Different types of visual cells in the photoreceptor layer of the retinae of the treeshrew (Tupaia belangeri chinensis) as revealed by scanning microscopy.

BACKGROUND: The retinae of treeshrew have never been evaluated by scanning electron microscopic studies. MATERIALS AND METHODS: This work described the visual cells in the photoreceptor layer of the retinae of treeshrew (Tupaia belangeri chinensis) living on the high plateau of Yunnan, China, via scanning electron microscopy. RESULTS: Results indicated five morphologically different types of cones, two of which contain oil droplets in their inner segments. To our knowledge, no prior studies have reported oil droplets in the visual cells of higher mammals, only in lower vertebrate and primitive mammals. In addition, this study revealed one type of degenerative visual cell without outer segments. CONCLUSIONS: The findings signal the needs for additional studies to understand the physiological functions and phylogenetic relationships of the diversity of visual cells in this group of mammal.

Cone photoreceptor reflectance variation in the northern tree shrew and thirteen-lined ground squirrel.

In vivo images of human cone photoreceptors have been shown to vary in their reflectance both spatially and temporally. While it is generally accepted that the unique anatomy and physiology of the photoreceptors themselves drives this behavior, the exact mechanisms have not been fully elucidated as most studies on these phenomena have been limited to the human retina. Unlike humans, animal models offer the ability to experimentally manipulate the retina and perform direct in vivo and ex vivo comparisons. The thirteen-lined ground squirrel and northern tree shrew are two emerging animal models being used in vision research. Both models feature cone-dominant retinas, overcoming a key limitation of traditional rodent models. Additionally, each possesses unique but well-documented anatomical differences in cone structure compared to human cones, which can be leveraged to further constrain theoretical models of light propagation within photoreceptors. Here we sought to characterize the spatial and temporal reflectance behavior of cones in these species. Adaptive optics scanning light ophthalmoscopy (AOSLO) was used to non-invasively image the photoreceptors of both species at 5 to 10 min intervals over the span of 18 to 25 min. The reflectance of individual cone photoreceptors was measured over time, and images at individual time points were used to assess the variability of cone reflectance across the cone mosaic. Variability in spatial and temporal photoreceptor reflectance was observed in both species, with similar behavior to that seen in human AOSLO images. Despite the unique cone structure in these animals, these data suggest a common origin of photoreceptor reflectance behavior across species. Such data may help constrain models of the cellular origins of photoreceptor reflectance signals. These animal models provide an experimental platform to further explore the morphological origins of light capture and propagation.

Inward collapse of the nasal cavity: Perinatal consolidation of the midface and cranial base in primates.

Living primates show a complex trend in reduction of nasal cavity spaces and structures due to moderate to severe constraint on interorbital breadth. Here we describe the ontogeny of the posterior end of the primate cartilaginous nasal capsule, the thimble shaped posterior nasal cupula (PNC), which surrounds the hind end of the olfactory region. We used a histologically sectioned sample of strepsirrhine primates and two non-primates (Tupaia belangeri, Rousettus leschenaulti), and histochemical and immunohistochemical methods to study the PNC in a perinatal sample. At birth, most strepsirrhines possess only fragments of PNC, and these lack a perichondrium. Fetal specimens of several species reveal a more complete PNC, but the cartilage exhibits uneven or weak reactivity to type II collagen antibodies. Moreover, there is relatively less matrix than in the septal cartilage, resulting in clustering of chondrocytes, some of which are in direct contact with adjacent connective tissues. In one primate (Varecia spp.) and both non-primates, the PNC has a perichondrium at birth. In older, infant Varecia and Rousettus, the perichondrium of the PNC is absent, and PNC fragmentation at its posterior pole has occurred in the former. Loss of the perichondrium for the PNC appears to precede resorption of the posterior end of the nasal capsule. These results suggest that the consolidation of the basicranial and facial skeletons happens ontogenetically earlier in primates than other mammals. We hypothesize that early loss of cartilage at the sphenoethmoidal articulation limits chondral mechanisms for nasal complexity, such as interstitial expansion or endochondral ossification.

The anatomy of the skin of the Chinese tree shrew is very similar to that of human skin.

