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.

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.

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.

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)

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.

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.

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.

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.

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.

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)

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)

Differentiation of U.S. and European isolates of porcine reproductive and respiratory syndrome virus by monoclonal antibodies

Monoclonal antibodies (MAbs) to two U.S. isolates of porcine reproductive and respiratory syndrome (PRRS) virus were prepared. Two MAbs specifically recognized a conserved epitope on the putative 15-kDa nucleocapsid protein of U.S. and European isolates of PRRS virus. Four other MAbs recognized epitopes on the 15-kDa protein of U.S. but not European isolates of PRRS virus. Collectively, this indicates that PRRS viruses contain both conserved and divergent epitopes on the 15-kDa viral protein.

Motor cortical activity during voluntary gait modifications in the cat. I. Cells related to the forelimbs

1. The discharge patterns of 91 identified pyramidal tract neurons (PTNs), located within the forelimb region of area 4 of the cat motor cortex, were recorded during the voluntary modifications of gait needed to step over obstacles attached to a moving treadmill belt. Recordings were made simultaneously from flexor and extensor muscles acting around the shoulder, elbow, wrist, and digits of the forelimb contralateral to the recording site. 2. Analysis of the changes in electromyographic (EMG) activity during the gait modification showed increases in the activity of most flexor muscles of the shoulder and elbow, as well as in the wrist and digit dorsiflexors, when the contralateral forelimb was the first to pass over the obstacle. This period of augmented activity could be subdivided into two parts: one associated with the initial flexion of the limb that was needed to bring it above and over the obstacle (phase I), and the second associated with increased wrist dorsiflexor muscle activity before foot contact (phase II). 3. The discharge frequency of a total of 57/91 (63%) of the recorded PTNs was significantly increased during the gait modification when the limb contralateral to the recording site was the first to step over the obstacle; six of these neurons also showed a significant decrease in their discharge in a different part of the step cycle. In a further 21/91 (23%) neurons, discharge frequency was only decreased, whereas the remaining 13/91 (14%) PTNs showed similar patterns of activity both during control walking and during the gait modifications. 4. Most of those neurons (47/57) in which significant increases in firing frequency were observed, discharged maximally during the period of increased activity of the physiological flexor muscles. Twenty-three of these cells (23/47) discharged maximally in phase I, and 12 (12/47) in phase II. A third population of PTNS (12/47) started to increase their discharge in the stance phase of the step cycle immediately preceding the modified cycle. Seven (7/57) PTNs increased their discharge during the stance phase of the modified cycle, and the remaining three could not be classified as being preferentially related to any one part of the step cycle. 5. The frequency modulation of 41/57 PTNs was less when the leg contralateral to the recording site was the second to encounter the obstacle. In many neurons there was also an appreciable change in the time in the step cycle that peak discharge occurred. These changes in amplitude and timing paralleled the changes observed in the temporal relationships of the muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity of medullary reticulospinal neurons during fictive locomotion

1. The pattern of discharge of medullary reticulospinal neurons, identified by antidromic stimulation applied at the L1-L2 segment of the spinal cord, was studied during fictive locomotion, occurring spontaneously, or evoked by stimulation of the mesencephalic locomotor region in high-decerebrate, paralyzed cats. Unitary recordings were made in the medial reticular formation (P5.0-14.0 mm; L0.5-2.0 mm), and the fictive locomotor pattern was monitored by recording the electroneurogram (ENG) of representative flexor and extensor muscle nerves from each of the four limbs. 2. In total, 117 reticulospinal neurons were recorded in 15 cats. Among these, 73.5% (86/117) modified their discharge at the onset of locomotion. These cells were divided into three subpopulations: 34/86 of the cells always maintained a fixed temporal relationship with the activity of one of the recorded nerves (ENG-related = 39.6%); the pattern of discharge of 42/86 cells was related to the locomotor rhythm [(LR-related-48%)] but was not temporally correlated with any of the recorded nerves; and the remaining 10 cells increased their firing frequency at the onset of locomotion but remained tonic (TONIC-11.6%). 3. Of the ENG-related neurons, 64.8% were temporally correlated to extensor nerve activity, whereas the remaining 35.2% were correlated to flexor nerves. These neurons were either related to forelimb (55.9%) or hindlimb (44.1%) nerves lying either ipsilateral (38.2%) or contralateral (61.8%) to the recording site. A few neurons (n = 3; 8.8%) were related to nerve activity of more than one limb. 4. The pattern of discharge of the LR-related neurons, although not correlated to the activity of any one recorded nerve, could be preferentially related to the locomotor rhythm in either the forelimbs (12/23) or hindlimbs (11/23). 5. ENG- and LR-related reticulospinal neurons were intermingled in the medial reticular formation. In both cases, cells related to the forelimbs were located more dorsally than those related to the hindlimbs. It is suggested that both the ENG- and LR-related neurons represent a single functional population of reticulospinal neurons that is part of an intrinsically organized reticulospinal system that functions to coordinate the activity of the skeletal musculature. 6. The present results show that the majority of reticular neurons projecting as far as the lumbar spinal cord are phasically modulated during locomotion, even in the absence of phasic peripheral afferent inputs. Moreover, the complexity of the discharge patterns in paralyzed animals was found to be similar to that observed in the intact cat.(ABSTRACT TRUNCATED AT 400 WORDS)

