What is your diagnosis? Gastrocnemius enthesiopathy.
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Achilles Tendon↗
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The locomotor discharge characteristics of ankle flexor gamma-motoneurones in the decerebrate cat.
1. The discharge patterns of ankle flexor, tibialis anterior (TA), gamma-motoneurones were recorded during locomotion in the decerebrate cat. 2. At rest gamma-efferents had no background discharge. During locomotion two patterns of gamma activity could be distinguished. Most units (16) were phasically recruited with homonymous electroneurogram (ENG) activity, while the remainder (5) were tonically active throughout the step cycle. 3. The modulation of phasic units was greater (P < 0.01) than tonic neurones. Phasic units had lower (P < 0.02) mean, but higher (P < 0.01) peak, rates during the step cycle. 4. The discharge rate of both types of efferent increased around the onset of ENG activity and peaked during ENG activity, or shortly after its cessation. The conduction velocities of phasic and tonic units overlapped widely. 5. It is proposed, on the basis of muscle spindle afferent recordings during locomotion, that TA phasic and tonic units correspond to static and dynamic gamma-motoneurones, respectively. This correspondence is functionally advantageous for the role of ankle flexor muscles during locomotion. Thus phasic static gamma discharge during flexion would aid muscle contraction via increased Ia afferent activity, while tonic dynamic gamma firing would enhance Ia afferent stretch sensitivity throughout the step cycle. Such enhancement during flexion would oppose unexpected muscle lengthening while, during extension, it would contribute to reciprocal inhibition of ankle extensor muscles. 6. The results are discussed in relation to strategies of gamma usage during rhythmic movements. It is postulated that, for such behaviour, muscle contraction is accompanied by coactivity in static and dynamic gamma-motoneurones. A functional rationale is suggested for this strategy.
Action Potentials↗
Mechanical factors in the initiation of eccentric contraction-induced injury in rat soleus muscle.
1. Mechanical factor(s) associated with the initiation of eccentric contraction-induced muscle injury were investigated in isolated rat soleus muscles (n = 180; 42 protocols with 4-6 muscles per protocol). Five eccentric contractions were performed with 4 min between contractions. Three levels of peak eccentric contraction force (100, 125 and 150% of pre-injury maximal isometric tetanic tension, P0), length change (0.1, 0.2 and 0.3 muscle length, L0) and lengthening velocity (0.5, 1.0 and 1.5 L0/s) were utilized. Force was varied with stimulation frequency (10-150 Hz). The eccentric contractions were initiated at muscle lengths of 0.85 or 0.90 L0. Following the fifth eccentric contraction, the muscle was incubated in Krebs-Ringer buffer for 60 min. Peak isometric twitch tension (PT), P0, maximal rate of tension development (+ dP/dt), maximal rate of relaxation (-dP/dt), and creatine kinase (CK) release were measured prior to the five eccentric contractions and at 15 min intervals during the incubation period. Total muscle [Ca2+] was measured after 60 min incubation. 2. The mean (+/- S.E.M.) initial decline in P0 for the muscles performing the most injurious protocol was 13.6 +/- 4.8% (n = 6); P0 in control muscles immediately following performance of five isometric contractions was elevated 1.2 +/- 1.0% (n = 8). These means were different at probability, p = 0.005. Mean [ATP] in muscles immediately following the isometric control and most injurious protocols, respectively, were 16.30 +/- 1.49 and 19.84 +/- 1.38 mumol/g dry wt (p = 0.229). 3. Decrements in P0, PT, +dP/dt, and -dP/dt immediately after the injury protocol were related most closely to the peak forces produced during the eccentric contractions; greater initial declines in P0, +dP/dt and -dP/dt were also observed at higher lengthening velocities independent of peak force. Slow declines in P0 and -dP/dt during the 60 min incubation following the injury protocol were greatest for muscles performing contractions at the longer initial length. CK release was independent of all mechanical factors with the exception of lengthening velocity. CK activity at 45 and 60 min into the incubation period was greater for muscles lengthened at the highest velocity used (1.5 L0/s). Mean total muscle [Ca2+] for muscles performing the eccentric contractions was elevated by 38% over isometric control muscles but the elevation was unrelated to any of the four mechanical factors. 4. These data support the hypothesis that eccentric contraction-induced injury is initiated by mechanical factors, with muscle tension playing the dominant role.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Materials fatigue initiates eccentric contraction-induced injury in rat soleus muscle.