The Chinese tree shrew (Tupaia belangeri chinensis) is a small mammal closely related to primates. It has a small body size, low maintenance cost, and a relatively short reproductive cycle, all of which has made it the ideal model for the study of a variety of human diseases. In this study, we compared the anatomy of the skin of the Chinese tree shrew with that of the rhesus macaque, mouse and human, with the intention of providing the basic data required for the creation of skin disease models using this animal. Paraffin sections, hematoxylin-eosin (H&E) staining, masson staining and immunohistochemical techniques were used to examine the dorsal skin structure of the Chinese tree shrew. The epidermis was shown to be composed of 1-2 layers of cells. There were hair follicles, sebaceous glands and sweat glands in the dermis and the subcutaneous tissue, with apocrine glands being more common than eccrine glands. Both Keratin5 (KRT5) and Keratin10 (KRT10) were expressed in the skin of the Chinese tree shrew, with a localization in the cytoplasm. Overall, the skin morphology and histology of the Chinese tree shrew was basically the same as that of the human. We propose that the Chinese tree shrew has a strong potential to be used for creating animal models to help elucidate the molecular mechanisms underlying a variety of skin diseases.

Establishment of brain ischemia model in tree shrew.

BACKGROUND: Tree shrew, as a kind of small and inexpensive animal between insectivores and primates with the general anatomy being similar to human, could be considered as developed animal model for brain ischemia (BI) study. However, there is no neural behavior scores criterion from tree shrew with BI up to now. METHODS: To produce BI model of tree shrew, a novel systematic neurobehavioral assessment scale, named as neural behavior scores (NBS) including aggressive behavior, seeking behavior, gait, startle reflex, high jump and warped-tail phenomenon was firstly established and used in this study. Moreover, magnetic resonance imaging (MRI) was performed on the first day after the operation to detect the imaging changes caused by ischemia. Then TTC, HE staining and immunofluorescent staining for GFAP and NeuN, were performed 24 h after surgery respectively. RESULTS: NBS in BI group were significantly higher than that of sham operation group at 1d, 3d, 5d and 7d after ischemia. Meanwhile, compared with the sham operation group, the T2 images demonstrated significant higher signal and local brain swelling after cerebral ischemia in tree shrews. The staining of TTC and HE showed apparent infarction and necrosis of the cerebral region, and most of neurons exhibited a shrink. CONCLUSION: We have successfully established the BI model of tree shrew, confirmed by NBS (a new developed method), MRI, HE staining, TTC staining and immunofluorescence staining. It is the first time to report a novel neurobehavioral assessment scale for BI in tree shrew.

Nuclear organization of some immunohistochemically identifiable neural systems in two species of the Euarchontoglires: A Lagomorph, Lepus capensis, and a Scandentia, Tupaia belangeri.

The present study describes the organization of the nuclei of the cholinergic, catecholaminergic, serotonergic and orexinergic systems in the brains of two members of Euarchontoglires, Lepus capensis and Tupaia belangeri. The aim of the present study was to investigate the nuclear complement of these neural systems in comparison to previous studies on Euarchontoglires and generally with other mammalian species. Brains were coronally sectioned and immunohistochemically stained with antibodies against choline acetyltransferase, tyrosine hydroxylase, serotonin and orexin-A. The majority of nuclei revealed in the current study were similar between the species investigated and to mammals generally, but certain differences in the nuclear complement highlight potential phylogenetic interrelationships within the Euarchontoglires and across mammals. In the northern tree shrew the nucleus of the trapezoid body contained neurons immunoreactive to the choline acetyltransferase antibody with some of these neurons extending into the lamellae within the superior olivary nuclear complex (SON). The cholinergic nature of the neurons of this nucleus, and the extension of cholinergic neurons into the SON, has not been noted in any mammal studied to date. In addition, cholinergic neurons forming the medullary tegmental field were also present in the northern tree shrew. Regarding the catecholaminergic system, the cape hare presented with the rodent specific rostral dorsal midline medullary nucleus (C3), and the northern tree shrew lacked both the ventral and dorsal divisions of the anterior hypothalamic group (A15v and A15d). Both species were lacking the primate/megachiropteran specific compact portion of the locus coeruleus complex (A6c). The nuclei of the serotonergic and orexinergic systems of both species were similar to those seen across most Eutherian mammals. Our results lend support to the monophyly of the Glires, and more broadly suggest that the megachiropterans are more closely related to the primates than are any other members of Euarchontoglires studied to date.

