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Biomedical subjects

N Holder

Publications and source records attributed to N Holder.

At least 73 records · Page 4Linked to original sources
PubMed1986

The effect of replacing different regions of limb skin with head skin on regeneration in the axolotl.

Head skin was used to replace different halves of limb skin from the upper and lower arms of axolotls. Replacement of upper arm posterior skin caused the regeneration of a high proportion of single-digit limbs while replacement of dorsal, ventral or anterior skin caused only minor defects to the normal skeletal pattern. When dorsal or ventral skin was replaced, however, regenerates often lacked dorsal or ventral muscle. Results from the lower arm were different in that replacement of any half of limb skin failed to cause defects either in the skeletal or muscular pattern. These results are used in conjunction with previous work (Wigmore & Holder, 1985; Wigmore, 1986) to suggest that posterior skin is essential for regeneration of the anteroposterior axis and dorsal and ventral skin is necessary for the differentiation of the muscle pattern in regenerates from the upper arm. In the lower arm no localized region of skin appears to be essential for regeneration of the normal pattern and the patterning mechanism may have a different spatial organization.

Ambystoma mexicanum↗
PubMed1986

The regeneration of double dorsal and double ventral limbs in the axolotl.

Surgically made double dorsal and double ventral upper arms, comprising double extensor and double flexor muscles respectively, were amputated immediately following operation; both limb types regenerated. In terms of skeletal anatomy, a range of limb types was found. These included four-digit limbs of normal cartilage pattern, and hypomorphic limbs having from one to three digits. All of the double dorsal and the majority of the double ventral limbs were symmetrical in the dorsal-ventral axis. This was detected by analysing their muscle patterns at carpal and mid-forearm level, and muscle and epidermal characteristics in the metacarpal region are discussed in terms of the significance of healing time and stump pattern on the regenerative ability of surgically created limb regions.

Ambystoma↗
PubMed1985

A horseradish peroxidase study of motorneuron pools of the forelimb and hindlimb musculature of the axolotl.

Motorneuron pools innervating axolotl limb muscles have been investigated by using the retrograde neuronal tracer horseradish peroxidase. Four muscles in the forelimb (biceps, anconeus, flexor digitorum and extensor digitorum) and four functionally equivalent muscles in the hindlimb (puboischiotibialis, iliotibialis, flexor digitorum and extensor digitorum) were studied. Motorneuron pools were characterized by using four criteria: position in the rostrocaudal axis; position of the median in the rostrocaudal axis; number of labelled cells; position of cells in the transverse plane of the spinal cord. Each pool was uniquely defined by the four characteristics, although overlap was found between pools. Two types of motorneuron were found in each pool, distinguished on the basis of size, shape and position in the spinal cord. The first type constituted the majority of cells in a pool, and occupied different positions in the transverse plane for each muscle. The second type was less common and always occupied a characteristic medial ventral position. These data will allow an assay of correct or incorrect innervation in experiments on the regeneration of specific neuromuscular connections in these animals.

Ambystoma↗
PubMed1985

Motorneuron pools innervating muscles in vitamin A-induced proximal-distal duplicate limbs in the axolotl.

Serially duplicated limbs containing two sets of proximal muscles were created in axolotls by vitamin A treatment. The innervation of three replicated proximal muscles was studied by using retrograde transport of horseradish peroxidase. These were the forelimb muscles biceps (seven cases) and anconeus (five cases) and the hindlimb muscle puboischiotibialis (five cases). In two cases (both of anconeus) innervation was from a correct motorneuron pool. In the other 15 cases the innervation was from an incorrect, distal limb muscle, motorneuron pool. These results are interpreted as evidence against long range signals between nerve and muscle controlling specific nerve regeneration. However, the data are compatible with models of axonal guidance that use local pathway cues.

Ambystoma↗
PubMed1985

Organization of skeletal muscle in the urodele Triturus cristatus: muscle fibre types and motor units.

Four muscle fibre types are described in the biceps and extensor digitorum communis muscles of the newt forelimb. The histological criteria forming the basis for the distinctions include differential staining with p-phenylenediamine and succinate dehydrogenase histochemistry and electron microscopy. In addition, three distinctive motor unit types are described for the biceps muscle. These are fast units, slow units and intermediate units. The structure of muscle fibre and the physiological characteristics of muscle fibres belonging to each motor unit, have been correlated by using iontophoretic passage of Lucifer yellow into muscle fibres belonging to physiologically characterized motor units and their subsequent histological identification by the succinate dehydrogenase reaction. The three motor unit types correspond to slow muscle fibres, intermediate muscle fibres and two classes of fast muscle fibres.

