Origins of radial symmetry identified in an echinoderm during adult development and the inferred axes of ancestral bilateral symmetry

How the radial body plan of echinoderms is related to the bilateral body plan of their deuterostome relatives, the hemichordates and the chordates, has been a long-standing problem. Now, using direct development in a sea urchin, I show that the first radially arranged structures, the five primary podia, form from a dorsal and a ventral hydrocoele at the oral end of the archenteron. There is a bilateral plane of symmetry through the podia, the mouth, the archenteron and the blastopore. This adult bilateral plane is thus homologous with the bilateral plane of bilateral metazoans and a relationship between the radial and bilateral body plans is identified. I conclude that echinoderms retain and use the bilateral patterning genes of the common deuterostome ancestor. Homologies with the early echinoderms of the Cambrian era and between the dorsal hydrocoele, the chordate notochord and the proboscis coelom of hemichordates become evident.

Zebrafish dentition in comparative context

Studies of the zebrafish (Danio rerio) promise to contribute much to an understanding of the developmental genetic mechanisms underlying diversification of the vertebrate dentition. Tooth development, structure, and replacement in the zebrafish largely reflect the primitive condition of jawed vertebrates, providing a basis for comparison with features of the more extensively studied mammalian dentition. A distinctive derived feature of the zebrafish dentition is restriction of teeth to a single pair of pharyngeal bones. Such reduction of the dentition, characteristic of the order Cypriniformes, has never been reversed, despite subsequent and extensive diversification of the group in numbers of species and variety of feeding modes. Studies of the developmental genetic mechanism of dentition reduction in the zebrafish suggest a potential explanation for irreversibility in that tooth loss seems to be associated with loss of developmental activators rather than gain of repressors. The zebrafish and other members of the family Cyprinidae exhibit species-specific numbers and arrangements of pharyngeal teeth, and extensive variation in tooth shape also occurs within the family. Mutant screens and experimental alteration of gene expression in the zebrafish are likely to yield variant tooth number and shape phenotypes that can be compared with those occurring naturally within the Cyprinidae. Such studies may reveal the relative contribution to trends in dental evolution of biases in the generation of variation and sorting of this variation by selection or drift.

Comparative morphometrics of the primate apical tuft

The relationship between the structure and function of the primate apical tuft is poorly understood. This study addresses several hypotheses about apical tuft morphology using a large modern primate comparative sample. Two indices of tuft size are employed: expansion and robusticity. First, comparisons of relative apical tuft size were drawn among extant nonhuman primate groups in terms of locomotion and phylogenetic category. Both of these factors appear to play a role in apical tuft size among nonhuman primates. Suspensory primates and all platyrrhines had the smallest apical tufts, while terrestrial quadrupeds and all strepsirrhines (regardless of locomotor category) had the largest tufts. Similarly, hypotheses regarding the apical tufts of hominins, especially the large tufts of Neandertals were addressed using a comparison of modern warm- and cold-adapted humans. The results showed that cold-adapted populations possessed smaller apical tufts than did warm-adapted groups. Therefore, the cold-adaptation hypothesis for Neandertal distal phalangeal morphology is not supported. Also, early modern and Early Upper Paleolithic humans had apical tufts that were significantly less expanded and less robust than those of Neandertals. The hypothesis that a large apical tuft serves as support for an expanded digital pulp is supported by radiographic analysis of modern humans in that a significant correlation was discovered between the width of the apical tuft and the width of the pulp. The implications of these findings for hypotheses about the association of apical tuft size and tool making in the hominin fossil record are discussed.

