Energy cost of propulsion in standard and ultralight wheelchairs in people with spinal cord injuries.
BACKGROUND AND PURPOSE: Wheelchair- and subject-related factors influence the efficiency of wheelchair propulsion. The purpose of this study was to compare wheelchair propulsion in ultralight and standard wheelchairs in people with different levels of spinal cord injury. SUBJECTS: Seventy-four subjects (mean age=26.2 years, SD=7.14, range=17-50) with spinal cord injury resulting in motor loss (30 with tetraplegia and 44 with paraplegia) were studied. METHOD: Each subject propelled standard and ultralight wheelchairs around an outdoor track at self-selected speeds, while data were collected at 4 predetermined intervals. Speed, distance traveled, and oxygen cost (VO2 mL/kg/m) were compared by wheelchair, group, and over time, using a Bonferroni correction. RESULTS: In the ultralight wheelchair, speed and distance traveled were greater for both subjects with paraplegia and subjects with tetraplegia, whereas VO2 was less only for subjects with paraplegia. Subjects with paraplegia propelled faster and farther than did subjects with tetraplegia. CONCLUSION AND DISCUSSION: The ultralight wheelchair improved the efficiency of propulsion in the tested subjects. Subjects with tetraplegia, especially at the C6 level, are limited in their ability to propel a wheelchair. (+info)
Does nicotine modify the psychotoxic effect of methamphetamine? Assessment in terms of locomotor sensitization in mice.
In this study, effects of nicotine on locomotor sensitization to methamphetamine in mice were investigated to assess whether nicotine modified induction and expression of psychotoxic action of methamphetamine. Although nicotine (0.03-1 mg/kg s.c.) had no effect at first administration, 5-time nicotine administrations at 3-day intervals progressively developed a significant locomotor stimulant effect, and caused an enhanced sensitivity (cross-sensitization) to methamphetamine (2 mg/kg s.c.). Five-time administrations of methamphetamine (2 mg/kg) at 3-day intervals produced not only a locomotor sensitization to methamphetamine itself, but also a cross-sensitization to nicotine (0.1-1 mg/kg). Nicotine (0.03-1 mg/kg) did not affect the locomotor stimulant effect of methamphetamine (2 mg/kg) in the drug-naive mice. However, nicotine acted dose-dependently to reduce the progressive enhancement of the locomotor stimulant effect of methamphetamine during 5-time repeated administrations. Mice treated with coadministration of methamphetamine with nicotine (1 mg/kg) showed less sensitization to methamphetamine than mice treated with methamphetamine alone. In addition, nicotine (1 mg/kg) inhibited the locomotor stimulant effect of methamphetamine in mice sensitized to methamphetamine. These results suggest that methamphetamine and nicotine produce a symmetrical cross-sensitization, although nicotine may act to inhibit the induction and expression of locomotor sensitization to methamphetamine in mice. (+info)
Active signaling of leg loading and unloading in the cockroach.
The ability to detect changes in load is important for effective use of a leg in posture and locomotion. While a number of limb receptors have been shown to encode increases in load, few afferents have been demonstrated to signal leg unloading, which occurs cyclically during walking and is indicative of slipping or perturbations. We applied mechanical forces to the cockroach leg at controlled rates and recorded activities of the tibial group of campaniform sensilla, mechanoreceptors that encode forces through the strains they produce in the exoskeleton. Discrete responses were elicited from the group to decreasing as well as increasing levels of leg loading. Discharges of individual afferents depended on the direction of force application, and unit responses were correlated morphologically with the orientation of the receptor's cuticular cap. No units responded bidirectionally. Although discharges to decreasing levels of load were phasic, we found that these bursts could effectively encode the rate of force decreases. These discharges may be important in indicating leg unloading in the step cycle during walking and could rapidly signal force decreases during perturbations or loss of ground support. (+info)
Plantar aponeurosis and internal architecture of the ball of the foot.
