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PubMedDate not supplied

The lateral spread of ictal discharges in neocortical brain slices.

The in vitro brain slice technique was used to examine the lateral propagation of spontaneous electrographic ictal episodes across adjacent areas of guinea pig neocortex. Epileptiform activity was induced by perfusing slices with Mg-free artificial CSF. Simultaneous field potential recordings of ictal episodes were obtained from 4 micropipettes placed 1-3 mm apart across coronal slices in middle-cortical layers. Two types of lateral spread were characterized. Ictal episodes often developed focally and then spread as a slowly moving wavefront traveling at less than 0.3 mm/sec into adjacent, uninvolved cortex. By contrast, other episodes began nearly synchronously at all cortical sites. The individual afterdischarges that composed each ictal episode propagated rapidly across the cortex at greater than 30 mm/sec and were triggered by multiple pacemakers. Ictal episodes always terminated abruptly across the entire slice. The NMDA-receptor antagonist, 2-amino-phosphono-valerate, applied focally between recording sites, blocked rapid propagation across treated areas and resulted in the emergence of spatially separate, independent pacemakers. Pacemaker failure is the proposed mechanism for simultaneous and generalized termination of ictal episodes in this in vitro model of epileptogenesis.

2-Amino-5-phosphonovalerate↗
PubMed2006

Imaging of small high-density structures in CT A phantom study.

RATIONALE AND OBJECTIVES: The aim of this work is to study how the limited spatial resolution of a computed tomographic (CT) system affects the imaging of small high-density structures. This knowledge is relevant not only to understand and interpret clinical data, but also to apply and develop quantification methods for calcifications and stented vessels. MATERIALS AND METHODS: A dedicated phantom containing small differently sized aluminum cylinders was imaged on a 64-slice multidetector row CT (MDCT) while varying acquisition and reconstruction parameters from a high-resolution protocol. In addition, a bead phantom was imaged to estimate the point spread function (PSF) for the different parameter settings. The accuracy in determining object density and size was established for various imaging protocols and compared with simulations based on the estimated PSF. RESULTS: Attenuation values and size measurements were accurate for objects larger than two times the size of the system PSF at the full-width-at-half-maximum. For smaller objects, attenuation values were increasingly underestimated and size was increasingly overestimated. The convolution kernel had the most influence on object signal and size. Use of edge-enhancing kernels yielded more accurate size measurements and higher signal for small objects. However, their application was constrained by noise amplification and edge-ringing artifacts, which led to lower signal-to-noise ratio, degrading the visualization of low densities and small high-density objects. CONCLUSION: Results presented in this report provide insight into limitations in the quantification of small high-density structures and their effect on the visualization of surrounding tissues with recently developed MDCT systems.

Calcinosis↗
PubMed2006

Cooperative non-cell and cell autonomous regulation of Nodal gene expression and signaling by Lefty/Antivin and Brachyury in Xenopus.

Dynamic spatiotemporal expression of the nodal gene and its orthologs is involved in the dose-dependent induction and patterning of mesendoderm during early vertebrate embryogenesis. We report loss-of-function studies that define a high degree of synergistic negative regulation on the Xenopus nodal-related genes (Xnrs) by extracellular Xenopus antivin/lefty (Xatv/Xlefty)-mediated functional antagonism and Brachyury-mediated transcriptional suppression. A strong knockdown of Xlefty/Xatv function was achieved by mixing translation- and splicing-blocking morpholino oligonucleotides that target both the A and B alloalleles of Xatv. Secreted and cell-autonomous inhibitors of Xnr signaling were used to provide evidence that Xnr-mediated induction was inherently long-range in this situation in the large amphibian embryo, essentially being capable of spreading over the entire animal hemisphere. There was a greater expansion of the Organizer and mesendoderm tissues associated with dorsal specification than noted in previous Xatv knockdown experiments in Xenopus, with consequent exogastrulation and long-term maintenance of expanded axial tissues. Xatv deficiency caused a modest animal-ward expansion of the marginal zone expression territory of the Xnr1 and Xnr2 genes. In contrast, introducing inhibitory Xbra-En(R) fusion constructs into Xatv-deficient embryos caused a much larger increase in the level and spatial extent of Xnr expression. However, in both cases (Xatv/Xlefty-deficiency alone, or combined with Xbra interference), Xnr2 expression was constrained to the superficial cell layer, suggesting a fundamental tissue-specific competence in the ability to express Xnrs, an observation with direct implications regarding the induction of endodermal vs. mesodermal fates. Our experiments reveal a two-level suppressive mechanism for restricting the level, range, and duration of Xnr signaling via extracellular inhibition by Xatv/Xlefty coupled with potent indirect transcriptional repression by Xbra.

