Regulation of the mechanical properties of tree shrew sclera by the visual environment.
Experiments in several species have shown that the axial elongation rate of the developing eye can be increased or decreased by manipulating the visual environment, indicating that a visually guided emmetropization mechanism controls the enlargement of the vertebrate eye during postnatal development. Previous studies in tree shrews (Tupaia glis belangeri) suggest that regulation of the mechanical properties of the sclera may be an important part of the mechanism that controls the axial elongation rate in this mammal. To learn whether the mechanical properties of the sclera change when the axial elongation rate is increased or decreased under visual control, uniaxial mechanical tests were performed on 3-mm wide strips of tree shrew sclera. The creep rate was measured under 1, 3, and 5 g of tension, maintained for 30 min at each level. The modulus of elasticity was calculated from the elastic extension that occurred when the force was increased from 0 to 1 g, 1 to 3 g, and 3 to 5 g. Both were measured in the sclera of both eyes from animals exposed to four experimental conditions: (1) Normal development, at intervals from the day of natural eyelid opening (day 1 of visual experience [VE]) to greater than 5 years of age; (2) Monocular form deprivation (MD), for varying lengths of time; (3) Recovery from MD; (4) Monocular -5 D lens treatment. The creep rate was low in normal animals (1-2% elongation/h), did not change significantly between day 1 and day 75 of VE, and was not significantly different between the two eyes. Four days of MD produced a 200-300% increase in creep rate in the sclera from deprived eyes. Creep rate remained similarly elevated after 11 and 21 days of MD. After 2 days of recovery, which followed 11 days of MD, the creep rate of sclera from the recovering eyes was below normal levels. In animals that wore a monocular -5 D lens for up to 21 days, creep rate increased, and then decreased, in concert with the increase, and decrease, in axial elongation rate as the eyes compensated for the lens. The modulus of elasticity of the sclera was not significantly affected by any manipulation. The temporal correspondence between changes in axial elongation rate and changes in creep rate support the hypothesis that regulation of the time-dependent mechanical properties of fibrous mammalian sclera plays a role in controlling axial elongation rate during both normal emmetropization and the development of refractive errors. (+info)
Immunohistochemical survey of the gut endocrine cells in the common tree shrew (Tupaia belangeri).
Regional distribution and relative frequency of endocrine cells in the gastrointestinal tract of the common tree shrew (Tupaia belangeri) were studied immunohistochemically. Ten types of immunoreactive endocrine cells were localized in the gastric mucosa, i.e., chromogranin-, serotonin-, gastrin-, somatostatin-, bovine pancreatic polypeptide (BPP)-, enteroglucagon-, pancreatic glucagon-, peptide tyrosine tyrosine (PYY)-, motilin-, and substance P (SP)-immunoreactive (IR) cells. In the intestine, 13 types of immunoreactive cells were observed, i.e., chromogranin-, serotonin-, somatostatin-, gastrin-, BPP-, enteroglucagon-, PYY-, secretin-, cholecystokinin (CCK)-, gastric inhibitory peptide (GIP)-, motilin-, neurotensin-, and SP-IR cells. The regional distribution and relative frequency of the cell types varied along the gastrointestinal tract. Basically, the types, distribution, and relative frequency of the gut endocrine cells were similar to those reported in other mammalian species. However, some characteristic findings were noted in the present study: (1) the considerably large number of gastrin-IR cells in the pyloric region; (2) numerous serotonin-IR cells in the stomach; (3) appreciable number of BPP-IR cells in the transitional region of the stomach; and (4) wide distribution of PYY- and motilin-IR cells in the gut. (+info)
Geographical variation of the skull morphology of the common tree shrew (Tupaia glis).
Geographical variation was examined morphologically in the common tree shrew (Tupaia glis) in some Indochinese and Malayan regions. Osteometrical examination and principal component analysis elucidated the morphological differences among various populations. The populations from southern and western Thailand were distinguished morphologically from the other populations. Variation in males from south Thailand and Kuala Lumpur suggests that the Isthmus of Kra may have an influence on the variation of skull morphology. However, the Isthmus of Kra was not completely considered as a factor of geographical separation in this species, because we could not confirm the separation in skull size and shape between the localities at least in females. While, the Kanchanaburi population in western Thailand was significantly smaller than the other population in skull size, and constituted the morphologically separable group in our study. (+info)
Functional specificity of callosal connections in tree shrew striate cortex.
