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D Kernell

Publications and source records attributed to D Kernell.

At least 55 records · Page 3Linked to original sources
PubMed1991

Recovery after intense chronic stimulation: a physiological study of cat's fast muscle.

Adult cats were used to study the recovery of muscles that had become altered by long-term electrical stimulation. Chronic activation was delivered to the deafferented common peroneal nerve (no pain, no reflexes), and contractile properties were measured for peroneus longus muscle. After 4 wk of great daily amounts of treatment at moderately high pulse rates (30-40 Hz delivered during 50% of daily time), the peroneus longus became considerably weaker, demonstrated a longer time course of twitches and a slower rate of rise of tetanic force, and became less fatigable. Furthermore, its twitch-to-tetanus ratio decreased, and there was no longer any depression of electromyogram (EMG) amplitude during fatigue tests. After 4 wk of subsequent rest it was found that 1) twitch speed and maximum tetanic force had returned to nearly normal values, 2) fatigue resistance showed some return toward normal but was still significantly enhanced, and 3) no significant recovery had yet occurred of the altered twitch-to-tetanus ratio, the abolished EMG depression, or the slowed rate of rise of tetanic tension. During the poststimulation recovery period, the progressive increase of isometric twitch speed was not promoted by the administration of small daily amounts of high-rate stimulation (100-Hz bursts). The results support the conclusions that 1) the time course of recovery differs among physiological properties, 2) the EMG and force reactions that occur during a fatigue test are not strongly coupled, as demonstrated by the alterations of their relationship during poststimulation recovery, and 3) in cat's fast muscles, there is still no evidence for rate-specific effects of chronic stimulation on isometric twitch speed.

Animals↗
PubMed1991

Myofibrillar ATPase histochemistry of rat skeletal muscles: a "two-dimensional" quantitative approach.

In histochemical investigations of skeletal muscle, the fibers are commonly classified into three types according to their staining for myofibrillar ATPase (mATPase). In serial sections of skeletal muscles from normal Wistar rats, we compared two common staining methods for mATPase: (a) an ac-ATPase technique, with pre-incubation at pH 4.7, and (b) a fixed alk-ATPase technique, using treatment with 5% paraformaldehyde followed by pre-incubation at pH 10.4. In addition, the same fibers were stained in subsequent serial sections for succinate dehydrogenase (SDH) activity. Staining intensities were objectively evaluated by microphotometric measurements of optical density. Combining both mATPase methods in consecutive serial sections ("two-dimensional approach") led to the identification of four distinct clusters of fibers: Types I, IIA, and two subgroups of Type IIB, as separated by their staining densities for fixed alk-ATPase (IIBd dark, IIBm moderate). The mean intensity of SDH staining per fiber type, as measured in the central core of the fibers, was ranked such that IIA greater than I greater than IIBd greater than IIBm. The analyzed muscles (tibialis anterior, biceps brachii) were markedly heterogeneous with respect to the topographic distribution of different fiber types. In comparison to other muscle portions, the regions containing Type I fibers ("red" portions) showed a higher IIBd vs IIBm ratio and more intense SDH staining for either subtype of the IIB fibers. The IIBd fibers probably correspond to the Type 2X fibers of Schiaffino et al.

Adenosine Triphosphatases↗
PubMed1990

Synaptic effects on recruitment gain: a mechanism of importance for the input-output relations of motoneurone pools?

The present theoretical analysis concerns quantitative aspects of the graduation of motoneuronal recruitment. It is pointed out that variations in the relative distribution of synaptic input to low- and high-threshold cells will serve to alter the ultimate magnitude of the threshold differences between them. These threshold differences determine the pool's 'recruitment gain', i.e. the ease with which a variation of excitatory drive to the pool may alter the number of active motoneurones. In this context, not only the command signal itself but also any steady synaptic 'background' activity is of importance, whereby the background effects on recruitment gain depend on the presence of differences in intra-pool distribution between these synapses and those of the command signal. Given the appropriate intra-pool distribution, even inhibitory background effects might serve to increase the recruitment gain. It is stressed that synaptic effects on recruitment gain should be taken into account when analyzing the input-output relations of motoneurone pools.

