Design and evaluation of a stand-up motorized prone cart

BACKGROUND/OBJECTIVE: Prone carts are used for mobility by individuals with spinal cord injury in whom seated mobility (wheelchair) is contraindicated due to ischial or sacral pressure ulcers. Currently available prone carts are uncomfortable, subjecting the user to neck and shoulder strain, and make social interaction and performing activities of daily living difficult. A better design of prone carts is needed. In addition, standing devices have shown some medical benefits. The objective was to design and evaluate an improved prone cart that facilitates standing. DESIGN: Engineering development project with user feedback through questionnaire. Users selected by convenience sampling. METHODS: A marketing survey was performed of nurse managers of spinal cord injury units. Then 2 prototype carts were designed and built. These carts are able to tilt up to 45 degrees and have a joystick-controlled motor for propulsion and other design features, including a workspace storage shelf and rearview mirrors. The carts were evaluated by both patients and caregivers at 2 Veteran's Administration hospitals. OUTCOME MEASURES: Questionnaire of subjects, both patients and caregivers, who used the cart. FINDINGS: Both patients and caregivers liked the carts and the ability to assume a nonhorizontal body angle. The major complaint about the cart was that it seemed too long when it came to making turns. CONCLUSION: This prone cart design is an improvement over the standard, flat variety. However, further design changes will be necessary. This study provided valuable information that will be useful in the next-generation prone cart design project.     

A regional model (Northeastern Brazil) of induced mal-nutrition delays ontogeny of reflexes and locomotor activity in rats

Abstract

The aim of this study was to investigate the effects of malnutrition, induced by a regional basic diet (RBD), on motor development. RBD is a 7.87%-protein diet based on aliments typical of Northeastern Brazil, elaborated after nutritional investigation by Teodosio et al. (1979). Female rats were treated with RBD during lactation. The reflex ontogenesis and the development of locomotor activity in their offspring were assessed. Malnourished (MN) rats showed a delay in reflex maturation and in locomotor activity evolution. The decreased locomotor activity may be related to the reduced movement experiences induced by the delay in the reflex maturation. Occurring during the critical period of brain development, this fact could jeopardize all the steps in future locomotion evolution. The present results confirm deleterious effects of RDB-induced malnutrition on the somatic development and maturation of the nervous system (NS).     

The use of state-dependent modulation of spinal reflexes as a tool to investigate the organization of spinal interneurons

This review examines the proposition that state-dependent modulation of transmission through spinal reflex pathways can be used as an investigative tool to reveal details about the organization of spinal interneurons into functional circuits. The first set of examples includes the use of spinal and supraspinal lesions, as well as the administration of the drug l-dihydroxyphenylalanine (l-DOPA), to produce different, relatively stable ”states” of the central nervous system (CNS), revealing previously unsuspected spinal pathways activated by the flexor reflex afferents (FRA). The second set of examples deals with the use of fictive locomotion and scratching to investigate the organization of oligosynaptic excitatory and inhibitory reflex pathways from cutaneous and muscle afferents. As in the first set of examples, several hitherto unknown reflex pathways have been found only during the flexion or extension phases of rhythmic locomotion, which are regarded as different CNS states. Differences in the patterns of control can be used to infer the existence of distinct sets of reflex pathway interneurons that have remarkably precise input/output relations. Received: 4 February 1999 / Accepted: 19 April 1999     

Forelimb locomotor assessment scale (FLAS): Novel assessment of forelimb dysfunction after cervical spinal cord injury

We describe here a novel forelimb locomotor assessment scale (FLAS) that assesses forelimb use during locomotion in rats injured at the cervical level. A quantitative scale was developed that measures movements of shoulder, elbow, and wrist joints, forepaw position and digit placement, forelimb–hindlimb coordination, compensatory behaviors adopted while walking, and balance. Female Sprague-Dawley rats received graded cervical contusions ranging from 200 to 230 (“mild,” n = 11) and 250–290 kdyn (“moderate,” n = 13) between C5 and C8. Rats were videotaped post-injury as they walked along an alley to determine deficits and recovery of forelimb function. Recovery of shoulder and elbow joint movement occurred rapidly (within 1–7 days post-injury), whereas recovery of wrist joint movement was slower and more variable. Most rats in all groups displayed persistent deficits in forepaw and digit movement, but developed compensatory behaviors to allow functional forward locomotion within 1–2 weeks post-injury. Recovery of forelimb function as measured by the FLAS reached a plateau by 3 weeks post-injury in all groups. Rats with mild contusions displayed greater locomotor recovery than rats with moderate contusions, but exhibited persistent deficits compared to sham controls. Reliability was tested by having seven raters (three internal, four external) from different laboratories, independently and blindly score videos of all rats. The multivariate correlation between all raters, all animals, and all time points ranged from r² = 0.88–0.96 (p < 0.0001), indicating a high inter-rater reliability. Thus, the FLAS is a simple, inexpensive, sensitive, and reliable measure of forelimb function during locomotion following cervical SCI.     