Alternative Splicing↗
PubMed1999

Temporal constraints on the grouping of contour segments into spatially extended objects.

The speed of contour integration was investigated in a task that can be solved by grouping contour segments into elongated curves. Subjects had to detect a continuous curve, which could be intersected by one or two other curves. At locations where these curves came in close proximity, the assignment of contour segments to the different curves could be based on collinearity. Reaction times exhibited a strong dependence on (1) the presence of intersections among curves; and (2) the context provided by the stimulus set from which individual stimuli were selected. Reaction times were shortest when grouping of contour segments depended on information at a single location in the visual field. In this condition, responses to stimuli containing an intersection were faster than responses to stimuli that did not. When responses were determined by information at spatially separate locations, responses were delayed, and every intersection increased the reaction time considerably. This result contrasts with earlier investigations which have suggested that contour integration on the basis of collinearity is performed pre-attentively but is in accordance with studies on curve tracing. We propose that the assignment of contour segments to equally coherent curves, a process which may be called figure-figure segregation, is a function of object-based attention. Moreover, the protracted reaction times for some of the stimuli indicate that spread of attention within an object costs time. This implies that object recognition is not always as fast as is sometimes assumed.

Attention↗
PubMedDate not supplied

[The combined use of instrumental and laboratory examinations in multiple sclerosis: is the diagnostic facilitation real?].

Spatial-temporal dissemination of neurological signs is an essential criterion for establishing a definite diagnosis of Multiple Sclerosis (MS). Unfortunately, we often observe patients who present a history consistent with MS but without objectivity indicating the presence of at least two or more distinct lesions of Central Nervous System (CNS). In recent years, many Authors have emphasized the use of Multimodal Evoked Responses (MER), Cerebrospinal Fluid (CSF) analysis for the research of Oligoclonal Bands (OB), and Magnetic Resonance Imaging (MRI) as highly sensitive techniques for demonstrating the spreading of the lesions. This study, carried out to evaluate whether the combined use of these three methods would increase the diagnostic MS sensitivity, comprises 62 patients classified in Definite (n = 24). Probable (n = 18) and Possible (n = 20) MS according to the clinical criteria of McAlpine. All our cases fulfilled a complete ER evaluation (VER, SER, BAER), a paired CSF and serum Isoelectric focusing (IEF) and a cerebral MRI. Moreover, IgG Index was also estimated. CSF IEF was the most sensitive test in Definite (91.7%) and Possible (80.0%) MS, nearly followed by MRI (87.5% and 45.0% respectively). VER (87.5% and 60.0%) and SER (87.5% and 65.0%). On the contrary, MRI showed the higher sensitivity in Probable MS (94.4%). The course of the disease influenced only SER and VER in all diagnostic group, while the duration correlated positively with BAER and VER. Only VER and BAER, finally, supplied additional information about the not revealed clinically or by MRI CNS disorders. Thus, our data further emphasize the value of combining these laboratory tests for establishing an early and more accurate diagnosis of MS.

Brain↗
PubMed2006

Temporal differentiation and spatial coexistence of sexual and facultative asexual lineages of an aphid species at mating sites.

Cases of coexisting sexual and asexual relatives are puzzling, as evolutionary theory predicts that competition for the same ecological niches should lead to the exclusion of one or the other population. In the cyclically parthenogenetic aphid, Rhopalosiphum padi, sexual and facultative asexual lineages are admixed in space at the time of sexual reproduction. We investigated how the interaction of reproductive mode and environment can lead to temporal niche differentiation. We demonstrated theoretically that differential sensitivity of sexual and facultatively asexual aphids to an environmental parameter (mating host suitability) shapes the two strategies: whereas the sexual lineages switch earlier to the production of sexual forms, the facultative asexual lineages delay and spread out their investment in sexual reproduction. This predicted pattern of niche specialization is in agreement with the temporal structure revealed in natura by demographic and genetic data. We propose that partial loss of sex by one pool of aphids and subsequent reduction in gene flow between lineages may favour temporal specialization through disruptive selection.

