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Biomedical subjects

R R Roy

Publications and source records attributed to R R Roy.

At least 163 records · Page 9Linked to original sources
PubMed1992

Potential of adult mammalian lumbosacral spinal cord to execute and acquire improved locomotion in the absence of supraspinal input.

The neural circuitry of the lumbar spinal cord can generate alternating extension and flexion of the hindlimbs. The hindlimbs of adult cats with complete transection of the spinal cord at a low thoracic level (T12-T13) can perform full weight-supporting locomotion on a treadmill belt moving at a range of speeds. Some limitations in the locomotor capacity can be associated with a deficit in the recruitment level of the fast extensors during the stance phase and the flexors during the swing phase of a step cycle. The level of locomotor performance, however, can be enhanced by daily training on a treadmill while emphasizing full weight-support stepping and by providing appropriately timed sensory stimulation, loading, and/or pharmacologic stimulation of the hindlimb neuromuscular apparatus. Furthermore, there appears to be an interactive effect of these interventions. For example, the maximum treadmill speed that a spinal adult cat can attain and maintain is significantly improved with daily full weight-supporting treadmill training, but progressive recruitment of fast extensors becomes apparent only when the hindlimbs are loaded by gently pulling down on the tail during the stepping. Stimulation of the sural nerve at the initiation of the flexion phase of the step cycle can likewise markedly improve the locomotor capability. Administration of clonidine, in particular in combination with an elevated load, resulted in the most distinct and consistent alternating bursts of electromyographic activity during spinal stepping. These data indicate that the spinal cord has the ability to execute alternating activation of the extensor and flexor musculature of the hindlimbs (stepping) and that this ability can be improved by several interventions such as training, sensory stimulation, and use of some pharmacologic agents. Thus, it appears that the spinal cord, without supraspinal input, is highly plastic and has the potential to "learn," that is, to acquire and improve its ability to execute full weight-supporting locomotion on a treadmill belt.

Animals↗
PubMed1991

Coordination of motor pools controlling the ankle musculature in adult spinal cats during treadmill walking.

The coordination of the motor pools of two ankle plantar-flexor, i.e. the soleus (Sol) and medial gastrocnemius (MG), and an ankle dorsiflexor, i.e. the tibialis anterior (TA) was quantified by comparing the EMG amplitude relationships in muscle pairs in normal and trained adult spinalized cats during treadmill walking across a range of relatively slow speeds (0.1 to 1.0 m/s). The effects of increased tactile stimulation or loading on locomotor performance were also studied in the spinal cats. Joint probability density distributions in the spinalized cats showed a low level of MG activation relative to Sol which did not change as speed increased. In general, the coordination between Sol and MG was similar in normal and spinal cats. However, towards the final phase of the extensor burst, the MG EMG amplitude decayed prematurely in spinal cats, particularly at higher speeds. Preferential elevation of MG relative to Sol activity was seen as a result of tactile stimulation. An elevated load resulted in a higher level of MG activation relative to Sol, prolonged MG activity at the end of the extensor burst, and the reduction in the clonic pattern of EMG typical of spinal cats. Spinalized cats showed an increased incidence of Sol-TA coactivation, especially at the higher speeds, due in part to the tonic activity in the TA. However, the overall reciprocal relationship between these antagonists was maintained. This reciprocity was preserved, but the high level of coactivation was unaffected by tactile stimulation. An elevated load, however, resulted in less Sol-TA coactivation. These results suggest that the coordination between synergists (Sol-MG) and between antagonists (Sol-TA and MG-TA), as well as the level of activation are modulated in the adult spinal cat similar to that observed in the normal cat. Further, there are specific types of proprioceptive-cutaneous information that can affect selected phases of the step cycle such that full weight-supporting stepping is significantly improved.

Animals↗
PubMed1991

Physiological and developmental implications of motor unit anatomy.

