Ventral pallidal microinjections of receptor-selective opioid agonists produce differential effects on circling and locomotor activity in rats

Locomotor activity was investigated following microinjections of receptor-selective opioid agonists into the ventral pallidum (VP) of rats. In Expt. 1, male Long-Evans rats were treated with unilateral microinjections of the μ agonist [d-Ala²-MePhe⁴, Gly-ol⁵]-enkephalin (DAGO), the σ agonist [d-Pen²,d-Pen⁵]-enkephalin (DPDPE) or the κ agonist U50,488H, and the rate and duration of circling behavior were measured. DAGO (0.01, 0.1, 1.0 nmol) procedure a dose-dependent increse in contralateral circling; pretreatment with 1.0 mg/kg naltrexone blocked the circling induced by the highest dose. The behavioral effect was largest when injections were targeted at the VP rather than structures dorsal to the VP. In contrast to DAGO, intrapallidal DPDPE (0.01, 0.1, 1.0, 10.0 nmol) produced a slight increase in contralateral circling only at the highest dose and U50, 488H (0.01, 0.1, 1.0, 10.0 nmol) produced no effect. In Expt. 2, the effects of bilateral injections of DAGO, DPDPE and U50,488H were tested in photocell activity ☐es. DAGO produced a dose-dependent increase in locomotor activity and this increase was decreased by 1.0 mg/kg naltrexone. A slight increase in activity was observed with the highest dose of DPDPE, and a slight decrease was observed with the highest dose of U50,488H. These findings confirm that opiate actions in the VP contribute to opiate-induced locomotion and suggest that μ and to some extent σ receptors are involved in this behavior.     

Effects of walking with loads above the ankle on gait parameters of persons with hemiparesis after stroke

Background

Walking with a load at the ankle during gait training is a simple way to resist lower limb movements to induce functional muscle strengthening. This study investigated the effects of walking with different loads attached above the paretic ankle on biomechanical gait parameters during over ground walking in post-stroke participants.

Methods

Ten participants with moderate chronic hemiparesis were evaluated while walking over ground with three different loads (0.5, 1.0, and 1.5 kg) attached above the paretic ankle. Gait speed, cadence, step lengths as well as hip and knee angular displacements, joint moments and power of the paretic limb were compared while walking with and without loads.

Findings

Walking with a load led to an increased in gait speed (+ 0.03–0.05 m/s), and in step length of the paretic leg (+ 5.6 to 9.4% step length, effect size = 0.49–0.63), but not of the non-paretic leg. The proportion of the stance and swing phases did not change. Maximal joint moments (+ 20 to 48%, effect size = 0.26–0.55) and power (+ 20 to 114%, effect size = 0.30–0.57) increases varied across participants but were mostly affected in early stance at the hip and during the late swing phase at the knee. Mean angular displacement changes were less than 4°.

Interpretation

Post-stroke participants are able to increase hip and knee power bursts to meet the increased mechanical demand of added loads attached to the paretic ankle, while preserving the basic pattern of walking. Further study is needed before using loading to functionally strengthen paretic muscles.     

Movement-induced depression of soleus H reflexes is consistent in humans over the range of excitatory afferents involved

The presumption that the H reflex arises exclusively from la afferent discharge has been challenged. If the reflex is comprised of many afferent responses, then movement-induced H reflex inhibition witnessed at one point in the recruitment curve may be quite different from the inhibition at another point in the curve. H reflex recruitment curves were constructed for three subjects during passive pedalling, isolated knee rotation and isolated hip rotation. Compared to control recruitment curves, these curves were reduced across the full spectrum of stimulus intensities. This suggests one of two possibilities: (1) all afferents contributing to the H reflex are subject to the same source and modality of inhibition; or (2) there is only one afferent type contributing to the reflex.     

The relationship between the kinematics of passive movement, the stretch of extensor muscles of the leg and the change induced in the gain of the soleus H reflex in humans

The gain of the H reflex attenuates during passive stepping and pedalling movements of the leg. We hypothesized that the kinematics of the movement indirectly reflect the receptor origin of this attenuation. In the first experiment, H reflexes were evoked in soleus at 26 points in the cycle of slow, passive pedalling movement of the leg and at 13 points with the leg static (the ankle was always immobilized). Maximum inhibition occurred as the leg moved through its most flexed position (P < 0.05). Inhibition observed in the static leg was also strongest at this position (P < 0.05). The increase in inhibition was gradual during flexion movement, with rapid reversal of this increase during extension. In the second experiment, the length of stretch of the vasti muscles was modelled. Variable pedal crank lengths and revolutions per minute (rpm) altered leg joint displacements and angular velocities. Equivalent rates of stretch of the vasti, achieved through different combinations of joint displacements and velocities, elicited equivalent attenuations of mean reflex magnitudes in the flexed leg. Reflex gain exponentially related to rate of stretch (R² = 0.98 P < 0.01). The results imply that gain attenuation of this spinal sensorimotor path arises from spindle discharge in heteronymous extensor muscles of knee and/or hip, concomitant with movement.     

