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At least 883 records · Page 49Linked to original sources
PubMed1993

The distal hindlimb musculature of the cat: multiaxis moment arms at the ankle joint.

The cat hindlimb muscles have been classified, traditionally, as flexors and extensors, based on their actions in the parasagittal plane and their patterns of recruitment during locomotion and reflex responses. This study provides a detailed examination of the relative magnitudes of the various moment arms of the cat ankle muscles and the interdependent effects of position in the various axes of motion. We used a method based on observing small sliding movements of tendon in response to small angular displacements of the joint. Surprisingly, we found that the ankle joint of the cat permits substantial motion in three axes (eversion/inversion and abduction/adduction as well as extension/flexion) and many muscles crossing the ankle joint have their largest moment arms about axes other than extension/flexion. These moment arms often depended on the joint position in the axis of the moment arm and, to a lesser degree, on the extension/flexion angle as well. For some muscles (notably peroneus longus) there was sufficient variability that the predominant action in neutral posture (axis with the largest moment arm) could change from animal to animal, which may be related to heterogeneities of locomotor and reflex recruitment reported in the companion paper.

Animals↗
PubMed1985

Weight bearing: its lack of effect on fracture healing.

The load transmitted through fresh fractures of the tarsometatarsus of adult chickens was varied by 40% more, or less, than the body weight to determine the effect of load-bearing on fracture healing. The healing fracture was examined for size and strength at 14 days, but no significant differences were detected in any group. The technique was sensitive enough to detect the differences between healing fractures at 7, 10 and 14 days. In this experiment load transmission was not found to be an important factor in fracture healing.

Animals↗
PubMed1988

Excitability changes of ankle extensor group Ia and Ib fibers during fictive locomotion in the cat.

The present study examines the modulation of gastrocnemius-soleus (GS) monosynaptic reflexes as well as the intraspinal threshold changes of GS group I primary afferent terminals ending in the intermediate and motor nuclei during fictive locomotion in high decerebrate cats. The amplitude of the monosynaptic reflexes (MSR's) evoked in the medial gastrocnemius by stimulation of the lateral gastrocnemius nerve was increased during the extensor (E) phase, decreased during the flexion (F) phase of the step cycle and remained transiently increased after spontaneous episodes of fictive stepping. The intraspinal threshold of populations and of single group Ia GS afferent fibers ending in the motor pool, as well as of single Ia and Ib fibers ending in the intermediate nucleus, showed a sustained reduction during the episodes of fictive locomotion with superimposed cyclic changes in phase with the step cycle. During fictive walking and trotting the reduction of the intraspinal threshold of both Ia and Ib fiber terminals was maximal during the middle or late portion of the F-phase. During fictive gallop elicited by stimulation of the superficial peroneus nerve, the decrease in the intraspinal threshold of the Ia afferent fibers occurred however in phase with the activity of the GS motoneurons. During episodes of fictive locomotion slow, sustained negative DC potential shifts lasting tents of seconds, reflecting an increase in the extracellular potassium concentration were recorded at the base of the dorsal horn and in the intermediate nucleus. The present findings support the existence of tonic and phasic depolarization of the intraspinal terminals of GS group Ia and Ib primary afferents during spontaneous fictive locomotion. It is suggested that accumulation of potassium ions in the extracellular space contributes mainly to the sustained depolarization of group I fibers. The phasic depolarization would be mostly due to the activation of specific sets of interneurons and may, in the case of Ia fibers, contribute to the cyclic modulation of the MRS elicited during fictive locomotion.

Afferent Pathways↗
PubMed1992

Cultured embryonic bone shafts show osteogenic responses to mechanical loading.

Pairs of 17-day embryonic chick tibiotarsi were removed and maintained in organ culture. One of each pair was subjected to a single 20-minute period of intermittent loading at 0.4 Hz, producing peak longitudinal compressive strains of 650 microstrain (mu epsilon). In the 18-hour culture period following loading, alkaline phosphatase levels in the osteoblasts of the loaded tibiotarsi were maintained whereas in controls they declined. In situ hybridization using a collagen type I cRNA riboprobe showed a substantial increase in expression of mRNA for collagen type I in the periosteal tissue of bones that were cultured for 18 hours after loading compared with that in similarly cultured controls and bones cultured for 4 hours. These results demonstrate that appropriate loading of embryonic chick bones in organ culture elicits adaptive regulation of matrix synthesis as evidenced by increased expression of the gene for type I collagen and alkaline phosphatase activity. This model may be useful as it must contain all the obligatory steps between strain change in the matrix and modified osteogenic activity.

