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PubMed1976

Neurotrophic activity of brain extracts in forelimb regeneration of the urodele, Triturus.

The loss in protein synthesis which the regenerating forelimb of the newt suffers after denervation can be recovered by infusing into it an extract of newt soluble brain protein. Moreover, the synthesis of basic protein shows a greater response to the active brain principle than does that of acidic protein. The active agent of the nervous tissue is destroyed by heat and trypsin digestion. Extracts of liver and spleen, similarly prepared, do not evoke recovery of lost protein synthesis. Synaptosomal extracts of the frog brain also cause recovery of protein synthesis in the denervated regenerate, demonstrating the likelihood that the active agent is not species-specific within these amphibians, that it is a constituent of the neuronal fraction of nervous tissue, and that it is present in axonal terminals. Additional experiments showed that the nervous agent is likely a basic protein, and that the amount of protein infused is of the order of only 1.0% of the total regenerate protein. The significance of the findings is discussed in relation to the nature of the effect on protein synthesis and the nature of the active principle.

Animals↗

PubMed1977

The effect of light on forelimb regeneration in the newt.

The forelimb of the newt, Triturus (Notophthalamus) viridescens, was bilaterally amputated and the animals subjected to different photoperiods during the period of regeneration, namely (1) continuous light, (2) 15 hours of light/day and (3) total darkness. Animals exposed to continuous light reached the palette regeneration stage four to five days before those kept in total darkness with the 15 hours of light/day animals being intermediate. The difference in regeneration rate was first evident in the moderate early stage (blastema accumulation stage); it then increased during subsequent stages and the difference persisted during the observation period. In an attempt to determine whether the retina was the receptor of light affected, some animals were blinded at the time of amputation and subjected to continuous light. Their rate of regeneration was similar to sighted animals subjected to continuous light but greater than sighted animals in total darkness. The pineal is discussed as the likely mediator of the photo effect.

Animals↗

PubMed1981

Newt forelimb regeneration blastemas in vitro: cellular response to explanation and effects of various growth-promoting substances.

Macromolecular synthesis was studied in cultured newt forelimb blastemas. Late bud stage blastemas were explanted into organ culture and thus denervated. When the response of the blastemas to explantation was examined, it was found that a peak in 3H-leucine incorporation occurred at 2 hr of incubation, and a similar peak in 3H-thymidine incorporation occurred at 3-4 hr. After these initial increases, both parameters declined to levels lower than those determined at the time of explantation. The peaks in macromolecular synthesis reported here in vitro are similar to those observed in blastemas in vivo after denervation (Singer, '74). In the second part of the study, the ability of various growth-promoting substances to stimulate DNA synthesis in cultured blastemas was investigated. Increasing concentrations of fetal bovine serum caused increased levels of 3H-thymidine incorporation, with maximal stimulation at 30% serum. Newt brain extract (NBVE) was as effective as additional serum, with optimal stimulation at 100 micrograms total NBE protein per ml culture medium. Fibroblast growth factor (FGF), derived from brain tissue, at a concentration of 10 ng/ml was as effective as both 30% serum and the optimal concentration of NBE. Epidermal growth factor (EGF) produced a maximal effect at 1 ng/ml. Neither nerve growth factor nor the platelet-derived growth factor were stimulatory. Bovine insulin was highly active in stimulating DNA synthesis at concentrations from 1-10 micrograms/ml. The requirement of nerves for blastemal development, as well as the possible roles of the various growth-promoting substances in this process, are discussed.

Animals↗

PubMed1984

Cell cycle and histological effects of reinnervation in denervated forelimb stumps of larval Ambystoma.

Although nerves are a requirement for regeneration of a salamander limb, denervation of an amputated larval Ambystoma forelimb does not permanently prevent the limb from regenerating. When nerves grow back into the distal stump in sufficient numbers, regeneration occurs. In this study we examined histological and cell cycle events in denervated limb stumps of Ambystoma as they became reinnervated and began to regenerate. Prior to reinnervation and regeneration, dedifferentiated cells are present in the distal stump but are rarely synthesizing DNA or undergoing mitosis and are densely packed. About 2 days after the distal tip of the stump becomes reinnervated, the limb tip appears to "expand" as cells become less densely packed, and cell cycle activity begins. Mitotic index (MI) and labeling index (LI) increase slowly compared to MI and LI in control amputated limbs. Evidence for the localization of cycling activity is presented. In reinnervated stumps, the increase in LI precedes the increase in MI, suggesting that most of the cells are initiating cycling from the G1 phase.