Distributions of vesicular glutamate transporters 1 and 2 in the visual system of tree shrews (Tupaia belangeri).

Vesicular glutamate transporter (VGLUT) proteins regulate the storage and release of glutamate from synapses of excitatory neurons. Two isoforms, VGLUT1 and VGLUT2, are found in most glutamatergic projections across the mammalian visual system, and appear to differentially identify subsets of excitatory projections between visual structures. To expand current knowledge on the distribution of VGLUT isoforms in highly visual mammals, we examined the mRNA and protein expression patterns of VGLUT1 and VGLUT2 in the lateral geniculate nucleus (LGN), superior colliculus, pulvinar complex, and primary visual cortex (V1) in tree shrews (Tupaia belangeri), which are closely related to primates but classified as a separate order (Scandentia). We found that VGLUT1 was distributed in intrinsic and corticothalamic connections, whereas VGLUT2 was predominantly distributed in subcortical and thalamocortical connections. VGLUT1 and VGLUT2 were coexpressed in the LGN and in the pulvinar complex, as well as in restricted layers of V1, suggesting a greater heterogeneity in the range of efferent glutamatergic projections from these structures. These findings provide further evidence that VGLUT1 and VGLUT2 identify distinct populations of excitatory neurons in visual brain structures across mammals. Observed variations in individual projections may highlight the evolution of these connections through the mammalian lineage.

Mapping bone cell distributions to assess ontogenetic origin of primate midfacial form.

Midfacial reduction in primates has been explained as a byproduct of other growth patterns, especially the convergent orbits. This is at once an evolutionary and developmental explanation for relatively short snouts in most modern primates. Here, we use histological sections of perinatal nonhuman primates (tamarin, tarsier, loris) to investigate how orbital morphology emerges during ontogeny in selected primates compared to another euarchontan (Tupaia glis). We annotated serial histological sections for location of osteoclasts or osteoblasts, and used these to create three-dimensional "modeling maps" showing perinatal growth patterns of the facial skeleton. In addition, in one specimen we transferred annotations from histological sections to CT slices, to create a rotatable 3D volume that shows orbital modeling. Our findings suggest that growth in the competing orbital and neurocranial functional matrices differs among species, influencing modeling patterns. Distinctions among species are observed in the frontal bone, at a shared interface between the endocranial fossa and the orbit. The medial orbital wall is extensively resorptive in primates, whereas the medial orbit is generally depositional in Tupaia. As hypothesized, the orbital soft tissues encroach on available interorbital space. However, eye size cannot, by itself, explain the extent of reduction of the olfactory recess. In Loris, the posterior portion of medial orbit differed from the other primates. It showed evidence of outward drift where the olfactory bulb increased in cross-sectional area. We suggest the olfactory bulbs are significant to orbit position in strepsirrhines, influencing an expanded interorbital breadth at early stages of development.

Comparing Dirichlet normal surface energy of tooth crowns, a new technique of molar shape quantification for dietary inference, with previous methods in isolation and in combination.

Inferred dietary preference is a major component of paleoecologies of extinct primates. Molar occlusal shape correlates with diet in living mammals, so teeth are a potentially useful structure from which to reconstruct diet in extinct taxa. We assess the efficacy of Dirichlet normal energy (DNE) calculated for molar tooth surfaces for reflecting diet. We evaluate DNE, which uses changes in normal vectors to characterize curvature, by directly comparing this metric to metrics previously used in dietary inference. We also test whether combining methods improves diet reconstructions. The study sample consisted of 146 lower (mandibular) second molars belonging to 24 euarchontan taxa. Five shape quantification metrics were calculated on each molar: DNE, shearing quotient, shearing ratio, relief index, and orientation patch count rotated (OPCR). Statistical analyses were completed for each variable to assess effects of taxon and diet. Discriminant function analysis was used to assess ability of combinations of variables to predict diet. Values differ significantly by diets for all variables, although shearing ratios and OPCR do not distinguish statistically between insectivores and folivores or omnivores and frugivores. Combined analyses were much more effective at predicting diet than any metric alone. Alone, relief index and DNE were most effective at predicting diet. OPCR was the least effective alone but is still valuable as the only quantitative measure of surface complexity. Of all methods considered, DNE was the least methodologically sensitive, and its effectiveness suggests it will be a valuable tool for dietary reconstruction.