There is increasing evidence that the architectural design and arrangement of the fibers within a motor unit have important physiological and developmental ramifications. Limited data, however, are available to directly address this issue. In the present study the physiological properties of one motor unit in each of seven cat tibialis anterior (TA) muscles were determined. Each of these units then was repetitively stimulated to deplete the glycogen in all muscle fibers within the unit. Subsequently, the length, type of ending, and spatial distribution of fibers sampled from these physiologically and histochemically typed motor units were determined. Four fast fatigable (FF), one fast, fatigue resistant (FR), and two slow (S) motor units (MU) were studied. The samples consisted of all those glycogen-depleted fibers (9-27) contained within a single fascicle or a circumscribed area of each of the motor unit territories. The mean fiber lengths for the two slow motor units were 35.9 and 45.5 mm. The mean fiber lengths for the fast motor unit samples ranged from 8.8 to 48.5 mm. Some fibers of both the fast and slow units reached lengths of 58 mm. Most of the fibers in the slow units extended the entire distance between the proximal and distal musculotendinous planes, had relatively constant cross-sectional areas, and terminated at the tendon as blunt endings. In contrast, the majority of the fibers in the fast units terminated intrafascicularly at one end, and the cross-sectional area decreased progressively along their lengths, that is, showed a tapering pattern for a significant proportion of their lengths. Therefore, the force generated by units that end midfascicularly would appear to be transmitted to connective tissue elements and/or adjacent fibers. All fibers of a fast unit within a fascicle were located at approximately the same proximo-distal location. Thus, developmentally the selection of muscle fibers by a motoneuron would seem to be influenced by their spatial distribution. The architectural complexities of motor units also have clear implications for the mechanical interactions of active and inactive motor units. For example, the tension capabilities of a motor unit may be influenced not only by the spatial arrangement of its own fibers, but also by the level of activation of neighboring motor units.

Animals↗
PubMed1991

Regulation of skeletal muscle fiber size, shape and function.

There is convincing evidence that the cross-sectional area, the type of myosin expressed, the potential for oxidative phosphorylation and the number of myonuclei of a skeletal muscle fiber are closely interdependent. Each of these variables, as well as the shape of the fiber, has identifiable physiological consequences. Further, it is suggested that the cytoplasmic to myonucleus ratio is a function of the myosin type and the amount and/or rate of protein synthesis and degradation. Although the neuromuscular activity (electromyographic activity) as well as the associated mechanical and metabolic events have significant regulatory influences on protein metabolism, there are other important regulatory factors independent of these activity-related events. Both the activity and non-activity related regulatory mechanisms probably occur via a cascade of cellular events. The specific combinations of cellular responses that occur may define the nature of the modulatory effects on specific proteins. In spite of the complexity of the regulatory mechanisms of protein modulation and how these responses are structurally integrated into or removed from functional fibers, it is suggested that controlled studies of human neuromuscular function can be more accurately defined and interpreted when fiber and muscle size and shape are considered.

Animals↗
PubMed1991

A physiological basis for the development of rehabilitative strategies for spinally injured patients.

After a decade of studies using animal models, there is sufficient information to encourage a reassessment of the potential for recovery of motor function following spinal cord injury in humans. This review focuses on the response of the lumbosacral motor system following spinal cord injury and the effects of rehabilitative strategies such as weight support, loading, and administration of specific pharmacological agonists and antagonists on the maintenance and/or recovery of motor function. Based on clinical experience and review of related studies, the authors suggest a list of eight strategies for the improvement of rehabilitative protocols.

Animals↗
PubMed1991

Mechanical and morphological properties of chronically inactive cat tibialis anterior motor units.

1. The lumbar spinal cord was functionally isolated in ten cats by cord transection at the junctions of segments T12-T13 and L7-S1 and cutting bilaterally all dorsal roots between the two transections. Two 24 h EMG recording sessions were used to verify that muscles in the lower limb were virtually electrically silent. The cats were maintained in excellent health for 6 months. 2. Six months after spinal cord isolation, an acute experiment was performed to isolate a single motor unit from the tibialis anterior of each hindlimb using ventral root splitting techniques. Each motor unit was characterized physiologically as either fast fatigable (FF, n = 11), fast fatigue resistant (FR, n = 4), fast intermediate (FI, n = 2), or slow (S, n = 1), and repetitively stimulated to deplete the motor unit of its glycogen. 3. Maximum tensions of the fast motor units were lower than mean maximum tensions of control, whereas the S motor unit remained within the range observed in controls. In general, the isometric contractile properties, as well as fatigability, were within the ranges for each of the motor unit types in control cats. The mean fibre cross-sectional areas of the fibres within the FR and FF motor units were approximately 40 and 50% smaller than control, while the mean fibre size of the fibers within the S motor unit was similar to control. 4. Innervation ratios and specific tensions for all experimental motor units were within the ranges of those reported for tibialis anterior motor units in control cats. Thus, it appears that the decrease in maximum tension of the fast motor units was primarily related to a reduction in fibre size. 5. The spatial distribution of the fibres within fast motor units of a spinally isolated cat, as measured by interfibre distances of the motor unit fibres, was similar to that reported for control tibialis anterior motor units. 6. These data suggest that factors independent of activity play a prominent, if not dominant, role in maintaining the complement of motor unit types typical of adult cat muscles. In addition, normal innervation patterns appear to be maintained in the absence of activity.

