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PubMed2002

Multiple mechanisms of perichondrial regulation of cartilage growth.

We previously observed that the perichondrium (PC) and the periosteum (PO) negatively regulate endochondral cartilage growth through secreted factors. Conditioned medium from cultures of PC and PO cells when mixed (PC/PO-conditioned medium) and tested on organ cultures of embryonic chicken tibiotarsi from which the PC and PO have been removed (PC/PO-free cultures) effect negative regulation of growth. Of potential importance, this regulation compensates precisely for removal of the PC and PO, thus mimicking the regulation effected by these tissues in vivo. We have now examined whether two known negative regulators of cartilage growth (retinoic acid [RA] and transforming growth factor-beta1 [TGF-beta1]) act in a manner consistent with this PC/PO-mediated regulation. The results suggest that RA and TGF-beta1, per se, are not the regulators in the PC/PO-conditioned medium. Instead, they show that these two factors each act in regulating cartilage growth through an additional, previously undescribed, negative regulatory mechanism(s) involving the perichondrium. When cultures of perichondrial cells (but not periosteal cells) are treated with either agent, they secrete secondary regulatory factors into their conditioned medium, the action of which is to effect precise negative regulation of cartilage growth when tested on the PC/PO-free organ cultures. This negative regulation through the perichondrium is the only activity detected with TGF-beta1. Whereas, RA shows additional regulation on the cartilage itself. However, this regulation by RA is not "precise" in that it produces abnormally shortened cartilages. Overall, the precise regulation of cartilage growth effected by the action of the perichondrial-derived factor(s) elicited from the perichondrial cells by treatment with either RA or TGF-beta1, when combined with our previous results showing similar--yet clearly different--"precise" regulation by the PC/PO-conditioned medium suggests the existence of multiple mechanisms involving the perichondrium, possibly interrelated or redundant, to ensure the proper growth of endochondral skeletal elements.

Animals↗
PubMed1981

Studies of digit regeneration and their implications for theories of development and evolution of vertebrate limbs.

Simple amputation of various combinations of hindlimb digits of Notophthalmus viridescens resulted in a variety of abnormal regenerates. The abnormalities included the formation of adventitious digits and branched digits, fusion between digits, and increases and decreases in the normal number of phalanges. The type of abnormality was correlated with the proximal-distal level of amputation and with the identity of the digits removed. These results are discussed in the context of a model for normal digit formation. An important feature of this model is that the normal regeneration of separate digits is dependent upon precise and orderly interactions between different parts of the limb circumference. In the experiments we report, the disruption of these orderly interactions leads to a variety of abnormalities. In addition, the model for digit formation presented here is discussed in light of its implications for evolutionary trends in the tetrapod limb.

Amputation, Surgical↗
PubMed1983

Epigenesis in developing avian scales. I. Qualitative and quantitative characterization of finite cell populations.

Throughout a period from day 8.5 to day 12.5 of incubation of a chick embryo, a finite cell population of scale epidermis was characterized from various view points such as cellular organization, position, shape, area, number of constituent cells, density, and cell proliferation activity. In this study, the preparation of whole mount specimens was found to be quite valuable. On day 8.5, cells in the prospective scale region could be morphologically distinguished in the tarsometatarsus at a certain distance proximally away from the tarsometatarsal-phalangeal joint. --On day 9.25, about 1,100 cells became highly columnar in shape and densely associated, forming a placode structure. In both distally and proximally adjacent regions of this placode, the cells were semiquadrate in shape and loosely associated, leading to the formation of the interplacode structures. Such contrasting difference in cell organization between placode and interplacode was preserved from day 9.25 to day 11. During this period, both the area and number of constituent cells increased greatly in the placode and only slightly in the interplacode. However, cell proliferation activity was completely suppressed in the placode, and quite active in the interplacode. The activity in cell proliferation proved to be inversely correlated with the density of basal cells. Throughout the present study, it has been demonstrated that the early development of scale epidermis is achieved through a coordinated activity of the two discrete cell populations: the placode and interplacode.

Animals↗
PubMed2006

Ultrastructure of tarsal sensilla and other integument structures of two Pseudocellus species (Ricinulei, Arachnida).