1. The initiation of exercise-induced muscle injury is thought to be the result of high tensile stresses produced in the muscle during eccentric contractions. Materials science theory suggests that high tensile stresses could initiate the injury during the first eccentric contraction (normal stress theory) or after multiple eccentric contractions (materials fatigue). It was the objective of this study to investigate the two possibilities. 2. Rat soleus muscles (n = 66; 11 protocols with 6 muscles per protocol) were isolated, placed in an oxygenated Krebs-Ringer buffer at 37 degrees C, and baseline measurements were made. The muscle then performed an injury protocol which consisted of between zero and ten eccentric contractions (muscle starting length = 0.90 soleus muscle length, L0; length change = 0.25 L0; velocity = 1.5 L0/s; peak force = 180% maximal isometric tetanic tension (P0); time between contractions = 4 min; total duration of the injury protocol = 40 min). At the end of the injury protocol, the muscle was incubated in buffer for 1 h; every 15 min, an isometric twitch and tetanus were performed and lactate dehydrogenase (LDH) release was measured. Total muscle [Ca2+] was measured at the end of the incubation. 3. Change-point regression analysis indicates that at 0 min into the incubation, declines in P0, maximal rate of tension development (+dP/dt), maximal rate of relaxation (-dP/dt), and muscle stiffness (dP/dx) became significantly greater after eight eccentric contractions (p < or = 0.05). No relation was found between the number of eccentric contractions performed and the LDH activity at 0 min into the incubation, although after 60 min of incubation, LDH activity in the buffer was linearly related to eccentric contraction number (p = 0.01). There was no relationship between total muscle [Ca2+] and eccentric contraction number. These findings support the materials fatigue hypothesis of exercise-induced muscle injury.
Animals↗
Ankle extensor group I afferents excite extensors throughout the hindlimb during fictive locomotion in the cat.
1. The effects of stimulating hindlimb extensor nerves (100-200 ms trains, 100 Hz, < or = 2 times threshold) during the flexor and extensor phases of the locomotor step cycle were analysed in the decerebrate, paralysed cat during fictive locomotion evoked by stimulation of the mesencephalic locomotor region. 2. Stimulation during extension of either the medial gastrocnemius (MG), lateral gastrocnemius-soleus (LGS) or plantaris (Pl) nerves was equally effective in increasing the duration and amplitude of electroneurogram (ENG) activity recorded in ipsilateral ankle, knee and hip extensor nerves. Enhancement of extensor ENG activity could be evoked with near threshold stimulation intensity and appeared within 10-40 ms of the onset of ankle extensor nerve stimulation. Stimulation of anterior biceps during extension occasionally evoked a modest increase in the duration of activity of hip, knee and ankle extensors. Stimulation of quadriceps during extension enhanced the activity of proximal extensors and soleus, but inhibited other ankle extensors. 3. Selective activation of ankle extensor Ia spindle afferents by muscle stretch also enhanced ipsilateral extension. It is argued that both muscle spindle and tendon organ afferents can contribute to the increase in extensor nerve activity evoked by group I stimulation intensity during fictive locomotion. 4. During flexion, stimulation of either the MG, Pl or LGS nerves at group I strength terminated on-going activity in ipsilateral flexors and initiated a burst of activity in ipsilateral hip, knee and ankle extensors, i.e. reset the step cycle to extension. 5. Low strength stimulation of the mixed muscle and cutaneous nerve innervating the plantar aspect of the foot produced extension enhancement and resetting similar to that evoked by group I muscle afferent stimulation. Stimulation of the cutaneous nerve supplying the dorsal aspect of the foot during extension enhanced extensor activity, and during flexion, enhanced the activity of flexors. 6. The effects reported here during fictive locomotion may also occur during overground locomotion with natural activation of group I muscle spindle and tendon organ afferents. Extensor spindle and tendon organ afferents may thus serve as an excitatory reflex system helping to shape the amplitude, duration and timing of ipsilateral extensor activity. Increased or unexpected activation of group I ankle extensor afferents or plantar foot afferents during locomotion could also compensate for increased loading of the limb.