Visuomotor coordination in locomotion

This article reviews the recent literature concerning the role of visual information in the control of locomotion with an emphasis on the neurophysiological mechanisms that underlie visually triggered, voluntary, gait modifications. Data are presented to show how these gait modifications may be encoded by the motor cortex, and how they may interact with the basic locomotor rhythm.

Functional organization within the medullary reticular formation of the intact unanesthetized cat. III. Microstimulation during locomotion

1. This article presents the results from stimulation in 21 loci within the medullary reticular formation (MRF; between 0.5 and 2.5 mm from the midline) and in 5 loci in the medial longitudinal fasciculus (MLF) of four intact, unanesthetized cats during locomotion. Stimulus trains (11 pulses, 0.2-ms duration, 330 Hz, stimulus strength 35 microA) were applied at those loci in each track at which the most widespread effects in each of the four limbs were obtained with the cat at rest. Electromyograms were recorded from flexor and extensor muscles of each limb. 2. As previously reported, stimulation with the cat at rest generally evoked brief, short-latency, twitch responses in both flexor and extensor muscles of more than one limb. In contrast, stimulation during locomotion evoked a more complex pattern of activity in which responses were normally evoked in one or other of the muscle pairs and incorporated into the locomotor pattern. 3. In the majority of sites, the stimulation evoked excitatory responses in the flexor muscles of each of the four limbs during that period of the step cycle in which each respective muscle was naturally active; stimulation in the stance phase of locomotion, although less effective, was also capable of producing responses in these muscles. All three ipsilateral extensor muscles studied [long and lateral heads of triceps and vastus lateralis (Tri, TriL, and VL, respectively)] were normally inhibited during their phase of muscle activity, although excitatory responses were occasionally seen. Responses in the contralateral (co) Tri were invariably excitatory and were largest during the period of muscle activity, whereas responses during the period of activity of the coVL were mixed, with both excitatory and inhibitory responses being seen from any one locus. 4. Excitatory responses were normally largest when stimulation was applied during the time that the muscle was active during the locomotor cycle. Responses evoked at times when the muscle was inactive were sometimes larger than those evoked with the animal at rest; such responses were most commonly seen in the hindlimb flexors and in the coVL. 5. In both flexors and extensors of each of the four limbs, the latency of the responses was greatest when the cat was at rest and least for stimuli given during the period of activity of the respective muscle. Average latencies during the period of muscle activity ranged from a minimum of 9.0 +/- 2.6 (SD) ms for inhibitory responses in the ipsilateral Tri and TriL to a maximum of 17.1 +/- 3.0 ms for the responses evoked in the ipsilateral semitendinosus.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of circular statistics to the study of neuronal discharge during locomotion

An application of circular statistics is described which permits one to readily and efficiently describe neuronal discharge patterns recorded during locomotion. The method can be adapted to any data which are normally plotted as post-event histograms (PEHs) and can also be used to describe the pattern of electromyographic (EMG) activity during the step cycle. Data can be objectively classified with respect to both the mean direction and amplitude of their discharge, as well as to the variability (angular deviation) of that discharge. In addition, the Rayleigh test for directionality can be used to determine whether cells are modulated or unmodulated. Finally, the ability to describe each cell's discharge as a single vector allows the data from several different neurones to be displayed on a single figure and provides an efficient method for comparing the discharge of a population of cells under two or more different conditions.

Swan-Ganz catheter-induced massive hemoptysis and pulmonary artery false aneurysm

Swan-Ganz catheter-induced massive hemoptysis and later pulmonary artery false aneurysm occurred in a patient with prosthetic mitral regurgitation. This patient was successfully managed by double-lumen endotracheal intubation, control of pulmonary hypertension, reversal of anticoagulation, mitral valve re-replacement, and transcatheter embolization. The pertinent literature is reviewed.

