Outbreak of hind limb paralysis in young CFW Swiss Webster mice

An outbreak of paralysis among 16- to 20-week-old CFW Swiss Webster sentinel mice developed in one of our barrier facilities. Two months after arrival and over a period of four weeks, six of 400 mice purchased from an approved vendor, developed progressive hind limb paralysis without other clinical signs of disease. On the basis of the histopathologic changes and negative serologic test results, lymphoblastic lymphoma causing compression of the spinal cord was diagnosed. There were two leading features to this outbreak: its unusual epidemiologic presentation, and the localization of the lesions principally in the lumbar muscles. A presumptive diagnosis of retroviral infection with Abelson's murine leukemia virus (A-MuLV) was established on the basis of histopathologic and immunohistochemical findings. Little is known about retroviral status in many commercial colonies, and few users report presence of spontaneous lymphomas. This report points out complications derived from commercially available animals that carry endogenous retroviruses. It also emphasizes the need of diagnosing and reporting clusters of hind limb paralysis or lymphomas in mice to assess the prevalence and relevance of retroviral infections in commercial colonies.     

A case of fibrosarcoma on the perivertebral surface of a ferret with hind limb paralysis

A 2.5 year-old female ferret had a stiff palpable mass arising from the dorsal surface of the thoracic (T) to lumbar (L) vertebrae with paralysis of the hind limbs. By myelography the dorsal and ventral lines of contrast were not observed in the area forwarded of L3. Grossly, the tumor encircled the dorsal vertebrae. Microscopically, tumor cells were proliferated intimately and were attached to the vertebrae surface involving surrounding fatty and connective tissues. The tumor consisted of fibroblastic cells with prominent cellular atypia. The bromodeoxyuridine (BrdU) labeling index to examine cellular kinetics was high (11.8%). Based on macro and micropathological features, the present tumor was diagnosed as periosteal fibrosarcoma arising from perivertebral connective tissue.     

The incidence and properties of beta axons to muscle spindles in the cat hind limb.

The distribution of beta axons to muscle spindles in the tenuissimus and abductor digiti quinti medius (A.D.Q.M.) muscles of the hind limb of the cat was determined by testing the action of single motor axons, capable of producing extrafusal contraction, isolated in the ventral spinal roots on the discharges of individual muscle spindle primary sensory endings recorded in the dorsal spinal roots. The proportion of spindles with beta innervation was 41% in A.D.Q.M. and 30% in tenuissimus. The proportion of fast motor axons that were beta axons was 28% in the A.D.Q.M. and 11% in tenuissimus; usually each beta axon innervated a single spindle while no spindle received more than two beta axons. The beta axons were dynamic in nature and those to any one muscle tended to have slightly lower conduction velocities than the alpha axons though some overlap did occur. The extent to which beta axons can account for the fact that in isolated spindles axons selective to either nuclear bag or nuclear chain fibres are found in about equal proportions whereas a ratio of three static to one dynamic gamma axons is found electrophysiologically is discussed. An explanation for the low incidence of beta innervation previously found electrophysiologically and the considerably higher incidence found histologically is given.     

Postnatal development of node-paranode regions in two hind limb nerves of the cat

Node-paranode regions of large myelinated axons from the nerves to the lateral gastrocnemius muscle (ankle extensor) and the anterior tibial muscle (ankle flexor) were studied in the cat during postnatal development and examined with regard to the occurrence of paranodal Schwann cell Marchi-positive bodies and mitochondria. It was found, in newborn kittens with respect to both parameters, that paranodes of flexor nerve fibers, being part of the functionally more developed ankle flexor reflex arc [cf. Mellström, A. (1971). Acta Physiol. Scand., 82, 477–489], appeared more mature than did those of extensor nerve fibers, which are part of the less developed ankle extensor reflex arc. It is concluded that the maturation of large feline hind limb muscle nerve fibers runs through a “nodalization” process similar to that described earlier for feline lumbar spinal root fibers [cf. Berthold, C.-H. (1973). Neurobiology, 3, 339–352] and that this normally occurring, rather striking remodeling of the node-paranode regions is likely to be functionally significant.     