A comparative volumetric analysis of the amygdaloid complex and basolateral division in the human and ape brain

The amygdaloid complex functions to facilitate effective appraisal of the social environment and is an essential component of the neural systems subserving social behavior. Despite its critical role in mediating social interaction, the amygdaloid complex has not attracted the same attention as the isocortex in most evolutionary analyses. We performed a comparative analysis of the amygdaloid complex in the hominoids to address the lack of comparative information available for this structure in the hominoid brain. We demarcated the amygdaloid complex and the three nuclei constituting its basolateral division, the lateral, basal, and accessory basal nuclei, in 12 histological series representing all six hominoid species. The volumes obtained for these areas were subjected to allometric analyses to determine whether any species deviated from expected values based on the other hominoids. Differences between groups were addressed using nonparametric comparisons of means. The human lateral nucleus was larger than predicted for an ape of human brain size and occupied the majority of the basolateral division, whereas the basal nucleus was the largest of the basolateral nuclei in all ape species. In orangutans the amygdala and basolateral division were smaller than in the African apes. While the gorilla had a smaller than predicted lateral nucleus, its basal and accessory basal nuclei were larger than predicted. These differences may reflect volumetric changes occurring in interconnected cortical areas, specifically the temporal lobe and orbitofrontal cortex, which also subserve social behavior and cognition, suggesting that this system may be acted upon in hominoid and hominid evolution.

Two types of bilateral symmetry in the Metazoa: chordate and bilaterian

The chordate sagittal plane is perpendicular to the sagittal plane primitive for the bilaterally symmetrical metazoans (Bilateria). The earliest metazoans, when symmetrical at all, were probably radial in symmetry. The axis of symmetry was vertical and the mouth, when present, opened either upward or downward. The Bilateria evolved from the primitive metazoan condition by acquiring bilateral symmetry, mesoderm, a brain at the anterior end and protonephridia. Perhaps in the stem lineage of the Bilateria a hydroid-like or medusoid-like ancestor fell over on one side onto a substrate (pleurothetism). If so, the anteroposterior axis of Bilateria would be homologous with the vertical axis of radial symmetry in coelenterates. The bilaterian plane of symmetry arose to include the anteroposterior axis. The Deuterostomia (the Hemichordata, Echinodermata and Chordata) evolved within the Bilateria by producing the mouth as a secondary perforation. Within the deuterostomes the echinoderms and chordates constitute a monophyletic group named Dexiothetica. Hemichordates retain the primitive bilaterian sagittal plane. The Dexiothetica derive from an ancestor like the present-day hemichordate Cephalodiscus which had lain down on the primitive right side (dexiothetism) and acquired a calcite skeleton. The echinoderms evolved from this ancestor by losing the ancestral locomotory tail and gill slit, becoming static, moving the mouth to the centre of the new upper surface and developing radial pentameral symmetry. The chordates evolved from the same ancestor by developing a notochord in the tail, losing the water vascular system, evolving a filter-feeding pharynx and developing a new vertical plane of bilateral symmetry perpendicular to the old bilaterian plane. Evidence derived from certain bizarre Palaeozoic marine fossils (calcichordates) gives a detailed history of the early evolution of echinoderms and chordates and shows how the new bilateral symmetry was gradually acquired in chordates. This symmetry began in the tail (which contained the notochord and was also the leading end in locomotion) and advanced forward into the head.

Craniomandibular morphology supporting the diphyletic origin of mangabeys and a new genus of the Cercocebus/Mandrillus clade, Procercocebus

Previous studies have noted skeletal and dental differences supporting the diphyletic origin of the mangabeys. Documented postcranial and dental characters are congruent with molecular data and thus support a close relationship between Cercocebus and Mandrillus (mandrills and drills) on the one hand and Lophocebus, Papio (baboons), and Theropithecus (geladas) on the other. Most of these characters, however, are postcranial and difficult to assess in the papionin fossil record because associated material is rare. In order to assess the African papionin fossil record and determine the evolutionary history of this group, cranial characters are critical. Here, a set of craniomandibular morphologies are documented that support the diphyletic origin of the mangabeys and more broadly support the molecular African papionin clades (i.e., Cercocebus/Mandrillus vs. Lophocebus/Papio/Theropithecus). These characters are then used to identify a series of fossil crania from Taung as representative of a new member of the Cercocebus/Mandrillus clade, Procercocebus antiquus. Procercocebus antiquus is closest in morphology to the extant taxon Cercocebus torquatus, and a probable ancestor-descendant relationship between Procercocebus and Cercocebus is suggested. Paleoecological reconstructions also suggest that a predator-prey relationship between African crowned eagles and the Procercocebus-Cercocebus lineage has existed for approximately the last two million years. Implications for Cercocebus biogeography and evolution are discussed.

