Kazuyo Shimai

Morphological development of retinal ganglion cells in the chick embryo.

Abstract The morphological changes of the external shapes of the developing ganglion cells in the chicken retina were investigated by light microscopy and chiefly with Golgi methods. At stage 20, the neural retina revealed an almost pseudostratified type of arrangement of epithelial cells on routine staining. In silver-impregnation images, most cells in the neural retina showed bipolarly elongated shapes. The inner process of this cell extended toward the vitreous side and attached to the inner limiting membrane, and the outer process extended toward the scleral side and attached to the outer limiting membrane. At stage 25, the ganglion cells sprouted an axon from the inner process or sent an axon directly from the perikaryon of the vitreous side. Next, the original processes, which had attached at first to the inner and outer limiting membranes, disappeared. At stage 29, spine-like processes appeared, extending in every direction from the cell body. At stage 31, some of these spine-like processes grew more extensively to form the dendrites, but the others disappeared. At stage 34, the cells began to form the ganglion cell layer, and their dendrites extended into tertiary branches. At stage 39, the cells could be classified into six types according to the branching pattern of the dendrites, which was identical with the ganglion cells after hatching. This indicated that the fundamental differentiation of ganglion cells could be regarded as essentially completed at stage 39.

Faulty development of cortical neurons in the Snell dwarf cerebrum.

In the Snell dwarf motor cortex, area 6 of Caviness, the cell number, the stratification of neurons and the portion of layer-widths were absolutely identical to those of the controls. By means of the Golgi-Cox method modified by Ramon-Moliner, however, the pyramidal neuron was found to have small perikarya, short primary dendrites with sparse branchings, and a low spine density on the dendrites. The corpus callosum of the dwarf contained a reduced number of fibers compared to that of the controls, and the staining for myelin basic protein revealed a considerable reduction of positive-fibers of radiation in this area. The content of Thy-1 antigen in the cerebrum, cerebellum and brainstem, was significantly lower than that of controls, but the monoamine content was normal in the cerebrum and brainstem. From these results, it appears that the Snell dwarf cerebrum shows retarded neuronal growth; a reduction in size of neurons, an underdevelopment of axons and dendrites, and a retarded maturation of spine, in addition to arrested glial proliferation. At present, it is unclear which hormone deficient in these mutants, growth hormone or thyroxine, is the essential potentiator for neuronal growth.

Cytoarchitectonic abnormalities in hippocampal formation and cerebellum of dreher mutant mouse

The laminated structures in the hippocampal formation and cerebellum of homozygous dreher mice were compared to their littermates and to C57BL/6J mice in Nissl- and myelin-stained preparations. In the dreher dentate gyrus, ectopic granule cells were situated in the molecular layer, and frequently there was either partial or complete absence of the infrapyramidal limb of the granule cell layer. In the dreher hippocampus, the cells of the pyramidal cell layer in area CA3 formed widely dispersed arrangements, and there were ectopically situated pyramidal cells in the stratum radiatum and stratum oriens. In the dreher cerebellum, 3 abnormal patterns were observed: (1) disruptions of foliation with normal cytoarchitectonic structure, (2) foliation with a mixture of normal laminated structure and abnormal laminated structure, and (3) almost complete absence of the cerebellum. In abnormal folia exhibiting the second or third pattern, islands consisting of agglomerations of both granule cells and Purkinje cells or just granule cells were observed. The neuronal heterotopias and cytoarchitectonic disorganization observed in the present study are apparently secondary to disruption of cell proliferation and neuronal migration produced directly or indirectly by the dreher mutation. In addition, the fact that the phenotypic abnormalities in homozygous dreher mice produces different abnormal morphologies in different specimens may be useful for analyzing the development of the hippocampal formation and cerebellum.

Immunohistochemical Localization of 2′,3′‐Cyclic Nucleotide 3′‐Phosphodiesterase and Myelin Basic Protein in the Chick Retina

Abstract: Antisera against bovine 2′,3′‐cyclic nucleotide 3′‐phosphodiesterase (CNPase) and against chick myelin basic protein (MBP) were raised in New Zealand white rabbits. The specificity of CNPase antiserum was examined by Ouchterlony double‐immunodiffusion test and immunoadsorption assay. With use of the specific antiserum, immunohistochemical localizations of CNPase and MBP were investigated in the chick retina. Light microscopic immunohistochemical studies have shown that MBP is localized in the optic nerve fiber layer and that CNPase is localized in the optic nerve fiber and photo‐receptor layers. Electron microscopic immunohistochemical examinations demonstrated that the myelin‐like neural sheaths in the optic nerve fiber layer were clearly stained by both antisera, whereas the membranes of the Müller cell were not stained. In the photoreceptor layer, membranes of the inner and outer segments of rod and cone photoreceptor cells were intensely stained by CNPase antiserum. However, these portions were not stained by MBP antiserum. Membranes of bipolar cells, amacrine cells, horizontal cells, and ganglion cells were not stained by either antiserum.