Functional organization within the medullary reticular formation of intact unanesthetized cat. II. Electromyographic activity evoked by microstimulation

1. The present study has examined the detailed organization of the medullary reticular formation (MRF) as revealed by microstimulation (33-ms trains of 0.2-ms duration pulses at 330 Hz and 35 microA or less) in the intact, chronically implanted, unanesthetized cat. Stimulus-locked electromyographic (EMG) responses were recorded from flexors and extensors of each of the four limbs, as well as bilaterally from muscles of the neck and back, during stimulation of the same 592 loci that formed the basis of the preceding article. 2. The thresholds of the responses were different for each group of muscles, with, on the average, the neck muscles being activated at the lowest range of currents, 13.8-16.5 microA; forelimb muscles at 16.9-17.9 microA; back muscles at 25.4-25.7 microA; and hindlimb muscles at 21.1-25.7 microA. 3. Whereas stimulation within the MRF evoked movement of the head only to the stimulated side (preceding article), analysis of the EMG responses showed there was frequently bilateral activation of the neck muscles. Similarly, even though stimulation produced predominantly ipsilateral elbow flexion and contralateral elbow extension, most loci caused cocontraction of antagonistic muscles at these joints. Cocontraction was also frequently observed for the hindlimbs. Reciprocal activation of antagonistic muscles was less frequent but was observed in the ipsilateral forelimb as well as in both hindlimbs; it was never observed in the contralateral forelimb. 4. Although excitatory responses were observed from widespread regions for all of the muscles under study, those regions of the MRF that evoked the strongest responses in each muscle showed a large degree of segregation. Muscles of the ipsilateral forelimb were most strongly activated from the rostrodorsal MRF, whereas muscles of the contralateral forelimb were most strongly effected by stimulation caudoventrally. Muscles of the hindlimbs were more strongly activated from the rostral brain stem, although with some exceptions. Responses in axial muscles were evoked from widespread regions of the brain stem but were concentrated further caudally than were the limb muscles. 5. Excitatory responses were much more prevalent than inhibitory responses and were evoked from all regions of the MRF, including the most caudal and ventral areas. The shortest latency responses in each track were, on the average, as follows: 6.6-8.8 ms for the neck; 11.2-13.4 ms for the forelimbs; 13.8-14.2 ms for the back; and 15.9-17.2 ms for the hindlimbs. Inhibitory responses were also evoked from widely distributed regions, which were intermingled with those loci evoking excitatory responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional organization within the medullary reticular formation of intact unanesthetized cat. I. Movements evoked by microstimulation

1. The present article described the various patterns of movement evoked in the limbs and neck by microstimulation (33-ms trains, 330 Hz, 0.2-ms pulses at less than or equal to 35 microA) of the medullary reticular formation (MRF) of seven chronically implanted, unanesthetized, intact cats. Altogether 878 loci were stimulated in 83 penetrations. However, as stimulation in the more lateral regions of the MRF was less effective, the results are based on stimulation in 592 loci made in 56 penetrations at distances of between 0.5 and 2.5 mm lateral to the midline. 2. Of these 592 loci, movement of one or more parts of the body was evoked from a total of 539 (91%) sites. Most of these movements were compound in nature, involving movement of one or more limbs as well as the head. Discrete movements were observed only with respect to the head; limb movements were always accompanied by head movement. In addition, hindlimb movements were always accompanied by forelimb movements, although the inverse was generally not true. 3. The most common effects of the stimulation were as follows: a turning of the head to the ipsilateral side (79% of stimulated sites); flexion of the ipsilateral elbow (41%); and extension of the contralateral elbow (45%). Effects in the hindlimbs were more variable and less frequent, with the majority of the effective loci causing flexion of the ipsilateral knee (9%) together with extension of the contralateral knee (8%). In total, including both flexion and extension, 18% of the stimulated sites caused movement of the ipsilateral hindlimb and 11% of the contralateral hindlimb. 4. Although movements of the head were obtained from the whole extent of the brain stem, movements of the forelimbs showed a dorsoventral organization with flexion of the ipsilateral elbow being evoked from the more dorsal regions of the brain stem, whereas contralateral elbow extension was evoked more frequently from the ventral regions. There was a large area of overlap from which movements of both limbs could be obtained simultaneously. Movements of the hindlimbs were more frequently evoked from central and ventral areas of the brain stem and from the most rostral aspect of the explored region. 5. In examining the combinations of movements evoked by the MRF stimulation, it was found that the most commonly evoked pattern was movement of the head to the stimulated side together with flexion of the ipsilateral forelimb and extension of the contralateral forelimb (26.5% of sites).(ABSTRACT TRUNCATED AT 400 WORDS)

Motor cortical cell discharge during voluntary gait modification

Kinematic and electromyographic data were recorded together with motor cortical cell discharge during a task which required the cat to modify its gait in order to step over 3 different types of obstacles fixed to a moving treadmill belt. In order to negotiate the obstacles the cat made large adjustments in limb trajectory which were associated with equally large changes in forelimb flexor muscle activity. Sixteen of 57 identified pyramidal tract neurones recorded from area 4 of two cats increased their peak discharge rate during this gait adjustment. It is suggested that the motor cortex plays a role in adjusting the flexor muscle activity to the requirements of the locomotor task.

