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PubMed1994

Model phylogenies to explain the real world.

Phylogenetic trees based on gene sequence data contain information about the evolutionary processes responsible for their genesis. Methods have now been developed which help to reveal those processes. The methods are based on simple models of evolutionary change but, when applied across individuals in a population, rather than across species in a higher-level taxon, they can reveal the past history of population change. Examples from salamanders and viruses are used to illustrate how the past history of changes in speciation rate and the origin of epidemics can be inferred in the absence of fossil material or historical documentation.

Animals↗
PubMed1977

Retinofugal projections in the lepidosirenid lungfishes.

Autoradiographic and silver methods indicate that the African and South American lungfishes, Protopterus and Lepidosiren, lack ipsilateral retinal projections. Contralaterally, the retina projects to the preoptic nucleus of the hypothalamus, to four discrete areas located in the lateral neuropil of the thalamus, to a superficial pretectal neuropil, to the upper half of the tectal neutropil, and to a laterally situated basal optic neuropil located in the rostral tegmentum. The overall pattern of the primary retinofugal projections is markedly similar to that of amphibians which suggests that lungfishes may be more closely related to amphibians than to actinopterygian fishes. Neotenic trends in both lepidosirenid lungfishes and urodeles may be expressions of parallelism, hence Latimeria and Neoceratodus must be examined to resolve this phylogenetic problem. A 300-fold range in the size of the eye, indicated by the number of ganglion cells present, occurs among lungfishes, salamanders and frogs. This variation may have implications for recognizing the morphological expression of selection operating on the visual systems of lepidosirenids and amphibians.

Animals↗
PubMed1981

Ultrastructural changes in olfactory receptor neurons following olfactory nerve section.

Unilateral olfactory nerve section was performed in the salamander, Ambystoma tigrinum. An ultrastructural study was performed to investigate the changes occurring during degeneration and replacement of the mature olfactory receptor neurons. Experimental and contralateral control tissues were examined following postoperative survival periods ranging from 12 hours to 90 days. Normal bipolar receptor neurons have a fusiform cell body containing a thin rim of cytoplasm and an ovoid nucleus with a characteristic "checkerboard" chromatin pattern. A single apical dendrite projects to the surface of the epithelium, where numerous cilia extend from its apex into the overlying mucus. A single, unmyelinated, unbranching axon originates at the basal pole of the cell. After nerve section, retrograde degeneration of the mature neurons occurs. Early degenerative changes include pronounced condensation of the nuclear chromatin, increased number of nuclear membrane infoldings, and dilation of the space between the membranes of the nuclear envelope. At a later stage, the cytoplasm of the cell increases in volume and its organelle systems break down, resulting in accumulation of various forms of cell inclusions. Subsequently, proliferation of cells in the basal region of the epithelium occurs. Between 3 week and 2 months following nerve section, these cells differentiate into mature neurons. By 3 months, neurons within the epithelium have resumed their normal ultrastructure. Correlation of the time course of the ultrastructural changes with previously reported neurophysiological studies indicates that neuronal activity of the epithelium is dependent upon the presence of fully differentiated olfactory receptor neurons.

Ambystoma↗
PubMed1986

Localization of motoneurons innervating the extraocular muscles in Salamandra salamandra L. (Amphibia, Urodela).

The central innervation patterns of the extraocular muscles were investigated in the European fire salamander Salamandra salamandra L. by means of the horseradish peroxidase method. The ipsilateral portion of the nucleus nervi oculomotorii, which is located in the rostral ventral tegmentum mesencephali, supplies the musculi recti inferior and medialis and the musculus obliquus inferior without a clear somatotopic representation of the motoneurons. The musculus rectus superior is innervated mainly by a contralateral portion of this nucleus. A definite nucleus Edinger-Westphal could not be recognized. The nucleus nervi trochlearis, which rostrally joins the nucleus nervi oculomotorii with a gap of only about 40 micron between the nuclei, is situated completely contralateral to the musculus obliquus superior supplied by it. The nucleus nervi abducentis, innervating the musculus rectus lateralis, and the nucleus accessorius nervi abducentis, supplying the musculus retractor bulbi, are found in the ipsilateral medulla oblongata and exhibit a large rostrocaudal extension from the eighth cranial nerve to the first root of the vagus nerve. Dendrites of the nucleus nervi oculumotorii and of the nucleus accessorius nervi abducentis extend into neuropil areas receiving primary sensory afferents.