Animals↗
Disynaptic group I excitation of synergist ankle extensor motoneurones during fictive locomotion in the cat.
1. Intracellular recording from medial gastrocnemius (MG) motoneurones was used to examine postsynaptic potentials produced by electrical stimulation of the plantaris nerve at group I strength at rest and during fictive locomotion. Fictive locomotion was evoked by stimulation of the midbrain locomotor region (MLR) in decerebrate cats or in decerebrate, acute low-spinal cats by perineal stimulation following intravenous administration of clonidine and naloxone. 2. In both MLR and spinal fictive locomotor preparations, stimulation of plantaris nerve group I afferents at rest evoked short-latency (< 2 ms) IPSPs in MG motoneurones. During the extensor phase of MLR-evoked locomotion, the same stimulation produced short-latency (1.6-1.8 ms) EPSPs. Such latencies suggest mediation by one interneurone interposed between plantaris nerve group I afferents and MG motoneurones. Non-monosynaptic, short-latency excitation was not seen at rest nor during the flexion phase of the step cycle. 3. Group I EPSPs during the extensor phase of MLR-evoked locomotion were evoked by stimulation at intensities ranging from 1.4-2 times threshold (T). The effectiveness of stimulation intensities < 1.5 T suggests that activation of group II afferents is not required to evoke disynaptic excitation. Selective activation of group Ia afferents by stretches of the Achilles tendon also produced disynaptic EPSPs during extension. 4. During fictive locomotion in spinal animals pretreated with clonidine, short-latency group I EPSPs were not seen but group I IPSPs recorded at rest disappeared or were greatly attenuated. The failure of depolarizing current to reveal group I IPSPs suggests that fictive locomotion involves an inhibition of the inhibitory interneurones that operate at rest. In both clonidine-treated spinal and MLR preparations, trains of stimuli at group I strength evoked longer-latency and slowly rising potentials that were more prominent during the flexor phase of fictive locomotion. 5. These results show a reduction in short-latency group I inhibition of synergists in both MLR and clonidine-treated spinal preparations during fictive locomotion. In addition, activation of group I afferents evokes short-latency excitation of synergists during extension in the MLR preparation. Such excitatory reflexes activated by ankle extensor group Ia and Ib afferents may form an excitatory feedback system, reinforcing on-going extensor activity during the stance phase of the step cycle.
Animals↗
Static and dynamic gamma-motor output to ankle flexor muscles during locomotion in the decerebrate cat.
In locomotion, the flexor muscles of the leg are mainly concerned with the relatively constant task of raising the foot, whereas the extensors have the more variable task of support and propulsion at different speeds. This suggests that the way in which the fusimotor system works may differ between the two muscle groups. Observations previously made of the static and dynamic gamma-motor firing patterns in the ankle extensor medial gastrocnemius (MG) have therefore been repeated in the flexor tibialis anterior (TA). One or more single gamma-motor axons, dissected from a small filament of TA nerve, were recorded simultaneously with a number of single spindle afferents in dorsal rootlets. Cats were decerebrated and locomoted spontaneously on a treadmill. Identification of each gamma-motor axon depended on relating the changes in firing caused by midbrain stimulation to the changes in static and dynamic behaviour of the spindle afferents in response to repetitive ramp and hold stretches. Static gamma axons all showed a smooth modulation in frequency, increasing in phase with muscle shortening, superimposed on a minimum frequency of about 20-30 impulses s(-1). Dynamic gamma axons showed interrupted firing with the frequency rising abruptly from zero at the onset of shortening, and falling again to zero shortly after the onset of lengthening. The frequency during the active periods was relatively constant, even when movement amplitudes varied. The basic similarity in the static and dynamic gamma discharge patterns for the two muscles suggests that the strategy of gamma-motor control is common to both flexors and extensors. The static gamma pattern is thought to be a 'temporal template' of the expected movement, effectively expanding the dynamic response range of the spindles in active movements. The dynamic gamma pattern sensitizes the primary afferents to detect the onset of muscle lengthening and to detect departures from the intended movement trajectory.