Animals↗
PubMed1991

Simulated bipolar cells in fovea of human retina. I. Computer simulation.

This static bipolar cell (BC) model of the human fovea is based on a number of reasonable assumptions. The human fovea is directly responsible for visual acuity and color vision. The fovea can be considered as having two parts; a central fovea with only red- and green-sensitive cones and a parafovea with blue-sensitive cones added to the other two. A cone mosaic can be precisely organized spatially into unit hexagons that specify inputs to horizontal cells (HC) and BCs. The retina up to and including BCs is piece-wise linear, i.e. at a given steady-state adapting light intensity BC outputs are linear functions of the physical image. BC centers receive inputs directly from weighted cones, while antagonistic surrounds receive inverted inputs from HCs. Appropriate optical and chromatic filtering due to the eye that are taken from human data are incorporated into the model. Chromatic aberrations are simulated by three separate point spread functions that also are taken from human data. Automatic gain control of cones is a function of intensity and wavelength of the steady adapting light.

Color Perception↗
PubMed1982

Resolution and contrast recovery at depth in planar nuclear images.

Resolution and contrast recovery in planar nuclear images at depth with a high purity germanium (HPGe) camera has been achieved through use of a weighted back projection (WBP) method. The algorithm can be derived from Bayes' theorem using the point spread function of the camera. The variations in the formulation of WBP (one single pass and two iterative procedures) are presented with the characteristics and performance of each method. The evaluation procedure determines the behaviour of signal-to-noise ratio, contrast and texture after application of the algorithm. Both real and simulated cold lesions obtained with the HPGe camera are studied with sizes ranging from 3 mm to 17 mm and background count densities from 100 to 6400 counts cm2. Application of WBP is shown to increase spatial resolution and contrast without a concomitant reduction in signal-to-noise ratio. Images obtained with the HPGe camera and processed with WBP are presented. The algorithm has been applied to the scintillation camera, yielding significant resolution and contrast recovery despite the presence of scatter and textured noise present in the HPGe images.

Animals↗
PubMed2004

Stochastic and spatial dynamics of nematode parasites in farmed ruminants.

Host-parasite systems provide powerful opportunities for the study of spatial and stochastic effects in ecology; this has been particularly so for directly transmitted microparasites. Here, we construct a fully stochastic model of the population dynamics of a macroparasite system: trichostrongylid gastrointestinal nematode parasites of farmed ruminants. The model subsumes two implicit spatial effects: the host population size (the spatial extent of the interaction between hosts) and spatial heterogeneity ('clumping') in the infection process. This enables us to investigate the roles of several different processes in generating aggregated parasite distributions. The necessity for female worms to find a mate in order to reproduce leads to an Allee effect, which interacts nonlinearly with the stochastic population dynamics and leads to the counter-intuitive result that, when rare, epidemics can be more likely and more severe in small host populations. Clumping in the infection process reduces the strength of this Allee effect, but can hamper the spread of an epidemic by making infection events too rare. Heterogeneity in the hosts' response to infection has to be included in the model to generate aggregation at the level observed empirically.

Animal Husbandry↗
PubMed2006

Ultrasonic tracking of acoustic radiation force-induced displacements in homogeneous media.

The use of ultrasonic methods to track the tissue deformation generated by acoustic radiation force is subject to jitter and displacement underestimation errors, with displacement underestimation being primarily caused by lateral and elevation shearing within the point spread function (PSF) of the ultrasonic beam. Models have been developed using finite element methods and Field II, a linear acoustic field simulation package, to study the impact of focal configuration, tracking frequency, and material properties on the accuracy of ultrasonically tracking the tissue deformation generated by acoustic radiation force excitations. These models demonstrate that lateral and elevation shearing underneath the PSF of the tracking beam leads to displacement underestimation in the focal zone. Displacement underestimation can be reduced by using tracking beams that are narrower than the spatial extent of the displacement fields. Displacement underestimation and jitter decrease with time after excitation as shear wave propagation away from the region of excitation reduces shearing in the lateral and elevation dimensions. The use of higher tracking frequencies in broadband transducers, along with 2D focusing in the elevation dimension, will reduce jitter and improve displacement tracking accuracy. Relative displacement underestimation remains constant as a function of applied force, whereas jitter increases with applied force. Underdeveloped speckle (SNR < 1.91) leads to greater levels of jitter and peak displacement underestimation. Axial shearing is minimal over the tracking kernel lengths used in acoustic radiation force impulse imaging and thus does not impact displacement tracking.