On the basis of its internal structure, the ball of the foot can be divided into three transverse areas, each with a different mechanical function: (1) an area proximal to the heads of the metatarsals in which the retinacula cutis are developed into a series of transverse bands, and in which the deep fibres of the plantar aponeurosis form ten sagittal septa connected to the deep transverse metatarsal ligament and through this the proximal phalanges of the toes, (2) an area below the heads of the metatarsals in which vertical fibres from the joint capsules and the sides of the fibrous flexor sheaths form a cushion below each metatarsal head, and in which fat bodies cover the digital nerves and vessels in their passage between the cushions, and (3) a distal area which comprises the interdigital web. The superficial fibres of the plantar aponeurosis are inserted into the skin of this distal area, and deep to them the plantar interdigital ligament forms a series of transverse lamellae connected to the proximal phalanges by a mooring ligament which arches from one fibrous flexor sheath to the next. When the metatarsophalangeal joints are extended, the fibres of the three areas are tensed and the skin is anchored firmly to the skeleton. The direction of the fibres in the distal and proximal area promotes the transfer of forces exerted on the skin during push-off and braking respectively, while the intermediate area is adapted to bear the weight of the body. A concentration of Pacinian corpuscles is found along the digital nerves in the weight-bearing area below the transverse metatarsal ligament. The nerves for the second, and especially for the third, interstice are close to or in contact with the sharp proximal edges of the sagittal septa. (+info)
Mound-cell movement and morphogenesis in Dictyostelium.
To examine the mechanisms of cell locomotion within a three-dimensional (3-D) cell mass, we have undertaken a systematic 3-D analysis of individual cell movements in the Dictyostelium mound, the first 3-D structure to form during development of the fruiting body. We used time-lapse deconvolution microscopy to examine two strains whose motion represents endpoints on the spectrum of motile behaviors that we have observed in mounds. In AX-2 mounds, cell motion is slow and trajectories are a combination of random and radial, compared to KAX-3, in which motion is fivefold faster and most trajectories are rotational. Although radial or rotational motion was correlated with the optical-density wave patterns present in each strain, we also found small but significant subpopulations of cells that moved differently from the majority, demonstrating that optical-density waves are at best insufficient to explain all motile behavior in mounds. In examining morphogenesis in these strains, we noted that AX-2 mounds tended to culminate directly to a fruiting body, whereas KAX-3 mounds first formed a migratory slug. By altering buffering conditions we could interchange these behaviors and then found that mound-cell motions also changed accordingly. This demonstrates a correlation between mound-cell motion and subsequent development, but it is not obligatory. Chimeric mounds composed of only 10% KAX-3 cells and 90% AX-2 cells exhibited rotational motion, suggesting that a diffusible molecule induces rotation, but many of these mounds still culminated directly, demonstrating that rotational motion does not always lead to slug migration. Our observations provide a detailed analysis of cell motion for two distinct modes of mound and slug formation in Dictyostelium. (+info)
Gliding mutants of Myxococcus xanthus with high reversal frequencies and small displacements.
Myxococcus xanthus cells move on a solid surface by gliding motility. Several genes required for gliding motility have been identified, including those of the A- and S-motility systems as well as the mgl and frz genes. However, the cellular defects in gliding movement in many of these mutants were unknown. We conducted quantitative, high-resolution single-cell motility assays and found that mutants defective in mglAB or in cglB, an A-motility gene, reversed the direction of gliding at frequencies which were more than 1 order of magnitude higher than that of wild type cells (2.9 min-1 for DeltamglAB mutants and 2.7 min-1 for cglB mutants, compared to 0.17 min-1 for wild-type cells). The average gliding speed of DeltamglAB mutant cells was 40% of that of wild-type cells (on average 1.9 micrometers/min for DeltamglAB mutants, compared to 4.4 micrometers/min for wild-type cells). The mglA-dependent reversals and gliding speeds were dependent on the level of intracellular MglA protein: mglB mutant cells, which contain only 15 to 20% of the wild-type level of MglA protein, glided with an average reversal frequency of about 1.8 min-1 and an average speed of 2.6 micrometers/min. These values range between those exhibited by wild-type cells and by DeltamglAB mutant cells. Epistasis analysis of frz mutants, which are defective in aggregation and in single-cell reversals, showed that a frzD mutation, but not a frzE mutation, partially suppressed the mglA phenotype. In contrast to mgl mutants, cglB mutant cells were able to move with wild-type speeds only when in close proximity to each other. However, under those conditions, these mutant cells were found to glide less often with those speeds. By analyzing double mutants, the high reversing movements and gliding speeds of cglB cells were found to be strictly dependent on type IV pili, encoded by S-motility genes, whereas the high-reversal pattern of mglAB cells was only partially reduced by a pilR mutation. These results suggest that the MglA protein is required for both control of reversal frequency and gliding speed and that in the absence of A motility, type IV pilus-dependent cell movement includes reversals at high frequency. Furthermore, mglAB mutants behave as if they were severely defective in A motility but only partially defective in S motility. (+info)
Recovery of locomotion after ventral and ventrolateral spinal lesions in the cat. II. Effects of noradrenergic and serotoninergic drugs.