Abducens Nerve↗
PubMed1988

Topologic and connectional analysis of the dorsal thalamus of Triturus alpestris (amphibia, urodela, salamandridae).

A morphological and connectional analysis was performed on the dorsal thalamus of the alpine newt, Triturus alpestris. We have used a graphic reconstruction technique for the evaluation of the connectional (HRP) data. On the basis of these reconstructions, we propose a subdivision of the salamandrid dorsal thalamus into subhabenular, anteroventral, and posterodorsal zones. Each of these zones is defined by its telencephalic projections ("ascending thalamofugal systems"). The posterodorsal zone projects to the striatum, the anteroventral zone to the pallium. The subhabenular zone projects to the subpallial telencephalon and to the tegmentum. This zonal subdivision allows a more detailed comparison of the salamandrid dorsal thalamic features with ranid dorsal thalamic structures. We compare our dorsal thalamic zones to the ones proposed by Herrick (J. Comp. Neurol. 62:239-261, '35, The Brain of the Tiger Salamander. Chicago: The University of Chicago Press, '48). Furthermore, using the same reconstructive technique, we undertook an analysis of the spatial relations of various inputs to the salamandrid dorsal thalamus ("thalamopetal systems"). Besides the well-known retinal inputs, we identified the tectum and the tegmentum as sources of inputs to the thalamus. We provide evidence that there is no extensive multi- or unimodal overlap of these thalamopetal systems.

Afferent Pathways↗
PubMed1988

Morphology of the caudal spinal cord in Rana (Ranidae) and Xenopus (Pipidae) tadpoles.

Using a variety of neuroanatomical and histological techniques, we compare the spinal cord and peripheral nerve distribution in the tails of larvae from Xenopus laevis and three species of Rana. The relatively large, postsacral spinal cord of Xenopus contains abundant motoneurons and their axons. Spinal nerves exit from the spinal cord in a regular array, one nerve per myotome, from the cervical region to near the end of the tail. Somata of motoneurons innervating caudal myotomes are found along the entire length of the tail. In contrast, the caudal cord of Rana is reduced to a filum terminale consisting of little more than an ependymal tube; spinal nerves to all caudal myotomes leave the cord in the sacral region and reach their motor targets via a cauda equina and caudal plexus. Motoneuron cell bodies innervating caudal myotomes are found only in the sacral region. The Rana larval pattern is similar to that of adult frogs and mammals, whereas the Xenopus larval pattern is more like that of salamanders and reptiles. These gross neuroanatomical differences are not due to differences in the size or developmental stage of the tadpoles, but instead are associated with differences in the swimming behavior of the larvae. The presence of motoneurons in the caudal spinal cord of Xenopus may provide local intermyotomal control within the tail; the elongated topography of the cord appears to permit finer, rostral-to-caudal regulation of neuromuscular activity. The Rana spinal cord, on the other hand--with motoneurons clustered anteriorly--may produce concurrent firing of adjacent ipsilateral myotomes, but at the expense of fine intermyotomal regulation. The fact that nerves in the tail of Xenopus enter and exit from the spinal cord locally, as opposed to far anteriorly as in Rana, means that for tadpoles of the same size, reflex arc lengths are many times shorter in Xenopus.

Animals↗
PubMed1988

Origins of descending projections to the medulla oblongata and rostral medulla spinalis in the urodele Salamandra salamandra (amphibia).