Models, Neurological↗
PubMed1990

Electromyogram and force during stimulated fatigue tests of muscles in dominant and non-dominant hands.

Mechanical and electrical properties were studied for the first dorsal interosseous muscle of the dominant (d-FDI) and non-dominant hand (nd-FDI). Observations were made before, during and after a fatigue test, fatigue being evoked by percutaneous electrical stimulation of the ulnar nerve. The test consisted of 30 Hz bursts of ten supramaximal 0.1 ms pulses, repeated once a second for 5 min. The measurements included the amplitude of the first and fifth compound muscle action potentials (M-waves) within bursts, the peak burst force and the amplitude and time course of single twitches. At the end of the fatigue test, burst force had decreased to about the same extent in the FDI of both hands. The final decline in first M-wave amplitude was, however, significantly more pronounced for the nd-FDI than for the d-FDI. There were no longer any significant discrepancies between the two muscles after a subsequent recovery-period of 15 min. Comparisons among nd-FDI of various individuals demonstrated the presence of significant inter-individual differences in fatigue-related force-drop without any associated differences in M-wave decline. Intra-individual variability was similar for fatigue-related force-drop and M-wave decline.

Adolescent↗
PubMed1990

The "fastness" of rat motoneurones: time-course of afterhyperpolarization in relation to axonal conduction velocity and muscle unit contractile speed.

In normal adult rats, intracellular recordings were obtained from motoneurones of the medial gastrocnemius (MG) and other tibial-nerve muscle branches. Among the whole population of tibial motoneurones, there was a significant negative correlation between the duration of afterhyperpolarization (AHP) and axonal conduction velocity (CV). However, this AHP vs CV relationship differed from that previously demonstrated in cats, in that for a given axonal CV, the AHPs were briefer in the rat than in the cat. For MG cells, twitches were also recorded from their muscle units. As has previously been observed in cats, there was a significant correlation between the time-course of the AHP of a motoneurone and the time-course of its muscle unit twitch. This relationship was, in principle, similar between the two species, but the AHPs and the twitches were briefer in the rat. The present results provide the first demonstration, for the rat model, of the presence of a functionally relevant "speed-match" between the intrinsic properties of alpha-motoneurones and those of their muscle units.

Animals↗
PubMed1989

Distribution of activity within the cat's peroneus longus muscle when activated in different ways via the central nervous system.

We have studied whether a mechanically homogenous muscle (all units giving joint-torques in the same direction) would display different distributions of activity in response to different types of activation via the central nervous system. In adult cats anaesthetized with pentobarbitone, long-lasting contractions were evoked in m. peroneus longus (PerL), a mixed ankle dorsiflexor muscle. The contractions were elicited by continuous repetitive stimulation of: (1) the superficial peroneal nerve (NP, flexion reflex); and (2) the contralateral motor cortex (MC). During these contractions, isometric force was monitored and fine-wire electromyographic recordings (EMG) were simultaneously obtained from anterior and posterior portions of the PerL. The relative degree of activation in anterior vs posterior muscle portions was quantified by measuring, at various force levels: (1) the average spike amplitude (Spike); and (2) the total number of spikes per unit time (Count; 0.5-s measurement periods). For both types of stimulation (MC and NP), the results indicated that activation was more effective for posterior than for anterior muscle portions: the Spike-measurements were typically higher in posterior than in anterior PerL and, for MC-elicited contractions, this was true for the Count-measurements as well. With respect to both types of EMG-quantification (Spike and Count), the 'posterior bias' of activity was significantly more pronounced for the cortically evoked contractions than for those elicited via stimulation of the peroneal nerve. As it is known that anterior and posterior PerL portions tend to be innervated by rostral and caudal motoneurones, respectively, these findings indicate that different inputs to the PerL motoneurone pool may differ significantly with respect to the intraspinal spatial distribution of synaptic effects among the motoneurones. The results were discussed in relation to the organization of task-related recruitment schemes.

Animals↗
PubMed1989

Size and remoteness: two relatively independent parameters of dendrites, as studied for spinal motoneurones of the cat.