Acoustics↗
PubMed2006

Establishment of transgenic herbicide-resistant creeping bentgrass (Agrostis stolonifera L.) in nonagronomic habitats.

Concerns about genetically modified (GM) crops include transgene flow to compatible wild species and unintended ecological consequences of potential transgene introgression. However, there has been little empirical documentation of establishment and distribution of transgenic plants in wild populations. We present herein the first evidence for escape of transgenes into wild plant populations within the USA; glyphosate-resistant creeping bentgrass (Agrostis stolonifera L.) plants expressing CP4 EPSPS transgenes were found outside of cultivation area in central Oregon. Resident populations of three compatible Agrostis species were sampled in nonagronomic habitats outside the Oregon Department of Agriculture control area designated for test production of glyphosate-resistant creeping bentgrass. CP4 EPSPS protein and the corresponding transgene were found in nine A. stolonifera plants screened from 20,400 samples (0.04 +/- 0.01% SE). CP4 EPSPS-positive plants were located predominantly in mesic habitats downwind and up to 3.8 km beyond the control area perimeter; two plants were found within the USDA Crooked River National Grassland. Spatial distribution and parentage of transgenic plants (as confirmed by analyses of nuclear ITS and chloroplast matK gene trees) suggest that establishment resulted from both pollen-mediated intraspecific hybridizations and from crop seed dispersal. These results demonstrate that transgene flow from short-term production can result in establishment of transgenic plants at multi-kilometre distances from GM source fields or plants. Selective pressure from direct application or drift of glyphosate herbicide could enhance introgression of CP4 EPSPS transgenes and additional establishment. Obligatory outcrossing and vegetative spread could further contribute to persistence of CP4 EPSPS transgenes in wild Agrostis populations, both in the presence or absence of herbicide selection.

Agriculture↗
PubMed1999

Habitat-specific genetic effects on growth rate and morphology across pH and water-level gradients within a population of the moss Sphagnum angustifolium (Sphagnaceae).

To study genetic adaptations in bryophytes on small ecological and spatial scales and to assess the adaptive significance of morphological trait variation, genotypes of Sphagnum angustifolium originating from habitats characterized by different pH and height above water table were clonally propagated and grown along the same gradients that exist in the field. Clones from ombrotrophic habitats grew consistently better ombrotrophically than clones from minerotrophic habitats and vice versa, suggesting that the genotypes were adapted to different pH levels. Genetic variation was found in several morphological traits, but habitat-specific genetic effects were detected only in length of spreading branches. Covariation between morphology and growth was generally environmentally induced. Positive and negative cross-environment genetic correlations suggested the presence of constraints on adaptive reaction norm evolution. The indications of small-scale genetic adaptations suggest either selective establishment of genotypes adapted to specific habitats, strong selective forces operating at the later stages of the life cycle, restricted gene flow over short distances, or a combination of these. In contrast to prevailing views, these results indicate that bryophytes are likely to respond genetically to small-scale environmental gradients.

Journal Article↗
PubMed2005

Recent, allopatric, homoploid hybrid speciation: the origin of Senecio squalidus (Asteraceae) in the British Isles from a hybrid zone on Mount Etna, Sicily.