Ricinuleids are one of the least investigated groups of Arachnida. In particular, knowledge of their ultrastructure is poor. Observations of the distal tarsomeres of ricinuleids show differences in their shape and equipment of surface structures. Legs I and II are used by the Ricinulei to explore their surroundings with tentative movements. The tarsomeres of these legs show similarities in shape and surface structures that distinguish them from those of legs III and IV. In this study, 11 different structures of the tarsomere surfaces of two cave-dwelling species, Pseudocellus pearsei and P. boneti from México, were investigated for the first time with scanning and transmission electron microscopy and discussed regarding their possible function: 1) a single treelike ramifying seta resembles a no pore single-walled (np-sw) sensillum; 2) setae occurring in a small number and possessing a bipartite shaft represent terminal pore single-walled (tp-sw) sensilla. The surface of the proximal half of the shaft shows small branches. The distal half has a smooth surface; 3) long setae with conspicuous longitudinal lamellae show characteristics of chemoreceptive wall pore single-walled (wp-sw) sensilla; 4) frequent small wp-sw sensilla with flat and irregular lamellae; 5) very short wp-sw sensilla occurring solitary or in groups; 6) a few short setae with smooth surface correspond to wp-sw sensilla; 7) a single short clubbed seta articulating in a flat pit is considered to be a np-sw sensillum; 8) common long setae with a pointed tip show characteristics of mechanoreceptive np-sw sensilla; 9) ventral setae with adhesive and mechanosensory function are accompanied by multicellular "class III" glands; 10) slit organs with mechanoreceptive function; and 11) dome-like tubercles with no indication of sensorial function. Several of these sensilla form a sensory field on the dorsofrontal surface which is particularly pronounced on the distal tarsomeres of legs I and II.

Animals↗
PubMed1976

The functional anatomy of the hindlimb of some African Viverridae (Carnivora).

The functional anatomy of the hindlimb of 12 species of viverrids was studied with relation to locomotion. The animals were allocated to primary locomotor categories on the basis of their anatomy and locomotion. The climbing, arboreal walking category (Nandinia binotata) is characterized by a small sacroiliac articulation, the iliopsoas inserts onto a medially located lesser trochanter and the femoral condyles are not posteriorly placed. The hindfoot is plantigrade and its structure permits considerable movement. The pads are soft and the claws retractile. Representatives of the arboreal and terrestrial walking and jumping category (Genetta genetta, G. servalina, G. tigrina) have a plantigrade forefoot and digitigrade hindfoot. The lesser trochanter is more posteriorly placed than in the climbing category. A previously undescribed muscle, the caudofemoralis profundus extends from several anterior caudal vertebrae to the femur. The tibio-astragular joint restricts supination of the foot. There is little mediolateral movement in the digitidgrade foot. The claws are retractile. In the general terrestrial walking and scrambling group (Helogale parvula, Mungos mungo, Atilax paludinosus, Bdeogale crassicauda, Herpestes ichneumon, H. sanguineus) the animals have essentially similar hindlimbs except for size differences and modifications to the feet. Helogale and Mungos have large medial epicondyles on the humerus and large terminal phalanges. Bdeogale has a vestigial first metatarsal, while Atilax can splay its digits. In all species the distal phalanges are non-retractile. The trotting category (Civettictis civetta, Ichneumia albicauda) is characterized by longer epipodials and metapodials and a more proximal position of muscle bellies. Most of the adaptations minimize rotation, adduction and abduction of the leg and supination of the foot. The metatarsals are closely adjoined and the distal phalanx is stout and non-retractile. There appear to be two levels of locomotory adaptation. Major adaptations affect the whole appendicular skeleton and are used to assign animals to primary locomotor categories. Minor adaptations occur mainly in the foot and indicate the more specific habits of the animal.

Africa↗
PubMed1994

Properties of twitch motor units of the ankle extensor muscles in the bullfrog Rana catesbeiana.

A study of the mechanical properties of the twitch motor units in the ankle extensor muscles of bullfrogs was undertaken to expand our view of the diversity of motor unit properties among vertebrates. Two muscles were chosen that represent a wide range of extensor function: the plantaris longus (PL) is a large muscle providing most of the force for ankle extension in hopping and swimming, and the tibialis posticus (TP) is relatively small and may act as an ankle stabilizer or be primarily postural in function. Both muscles have highly fatigable motor units, but also some (especially in TP) low or non-fatigable ones. Mean tetanic tensions of motor units in both muscles are relatively large as compared with those of mammals but are especially large in PL. No clear correlations were found between contraction times and either motor unit tetanic tensions or fatigability, nor did the motor units fall into clearly defined types based on any functional parameters. Overall contraction and relaxation times are slow compared with those of mammals and are somewhat slow compared to those of other frogs; unlike results from earlier studies, the large units of PL are slower than the small units of TP. This results in PL units reaching fused tetani at lower stimulus frequencies. The twitch/tetanus and force/frequency ratios in PL motor units are much larger than those of TP, giving PL units greater relative forces at lower stimulus rates. These results are discussed in the context of motor unit function.