Adaptation, Physiological↗
PubMed1993

Effect of etodolac on type-II collagen-induced arthritis in mice.

We tested the effect of etodolac on the development of type-II collagen-induced arthritis in DBA/1J mice. It was administered orally once daily for 35 days after the primary immunization with type-II collagen. Etodolac (10 mg/kg) significantly inhibited the development of signs of arthritis on day 28 to day 35. Indomethacin (1 mg/kg) also significantly inhibited it on day 29 to day 34. Radiographic examination showed that etodolac (10 mg/kg) significantly prevented the development of osteopenia, bone erosion and new bone formation of the joints on day 35, while indomethacin (1 mg/kg) significantly prevented only the development of bone erosion. Histopathological examination showed that both etodolac (10 mg/kg) and indomethacin (1 mg/kg) significantly prevented the development of synovitis, erosion of cartilage of the joints and bone destruction of the limbs on day 35. Etodolac and indomethacin did not affect the serum level of anti-type-II collagen antibodies. These results suggest that etodolac and indomethacin suppress type-II collagen-induced arthritis without affecting humoral immune responses.

Animals↗
PubMed1986

Bone modeling during growth: dynamic strain equilibrium in the chick tibiotarsus.

Bone loading was quantified, using in vivo strain recordings, in the tibiotarsus of growing chicks at 4, 8, 12, and 17 weeks of age. The animals were exercised on a treadmill at 35% of their maximum running speed for 15 minutes/day. In vivo bone strains were recorded at six sites on the tibiotarsus. Percentages of the bone's length and a percentage of top running speed were used to define functionally equivalent sites on the bone, and a consistent exercise level over the period of growth was studied. The pattern of bone strain defined in terms of strain magnitude, sign, and orientation remained unchanged from 4-17 weeks of age, a period when bone mass and length increased 10-fold and threefold, respectively. Our findings support the hypothesis that bones model (and remodel) during growth to achieve and maintain a similar distribution of dynamic strains at functionally equivalent sites. Because strain magnitude and sign (tensile versus compressive) differed among recording sites, these data also suggest that cellular responses to strain-mediated stimuli differ from site to site within a bone.

Animals↗
PubMed1989

Eicosanoic fatty acid reduction in the tibiotarsus of biotin-deficient chicks.

Day-old male broiler chicks (Hubbard x Hubbard) were fed a purified diet containing biotin at 0 microgram/kg of diet (biotin-deficient) or 500 micrograms/kg of diet (biotin-adequate). Biotin-deficient (BD) chicks had decreased growth and feed efficiency and greater twisted leg and dermatitis symptoms than biotin-adequate (BA) chicks. Lipids in cortical bone of the tibiotarsi in BD chicks contained higher levels of linoleate, gamma-linolenate, and alpha-linolenate. Prostaglandin precursors, dihomo-gamma-linolenate (20:3 omega 6), arachidonate (20:4 omega 6), and eicosapentaenoate (20:5 omega 3) were all lower in BD chicks compared with BA chicks. Periosteal bone appositional and bone formation rates, and percent new bone formation were reduced in the tibiotarsi of BD chicks. Anatomically there were two different bone modeling patters at the mid-diaphysis. The cortex was thickest laterally in chicks fed the BA diet and thickest medially in chicks fed the BD diet. The quantitative differences in bone growth and the distinct bone modeling patterns, coupled with corresponding decreases in PG precursors, suggest that biotin deficiency may alter bone growth and modeling via a PG-dependent mechanism.

Animals↗
PubMed2000

Fractographic examination of racing greyhound central (navicular) tarsal bone failure surfaces using scanning electron microscopy.

The greyhound is a fatigue fracture model of a short distance running athlete. Greyhounds have a high incidence of central (navicular) tarsal bone (CTB) fractures, which are not associated with overt trauma. We wished to determine whether these fractures occur because of accumulation of fatigue microdamage. We hypothesized that bone from racing dogs would show site-specific microdamage accumulation, causing predisposition to structural failure. We performed a fractographic examination of failure surfaces from fractured bones using scanning electron microscopy and assessed microcracking observed at the failure surface using a visual analog scale. Branching arrays of microcracks were seen in failure surfaces of CTB and adjacent tarsal bones, suggestive of compressive fatigue failure. Branching arrays of microcracks were particularly prevalent in remodeled trabecular bone that had become compact. CTB fractures showed increased microdamage when compared with other in vivo fractures (adjacent tarsal bone and long bone fractures), and ex vivo tarsal fractures induced by monotonic loading (P < 0.02). It was concluded that greyhound racing and training often results in CTB structural failure, because of accumulation and coalescence of branching arrays of fatigue microcracks, the formation of which appears to be predisposed to adapted bone.