A kinematic and electromyographic study of cutaneous reflexes evoked from the forelimb of unrestrained walking cats

A kinematic and electromyographic (EMG) analysis was undertaken of the responses evoked in the forelimb of the cat by either mechanical obstruction of the forelimb during the swing phase of locomotion or by electrical stimulation of low-threshold cutaneous afferents during both swing and stance. Mechanical obstruction of the forelimb with a stiff metal rod evoked a complex response that allowed the cat to smoothly negotiate the obstacle without undue disruption of the overall locomotor rhythm. The initial movements were a flexion of the shoulder, together with a locking of the elbow joint, and a dorsiflexion of the wrist, which caused the limb to withdraw from the obstacle. They were followed by an extension of the shoulder, a flexion of the elbow, and a ventroflexion of the wrist, which together brought the limb forward and above the obstacle. The associated and complex pattern of short- and long-latency EMG responses was shown to be related to different aspects of the movement. At the shoulder there was a strong activation of flexor muscles; these responses were of long duration (greater than or equal to 100 ms) and generally lasted throughout the period of shoulder flexion. At the elbow, both flexor and extensor muscles were activated at short latency (9-13 ms). In flexors, this was followed by a cessation and subsequently an augmentation and prolongation of their activity. Dorsiflexors of both the wrist and digits were activated at short latency (10-12 ms) and remained active throughout the period of dorsiflexion of these joints. An injection of a local anesthetic into the area of skin contacted by the metal rod reduced or abolished all of the reflex responses, which suggests that the integrity of cutaneous reflex pathways is essential for the elaboration of these responses. Electrical stimulation of a cutaneous nerve innervating the distal forelimb (the superficial radial nerve) resulted in qualitatively similar, although weaker, responses to those obtained with the mechanical stimulation. Terminal experiments confirmed that these responses were mediated by low-threshold cutaneous afferents. Electrical stimulation also evoked short-latency excitatory responses (10-12 ms) in extensor muscles of the elbow. Generally, the largest reflex effects were obtained during the period of swing for flexor, extensor, and bifunctional muscles. During stance the stimulus was normally ineffective in exciting flexor muscles and in extensors evoked a short-latency inhibition, which was frequently followed by an increase in activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Discharge patterns of reticulospinal and other reticular neurons in chronic, unrestrained cats walking on a treadmill

Recordings were made from single units in the medullary reticular formation (MRF) between AP-4.2 and AP-12.9 and from the midline to 3.7 mm lateral in chronically prepared, unrestrained cats walking on a treadmill. Recordings were made with rigid microelectrodes held in a microdrive, and reticulospinal neurons were identified by antidromic stimulation of their axons through microwires chronically implanted into the spinal cord at the L2 level. Electromyograms (EMGs) were recorded from flexor and extensor muscles of the fore- and hindlimbs as well as from back and neck muscles. In total, 295 cells were recorded from 40 penetrations in 4 cats; 252 of these cells were recorded from the more medial regions of the reticular formation encompassing the gigantocellular, magnocellular, and lateral tegmental fields; 38.5% of these (97/252) were antidromically identified from the spinal cord. The remaining 43 neurons (43/295) were recorded from a more lateral and ventral position. These medial and ventrolateral groups of neurons differed not only in position but also in aspects of their discharge during locomotion. Rank-ordered raster displays, triggered from the onset of each recorded muscle, were used to correlate neuronal and muscular activity. The discharge rate of 31% of the reticulospinal neurons (30/97) was modulated once or twice in each step cycle and was strictly related to one or more of the recorded EMGs (EMG-related neurons) on the basis of the pattern of discharge. The discharge of 33/97 (34%) of the neurons was modulated at the periodicity of the locomotor rhythm but could not be correlated with any of the recorded EMGs (locomotor-related cells), whereas the remaining 34/97 neurons (35%) were either silent, fired tonically, or were not related to the locomotor pattern (unrelated cells). Of the EMG-related neurons 27% were related to flexor muscles and the remaining 63% to extensor muscle activity. The discharge pattern of all except two of the flexor-related neurons was correlated with hindlimb muscle activity, whereas that of the extensor-related neurons was correlated almost equally with fore- and hindlimb muscles. Correlations were found with muscles lying both ipsilaterally and contralaterally to the site of the recordings. Although the locomotor-related neurons showed no preferential relation with any of the recorded EMGs, a comparison of the depth of modulation of their discharge measured from postevent histograms suggested that more of these cells were related to the forelimb than to the hindlimb.(ABSTRACT TRUNCATED AT 400 WORDS)