Aminopyridines↗
PubMed1985

Regeneration of axolotl hindlimbs bearing surgically created discontinuities in the anterior-posterior axis.

The pattern regulation process in amphibian limbs has been examined with respect to the presence of discontinuities in the anterior-posterior (a-p) axis. Limbs bearing such discontinuities were surgically created by contralateral exchange of either dorsal or ventral half thighs and these limbs were then amputated immediately after surgery. The results demonstrate that a-p discontinuities lead to the formation of extra limb structures during distal outgrowth in contrast to the mosaic behaviour of comparable limb stumps which contain dorsal-ventral (d-v) discontinuities (Holder & Weekes, 1984). It is evident, therefore, that pattern regulation in the transverse limb axes is accomplished by basically different mechanisms. The structure of the limbs in the present study was examined in Victoria-blue-stained wholemounts and serial sections. The results allow some discussion of the basic mechanisms for pattern regulation in the two transverse limb axes and the relationship between them.

Ambystoma mexicanum↗
PubMed1985

Regeneration from isolated half limbs in the upper arm of the axolotl.

A technique enabling the isolation of half limb stumps using strips of skin from the head is described. Using this technique posterior, dorsal and ventral halves of the upper arms of axolotls were constructed. All halves produced regenerates and regional differences were shown in the regenerative and regulative abilities of the different halves. Posterior half stumps regenerated limbs with a mean digit number of 3.9 and had a normal dorsoventral muscle pattern. Anterior halves produced hypomorphic limbs with a mean digit number of 1.2 while dorsal and ventral halves produced an average of 3.8 and 2.6 respectively. Regenerates from dorsal half stumps had a normal dorsoventral axis but the majority of those from ventral halves were either double ventral or had little muscle on the dorsal side of the limb.

Ambystoma mexicanum↗
PubMed1984

Directed regrowth of axons from a misrouted nerve to their correct muscles in the limb of the adult newt.

When the forearm flexor nerve (f.f.n.) of the newt forelimb is surgically rerouted to the ventral body wall, regrowth of axons occurs and these axons reinnervate the muscle targets of the f.f.n. This process of nerve regeneration has been studied in detail over a 12 week period by using light and electron microscopy, electrophysiology and nerve fibre tracking after filling with cobalt chloride. The regrowing axons were analysed by electron microscopy and it is shown that they derive from the rerouted nerve at the position at which the f.f.n. leaves its normal ventral limb pathway. Axons in the pathway do not originate from the cut end of the f.f.n. on the ventral body wall. The regrowing axons are identified within the body of the rerouted nerve and they leave the f.f.n. by growing through the perineurium. Schwann cells are invariably associated with the regrowing axons and the pathway through which the growth cones and neurites grow consists predominantly of extracellular matrix fibrils. The stages of maturation of the regenerated f.f.n. including fasiculation of neurites, myelination and reformation of a perineurium are also described. The results of the study are discussed in terms of current ideas as to how specific regeneration of a correct and functional peripheral nervous system is achieved in urodele amphibians.

Animals↗
PubMed1984

Regeneration of surgically created mixed-handed axolotl forelimbs: pattern formation in the dorsal-ventral axis.

The regeneration of surgically created mixed-handed limb stumps is examined in the axolotl. Operations were performed in the lower arm and upper arm regions and grafts were allowed to heal for approximately one month prior to amputation or were amputated immediately. In the lower arm group both anterior and posterior limb halves were inverted, whereas only posterior halves were inverted in the upper arm group. Almost all the limbs regenerated were normal in the anterior-posterior axis, whereas a range of limb types were found when the dorsal-ventral axis was analysed using the metacarpal muscle pattern and epidermal Leydig cell number as positional markers. The carpal and forearm muscle patterns were also analysed in order to assess whether the pattern determined from analysis at the metacarpal level reflected that seen at more proximal levels. The results are discussed in terms of the possible role of cell contribution from the stump to the blastema and the relevance of the study to models of pattern regulation.

Ambystoma↗
PubMed1984

Morphogenesis of the amphibian limb blastema: the relationship between pattern and form.

A relationship between pattern formation and field shape is established following the formation of rounded blastemas on lower arm limb stumps after treatment with vitamin A. Pattern formation is not affected by alteration in blastemal shape caused by removal of the dermis from the thigh region of the leg. We conclude, therefore, that blastemal shape does not play a causal role in establishing limb pattern. Data relating the number of cells present between the cardinal axial poles of blastemas and the size of blastemas is discussed in terms of short are intercalation and short range cell-cell interactions during pattern regulation.