Descending projections to the medulla oblongata and rostral medulla spinalis have been examined in the urodele Salamandra salamandra with retrograde horseradish peroxidase tracing. Ipsilateral projections originate from the striatum and the nucleus ventrolateralis thalami and reach the medulla oblongata. The ipsilateral nucleus praeopticus magnocellularis reaches the medulla spinalis. The rostral part of the nucleus tuberculi posterioris projects to the ipsilateral medulla oblongata; its caudal part projects further caudally. Tectal efferents and the efferents of the nucleus praetectalis profundus project bilaterally, the nucleus praetectalis superficialis, nucleus mesencephalicus nervi trigemini, torus semicircularis, nucleus Darkschewitsch, and nucleus fasciculi longitudinalis medialis project ipsilaterally to the medulla oblongata. The nucleus mesencephalicus nervi trigemini, nucleus fasciculi longitudinalis medialis, and tectal efferents reach the rostral medulla spinalis. The nucleus ruber projects mainly via the contralateral dorsolateral funiculus to the medulla spinalis. A largely crossed medullary projection arises in the nucleus dorsalis tegmenti pars anterior, a bilateral projection arises in the nucleus dorsalis tegmenti pars posterior, and an ipsilateral projection arises in the nucleus ventralis tegmenti pars anterior. Cerebellar and statoacoustic efferents descend to the medulla spinalis. The nucleus reticularis isthmi, superior, medius and inferior as well as the nucleus raphes exhibit spinal trajectories. The nucleus vestibularis magnocellularis projects bilaterally, the nucleus vestibularis medialis projects ipsilaterally spinalward. The supposed nucleus descendens nervi trigemini descends mainly contralaterally. A small spinal projection arises in the nucleus tractus solitarii. The results indicate that salamander brains display elaborate descending connections which are similar to those in other vertebrates despite their scarcely differentiated neuronal cytoarchitecture.

Animals↗
PubMed1990

Immunolabelling by a newt retinal pigment epithelium antibody during retinal development and regeneration.

The binding of RPE-1, a mouse monoclonal antibody selective for newt retinal pigment epithelium, was followed in eyes undergoing embryonic development and retinal regeneration. Using the indirect immunofluorescence technique on frozen sections, we observed bright and continuous labelling exclusively in the retinal pigment epithelium (RPE) of normal adult newts, but labelling became diminished near the ora serrata region and stopped abruptly at the ciliary margin. During development, labelling was not detected in the retinal pigment epithelium (RPE) until the formation of photoreceptor outer segments and was not observed in any other ocular tissue. There was no correlation between the appearance of pigment in retinal pigment epithelial cells and their labelling with the RPE-1 antibody. Furthermore, albino salamander embryos showed the same pattern of labelling with RPE-1 as that seen in age-matched pigmented animals. During retinal regeneration, RPE cells were labelled less intensely, but heavy labelling was observed in the newly formed retinal cells. With time, labelling in regenerated retina receded, so that by the end of regeneration, labelling by RPE-1 was once more restricted to the RPE cells. The identification of RPE-1 as a marker for postmitotic retinal neurons about to undergo differentiation provides a promising approach for further studies of regeneration with the help of molecular tools.

Albinism↗
PubMed1990

Selective labeling of sensory hair cells and neurons in auditory, vestibular, and lateral line systems by a monoclonal antibody.

This study reports that zn-1, a monoclonal antibody, labels hair cells but not supporting cells in the inner ear and the lateral line of the axolotl salamander, Ambystoma mexicanum. Zn-1 immunocytochemically labels the cytoplasm and stereocilia of mature hair cells in the sacculus, in the utriculus, and in the mechanoreceptive neuromast organs of the lateral line. Lower levels of labeling mark newly formed hair cells in the periphery of the sacculus and in regenerating neuromasts. Zn-1 also selectively labels neuronal processes and perikarya in the lateral line nerves and ganglia and the VIIIth cranial nerve and ganglion. Processes and perikarya are labeled by zn-1 in the dorsolateral medulla oblongata, at sites of termination of the afferent octaval and lateral line neurons. Western blot analysis revealed that zn-1 labels one or more proteins with molecular weights of 80 and 160 kDa. The identity of these protein bands remains to be determined. The presence of a specific epitope expressed in both hair cells and neurons, but not in supporting cells, in the vestibular and auditory epithelia of the ear and in the mechanoreceptive neuromasts of the lateral line suggests shared cytogenetic heritages. These findings are consistent with a close evolutionary relationship between otic and lateral line senses, such as that inherent to the theoretical evolutionary scheme outlined in van Bergeijk's "acousticolateralis hypothesis." The protein recognized by zn-1 is as yet unidentified, but its conservative evolution suggests that it may serve an important function in the statoacoustic and lateral line systems.