Potentiation of amphetamine-induced locomotor activity following NMDA-induced retrohippocampal neuronal loss in the rat

The present experiment assessed the locomotor response to a low dose (1 mg/kg) of systemic gemd-amphetamine in rats with cytotoxic lesions of the retrohippocampus (entorhinal and extra-subicular cortices), compared with vehicle-operated shams and unoperated controls. Under spontaneous and saline conditions, both the sham and the lesioned animals were more active than unoperated controls, and they did not differ from each other. Systemic gemd-amphetamine produced increased locomotion in all groups, but this effect was potentiated in animals with retrohippocampal lesions; two control groups did not differ from each other in their response to the drug. The present results are consistent with the suggestion that cell loss within the retrohippocampal region could affect the functional response of nucleus accumbens to amphetamine. The results are discussed in terms of the interaction between the retrohippocampus and nucleus accumbens in the control of mesolimbic dopamine release and the possible implications for schizophrenia.     

Pharmacologically evoked fictive motor patterns in the acutely spinalized marmoset monkey (Callithrix jacchus)

The existence of a spinal network capable of generating rhythmic alternating activity resembling locomotion still has not been firmly established in primates, including man, although evidence for one is accumulating. The present study investigated whether it is possible to activate such a network by administration of a variety of pharmacological agents to acutely spinalized marmoset monkeys (Callithrix jacchus) in the absence of phasic afferent input to the spinal cord. Fourteen marmoset monkeys were decerebrated, spinalized, and paralyzed. The nerves supplying both hindlimbs were cut and recorded from. In 5 monkeys the effect of electrical stimulation of the brainstem was investigated before spinalization. In 3 of these monkeys, rhythmic activity alternating between extensors and flexor nerves was seen. In the 2 other monkeys only synchronized activity was elicited. In acutely spinalized monkeys, administration of l-3,4-dihydroxyphenylalanine (l-dopa; 3–4 h after treatment with nialamide) failed to evoke any rhythmic alternating activity. In contrast, administration of clonidine elicited alternating activity in all of 8 monkeys tested. In 4 of these monkeys, the activity was restricted to alternation between ipsilateral and contralateral flexor nerves, whereas alternating activity between ipsilateral flexors and extensors was also seen in the other 4 monkeys. Administration of excitatory amino acids (NMDA or NMA) also elicited rhythmic alternating activity in 7 of 10 spinalized monkeys. In 4, rhythmic alternating activity was seen between extensors and flexors on one limb as well as between ipsilateral and contralateral flexors. In 3 monkeys NMDA/NMA produced alternation between extensors and flexors of one limb without alternation between the ipsilateral and contralateral sides. Administration of noradrenaline failed to elicit any rhythmic activity, but rather completely depressed already existing activity. Administration of serotonin (5-HT) was ineffective in facilitating alternating activity in 6 of 8 monkeys and was facilitatory to rhythmic activity in the other 2. We suggest that these data provide further evidence of a network capable of eliciting rhythmic alternating activity resembling locomotion in the primate spinal cord. The network, however, seems to be more difficult to activate pharmacologically in those conditions than in other mammals. This may especially be the case in higher primates, including man. Received: 6 November 1997 / Accepted: 21 April 1998     

Dose-dependent effects of the D3-preferring agonist 7-OH-DPAT on motor behaviors and place conditioning

Dose-dependent effects of 7-OH-DPAT on several behaviors, including place preference, were assessed. Three 2-day conditioning trials were conducted. On 1 day, animals received an injection of one of eight doses of 7-OH-DPAT (0–5 mg/kg) and were placed into a distinct compartment for 40 min. On the other day, animals received an injection of saline and were placed into a different compartment for 40 min. Locomotion, sniffing, and yawning were measured following the first and last injection of 7-OH-DPAT. Place conditioning was assessed on the day following the last trial. 7-OH-DPAT produced a U-shaped dose-dependent change in locomotion and sniffing, and an inverted U-shaped dose-dependent change in yawning. Additionally, repeated administration of 0.1 mg/kg sensitized yawning, whereas 5 mg/kg sensitized locomotion. None of the doses of 7-OH-DPAT produced conditioned place preference, however, there was a trend for conditioned place aversion at 0.03 mg/kg. By contrast, LiCl (127 mg/kg) produced conditioned place aversion and amphetamine (1 mg/kg) produced conditioned place preference using the same conditioning parameters. A subsequent experiment in which the number of animals and conditioning trials were increased demonstrated that the 0.03 mg/kg dose of 7-OH-DPAT produced conditioned place aversion. 7-OH-DPAT has a higher affinity for D₃ receptors relative to D₂ receptors. Therefore, it is suggested that intermediate doses (0.01–0.1 mg/kg) that increase yawning, and decrease locomotion and sniffing, may preferentially occupy D₃ receptors. Furthermore, the results suggest that these putative D₃-preferring doses have weak aversive effects.     