1. The spatial extent of motoneuronal dendrites was analysed using data from the fifty-two dendritic trees of four completely reconstructed cat motoneurones that had been labelled with intracellularly injected horseradish peroxidase. The cells belonged to m. triceps surae, and their physiological properties covered much of the known range for this muscle. 2. The percentage of total dendritic area extending beyond a radial somatofugal distance of 750 microns (PA750) was selected as an index of 'dendritic remoteness'. 3. The value of our standard remoteness index PA750 was well correlated with a number of other possible remoteness measures, such as the percentage of total dendritic area beyond 500 or 1000 microns or the percentage of cumulative dendritic length beyond 750 or 1000 microns. 4. Most of the dendritic parameters could be classified as belonging either to a cluster of remoteness-related properties or to a cluster of size-related properties. Remoteness-related properties were significantly correlated with PA750 but not with stem diameter. Size-related properties were significantly correlated with stem diameter but not with the remoteness index PA750. The remoteness-related properties included the mean somatofugal distance to branch points, the mean and maximum distance to terminal ending and, somewhat less distinctly, the mean length of terminal branches. The size-related properties included the total dendritic area, the cumulative dendritic length, and the total number of branch points and terminal endings. 5. The extent of area expansion at branch points and the overall extent of tapering were not systematically related to differences in remoteness. 6. The relative degree of remoteness was greater for medial than for lateral dendrites. 7. Even in the present limited sample of cells, there were marked and systematic differences between different neurones with respect to the relative remoteness of their dendrites. The slowest and most high-resistance motoneurone was the one with the most remote dendrites. On the whole there was, however, a considerable degree of independence between the variation in dendritic remoteness and the variation in physiologically determined properties (axonal conduction velocity, input resistance, after-hyperpolarization). 8. In the discussion it is suggested that differences in dendritic remoteness might lead to a selectivity between the various members of a given motoneurone pool with respect to their reception of topographically distributed systems of synapses. It is proposed that such differences might be of interest in relation to, for instance, the organization of innervation to motoneurones belonging to different task groups within the same muscle.

Animals↗
PubMed1989

Dendrites of cat's spinal motoneurones: relationship between stem diameter and predicted input conductance.

1. The electroanatomy of motoneuronal dendrites was analysed using data from fifty-two dendritic trees of four completely reconstructed cat spinal motoneurones that had been labelled with intracellularly injected horseradish peroxidase. The cells belonged to m. triceps surae, and their physiological properties covered much of the known range for this muscle. 2. For each dendritic tree, the input conductance, as seen from the soma, was calculated by the method of Rall (1959), using anatomical measurements of the length and diameter of all branches and different assumed values for dendritic membrane resistivity. 3. There was a strong positive correlation between dendritic stem diameter and the calculated dendritic input conductance. Dendritic input conductance was approximately equal to a constant x (stem diameter)3/2 x (dendritic membrane resistivity)-0.76. 4. The relationship between dendritic stem diameter and computed input conductance was equal to that of Rall's equivalent-cylinder model of a dendritic tree. However, from a number of other points of view, the properties of the reconstructed dendrites differed from those of the model: (a) at branch points, the sum sigma(daughter diameters 3/2) was, on average, 19% greater than the 3/2 power of the parent diameter; (b) dendritic branches often showed a significant amount of tapering, and the mean overall degree of diameter decrease per branch was about 12%; (c) the termination of dendritic branches occurred at widely different distances from the soma within single dendritic trees (true for anatomical as well as for computed electrotonic distances). 5. When used in conjunction with previously published measurements of motoneuronal input resistance and proximal anatomy (Kernell & Zwaagstra, 1981), the present results gave further support to the conclusion that differences in membrane resistivity are of great importance for differences in motoneuronal input resistance. Furthermore, this conclusion was also confirmed by direct observation of the properties of the present four motoneurones: irrespective of the assumed ratio between somatic and dendritic membrane resistivity, there was a statistically significant positive correlation between the measured neuronal input resistance and the required membrane resistivity of soma and dendrites.

Animals↗
PubMed1987

Fibre sizes and histochemical staining characteristics in normal and chronically stimulated fast muscle of cat.

