Müller glial cells of the primate foveola: An electron microscopical study.

Previous studies on the ultrastructure of the primate foveola suggested the presence of an inverted cone-like structure which is formed by 25-35 specialized Müller cells overlying the area of high photoreceptor density. We investigated the ultrastructure of the Müller cells in the foveola of a human and macaque retina. Sections through the posterior poles of an eye of a 40 years-old human donor and an eye of an adult cynomolgus monkey (Macaca fascicularis) were investigated with transmission electron microscopy. The foveola consisted of an inner layer (thickness, 5.5-12 µm) which mainly contained somata (including nuclei) and inner processes of Müller cells; this layer overlaid the central Henle fibers and outer nuclear layer. The inner layer contained numerous watery cysts and thin lamelliform and tubular Müller cell processes which spread along the inner limiting membrane (ILM). The cytoplasm of the outer Müller cell processes became increasingly dispersed and electron-lucent in the course towards the outer limiting membrane. The ILM of the foveola was formed by a very thin basal lamina (thickness, <40 nm) while the basal lamina of the parafovea was thick (0.9-1 µm). The data show that there are various conspicuous features of foveolar Müller cells. The numerous thin Müller cell processes below the ILM may smooth the inner surface of the foveola (to minimize image distortion resulting from varying light refraction angles at an uneven retinal surface), create additional barriers to the vitreous cavity (compensating the thinness of the ILM), and provide mechanical stability to the tissue. The decreasing density of the outer process cytoplasm may support the optical function of the foveola.

Biomechanical properties of retinal glial cells: comparative and developmental data.

The biomechanical properties of Müller glial cells may have importance in understanding the retinal tissue alterations after retinal surgery with removal of the inner limiting membrane and during the ontogenetic development, respectively. Here, we compared the viscoelastic properties of Müller cells from man and monkey as well as from different postnatal developmental stages of the rat. We determined the complex Young's modulus E = E' + iE″ in a defined range of deforming frequencies (30, 100, and 200 Hz) using a scanning force microscope, where the real part E' reflects the elastic property (energy storage or elastic stiffness) and the imaginary part E″ reflects the viscous property (energy dissipation) of the cells. The viscoelastic properties were similar in Müller cells from man, monkey, and rat. In general, the elastic behavior dominated over the viscous behavior (E' > E″). The inner process of the Müller cell was the softest region, the soma the stiffest (Einnerprocess(')Eglia(')). These relations were also observed during the postnatal development of the rat. It is concluded that, generally, retinal cells display mechanics of elastic solids. In addition, the data indicate that the rodent retina is a reliable model to investigate retinal mechanics and tissue alterations after retinal surgery. During retinal development, neuronal branching and synaptogenesis might be particularly stimulated by the viscoelastic properties of Müller cell processes in the inner plexiform layer.

Comparison of cellular localisation of the Ca2+ -binding proteins calbindin, calretinin and parvalbumin in the retina of four different Macaca species.

Ca2+ -binding proteins are differentially expressed in the nervous system; their functional role often remains unclear. This immunohistochemical study aimed at characterising and comparing the expression pattern of the Ca2+ -binding proteins calbindin (Calb), calretinin (Calr) and parvalbumin (Parv) in the retina of four species of macaque monkeys: Macaca fascicularis (cynomolgus macaque), M. mulatta (rhesus macaque), M. thibetana (Tibetan macaque) and M. fuscata (Japanese macaque). Calb was found in cone photoreceptors and in a subset of bipolar cells. Calr was expressed in a subpopulation of amacrine cells. Parv was present in horizontal and ganglion cells. In addition, Müller cells were stained using antibodies against the specific marker cellular retinaldehyde-binding protein (CRALBP). Immunostainings were used for calculation of the density of different cell populations. The expression pattern was similar between the examined species and between retinal regions.

Thymus development in Macaca fascicularis (Cynomolgus monkey): an approach for toxicology and embryology.

Thymus development was studied in the cynomolgus monkey from day 35 of gestation (gd 35) to the stage of advanced involution in a 21-year-old monkey. Special emphasis was placed on thymus cell generation and cellular pattern formation. At gd 35, the epithelial bud of the thymus was visible in a sagittal position at the level of the thoracic aperture. At gd 50, first lymphocyte-like cells and few Human Leukocyte Antigen-D Region (HLA-DR) immunoreactive cells appeared. The cortico-medullary differentiation, Hassall's body precursors and faint immunoreactivity for T-lymphocytes (CD 3-positive) were detected from gd 60 onwards. First macrophages (CD 68 positive) were apparent at day 70, first CD 20 immunoreactive cells (B-lymphocyte-like cells) at gd 85, and natural killer cells (M1014 immunoreactive) at gd 100. At gd 100 all evaluated cell populations present in the adult cynomolgus monkey thymus were in place, whereas no B- and T-cell precursors or (CD 34 and CD 117, respectively) dendritic cells (CD 35 positive cells) were present. All these immunopositive cells persisted, partly with changing distribution patterns, until the advanced age of 21 years with the exception of natural killer cells, which were present only until adult ages (evaluation at 4-7 years). The rationale of this study was to analyse thymic development in the cynomolgus monkey and to evaluate the relevance of the development of thymus in non-human primate as a model for corresponding human targeted toxicological research.