c-Fos expression in the visual system of the tree shrew (Tupaia belangeri).

UNLABELLED: c-Fos is a nuclear phosphoprotein coded by the proto-oncogen c-fos which can be detected immunohistochemically after both physiological and pathological stimuli. This property is of great importance, because it offers a valuable tool for morphofunctional identification of activated neurons. We have studied the neuronal activity in the visual pathway of Tupaia belangeri within the following anatomical structures: retina, superior colliculus (SC), dorsal lateral geniculate nucleus (dLGN), pulvinar (Pu), parabigeminal (PBG) nucleus and primary visual cortex (V1) analyzing the c-Fos expression after exposing the tree shrews to different light stimuli (white light -control positive group-, green light, blue light and darkness conditions -control negative group-). Our findings suggest that in the retina, the ganglion cells and the cells of the inner nuclear layer respond better to blue and green light stimuli, when comparing the c-Fos expression between white, green, blue lights and darkness conditions. However, in the SC, dLGN, Pu, PBG nucleus and V1 another pattern of c-Fos expression is observed: a maximum expression for the control positive group, a minimum expression for the control negative group and intermediate expressions within the blue and green light groups. CONCLUSION: the expression levels of c-Fos protein are able to show significant differences between distinct light stimuli in all anatomical structures studied (retina, SC, dLGN, Pu, PBG and V1) of T. belangeri.

Architectonic subdivisions of neocortex in the tree shrew (Tupaia belangeri).

Tree shrews are small mammals that bear some semblance to squirrels, but are actually close relatives of primates. Thus, they have been extensively studied as a model for the early stages of primate evolution. In this study, subdivisions of cortex were reconstructed from brain sections cut in the coronal, sagittal, or horizontal planes, and processed for parvalbumin, SMI-32-immunopositive neurofilament protein epitopes, vesicle glutamate transporter 2 (VGluT2), free ionic zinc, myelin, cytochrome oxidase, and Nissl substance. These different procedures revealed similar boundaries between areas, suggesting the detection of functionally relevant borders and allowed a more precise demarcation of cortical areal boundaries. Primary cortical areas were most clearly revealed by the zinc stain, because of the poor staining of layer 4, as thalamocortical terminations lack free ionic zinc. Area 17 (V1) was especially prominent, as the broad layer 4 was nearly free of zinc stain. However, this feature was less pronounced in primary auditory and somatosensory cortex. In primary sensory areas, thalamocortical terminations in layer 4 densely express VGluT2. Auditory cortex consists of two architectonically distinct subdivisions, a primary core region (Ac), surrounded by a belt region (Ab) that had a slightly less developed koniocellular appearance. Primary motor cortex (M1) was identified by the absence of VGluT2 staining in the poorly developed granular layer 4 and the presence of SMI-32-labeled pyramidal cells in layers 3 and 5. The presence of well-differentiated cortical areas in tree shrews indicates their usefulness in studies of cortical organization and function.

A precise form of divisive suppression supports population coding in the primary visual cortex.

The responses of neurons in the primary visual cortex (V1) to an optimally oriented grating are suppressed when a non-optimal grating is superimposed. Although cross-orientation suppression is thought to reflect mechanisms that maintain a distributed code for orientation, the effect of superimposed gratings on V1 population responses is unknown. Using intrinsic signal optical imaging, we found that patterns of tree shrew V1 activity evoked by superimposed equal-contrast gratings were predicted by the averages of patterns evoked by individual component gratings. This prediction held across contrasts, for summed sinusoidal gratings or nonsumming square-wave gratings, and was evident in single-unit extracellular recordings. Intracellular recordings revealed consistent levels of suppression throughout the time course of subthreshold responses. These results indicate that divisive suppression powerfully governs population responses to multiple orientations. Moreover, the specific form of suppression that we observed appears to support independent population codes for stimulus orientation and strength and calls for a reassessment of mechanisms that underlie cross-orientation suppression.

