Biomedical subjects

T Drew

Publications and source records attributed to T Drew.

At least 19 recordsLinked to original sources

PubMed1998

Total radiated power, infrared output, and heat generation by cold light sources at the distal end of endoscopes and fiber optic bundle of light cables.

BACKGROUND: Skin burns and ignition of drapes have been reported with the use of cold light sources. The aim of the study was to document the temperature generated by cold light sources and to correlate this with the total radiated power and infrared output. METHODS: The temperature, total radiated power, and infrared output were measured as a function of time at the end of the endoscope (which is inserted into the operative field) and the end of the fiber optic bundle of the light cable (which connects the cable to the light port of the endoscope) using halogen and xenon light sources. RESULTS: The highest temperature recorded at the end of the endoscope was 95 degrees C. The temperature measured at the optical fiber location of the endoscope was higher than at its lens surface (p < 0.0001). At the end of the fiber optic bundle of light cables, the temperature reached 225 degrees C within 15 s. The temperature recorded at the optical fiber location of all endoscopes and light cables studied rose significantly over a period of 10 min to reach its maximum (p <0.0001) and then leveled off for the duration of the study (30 min). The infrared output accounted only for 10% of the total radiated power. CONCLUSIONS: High temperatures are reached by 10 min at the end of fiber optic bundle of light cables and endoscopes with both halogen and xenon light sources. This heat generation is largely due to the radiated power in the visible light spectrum.

Cold Temperature↗

PubMed1998

Computer-controlled endoscopic performance assessment system.

We have devised an advanced computer-controlled system (ADEPT) for the objective evaluation of endoscopic task performance. The system's hardware consists of a dual gimbal mechanism that accepts a variety of 5.0-mm standard endoscopic instruments for manipulation in a precisely mapped and enclosed work space. The target object consists of a sprung base plate incorporating various tasks. It is covered by a sprung perforated transparent top plate that has to be moved and held in the correct position by the operator to gain access to the various tasks. Standard video endoscope equipment provides the visual interface between the operator and the target-instrument field. Different target modules can be used, and the level of task difficulty can be adjusted by varying the manipulation, elevation, and azimuth angles. The system's software is designed to (a) prompt the surgeon with the information necessary to perform the task, (b) collect and collate data on performance during execution of specified tasks, and (c) save the data for future analysis. The system was alpha and beta tested to ensure that all functions operated correctly.

Endoscopy↗

PubMed1998

Corticoreticular pathways in the cat. I. Projection patterns and collaterization.

This paper summarizes and compares the projection patterns and the receptive fields of cortical neurons in areas 4 and 6 that project to the pontomedullary reticular formation (PMRF). A total of 326 neurons were recorded in area 4 and 129 in area 6 in four awake, unrestrained cats that were chronically implanted with arrays of electrodes in the PMRF and the pyramidal tract (PT). In area 4, 47% of the neurons projected to the caudal PT but not to the PMRF (PTNs); 19% were activated only from the PMRF [corticoreticular neurons (CRNs)], whereas 27% were activated from both the PT and the PMRF (PTN/CRNs). More PTN/CRNs conducted at velocities >20 m/s (82%) than did CRNs (23%). In area 6, only 19% of the neurons were identified as PTNs, 12% were PTN/CRNs and 31% were CRNs; a further 38% could not be activated from either structure. Collateral branches within the PMRF conducted at maximum velocities of 20 m/s (average = 6.5 m/s). No significant differences in the conduction velocities of the collateral branches were found either between fast and slow PTNs or between area 4 and area 6 neurons. A large proportion of neurons in area 4 (85/173, 49%) were activated by passive manipulation of the more distal, contralateral forelimb, with approximately equal numbers being classed as PTNs, PTN/CRNs and CRNs. Most neurons in area 6 for which a receptive field could be found were excited by lightly touching or tapping the face and neck; a receptive field could not be determined for 39% of the area 6 neurons compared with only 5% of those in area 4. Finally, there was evidence that neurons in quite widespread areas of the pericruciate cortex, including both areas 4 and 6 projected onto similar, restricted regions of the PMRF. The fact that the cortical projection from area 4 to the PMRF includes a high percentage of fast PTNs with a receptive field on the distal forelimb is consistent with the view that this projection may serve to integrate movement and the dynamic postural adjustments that accompany them. The fact that the cortical projection from area 6 to the PMRF is primarily from slow PTNs with receptive fields on the face, neck and back is consistent with a role for this cortical area in adjusting the general posture of the animal on which movements are superimposed.

