly underlying the control of biped locomotion. The model precisely specifies how any two segments in the limb interact, and how a change in gait velocity affects the orientation of the intersegmental coordination plane mainly through a change in phase shifts between the segments. Implications of this study with respect to neural control of locomotion and other motor activities are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.