Metabolic profile of the perivertebral muscles in small therian mammals: implications for the evolution of the mammalian trunk musculature.

In order to gain a better understanding of the ancestral properties of the perivertebral muscles of mammals, this study investigated the fiber type composition of these muscles in six small, extant therians (two metatherians and four eutherians) similar in body shape to early mammals. Despite a few species-specific differences, the investigated species were very similar in their overall distribution of fiber types indicating similar functional demands on the back muscles in mammals of this body size and shape. Deep and short, mono- or multisegmental muscles (i.e., mm. interspinales, intermammillares, rotatores et intertransversarii) consistently showed the highest percentage of slow, oxidative fibers implying a function as local stabilizers of the vertebral column. Superficial and large, polysegmental muscles (i.e., mm. multifidus, sacrospinalis, iliopsoas et psoas minor) were predominantly composed of fast, glycolytic fibers suggesting they function to both globally stabilize and mobilize the spine during rapid non-locomotor and locomotor activities. Some muscles contained striking accumulations of oxidative fibers in specific regions (mm. longissimus et quadratus lumborum). These regions are hypothesized to function independently from the rest of the muscle belly and may be comparable in their functionality to regionalized limb muscles. The deep, central oxidative region in the m. longissimus lumborum appears to be a general feature of mammals and likely serves a proprioceptive function to control the postural equilibrium of the pelvic girdle and lumbar spine. The potential functions of the m. quadratus lumborum during ventilation and ventral stabilization of the vertebral column are discussed. Because representatives of the stem lineage of mammals were comparable in their body proportions and probably also locomotor parameters to the species investigated here, I suggest that the described fiber type distribution is representative of the ancestral condition in mammals. The origin of mammals was associated with a substantial enlargement of the epaxial muscles and the addition of subvertebral muscle mass. Because this novel muscle mass is mainly composed of fast, glycolytic fibers in extant species, it is plausible that these changes were associated with the evolution of increased sagittal mobility in the posterior trunk region in the therapsid ancestors of mammals. The caudally increasing role of sagittal bending in body propulsion is consistent with the overall increase in the percentage of glycolytic fibers in the cranio-caudal direction. The evolution of mammals was also associated with a loss of ribs in the posterior region of the trunk. This loss of ribs is thought to have decreased the stability of the posterior trunk, which may explain the observed greater oxidative capacity of the caudal local stabilizers. The increased need for postural feedback in the more mobile lumbar region may also explain the evolution of the proprioceptive system in the m. longissimus lumborum. Furthermore, the anatomical subdivision of the transversospinal muscle into several smaller muscle entities is suggested to facilitate their functional specialization.

Diversity in mammalian chiasmatic architecture: ipsilateral axons are deflected at glial arches in the prechiasmatic optic nerve of the eutherian Tupaia belangeri.

Permanent ipsilaterally projecting axons approach the chiasmatic midline in rodents but are confined to lateral parts of the optic chiasm in marsupials. Hence, principally different mechanisms were thought to underlie axon pathway choice in eutherian (placental) and marsupial mammals. First evidence of diversity in eutherian chiasmatic architecture came from studies in the newborn and adult tree shrew Tupaia belangeri (Jeffery et al. [1998] J. Comp. Neurol. 390:183-193). Here, as in marsupials, ipsilaterally projecting axons do not approach the midline. The present study aims to clarify how the developing tree shrew chiasm is organized, how glial cells are arranged therein, and the extent to which the tree shrew chiasm is similar to that of marsupials or other eutherians. By using routinely stained serial sections as well as immunohistochemistry with antibodies against glial fibrillary acidic protein, vimentin, and medium-molecular-weight neurofilament protein, we investigated chiasm formation from embryonic day 18 (E18) to birth (E43). From E22 onward, ipsilaterally projecting axons diverged from contralaterally projecting axons in prechiasmatic parts of the optic nerve. They made sharp turns when arriving at glial arches found at the transition from the optic nerve to the chiasm. Thus, during the ingrowth period of axons, Tupaia belangeri and marsupials have specialized glial arrays in common, which probably help to deflect ipsilaterally projecting axons to lateral parts of the chiasm. Our observations provide new evidence of diversity in eutherian chiasmatic architecture and identify Tupaia belangeri as an appropriate animal model for studies on the mechanisms underlying axon guidance in the developing chiasm of higher primates.