Normal ocular development in young rhesus monkeys (Macaca mulatta)

PURPOSE

The purpose of this study was to characterize normal ocular development in infant monkeys and to establish both qualitative and quantitative relationships between human and monkey refractive development.

METHODS

The subjects were 214 normal rhesus monkeys. Cross-sectional data were obtained from 204 monkeys at about 3 weeks of age and longitudinal data were obtained from 10 representative animals beginning at about 3 weeks of age for a period of up to 5 years. Ocular development was characterized via refractive status, corneal power, crystalline lens parameters, and the eye's axial dimensions, which were determined by retinoscopy, keratometry, phakometry and A-scan ultrasonography, respectively.

RESULTS

From birth to about 5 years of age, the growth curves for refractive error and most ocular components (excluding lens thickness and equivalent lens index) followed exponential trajectories and were highly coordinated between the two eyes. However, overall ocular growth was not a simple process of increasing the scale of each ocular component in a proportional manner. Instead the rates and relative amounts of change varied within and between ocular structures.

CONCLUSION

The configuration and contribution of the major ocular components in infant and adolescent monkey eyes are qualitatively and quantitatively very comparable to those in human eyes and their development proceeds in a similar manner in both species. As a consequence, in both species the adolescent eye is not simply a scaled version of the infant eye.

Social intelligence in the spotted hyena (Crocuta crocuta)

If the large brains and great intelligence characteristic of primates were favoured by selection pressures associated with life in complex societies, then cognitive abilities and nervous systems with primate-like attributes should have evolved convergently in non-primate mammals living in large, elaborate societies in which social dexterity enhances individual fitness. The societies of spotted hyenas are remarkably like those of cercopithecine primates with respect to size, structure and patterns of competition and cooperation. These similarities set an ideal stage for comparative analysis of social intelligence and nervous system organization. As in cercopithecine primates, spotted hyenas use multiple sensory modalities to recognize their kin and other conspecifics as individuals, they recognize third-party kin and rank relationships among their clan mates, and they use this knowledge adaptively during social decision making. However, hyenas appear to rely more intensively than primates on social facilitation and simple rules of thumb in social decision making. No evidence to date suggests that hyenas are capable of true imitation. Finally, it appears that the gross anatomy of the brain in spotted hyenas might resemble that in primates with respect to expansion of frontal cortex, presumed to be involved in the mediation of social behaviour.

Evolutionary and comparative anatomical investigations of the autonomic cardiac nervous system in the African cercopithecidae

The purpose of this study was to clarify the general architecture and morphological variations of the autonomic cardiac nervous system (ACNS) in the African Cercopithecidae (Old World monkeys), and to discuss the evolutionary changes between this system in African/Asian Cercopithecidae and humans. A detailed macroscopic comparative morphological investigation of the ACNS was performed by examining the left and right sides of 11 African cercopithecid specimens, including some previously unreported species (Abyssinian colobus, Angola pied colobus, Savanna monkey, and lesser white-nosed guenon). The common characteristics of the ACNS in the African Cercopithecidae are described in detail. Consequently, homologies of the ACNS between Asian (macaques) and African Cercopithecidae, and differences between the Asian/African Cercopithecidae and humans, were found. In particular, differences in the sympathetic (cardiac) systems of the Cercopithecidae and humans were recognized, despite the similar morphology of the parasympathetic vagal (cardiac) system. These differences include the composition of the cervicothoracic ganglion, the lower positions of the middle cervical and cervicothoracic ganglia, and the narrow range for the origin of the cardiac nerves in the Cercopithecidae, compared with that in humans. In conclusion, these findings are considered with regard to the morphology of the last common ancestors of the Cercopithecidae.