Vasomotor innervation in the hind limb muscles of the normal and 6-hydroxydopamine treated cat

Summary Vasomotor nervous distribution to arteries in the cat gastrocnemius and soleus muscles was investigated in the normal and 6-hydroxydopamine treated animal. Muscle samples were processed for the demonstration of acetylcholinesterase by a thiocholine method and for the presence of catecholamines by a formol fluorescence technique. In isolated perfused muscle preparations noradrenaline or adrenaline increased perfusion pressure while acetylcholine or isoprenaline decreased this pressure. A beaded fluorescent periarterial plexus (not visualised after reserpine treatment) was observed. Vasomotor axons, all of which were ACHE-negative, exhibited degenerative changes following 6-hydroxydopamine injection, while ACHE-positive axons outside the adventitial sheath were unaffected. No indication of cholinergic periarterial nerves was found and our evidence suggests that the vasomotor innervation is adrenergic sympathetic in nature.This work was supported by a grant from the Medical Research Council. During the tenure of a Wellcome Trust Fellowship, Dr. F. Joó is on leave of absence from Jozsef Attila University, Szeged, Hungary. The electron microscope is on permanent loan to one of us (J. D. L.) from the Wellcome Trust. We are most grateful to Mrs. G. Howells and Miss D. Morgan for technical assistance and to Mr. P. Hire for photographic help.     

The cat step cycle: hind limb joint angles and muscle lengths during unrestrained locomotion

The development of the polarity and bilateral asymmetry of the future adult zooid has been traced to their earliest morphological expression in the palleal bud of Botryllus. The account is based upon continued observation of living buds. The polarized antero-posterior and dorso-ventral axes are first expressed by the skewing of a symmetrical, hemispherical bud towards the anterior end of the parental bud. Identification of these axes is reinforced by the development of a loop-like blood circulation, the primary circulation, in the horizontal plane during the enlargement of the skewed hemisphere to form a stalked vesicle. Bilateral asymmetry is first expressed by the asymmetrical expansion of the vesicle stage. The right posterior corner of the vesicle expands further posteriorly and becomes more acute than the left posterior corner. This larger expansion persists throughout the development of the right atrial cavity, which finally expands across the mid-line to partially surround the gut. The bilateral asymmetry, expressed in the expanded vesicle, is reinforced by the development in sequence of a rounded gut rudiment and a pericardial rudiment in positions that would be expected from the asymmetry of the expanded vesicle. The first appearance of the gut rudiment occurs earlier than had been recognized previously. Conflicting accounts of the time and mode of formation of the pericardial rudiment have been clarified. The results of this study are discussed in the context of determination of bud territory, polarity and bilateral asymmetry.     

Fusimotor reflexes influencing secondary muscle spindle afferents from flexor and extensor muscles in the hind limb of the cat.

The purpose of this study was to investigate secondary muscle spindle afferents from the triceps-plantaris (GS) and posterior biceps and semitendinosus (PBSt) muscles with respect to their fusimotor reflex control from different types of peripheral nerves and receptors. The activity of single secondary muscle spindle afferents was recorded from dissected and cut dorsal root filaments in alpha-chloralose anaesthetized cats. Both single spindle afferents and sets of simultaneously recorded units (2-3) were investigated. The modulation and mean rate of firing of the afferent response to sinusoidal stretching of the GS and PBSts muscle were determined. Control measurements were performed in the absence of any reflex stimulation, while test measurements were made during reflex stimulation. The reflex stimuli consisted of manually performed movements of the contralateral hind limb, muscle stretches, ligament tractions and electrical stimulations of cutaneous afferents. Altogether 21 secondary spindle afferents were investigated and 20 different reflex stimuli were employed. The general responsiveness (i.e. number of significant reflex effects/number of control-test series) was 52.4%, but a considerable variation between different stimuli was found, with the highest (89.9%) for contralateral whole limb extension and the lowest (25.0%) for stretch of the contralateral GS muscle. The size of the response to a given stimulus varied considerably between different afferents, and, in the same afferent, different reflex stimuli produced effects of varying size. Most responses were characterized by an increase in mean rate of discharge combined with a decrease in modulation, indicative of static fusimotor drive (Cussons et al., 1977). Since the secondary muscle spindle afferents are part of a positive feedback loop, projecting back to both static and dynamic fusimotor neurones (Appelberg Et al., 1892 a, 1983 b; Appelberg et al., 1986), it is suggested that the activity in the loop may work like an amplified which, during some circumstances, enhance the effect of other reflex inputs to the system (Johansson et al., 1991 b).     