Animals↗

PubMed1998

Corticoreticular pathways in the cat. II. Discharge activity of neurons in area 4 during voluntary gait modifications.

We propose that the descending command from area 4 that is responsible, in part, for the change in limb trajectory required to step over an obstacle in one's path also plays a role in triggering the anticipatory postural modifications that accompany this movement. To test this hypothesis, we recorded the discharge characteristics of identified classes of corticofugal neurons in area 4 of the cat. Neurons were identified either as: pryamidal tract neurons (PTNs) if their axon projected to the caudal pyramidal tract (PT) but not to the pontomedullary reticular formation (PMRF); as corticoreticular neurons (CRNs) if their axon projected to the PMRF but not to the PT; and as PTN/CRNs if their axon projected to both structures. Altogether, the discharge properties of 212 corticofugal neurons (109 PTNs, 66 PTN/CRNs, and 37 CRNs) within area 4 were recorded during voluntary gait modifications. Neurons in all three classes showed increases in their discharge frequency during locomotion and included groups that increased their discharge either during the swing phase of the modified step, during the subsequent stance phase, or in the stance phase of the cycle preceding the step over the obstacle. A slightly higher percentage of CRNs (39%) discharged in the stance phase prior to the gait modification than did the PTNs or PTN/CRNs (20% and 17% respectively). In 37 electrode penetrations, we were able to record clusters of 3 or more neurons within 500 micro(m) of each other. In most cases, PTN/CRNs recorded in close proximity to PTNs had similar receptive fields and discharged in a similar, but not identical, manner during the gait modifications. Compared with adjacent PTNs, CRNs normally showed a more variable pattern of activity and frequently discharged earlier in the step cycle than did the PTNs or PTN/CRNs. We interpret the results as providing support for the original hypothesis. We suggest that the collateral branches to the PMRF from corticofugal neurons with axons that continue at least as far as the caudal PT provide a signal that could be used to trigger dynamic postural responses that are appropriately organized and scaled for the movements that are being undertaken. We suggest that the more variable and earlier discharge activity observed in CRNs might be used to modify the postural support on which the movements and the dynamic postural adjustments are superimposed.

Animals↗

PubMed1997

Organization of the projections from the pericruciate cortex to the pontomedullary brainstem of the cat: a study using the anterograde tracer Phaseolus vulgaris-leucoagglutinin.

The anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) was used to study the distribution and density of the projections that originate from four identified subdivisions of the pericruciate cortex (namely, the forelimb and hind limb representations of area 4, area 6a beta, and area 6a gamma) and that terminate in the pontomedullary brainstem in the cat. Injections of PHA-L in all areas of the pericruciate cortex labelled numerous fibers and their terminal swellings in the brainstem. The major target regions of all four cortical areas were the pontine nuclei and the pontomedullary reticular formation (PMRF). Injections into both the forelimb and hind limb representations of area 4 and into area 6a beta resulted in a dense pattern of terminal labelling in restricted regions of the medial and lateral parts of the ipsilateral pontine nuclei. The labelling following the area 6a beta injection was spatially distinct from that seen following the area 4 injections. Injections into the forelimb representation of area 4 as well as into area 6a beta and 6a gamma resulted in the labelling of numerous terminal swellings bilaterally in the PMRF; in contrast, there were few labelled terminal swellings in the PMRF following injections into the hind limb representation of area 4. Terminal swellings on individual corticoreticular fibers were far less densely aggregated than those in the pontine nuclei. The dense pattern of innervation to restricted regions of the pontine nuclei supports previous suggestions that the corticopontine projections retain a high degree of topographical specificity that could be used in the control of discrete voluntary movements. In contrast, the more diffuse pattern of the projections to the PMRF may facilitate the selection and activation of the complex postural patterns that accompany voluntary movement.

Animals↗

PubMed1997

Organization of the projections from the pericruciate cortex to the pontomedullary reticular formation of the cat: a quantitative retrograde tracing study.