1. Normal and chronically stimulated peroneus longus muscles of the cat's hind limb were studied with respect to fibre size and staining properties for myofibrillar (myosin) adenosine triphosphatase (ATPase) and succinate dehydrogenase (SDH) activity. The intensity of staining for SDH activity was measured by microphotometry from the central portions of the muscle fibres ('core-SDH staining'). For comparison, histochemical properties were also studied in non-stimulated soleus muscles. 2. On account of the pH sensitivity of their myofibrillar ATPase, about 18% of the fibres in normal peroneus longus muscles were classified as type I, and about half of the remainder as II A and II B respectively. 3. In the normal peroneus longus muscles, the mean diameter of single muscle fibres generally varied between about 25 and 75 micron, whereby the average size of type I less than type II. 4. In the normal peroneus longus muscles the staining intensity for core SDH varied over a wide range. The average heaviness of staining was clearly ranked in the order type I greater than type II A greater than type II B. 5. Chronic stimulation was given to the deafferented common peroneal nerve by aid of a portable and remotely controlled mini-stimulator. The stimulation was delivered in 'tonic' patterns (greater than or equal to 50% of total time taken up by activity) of 'fast' (20 or 40 Hz) or 'slow' (5 or 10 Hz) rates. 6. Prior to the period of long-term stimulation, the cats had been subjected to a dorsal rhizotomy and hemispinalization on the ipsilateral (left) side. In the absence of chronic stimulation, these operations had no evident effects on the sizes or staining properties of peroneus longus fibres. 7. After 8 weeks of treatment with tonic patterns of stimulation, the fibres of peroneus longus muscles clearly became more similar to each other with respect to their diameter as well as their staining for ATPase and SDH activity. With respect to ATPase staining, however, the chronically stimulated peroneus longus fibres had become more similar to non-stimulated soleus fibres than to non-stimulated type I fibres of peroneus longus. With respect to the staining for core SDH, the chronically stimulated fibres all became similar to normal II A fibres of peroneus longus. The 'fast' and 'slow' patterns of chronic stimulation had the same effects on the staining properties. 8. Chronically stimulated peroneus longus muscles showed a decrease in fibre diameter which corresponded, roughly, to the concomitant decrease in muscle weight.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphatases↗
PubMed1987

Effects of physiological amounts of high- and low-rate chronic stimulation on fast-twitch muscle of the cat hindlimb. I. Speed- and force-related properties.

1. Long-term electrical stimulation was given during 4 or 8 wk to the peroneal nerve of deafferented hindlimbs in hemispinalized adult cats. Four different stimulation patterns were compared: 100-Hz bursts covering 5% of daily time (F1), 10-Hz bursts covering 5% of daily time (S1), pattern S1 plus added 100-Hz bursts during 0.5% of daily time (S1F2), and, finally, only the latter 100-Hz bursts (F2), again during 0.5% of daily time. 2. During the course of chronic stimulation, frequent noninvasive measurements were made of the twitch of the ankle dorsiflexors. In a terminal acute experiment under general anesthesia, performed after 4 or 8 wk of treatment, measurements were made of isometric contractile properties (speed, force) for one of the stimulated peroneal muscles, m. peroneus longus (PerL). Thereafter, the PerL muscle was removed for further histochemical/histological analysis. 3. Findings from chronically stimulated PerL muscles were compared with three kinds of control PerL muscles: 1) those from the contralateral (control) hindlimb of chronically treated animals, 2) those from the operated side of animals that had been deafferented and hemispinalized but not subjected to chronic stimulation, 3) those from normal animals that had not been subjected to chronic treatment. With respect to the presently studied parameters, the three kinds of control muscles rendered very similar results. 4. All the presently used patterns of chronic stimulation made the PerL muscles slower with respect to twitch contraction time, half-relaxation time, and tension-frequency relation. Patterns covering 5-5.5% of daily time (F1, S1, S1F2) also caused an increase in the percentage of fibers classified as 'slow' (type I) on basis of their staining for myosin adenosine triphosphatase (ATPase). 5. Among patterns covering 5% of daily time, the change in ATPase histochemistry and the degree of physiological slowing was at least as pronounced after chronic stimulation at 100 Hz (F1) as after treatment at 10 Hz (S1). The slowing produced by pattern S1 was not more pronounced than that caused by this pattern (10 Hz) plus an equal number of pulses at 100 Hz (S1F2). 6. The slowing produced by the presently used patterns of chronic stimulation took place within the initial 2-3 wk. 7. Patterns F1 and S1 caused a decrease in maximum tetanic force as well as in mean fiber diameter.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Effects of physiological amounts of high- and low-rate chronic stimulation on fast-twitch muscle of the cat hindlimb. II. Endurance-related properties.