Ambystoma↗
PubMed1984

Skin glands in the axolotl: the creation and maintenance of a spacing pattern.

The morphogenesis of skin glands in the larval axolotl is described at the light microscope level. The glands are derived from the epidermis, but are eventually located in the dermis. The glands are non-randomly arranged within the skin and the spacing pattern tends towards a hexagonal array in two dimensions. Analysis of the spacing pattern in animals of different sizes reveals that a clear relationship exists between gland size and the distance between glands. Occasionally, new small glands are inserted into the pattern, suggesting that the spacing of glands in under a dynamic control throughout the growth of the axolotl. The possible mechanisms underlying the creation and maintenance of the pattern are discussed.

Ambystoma↗
PubMed1983

Developmental constraints and the evolution of vertebrate digit patterns.

The skeletal makeup of the digits of 145 hands and feet from species from the four classes of tetrapod vertebrates is analysed. The analysis leads to the conclusion that developmental constraints are very influential in the evolution of vertebrate digit patterns. Furthermore, 98% of the patterns analysed fall within the specific constraints of the Stock & Bryant (1981) version of the polar coordinate model for the formation of digit patterns during development and pattern regulation. Three cases of apparently forbidden morphology are discussed in terms of the phenomenon of differential growth during development.

Adaptation, Biological↗
PubMed1983

The form and structure of supernumerary hindlimbs formed following skin grafting and nerve deviation in the newt Triturus cristatus.

The results of a series of skin grafting experiments performed on the hindlimb of the newt Triturus cristatus are described. In an attempt to limit the position of origin and the complexity of supernumerary limb outgrowths four experimental features were varied. These were 1) size of skin grafts; 2) their position of origin; 3) the position to which they were grafted; and 4) the presence or absence of nerves of two different sizes at the graft site. The degree of distal outgrowth and the pattern of the supernumerary structures in the anterior to posterior and dorsal to ventral axes were assessed. The results are discussed in terms of the control of pattern regulation in localized populations of limb blastema cells.

Animals↗
PubMed1983

The structure of supernumerary limbs formed after 180 degrees blastemal rotation in the newt Triturus cristatus.

The structure of supernumerary limbs formed following 180 degrees ipsilateral blastema rotations in the arm of the newt Triturus cristatus is analysed. Both the skeletal pattern and the muscle patterns are examined. As is the case after comparable experiments in the axolotl (see, for example, Maden & Mustafa, 12982) the extra limbs which form show a range of anatomies. Limbs symmetrical about the dorsal-ventral and anterior-posterior axis are reported as well as some limbs which were part symmetrical and part asymmetrical. It is clear that newts and axolotls appear to react in similar ways to this particular experimental procedure.

Animals↗
PubMed1982

Selective reinnervation of skeletal muscle in the newt Triturus cristatus.

1. A study was made of the effectiveness of synapses formed by foreign and original nerves during reinnervation of skeletal muscle of the newt Triturus cristatus. The extensor cranialis nerve (e.c.n.) of the forelimb was implanted into the humeroantebrachialis muscle (biceps) which was denervated by cutting or crushing the forelimb flexor nerve (f.f.n.). 2. Although biceps became innervated by the implanted nerve, neuromuscular transmission was abnormal. The ratio of the tensions developed by biceps during single and repetitive (50 Hz) stimulation of e.c.n. was lower than either that obtained in normal biceps or during stimulation of f.f.n. after it had regenerated. Similarly, the mean quantal content of e.p.p.s evoked in biceps during stimulation of e.c.n. were lower (m = 17.1) than those evoked in normal muscles (m = 74.6) or during stimulation of the regenerated f.f.n. (m = 40.4). 3. Although the implanted e.c.n. had innervated biceps, after 2-3 months a sprout had grown out of the side of the nerve to reinnervate the extensor digitorum communis muscle (e.d.c.) of the forearm. The mean quantal content of e.p.p.s evoked in this muscle by stimulation of e.c.n. (m = 32.2) was higher than that of those e.p.p.s evoked by stimulation of e.c.n. (m = 32.2) was higher than that of those e.p.p.s evoked by stimulation of the same nerve in biceps (m = 17.1). 4. The results suggest that the synapses formed when a muscle is innervated by an inappropriate nerve are less effective than those formed when reinnervation by the correct nerve occurs. This may account for the tendency of the inappropriate synapses to regress following reinnervation by the correct nerve. In addition however, in the newt there seem to exist mechanisms which ensure that regenerating nerves reinnervate their correct muscles.

Animals↗