Dextran-amines were used as retrograde tracers to investigate the organization of cortical projections to different cytoarchitectonic regions of the pontomedullary reticular formation of the cat. Injections into the nucleus reticularis pontis oralis resulted in labelling of neurones in the proreus cortex and area 6a beta of the premotor cortex, with little labelling in the motor cortex (area 4). This labelling was predominantly ipsilateral to the injection site. In contrast, injections into the nucleus reticularis pontis caudalis (NRPc), nucleus reticularis gigantocellularis (NRGc), and nucleus reticularis magnocellularis (NRMc) resulted in bilateral labelling--primarily in areas 6a beta, 6a gamma, and in the rostromedial region of area 4--with little labelling in the proreus cortex. In general, the cortical projections to the caudal NRGc and the NRMc were larger than those to the NRPc. More than 25% of the total projections to each of the latter three reticular regions arose from the medial part of area 4. Labelling in the hindlimb regions of area 4 was largest following the NRMc injections and smallest after injections in the NRPc. The projections to the NRPc originated from more medial parts of areas 4 and 6 than did the projections to the caudal region of the NRGc. These results suggest that areas 4 and 6 may be able to differentially activate different regions of the pontomedullary reticular formation depending on the movement that is made and perhaps also on the context of that movement.

Animals↗

PubMed1997

Establishment of serial persistent infections with bovine viral diarrhoea virus in cattle and sheep and changes in epitope expression related to host species.

A pestivirus was transmitted by contact from a persistently infected (P.I.) bullock to pregnant sheep. This resulted in the birth of P.I. lambs, one of which in turn was able to transmit virus by contact to pregnant cattle. Two of these animals gave birth to P.I. calves, from one of which the virus was again transmitted by contact with pregnant sheep, leading to another generation of P.I. lambs. The expression of one or more epitopes on the E2 glycoprotein of the viruses isolated from this series of alternate cattle-sheep transmissions appeared to depend on the host species. Thus, several monoclonal antibodies which bound strongly to, and neutralised, viruses isolated from the bovine hosts, failed to bind or neutralise in the case of sheep isolates. The viral consensus sequences of the E2 gene as well as parts of the 5' untranslated region and of the Npro and capsid genes were compared between the different isolates. This revealed a high degree of genetic stability. However, a single codon change at amino acid position 9 of the E2 gene correlated with and was able to cause the loss of particular epitopes.

Animals↗

PubMed1997

Psychomotor skills for endoscopic manipulations: differing abilities between right and left-handed individuals.

OBJECTIVE: The objective of this study was to compare the psychomotor aptitudes relevant to endoscopic manipulations between right-handed and left-handed subjects. SUMMARY BACKGROUND DATA: There has been little research on the psychomotor performance in relation to minimal access surgery and there are no psychomotor tests to evaluate aspects of psychomotor abilities relevant to endoscopic manipulations. METHODS: A microprocessor-controlled psychomotor tester was developed for objective evaluation of endoscopic performance. The task involved negotiating ten target holes with a probe under videoscopic imaging. Subjects consisted of two groups of 10 medical students: right- and left-handed. After a prestudy familiarization session, each subject performed two test runs with one hand, followed by two runs with the other hand. These test runs were repeated 1 week later. The outcome measures were the total execution time, force on backplate, angular deviations, error rate, and first-time accuracy. RESULTS: A significant difference in the error rate and first time accuracy was observed between subjects (p < 0.001 and p < 0.001, respectively) and between the dominant and nondominant hands (p < 0.001 and p < 0.025, respectively), with no significant change with practice. Right-handed subjects performed better with either hand in terms of error rate (p < 0.001) and first time accuracy (p < 0.001). Practice improved the execution time (p < 0.001) and the degree of angular deviations (p < 0.02). CONCLUSIONS: Right-handed subjects perform less errors and exhibit better first time accuracy. The parameters that improve with practice reflect the positive effect of training, whereas others, such as errors rate and first time accuracy which do not, reflect innate abilities.

Endoscopy↗

PubMed1996

Responses of medullary reticulospinal neurones to stimulation of cutaneous limb nerves during locomotion in intact cats.

