Yolanda Segovia

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.

A different ultrastructural face of ribbon synapses in the rat retina

Ribbon synapses located exclusively within retinal, cochlear and vestibular connections belong to the most interesting cellular structures but their molecular nature and functions had remained unclear. The study has provided a descriptive morphological analysis of rat eye ribbon synapses using high‐resolution transmission electron microscopy (TEM). An original collection of untypical, rarely present in the literature sagittal or tangential sections through the single RIBEYE domain of the particular ribbon have been delivered.