1. Long-term electrical stimulation was given to the peroneal nerve of deafferented hindlimbs in hemispinalized adult cats. The amount of stimulation covered 0.5-5.5% of total time per day, different in different animals. For some aspects of the present study, use was also made of cats subjected to "tonic" patterns of chronic stimulation (typically covering 50% of total time; 10, 16). 2. In a terminal acute experiment under general anesthesia, performed after 4 or 8 wk of long-term stimulation, one of the treated peroneal muscles (m. peroneus longus, PerL) was used for measurements of the resistance to contractile fatigue. The fatigue test consisted of 0.33-s bursts of motor-nerve stimulation at 40 Hz, repeated once a second for 4 min (6, 7). During this fatigue test, the evoked compound spikes of the muscle were recorded by electromyographic (EMG) techniques. Following the physiological procedures, PerL was removed for further histochemical analysis. In transverse sections, measurements of optical density were made in central regions of single fibers after staining for the activity of an oxidative enzyme, succinate dehydrogenase (core SDH). 3. Findings from chronically stimulated PerL muscles were compared with three kinds of control PerL muscles: 1) those contralateral to the stimulated ones, 2) those from the operated side of animals that had been deafferented and hemispinalized but not subjected to chronic stimulation, and 3) those from untreated normal animals. 4. Stimulation patterns covering both greater than or equal to 50% and 5-5.5% of daily time gave a marked improvement of fatigue resistance. Pulse rate seemed of little importance for these effects. The pattern covering only 0.5% of total daily time caused no increase of contractile endurance beyond that of normal muscles. 5. During the fatigue test of a control muscle (see above), the amplitude of the compound EMG spikes typically showed a marked decline. This "EMG depression" was effectively counteracted by all the present patterns of chronic stimulation, including the 0.5% pattern. 6. Fibers of chronically stimulated muscles became more similar to each other with respect to their density of core SDH staining. However, among muscles treated during 0.5-5.5% of total daily time, the degree and pattern of change in core SDH staining was not related to the amount and pattern of chronic stimulation or to the resulting degree of contractile endurance.

Animals↗
PubMed1986

Soma size and oxidative enzyme activity in normal and chronically stimulated motoneurones of the cat's spinal cord.

In normal adult cats we measured the density of staining for the activity of succinate dehydrogenase (SDH staining) in ventral horn cells of different sizes. The measurements were restricted to that part of the lumbar ventral horn (L6-L7) which is known to contain motoneurones of the peroneal nerve. A statistically significant tendency was found for the SDH staining to be denser in smaller than in larger neurones within the size range of a motoneurones (soma diameter greater than 40 microns). These results are consistent with recently published evidence for ventral horn cells of rats and qualitatively similar relationships between size and SDH staining have also been observed among skeletal muscle fibres (confirmed for mixed muscle of cat in present study). In hindlimb muscles, size as well as SDH staining are known to be markedly activity-dependent. We tested whether this is the case for peroneal motoneurones as well by analyzing the effects of chronic nerve stimulation on the properties of neurones within the appropriate region of the ventral horn. Prior to the final acute experiment, these cats had been subjected to a left-side dorsal rhizotomy and hemispinalization. By aid of a portable mini-stimulator, the left-side common peroneal nerve was activated by repetitive pulses during 50% of total time per day (intra-activity rate: 10, 20 or 40 Hz). After 8 weeks of such treatment, cell sizes as well as the densities of SDH staining showed hardly any differences between peroneal ventral horn cells of the experimental and control sides of the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Neuronal and muscle unit properties at different rostro-caudal levels of cat's motoneurone pool.