The present study was designed to determine whether the transmission of cutaneous afferent information from the limbs to the medullary reticular formation is phasically modulated during locomotion. Experiments were carried out in three chronically prepared, intact cats in which nerve cuff electrodes were placed, bilaterally, on the superficial radial and the superficial peroneal nerves. Thirty-seven reticulospinal neurones (RSNs) were identified by stimulation of their axons in the lumbar spinal cord (L2); 29 of 37 of these were recorded with the cat at rest, 28 of 37 during locomotion and 20 of 37 both at rest and during locomotion. Low-threshold stimulation of the cutaneous nerves evoked excitatory responses in the majority of RSNs both at rest and during locomotion. In the 28 of 37 RSNs recorded during locomotion, it was possible to record the evoked response to stimulation of all four limb nerves, giving a total of 184 tested cases [RSNs tested x number of nerves stimulated x phase of stimulation (swing or stance)]. The responses of most RSNs to cutaneous stimulation were modulated in a phase-dependent manner during locomotion. The maximal responses in most, but not all, cases were obtained during the swing phase of the limb that was stimulated and were largely independent of the discharge pattern of the cell. We interpret this result as indicating that the efficacy of transmission of the afferent information is determined more by the excitability of the spinal relay neurones than by the level of excitability of the RSNs in the brainstem. It is suggested that the base discharge pattern of RSNs might be largely determined by their central afferent input, while peripheral afferent inputs would primarily serve to modify the RSN discharge pattern in response to perturbations.

Afferent Pathways↗

PubMed1996

A microprocessor-controlled psychomotor tester for minimal access surgery.

BACKGROUND: There is little reported information on psychomotor performance in relation to minimal access surgery (MAS). METHODS: A microprocessor-controlled endoscopic psychomotor tester (the Dundee Endoscopic Psychomotor Tester-DEPT) has been developed to evaluate psychomotor aspects of MAS. Experiments were conducted on 20 medical undergraduates to evaluate accuracy and reliability of the tester. RESULTS: The study demonstrated a significant difference between subjects (p < 0.01). It also identified three individuals who enacted 16, 22, and 40 errors while the majority (85%) sustained less errors with a median of 4.5. CONCLUSIONS: DEPT provides a standard, reproducible, objective real-time scoring system. It identifies individuals who cannot adjust to endoscopic viewing and therefore manipulate from endoscopic images.

Clinical Competence↗

PubMed1996

A numerical model of an intensive care ventilator-humidifier system.

Current intensive care ventilator-humidifier systems neither monitor nor adequately control inspired gas humidity. Problems of low delivered humidity and condensation within ventilator circuitry are commonly encountered. To help to address these problems, a numerical model of a complete ventilator-humidifier-patient intensive care system has been developed. The model, based on a finite difference technique, can predict pressures, flow-rates, temperatures and relative humidities at discrete points throughout the system. A comparison of numerical predictions and measurements in a real system is reported. A strong qualitative agreement is demonstrated in all cases studied, and a good quantitative agreement is obtained in most cases. It is concluded that such models could be used to assess methods of controlling ventilator-humidifier systems to prevent the occurrence of condensation. Similar models could be developed for other medical gas delivery systems.

Biomedical Engineering↗

PubMed1996

A comparison of treadmill locomotion in adult cats before and after spinal transection.

1. The aim of this study was to document the kinematics and the electromyographic activity recorded from several muscles during treadmill locomotion in the same cat (N = 4), before and after spinalization by using a chronic implantation method. Because identical experimental and control conditions were used, it was possible to establish similarities and differences in the timing and amplitude of the muscular activity and kinematics under the intact and spinal conditions in the same animal. The data presented in this paper were collected when the cats had fully recuperated a stable locomotor pattern, walking at a constant speed of approximately 0.4 m/s. 2. The adult spinal cats retained many of the general locomotor features and electromyographic (EMG) characteristics seen before transection. However, there were also important differences. 3. There was a reduction in the step length that was principally due to the forward placement of the paw at the onset of the stance. Similarly, there was a decrease in the step cycle duration which was attributed to a reduction of both the stance and swing phases. 4. The overall angular excursions of the hip, knee, and ankle were generally similar, although joints were sometimes more flexed at all phases of the step cycle. In contrast, the overall excursions of the metatarsophalangeal joints was much greater in all four cats after spinalization due to a paw drag during the initial portion of the swing phase that exaggerated the plantarflexion. 5. There was an increase in the EMG amplitude of the flexor muscles at two of three joints (i.e., hip, knee, and ankle) in each cat after spinalization. The change in the EMG amplitude of the extensors did not appear to be as consistent as that observed in the flexor muscles. When looking at each cat individually, the postspinalization extensor activity decreased at two of three joints in two cats, whereas the opposite was true for the other two cats. 6. There was a delay in the onset of the knee flexor (semitendinosus) activity while the ankle dorsiflexor (tibialis anterior) activity started earlier with respect to the beginning of the swing phase. The onset of hip flexors was somewhat more variable. This change in the timing of flexor activity was most probably responsible for the paw drag at the onset of the swing phase. 7. The present results reveal that despite the few differences, the spinal cord and the hindlimbs afferents are capable of generating very good locomotor patterns with almost normal kinematics and EMG characteristics.