Electrical activity in sympathetic fibres to hind limb muscles of the cat produced by hypothalamic stimulation

Electrical stimulation of the "Defence Area" of the hypothalamus in anaesthetized cats was accomplished by stereotaxic placement of bipolar stainless steel electrodes; the spinal cord was sectioned at L4. The muscle blood flow in one hind limb was recorded with an electromagnetic flowmeter. Increases of between 100% and 300% were observed during hypothalamic stimulation. Electroneurographic recordings from small nerve filaments supplying tibialis anterior muscle revealed two populations of neurones whose activity was abolished by lumbar sympathectomy. It appears that the increased blood flow in skeletal muscle during stimulation of the hypothalamic "Defence Area" is brought about by a simultaneous inhibition of vasoconstrictor activity and increase in cholinergic vasodilator discharge.     

Spinal reflexes as a basis for tremor in the premammillary cat.

A maintained tremor observed in premammillary cats has been studied by varying the load attached to the soleus muscle, by electrical recording, and stimulation. The frequency and amplitude of the tremor varies widely with changes in elastic or inertial loading (springs or flywheels). These variations agree well with predictions based on the idea that the tremor is maintained by relfexes reinforcing a tendency for oscillation in a mass-spring system (which includes the elasticity of the muscle). Spinal stretch reflexes are probably responsible since a relatively fixed delay of 8.5 +/- 2.9 ms is observed between the peaks of recorded afferent and electromyographic activity. Stimulation of the lateral gastrocnemius--soleus nerve completely resets the tremor, again suggesting a reflex origin.     

Comparison of hind limb muscle mass in neonate and adult prosimian primates

Little ontogenetic data exist to indicate whether muscular organization of neonates reflects adult locomotion (e.g., leaping) or infant activities like clinging or the initial quadrupedal phase of locomotion that typifies most infant primates. In the present study, five species of primates with contrasting modes of locomotion were examined. Twenty-eight preserved neonatal and adult cadavers were studied by careful dissection of the hip, thigh, and leg muscles. Wet weights were taken of limb muscles after removal, and the muscles were combined into major functional groups (e.g., flexors, extensors) of each limb segment. Results demonstrate that the distribution of muscle mass within the thigh and within the leg are similar between neonates and adults for all species, with major groups varying by 5% or less in all but two age comparisons. Crural indices of the neonates are nearly identical to those of the adults, but leg/thigh muscle mass ratios were higher in the neonates. Species vary greatly in the percentage of adult limb segment muscle mass present in neonates, with Tarsius syrichta having the greatest percentage for all segments and two lemurids showing the least. These results primarily track differences in relative body mass at birth rather than developmental differences. The adaptive distribution of muscle, as discussed previously for adult prosimians, appears to be established at birth. Neonates of leaping species already have much larger quadriceps muscles than quadrupeds. Differences between large- and small-bodied leapers (e.g., pronounced superficial plantarflexor masses in tarsiers and pronounced deep plantarflexor masses in sifakas) also are present in neonates. Ratios of muscle mass over body mass are smaller in all neonates than in their adult counterparts, suggesting that the neonates are relatively poorly muscled, and that muscle mass must increase with positive allometry during growth.     

A kinematic and strain gauge study of the reciprocal apparatus in the equine hind limb.

Hind limb kinematics were recorded in five horses at walk and trot using an opto-electronic CODA-3 system. Simultaneously, in vivo strain in the completely tendinous peroneus tertius muscle was registered by implanted mercury-in-silastic strain gauges. The origin-insertion length patterns of the peroneus tertius were calculated from raw kinematic data and from data corrected for the error caused by skin displacement, and compared with the directly measured strain. The strain patterns calculated from externally measured kinematic data appeared to be in accordance with the directly measured strain gauge data. However, a correction for skin displacement is an obligatory prerequisite to obtain reliable results. The amplitudes of strain did not exceed 3% and appeared to be of about the same magnitude at both walk and trot.     

Extracellular potassium concentration in normal and denervated hind limb muscles of the rat

K+-sensitive electrodes with a side pore were used for measuring extracellular potassium levels in control muscles and in the gastrocnemius, extensor digitorum and soleus muscles of the rat, one, 8 and 14 days after denervation. In all cases, the extracellular potassium level was close to 5 mmol.1-1. There were no substantial differences between muscles of different functional and morphological types and between control and denervated muscles. Elevated extracellular potassium cannot therefore be the reason for increased sensory outflow of impulses observed after motor denervation.