Animals↗
PubMed2001

The morphological basis of hallucal orientation in extant birds.

The perching foot of living birds is commonly characterized by a reversed or opposable digit I (hallux). Primitively, the hallux of nonavian theropod dinosaurs was unreversed and lay parallel to digits II-IV. Among basal birds, a unique digital innovation evolved in which the hallux opposes digits II-IV. This digital configuration is critical for grasping and perching. I studied skeletons of modern birds with a range of hallucal designs, from unreversed (anteromedially directed) to fully reversed (posteriorly directed). Two primary correlates of hallucal orientation were revealed. First, the fossa into which metatarsal I articulates is oriented slightly more posteriorly on the tarsometatarsus, rotating the digit as a unit. Second, metatarsal I exhibits a distinctive torsion of its distal shaft relative to its proximal articulation with the tarsometatarsus, reorienting the distal condyles and phalanges of digit I. Herein, I present a method that facilitates the re-evaluation of hallucal orientation in fossil avians based on morphology alone. This method also avoids potential misinterpretations of hallucal orientation in fossil birds that could result from preserved appearance alone.

Animals↗
PubMed1993

The effect of position of immobilisation on resting length, resting stiffness, and weight of the soleus muscle of the rabbit.

The extent of immobilisation-induced adaptations of muscle length and muscle weight is known to be profoundly influenced by the position (or length) at which the muscle is immobilised. However, the effect of the full range of positions of immobilisation on subsequent adaptations of muscle length and weight has not yet been investigated. To examine further the effect of position of immobilisation, we used cast-immobilisation of the hind limbs of 23 rabbits, in various positions between full plantar flexion and full dorsiflexion. Six muscles from non-immobilised rabbits were used as the controls. After 10 days of immobilisation, the wet weight of the soleus muscle and the resting length and resting stiffness of the soleus muscle-tendon unit were determined. Immobilisation in a shortened position was associated with a significantly greater decrease in length and weight than was immobilisation in a lengthened position. In addition, immobilisation produced significant increases in the resting stiffness of muscle-tendon units, although there was no evidence of a position-dependent increase in stiffness. Muscle weight was influenced by the position of immobilisation in a nonlinear way. The data support the views that the pre-immobilisation resting length of the muscle represents a threshold length and that immobilisation at lengths longer than this retards immobilisation-induced atrophy.

Animals↗
PubMed1994

Effects of immobilization on Achilles tendon healing in a rat model.

The aim of this study was to evaluate the effects of immobilization and mobilization on the functional and biomechanical recovery of injured Achilles tendons. Male Sprague-Dawley rats were allocated randomly into four groups: (a) sham operation, (b) division only (surgical transection of the Achilles tendon without immobilization), (c) "dummy" external fixation (division of the Achilles tendon and application of Kirschner wires), and (d) rigid external fixation (division of the Achilles tendon and immobilization with Kirschner wires connected by two triangular frames). All procedures were performed on the right lower limb; the left, uninjured, lower limb served as an internal control. Kirschner wires and external fixators were removed on day 12. Functional performance was determined from measurements of hind pawprints of rats walking preoperatively and on postoperative days 1, 3, 5, 7, 9, 11, 13, and 15. On day 15, the animals were killed and biomechanical evaluations were performed on both the injured and the uninjured Achilles tendon constructs. No functional or mechanical deficits were observed in the sham-operation group. Animals subjected to division of the Achilles tendon had an initial functional deficit that returned to near normal by day 15. The application of Kirschner wires was associated with an impairment of the functional performance of the rat as well as of the mechanical properties of the tendon-bone constructs. Immobilization by connection of the Kirschner wires to an external frame had an additional, highly significant (p < 0.001) detrimental effect on the functional and mechanical recovery of Achilles tendon-calcaneal complexes.

Achilles Tendon↗
PubMed1990

Quantification of fluid changes in rat leg joints with adjuvant arthritis by a one-dimensional magnetic resonance imaging experiment.