Homoploid hybrid speciation occurs through stabilization of a hybrid segregate (or segregates) isolated by premating and/or postmating barriers from parent taxa. Theory predicts that ecological and spatial isolation are of critical importance during homoploid hybrid speciation, and all confirmed homoploid hybrid species are ecologically isolated from their parents. Until recently, such species have been identified long after they originated, and consequently it has not been possible to determine the relative importance of spatial and ecological isolation during their origin. Here we present evidence for the recent origin (within the past 300 years) of a new homoploid hybrid species, Senecio squalidus (Asteraceae), in the British Isles, following long-distance dispersal of hybrid material from a hybrid zone between S. aethnensis and S. chrysanthemifolius on Mount Etna, Sicily, Italy. Historical records show that such hybrid material from Sicily was introduced to the Oxford Botanic Garden in Britain in the early part of the 18th century and that S. squalidus began to spread from there after approximately 90 years. A survey of randomly amplified polymorphic DNA/intersimple sequence repeats (RAPD/ISSR) marker variation demonstrated that S. squalidus is a diploid hybrid derivative of S. aethnensis and S. chrysanthemifolius that grow at high and low altitudes, respectively, on Mount Etna and that form a hybrid zone at intermediate altitudes. Senecio squalidus contained 11 of 13 RAPD/ISSR markers that were recorded at high frequency in S. chrysanthemifolius but were absent or occurred at low frequency in S. aethnensis, and 10 of 13 markers for which the reverse was true. Bayesian admixture analysis showed that all individuals of S. squalidus surveyed were of mixed ancestry with relatively high mean proportions of ancestry derived from both S. chrysanthemifolius and S. aethnensis (0.644 and 0.356, respectively). We argue that long-distance isolation of hybrid material from its parents on Mount Etna would have helped favor the origin and establishment of S. squalidus in the British Isles, regardless of whether the initial hybrid material introduced to Britain was preadapted to local conditions.

Altitude↗
PubMed1977

[Spatial deployments of morphogenetic movements as elements of the oral field in anuran amphibians. II. The structure of the oral field].

The structure of morphogenetic movements in the oral field of Anura was studied. The movement of any region of the oral field depends on several "elementary waves" of morphogenetic rearrangements, each of them being swept in space along the same cell layer. The waves of morphological rearrangements of cells from different layers are coupled with each other in a stable manner. The cells of the given layer are involved in their morphogenetic movements consecutively, whereas the morphogenetic movements of cells in the interrelated layers are developed in parallel. The waves of morphological rearrangements are those of contact polarization of the cells and, under certain conditions, are spread within several minutes.

Amphibians↗
PubMed2005

Developmental appearance of dentin matrix protein 1 during the early dentinogenesis in rat molars as identified by high-resolution immunocytochemistry.

Dentin matrix protein 1 (DMP 1) is an acidic phosphoprotein that has been postulated to play an important role in mineralized tissue formation. We have examined rat molar tooth germs by applying a high-resolution immunocytochemical approach with the purpose to identify the temporal and spatial localization of DMP 1 at the onset of dentinogenesis. Upper molar tooth germs of 2- to 3-day-old Wistar rats were fixed in a cacodylate-buffered 0.1% glutaraldehyde + 4% formaldehyde fixative, left unosmicated and embedded in LR White resin. The sections were incubated with a polyclonal DMP 1 antibody for postembedding colloidal gold immunolabeling and examined in a Jeol 1010 transmission electron microscope. The earliest localization of DMP 1 was in the Golgi region as well as in the nucleus of differentiating odontoblasts. When mineralization spread from matrix vesicles to the surrounding matrix, DMP 1 was extracellularly detected around the mineralizing globules. In the regions of fully mineralized mantle dentin, it was present in the mineralized regions, mainly around the peritubular dentin. The appearance of DMP 1 during early dentinogenesis implies a direct role for this protein in both odontoblast differentiation and matrix mineralization.

Animals↗
PubMed2006

Competing selfish genetic elements in the butterfly Hypolimnas bolina.

Maternally inherited selfish genetic elements are common in animals . Whereas host genetics and ecology are recognized as factors that may limit the incidence of these parasites , theory suggests one further factor-interference with other selfish elements-that could affect their prevalence . In this paper, we show that spatial heterogeneity in the occurrence of the male-killing Wolbachia wBol1 in the tropical butterfly Hypolimnas bolina is caused by a second infection that can exclude the male-killer. We first provide evidence of a second Wolbachia strain, wBol2, present in most populations that do not carry the male-killer but rare or absent when the male-killer is present. Crossing data indicate that wBol2 in males induces cytoplasmic incompatibility to both uninfected and wBol1-infected females. The wBol2 infection can therefore not only spread through uninfected populations but also resist invasion by wBol1. Thus, we provide empirical support for the hypothesis that the incidence of particular selfish genetic elements can limit the presence of competing types.

Animals↗
PubMed2006

Biogenic emissions of isoprenoids and NO in China and comparison to anthropogenic emissions.

