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PubMed1987

Antagonism by methysergide of neurogenic vasoconstriction in the dog forelimb.

In the flow-regulated dog forelimb, electrical stimulation of the efferent median nerve produced frequency-dependent increases in perfusion pressure. These vasoconstrictor effects were attenuated by a large dose of phentolamine, an alpha 1 and alpha 2 blocking drug. Administration of methysergide after phentolamine completely reversed the vasoconstrictor responses to vasodilation at most frequencies of stimulation. In the absence of phentolamine pretreatment, even a lower dose of methysergide reversed or caused biphasic responses (attenuated constriction followed by dilatation) during the nerve stimulation at the lower frequencies (0.5-4.0 Hz). This lower dose of methysergide completely abolished vascular effects of exogenous 5-hydroxytryptamine (5-HT) and potentiated those of norepinephrine; hence, the antagonism by methysergide of neurally mediated vasoconstriction is not caused by an action on alpha-adrenergic receptors. Unlike methysergide, selective 5-HT2 antagonists ketanserin and ritanserin have no modifying effect on exogenous 5-HT responses. These studies have provided pharmacological evidence that suggests that 5-HT may be the neurotransmitter mediating neurogenic vasoconstriction in the dog forelimb, and that this effect does not involve activation of 5-HT2 receptors.

Animals↗
PubMed1986

Descriptive and functional morphology of the neck and forelimb of the striped hyena (Hyaena hyaena, L. 1758).

The musculature of the neck and the forelimb of Hyaena hyaena is described and the biomechanical implications of some morphological aspects of muscles and skeleton are discussed. The extensors of the head and neck, the protractors and retractors of the forelimb and the extensors of the shoulder, elbow and carpal joints are relatively stronger developed than those in Canidae and Felidae. Moreover these muscles have larger moments about the joints. This is considered as an adaptation to lifting and carrying large and heavy prey or carrion.

Animals↗
PubMed1985

Effects of dopamine and vasopressin on histamine-induced increases in macromolecular permeability in the canine forelimb.

Local intra-arterial infusions of histamine, 16 micrograms base/min, for 60 minutes produced increases in lymph flow, lymph total protein concentration, the lymph/plasma total protein ratio, and weight in canine forelimbs perfused at constant flow. The weight gains were far greater than can be accounted for by an increase in vascular volume, and must, therefore, be attributed to edema formation. Treatment with dopamine (2, 4, or 8 micrograms base/min) or arginine vasopressin (AVP) initially produced an increase in perfusion pressure reflecting constriction of the forelimb vasculature. AVP prevented the histamine-induced increase in lymph flow, lymph total protein concentration, the L/P total protein ratio, and weight gain. In contrast, treatment with DA at three different dose levels failed to affect the histamine response. The increases in lymph flow, lymph total protein concentration, lymph/plasma total protein ratio, and weight were comparable to that produced by histamine in the absence of DA. These data fail to provide evidence for DA mediated regulation of macromolecular permeability, and suggest that endothelial cells either do not contain DA receptors, or that their activation does not affect macromolecular permeability.

Animals↗
PubMedDate not supplied

[Connections of the representational area of the distal section of the forelimb in the rat sensorimotor cortex].

Using horseradish peroxidase, studies have been made on the distribution of retrogradely labeled nervous cells in the sensorimotor cortex of rats. The enzyme was injected into electrophysiologically identified zone of representation of the distal part of the forelimb in areas S2 and S1. It was found that this zone in S2 contains afferent connections mainly from representation of the same extremity in S1 and only a few afferents from other areas of S1, S2 and M1 of the same hemisphere. Single labeled neurones were found in areas S2, S1 and M1 of the contralateral hemisphere. Representation of the forelimb in S1 receives mainly cortical afferents from the same region of S1 and from single cells of homologous zones S2 of the same and S1 of the contralateral hemisphere. Connections from S1 to S2 are more numerous than the opposite ones. In contrast to cats and monkeys, in rats afferent cortical fibers to zone S2 pass not only from the third layer, but also from the fifth and sixth layers of the cortex. It is suggested that during progressive development of the neocortex in mammals, the increase in the degree of separation of neurones (which give origin to corticofugal and cortical connections) among different layers of the cortex takes place.

Afferent Pathways↗
PubMed1985

[Afferents from a single muscle of the forelimbs and fastigial neurons of the cerebellum].