Pediatric material properties: a review of human child and animal surrogates

Because pediatric tissue is difficult for researchers to obtain, the biomechanical responses of adult humans have been studied much more extensively than those of children. Piglets, chimpanzees, and other animals have been used as child surrogates, but the tissue properties and responses to impact forces obtained from these animals may not directly correlate with the human child, and this correlation is not well understood. Consequently, only a handful of human pediatric tissue properties are known. Child anthropomorphic test devices employed in automotive safety have been developed largely by scaling data obtained from adult human cadaveric tests, where various scaling methods have been used to account for differences in geometry, material properties, or a combination of these two parameters. Similar scaling techniques have also been implemented to develop injury assessment reference values for child anthropomorphic test devices. Nevertheless, these scaling techniques have not yet proven to be accurate, in part because of the lack of pediatric data. In this review, the properties of pediatric human and animal surrogate tissue that have been mechanically tested are evaluated. It was found that most of the pediatric tissue that has previously been tested pertains to the head, neck, cervical spine, and extremities. It is evident that some body regions, such as the head and neck, have been tested to some extent since injuries to these regions are critical from an injury perspective. On the other hand, there is limited pediatric data available for the thorax, abdomen, thoracic and lumbar spines and fetal-related tissue. This review presents the pediatric data available in the literature and highlights the body regions where further testing is needed.

Paleobiology and comparative morphology of a late Neandertal sample from El Sidron, Asturias, Spain

Fossil evidence from the Iberian Peninsula is essential for understanding Neandertal evolution and history. Since 2000, a new sample approximately 43,000 years old has been systematically recovered at the El Sidrón cave site (Asturias, Spain). Human remains almost exclusively compose the bone assemblage. All of the skeletal parts are preserved, and there is a moderate occurrence of Middle Paleolithic stone tools. A minimum number of eight individuals are represented, and ancient mtDNA has been extracted from dental and osteological remains. Paleobiology of the El Sidrón archaic humans fits the pattern found in other Neandertal samples: a high incidence of dental hypoplasia and interproximal grooves, yet no traumatic lesions are present. Moreover, unambiguous evidence of human-induced modifications has been found on the human remains. Morphologically, the El Sidrón humans show a large number of Neandertal lineage-derived features even though certain traits place the sample at the limits of Neandertal variation. Integrating the El Sidrón human mandibles into the larger Neandertal sample reveals a north-south geographic patterning, with southern Neandertals showing broader faces with increased lower facial heights. The large El Sidrón sample therefore augments the European evolutionary lineage fossil record and supports ecogeographical variability across Neandertal populations.

Quantitative analysis of human mandibular shape using three-dimensional geometric morphometrics

Human mandibular morphology is often thought to reflect mainly function, and to be of lesser value in studies of population history. Previous descriptions of human mandibles showed variation in ramal height and breadth to be the strongest difference among recent human groups. Several mandibular traits that differentiate Neanderthals from modern humans include greater robusticity, a receding symphysis, a large retromolar space, a rounder gonial area, an asymmetric mandibular notch, and a posteriorly positioned mental foramen in Neanderthals. Nevertheless, the degree to which these differences are part of modern human variation and/or are related to size and function remains unclear. The aim of this study was to document geographic and functional patterning in the mandibular shape of recent humans, to assess the effects of allometry on mandibular form, and to quantitatively evaluate proposed "Neanderthal" mandibular traits through comparison with samples of geographically diverse recent humans. Data were collected in the form of three-dimensional coordinates of 28 landmarks. Unlike previous studies, this analysis found that modern human mandibular shape exhibits considerable geographic patterning, with some aspects of mandibular morphology reflecting a climatic gradient, and others, a functional specialization. Population history is also reflected in mandibular form, albeit relatively weakly. Proposed "Neanderthal" traits were found to separate Neanderthal from modern human mandibles successfully in the statistical analysis. Of these, the retromolar gap was found to be related to increased mandibular size in modern humans. The status of this trait as a Neanderthal autapomorphy should therefore be treated with caution.