A simple and reliable method for quantifying the fluid content and characterizing the tissue T2 relaxation properties of animal extremities has been devised. This one-dimensional magnetic resonance imaging experiment, applied to the adjuvant arthritis model in rats, provides a useful, noninvasive monitor of the course of the disease in vivo. Tissue is characterized through the analysis of the biexponential T2 decay of the NMR-active hydrogen in the rat leg joint tissue. Long and short T2 components are identified, both of which are sensitive to the arthritic process. The long component is suggested to come from edema and increases by a factor of ca. 9 during the course of the disease, whereas the short T2 component may represent cellular influx into the joint and increases by a factor of ca. 3. These changes correlate with the severity of the disease and can be used to monitor therapeutic response. The main advantage of the technique over the more traditional two-dimensional imaging approach is that only one spatial variable has to be resolved, resulting in shorter imaging time.

Animals↗
PubMed1991

External recording of twitch time course in cat ankle muscles.

In chronic experiments concerning the activity-dependent plasticity of muscle properties, a simple and noninvasive method was used for monitoring changes of twitch speed in conscious adult cats. The animals had been provided with implanted electrodes for nerve stimulation, and a hand-held force transducer was pressed against the fully extended ankle joint while single test pulses were delivered to the common peroneal nerve. In the present report, this technique for the recording of ankle twitches is subjected to critical analysis and evaluation. The measurements were highly reproducible with respect to contraction time (time-to-peak) but less so for half-relaxation time and twitch amplitude; other methods should be used for the long-term monitoring of contractile force. The total force (torque) of the ankle twitch was mainly produced by tibialis anterior (about 45%), peroneus longus (PerL; 27%) and extensor digitorum longus (23%). The ankle twitch produced by PerL alone had about the same contraction time as that of all the muscles together. Among muscles that had become changed as a result of long-term electrical stimulation there was, in general, a good correspondence between the contraction times from simple external recordings of ankle twitches and those separately measured for PerL under general anesthesia (force transducer then directly connected to PerL tendon).

Animals↗
PubMed1992

Loss and renewal of thick myofilaments in glucocorticoid-treated rat soleus after denervation and reinnervation.

Denervation of rat soleus muscle and simultaneous administration of high doses of corticosteroids for 7 days caused marked muscle fiber atrophy and selective loss of thick myofilaments from many muscle fibers by light and electron microscopy. Myosin heavy chain/actin ratios were greatly reduced on polyacrylamide gel electrophoresis. Nerve crush instead of cut permitted reinnervation after 2 weeks and demonstrated the reversibility of the muscle changes within a week after reinnervation. There was formation of new thick filaments and their reintegration into myofibrils without further breakdown, although large areas of Z-disc streaming appeared. The mechanism of A-band breakdown remains obscure, but it presumably starts with limited proteolysis and continues with disaggregation of myosin molecules. This is consistent with our observation that the muscle fibers retain a relatively good reactivity to antibodies against myosin heavy chain 1 week after denervation and corticosteroid administration. A syndrome recalling these experiments is seen in severely asthmatic patients receiving corticosteroids and pharmacologically paralyzed for mechanical respiration.

Actin Cytoskeleton↗
PubMed1995

Treatment of arthritis in Lewis rats by a monoclonal antibody against alpha beta T cell receptor: differential sensitivity of Yersinia-induced arthritis versus adjuvant arthritis.

Lewis rats experimentally infected with Yersinia enterocolitica develop sterile arthritis similar to Yersinia-associated reactive arthritis in humans. To investigate the putative role of alpha beta T cells in the pathogenesis of Yersinia-induced arthritis (YIA) rats were treated with the monoclonal antibody (mAb) R73 mAb directed against the rat alpha beta T cell receptor. In spite of reduction of alpha beta T cells in peripheral blood and in liver lesions of Yersinia-infected rats this serotherapy had no suppressive effect on YIA. Moreover, R73 mAb treatment had no influence on the number of alpha beta T cells in the inflammed synovial tissue. In contrast, R73 mAb serotherapy in Mycobaterium tuberculosis-immunized rats blocked development of adjuvant arthritis (AA) and suppressed the presence of alpha beta T cells in the synovial tissue. These results suggest fundamental differences between the immunopatho-mechanism of YIA caused by bacterial infection and AA induced by bacterial immunization and known to be T cell mediated. These data might have consequences for putative serotherapy of arthritis in humans.

Animals↗
PubMed1998

Effects of thrombospondin-1 on disease course and angiogenesis in rat adjuvant-induced arthritis.

