Magdalena García

Two types of mitochondria are evidenced by protein kinase C immunoreactivity in the Müller cells of the carp retina

The localization of protein kinase C (PKC) was studied immunocytochemically in the Müller cells of the carp retina. Electron microscope immunocytochemistry (using a monoclonal antibody to the alpha and beta isoenzymes of PKC) showed PKC-immunoreactivity mainly inside some mitochondria, especially along the mitochondrial cristae whereas other mitochondria in the same Müller cells showed no staining. Despite a detailed analysis we did not find any significant morphological difference between labeled and unlabeled mitochondria. These results demonstrate, for the first time, the presence of PKC immunoreactivity inside mitochondria and suggest that individual mitochondria may differ in signal transduction pathway.

Dendrites of rod dominant ON-bipolar cells are coupled by gap junctions in carp retina

Gap junctions are supposed to be the anatomical substrate for electrical coupling between neurons. In fish retina, bipolar cells are electrically coupled and their receptive field diameters are always larger than dendritic field size, however, gap junctions have not been described between dendrites of bipolar cells. In this paper, using immunostaining for protein kinase C, we show that every rod dominant ON-bipolar cell is connected with its neighboring dendrites by gap junctions forming a plexus in the outer plexiform layer. These dendritic processes provide the site of electrical coupling. We suggest that dendrites of bipolar cells could be involved in lateral pathways in retina.

Formation and dissolution of spinules and changes in nematosome size require optic nerve integrity in black bass (Micropterus salmoides) retina

Teleost retinas adapted to light show numerous spinules invaginated in the cone pedicles and small nematosomes in the distal horizontal cells. Darkness induces the dissolution of spinules and the presence of large and numerous nematosomes. The aim of this work is to study the influence of optic nerve integrity on spinule formation/dissolution and changes in nematosome size during light or dark adaptation of black bass (Micropterus salmoides) retinas. Eyes from fish, dark- or light-adapted, were removed and the eyecups placed in oxygenated Ringers solution and immediately exposed to light or dark, respectively, for 1 h. The number of spinules per pedicle and the nematosome diameter were measured on electron micrographs. Isolation of eyecups in the dark, impaired both spinule formation and nematosome size reduction when they were superfused in light. In the same way, isolation of eyecups in the light, impaired both spinule dissolution and nematosome size increase when they were superfused in dark. No significant differences in spinule number and nematosome size, following dopamine superfusion, were found in comparison to retinas superfused with Ringers solution only. Our results suggest: (1) optic nerve integrity is necessary to yield spinule formation/disruption and changes in nematosome size during light or dark adaptation. (2) dopamine does not appear to be the primary agent responsible for spinule formation.

Interocular effect of actin depolymerization on spinule formation in teleost retina

Teleost retinas adapted to light show numerous spinules invaginated in the cone pedicles whereas darkness induces a reduction in the number of spinules. Horizontal cells show nematosomes whose size decreases as the number of spinules increases. We have investigated the involvement of actin filaments in spinule formation, by using cytochalasin D through intraocular injection into an eye. The ultrastructural analysis reveals that cytochalasin D impairs spinule formation and nematosome-size reduction in both treated and contralateral untreated retinas.

The structure of the retina of the Eurasian Eagle-owl and its relation to lifestyle

The retinal layers of birds are the same as those of other vertebrates; however, some variations exist in morphology, areas of visual acuity, and retinal vascularisation. Moreover, as a result of the relationship between environment, visual perception and behaviour, some variations are observed between diurnal and nocturnal birds. In this study, we have investigated the retina of the Eurasian Eagle-owl (Bubo bubo hispanicus) by optical microscopy. The results indicate that the retina has features of both nocturnal and diurnal birds. The pigment epithelium cells have long prolongations filled with melanin granules. The rod is the dominant photoreceptor, but simple cones are abundant. Yellow and colourless oil droplets and paraboloid are present in the inner segment of cones. In the inner nuclear layer, the cell bodies of horizontal cells can easily be recognised by a large and pale cytoplasm. Bipolar cell perikarya are identified by their dark nuclei and the round and narrow cytoplasm. Amacrine cells, located in the inner border of the inner nuclear layer, have a round perikarya and lightly stained nuclei. Müller cells bodies, also located in this region, have an irregular shape. Finally, ganglion cells which are characterised by the prominent nuclei and nucleoli vary in size and abundance depending on different regions in the retina. The morphological characteristics of this retina indicate that B. b. hispanicus have a high light sensitivity, the capacity to discriminate colour, a complex visual processing in the inner retina in order to mediate contrast and motion and, possibly, an elevated acuity in areas of high photoreceptor and ganglion cell density.