Responses of neurons in the medial nucleus of cerebellum (CBM) were studied on stimulation of ipsilateral and contralateral homonymous muscles, in decerebrated cats. The aim was to find out to what extent information from homonymous muscles of the forelimbs converge on the same CBM neurons and whether the probability of such a convergence depends on location (axial, proximal, distal) or function (flexor, extensor) of the tested muscles. The analysis was limited to the neurons belonging to the rostral part of the nucleus which is known to control the ipsilateral muscle periphery. Neuronal activity was recorded extracellularly using tungsten microelectrodes (5-12 M omega) and muscle stimulation was performed by bipolar coated steel electrodes, with the exception of the tip. At least 6 pairs of homonymous muscles were generally stimulated: two axial, two proximal and two distal in both forelimbs. Care was taken that, when a muscle was stimulated, the others were not activated either directly or in a reflex way. Out of the 65 neurons studied, 60 (92%) were responsive to muscle stimulation. It was specifically observed that a high percentage of cells reacted to stimulation of distal muscles (74% to ipsilateral and 71% to contralateral ones). More than half (55%) of the neurons were responsive to activation of a pair of homonymous distal muscles and about one third of them (31%) to both the pairs of distal muscles. On the contrary the percentage of responses to proximal muscles was reduced foremost in the ipsilateral ones (23%) and only an exiquous percentage of cells (15%) received information from the homonymous proximal muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1979

Segmental innervation of the chick forelimb following embryonic manipulation.

A number of studies have shown that the segmental innervation of some muscles in the developing limb undergoes some modification during the earliest stages of ontogeny. These observations can be interpreted in support of the hypothesis that the motor axons and muscles are matched during this period of development. As a further test of this suggestion we have made a quantitative examination of the motor innervation of the chick forelimb under conditions of controlled abnormal development. Embryos were surgically manipulated at stages before the motor axons invade the limb. The operations were controlled such that forelimbs were induced with segments deleted or reduplicated or simply that a segment of the spinal cord had been deleted. In preparations with abnormal limbs the motor innervation of the muscles present was the same as for those muscles in the normal limb. Where a spinal segment had been deleted the limbs developed normally and their innervation was completed by the remaining brachial segments. These results suggest that any particular matching property of a developing muscle does not develop as a consequence of its position in the limb relative to those segments of the limb proximal to it. Furthermore, that some muscles which are normally innervated by two spinal segments can be completely innervated by one of those spinal segments, in the absence of the other, suggests that any matching between growing axons and developing muscle cells is hierarchical rather than strictly all-or-nothing.

Animals↗
PubMed1983

Responses of forelimb extensors to sinusoidal stimulation of macular labyrinth and neck receptors.

In precollicular decerebrate cats the multiunit EMG activity was recorded from forelimb extensors (triceps brachii) during isolated or combined sinusoidal stimulation of labyrinth and neck receptors at frequencies of 0.026--0.15 Hz. As expected from previous work, the first harmonic component of the EMG responses to roll tilt of the animal leading to selective stimulation of labyrinth receptors was characterized by an increased activity during side-down tilt and a decreased activity during side-up tilt (labyrinth responses); on the other hand just the opposite changes were elicited for the same directions of neck rotation (neck responses). For the peak amplitude of displacement of 10 degrees, the responses were always related to position and not to velocity of displacement. In some experiments in which the sensitivity of the neck responses was usually comparable to that of the labyrinth responses and the corresponding peaks were almost 180 degrees out of phase, a cancellation of the responses occurred during head rotation, leading to costimulation of labyrinth and neck receptors. In other experiments, however, in which the sensitivity of the neck responses was higher than that of the labyrinth responses, the forelimb extensors responded to head rotation in a fashion predictable from the vectorial summation of the responses obtained from separate macular and neck stimulation.

Animals↗
PubMed1983

Electromyographic response to displacement of different forelimb joints in the squirrel monkey.