Fiber type distribution in the shoulder muscles of the tree shrew, the cotton-top tamarin, and the squirrel monkey related to shoulder movements and forelimb loading.

Muscle fiber type composition of intrinsic shoulder muscles was examined in tree shrews, cotton-top tamarins, and squirrel monkeys with respect to their shoulder kinematics and forelimb loading during locomotion. Enzyme- and immunohistochemical techniques were applied to differentiate muscle fiber types on serial cross-sections of the shoulder. In the majority of the shoulder muscles, the proportions of fatigue resistant slow-twitch fibers (SO) and fatigable fast-twitch fibers (FG) were inversely related to each other, whereas the percentage of intermediate FOG-fibers varied independently. A segregation of fatigue resistant SO-fibers into deep muscle regions is indicative of differential activation of histochemically distinct muscle regions in which deep regions stabilize the joint against gravitational loading. In all three species, this antigravity function was demonstrated for both the supraspinatus and the cranial subscapularis muscle, which prevent passive joint flexion during the support phase of the limb. The infraspinatus muscle showed a high content of SO-fibers in the primate species but not in the tree shrew, which demonstrates the "new" role of the infraspinatus muscle in joint stabilization related to the higher degree of humeral protraction in primates. In the tree shrew and the cotton-top tamarin, a greater proportion of the body weight is carried on the forelimb, but the squirrel monkey exhibits a weight shift to the hind limbs. The lower amount of forelimb loading is reflected by an overall lower proportion of fatigue resistant muscle fibers in the shoulder muscles of the squirrel monkey. Several muscles such as the deltoid no longer function as joint stabilizers and allow the humerus to move beyond the scapular plane. These differences among species demonstrate the high plasticity of the internal muscle architecture and physiology which is suggested to be the underlying reason for different muscle activity patterns in homologous muscles. Implications for the evolution of new locomotor modes in primates are discussed.

On the postnatal development of the striate cortex (V1) in the tree shrew (Tupaia belangeri).

Histological serial sections, three-dimensional reconstructions and morphometry served to study the postnatal development of V1 in tree shrews. The main objectives were to evaluate the expansion of V1, the implications of its growth on the occipital cortex and, vice versa, the effects of the expanding neocortex on the topography of V1. The future V1 was identified on postnatal day 1 by its granular layer IV, covering the superior surface of the occipital cortices including the poles. A subdivision of layer IV, distinctive for the binocular part, was evident in the central region. V1 expanded continuously with age into all directions succeeded by the maturation of layering. The monocular part was recognized from day 15 onward, after the binocular part had reached its medial border. In reference to the retinotopic map of V1, regions emerged in a coherent temporo-spatial sequence delineating the retinal topography in a central to peripheral gradient beginning with the visual streak representation. The growth of V1 was greatest until tree shrews open their eyes, culminated during adolescence, and completed after a subsequent decrease in the young adult. Simultaneous expansion of the neocortex induced a shifting of V1. Translation and elongation of V1 entailed that the occipital cortex covered the superior colliculi along with a downward rotation of the poles. The enlargement of the occipital part of the hemispheres was in addition associated with the formation of a small occipital horn in the lateral ventricles, indicating an incipient 'true' occipital lobe harbouring mainly cortices involved in visual functions.

Postnatal allometry of the skeleton in Tupaia glis (Scandentia: Tupaiidae) and Galea musteloides (Rodentia: Caviidae)--a test of the three-segment limb hypothesis.

During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species.