Animals↗
PubMed1991

Enzymatic responses of cat medial gastrocnemius fibers to chronic inactivity.

The role of neuromuscular activity in maintaining the normal enzyme heterogeneity found in a predominantly fast mixed muscle was studied. Enzymatic profiles of single fibers in the adult cat medial gastrocnemius (MG) were examined after almost complete elimination of neuromuscular activity for 6 mo. Inactivity was achieved by spinal cord isolation (SI), i.e., spinal transection at T12-T13 and L7-S1 combined with bilateral dorsal rhizotomy between the two transection sites. Cross-sectional area and succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) activities were determined in a population of fibers identified in frozen serial cross sections. Each fiber was categorized as light or dark on the basis of its staining characteristics for qualitative myosin adenosinetriphosphatase (ATPase), alkaline preincubation, and its reaction to fast and slow myosin heavy chain (MHC) antibodies. SI resulted in a conversion of nearly all light (approximately 36% in the control) to dark ATPase fibers. Virtually all MG fibers in the SI cats reacted with the fast MHC antibody, whereas very few fibers reacted with slow MHC antibody. On the basis of fiber cross-sectional area, it was estimated that the MG atrophied by approximately 10% after SI. Compared with the mean of the dark and light ATPase fibers in control (weighted by the percent fiber type distribution), mean SDH activity was significantly lower (approximately 70%) and mean GPD activity was significantly higher (approximately 120%) in the SI cats. These data indicate that prolonged electrical silence of a mixed fast hindlimb extensor results in virtually all fibers expressing fast MHC as well as oxidative and glycolytic enzyme profiles normally observed in fast glycolytic fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

EMG patterns of rat ankle extensors and flexors during treadmill locomotion and swimming.

Intramuscular electromyography (EMG) was used to determine and compare the recruitment patterns of the rat soleus (Sol), tibialis anterior (TA), and a deep and a superficial portion of the medial gastrocnemius (MG) during treadmill locomotion at various speeds and inclines and during swimming. Raw EMG signals for 10-20 step or stroke cycles were rectified, averaged, and processed to determine cycle period (EMG onset of one cycle to EMG onset of the next cycle), EMG burst duration, and integrated area of the rectified burst (IEMG). Mean EMG per burst was calculated as IEMG/burst duration. IEMG/min was calculated as IEMG times the number of bursts (cycles) per minute. Cycle period and burst duration of the extensors decreased hyperbolically, while the TA burst duration was unchanged, with increased treadmill speed. With increased treadmill speed, IEMG was decreased in the Sol and unchanged in the MG and TA, whereas IEMG/min decreased in the Sol and increased in the MG and TA. An elevation in treadmill incline resulted in an increase in the activation levels of the MG but not in the Sol or TA. These data indicate that the additional power required at increased speeds and/or inclines of treadmill locomotion is derived from the recruitment of the fast extensors, e.g., the MG. The mean cycle period during swimming was similar to that observed during the fastest treadmill locomotion. EMG burst durations and amplitudes, however, were higher in the TA, relatively similar in the MG, and lower in the Sol during swimming than treadmill locomotion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Motoneuron and muscle fiber succinate dehydrogenase activity in control and overloaded plantaris.

