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Smooth muscle in human intracerebral arterioles.
Aterioles from the human cerebral cortex have been examined by electron microscopy in several patients aged 43 to 58 years. The wall of all arterioles (ranging in size from 10-70 microns in diameter) is composed of a single layer of endothelium and from one to 5 layers of smooth muscle cells. A basal lamina supports the endothelium and encloses the smooth muscle cells. Smooth muscle cells were identified by morphological criteria that included the presence of dense bodies, abundant microfilaments and numerous pinocytotic vesicles. Some of the intracerebral arterioles were observed in a constricted state indicating functional smooth muscle cells. The presence of functional smooth muscle cells in human intracerebral arterioles indicates that these arterioles are capable of vasoconstriction which may be a possible factor in some clinical conditions.
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Fate of neurohypophysial granule membranes after secretion in the rat: generation of a new apparent organelle by freezing and thawing secretory granules.
The contents and membranes of the secretory granules in the rat neurohypophysis were labelled in vivo with [35S]cysteine and [3H]choline respectively. Density-gradient centrifugation of the labelled granules showed the membrane label to be distributed largely between two peaks: one associated with intact granules and one with the characteristics of empty granule envelopes. Stimulation of hormones release in vitro led to the movement of membrane label from the intact granule fraction to the other one, consistent with the recapture of membrane as large vesicles. Freezing and thawing the crude granule fraction, ostensibly to aid osmotic fracture, produced a single membrane component with a density intermediate between the two original fractions.
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Ultrastructural obsevations on synaptic ribbons in the pineal organ of the goldfish.
Synaptic ribbons in the pineal organ of the goldfish were examined electron microscopically with particular attention to their topography. These structures were formed of parallel membranes, which were poorly preserved with OsO4 fixation and could be extracted from thin sections with pronase indicating their proteinaceous nature. Synaptic ribbons were closely apposed to the plasma membrane bordering dendrites of ganglion cells, but were also related to processes of both photoreceptor and supportive cells. Their close proximity to invaginations of the plasma membrane and portions of the endoplasmic reticulum suggest that they are involved in the turnover of cytoplasmic membranes. Tubular and spherical organelles of unknown function are also described.
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Electron microscopic study of the origin and formation of Reissner's fiber in the subcommissural organ of Cebus apella (Primates, Platyrrhini).
Two kinds of secretion are formed in cells of the subcommissural organ (SCO) of Cebus apella. The "light secretion" is found in saccules originating from the endoplasmic reticulum. This secretion is stored in the peripheral portion of the cells and is not involved in formation of Reissner's fiber (RF). In close association with the Golgi complex, electron-dense granules are developed, containing a finely granular substance. These granules accumulate beneath the apical plasmalemma of the cell. Their content is discharged into the third ventricle, where it occurs in the form of a thin layer of secretion. This material appears to constitute the RF at the level of the entrance to the mesencephalic aqueduct.
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The ventricular surface of the subcommissural organ: a scanning and transmission electron microscopic study.
The subcommissural organ of the rat has been studied by a combination of light, scanning and transmission electron microscopy. Special attention has been paid to the appearance of the ventricular surface of the organ. The ependyma-derived cells on the surface of the organ are extremely long with a width which diminishes steadily from the base, where the nucleus is situated, to the ventricular surface. This results in a fan-shaped arrangement of cells, the cytoplasm of each cell reaching the surface of the ventricular system. The apical surface of the cell has small ciliated extensions 1-1.5 micrometers in diameter protruding into the ventricular lumen. With conspicuous rough endoplasmic reticulum and Golgi apparatus, and microtubules in profusion, the subcommissural organ cells possess the hallmarks of active secreting cells. The surface of the cells shows pinocytic vesicles-suggesting exchange of materials with the cerebrospinal fluid.
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Synaptic ribbons during postnatal development of the pineal gland in the golden hamster (Mesocricetus auratus).
Synaptic ribbons, functionally enigmatic structures of mammalian pinealocytes, were studied during the postnatal development of the pineal gland in the golden hamster (Mesocricetus auratus). On day 4 post partum, synaptic ribbons appear in cells that have already started to differentiate into pinealocytes. Between days 4 and 9, an increase in the number of synaptic ribbons occurs, concomitant with the continuing differentiation of the pineal tissue. Between days 9 and 16, when differentiation of this tissue is almost completed, the number of synaptic ribbons decreases and approaches that characteristic of the adult pineal gland. During development, the synaptic ribbons increase in length, and dense core vesicles are frequently found in the vicinity of these structures. It is assumed that a functional relationship exists between dense core vesicles and the synaptic ribbons, which are considered to be engaged in a certain form of secretory activity of the mammalian pineal gland.
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Ultrastructural features of pituicytes in the neural lobe of adult rats.
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Schmidt-Lantermann incisures in the central nervous system.
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Ultrastructure of the human atrioventricular node.
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[The early phases of cilia formation and the problem of the origin of the basal body].