Afferent Pathways↗
PubMed1991

A light and electron microscopic study of the development of the Mauthner cell and vestibular nerve in the axolotl.

Vestibular axons form synapses on a restricted area of the lateral dendrite of the Mauthner cell, a large, identified brainstem neuron found in fish and amphibians. The differentiation of the vestibular nerve, medullary neuropil, and Mauthner cell of the axolotl (Ambystoma mexicanum) was studied to understand better the means by which this synaptic specificity arises. The Mauthner cell first extends a medial process and then a lateral dendrite. The latter initially elongates as a simple process and later sends out branches. As the lateral dendrite grows, vestibular axons enter the brainstem to form one of the earliest of several discrete axon fascicles that course longitudinally through the neuropil. The fascicles, many of which are identifiable on the basis of their location and axonal morphology, are the precursors of the longitudinal tracts of the mature salamander. The lateral dendrite grows dorsally over the orthogonally oriented fascicles, making contact with each at a characteristic time and place. The first afferents to form synapses do so on the soma and proximal lateral dendrite; subsequent afferent groups terminate more distally. Axons within a given fascicle form synapses with the Mauthner cell in a discrete and initially homogeneous domain. As dendritic branches form and the organization of the longitudinal fascicles becomes more complex, the homogeneity of axons terminating on a given region of the Mauthner cell surface is lost, but no major rearrangement or migration of terminals is apparent. These observations are consistent with both active recognition and passive spatiotemporal models of synaptic site specificity.

Ambystoma mexicanum↗
PubMed1995

Development of branchiomeric and lateral line nerves in the axolotl.

The differentiation of neural crest and ectodermal placodes was examined in the axolotl in order to clarify the contribution of these tissues to the formation of the sensory ganglia of the branchiomeric and lateral line cranial nerves in salamanders. The most rostral branchiomeric nerves, the profundal and trigeminal nerves, appear to arise solely from an ectodermal placode and from neural crest, respectively. The sensory ganglia of the more caudal branchiomeric nerves--the facial, glossopharyngeal, and vagal nerves--are formed by a medial component that differentiates from the dorsomedial surface of migrating bands of neural crest associated with each of the developing branchial arches and with one or more lateral components that arise from epibranchial placodes located immediately dorsal and caudal to each pharyngeal pouch. Neuroblasts destined to form these sensory ganglia begin to differentiate from the epibranchial placodes as early as stage 26, whereas neural crest-derived neuroblasts can be recognized by stage 30. Centrally directed neurites of both groups of neuroblasts enter the medulla by stage 34, and their peripherally directed neurites form recognizable rami by stage 35. Five cranial lateral line nerves, in addition to the octaval nerve, can be recognized in axolotls. Each of these nerves arises from a separate dorsolateral placode that initially gives rise to the neuroblasts of a sensory ganglion whose peripheral neurites innervate sensory receptors subsequently formed from each placode. The time course of the differentiation of these nerves and receptors is comparable to that of the branchiomeric nerves. The possible roles of rhombomeres and their associated regulatory genes and pharyngeal pouches in the induction and specification of neural crest and ectodermal placodes are explored.

Ambystoma mexicanum↗
PubMed1995

Immunohistological localization of tenascin-C in the developing and regenerating retinotectal system of two amphibian species.