To determine the level of coordination in succinate dehydrogenase (SDH) activity between plantaris motoneurons and muscle fibers, the soleus and gastrocnemius muscles were bilaterally excised in four cats to subject the plantaris to functional overload (FO). Five normal cats served as controls. Twelve weeks after surgery the right plantaris in each cat was injected with horseradish peroxidase to identify plantaris motoneurons. SDH activity then was measured in a population of plantaris motoneurons and muscle fibers in each cat. Control motoneurons and muscle fibers had similar mean SDH activities and a similar relationship between cell size and SDH activity. After FO, muscle fiber size doubled and mean muscle fiber SDH activity halved. Motoneuron mean SDH activity and size were unaffected by FO. Total SDH activity was unchanged in both the motoneurons and muscle fibers after FO. These changes suggest a selective increase in contractile proteins with little or no modulation of mitochondrial proteins in the muscle fibers, because total SDH activity was unchanged in muscle fibers after FO. These data demonstrate that although mean SDH activities were similar in control motoneurons and muscle fibers, mean SDH activities in these two cell types can change independently.

Animals↗
PubMed1991

Architectural and fiber type distribution properties of selected rhesus leg muscles: feasibility of multiple independent biopsies.

In experiments involving primates, e.g. before and after spaceflight, needle biopsies were thought to be a logical and feasible means of obtaining metabolic and morphological information from skeletal muscles. However, the feasibility of obtaining consistent, repeatable biopsies from individual muscles had to be demonstrated prior to the acceptance of this procedure. To study this approach, the architectural properties and the fiber type distributions at three levels and two regions along the proximo-distal axis of the soleus, medial gastrocnemius and tibialis anterior of adult rhesus monkeys were determined. In each muscle, biopsies were taken from specific regions where the fiber type distribution was determined. Within each region of each muscle, the fiber type populations were similar at the three levels studied. The percentage of fast or oxidative fibers in the biopsies and in the regions of the same muscle were highly correlated, i.e. r = 0.98 for both comparisons. In addition, based on normalized values (z scores), 25/26 and 22/26 biopsies were within the 95% confidence interval, i.e. the biopsies were a representative sample of the mean fiber type population of that region of the muscle. In all muscles, the mean fiber lengths were no more than one third the length of the muscle. Together, these data indicate the feasibility of obtaining independent, repeated biopsies having similar fiber types from each of the muscles studied.

Animals↗
PubMed1991

The effects of dynamic tension and reduced graft size on muscle regeneration in rabbit free muscle grafts.

In a study of 28 adult New Zealand White rabbits, the influence of tension and size on muscle regeneration in tibialis anterior free muscle grafts (without vascular anastomoses) was examined 6 months after transplantation. Three laboratory models were studied: (1) whole dynamic (WD) graft (allowing ankle excursion and, therefore, variable dynamic physiologic tension), (2) whole static (WS) graft (constant, fixed length and, thus, only isometric tension), and (3) longitudinally sliced (reduced radius) dynamic (SD) model. Bilateral orthotopic grafts of the tibialis anterior muscle were performed in 24 rabbits (eight animals in each of the three different model groups). Controls consisted of normal tibialis anterior muscle from four age-matched rabbits. All tibialis anterior muscle grafts were examined histologically (fiber counts) and functionally (determined by in situ contractile properties under maximal stimulation conditions). The WD grafts demonstrated a significantly higher number of regenerated fibers per muscle cross section (4819 +/- 589) than the WS (2221 +/- 603) or SD (1919 +/- 732) grafts. The amount of tetanic tension in the WD grafts was 35 percent of the control and twice as much as that of the WS grafts (WD 1.0 +/- 0.2 kg versus WS 0.5 +/- 0.4 kg; p less than 0.05). The SD grafts produced approximately one-third as much maximum tetanic tension as the WD grafts (0.3 +/- 0.1 kg versus 1.0 +/- 0.2 kg), demonstrating that the amount of recovery was similar in these two dynamic models, since only the longitudinal middle third of the muscle was grafted in the SD model. Free muscle grafts under dynamic tension, which allows excursion, have shown a greater amount of muscle-fiber regeneration and restoration of function compared with a graft with fixed length. The positive effect of dynamic mechanical tension on small autogenous free muscle grafts (without vascular anastomoses) is clinically significant in the reconstruction of facial and hand neuromuscular deficits when blood vessels are not available for reanastomosis. Future studies using the tibialis anterior WD and SD transplant models will strengthen our understanding of the events of spontaneous revascularization and skeletal muscle regeneration.

Analysis of Variance↗
PubMed1990

Weight-bearing hindlimb stepping in treadmill-exercised adult spinal cats.