Leukocyte extravasation into the synovium is important in rheumatoid arthritis (RA). Thrombospondin (TSP)-1 mediates cell adhesion and migration and inhibits angiogenesis, and it has been implicated in RA. However, little information is available on the role of TSP-1 in arthritis-associated inflammation and neovascularization. Therefore, we analyzed the effects of TSP-1 in adjuvant-induced arthritis (AIA), a rat model for RA. Hydron pellets containing TSP-1 were implanted in one ankle of AIA rats post-adjuvant injection, while the contralateral ankle received sham implants. Body weight loss and joint swelling were determined in comparison to nonimplanted AIA controls. In addition, synovial vessel counts were obtained in TSP-1-versus sham-implanted ankles of the same rat. The implantation of TSP-1 pellets into one ankle resulted in an enhancement of swelling in both ankles. Furthermore, TSP-1 exhibited a biphasic modulatory effect on synovial vessel counts (P < 0.05). In conclusion, TSP-1 implanted into one ankle of AIA rats may augment the severity of the disease. One possible explanation, among others, for the modulating effect of TSP-1 on inflammation may be its effect on arthritis-related angiogenesis.

Animals↗
PubMed2002

Electromyographic activity patterns of ankle flexor and extensor muscles during spontaneous and L-DOPA-induced locomotion in freely moving neonatal rats.

In rats, hindlimb postural and locomotor functions mature during the first 3 postnatal weeks. Previous evidence indicates that maturation of descending monoaminergic pathways is important for the postnatal emergence of locomotion with adequate antigravity postural support. Here we have studied the effect of the monoamine precursor L-DOPA on locomotor activity in freely moving postnatal rats (7-9 days old) using electromyographic recordings from ankle extensor (soleus) and flexor (tibialis anterior or extensor digitorum longus) muscles. Before pharmacological treatment, both muscles were usually silent at rest, and during spontaneous movements there was a high degree of coactivation between the two antagonists. This was due to a longer electromyographic (EMG) burst duration in flexors, which partly overlapped with the extensor burst. L-DOPA administration (150 mg/kg) resulted in a marked increase in postural tonic EMG activity in extensors which appeared gradually within 10 min after injection and was sufficient for the pups to maintain a standing posture with the pelvis raised above ground. Thereafter, episodes of locomotion characterized by rhythmic reciprocal bursts of EMG activity in flexor and extensor muscles were seen. The L-DOPA-induced rhythmic EMG pattern was also seen in postnatal rats subjected to a midthoracic spinal cord transection, indicating that the effect of L-DOPA on motor coordination is exerted primarily at the level of the spinal pattern generator. Analysis of EMG burst characteristics showed that the pattern of L-DOPA-induced locomotion in both intact and spinalized postnatal rats resembled in some respects that observed in adults during spontaneous locomotion. The appearance of reciprocal activation during L-DOPA-induced locomotion in neonates was primarily due to a shortening of the EMG burst duration in flexors, which reduced the degree of antagonist coactivation. These results show that the spinal cord has the potential to produce coordinated overground locomotion several days before such movements are normally expressed in the freely moving animal.

Animals↗
PubMed1993

Control of torque direction by spinal pathways at the cat ankle joint.

To study the biomechanics of the calcaneal tendon's complex insertion onto the calcaneus, we measured torque-time trajectories exerted by the triceps surae and tibialis anterior muscles in eight unanesthetized decerebrate cats using a multi-axis force-moment sensor placed at the ankle joint. The ankle was constrained to an angle of 110 degrees plantarflexion. Muscles were activated using crossed-extension (XER), flexion (FWR), and caudal cutaneous sural nerve (SNR) reflexes. Torque contributions of other muscles activated by these reflexes were eliminated by denervation or tenotomy. In two animals, miniature pressure transducers were implanted among tendon fibers from the lateral gastrocnemius (LG) muscle that insert straight into the calcaneus or among tendon fibers from the medial gastrocnemius (MG) that cross over and insert on the lateral aspect of calcaneus. Reflexively evoked torques had the following directions: FWR, dorsiflexion and adduction; SNR, plantarflexion and abduction; and XER, plantarflexion and modest abduction or adduction. The proportion of abduction torque to plantarflexion torque was always greater for SNR than XER; this difference was about 50% of the magnitude of abduction torque generated by tetanic stimulation of the peronei. During SNR, pressures were higher in regions of the calcaneal tendon originating from MG than regions originating from LG. Similarly, pressures within the MG portion of the calcaneal tendon were higher during SNR than during XER, although these two reflexes produced matched ankle plantarflexion forces. Selective tenotomies and electromyographic recordings further demonstrated that MG generated most of the torque in response to SNR, while soleus, LG, and MG all generated torques in response to XER.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Coordination between head and hindlimb motions during the cat scratch response.