Ultrastructural study of retinal development in the turtle Trachemys scripta elegans

The present study was conducted by using light and transmission electron microscopy to examine the morphologic development of turtle retina from embryonic stage 18 (S18) to S26 (hatching). Particular attention was paid to the formation of functional structures such as neurites, synapses, photoreceptors, among others, and the moment that chemical synapses appear in the outer and inner plexiform layers. The results show that retinal differentiation in the turtle follows the vitreal to scleral morphological differentiation of retinal cells. Moreover, the central region of the optic cup is most advanced compared to the peripheral parts. Early functional plexiform layers, based on appearance of synapses, precede the complete differentiation of photoreceptors. The first synaptic structures occur in the inner plexiform layer before the outer plexiform layer. Receptor outer segments and first synaptic ribbon in receptor synaptic terminals initiate the differentiation at the same time, but final maturation includes dendritic invaginations of bipolar and horizontal cells in the receptor terminals. We assume that at birth, the turtle retina has achieved the ability to see.

Ultrastructural characteristics of human oocytes vitrified before and after in vitro maturation

The development of an effective program that combines in vitro maturation (IVM) and cryopreservation for immature oocytes would represent a novel advance for in vitro fertilization (IVF), especially as a means to preserve the fertility of women in unique situations. The aim of this study was to analyze the ultrastructural characteristics of human oocytes, obtained after controlled ovarian stimulation, to determine whether IVM is best performed before or after vitrification. To this end, we analyzed the following features in a total of 22 MII oocytes: size, zona pellucida and perivitelline space, mitochondria number, M-SER (mitochondria-smooth endoplasmic reticulum) aggregates and M-V (mitochondria-vesicle) complexes, the number of cortical granules and microvilli, and the presence of vacuolization using transmission electron microscopy (TEM). Each oocyte presented a rounded shape, with an intact oolemma, and was surrounded by a continuous zona pellucida and perivitelline space. Statistical analysis comparing oocytes vitrified before or after IVM indicated that there were no significant differences between examined characteristics.

Light and electron microscopic studies on the retina of the booted eagle (Aquila pennata)

The retinal structure of the booted eagle (Aquila pennata) was investigated using light and electron microscopy. Particular attention is paid to the main ultrastructural features of the receptor cells. This study reveals six distinct varieties of cones. Unequal double cones differ in shape, structure, and length and are comprised by principal long and accessory short members. Principal member contains a green oil droplet and accessory member contains a paraboloid and a pale green droplet. Four types of single cones are distinguished on the basis of their morphology and oil droplets: red, green, blue, and ultraviolet. Cones outnumber rods in all regions. Two types of horizontal cells and several morphological types of amacrine cells are abundant. A large number of bipolar cells are divided into long longitudinal rows by Müller cell processes, a prominent feature of this retina. These processes extend through the external limiting membrane to reach the ellipsoid region of the cones. Moreover, thick processes divide the inner nuclear and plexiform layers and surround the myelinated ganglion cell axons at fairly regular intervals. In the ganglion cell layer and optic nerve fibre layer, abundant oligodendrocytes are present, close to the myelinated axons. The morphological characteristics of this retina indicate that A. pennata have good colour discrimination, a complex visual processing to mediate contrast and motion and an elevated acuity in areas of high cell densities.

Correction to: Ultrastructural study of retinal development in the turtle Trachemys scripta elegans

The present study was conducted by using light and transmission electron microscopy to examine the morphologic development of turtle retina from embryonic stage 18 (S18) to S26 (hatching). Particular attention was paid to the formation of functional structures such as neurites, synapses, photoreceptors, among others, and the moment that chemical synapses appear in the outer and inner plexiform layers. The results show that retinal differentiation in the turtle follows the vitreal to scleral morphological differentiation of retinal cells. Moreover, the central region of the optic cup is most advanced compared to the peripheral parts. Early functional plexiform layers, based on appearance of synapses, precede the complete differentiation of photoreceptors. The first synaptic structures occur in the inner plexiform layer before the outer plexiform layer. Receptor outer segments and first synaptic ribbon in receptor synaptic terminals initiate the differentiation at the same time, but final maturation includes dendritic invaginations of bipolar and horizontal cells in the receptor terminals. We assume that at birth, the turtle retina has achieved the ability to see.