Adaptation, Physiological↗
PubMed1998

Lead concentration in the bones of the feral pigeons (Columba livia): sources of variation relating to body condition and death.

This paper reports on lead concentrations in the tarsometatarsi of 84 individuals of adult feral pigeons Columba livia found dead or experimentally captured in Bratislava, Slovakia. The interrelationships between lead concentrations and time of death, place of death, body measurements, sex, condition, and plumage phenotype were investigated. Size and shape of pigeons was not correlated with bone lead contamination. Sex and plumage color and pattern were slightly associated with variation in bone lead levels, females and melanic (urban) phenotypes tending to have higher bone lead concentrations than males and blue-bar (wild) individuals. Birds with antibodies to chlamydiae did not contain significantly higher lead concentrations in the tarsometatarsi than birds without antibodies. Concentration of lead in tarsi was significantly higher in birds dying in winter, compared to birds dying at the end of summer. Chronic lead poisoning probably causes mortality in pigeons in winter. The natural stressor, cold weather, has the capability of exacerbating the effects of lead poisoning, and the mortality is due to lead exposure coupled with cold stress.

Analysis of Variance↗
PubMed2003

An MR-compatible device for the in situ assessment of isometric contractile performance of mouse hind-limb ankle flexors.

The goal of the present study was to develop and evaluate an isometric dynamometer for measuring mouse ankle flexor torque after electric stimulation of the nerve. The dynamometer was to be used within an magnetic resonance (MR) apparatus and should require minimal surgical intervention. To quantify the effect of the magnetic field on contractile parameters, measurements were performed both outside and inside the MR apparatus. The effect of magnetic field gradient switching that accompanies rapid MR scanning was tested also. The set-up required no surgical intervention except for chronic implantation of an electrode. The dynamometer has a high mechanical frequency response (270 Hz). Measured muscle strengths were identical outside and inside the MR scanner. However, during fast magnetic field gradient switching, the variability increased and the measured strength decreased slightly (7%). The noise level of the dynamometer (0.02-0.03 N.mm) was low compared with the strength of the dorsal flexors (2 N.mm). Fast gradient switching increased the noise level (0.07 N.mm). The dynamometer had no observable adverse effects on the quality of the MR images of the mouse hind limb. We conclude that the dynamometer enables accurate measurements of mechanical muscle performance during exercise protocols within an MR apparatus under physiological conditions.

Animals↗
PubMed2005

Analysis of avian bone response to mechanical loading-Part one: Distribution of bone fluid shear stress induced by bending and axial loading.

Mechanical loading-induced signals are hypothesized to be transmitted and integrated by a bone-connected cellular network (CCN) before reaching the bone surfaces where adaptation occurs. Our objective is to establish a computational model to explore how bone cells transmit the signals through intercellular communication. In this first part of the study the bone fluid shear stress acting on every bone cell in a CCN is acquired as the excitation signal for the computational model. Bending and axial loading-induced fluid shear stress is computed in transverse sections of avian long bones for two adaptation experiments (Gross et al. in J Bone Miner Res 12:982-988, 1997 and Judex et al. in J Bone Miner Res 12:1737-1745, 1997). The computed fluid shear stress is found to be correlated with the radial strain gradient but not with bone formation. These results suggest that the radial strain gradient is the driving force for bone fluid flow in the radially distributed lacunar-canalicular system and that bone formation is not linearly related to the loading-induced local stimulus.

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↗
PubMed1993

C-fos expression in rat lumbar spinal cord following peripheral stimulation in adjuvant-induced arthritic and normal rats.

Our previous data reported a maximal expression of the c-fos immediate-early gene in the lumbar spinal cord of the non-stimulated polyarthritic rat neurons, three weeks after Freund's adjuvant injection. The present study utilises c-fos expression to judge the reactivity of spinal neurons to calibrated mechanical pressure applied to the ankle joint, in both normal and arthritic rats under ketamine anesthesia. The results indicate that the number of Fos-like immunoreactive neurons (1) is slightly decreased in ketamine-anesthetized non-stimulated arthritic rats as compared to the non-anesthetized non-stimulated ones, (2) is significantly higher in both stimulated normal and arthritic animals as compared to non-stimulated animals, particularly in laminae I, II, V and VI of L3 and L4, and (3) is significantly increased in stimulated arthritic as compared to stimulated normal rats, in all laminae of lumbar spinal segments. The appearance of 'basal' Fos labeling during the adjuvant-induced arthritic disease and the increased number of Fos-like immunoreactive neurons in stimulated arthritic rats compared to stimulated normal animals indirectly suggests that these neurons are abnormally active and thus involved in the hyperalgesia of arthritic disease. Therefore the use of Fos-like immunoreactivity in the chronic pain model seems to be an appropriate tool to study possible effects of various pharmacological compounds, such as analgesics and anti-inflammatory drugs.