In this study, a regional dynamical model (WRF) is used to drive biogenic emission models to calculate high resolution (10x10 km) biogenic emissions of isoprene (C(5)H(8)), monoterpenes (C(10)H(16)), and nitric oxide (NO) in China. This high resolution biogenic inventory will be available for the community to study the effect of biogenic emissions on photochemical oxidants in China. The biogenic emissions are compared to anthropogenic emissions to gain insight on the potential impact of the biogenic emissions on tropospheric chemistry, especially ozone production in this region. The results show that the biogenic emissions in China exhibit strongly diurnal, seasonal, and spatial variations. The isoprenoid (including both isoprene and monoterpenes) emissions are closely correlated to tree density and strongly vary with season and local time. During winter (January), the biogenic isoprenoid emissions are the lowest, resulting from lower temperature and solar radiation, and highest in summer (July) due to higher temperature and solar radiation. The biogenic NO emissions are also higher during summer and lower during winter, but the magnitude of the seasonal variation is smaller than the emissions of isoprene and monoterpenes. The biogenic emissions of NO are widely spread out in the northern, eastern, and southern China regions, where high-density agricultural soil lands are located. Both biogenic NO and isoprenoid emissions are very small in western China. The calculated total biogenic emission budget is smaller than the total anthropogenic VOC emission budget in China. The biogenic isoprenoid and anthropogenic VOC emissions are 10.9 and 15.1 Tg year(-1), respectively. The total biogenic and anthropogenic emissions of NO are 5.9 and 11.5 Tg(NO) year(-1), respectively. The study shows that in central eastern China, the estimated biogenic emissions of isoprenoids are very small, and the anthropogenic emissions of VOCs are dominant in this region. However, in northeastern and southern China, there are relatively large biogenic emissions of isoprenoids, leading to an important impact on the ozone production in these regions. Furthermore, the emissions of isoprenoids are highest during summer and noontime, which correlates to the peak of ozone production period. For example, the ratio between summer and winter for the emissions of isoprenoids is about 15 in China. As a result, the biogenic emissions of isoprenoids are significantly larger than the anthropogenic emissions of VOCs in China during daytime in summer. Biogenic NO emissions are mostly produced by agricultural soils which co-exist with large populations and human activity. As a result, the biogenic emissions of NO are mostly overlapped with the anthropogenic emissions of NO, leading to the enhancement in NO concentrations in the high anthropogenic NO emission regions. Finally, the future emissions of isoprene and monoterpenes over China are estimated. The results show that the future biogenic emissions may increase significantly due to land cover changes in central eastern China, which could have a very important impact on ozone formation in this region. However, these estimates are highly uncertain and are presented as a potential scenario to show the importance of possible changes of biogenic emissions in China.

Air Pollutants↗
PubMed1999

The neural induction process; its morphogenetic aspects.

This posthumous review of early embryonic inductions concludes: 1) the amphibian egg has only two distinct components, animal and vegetal. Interactions at their mutual boundary forms meso-endoderm. This is "meso-endoderm induction", not just "mesoderm induction". 2) The dorso-ventral polarity of the yolk mass implies a dorsally situated inducing centre. 3) Accumulation of cells into one, two, three or many cell masses [problastopores] along the circumference of the meso-endoderm results in as many axes, implying a self-organizing capacity of meso-endoderm. 4) Induction of the meso-endoderm is slow, spreading cell to cell through the animal moiety from the boundary of the vegetal yolk mass towards the animal pole. 5) Interaction between mesoderm and ectoderm is a separate step leading to cranio-caudal differentiation of the archenteron roof. 6) The initial invaginating endoderm and mesoderm, representing the future pharynx endoderm and prechordal plate mesoderm, first contacts the most posterior presumptive neurectoderm after having passed the still uninvaginated trunk mesoderm. At that moment an antero-posterior level neural induction actually starts. 7) The ectoderm contraction wave coincides spatially and temporally with the induced neural plate. 8) Two successive homoiogenetic waves of inductive activity pass through the presumptive neurectoderm in the anterior direction, the first one, "activation", giving rise to neural differentiation and ultimately forebrain, the second one, "transformation", to more caudal CNS structures. These are separate, successive steps in CNS regional induction. 9) The midbrain represents a secondary formation in the neural plate. 10) The observed changes in morphogenesis may depend upon separate, successive binary decisions via [cell and] nuclear state splitters [involving differentiation waves].

Ambystoma↗