Ambystoma↗

PubMed1991

Regenerative capacity of forelimb buds after amputation in mouse embryos at the early-organogenesis stage.

The ability of mouse forelimb buds at stage 1 (Wanek et al., '89a) of development to regenerate after amputation was investigated. The findings were as follows: 1. Outgrowths in the form of hillocks were found at the sites of amputation in 116 (95%) out of 122 embryos examined 24 hours after amputation. Examination of the amputated region after various intervals of time revealed that the outgrowths were established from flank tissues at the anterior and posterior borders of the wound. 2. Ectodermal thickening was found on the distal margin of the outgrowths in 21 (66%) out of 32 specimens examined. These thickenings were histologically similar to the apical ectodermal ridge (AER) present on the control limb buds. 3. Alkaline phosphatase activity was detected on the ectodermal thickening in 11 (79%) out of 14 experimental limb buds examined. The pattern of expression of alkaline phosphatase activity was similar to that observed in control limb buds. 4. There was no correlation between the size of the outgrowths and the presence of the ectodermal thickening or the enzymatic activity. The outgrowths developed despite the absence of ectodermal thickening and enzymatic activity, suggesting that the thickening and the presence of alkaline phosphatase are not crucial for the initiation and formation of the outgrowths. 5. Explants of the outgrowths, when grafted beneath adult kidney capsules, differentiated extensively into various tissues, which included bones, epiphyseal plates, skeletal muscles, and skin derivatives. Control explants also gave rise to the same spectrum of tissues. Hence, the flank tissues surrounding the site of amputation in E10 mouse embryos can regenerate to form a structure that is morphologically and histochemically similar to a limb bud and the mesenchyme within the structure is histogenetically competent to produce the variety of tissues that is normally found in the adult limb.

Alkaline Phosphatase↗

PubMed1992

Epimorphic vs. tissue regeneration in Xenopus forelimbs.

Postmetamorphic froglets of Xenopus laevis regenerate hypomorphic unbranched spikes from amputated arm stumps. These are composed primarily of cartilage, produced from blastemalike structures sparsely populated with cells and rich in connective tissue. Some consider these outgrowths to be an example of epimorphic regeneration produced from blastemas, albeit deficient ones. Others interpret them as a case of tissue regeneration derived from fibroblastemas augmented by chondrocytes and periosteal and perichondrial fibroblasts. To resolve these alternatives, forelimbs were amputated proximal to the wrist, skinned, and inserted through the body wall into the abdominal cavity. In the absence of skin, epidermal wound healing failed to occur and blastemas could not develop. After 2 months, by which time controls had regenerated spikes averaging 3.38 mm long, the denuded stumps had not given rise to outgrowths. They typically developed cartilaginous caps on the severed ends of the radius-ulna, and in rare cases formed amorphous growths of cartilage. If blastema formation is considered diagnostic of epimorphic regeneration and tissue regeneration can proceed in the absence of epidermal wound healing and blastema formation, these findings lead to the conclusion that Xenopus limb regeneration is epimorphic.

Animals↗

PubMed2004

Forelimb spike regeneration in Xenopus laevis: Testing for adaptiveness.

Experiments were designed to test adaptability of forelimb spike regenerates in Xenopus laevis froglets. The results show that when amputation is at the radius/ulna level, regeneration occurs in 100% of the cases and a single spike of cartilage is the result. The spike regenerates originating from radius/ulna level amputations can be used for feeding and froglet growth is only minimally compromised by the spike. The spike grows in length as the froglet body grows and thus is in homeostasis with the body. The spike develops nuptial pad tissue in reproductively mature males and is occasionally molted, indicating responsiveness to gonadal and thyroid hormones. Finally, and most important, the spike can be used for amplexus and successful mating. In contrast, spikes originating from humerus level amputations were considerably shorter and regeneration from that limb level was less frequent. When amputation was at the body wall regeneration did not occur.