Microvascularization of thalamus and metathalamus in common tree shrew (Tupaia glis).

The microangioarchitecture of the thalamus and metathalamus in common tree shrew (Tupaia glis) was studied using vascular corrosion cast/stereomicroscope and SEM technique. The arterial supply of the thalamus and metathalamus was found to originate from perforating branches of the posterior communicating artery, the posterior cerebral artery, the middle cerebral artery, and the anterior choroidal artery. These perforating arteries gave rise to numerous bipinnate arterioles which in turn, with decreasing vessel diameters, branched into a non-fenestrated capillary bed. Venous blood from the superficial parts of the thalamus and metathalamus was collected into the thalamocollicular vein, whereas venous blood from internal aspects of the thalamus was conveyed to the internal cerebral vein. Some venous blood from the most rostral part of the thalamus flowed into tributaries of the middle cerebral vein before draining into the cavernous sinus. Further, the thalamic and metathalamic vascular arrangement was found to be of centripetal type. In addition, thalamic arterial anastomosis was rarely observed. Thus, obstruction of thalamic blood supply could easily lead to thalamic infraction.

Apoptosis and proliferation in developing, mature, and regressing epibranchial placodes.

Epibranchial placodes and rhombencephalic neural crest provide precursor cells for the geniculate, petrosal, and nodose ganglia. In chick embryos and in Tupaia belangeri, apoptosis in rhombomeres 3 and 5 helps to select premigratory precursor cells and to segregate crest cell streams derived from the even-numbered rhombomeres. Much less is known about the patterns and functions of apoptosis in epibranchial placodes. We found that, in Tupaia belangeri, combined anlagen of the otic placode and epibranchial placode 1 transiently share a primordial low grade thickening with post-otic epibranchial placodes. Three-dimensional reconstructions reveal complementary, spatially, and temporally regulated apoptotic and proliferative events that demarcate the otic placode and epibranchial placode 1, and help to individualize three pairs of epibranchial placodes in a rostrocaudal sequence. Later, rostrocaudal waves of proliferation and apoptosis extend from dorsal to ventral parts of the placodes, paralleled by the dorsoventral progression of precursor cell delamination. These findings suggest a role for apoptosis during the process of neuroblast generation in the epibranchial placodes. Finally, apoptosis eliminates remnants of the placodes in the presence of late invading macrophages.

Organization of the main olfactory bulbs of some mammals: musk shrews, moles, hedgehogs, tree shrews, bats, mice, and rats.

We immunohistochemically examined the organization of the main olfactory bulbs (MOBs) in seven mammalian species, including moles, hedgehogs, tree shrews, bats, and mice as well as laboratory musk shrews and rats. We focused our investigation on two points: 1) whether nidi, particular spheroidal synaptic regions subjacent to glomeruli, which we previously reported for the laboratory musk shrew MOBs, are also present in other animals and 2) whether the compartmental organization of glomeruli and two types of periglomerular cells we proposed for the rat MOBs are general in other animals. The general laminar pattern was similar among these seven species, but discrete nidi and the nidal layer were recognized only in two insectivores, namely, the mole and laboratory musk shrew. Olfactory marker protein-immunoreactive (OMP-IR) axons extended beyond the limits of the glomerular layer (GL) into the superficial region of the external plexiform layer (EPL) or the nidal layer in the laboratory musk shrew, mole, hedgehog, and tree shrew but not in bat, mouse, and rat. We observed, in nidi and the nidal layer in the mole and laboratory musk shrew MOBs, only a few OMP-IR axons. In the hedgehog, another insectivore, OMP-IR processes extending from the glomeruli were scattered and intermingled with calbindin D28k-IR cells at the border between the GL and the EPL. In the superficial region of the EPL of the tree shrew MOBs, there were a small number of tiny glomerulus-like spheroidal structures where OMP-IR axons protruding from glomeruli were intermingled with dendritic branches of surrounding calbindin D28k-IR cells. Furthermore, we recognized the compartmental organization of glomeruli and two types of periglomerular cells in the MOBs of all of the mammals we examined. These structural features are therefore considered to be common and important organizational principles of the MOBs.