Action Potentials↗
The relative position of EDL muscle affects the length of sarcomeres within muscle fibers: experimental results and finite-element modeling.
BACKGROUND: Effects of extramuscular connective tissues on muscle force (experimentally measured) and lengths of sarcomeres (modeled) were investigated in rat. It was hypothesized that changes of muscle-relative position affect the distribution of lengths of sarcomeres within muscle fibers. METHOD OF APPROACH: The position of extensor digitorum longus muscle (EDL) relative to intact extramuscular connective tissues of the anterior crural compartment was manipulated without changing its muscle-tendon complex length. RESULTS: Significant effects of EDL muscle relative position on proximal and distal EDL forces were found, indicating changes of extramuscular myofascial force transmission. EDL isometric force exerted at its proximal and distal tendons differed significantly. Finite-element modeling showed that the distribution of lengths of sarcomeres is altered by changes of muscle-relative position. CONCLUSIONS: It is concluded that forces exerted on a muscle via extramuscular myofascial pathways augment distributions of lengths of sarcomeres within that muscle.
Animals↗
Reflex activation patterns in relation to multidirectional ankle torque in decerebrate cats.
Cutaneous reflexes have been described primarily according to their actions in the flexion/extension plane. It is shown here, by measuring electromyography and isometric force in decerebrate cats, that ankle muscles are activated in relation to their actions in the abduction/adduction plane during sural nerve (SNR) and crossed-extension (XER) reflexes. Ankle adductors (tibialis posterior, extensor digitorum longus, and flexors digitorum and hallucis longus) were active in XER, but not in SNR. Muscles producing ankle abduction (medial and lateral gastrocnemii and peroneus longus and brevis) were consistently more strongly activated in SNR than in XER. This differential pattern of muscle activation results in greater abduction torque at the ankle in SNR than in XER. These data demonstrate reflex organization in relation to the multidirectional torque generated by individual muscles.
Animals↗
Neuromuscular compartments of cat lateral gastrocnemius produce different torques about the ankle joint.
The primary purpose of this study was to establish whether the neuromuscular compartments of cat lateral gastrocnemius produce different mechanical actions on the skeletal system, by determining the contributions made by these compartments to the torques produced about the ankle joint. It was postulated that neuromuscular compartments might represent output elements of the spinal circuits. If so, they should produce unique mechanical actions. Isometric torques about the center of the ankle joint produced by the neuromuscular compartments of the cat lateral gastrocnemius were measured with a multiaxis force-moment sensor connected to the plantar surface of the foot. Individual compartment torques were elicited by activation of the primary compartment branches of the lateral gastrocnemius nerve. The magnitude of the individual torque components, and thus of the resultant torque, was significantly different between compartments. In three of the four lateral gastrocnemius compartments, significantly different torque trajectories were noted. The results, together with those from previous studies demonstrating that compartments can be activated in a task-dependent manner, suggest that neuromuscular compartments represent anatomical substrates that can be used by the nervous system for regulating movement.
Animals↗
Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan.
Partial skeletons of two new fossil whales, Artiocetus clavis and Rodhocetus balochistanensis, are among the oldest known protocetid archaeocetes. These came from early Lutetian age (47 million years ago) strata in eastern Balochistan Province, Pakistan. Both have an astragalus and cuboid in the ankle with characteristics diagnostic of artiodactyls; R. balochistanensis has virtually complete fore- and hind limbs. The new skeletons are important in augmenting the diversity of early Protocetidae, clarifying that Cetacea evolved from early Artiodactyla rather than Mesonychia and showing how early protocetids swam.
Animals↗
Evolution. The ancestry of whales.
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Animals↗
Sex-biased hatching order and adaptive population divergence in a passerine bird.