Adaptation, Physiological↗

PubMed1979

Partial regeneration of the above-elbow amputated rat forelimb. II. Electrical and mechanical facilitation.

This investigation was undertaken to examine the observations of Becker ('72) pertaining to the electrical facilitation of partial limb regenerative responses by means of Ag-Pt wire couples applied to the limb stumps of young, forelimb-amputated white rats. Additionally, in order to examine the possible role of mechanical effects of such device implantations, we have employed uncoupled devices delivering no current or potential difference. In the present experiments, in response to coupled device implantation, cartilage and bone were actively formed in the vicinity of the Pt electrode tip. These tissues contributed to the lengthwise extension of the limb and to the partial restoration of the distal humeral extremity. In limbs bearing the uncoupled electrical devices, qualitatively similar responses were noted, but osteogenesis was diminished in extent compared to that seen in limbs bearing the active or coupled devices. It is therefore necessary to consider the role of mechanical factors in the elicitation of the observed regenerative responses. Myogenesis was enhanced in electrically stimulated limbs, but not in those rats bearing uncoupled devices.

Amputation, Surgical↗

PubMed1990

Density of muscle spindle profiles in the intrinsic forelimb muscles of the dog.

The concept of parallel muscle combinations, in which spindle density is significantly higher in small muscles compared to their larger counterparts in large-small muscle combinations acting across a joint, is supported by the results of this study regardless of the joint. Analysis of the canine data as well as previously published guinea pig forelimb and human pelvic limb data revealed no significant difference in spindle density between antigravity and non-antigravity muscles. Furthermore, a gradual increase in spindle density from proximal to distal on the limb was not found, although spindle density was significantly higher in the intrinsic manus or pes muscles compared to more proximal limb muscles in all three species. The significant differences in spindle densities in parallel muscle combinations and in manus/pes versus proximal muscles are discussed relative to their possible role in the control of locomotion.

Animals↗

PubMed2003

Embryonic mesencephalic grafts increase levodopa-induced forelimb hyperkinesia in parkinsonian rats.

Recent observations from clinical trials of neural grafting for Parkinson's disease (PD) have demonstrated that grafted dopamine neurons can worsen dyskinesias in some graft recipients. This deleterious side effect reveals a new challenge for neural transplantation, that of elucidating mechanisms underlying these postgraft dyskinesias. One problem facing this challenge is the availability of a cost-effective and reliable animal model in which to pursue initial investigations. In the current study, we investigated the interaction of an embryonic ventral mesencephalic (VM) dopamine (DA) neuron graft on levodopa (LD)-induced dyskinetic movements in unilaterally 6-hydroxydopamine-lesioned rats. Rats were administered LD (levodopa-carbidopa, 50:5 mg/kg) twice daily for 6 weeks after either a sham graft or VM DA graft. Although a single solid graft of embryonic DA neurons can prevent progression of some lesioned-induced behavioral abnormalities such as LD-induced rotation and dystonia, it significantly increases hyperkinetic movements of the contralateral forelimb. This differential effect of grafted neurons on abnormal behavioral profiles is reminiscent of that reported in grafted patients with PD. Data from this study illustrate important similarities between this model of parkinsonism and PD in human patients that make it suitable for initial preclinical investigations into possible mechanisms underlying postgraft aggravation of dyskinetic movements.

Animals↗

PubMed1985

Cadmium-induced forelimb ectrodactyly: a proposed mechanism of teratogenesis.