Cross-tolerance studies of serotonin receptors involved in behavioral effects of LSD in rats

Like hallucinogenic 5-HT₂ agonists, LSD (d-lysergic acid diethylamide) produces characteristic decreases in locomotor activity and investigatory behaviors of rats tested in a novel environment. Because LSD is an agonist at both 5-HT_1A and 5-HT₂ receptors, however, the respective influences of these different receptors in the behavioral effects of LSD remain unclear. In particular, the paucity of selective 5-HT_1A antagonists has made it difficult to assess the specific contribution of 5-HT_1A receptors to the effects of LSD. An alternative approach to the delineation of receptor-specific effects is the use of cross-tolerance regimens. In the present studies, rats were pretreated with saline, 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT) (0.5 mg/kg SC), 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (1.0 mg/kg SC), or LSD (60 µg/kg SC), every 12 h for 5 or 8 days. Thirty-six hours later, rats were tested in a behavioral pattern monitor 10 min after injection of saline, 0.5 mg/kg 8-OH-DPAT, 1.0 mg/kg DOI, or 60 µg/kg LSD. As expected, tolerance to the decreases in locomotor activity produced by acute administrations of 8-OH-DPAT, DOI, or LSD occurred when rats were pretreated chronically with 8-OH-DPAT, DOI, or LSD, respectively. Furthermore, pretreatment with either 8-OH-DPAT or DOI produced cross-tolerance to LSD. These results support the hypothesis that the effects of LSD in this model reflect a combination of 5-HT_1A and 5-HT₂ effects and support the view that there is an interaction between 5-HT_1A and 5-HT₂ receptors.     

Psychomotor stimulant effects ofd-amphetamine,MDMA and PCP: aggressive and schedule-controlled behavior in mice

The objective of the present experiments was to characterize psychomotor stimulant effects ofd-amphetamine, methylenedioxymethamphetamine (MDMA) and phencyclidine (PCP) on conditioned performance and on aggressive behavior in mice. In a novel protocol with alternating periods of schedule-controlled responding and aggressive behavior toward an intruder it was possible to assess a range of species-specific agonistic acts, postures, and motor activities as well as response rates and patterns engendered by a multiple Fixed Interval (FI) and Fixed Ratio (FR) schedule within the same animal. Initially, it was confirmed thatd-amphetamine and, less reliably, MDMA and PCP, increased FI, but not FR responding in mice. In the next experiment, mice confronted an intruder at the midpoint of the 1-h daily session; following the display of aggressive behavior, the rate of FI responding showed an amphetamine-like increase, whereas only a transient change occurred after non-aggressive encounters. Thirdly, using this new protocol, PCP,d-amphetamine and MDMA altered FI and FR responding in a way that was closely similar to the first experiment. Low PCP andd-amphetamine doses increased aggressive behavior erratically in certain individuals, but not reliably for the group. MDMA dose-dependently decreased aggressive behavior, and all drugs disrupted aggressive behavior at higher doses. The characteristic increases in walking and decreases in rearing after higher doses of PCP andd-amphetamine were greatly attenuated when the intruder was present. The rate-increasing effects ofd-amphetamine, MDMA and PCP occurred in the early portion of the fixed interval when the control rate is typically low; by contrast, low attack rates during the later portion of the confrontation with the intruder remained unaffected. The dose-dependent quantitatively and qualitatively differentiated profile of effects on schedule-controlled responding, motor activity and aggressive behavior suggest that the common properties ofd-amphetamine, MDMA and PCP pertain mostly to the disruption of organized behavior patterns and activation of repetitive motor routines at high doses, but point to different mechanisms for modulating aggressive behavior and conditioned performance at lower doses.     

Simple artificial neural network models can generate basic muscle activity patterns for human locomotion at different speeds

 A neural network model has been developed to represent the shaping function of a central pattern generator (CPG) for human locomotion. The model was based on cadence and electromyographic data obtained from a single human subject who walked on a treadmill. The only input to the model was the fundamental timing of the gait cycle (stride rate) in the form of sine and cosine waveforms whose period was equal to the stride duration. These simple signals were then shaped into the respective muscle activation patterns of eight muscles of the lower limb and trunk. A network with a relatively small number of hidden units trained with back-propagation was able to produce an excellent representation of both the amplitude and timing characteristics of the EMGs over a range of walking speeds. The results are further discussed with respect to the dependence of some muscles upon sensory feedback and other inputs not explicitly presented to the model. Received: 9 February 1998 / Accepted: 13 August 1998