Animals↗

PubMed1996

Effects of bilateral lesions of the dorsolateral funiculi and dorsal columns at the level of the low thoracic spinal cord on the control of locomotion in the adult cat. I. Treadmill walking.

1. A quantitative and longitudinal analysis of locomotion was made after bilateral lesions of the dorsolateral funiculi (DLF) and/or the dorsal columns (DC) in the lower thoracic cord (T12 or T13) in five adult cats. All cats were chronically implanted several weeks before the spinal cord lesion to permit the recording of electromyographic (EMG) activity from selected flexor and extensor muscles of the fore- and hindlimbs of each side. This allowed each cat to act as its own control when comparing the pattern and amplitude of EMG activity before and after the lesion. All experiments were also videotaped to allow an analysis of the kinematic changes before and after the lesions. Kinematic data were only analyzed for the side of the cat facing the camera; for all cats this was the left side. 2. After recovery periods of 2-5 mo, wheat-germ-agglutinated horseradish peroxidase (WGA-HRP) was injected caudal to the lesion site (normally at L2). The extent of the lesion was verified both histologically and by evaluating the number of HRP-labeled neurons in different supraspinal structures. These analyses showed that the cortico- and rubrospinal tracts (CST and RST, respectively) were completely interrupted, bilaterally, in two of five of the cats; in one of these cats the DCs were also interrupted. In the other three cats there was more variable damage, and the CST and RST were only completely interrupted on the right side of one of these animals. The DCs were completely sectioned in two of these cats. 3. During the 1st wk subsequent to the lesion, most cats had difficulty in supporting their weight and in walking. However, within 10 days all were able to walk, unaided, for extended periods on the treadmill at speeds of at least 0.35 m/s. In the two cats with the complete, bilateral DLF lesions, the animals dragged both their left and right hindpaws along the treadmill belt during the swing phase of the step cycle (paw drag) throughout the testing period of 3-5 mo. In the other three cats, paw drag in either hindlimb was only seen in the 1st 2-3 wk after the lesions, with the exception of the cat with the complete lesion of the DLF on the right side, which showed sustained paw drag in the right hindlimb throughout the testing period. 4. Significant increases in step cycle and swing duration following the lesion were observed only in the two cats with the largest lesions. In all five cats, statistical comparisons of the slopes from a linear regression analysis showed that the relationship between swing and step cycle duration was unchanged by the lesions. 5. Joint angles in the left hindlimb of the two cats with the largest lesions were generally smaller (more flexed) than in the prelesion controls. This was particularly true for the knee and ankle joints. The other three cats showed changed joint angle values for the hip, knee, and ankle only in the 1st 2-3 wk after the lesions. All of the cats, except the one with the least damage to the left DLF, exhibited increased joint excursions at the metatarsophalangeal (MTP) joint of the left limb throughout the recovery period. 6. There were sustained changes in the coupling between the hip and the knee of the left limb, together with smaller changes in the coupling of the knee and ankle in the two cats with the complete lesions of the DLF. In contrast to the prelesion controls, flexion at the ankle occurred before swing onset in these same two cats. The changes in the coordination between the hip and the knee were associated with changes in the temporal coupling between the hip flexor, sartorius (Srt), and the knee flexor, semitendinosus (St). Despite some improvement, the coupling between these two muscles never fully recovered to the prelesion values. Similar, but smaller, changes in the delay between Srt and St were also seen in two of the other three cats. (ABSTRACT TRUNCATED)

Animals↗

PubMed1996

Locomotor capacities after complete and partial lesions of the spinal cord.

This paper first reviews some of the observations made on the locomotor capabilities of several animal species with a special emphasis on cats and including primates and man after complete spinal lesions. We show that animals can perform well-coordinated walking movements of the hindlimbs when they are placed on a treadmill belt and this locomotion is also adaptable to speed and perturbations. Cats with partial spinal lesions of the ventral and ventrolateral parts of the cord can perform voluntary quadrupedal locomotion overground or on the treadmill albeit with deficits in weight support and interlimb coordination. We also show that some drugs such as clonidine (an alpha-2 noradrenergic agonist) can be used to trigger locomotion in early-spinal cats and discuss the effects of various neurotransmitter systems on the expression of the locomotor pattern in both complete and partial spinal cats. It is concluded that a pharmacological approach could be used, in combination with other approaches, such as locomotor training and functional electrical stimulation, to improve locomotor functions after spinal cord injuries in humans.