We have attempted to elucidate the mechanism of cadmium teratogenesis utilizing inbred mouse strains sensitive (C57BL/6J) or resistant (SWV) to the embryotoxic effect of this common heavy metal contaminant. Carbonic anhydrase activity of whole-embryo homogenates was moderately depressed in C57BL/6J mice compared to a slight and transient decrease in the resistant SWV mice. Embryonic erythrocytes were similarly examined, and the cadmium did not have any effect on carbonic anhydrase activity in either strain. Likewise, histochemical examination of carbonic anhydrase activity did not reveal any effect of cadmium in the embryos of their strain. Generally, the zinc concentration of embryos was not affected by cadmium administration. However, increased levels of zinc were observed in cadmium-exposed yolk sacs of both strains suggesting that cadmium produces an adverse effect on yolk sac function. Untreated C57BL/6J units (embryo plus surrounding extraembryonic membranes), embryos, and yolk sacs had much lower hemoglobin concentrations than those observed in untreated SWV units, embryos, and yolk sacs. Additionally, cadmium exposure significantly decreased C57BL/6J embryonic hemoglobin levels on gestation day 10 (PM) and increased C57BL/6J yolk sac hemoglobin levels on gestation days 10 (AM) and 10 (PM). No difference in hemoglobin concentration was observed between untreated and cadmium-treated SWV embryos or yolk sacs. We propose that cadmium induces forelimb ectrodactyly by creating an acidotic embryonic environment and that the primary site at which cadmium exerts its teratogenic effect might be the yolk sac.

Abnormalities, Drug-Induced↗

PubMed1990

Induction of postaxial forelimb ectrodactyly with anticonvulsant agents in A/J mice.

Exposure of A/J mice on day 9.5 of gestation to the derivatives of three acidic anticonvulsant agents, namely dimethadione, sodium valproate, and sodium diphenylhydantoin, each induced postaxial forelimb ectrodactyly predominantly of the right side. This specific malformation has previously been associated with the administration of acetazolamide to rodents; however, several agents can induce this same defect including other carbonic anhydrase inhibitors, carbon dioxide, cadmium, ethanol, ammonium chloride, and 13-cis retinoic acid. The relative potency of the three agents indicates no direct relationship to the pKa of the acid. Other than ectrodactyly, each of the anticonvulsant agents induced a compound-specific spectrum of malformations despite the uniform administration time. This finding suggests that these agents are capable of acting via different mechanisms or by the differential spatial and temporal dynamics of a common mechanism.

Abnormalities, Drug-Induced↗

PubMed1996

Differential spinal projections from the forelimb areas of the rostral and caudal subregions of primary motor cortex in the cat.

We used anterograde transport of WGA-HRP to examine the topography of corticospinal projections from the forelimb areas within the rostral and caudal motor cortex subregions in the cat. We compared the pattern of these projections with those from the somatic sensory cortex. The principal finding of this study was that the laminar distribution of projections to the contralateral gray matter from the two motor cortex subregions was different. The rostral motor cortex projected preferentially to laminae VI-VIII, whereas caudal motor cortex projected primarily to laminae IV-VI. Confirming earlier findings, somatic sensory cortex projected predominantly to laminae I-VI inclusive. We found that only rostral motor cortex projected to territories in the rostral cervical cord containing propriospinal neurons of cervical spinal segments C3-4 and, in the cervical enlargement, to portions presumed to contain Ia inhibitory interneurons. We generated contour maps of labeling probability on averaged segmental distributions of anterograde labeling for all analyzed sections using the same algorithm. For rostral motor cortex, heaviest label in the dorsal part of lamina VII in the contralateral cord was consistently located in separate medial and lateral zones. In contrast, no consistent differences in the mediolateral location of label was noted for caudal motor cortex. To summarize, laminae I-III received input only from the somatic sensory cortex, while laminae IV-V received input from both somatic sensory and caudal motor cortex. Lamina VI received input from all cortical fields examined. Laminae VII-IX received input selectively from the rostral motor cortex. For motor cortex, our findings suggest that projections from the two subregions comprise separate descending pathways that could play distinct functional roles in movement control and sensorimotor integration.

Animals↗

PubMed1990

Integration in descending motor pathways controlling the forelimb in the cat. 16. Visually guided switching of target-reaching.

