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Three-dimensional aspects and synaptic relationships of a Golgi-impregnated spiny stellate cell reconstructed from serial thin sections.
A Golgi-impregnated spiny stellate cell was selected from layer IV of SmI cortex in a mouse whose ipsilateral ventrobasal complex had been lesioned. The neuron was gold-toned, thin sectioned and then reconstructed in three dimensions using wooden sheets of appropriate thickness. These procedures enabled the numbers and distribution of thalamocortical and other synapses onto the reconstructed neuron to be determined. Results show the cell body to be roughly spherical and to receive 49 symmetrical synapses and four synapses which are intermediate between the asymmetrical and symmetrical type. A single, clearly asymmetrical axosomatic synapse is made by a degenerating, thalamocortical axon terminal. Five primary dendrites and their branches were reconstructed and, interestingly, these processes are distinctly elliptical in cross-section. The reconstructed dendrites receive 68 symmetrical synapses onto their shafts and 373 synapses onto spines of which 359 are asymmetrical and 14 symmetrical. Forty-eight, or about 13%, of the asymmetrical axospinous synapses are made by degenerating, thalamocortical axon terminals. An intriguing finding is that in many regions of the dendritic tree, two or more spines involved in thalamocortical synapses are attached to the dendritic shaft at intervals of 5 +/- 0.5 micron.
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Structural changes in the pars intermedia of the cichlid teleost Sarotherodon mossambicus as a result of background adaptation and illumination. II. The PAS-positive cells.
The pars intermedia of Sarotherodon mossambicus contains two structurally different endocrine cell types. The predominant cell type is assumed to synthesize MSH and related peptides. The second cell type is PAS positive; its function and products are unknown. In this second cell type changes occur in relation to background colour and illumination. Thus, PAS positive cells of fish adapted to a white background are less numerous and metabolically less active than those of fish adapted to a black background, [corrected] and are most active in fish kept in total darkness. In blinded fish, whether in light or in darkness, the activity of the PAS positive cells is similar to that of the black background-adpated animals. The significance of these responses in relation to the control of background adaptation is discussed.
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Fine structure of the rhombencephalic tela of the bullfrog, Rana catesbeiana.
The posterior rhombencephalic tela choroidea of the bullfrog was examined by electron microscopy. This membrane, the pia-ependymal roof of the caudal hindbrain, contains a large central region characterized by cuboidal ependymal cells which surround sizable microscopic apertures -- the interependymal pores. Ultrastructurally ependymal cells of this area are characterized by infrequent apical microvilli and cilia. They contain irregularly shaped nuclei and few cytoplasmic organelles that are largely apical in position. The most striking feature is an abundance of cytoplasmic filaments forming an extensive cytoskeleton. Laterally these cells are joined by numerous elaborate desmosomes. The majority of the ependymal cells have a basal lamina consisting of single, double, or triple laminae lying parallel to the basal plasma membrane. Several unusual specializations are seen at the margins of the interependymal pores. The ependymal cells have lateral cytoplasmic processes that form the actual border of each pore. These processes originate from the apical surface of the cell and partially enclose an elaborate network of basal lamina associated with the interependymal pores. These findings demonstrate microscopic apertures in the roof of the fourth ventricle in the bullfrog that are associated with an unusual form of supportive ependyma.
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Electron microscopic studies on the pineal organ of the antarctic penguin, (Pygoscelis papua).
The pineal organ of the migratory antarctic penguin, Pygoscelis papua, has a lobular structure. Clusters formed by different types of parenchymal cells are separated by connective tissue septa containing blood vessels. The predominant cell type displays a well-developed Golgi complex, free ribosomes, clear and granular vesicles (secretory granules), and lysosomes. Other cell types found in the gland are supporting and ependymal-like cells. The former contain dense bodies and filament bundles, the latter possess abundant cilia and clusters of ribosomes. Typical photoreceptor elements are lacking. Blood vessels are located within a perivascular space bordered by basal laminae. This perivascular space extends between the basal protrusions of the parenchymal cells. The presence of pinocytotic vesicles, secretory granules and cytoplasmic processes in the vicinity of these spaces suggests active sites of transport and exchange of substances. Intercellular conaliculi-like spaces are surrounded by parenchymal cells rich in microvilli. These cancliculi are continuous with the cavities (invaginations) of secretory and other parenchymal cells.
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Enhanced replication of SARS-CoV-2 Omicron BA.2 in human forebrain and midbrain organoids.
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Morphological and biochemical changes in the pineal gland in pregnancy.
Although systematic and detailed studies of pineal structure and function during pregnancy are rare, the available evidence indicates that morphological and biochemical changes do take place in this gland during this reproductive state. The majority of studies indicate increased activity in cytoplasmic organelles and enzymes of pinealocytes during gestation. Changes in pineal and plasma melatonin levels in pregnancy have been described in a number of species. Results of biochemical studies emphasize the existence of the feedback system which involves the gonads, the hypothalamus and the pineal gland. More ultrastructural and biochemical studies on this intriguing gland in pregnancy are fully warranted.
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[Ultrastructure of epileptic foci in temporal epilepsy].
An electron microscopy study was conducted on the material of biopsies from the removed epileptic foci localized in the hippocamp and fields 21 and 38 of the temporal cortex of 11 patients with temporal epilepsy. There was the constant presence of so-called dark and altered light neurocytes whose cytoplasm had experienced considerable changes and was saturated with various inclusions. The axons and dendrites of the cells underwent peculiar degeneration. The authors revealed multiple agglutination of synaptic vesicles in the preterminals and synaptic buds, and also dark degeneration of the axonal endings in the absence of Waller's degeneration of axons. Marked changes in the walls of the capillaries were also found.
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Axo-dendritic abnormalities in a case of juvenile neuronal storage disease.
Axonal enlargements (meganeurites) and dendritic degeneration were found in the pyramidal neurons from the frontal cortex of a patient with juvenile neuronal storage disease studied with the aid of ultrastructural and Golgi methods. Meganeurites appeared as enlargements at the axon hillock-initial segment area and were similar to those described in other neuronal diseases; dendritic degeneration was heavy and appeared throughout the cell domain. These neuropile changes can be related to the precocious mental abnormalities observed in this group of diseases which depend on a storage phenomenon due to a lysosomal enzyme deficiency.
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The fine structure of the neural lobe of the mouse after transplantation under the kidney capsule.
The neurohypophysis of donor mice was implanted under the renal capsule of the recipients. The pituicytes survived while the neurosecretory axons disappeared. The ultrastructure of the glial cells was observed seven and nine weeks after transplantation. There were no signs of phagocytotic activity although remnants of axons were still present at seven weeks. The numerous processes of the pituicytes form a network with intercellular spaces wide in younger and narrower in older implants. The cells are connected by desmosomes and gap junctions. Pituicytes as well as blood vessels preserve their organotypic appearance. The transplant thus represents as experimental model for investigations on pituicytes in vivo in the absence of neurosecretory axons.
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Evolution of the pineal gland in the adult chicken.
The structural pattern of the pineal gland in the hen corresponds to a more advanced stage of the evolution which began in an early period of the animal's life. This evolution corresponds mainly to the transformation of the large follicular cavities into cellular 'rosettes'. The parafollicular layer disappears from the rosette wall which thus remains with only one row of cells (A and B pinealocytes). The cellular hypertrophy and the great development of the pinealocyte organelles in the adult pineal gland makes us think of this gland as a functionally active organ. This functional activity must have remained during the entire period of the time studied (1--5 years), due to the ultrastructural uniformity found and due to the fact that we could not observe any type of degenerative process in the gland.