Coordination between motions of the head and the hindlimb paw ipsilateral to the stimulated pinna were assessed during the scratch cycle in freely moving cats. Motor patterns were determined by electromyographic (EMG) recordings made from epimysial-patch electrodes surgically implanted on the biventer cervicis (BC), complexus (CM), obliquus capitis inferior (OC), and splenius (SP) muscles and by fine-wire EMG electrodes implanted in two ankle muscles, medial gastrocnemius (MG), and tibialis anterior (TA). To assess head motions during the three phases of the scratch cycle (precontact, contact, postcontact), several responses were filmed, and in some cats an in vivo force transducer was implanted on an ankle extensor muscle (MG or plantaris, PL) to determine the tension profile during the scratch cycle. During the scratch cycle, the head's trajectory was usually characterized by a small oscillation in which the head was pushed away during paw contact (as hindlimb joints extended) and then repositioned during the noncontact phases (as hindlimb joints flexed). Neck muscle activity did not occur during all responses or during all cycles of a single multicycle scratch response, and when it occurred, neck muscle EMG was characterized as phasic (a single burst during the cycle) or tonic (low-level activity during the entire cycle). Neck muscles ipsilateral (i) to the scratching limb exhibited phasic bursts more than contralateral (c) muscles, and phasic activity was most frequently observed in the iBC, iSP, iOC, and cOC muscles. The cOC was reciprocally active with the ipsilateral muscles, and its burst coincided with the postcontact phase and the ankle flexor (TA) burst. The ipsilateral muscles (iOC, iSP, iBC) were active during paw contact, and the termination of all three bursts occurred synchronously just after peak tension of the ankle extensor was reached. The iBC was active before the onset of paw contact and may have been responsible for repositioning the head, along with the cOC, during the precontact phase. The iOC became active after the onset of paw contact (22 ms) and was recruited more often when the peak extensor tendon force was high (10-16 N). The iSP, in contrast, was active during the contact phase of most scratch cycles examined and its recruitment appeared to be unrelated to tendon forces. Our data suggest that phasic neck muscle activity is not obligatory during the cat scratch response, but is related to certain conditions such as a higher than average tendon force of an ankle extensor during contact and the need to reposition the head during the noncontact phases of the cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Dynamic changes in the receptive field properties of spinal cord neurons with ankle input in rats with chronic unilateral inflammation in the ankle region.

The aim of this study was to determine the discharge and receptive field properties of spinal cord neurons with ankle input in spinal segments L4-6 in the rat, both under control conditions and during the course of an adjuvant-induced unilateral inflammation in the ankle. The extent of receptive fields in the skin and deep tissue was assessed using brush, pinch and compression stimuli. Neurons were categorized as nociceptive-specific or wide-dynamic-range neurons on the basis of their response thresholds and responses to suprathreshold stimuli. At all stages of inflammation (2, 6, 13 and 20 days post inoculation) the population of neurons with ankle input showed differences from the population of neurons with ankle input in control rats. There was a reduction in the number of neurons that appeared as nociceptive specific and a concomitant increase in the number of neurons showing a wide-dynamic-range response profile. The receptive fields of the neurons with ankle input were markedly larger in rats with inflammation in the ankle region and mainly spread proximally on the ipsilateral hindlimb and also to the abdomen and tail in some cases. There was also an increase in the number of neurons with contralateral excitatory inputs. The mechanical thresholds at the ankle joint and proximal parts of the ipsilateral hindlimb were less in arthritic rats than in controls. The proportion of spontaneously active neurons was also increased in rats during the initial and later stages of inflammation, although there was no significant increase in the mean spontaneous discharge frequency. These data show that there are long-term changes in the receptive field and response properties of neurons in intact rats with chronic unilateral adjuvant-induced inflammation similar to those described previously in spinal cats with acute inflammation (Neugebauer and Schaible 1990). It is presumed that similar afferent and spinal mechanisms are at work under acute and chronic inflammatory conditions which produce hyperexcitability in spinal neurons with joint input.

Animals↗