A task has been developed to investigate the ability of cats to switch the direction of an ongoing target-reaching forelimb movement with the aid of a visual cue. The cats were standing in front of two horizontal tubes (internal diameter 30 mm; shoulder level) with food. The entrances of the tubes were closed with opaque trap doors but during illumination inside a tube its trap door was unlocked allowing the cat to retrieve food with the paw. When the cats had learnt to select the illuminated tube for insertion the next step was to switch the illumination to the other tube during ongoing target-reaching. Limb lifting was performed when the light was switched on in one of the tubes and time was measured from breaking electrical contact between the paw and the floor. After 25-75 ms, illumination was shifted to the other tube and the latency to the earliest change in movement trajectory was measured. The trajectory was recorded with the aid of cameras detecting the position of infrared light emitting diodes fixed to the dorsal part of the wrist. Every 3 ms the position was fed into a computer, and the movement trajectory (horizontal and sagittal planes) was displayed graphically. The velocities in the direction of cartesian coordinates x, y and z (protraction, adduction-abduction, lifting) were also computed. Single tube trials and switching trials from either tube were made in a random series. In order to switch, the cats used a combination of braking the protraction and a sideways movement. Initially there was often some retraction of the paw to avoid hitting the trap door of the first illuminated tube, but with more proficiency braking decreased and the movement path became smoothly curved. During braking of protraction there was also deceleration of lifting but not enough to maintain a constant movement path in the sagittal plane. In sessions with single tube trials, the movement paths in the horizontal plane were reasonably straight. In sessions with intermixed switching trials the single tube paths became segmented or curved, seemingly in order to facilitate switching. The mean switching latency in four cats ranged from 83 to 118 ms. In the fastest cat the switching latency ranged from 70-106 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Candidate premotor neurones of skin reflex pathways to T1 forelimb motoneurones of the cat.

This study explored the locations and input-output properties of a large population of putative premotor neurones of skin reflex pathways in the cat. These neurones, interneurones excited by forelimb skin afferents and antidromically from the T1 motor nucleus (MN) and/or the lateral funiculus (LF, C8/T1 border), termed antidromic cells, were extracellularly recorded at C6-8. Selection of this site was based on data showing that cells retrogradely HRP labelled from the T1 MN were most numerous in C6-8 and the observation that transection of LF at the C8/T1 border abolished most skin-evoked postsynaptic potentials of T1 motoneurones. Antidromic cells were located in laminae IV-V, VI and VII. The latencies of antidromic excitation ranged from 0.4 to 1.8 ms, with a tendency for laminae IV-V cells to show longer latencies than laminae VI and VII cells. Latency of skin-evoked excitation ranged from 0.6 ms (IV-V cells), 0.8 ms (VI) and 1.4 ms (VII) to greater than 5 ms. The sum of the ortho- and antidromic latencies (estimated central latency) of individual cells explained the central latencies of skin-evoked postsynaptic potentials in T1 motoneurones. Skin-evoked firing responses (average of eight to ten cells) were earliest and largest in laminae IV-V antidromic cells, and latest and smallest in lamina VII cells. The antidromic cells who received inputs from muscle afferents and descending tracts. The following three results support the suggestion that the sampled antidromic cells are mostly premotor neurones. (1) Projection to the T1 MN via LF was verified in six laminae IV-VII antidromic cells, as tested with threshold mapping for antidromic excitation. (2) Three skin-excited axons of the middle LF projected to T1 MN, as revealed by intra-axonal staining (HRP). (3) PHA-L injection in laminae I-V of C8 anterogradely labelled terminals in lamina IX and LF axons at T1. It is suggested that last-order neurones of skin reflex pathways to T1 motoneurones are widely distributed in laminae IV-VII of C6-8 and consist of a variety of neurones with different locations and input patterns.

Animals↗

PubMed1996

Convergence of skin reflex and corticospinal effects in segmental and propriospinal pathways to forelimb motoneurones in the cat.