The electromyographic (EMG) reflex response evoked in muscles stretched by imposed angular joint displacement has previously been studied in a variety of muscles and species. In most muscles studied, the EMG response consists of an initial burst of activity at latencies comparable to tendon tap responses followed by one or more bursts of EMG activity occurring at latencies less than somatosensory reaction time. The longer latency bursts or peaks of activity have often been assumed to be of similar origin in functionally diverse muscles. The present experiments were performed to examine the EMG response to imposed joint displacement in several different muscles of the squirrel monkey forelimb. The EMG was studied in muscles stretched by elbow, wrist, and metacarpophalangeal joint extension. Early (M1) and long (M2) latency peaks of activity could be observed in the EMG responses of short head of biceps (SHB), flexor carpi ulnaris (FCU), and flexor digitorum profundus (FDP), at latencies which are similar to those reported in other primate species allowing for differences in the size of the animals. The intervals between these peaks did not correspond to the period of oscillations in tension which occurred after the onset of the joint extension. The M2 peak consistently occurred later in SHB than in FCU and FDP. The M1 peak was smaller in distal than in proximal muscles and was frequently absent in FDP at resting levels of EMG activity. The ratio of M1 to M1 + M2 activity for different muscles revealed that proximal muscles had prominent early with less prominent long latency activity, whereas distal muscles had minimal early latency activity with prominent long latency activity. The onset of EMG activity approached tendon tap latencies in FCU at high base line EMG levels but in most cases occurred at approximately twice tendon tap latencies in FDP at high base line EMG levels. The results demonstrate the presence of significant differences between the EMG response to joint displacement in the proximal-distal series of forelimb flexors. Differences in the reflex response to joint displacement are discussed in view of twitch times and motor unit composition of the muscles studied.

Animals↗
PubMed1983

Effects of delayed amputation on denervated forelimbs of adult newt.

Left forelimbs of adult newts were repeatedly denervated prior to and following amputation. Limb amputations were performed at 7-, 14-, 21-, 27-and 45-day intervals after the initial denervation. Regeneration was found in the sham-denervated and control animals but did not occur in any of the experimental cases; instead cicatrix formation and dermal wound healing ensued. Soft-tissue dedifferentiation was evident, however. We conclude from these results that forelimb regeneration in the adult newt is completely nerve dependent (for growth).

Amputation, Surgical↗
PubMed1982

Neurotrophic control of events in injured forelimbs of larval urodeles.

Denervated forelimbs and contralateral innervated forelimbs of Ambystoma larvae were injured internally distal to the elbow by compression with watchmaker's forceps. Innervated controls completely repaired the crush injury within one week; denervated limbs failed to repair the injury and exhibited varying degrees of limb regression. Histological examination revealed that the process of tissue dedifferentiation initiated by injury was more extensive in denervated, regressing limbs than in controls. In innervated limbs, both the DNA labeling index and the mitotic index peaked approximately 4--6 days after the injury and returned to baseline levels by 10 days. In denervated limbs, the DNA labelling index also increased and remained at an elevated level for at least 2 weeks after the injury, but significant mitotic activity was not observed. The data indicate that intact nerves are not needed for cellular dedifferentiation, cell cycle re-entry, and DNA synthesis in injured limbs, but are required for the cells to proliferate and repair the injury. These results are discussed together with those of similar experiments on the role of nerve during the initiation of epimorphic regeneration in amputated limbs.

Ambystoma↗
PubMed1982

Laminar distribution and convergence of deep and superficial peripheral inputs in the forelimb representation of rat SI somatosensory cortex.

The laminar distribution of single unit responses to stimulation of peripheral nerves (deep and superficial radial nerves) or to stimulation of peripheral receptive fields has been studied in the forelimb representation of the first somatic sensory cortex (SI) of the rat. 1. Under both conditions the majority of the responding units was located in layers IV, V and VI of the cortical area containing dense neuronal aggregates in layer IV. 2. Following electrical stimulation of the deep radial nerve (DRN) and of the superficial radial nerve (SRN), 18.9% of the neurons were observed to receive convergent inputs from both nerves. 3. Following natural stimulation of the forelimb, no evidence of convergent inputs on single neurons was obtained. 4. There was no clear submodality segregation in the receptive fields observed during vertical penetration.

Animals↗
PubMed1982

Forelimb tic in a horse.