Disruption of neuronal migration in the neocortex of the dreher mutant mouse

To analyze developmental abnormalities related to neuronal migration in the dreher mutant mouse, the neocortical cytoarchitecture of dreher and control mice were examined in Nissl-stained serial sections by light microscopy. In general, the dreher neocortex has six layers which are similar in size and thickness to those observed in normal mouse neocortex. However, in dreher neocortex, three types of abnormalities were found: (1) an increase in the number of diffusely distributed neurons in layer I, (2) small, ectopic collections of neurons in layer I, and (3) isolated disturbances of local cytoarchitecture characterized by neuron-free space distributed in areas between layer II to IV. The occurrence of small, punctate deficits in the dreher neocortex may be secondary to disruptions of the radial glial fiber system and neuronal migration. The fact that cytoarchitectonic abnormalities of several types were found in the dreher neocortex may be useful in analyzing the relationship between radial glial fibers and migrating young neurons, the synaptic connections which are formed by ectopically situated neurons, and the mechanism of formation of sporadically distributed neocortical abnormalities.

Junction-like structure appearing at apposing membranes in the double cone of chick retina

SummaryNo type of junction has yet been recognized between the two entities of the retinal double cone. In the present study, a junction-like structure was observed in serial sections of the double cone of the chick retina. It is recognized from the slightly outer part of the double cone to the outer limiting membrane. The apposing membranes are virtually parallel and separated by 5 to 7 nm of extracellular space. Dense material is associated on the cytoplasmic side of the opposing membranes. The structure resembles a gap junction, but there are no cross striations between the two membranes. Further experiments are required to establish this as a new type of junction.

Histochemical and Immunohistochemical Studies of the Cerebellum from the Reeler Mutant Mouse

The organization of the fiber connections and architecture of the cerebellum of reeler mutant mice was analyzed by an immunohistochemical and histochemical procedure. By immunohistochemical staining of the myelinated fiber arborization with antiserum against myelin basic protein, it was found in the reeler cerebellum that the fibers ran in all directions throughout the white matter. Some of the fibers surrounded Purkinje cells. The distribution of AChE-positive fibers was abnormal and some Purkinje cells surrounded by AChE-positive fibers were present. Molecular layers and glomeruli showed strong succinic dehydrogenase (SDH) activity. The white matter of the reeler cerebellum showed a mosaic of SDH-positive and -negative sites. The results indicate that changes in the distribution of myelinated fiber arborization and the change in the distribution of SDH and AChE activity are different in each part of the cerebellum as a result of the disorganization of the architecture of the reeler mutation.

Physiological and morphological studies of signal pathways in the carp retina

In the vertebrate retina, visual information received at the receptor mosaic is processed in the neuronal network, and the final output is sent out to higher visual centers through the optic nerve fibers. AS a result of signal processing, retinal ganglion cells have precise receptive fields that enable them lo respond to specific stimuli, such as the shape, color or movement of images. In the retinas of many vertebrate% the most commonly found receptive fields of ganglion cells consist of concentrically arranged center and surround areas which are antagonistic lo each other (Kuffler, 1953). These receptive fields are thought to enhance the contrast of an image. Visual signals generated in photoreceptors are passed on first lo bipolar cells and then to ganglion cells, and along this course are modified by lateral input from horizontal and amacrine cells. Since the receptive fields of ganglion cells are the end products of retinal network function. it is important to know the arrangement of the preceding neural connections to understand the behavior of various ganglion cells. Our studies on the carp retina are aimed to answer this question by physiological and morphological methods.

Abnormalities of foliation and neuronal position in the cerebellum of NZB/BINJ mouse.

To analyze developmental abnormalities related to neural migration in the NZB/BINJ mouse, the pattern of cerebellar foliation and neural position were compared with that of a normal mouse (C57BL/6J). Three abnormalities of cerebellar foliation--(1) lobe isolated from other cerebellar lobes, (2) lobes imbalanced in relative amounts or ratio of granular cell layer and molecular layer, (3) lobes in which some Purkinje cells and the molecular layer was embedded in the granular cell layer--were observed in NZB/BINJ mice. These morphological abnormalities were not limited to a specific lobe. On the other hand, abnormalities of neural position were observed in both granule and Purkinje cells. The pattern of ectopically-situated granule cells, in general, could be divided into 3 types: (1) large cell clusters extending from granular cell layer to the pia mater or middle part of the molecular layer, (2) clusters of various sizes scattered within the white matter and (3) clusters formed by combination of granule cells extending from two opposed granular cell layers to the molecular layer. The pattern of ectopically-situated Purkinje cells could be divided into 4 types: (1) ectopia of a group of cells from one part of the Purkinje cell layer, (2) ectopia of a single Purkinje cell observed in the molecular layer, (3) single Purkinje cell scattered within the white matter accompanied by clusters of ectopic granule cells and (4) ectopic Purkinje cells embedded in the granular cell layer. The abnormalities in position of both granule cells and Purkinje cells was not limited to a particular cerebellar lobe.(ABSTRACT TRUNCATED AT 250 WORDS)

Clasping structure in the double cone of the retina of the turtle (Gyoclemys reevesii).

SummaryThe double cone of the turtle retina was reconstructed three-dimensionally from electron micrographs of 400 serial sections. Cytoplasm of the accessory cone extends bilaterally to surround the principal cone incompletely. The cytoplasmic extensions are 0.1 μm in width and 2 μm in length at their longest portions. They arise at approximately the median portion of the ellipsoid (consisting of mitochondria) and terminate at the level of the outer limiting membrane. The possible function of these extensions as a clasping structure is discussed.