The expression pattern of the extracellular matrix molecule tenascin-C was investigated in the retinotectal system of the frog Discoglossus pictus and the salamander Pleurodeles waltl during development and optic nerve regeneration in the adult. In both species, the retina was devoid of tenascin-C immunoreactivity at all ages studied. During development, tenascin-C was distributed in a gradient in the optic nerve, with the highest immunoreactivity in the eye near part of the optic nerve. The myelin-associated glycoprotein was distributed in a gradient with opposite polarity. In Discoglossus, but not Pleurodeles, tenascin-C was detected in the anterior chiasm. In the tectum of both species, tenascin-C was observed in deep cellular and fiber layers but not in the layers receiving optic fibers or proliferative zones. The distribution patterns of tenascin-C were the same during development and in the adult, except for a disappearance of the molecule from the intraocular part of the optic nerve. After lesioning the optic nerve of adult animals, tenascin-C was strongly reexpressed in the intraocular part of the optic nerve but was only weakly upregulated in the distal optic nerve stump. In contrast, a chondroitin sulfate epitope was strongly upregulated in the distal optic nerve stump. These observations suggest that during development, tenascin-C serves as an attenuating barrier for myelinating cells in the optic nerve and contributes to the guidance of growing retinal ganglion cell axons. Due to its sustained expression in the adult, tenascin-C may have similar functions during regeneration of the lesioned adult retinotectal system.

Animals↗
PubMed2003

Regeneration or scarring: an immunologic perspective.

Complete regeneration of complex tissues and organs is usually precluded by fibrotic reactions that lead to scarring. Fish, salamanders, and larval anurans are among the few vertebrates capable of regenerating lost appendages, and this process seems to recapitulate ontogenic development of the structure in most respects. Recent work has revealed a capacity for excellent regeneration in certain mammalian tissues: embryonic or fetal skin and the ear of the MRL mouse. Analyses of these two systems suggest that processes of regenerative growth and patterning for the formation of new structures such as hair follicles may involve modulation of the inflammatory response to the injury in a way that reduces fibrosis and formation of scar tissue. We review evidence that this modulation includes changes in cytokine signaling and may involve properties of the extracellular matrix mediated by factors that include hyaluronic acid and "anti-adhesive substrates" such as tenascin-C. New studies and classic work on the capacity for limb regeneration in amphibians are then reviewed, focusing on the loss of this ability in prometamorphic anuran hindlimbs and the view that changing properties of the immune system may also underlie the declining regenerative potential in this system. Finally, we review recent work in comparative and developmental immunology, which raises the possibility that phylogenetic changes in regenerative capacity may be the result of evolutionary changes in cellular activities of the immune system.

Amphibians↗
PubMed2003

Urodele spinal cord regeneration and related processes.

Urodele amphibians, newts and salamanders, can regenerate lesioned spinal cord at any stage of the life cycle and are the only tetrapod vertebrates that regenerate spinal cord completely as adults. The ependymal cells play a key role in this process in both gap replacement and caudal regeneration. The ependymal response helps to produce a different response to neural injury compared with mammalian neural injury. The regenerating urodele cord produces new neurons as well as supporting axonal regrowth. It is not yet clear to what extent urodele spinal cord regeneration recapitulates embryonic anteroposterior and dorsoventral patterning gene expression to achieve functional reconstruction. The source of axial patterning signals in regeneration would be substantially different from those in developing tissue, perhaps with signals propagated from the stump tissue. Examination of the effects of fibroblast growth factor and epidermal growth factor on ependymal cells in vivo and in vitro suggest a connection with neural stem cell behavior as described in developing and mature mammalian central nervous system. This review coordinates the urodele regeneration literature with axial patterning, stem cell, and neural injury literature from other systems to describe our current understanding and assess the gaps in our knowledge about urodele spinal cord regeneration.

Animals↗
PubMed2007

Targeted gene delivery to differentiated skeletal muscle: a tool to study dedifferentiation.