The effects of serotoninergic and noradrenergic drugs (applied intrathecally) on treadmill locomotion were evaluated in two adult cats subjected to a ventral and ventrolateral spinal lesion (T13). Despite the extensive spinal lesion, severely damaging important descending pathways such as the reticulo- and vestibulospinal tracts, both cats recovered quadrupedal voluntary locomotion. As detailed in a previous paper, the locomotor recovery occurred in three stages defined as early period, when the animal could not walk with its hindlimbs, recovery period, when progressive improvement occurred, and plateau period, when a more stable locomotor performance was observed. At this latter stage, the cats suffered from postural and locomotor deficits, such as poor lateral stability, irregular stepping of the hindlimbs, and inconsistent homolateral fore- and hindlimb coupling. The present study aimed at evaluating the potential of serotoninergic and/or noradrenergic drugs to improve the locomotor abilities in the early and late stages. Both cats were implanted chronically with an intrathecal cannula and electromyographic (EMG) electrodes, which allowed determination, under similar recording conditions, of the locomotor performance pre- and postlesion and comparisons of the effects of different drugs. EMG and kinematic analyses showed that norepinephrine (NE) injected in early and plateau periods improved the regularity of the hindlimb stepping and stabilized the interlimb coupling, permitting to maintain constant locomotion for longer periods of time. Methoxamine, the alpha1-agonist (tested only at the plateau period), had similar effects. In contrast, the alpha2-agonist, clonidine, deteriorated walking. Serotoninergic drugs, such as the neurotransmitter itself, serotonin (5HT), the precursor 5-hydroxytryptophan (5HTP), and the agonist quipazine improved the locomotion by increasing regularity of the hindlimb stepping and by increasing the step cycle duration. In contrast, the 5HT1A agonist 8-hydroxy-dipropylaminotetralin (DPAT) caused foot drag in one of the cats, resulting in frequent stumbling. Injection of combination of methoxamine and quipazine resulted in maintained, regular stepping with smooth movements and good lateral stability. Our results show that the effects of drugs can be integrated to the residual voluntary locomotion and improve some of its postural aspects. However, this work shows clearly that the effects of drugs (such as clonidine) may depend on whether or not the spinal lesion is complete. In a clinical context, this may suggest that different classes of drugs could be used in patients with different types of spinal cord injuries. Possible mechanisms underlying the effect of noradrenergic and serotoninergic drugs on the locomotion after partial spinal lesions are discussed. (+info)
Gating of transmission in climbing fibre paths to cerebellar cortical C1 and C3 zones in the rostral paramedian lobule during locomotion in the cat.
1. Climbing fibre field potentials evoked by low intensity (non-noxious) electrical stimulation of the ipsilateral superficial radial nerve have been recorded in the rostral paramedian lobule (PML) in awake cats. Chronically implanted microwires were used to monitor the responses at eight different C1 and C3 zone sites during quiet rest and during steady walking on a moving belt. The latency and other characteristics of the responses identified them as mediated mainly via the dorsal funiculus-spino-olivocerebellar path (DF-SOCP). 2. At each site, mean size of response (measured as the area under the field, in mV ms) varied systematically during the step cycle without parallel fluctuations in size of the peripheral nerve volley. Largest responses occurred overwhelmingly during the stance phase of the step cycle in the ipsilateral forelimb while smallest responses occurred most frequently during swing. 3. Simultaneous recording from pairs of C1 zone sites located in the anterior lobe (lobule V) and C1 or C3 zone sites in rostral PML revealed markedly different patterns of step-related modulation. 4. The findings shed light on the extent to which the SOCPs projecting to different parts of a given zone can be regarded as functionally uniform and have implications as to their reliability as channels for conveying peripheral signals to the cerebellum during locomotion. (+info)