The organization of facilitatory convergence from cutaneous afferents (Skin) and the corticospinal tract (pyramidal tract, Pyr) in pathways to forelimb motoneurones of mainly distal muscles was studied in anaesthetized cats by analysing postsynaptic potentials (PSPs), which were spatially facilitated by combinations of stimuli to the two sources at different time intervals. Conditioning Pyr volleys facilitated Skin-evoked PSPs of fixed (1.2-3.6 ms) central latencies (Skin PSPs), suggesting that disynaptic and polysynaptic skin reflex pathways are facilitated from the pyramidal tract. The shortest latencies (1.2-1.7 ms) of pyramidal facilitation suggested direct connection of pyramidal fibres with last order neurones of skin reflex pathways. Conditioning Skin volleys facilitated Pyr-evoked PSPs of fixed, mostly disynaptic latencies (1.0-2.5 ms; Pyr PSPs), suggesting that pyramido-motoneuronal pathways are facilitated from Skin at a premotoneuronal level. The shortest pathway from skin afferents to the premotor neurones appeared to be monosynaptic. Although Pyr and Skin volleys were mutually facilitating, the facilitation curve of Pyr PSPs and that of Skin PSPs were discontinuous to each other, with the peak facilitation at different Skin-Pyr volley intervals. Transection of the dorsal column (DC) at the C5/C6 border had little effect on the latencies or amplitudes evoked by maximal stimulation and the pyramidal facilitation of Skin PSPs. In contrast, the facilitation of Pyr PSPs by Skin stimulation was greatly decreased after the DC transection, and the facilitation curve of Pyr PSPs was continuous to that of Skin PSPs, with no separate peak. Latencies of Pyr PSPs ranged similarly to those in DC intact preparations. More rostral DC transection (C4/C5 border) reduced Skin-facilitated Pyr excitatory PSPs (EPSPs) less than C5/C6 lesions, suggesting that the C5 segment also contains neurones mediating Skin-facilitated Pyr EPSPs. The results show that convergence from skin afferents and the corticospinal tract occurs at premotor pathways of different cervical segments. We suggest that corticospinal facilitation of skin reflex occurs mostly in the brachial segments and Skin facilitation of cortico-motoneuronal effects takes place largely in the rostral cervical segments and partly in the brachial segments.

Animals↗

PubMed1982

Formation of functional synapses in the adult cat red nucleus from the cerebrum following cross-innervating of forelimb flexor and extensor nerves. I. Appearance of new synaptic potentials.

We investigated the effects of cross-innervating the peripheral forelimb flexor and extensor nerves of adult cats on the time course of corticorubral EPSPs. Red nucleus neurons were identified by antidromic invasion from C1 or L1 spinal segments as innervating the upper spinal segments (C-cells) or sending axons to the lumbosacral cord (L-cells). In C-cells, a fast-rising component, superimposed on the slow-rising corticorubral EPSPs induced by the cerebral sensorimotor cortex or the cerebral peduncle (CP) stimulation, was noted. The mean time-to-peak of this component in cross-innervated cats operated more than two months earlier was 1.9 +/- 0.9 ms (n = 160), shorter than in normal cats (3.6 +/- 1.4 ms, n = 100). The same value in cats cross-innervated less than two months before was 2.7 +/- 1.0 ms (n = 53). The mean time-to-peak of CP-EPSPs from L-cells was 2.9 +/- 0.9 ms (n = 115). The fast-rising component had a latency of 0.96 +/- 0.19 ms (n = 122), and it was mediated by fibers with conduction velocities of less than 20 m/s. The projective area of the fast-rising component is organized somatotopically. Since it is more sensitive to membrane hyperpolarization than slow rising corticorubral EPSPs, it is mediated by synapses located more proximally than the corticorubral synapses of normal cats. The time course of facilitation by preceding cerebral peduncle stimulation of the nucleus interpositus (IP)-induced RN population responses was measured. It was characterized by a rapid, followed by a slower, rise time in the RN region where C-cells are concentrated. In contrast, the L-cell region was characterized by a slow rise time. In cats subjected to self-union of the peripheral flexor and extensor nerves, the majority of C-cells had CP-EPSPs with a time-to-peak within the normal range. Our results suggest that after cross-innervation sprouting and formation of functional synapses occur on the proximal portion of the soma-dendritic membrane of red nucleus neurons.

Animals↗

PubMed1984

Interaction of tonic neck and vestibular reflexes in the forelimb of the decerebrate cat.

Tonic neck reflexes, studied with EMG recording, have similar dynamics in forelimb extensor muscles of acutely labyrinthectomized cats, and in cats with intact labyrinths. The reflex occurs more frequently in the latter and its gain is higher. In intact preparations we evoked vestibular and tonic neck reflexes separately or in combination, at frequencies of 0.05-0.5 Hz. As expected from earlier work, the two reflexes oppose each other and frequently cancel; the two reflexes add linearly.

Animals↗