Assessment of placental transfer and the effect on embryo-fetal development of a humanized monoclonal antibody targeting lymphotoxin-alpha in non-human primates.

An enhanced embryo-fetal development study was conducted in cynomolgus monkeys using pateclizumab, a humanized IgG1 monoclonal antibody (mAb) targeting lymphotoxin-alpha. Pateclizumab administration between gestation days (GD) 20 and 132 did not induce maternal or developmental toxicities. The ratio of fetal-to-maternal serum concentration of pateclizumab was 0.73% on GD 50 and 61% by GD 139. Decreased fetal inguinal lymph node-to-body weight ratio was present in the high-dose group without microscopic abnormalities, a change attributable to inhibition of lymphocyte recruitment, which is a pharmacologic effect of pateclizumab during late lymph node development. The effect was observed in inguinal but not submandibular or mesenteric lymph nodes; this was attributed to differential susceptibility related to sequential lymph node development. Placental transfer of therapeutic IgG1 antibodies; thus, begins during the first trimester in non-human primates. Depending on the potency and dose levels administered, antibody levels in the fetus may be pharmacologically or toxicologically relevant.

Physiological properties of retinal Muller glial cells from the cynomolgus monkey, Macaca fascicularis--a comparison to human Muller cells.

Retinae from rabbits and laboratory rodents are often used as 'models' of the human retina, although there are anatomical differences. To test whether monkey eyes provide a better model, a physiological study of Muller glial cells was performed comparing isolated cells and retinal wholemounts from the cynomolgus monkey, Macaca fascicularis and from man. The membrane conductance of Muller cells from both species was dominated by inward and outward K(+) currents. Cells displayed glutamate uptake currents and responded to nucleotides by intracellular Ca(2+) increases. However, there were also species differences, such as a lack of GABA(A) receptors and of Ca(2+)-dependent K(+) currents in monkey cells. Thus, the use of Muller cells from cynomolgus monkeys may be advantageous for investigating a few specific properties; in general, monkey cells are no more similar to human cells than those from standard laboratory animals.

Reproductive/developmental toxicity and immunotoxicity assessment in the nonhuman primate model.

Nonhuman primates are being used increasingly as a non-rodent animal model during preclinical toxicology and safety assessment on the basis of proven similarity and comparability between nonhuman primates and humans. The validity of the nonhuman primate models applies to many aspects of toxicological testing and holds particularly true for the evaluation of reproductive toxicology and developmental toxicology. More recently, the advent of humanized antibodies and vaccines imposed further demand on nonhuman primate models since many immunotherapeutics do not interact with rodent receptors but frequently only cross-react with primate tissue. In this paper we discuss the suitability of primate models for reproductive, developmental and immunotoxicology testing, and present our initial data on the development of lymphatic organs and immune system in a nonhuman primate model.

Cerebellar localization of the NO-receptive soluble guanylyl cyclase subunits-alpha(2)/beta (1) in non-human primates.

Nitric-oxide-sensitive guanylyl cyclase (NO-sGC) plays a pivotal role in many second messenger cascades. Neurotransmission- and neuropathology-related changes in NO-sGC have been suggested. However, the cellular localization of NO-sGC in primate brains, including humans, remains unknown. Biochemical evidence has linked the alpha(2)-subunit of NO-sGC directly to neurotransmission in rodents. Here, we have used a recently characterized subunit-specific antibody for the localization of the alpha(2)-subunit on sections from the cerebelli of the common marmoset (Callithrix jacchus; New World monkey) and macaque monkeys (Macaca mulatta, M. fascicularis; Old World monkeys). In contrast to the more ubiquitous cytoplasmic presence of subunit-beta(1), the alpha(2)-subunit is mainly confined to the somato-dendritic membrane including the spines of the Purkinje cells. Only limited colocalization with presynaptically localized synaptophysin has been seen under our staining conditions, indicating a higher abundance of subunit-alpha(2) at the postsynaptic site. This localization indicates that subunit-alpha(2) links NO-sGC to neurotransmission, whereas subunit-beta(1) may act as a cytoplasmic regulator/activator by contributing to active heterodimer formation via translocation from the cytoplasm to the cell membrane. The last-mentioned action may be a prerequisite for generating nitric-oxide-dependent, subcellular, and postsynaptically localized cGMP signals along neuronal processes.