Although callosal connections have been shown to link extensive regions of primary visual cortex, the distribution of these connections with respect to the map of visual space and the map of orientation preference remains unclear. Here we combine optical imaging of intrinsic signals with injection of fluorescent microspheres to assess the functional specificity of callosal connections in the tree shrew. By imaging both hemispheres simultaneously while presenting a series of spatially restricted stimuli, we find that a substantial region of visual space is represented bilaterally. Each hemisphere includes a representation of the ipsilateral visual field that is highly compressed relative to that of the contralateral visual field and is most extensive in the lower visual field, where approximately 30(o) of central visual space are represented bilaterally. Callosal connections extend throughout the region of bilateral representation but terminate in a spatially restricted manner that links visuotopically corresponding sites in the two hemispheres. In contrast, callosal connections appear to terminate without regard for the map of orientation preference, showing little sign of the orientation-specific modular and axial specificity that is characteristic of long-range horizontal connections. By coordinating the activity in the two hemispheres in a way that preserves nearest neighbor relationships, callosal connections may best be viewed as elements of local circuits that operate within a single bilateral representation of visual space. (+info)
Psychophysical measurement of temporal modulation sensitivity in the tree shrew (Tupaia belangeri).
Temporal modulation sensitivity functions (MSFs) were measured behaviorally in three adult tree shrews (Tupaia belangeri). Shrews were trained to detect temporal sinusoidally-modulated full-field luminance variations in one of three stimuli, the two alternatives being static stimuli of equal size and time-averaged luminance (34 cd/m2). Modulation depth was varied trial-by-trial using a modified staircase technique under ambient illumination of 16 lux. Threshold modulation depths were determined for five temporal frequencies ranging from 3.7 to 47 Hz. Results revealed temporal MSFs that peaked at 15 Hz with a low-frequency roll-off and an extrapolated high-frequency cut-off beyond 50 Hz. These findings confirm the comparatively good temporal vision of Tupaia predicted by behavioral observations. (+info)
Multivariate analysis in skull osteometry of the common tree shrew from both sides of the Isthmus of Kra in Southern Thailand.
The Isthmus of Kra in Southern Thailand consists of a lowland of about 70 km in length. It has been suggested that the Isthmus may sink beneath the sea surface according to the change of level of the sea, and may function as a zoogeographical barrier in land mammals in this region. So, the geographical variation was osteometrically examined in skull of the common tree shrew (Tupaia glis) from the both sides of Isthmus of Kra. The osteometrical examination demonstrated that the skull is larger in southern population than in northern one. In the charts of the principal component analysis, however, the morphological separation between two populations can not be obviously seen in female. While, the results of the discriminant analysis indicated the morphological separation between the two populations. These findings suggest that the zoogeographical barrier of Isthmus of Kra may have influence on the osteometrical variation in the common tree shrew, when the Isthmus was covered with sea. (+info)
Osteometrical skull character in the four species of tree shrew.
The skull size and shape were osteometrically examined in the four species of the tree shrews (Tupaia tana, T. javanica, T. minor and T. dorsalis). We suggest that the skull characters were affected by the species specific behavior and terrestrial, arbo-terrestrial and arboreal life, among the genus Tupaia. The neurocranium was laterally narrower in the braincase area, and the splanchnocranium was longer only on dorsal side in T. tana, and these characters were opposite to T. minor. The principal component analysis confirmed the obviously separated clusters among T. tana, T. javanica and T. minor, affected by the adaptation for each behavior. T. dorsalis was considered as terrestrial species from the results of proportion analysis and the principal component analysis. (+info)
To what extent are the retinal capillaries ensheathed by Muller cells? A stereological study in the tree shrew Tupaia belangeri.
The cellular ensheathment of capillaries in the 3 outer capillary layers of the central retina of the adult tree shrew Tupaia belangeri was studied quantitatively by transmission electron microscopy. Using a stereological approach, the relative surface of capillary basal lamina ensheathed by Muller cells and by nonmacroglial cells (collectively termed non-Muller cells) was estimated in 5 animals. The participation of Muller cells was distinctly different in the 3 capillary layers studied. In the outermost capillary layer 1, the mean (standard deviation) percentage surface coverage by non-Muller cell processes was 46.8 (15.3)%. Much less of the capillary basal lamina was ensheathed by non-Muller cells in capillary layers 2 and 3 (3.0 (2.1)% and 0.3 (0.3)% respectively). The observed total variation of the stereological estimates for the surface fraction of Muller cells (expressed as the between-subject coefficient of variation) was significantly higher in capillary layer 1 (28.8%) compared with capillary layers 2 (2.2%) and 3 (0.3%). In capillary layer 1, the high observed total variation was due to a high biological variation among animals for the fractions of both Muller cell and non-Muller cell ensheathment. The rare occurrence of direct contacts between the capillary basal lamina and the perikarya of either microglial cells (capillary layer 3) or amacrine cells (capillary layer 2) corresponded well to the low stereological values obtained for the relative capillary surface ensheathed by non-Muller cells in these capillary layers. Previously, extensive and frequent contacts between the basal lamina of capillaries belonging to capillary layer 1 and horizontal cells had been observed in single sections. The present study quantitatively demonstrates a marked paucity of macroglial investment of capillaries located in capillary layer 1 of Tupaia. It can be concluded that horizontal cells ensheath most of the capillary surface not invested by Muller cells. (+info)