Bimodal effect of amphetamine on motor behaviors in C57BL/6 mice

Amphetamine-induced motor behaviors, i.e., locomotor and stereotypic activities, were simultaneously characterized in C57BL/6 mice, a strain commonly used for genetic studies. Our findings show relatively high levels of focused activities in drug-naive C57BL/6 mice, confirming the lively nature of this mouse strain. Acute amphetamine induced a dose-dependent, bimodal response: locomotion predominated at lower doses of amphetamine and was gradually displaced by stereotypic behavior as dose and time increased. The sum total of both behavioral activities increased with amphetamine dose, supporting the notion that amphetamine-induced locomotion and stereotypy form a continuum. These data provide a basis for using C57BL/6 mice as a strain to study the molecular and cellular mechanisms underlying psychostimulant effects, drug addiction and psychotic disorders.     

The effect of anterior cruciate ligament recontruction on lower extremity relative phase dynamics during walking and running

The purpose of this investigation was to use relative phase dynamics to evaluate gait in individuals with a reconstructed anterior cruciate ligament (ACL) during walking and running. Relative phase dynamics can describe the coordination strategies between the interacting segments at the lower extremity. Ten subjects who had undergone ACL reconstruction using the central third of their patellar tendon and ten healthy controls walked and ran on a treadmill at a self-selected pace. Relative phase dynamics were calculated for the foot–shank and shank–thigh coordinative relationships. Statistical differences between the groups were noted for the foot–shank relationship (p<0.05) during both walking and running and for the shank–thigh relationship (p<0.05) during walking. Our results indicate that current ACL reconstructive techniques may result in altered relative phase dynamics. These changes in relative phase dynamics could be related to a loss of sensory information about joint position and velocity that is typically provided by the intact ACL. Additionally, relative phase adaptations could be a learned response from the early stages of postsurgical rehabilitation. Relative phase dynamics provide quantitative information about the dynamic status of the ACL-reconstructed knee that cannot be gained from the conventional time-series evaluation of gait analysis data. Relative phase dynamics measures should supplement the conventional gait analysis measures that are used today for the clinical evaluation of the functional dynamic stability of the reconstructed knee. The examination of relative phase dynamics could be clinically important for the quantification of new ACL surgical interventions and of patient performance at various stages of rehabilitation. Further research should incorporate relative phase dynamics to understand the influence of ACL reconstruction on coordination and functional patient outcomes.     

大鼠运动行为的自动化检测与分类

目的 探讨大鼠行为的自动化检测与评估方法。方法 利用计算机自动化技术对大鼠运动行为进行记录，并对记录数据进行统计整理，找出具有代表意义重复性高的评估其运动行为特征的指标。结果 通过对大鼠各运动速率百分比加权求和得出实验动物运动水平值（M）可以反映其整体运动行为状况，根据运动速率可将大鼠在特定时间段内的活动区分为四种类型，实验动物入陌生环境头25分钟四种运动类型所占份额的百分比数值有较好的重复性。结论 在本室自行研制的实验动物运动行为自动化检测系统中，运动水平值（M）和头25分钟四种运动类型所占百分比值可作为衡量大鼠运动特征的重要指标。     

Strategies for recovery from a trip in early and late swing during human walking

The movement strategies and the underlying organization of the muscular responses for recovery from a tripping perturbation applied in early and late swing during walking were studied in humans. The latencies of the reflex response (60–140 ms) suggested that polysynaptic pathways are involved. The most common movement outcome was an elevating strategy of the swing limb in response to the early swing perturbation and a lowering strategy in response to the late swing perturbation. The elevating strategy comprised a flexor component of the swing limb and an extensor component of the stance limb. There was a temporal sequencing of the swing limb biceps femoris prior to the swing limb rectus femoris response to remove the limb from the obstacle prior to accelerating the limb over the obstacle. The extensor response of the stance limb generated an early heel-off to increase the height of the body. Thus, the lower limb joints collaborated to increase the height of the centre of mass and provide extra time to extend the swing limb in preparation for the landing. Flexion of the swing limb would be dangerous in response to the late swing perturbation as the swing limb is approaching the ground and the body mass has passed forward of the stance foot. Instead, a lowering strategy was accomplished by inhibitory responses of the swing limb vastus lateralis and/or excitatory responses of the swing limb biceps femoris. Both these responses resulted in a rapid lowering of the limb to the ground with a flat foot or forefoot landing and a shortening of the step length. Thus, in response to the late swing perturbation, the same recovery strategy was achieved by different patterns of muscle activation. These results demonstrate that the recovery strategies provided a functionally appropriate response for overcoming the obstacle and maintaining the ongoing locomotion.     

Variability as a characteristic of immature motor systems: an electromyographic study of swimming in the newborn rat

Swimming behaviour was studied in neonate rats by carrying out electromyographic recordings. The study showed that the early swimming pattern was characterized by highly instable temporal parameters. A decrease was found to occur with age in the variability of the instantaneous period in each leg and in that of the antiphase pattern. Moreover, a dissociation occurred during development between the foreleg and the backleg activity. While patterns involving the forelegs always remained extremely instable, a considerable improvement was found to occur with time in the hindlimb activity.