Animals↗

PubMed1996

Role of the motor cortex in the control of visually triggered gait modifications.

One important aspect of locomotor control is the ability of an animal to make anticipatory gait modifications to avoid obstacles, by stepping either around them or over them. This paper reviews some of the evidence that suggests that the motor cortex is one of the principal structures involved in the control of such anticipatory gait modifications in cats, in particular when they are triggered by a visual signal. Evidence for this statement is provided both from experiments in which the motor cortex has been lesioned or inactivated and from studies in which the activity of motor cortical neurones has been recorded during locomotor tasks in which visual information is required to ensure the correct positioning of the paw or an appropriate modification of the limb trajectory. Inactivation of small regions of the motor cortex with the GABA agonist muscimol results in changes in the limb trajectory so that cats hit an obstacle instead of stepping over it as they do normally. A similar disruption of the hindlimb trajectory is seen following lesions of the spinal cord at T13 that interrupt the corticospinal tract. The results from cell recording studies are complementary in that they show that the activity of many identified pyramidal tract neurones increases when the cat is required to modify the forelimb or hindlimb trajectory to step over obstacles. We suggest that the major function of this increased discharge frequency is to regulate the amplitude, duration, and temporal pattern of muscle activity during the gait modification to ensure an appropriate modification of limb trajectory. We further suggest that different groups of pyramidal tract neurones are involved in regulating the activity of groups of synergistic muscles active at different times in the gait modification. For example, some groups of pyramidal tract neurones would be involved in ensuring the appropriate and sequential activation of the muscle groups involved in the initial flexion of the elbow, while others would be active prior to the repositioning of the paw on the support surface. We discuss the possibility that the motor cortical activity seen during locomotion is the sum result of a feedforward signal, which provides visuospatial information about the environment, and feedback activity, which signals, in part, the state of the interneuronal pattern generating networks in the spinal cord. The way in which the resulting descending command may interact with the basic locomotor rhythm to produce the gait modifications is discussed.

Animals↗

PubMed1995

A kinematic and kinetic analysis of locomotion during voluntary gait modification in the cat.

As part of a study to characterize the postural reactions that occur during voluntary gait modification, we examined the kinematic, electromyographic (EMG), and kinetic responses that occurred when cats stepped over an obstacle placed in their path. Analyses of the kinematics as each of the forelimbs stepped over the obstacle showed that changes in joint angles were most pronounced at the elbow of the first (lead) limb, and at the shoulder of the second (trailing) limb. In the hindlimbs, there was a pronounced change in the knee joint angle in both the leading and trailing limbs. Examination of the horizontal and vertical velocities of the tip of the forepaw suggests that the movements can be divided into two phases: one in which the limb is rapidly lifted above and over the obstacle, and a slower one during which the limb is carefully repositioned on the floor. On the basis of the velocity profiles, we suggest that the repositioning of the paw on the support surface is more critically controlled for the forelimb than for the hindlimb. Analysis of the changes in the ground reaction forces in the supporting limbs during these gait modifications showed that there were two major increases in vertical reaction force. One of these occurred as the two forelimbs were straddling the obstacle, the other when the two hindlimbs were straddling it. There was also a net increase in the anteroposterior force that resulted in a small increase in propulsion as the cat stepped over the obstacle. Each change in the vertical ground reaction force was paralleled by a similar change in the amplitude of the EMG recorded from the respective extensor muscles. An analysis of the vertical displacement of the scapula and of the pelvis showed that there was a slight increase in the height of the scapula in the support limb just prior to and during the swing phase of the trailing forelimb, and a more pronounced and progressive change in the height of the pelvis prior to and during the passage of both hindlimbs over the obstacle. We suggest that the increases in vertical ground reaction force raise the height of the body sufficiently to allow, respectively, passage of the trail forelimb and each of the hindlimbs over the obstacle. The results are discussed with respect to both the biomechanical changes underlying these gait modifications and the neuronal mechanisms implicated in their control.

Animals↗

PubMed1994

Microstimulation of the medullary reticular formation during fictive locomotion.