Hindlimb locomotion on a motor-driven treadmill was studied in 5 cats spinalized at a low thoracic level adults. Six months after surgery, the cats were anesthetized and implanted for electromyographic (EMG) and force recordings in hindlimb muscles. For the last 5 months of the spinalization period, the hindlimbs of each cat were exercised daily for 30 minutes on a treadmill. Data were collected during hindlimb locomotion on a treadmill across the entire range of speeds each cat could accommodate. All trials were filmed (100 frames/s) for kinematic analysis. EMG data were recorded from the soleus (Sol), medial gastrocnemius (MG), tibialis anterior (TA) and extensor digitorum longus (EDL). Forces were recorded in vivo from the Sol and MG tendons. All cats could sustain full weight-bearing stepping without the need for mechanical stimulation of the tail. Although the general stepping pattern of the spinal cats was remarkably similar to that of normal cats, several key differences were identified. Compared to normal cats, the adult spinal cats walked at a lower range of speeds and exhibited a longer swing phase duration. The Sol produced forces and displayed activation periods comparable to those observed in normal cats. The MG of adult spinal cats, however, produced lower forces and had a later onset of activation in comparison to normal cats. Each of the muscles in all spinal cats exhibited tremor during stepping. These results suggest that there were limitations in the activation levels of some hindlimb flexor and extensor muscles during treadmill locomotion. These data further suggest that, in normal cats, accommodation to treadmill speed is accomplished by modulating supraspinal input to the lumbar spinal cord while leaving many of the timing details to be regulated by lumbar spinal networks.

Animals↗
PubMed1990

Expression of a fast fiber enzyme profile in the cat soleus after spinalization.

This study was designed to determine the effects of reduced neuromuscular activity on the expression of proteins associated with contractile and metabolic functions and the size of single muscle fibers in the cat soleus. Adult cats were spinalized (Sp) at T12-T13 and maintained in a healthy condition for 6 months. Some of the cats were trained to weight-support (Sp-WS) for 30 minutes per day beginning one month posttransection. Cross-sectional area (CSA), succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar adenosine triphosphatase (ATPase) activities were determined in a population of single fibers identified in frozen serial cross-sections. Each fiber was categorized as either light or dark based on its staining density for qualitative myosin ATPase, alkaline preincubation (pH 8.75). The Sp (45%) and Sp-WS (31%) groups had significantly higher percentages of dark ATPase fibers than control (less than 1%). All dark ATPase fibers were shown to react positively for a fast myosin heavy chain monoclonal antibody, while some of these fibers showed a reaction to both fast and slow myosin heavy chain antibodies. Overall mean fiber CSA were significantly smaller (approximately 25%) than control in both Sp groups. In the Sp-WS, but not the Sp cats, the dark fibers were larger than the light fibers (P less than 0.05), suggesting a preferential effect of postural training on the ATPase converted fibers. There were no significant differences among the three groups in any of the mean enzyme activities for either ATPase type fiber. However, there was a general tendency for the Sp cats to have elevated GPD and ATP activities per muscle; this appeared to be directly related to the percentage of fibers staining darkly for myosin ATPase. These data indicate that 6 months after spinalization some of the fibers of the slow muscle developed fast myosin staining patterns and oxidative and glycolytic enzyme profiles that are normally exhibited in fast fatigue-resistant motor units. Periods of daily weight-support appear to ameliorate some of these adaptations to spinalization. Further, the observation that SDH activities are maintained at control values in spinalized adult cats as well as in spinalized kittens (unpublished observations) suggest that, at least in the soleus, skeletal muscle fibers can maintain their oxidative potential even though there is a marked reduction in neuromuscular activity for 6 months.

Adenosine Triphosphatases↗
PubMed1990

Spatial distribution of muscle fibers within the territory of a motor unit.

The spatial distribution of muscle fibers belonging to a motor unit was studied in the soleus (SOL) and tibialis anterior (TA) of adult cats to provide a detailed description of the spatial patterns which exist within the territory of a motor unit. Glycogen depletion of the motor unit was achieved through repetitive stimulation of either the intracellularly identified motoneuron or the functionally isolated motor axon. Muscle fibers belonging to the stimulated unit were identified in serial cross-sections, and in the cross-section which contained the most depleted fibers the centroid of each depleted fiber was determined. Subsequently, three spatial analyses, ie, a quadrat analysis, a point-to nearest neighbor analysis and an interfiber distance analysis, were used to determine if motor unit fibers were distributed randomly throughout the territory of the unit. Motor unit fibers tended to be localized within the muscle cross-section and were not evenly or homogeneously distributed throughout the territory. In general, the analyses suggested that motor unit fibers may be arranged in clusters or subgroups of varying size. The data demonstrate three different quantitative analyses for studying the organization of muscle fibers of normal motor units, which can be used for objective assessment and diagnosis of neuromuscular diseases.