An 18-month-old male Quarter Horse was referred for evaluation of a tic that had started after injury to the right forelimb 4 weeks earlier. The right forelimb appeared paretic and had constant regular twitches of variable intensity that were usually sufficiently forceful to move the trunk, neck, and head. The horse frequently threw the limb forward. The twitch persisted during sleep but disappeared during general anesthesia and following sedation with xylazine. It was unaffected by acetylpromazine, diphenylhydantoin, diazepam, carbamazepine, trimethadione, procainamide, quinidine, propranolol, dantrolene, methocarbamol, dimethyl sulfoxide mixed with xylocaine, or by low volar nerve anesthesia. It remained unchanged during 21 days of hospitalization but had stopped 10 weeks after discharge. Electromyographic tracings of the limb and neck and radiographs of the cervical and proximal thoracic spine, scapulohumeral joints, and adjacent ribs were normal. A localized spinal cord lesion or peripheral neuropathy and neuralgia secondary to trauma were suspected.

Animals↗
PubMed1996

Projection of forelimb nerve afferents to external cuneate nucleus of the rat as revealed by intraneural injection of a neurotoxic lectin, Ricinus communis agglutinin.

This study seeks to extend the observations of previous studies of projection of primary afferent fibres from the forelimb nerves and muscles to the external cuneate nucleus (ECN) of mammals using a neurotoxic lectin, Ricinus communis agglutinin (RCA) to achieve chemical ganglionectomy of the dorsal root ganglia. Following intraneural injection of RCA into the three main forelimb nerves, namely the radial, ulnar and median nerves, terminal degeneration of the primary afferent fibres in the ECN was studied under the light microscope by means of the Fink-Heimer method. The results show that the primary afferent fibres from these three nerves project to the medial part of the ECN. The field of terminal degeneration take a crescentic form. The projection from the median nerve was most dorsally located whereas that from the radial nerve was the most ventral with extensive overlaps between them. Of the three nerves, the projection from the radial nerve was the most dense. Rostrocaudally, the three nerves also show extensive overlaps. The rostrocaudal extent of maximum terminal degeneration was greatest for the radial nerve and least for the median nerve. Analysis of variance showed that these differences were statistically significant. This suggests that the radial nerve has the most extensive projection to the ECN and the median nerve the least.

Animals↗
PubMed1977

Determination of anteroposterior polarity in the axolotl forelimb by an interaction between limb and flank rudiments.

1. It is shown that the mesoderm in the prospective forelimb-bud of the axolotl embryo is thickened and divided into somatic and splanchnic layers, while that of the flank is thinner and divided. The first sign of the limb-bud itself appears at stage 38. 2. A whole, a half or a third of a limb rudiment can develop into a normal or reduplicated limb when transplanted to the flank. 3. An anterior half of a limb rudiment fails to develop when transplanted to the head but will do so if accompanied by a small piece of flank tissue. 4. Small pieces of tissue from a wide area of the flank will cause reduplication of the forelimb if grafted to the anterior margin of the rudiment. It is shown that the whole of the reduplication is formed from host tissue and has the morphological character of the host. 5. Reduplications have posterior structures arranged symmetrically on both sides of midline. Both muscles and cartilages are duplicated. 6. It is suggested that the same interaction between prospective flank and limb is responsible for the capacity for growth on the head, the induction of reduplications and the formation of the anteroposterior pattern of the limb in normal development. 7. A simple rule is proposed which explains the occurrence of reduplications in classical work on the amphibian limb.

Ambystoma↗
PubMed1977

The protective action of zinc against the deleterious effects of cadmium in the regenerating forelimb of the adult newt, Notophthalmus viridescens.

Forelimbs of adult male newts (Notophthalmus viridescens) were amputated and immediately dipped in cadmium nitrate for 2 minutes; in addition, some of the newts were injected with zinc chloride 24 hours prior to, or 24 hours after amputation. Dipping the amputated forelimb of a newt in a solution of 0.4 M cadmium nitrate completely inhibited or retarded regeneration throughout the 65 days of observation. Other effects of cadmium administration included erythema of the limb, an extensive protrusion of the humerus, and in some cases atypical differentiation of regenerates. When zinc chloride was injected (0.04 mg/g of body weight) intraperitoneally into the newt 24 hours prior to limb amputation and cadmium dipping, the deleterious effects of cadmium treatment were prevented and normal regeneration occurred. When zinc chloride was administered 24 hours after amputation and cadmium dipping, it gave no protection against the cadmium. It is suggested that cadmium might inhibit regeneration through the inactivation of zinc metalloenzymes as a result of an exchange of cadmium for zinc. Zinc chloride administered to newts prior to cadmium treatment may prevent the replacement of zinc by cadmium.

Animals↗
PubMed1997

Organization of forelimb motoneuron pools in two bat species (Eptesicus fuscus and Myotis lucifugus).