A basal ceratopsian with transitional features from the Late Jurassic of northwestern China

Although the Ceratopsia and Pachycephalosauria, two major ornithischian groups, are united as the Marginocephalia, few synapomorphies have been identified due to their highly specialized body-plans. Several studies have linked the Heterodontosauridae with either the Ceratopsia or Marginocephalia, but evidence for these relationships is weak, leading most recent studies to consider the Heterodontosauridae as the basal member of another major ornithischian radiation, the Ornithopoda. Here, we report on a new basal ceratopsian dinosaur, Yinlong downsi gen. et. sp. nov. from the Late Jurassic upper part of the Shishugou Formation of Xinjiang, China. This new ceratopsian displays a series of features transitional between more derived ceratopsians and other ornithischians, shares numerous derived similarities with both the heterodontosaurids and pachycephalosaurians and provides strong evidence supporting a monophyletic Marginocephalia and its close relationship to the Heterodontosauridae. Character distributions along the marginocephalian lineage reveal that, compared to the bipedal Pachycephalosauria, which retained a primitive post-cranial body-plan, the dominantly quadrupedal ceratopsians lost many marginocephalian features and evolved their own characters early in their evolution.

The primate subarcuate fossa and its relationship to the semicircular canals part I: prenatal growth

Studies have reported a functional link between the arc size of the semicircular canals and locomotor agility across adult primates. However, canal size is spatially interlinked with the subarcuate fossa. This fossa can house the petrosal lobule of the paraflocculus, which also plays a role in coordinating head and eye movements. Consequently, it could be that it is the size of the petrosal lobule and fossa that are directly associated with locomotor agility, and not canal arc size. The apparent association of the latter would only follow from the spatial requirement of the canals to accommodate a suitably enlarged subarcuate fossa and petrosal lobule. This study aims to test the ontogenetic basis of this argument by examining high-resolution magnetic resonance images of fetal samples of Homo sapiens, Macaca nemestrina, and Alouatta caraya. Falsifiable null hypotheses examined are (1) that development of the subarcuate fossa is initiated by growth of the petrosal lobule, and (2) that growth of the semicircular canals and of the subarcuate fossa are independent. The findings confirm that the subarcuate fossa forms independently of a petrosal lobule in all three species, thereby falsifying the first hypothesis. Significant correlations were observed between size variables of the semicircular canals and the subarcuate fossa, particularly between the anterior canal and the opening of the fossa. These results falsify the hypothesis that the canals and fossa grow entirely independently. In the human sample, canal growth outpaces fossa growth, possibly because no petrosal lobule is present in humans. In the other two species, the subarcuate fossa simply seems to fill the space made available by canal growth. However, fossa enlargement cannot be excluded as an influence on size increase in the canals. Nevertheless, taken together, the results suggest that canal size is unlikely to be determined primarily by the spatial requirements of the subarcuate fossa and petrosal lobule, rather than by sensory demands reflected in the empirically established link with locomotor agility.

The primate subarcuate fossa and its relationship to the semicircular canals part I: prenatal growth