Anesthesia↗
PubMed1993

The effects of capsaicin, bradykinin, PGE2 and cicaprost on the discharge of articular sensory receptors in vitro.

The responses of articular sensory receptors to capsaicin, bradykinin, PGE2, and the selective IP-receptor agonist cicaprost were studied in a rat isolated hindlimb in vitro preparation. Long-term maintenance of normal sensory receptor function was achieved in vitro under conditions of combined superfusion and slow perfusion. Response characteristics to mechanical or chemical stimuli on articular sensory receptors identified in this study did not differ to those reported in vivo. This preparation lacks complex effects mediated via spinal or central reflex mechanisms and allows greater control over the physiological environment of the receptors being studied. These results support the conclusion that the effects of capsaicin, bradykinin and the prostanoids are mediated by distinct pharmacological receptors associated with articular sensory nerve endings. The potent potentiating effects of cicaprost on bradykinin-induced excitation suggests that these actions are mediated via IP-receptors.

Animals↗
PubMed1996

Spinal release of immunoreactive dynorphin A(1-8) with the development of peripheral inflammation in the rat.

Microprobes bearing immobilised antibodies to dynorphin A(1-8) were used to study the basal and evoked release of this prodynorphin derived peptide in the spinal cord of urethane anaesthetised normal rats and those with a peripheral inflammation. In the absence of any active peripheral stimulus the antibody microprobes detected immunoreactive (ir)-dynorphin A(1-8) in two areas (lamina I and laminae IV-V) in the dorsal horn of the spinal cord of normal rats. With the development of unilateral ankle inflammation over 3 to 5 days following subcutaneous injections of Freund's complete adjuvant, a basal presence of ir-dynorphin A(1-8) was found in both the dorsal and ventral horn regions of both sides of the spinal cord. Lateral compression of the ankles of the normal animals did not release ir-dynorphin A(1-8) during the period of stimulation, but this neuropeptide was detected in increased amounts in the ventral horn following the stimulus. By contrast, compression of inflamed ankles produced elevated levels of ir-dynorphin A(1-8) during the period of stimulus application at three major sites in the ipsilateral spinal grey matter. The largest peak was in the deep dorsal horn/upper ventral horn (laminae VI-VII), with further sites of significant release in the mid dorsal horn (laminae II-V) and the lower ventral horn. The observation that ir-dynorphin A(1-8) is physiologically released in the ventral and deep dorsal in addition to the superficial dorsal horn of the rat suggests an involvement of dynorphins in several aspects of spinal function.

Animals↗
PubMed1986

Kinematic assessment of a functional role for recurrent inhibition and selective recruitment.

It has been proposed that recurrent inhibition, which is presumed to act more powerfully on type S than on FR or FF motoneurons, and a selective recruitment order of synergistic motoneurons may function to prevent slowly contracting muscles from impeding rapid contractions. The possibility that such mechanical interactions do occur was investigated kinematically by analysis of plantar flexion in the rat hind limb under loaded and unloaded muscle conditions. The left limb was denervated to isolate the lateral gastrocnemius-soleus nerve and muscles. Plantar flexion was induced before and after soleus denervation by posterior tibial-nerve stimulation with the ankle in one of three positions: (i) resting (unloaded), (ii) dorsiflexed (held by a restraint bar), or (iii) with ankle position set by a load applied in series to the intact Achilles tendon. With the initial ankle position near maximal dorsiflexion, peak velocities of foot movements associated with passive elastic muscle properties approached one-half or more of the values achieved by active contractile mechanisms. Under unloaded and loaded conditions, no evidence was found in support of mechanical interference by the slower contracting soleus muscle of maximal lateral gastrocnemius shortening responses. Contributions of soleus tension to foot velocity and acceleration began to emerge with loads greater than 3 N. These findings are in agreement with previous reports that the slow-contracting soleus muscle, though fully activated, cannot contribute effectively to plantar flexion movements at speeds above a critical level.

Animals↗