Most species of birds can lay only one egg per day until a clutch is complete, and the order in which eggs are laid often has strong and sex-specific effects on offspring growth and survival. In two recently established populations of the house finch (Carpodacus mexicanus) in Montana and Alabama, breeding females simultaneously adjusted the sex and growth of offspring in relation to their position in the laying order, thereby reducing the mortality of sons and daughters by 10 to 20% in both environments. We show experimentally that the reduction in mortality is produced by persistent and sex-specific maternal effects on the growth and morphology of offspring. These strong parental effects may have facilitated the rapid adaptive divergence among populations of house finches.
Adaptation, Physiological↗
Avian persistence in fragmented rainforest.
What factors determine the persistence of species in fragmented habitats? To address this question, we studied the relative impacts of forest deterioration and fragmentation on bird species in 12 rainforest fragments in Kenya, combining 6 years of individual capture-recapture data with measurements of current captures and museum specimens. Species mobility, as estimated from species-specific dispersal rates, and tolerance to habitat deterioration, as estimated from change in fluctuating asymmetry with increasing habitat disturbance, explained 88% of the variation in patch occupancy among eight forest bird species. Occupancy increased with mobility and with tolerance to deterioration, where both variables contributed equally to this relationship. We conclude that individual-level study, such as of dispersal behavior and phenotypic development, can predict patterns of persistence at the species level. More generally, for conservation tactics to stand a high chance of success, they should include action both within sites, to minimize habitat deterioration, and across landscapes, to maximize dispersal.
Animals↗
Distinct characteristics of resistance to Borrelia burgdorferi-induced arthritis in C57BL/6N mice.
Studies of mice infected with Borrelia burgdorferi have indicated that the severity of arthritis is influenced by the genetic composition of the host: the C3H mouse develops severe arthritis while BALB/c and C57BL/6 mice develop mild arthritis. In this study, the effects of increasing infectious dose on the severity of arthritis were determined in these three mouse strains. C3H/He mice developed severe arthritis at all infectious doses, with 100% infection requiring 200 spirochetes. In BALB/cAnN mice, arthritis severity was dependent on infectious dose; symptoms were mild with infection by 200 B. burgdorferi and progressively more severe with increasing infectious dose. Infection of BALB/cAnN mice with 2 x 10(4) B. burgdorferi resulted in arthritis with severity identical to that in C3H/He mice. Spirochete levels in rear ankle joints of C3H/HeJ and C3H/HeN mice were relatively high, as detected by PCR, and did not increase with infectious dose. Spirochete levels in joints from BALB/cAnN mice increased with increasing infectious dose to levels found in severely arthritic C3H/He mice. Thus, resistance to severe arthritis in BALB/cAnN mice was conditional: it could be overcome by high infectious dose and the arthritis became severe when high levels of B. burgdorferi were present in joints. A unique response to increasing infectious dose was seen in C57BL/6N mice, which displayed mild to moderate arthritis at all doses of B. burgdorferi tested, up to 2 x 10(5). At all infectious doses, the levels of spirochetes in ankle joints of C57BL/6N mice were high, equivalent to those found in the severely arthritic C3H/He mice. The arthritis observed in infected (C57BL/6N x C3H/HeN)F1 mice was of severity intermediate between those of the two parental strains. The finding that resistance to severe arthritis in C57BL/6N mice could not be overcome by high infectious doses and was independent of spirochete levels in joints suggested that it was mediated by a distinct mechanism from that operating in BALB/cAnN mice.
Animals↗
Effect of intermittent stretch on immobilised muscle.
When muscle is immobilised in a shortened position there is a reduction in fibre length and an increase in the proportion of connective tissue. This results in reduced muscle compliance and a loss of range of joint motion. Experiments have been carried out to determine whether short periods of stretch are effective in preventing these changes. The soleus muscle of the mouse was immobilised in a shortened position for a period of 10 days by means of a plaster cast. Every two days the cast was removed and the muscle passively stretched for a 15 minute period. It was found that this treatment prevented the connective tissue changes but did not prevent the reduction in muscle fibre length, which in itself resulted in considerable loss of range of motion.
Animals↗
Correction of angular limb deformities in foals.
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Animals↗