The rostrocaudal organization of motoneurones of the cat's m.peroneus longus (PerL) was investigated with respect to motoneuronal size (soma diameter) as well as muscle unit contractile properties (twitch speed, fatigue resistance, maximum force). Sizes of cell bodies were measured after retrograde labelling with horseradish peroxidase. Other properties were studied by aid of electrical stimulation of rostro-caudally distinct subfilaments of ventral roots. A weak but significant tendency was found for units to become somewhat slower and more fatigue-resistant at caudal than at more rostral levels within the pool. Neurones of different sizes and unit properties were, however, very widely intermingled at all levels of the pool. Rostro-caudally distinct root filaments gave rise to differentially located electromyographic signals in the muscle. The experimental results led to the following main conclusions: a type-specific intraspinal innervation of PerL motoneurones is unlikely to be arranged predominantly on topographical principles; and the intraspinal site of PerL motoneurones is related to the intramuscular site of their muscle fibres.

Animals↗
PubMed1985

Somatotopic relations between spinal motoneurones and muscle fibres of the cat's musculus peroneus longus.

The cat's m.peroneus longus was analyzed with respect to the somatotopic relation between the rostro-caudal site of emergence of ventral root filaments (i.e. rostro-caudal site of motoneurones) and the intramuscular distribution of innervation. Rostro-caudally distinct fractions of ventral roots were stimulated repetitively in order to deplete their respective muscle fibres of glycogen. The intramuscular position of glycogen-depleted fibres was analyzed in transverse sections from different proximo-distal levels. At each level, depleted muscle fibres were dispersed across the whole muscle. No consistent relation was found between the spinal site of origin of a ventral root filament and the proximo-distal distribution of its fibres within the pennate muscle. A significant and evident tendency was found, however, for rostral root filaments (i.e. rostral motoneurones) to innervate a greater number of muscle fibres in anterior than in posterior muscle portions. For caudal root filaments, the opposite pattern of innervation was observed.

Animals↗
PubMed1984

Effects of fast and slow patterns of tonic long-term stimulation on contractile properties of fast muscle in the cat.

Different physiological rates of 'tonic' long-term electrical stimulation (rates 5-40 Hz; activity greater than or equal to 50% total time) were delivered to the left-side common peroneal nerve of the cat hind limb. The duration of treatment was 8 weeks, and the animals had previously been subjected to a left-side hemispinalization and dorsal rhizotomy. In the absence of stimulation, these operations had no slowing or weakening effects on peroneal muscle contraction. The minimum two-pulse interval that gave a summation of tension (neuromuscular refractory period) was longer for stimulated than for non-stimulated muscles. Twitches of chronically stimulated muscles had become prolonged by more than 100%. Corresponding changes were found in the tension-frequency relation and in the 'sag'-behaviour of the stimulated muscles. There were no differences between the 'fast' (20 or 40 Hz pulse rates) and the 'slow' (5 or 10 Hz pulse rates) patterns of tonic stimulation with respect to their effects on speed-related muscle properties. Furthermore, during the period of chronic stimulation, the prolongation of twitch contraction time occurred along the same time course for the fast and slow patterns of tonic treatment. All chronically stimulated muscles had become weaker than normal. In comparison to the slow patterns, the present fast patterns of long-term activation caused (1) a smaller amount of decline in maximum muscle force, (2) a smaller twitch: tetanus ratio, and (3) the retention of a normal amount of post-tetanic potentiation of twitch size (decreased by the slow patterns). When tested by a series of 40 Hz bursts, force was better maintained in chronically stimulated muscles than in normal ones. These effects on fatigue resistance were the same for the fast and slow patterns of long-term activation. In peroneus longus muscles contralateral to the side of chronic activation, an evident impairment had commonly occurred in the capability to maintain force during tetani at the high rates needed for a maximum tetanic contraction. The results are discussed in relation to problems concerning the long-term effects of motoneuronal activity patterns on the contractile properties of their muscle units.

Animals↗