1. The present study was designed to determine the effects of microstimulation of the medullary reticular formation (MRF) on the locomotor activity of the cat in the absence of phasic afferent feedback from the limbs. To this end, both short (33 ms) and long (200 ms) trains of stimuli (trains of 0.2-ms pulses at 330 Hz, 35 microA) were applied at 43 loci in the MRF (P:6-12 mm; L:0.5-1.5 mm), and in 3 loci in the medial longitudinal fasciculus (P7.5, L < 0.5 mm) during fictive locomotion in the decerebrate and paralyzed cat. The locomotor pattern was monitored by recording the activity of representative flexor and extensor muscle nerves from each of the four limbs. 2. Short trains of stimuli evoked transient excitatory and/or inhibitory responses in extensor and flexor nerves of each limb that were incorporated into the locomotor pattern. In the majority of sites, excitatory responses were obtained in the motor nerves to both flexor and extensor muscles of the fore- and hindlimbs. The exception to this rule was the ipsilateral triceps, in which the predominant response was inhibitory. The amplitude of these responses was dependent on the time of the locomotor cycle at which the stimulus was delivered, and it was always maximum during the period of activity of the respective nerve. 3. The shortest latency response in the nerves to different muscles of the forelimb averaged between 5.6 and 7.3 ms; for the hindlimbs the values were between 6.9 and 9.3 ms. 4. Changing the depth at which the stimulation was applied in any one trajectory usually produced changes only in the amplitude of the evoked responses but occasionally also caused a change in the sign of these responses, especially in the most ventral regions of the MRF. 5. At 72% of the loci (31/43), short trains of stimulation also changed the duration of the activity in the recorded nerves. These changes were often (20/31 loci) sufficiently strong to alter the duration of the overall locomotor cycle. If one considers only the largest changes produced at each locus, stimulation during the period of ipsilateral extensor activity produced an average reduction in the ipsilateral locomotor cycle duration of 12.8 +/- 8.8% (mean +/- SD), whereas stimulation when the ipsilateral flexor nerve was active produced an average increase in locomotor cycle duration of 27.1 +/- 20.8%. 6. Long trains of stimuli produced similar but larger effects than the shorter trains and always reset the locomotor rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Motor cortical activity during voluntary gait modifications in the cat. II. Cells related to the hindlimbs.

1. To determine whether the motor cortex is involved in the modification of the hindlimb trajectory during voluntary adjustments of the locomotor cycle, we recorded the discharge patterns of 72 identified pyramidal tract neurons (PTNs) within the hindlimb region of pericruciate area 4 during a task in which cats stepped over obstacles attached to a moving treadmill belt. Data were also recorded from representative flexor and extensor muscles of the fore- and hindlimbs contralateral to the recording site. 2. To step over the obstacles, the cats increased flexion sequentially at the knee, ankle, and then the hip to bring the leg above and over the obstacle. This flexion movement was followed by a strong extension of the whole limb that repositioned the foot on the treadmill belt. These changes in limb trajectory were associated with large changes in the level of the activity of many flexor and extensor muscles of the hindlimb, and especially of the knee flexor, semitendinosus. On the basis of the time of onset of the knee and ankle extensor muscles in those steps when the limb was the first to be brought over the obstacle, the swing phase of the modified step cycle was subdivided into two parts, Phase I and Phase II, which correspond respectively to the flexion of the limb (F) and the initial extension (E1). 3. The temporal sequence of the movement was the same whether the hindlimb was the first (lead) or second (trail) to step over the obstacle, although the relative time between flexion at the three joints was changed in the two conditions. 4. Seventy-two PTNs were recorded from the posterior bank of the cruciate sulcus during the voluntary gait modifications. Sixty-three (63/72) of these PTNs had receptive fields that were confined to the contralateral hindlimb, or were recorded from penetrations in which such cells were found. Nine (9/72) PTNs had receptive fields on both the contralateral fore- and hindlimbs. Microstimulation applied through the recording electrode evoked, in all cases, brief twitch responses only in contralateral hindlimb musculature. 5. Forty-two (42/63) of those PTNs with receptive fields confined to the hindlimb showed a significant increase in their discharge frequency when the limb contralateral to the recording site was the first to step over the obstacle (lead limb). Twenty-nine PTNs (29/63) discharged maximally during the swing phase (18 in Phase I and 11 in Phase II), including two PTNS that also increased their discharge frequency during stance.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