Studies have reported a functional link between the arc size of the semicircular canals and locomotor agility across adult primates. However, canal size is spatially interlinked with the subarcuate fossa. This fossa can house the petrosal lobule of the paraflocculus, which also plays a role in coordinating head and eye movements. Consequently, it could be that it is the size of the petrosal lobule and fossa that are directly associated with locomotor agility, and not canal arc size. The apparent association of the latter would only follow from the spatial requirement of the canals to accommodate a suitably enlarged subarcuate fossa and petrosal lobule. This study aims to test the ontogenetic basis of this argument by examining high-resolution magnetic resonance images of fetal samples of Homo sapiens, Macaca nemestrina, and Alouatta caraya. Falsifiable null hypotheses examined are (1) that development of the subarcuate fossa is initiated by growth of the petrosal lobule, and (2) that growth of the semicircular canals and of the subarcuate fossa are independent. The findings confirm that the subarcuate fossa forms independently of a petrosal lobule in all three species, thereby falsifying the first hypothesis. Significant correlations were observed between size variables of the semicircular canals and the subarcuate fossa, particularly between the anterior canal and the opening of the fossa. These results falsify the hypothesis that the canals and fossa grow entirely independently. In the human sample, canal growth outpaces fossa growth, possibly because no petrosal lobule is present in humans. In the other two species, the subarcuate fossa simply seems to fill the space made available by canal growth. However, fossa enlargement cannot be excluded as an influence on size increase in the canals. Nevertheless, taken together, the results suggest that canal size is unlikely to be determined primarily by the spatial requirements of the subarcuate fossa and petrosal lobule, rather than by sensory demands reflected in the empirically established link with locomotor agility.

The serial transformation hypothesis of vertebrate origins: comment on "The new head hypothesis revisited"

In "The New Head Hypothesis Revisited," R.G. Northcutt (2005. J Exp Zool (Mol Dev Evol) 304B:274-297) evaluates the original postulates of this hypothesis (Northcutt and Gans, 1983. Quart Rev Biol 58:1-28). One of these postulates is that the brain-particularly the forebrain-evolved at essentially the same time as many neural crest and neurogenic placode derivatives-including sensory ganglia, dermal skeleton and sensory capsules of the head, and branchial arches. Northcutt's subsequent paper in 1996 concluded with the idea that transitional forms might not have occurred at the origin of vertebrates. Butler proposed a "Serial Transformation" hypothesis in 2000, which disputed the latter idea in that paired eyes and an enlarged brain (but lacking telencephalon) were envisioned to have been gained before elaboration of most neural crest and neurogenic placodal derivatives. In 2003, J. Mallatt and J.-Y. Chen analyzed fossils of the Cambrian animal Haikouella, which strongly support its affinity to craniates and aspects of several hypotheses, including Butler's transformational model, because although branchial bars are present, most other neural crest and placodal derivatives are absent, while paired eyes and an enlarged brain (but probably without telencephalon) are present. A more complete picture of vertebrate origins can be realized when the various hypotheses are constructively reconciled.

Evolutionary patterns in early tetrapods. II. Differing constraints on available character space among clades

Radiations of large clades often accompany rapid morphological diversification. Evolutionary biologists debate the impact of external restrictions imposed by ecology, and intrinsic constraints imposed by development and genetics, on the rate at which morphological innovations are gained. These issues are particularly interesting for groups such as tetrapods, which evolved novel body plans relative to their piscine ancestors and which also invaded new ecosystems following terrestrialization. Prior studies have addressed these issues by looking at either ranges of morphological variation or rates of character change. Here, we address a related but distinct issue: the numbers of characters that freely vary within a clade. We modify techniques similar to those used by ecologists to infer species richnesses to estimate the number of potentially varying characters given the distributions of changes implied by a model phylogeny. Our results suggest both increasing constraints/restrictions and episodes of 'character release' (i.e. increasing the number of potentially varying characters). In particular, we show that stem lissamphibians had a restricted character space relative to that of stem amniotes, and that stem amniotes both had restrictions on some parts of character space but also invaded new character space that had been unavailable to stem tetrapods.

Evolutionary patterns in early tetrapods. I. Rapid initial diversification followed by decrease in rates of character change

Although numerous studies have examined morphological diversification during major radiations of marine taxa, much less attention has been paid to terrestrial radiations. Here, we examine rates of character change over phylogeny and over time for Palaeozoic limbed tetrapods. Palaeozoic tetrapods show significant decreases in rates of character change whether the rate is measured per sampled cladistic branch or per million years along phylogeny. Given changes per branch, rates decrease significantly from the Devonian through the Pennsylvanian, but not from the Pennsylvanian through the Permian. Given changes per million years, rates decrease significantly over each boundary, although the decrease is least significant over the Pennsylvanian-Permian boundary. Decreasing rates per million years through the Permian might be an artefact of the method being able to ascribe longer durations to Permian branches than to Carboniferous ones; however, it is difficult to ascribe the general pattern of decreasing rates of change over time to sampling biases or methodological biases. Thus, the results implicate biological explanations for this pattern.