Cellular dedifferentiation is required for functional regeneration in salamanders. Dedifferentiating multinucleate skeletal muscle gives rise to mononucleate cells during limb regeneration. Efficient methods and tools must be developed in order to understand the molecular cues underlying dedifferentiation. Here we describe a non-viral method to express extra-chromosomal DNA exclusively in terminally differentiated muscle without the need for cell purification steps. After cytoplasmic injection of various expression vectors into myotubes or myofibres, we detect long-lasting mRNA and protein expression in up to 70% of the injected cells. The combination of the transfection protocol with live imaging allows a time- and cost-effective screen of candidate genes in terminally differentiated muscle cells of both amphibian and mammalian origin.

Animals↗
PubMed2003

A high-throughput on-line microdialysis-capillary assay for D-serine.

A high-throughput method is described for the analysis of D-serine and other neurotransmitters in tissue homogenates. Analysis is performed by microdialysis-capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection in a sheath flow detection cell. Sample pretreatment is not required as microdialysis sampling excludes proteins and cell fragments. Primary amines are derivatized on-line with o-phthaldialdehyde (OPA) in the presence of beta-mercaptoethanol followed by on-line CE-LIF analysis. Under the separation conditions described here, D-serine is resolved from L-serine and other primary amines commonly found in biological samples. Each separation requires less than 22 s. Eliminating the need for sample pretreatment and performing the high-speed CE analysis on-line significantly reduces the time required for D-serine analysis when compared with traditional methods. This method has been used to quantify D-serine levels in larval tiger salamander retinal homogenates, as well as dopamine, gamma-amino-n-butyric acid (GABA), glutamate and L-aspartate. D-serine release from an intact retina was also detected.

Animals↗
PubMed1991

Localization and stoichiometry of electrogenic sodium bicarbonate cotransport in retinal glial cells.

An electrogenic Na+/HCO3- cotransport system was identified and characterized in freshly dissociated salamander Müller (glial) cells. Under voltage-clamp, these cells generated an outward current when external HCO3- concentration [( HCO3-]o) was raised. This current was Na(+)-dependent, Cl(-)-independent, and was blocked by the stilbenes 4,4'-diisothiocyanato-stilbene-2,2'-disulfonate (DIDS) and 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS), and by harmaline, demonstrating that the current was generated by a Na+/HCO3- cotransport system. Substantially larger currents were evoked when [HCO3-]o was raised at the Müller cell endfoot as compared to other cell regions, indicating that cotransporter sites are localized preferentially to the endfoot. The reversal potential of the current, which varied as a function of HCO3- and Na+ transmembrane gradients, indicated that the cotransporter has a HCO3-:Na+ stoichiometry of 3:1.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Microglial cells in the brain of Pleurodeles waltl (Urodela, Salamandridae) after wallerian degeneration in the primary visual system using Bandeiraea simplicifolia isolectin B4-cytochemistry.

In the brain of the salamander Pleurodeles waltl, microglial cells were investigated cytochemically with isolectin B4 (IB4) of Bandeiraea simplicifolia after optic nerve transection and during subsequent regeneration. Double-labeling with an antibody directed against the glial fibrillary acidic protein of astrocytes revealed no immunoreactivity in microglial cells and confirmed the absence of non-radial, free astroglial cells in the tectum. After two days, IB4-labeled microglial cells began to populate the rostral parts of the primary visual system. The origin of these early vimentin-immunoreactive microglial cells seemed to be mainly IB4-labeled cells in a perivascular position and meningeal macrophages. After 12 days, microglial cells infiltrated the tectum in four layers: one in the ependyma, one in the outermost periventricular grey, and two in the degenerating visual neuropil where activated microglial cells displayed a ramified morphology. After 3 weeks, microglial cells accumulated within the degenerating neuropil while reducing their processes. After 7 weeks, the number of microglial cells was still increased on the affected side. The subarachnoid space above the neuropil where regenerating retinal afferents arrived was filled with IB4-labeled macrophages. Only very few microglial cells were seen in co-existence with Müller cells in the lesioned and intact retinae, whereas microglial cells and macrophages were IB4-labeled in the optic nerve head and at the ora serrata.

Animals↗