Animals↗
PubMed1990

Metabolic and morphologic properties of single muscle fibers in the rat after spaceflight, Cosmos 1887.

The adaptation of a slow (soleus, Sol) and a fast (medial gastrocnemius, MG) skeletal muscle to spaceflight was studied in five young male rats. The flight period was 12.5 days and the rats were killed approximately 48 h after returning to 1 g. Five other rats that were housed in cages similar to those used by the flight rats were maintained at 1 g for the same period of time to serve as ground-based controls. Fibers were classified as dark or light staining for myosin adenosine triphosphatase (ATPase). On the average, the fibers in the Sol of the flight rats atrophied twice as much as those in the MG. Further, the fibers located in the deep (close to the bone and having the highest percentage of light ATPase and high oxidative fibers in the muscle cross section) region of the MG atrophied more than the fibers located in the superficial (away from the bone and having the lowest percentage of light ATPase and high oxidative fibers in the muscle cross-section) region of the muscle. Based on quantitative histochemical assays of single muscle fibers, succinate dehydrogenase (SDH) activity per unit volume was unchanged in fibers of the Sol and MG. However, in the Sol, but not the MG, the total amount of SDH activity in a 10-microns-thick section of a fiber decreased significantly in response to spaceflight. Based on population distributions, it appears that the alpha-glycerophosphate dehydrogenase (GPD) activities were elevated in the dark ATPase fibers in the Sol, whereas the light fibers in the Sol and both fiber types in the MG did not appear to change. The ratio of GPD to SDH activities increased in the dark (but not light) fibers of the Sol and was unaffected in the MG. Immunohistochemical analyses indicate that approximately 40% of the fibers in the Sol of flight rats expressed a fast myosin heavy chain compared with 22% in control rats. Further, 31% of the fibers in the Sol of flight rats expressed both fast and slow myosin heavy chains compared with 8% in control rats. Immunohistochemical changes in the MG were minimal. These data suggest that the magnitude and direction of enzymatic activity and cell volume changes are dependent on the muscle, the region of the muscle, and the type of myosin expressed in the fibers. Further, the ability of fibers to maintain normal or even elevated activities per unit volume of some metabolic enzymes is remarkable considering the marked and rapid decrease in fiber volume.

Adenosine Triphosphatases↗
PubMed1990

Enzymatic plasticity of medial gastrocnemius fibers in the adult chronic spinal cat.

The metabolic plasticity of single fibers in adult cat medial gastrocnemius (MG) 6 mo after complete spinal cord transection (Sp) at T12-T13 was studied. Some Sp cats were trained to weight support (Sp-WS) 30 min/day beginning 1 mo posttransection. Cross-sectional area, succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar adenosinetriphosphatase (ATPase) activities were determined in fibers identified in frozen serial sections. Fibers were categorized as light or dark based on myosin ATPase staining, alkaline preincubation. The percentage of dark ATPase fibers was higher in Sp and Sp-WS (approximately 85%) than in control (approximately 60%). All dark ATPase fibers reacted positively to a fast myosin heavy chain monoclonal antibody. In both spinal groups, a higher percentage of dark ATPase fibers reacted to both fast and slow myosin heavy chain antibodies than in controls. Neither Sp nor Sp-WS cats showed fiber atrophy. Compared with control, SDH activity was decreased in both fiber types of Sp cats. Daily weight-support training ameliorated this adaptation. There were no differences among the three groups in mean GPD and ATPase activities for either fiber type. There was a slight tendency, however, for spinal cats to have higher GPD and ATPase activities (independent of type) than control, probably reflecting the larger proportion of dark ATPase fibers in these cats. These observations indicate that 6 mo after spinalization in adult cats, some of the fibers of a fast muscle became "faster" and developed oxidative and glycolytic enzyme profiles that normally are exhibited in fast fatigable motor units.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