Anatomie comparée de la main

The pentadactyl scheme is common to all tetrapods, even in case of adaptative phenomenon (five digits are observed during ontogenesis), or in case of functional convergence The carpal organization with two rows is common too, if we take into account the desappearing of the central bones in mature man. The sellar shape of the trapeziometacarpal joint of the thumb, to often attributed to Man and his only thumb, is in fact the regular shape of all carpometacarpal articulations and present in very ancient primitive primate fossils. Some discontinuous caracters in Man (entepicondylar tunnel) are present in all individuals of some species (carnivors). Rarely present in Man, it can exceptionally produce a real pathology.

Homology of the reptilian coracoid and a reappraisal of the evolution and development of the amniote pectoral apparatus

As in monotreme mammals, the pectoral apparatus of basal (fossil) amniotes includes two coracoid elements, the procoracoid and metacoracoid. Among extant reptiles the metacoracoid has long been assumed lost; this notion is herein challenged. A comprehensive review of data from numerous sources, including the fossil record, experimental embryology, genetic manipulations and an analysis of morphology at the level cell condensations, supports the conclusion that the metacoracoid gives rise to the majority of the reptilian coracoid. By contrast, the reptilian procoracoid remains as a rudiment that is incorporated as a process of the (meta)coracoid and/or the glenoid region of the scapula early during development, prior to skeletogenesis. Application of this integrated approach corroborates and enhances previous work describing the evolution of the pectoral apparatus in mammals. A revised scenario of amniote coracoid evolution is presented emphasizing the importance of considering cell condensations when evaluating the homology of a skeletal complex.

Comparative anatomy of laboratory animal corneas with a new-generation high-resolution in vivo confocal microscope

PURPOSE

The aim of the current study was to compare the corneas of three commonly used laboratory animals with a new in vivo confocal microscope.

METHODS

Six eyes of three adult male New Zealand albino rabbits, six eyes of three adult male Lewis rats, and six eyes of three adult male Swiss mice were used in this study. Corneas were analyzed in vivo using the Rostock Cornea Module of the Heidelberg Retina Tomograph (HRT)-II. For all eyes, 20 confocal microscopic images of each layer, that is, the superficial and basal corneal epithelia, the Bowman layer, the anterior and posterior stroma, and the endothelium, were recorded. The images were then analyzed qualitatively and compared among animals. Cellular densities of anterior and posterior stroma keratocytes of rabbits and endothelium density of the three different animals were also measured and compared.

RESULTS

The Rostock Cornea Module of the HRT II was successfully used to analyze all corneal layers of these three commonly used laboratory animals. Although the cellular patterns of the corneal layers of these three animals, as observed with in vivo confocal microscopy, were quite similar, some differences were seen in terms of endothelial cell density and stroma appearance. Superficial cells were seen as hyper- and hyporeflective polygonal cells. Basal cells had dark cytoplasm without visible nuclei and were closely organized. A Bowman layer was observed in all three animals as an amorphous tissue containing fine subepithelial nerve plexus. In rabbits, the stroma consisted of an amorphous ground substance with hyper-reflective structures corresponding with keratocyte nuclei. In rats and mice, numerous reflective stellate structures with no clearly visible nuclei were observed within the stroma. Besides endothelial cell density, the endothelium was similar among the three animals and was seen as hyper-reflective cells with dark limits organized in a honeycomb pattern.

CONCLUSIONS

The Rostock Cornea Module of the HRT II can provide high-resolution images of all corneal layers of rabbits, rats, and mice without sacrificing animals or preparing tissue. This new device may be useful for evaluating the cornea during experimental animal studies.