The present investigation provides further evidence of the conservation of motor nuclei in amniotes. The position of six forelimb and shoulder motor pools were mapped in two species of bat, Eptesicus fuscus and Myotis lucifugus. The intraspinal locations of motor pools were revealed by labeling with the retrograde neuronal tracer WGA-HRP injected into the bellies of six muscles: m. pectoralis, m. spinodeltoideus, mm. triceps brachii (long and lateral heads), m. infraspinatus, m. supraspinatus, and m. biceps brachii. The positions of the labeled motor pools were reconstructed from serial transverse and horizontal sections of the spinal cord. WGA-HRP-labeled cells were located midway between cervical spinal nerves four and five to midway between cervical spinal nerve eight and the first thoracic spinal nerve. Individual motor pools formed fusiform clusters of cells with little intermingling of neurons between adjacent motor pools. The pectoralis motor pool contained significantly more motoneurons than all other motor pools for M. lucifugus. The pectoralis pool in E. fuscus contained more motoneurons than the biceps, supraspinatus, and infraspinatus, but not the spinodeltoid or the triceps brachii. The biceps, spinodeltoid, infraspinatus and supraspinatus pools were located rostrally; the pectoralis and triceps pools caudally. The pectoralis pool was the most medial and the spinodeltoid pool was the most lateral. These data suggest that the locations of shoulder and forelimb motor pools are ontogenetically and phylogenetically conserved across tetrapods and independent of the function of the muscles in adults.

Animals↗
PubMed1998

Effect of different full-limb casts on in vitro bone strain in the distal portion of the equine forelimb.

OBJECTIVE: To determine the ability of a full-limb transfixation pin cast to protect the distal portion of the equine forelimb from weight-bearing forces by measuring bone strain in vitro on cadaver limbs loaded in a mechanical testing machine. SAMPLE POPULATION: 6 forelimbs from 6 horses. PROCEDURE: Each limb was instrumented with 3 unidirectional metal foil electrical resistant strain gauges. Gauges were placed on the dorsal aspect of the distal portion of the radius and the mid-dorsal portion of the cortex of the third metacarpal bone and the first phalanx. Each limb was tested 3 times, once supported with a transfixation pin cast, once supported by a standard full-limb cast, and finally, uncast. The limbs were tested in a mechanical testing machine under axial loads ranging from 100 to 1,000 lb, and bone strains were recorded at each load. RESULTS: Compared with values for the uncast limb, the transfixation pin cast and the standard full-limb cast significantly (P < 0.001) reduced bone strain on the distal portion of the radius, third metacarpal bone, and first phalanx. Compared with the standard full-limb cast, the transfixation pin cast significantly (P < 0.001) reduced bone strain on the first phalanx. CONCLUSION AND CLINICAL RELEVANCE: Compared with the standard full limb cast, the full-limb transfixation pin cast is more protective of the first phalanx.

Animals↗
PubMed1998

Forelimb joint moments and power during the walking stance phase of horses.

OBJECTIVE: To calculate normative joint moments of force and power for the forelimb of walking horses as a benchmark against which to compare these mechanical variables in horses with specific lameness. ANIMALS: 4 Dutch Warmblood horses with no recent history of lameness. PROCEDURE: Horses were walked by hand through the test area, and data from 5 walking trials were collected for each horse. Two camera views were combined with vertical and craniocaudal ground reaction forces to calculate net moments of force in the sagittal plane across the carpal, metacarpophalangeal (fetlock), and distal interphalangeal (coffin) joints during the stance phase of the forelimb. Mechanical power was calculated as the product of net joint moment and the joint's angular velocity. RESULTS: During the early part of the stance phase, the carpal joint had oscillating periods of energy generation and absorption against a predominant flexor moment, then an absorption phase at the end of the stance phase, as the carpus flexed into swing against an extensor moment. The fetlock absorbed energy in the early part of the stance phase, then the terminal part was marked by a large generation of energy across the joint. A flexor moment was measured at the coffin joint throughout the stance phase, and this coincided with a long phase of energy absorption followed by a short phase of generation for push-off. CONCLUSION: Consistency of the power data indicates that typical profiles of work exist for each of the joints (carpus, fetlock, and coffin). CLINICAL RELEVANCE: Detection of changes to these profiles of work may contribute to diagnosis of specific lameness conditions.

Animals↗