Your browser does not allow saving data (e.g. private mode): bookmarks will be lost when the tab closes.
Search PubMed
Keywords, author, journal, years — results from PubMed, abstracts with Russian translation, bookmarks in your browser.
Found: 5 469
Page 194 of 547-
Aging in the rat olfactory bulb: quantitative changes in mitral cell organelles and somato-dendritic synapses.
Quantitative measurements of the major organelles in the mitral cell perikaryon as well as numbers of mitral somato-dendritic synapses, have been made on electron micrographs from rats aged 3 to 30 months. The volume fraction of the cisternae of rough endoplasmic reticulum (RER) is constant throughout the period studied. Hence the amount of RER per cell reflects changes in perikaryal size. Thus there is a 3-fold increase of volume of cisternae of RER per mitral cell from 3 to 27 months and a halving from 27 to 30 months. A similar pattern is seen for the volume of mitochondria per cell. The volumes of dense bodies and cisternae of the Golgi complex per cell show a different pattern, that of a linear increase throughout the period, with no suggestion of a decrease from 27 to 30 months. An interesting finding is that the volume fraction of ground substance (perikaryal cytoplasm exclusive of the measured organelles) shows a remarkably constant value from 3 to 27 months and then a highly significant decrease from 27 to 30 months. This decrease, restricted to the period from 27 to 30 months, suggests a fundamental breakdown in cellular homeostasis in the oldest animals. Numbers of somato-dendritic, mitral-to-granule synaptic junctions per mitral cell and per olfactory bulb show a significant increase from 3 to 24 and 27 months, respectively, and then a suggestive decrease from 24 and 27 to 30 months. This finding indicates that new synapse formation is possible in normal adult rats, perhaps even in quite old rats.
-
Synapses of optic nerve afferents in the rat suprachiasmatic nucleus. I. Identification, qualitative description, development and distribution.
Synapses of optic nerve afferents (optic synapses) in the rat suprachiasmatic nucleus (SCN) have been identified ultrastructurally. They are easily distinguished from other types of synapses. The optic boutons are characterized by the presence of large mitochondria with a swollen electron lucent matrix and an interconnected tubular system formed by their inner membrane. Other, more variable features include: 1) a scattered pattern of synaptic vesicles which are found throughout the entire presynaptic element with relatively little accumulation near the active zones; 2) the occurrence of dense core vesicles and glycogen granules; 3) the active zones, the majority of which is Gray-type I, but a minority can obviously be classified as Gray's type II; 4) the innervation of smaller peripheral dendrites and dendritic spines. Boutons of this kind are exclusively filled with anterogradely transported horseradish peroxidase injected into both eyes. Very few neuronal elements containing the typical mitochondria have been observed in the SCN on the 6th day post partum, increasingly more on the 9th and 12th day, but considerably higher numbers after opening of the eyes on the 17th and the following days. The location of normal and degenerating optic boutons was examined light- and electron microscopically. In the rostral third of the SCN there are relatively few optic synapses which are found close to the optic chiasma. In the middle portion of the SCN optic synapses increase in number; they are found not only in the ventral part of the nucleus but also in lateral regions. This becomes particularly obvious in the caudal third of the SCN.
-
[On the influence of puromycin on embryonic choroid plexus cells in vitro. An electronmicroscopic and histoautoradiographic study].
-
Responses of prolactin cells of two euryhaline marine fishes, Gillichthys mirabilis and Platichthys stellatus, to environmental salinity.
-
Further ultrastructural data on the cytoplasmic nucleolus resembling bodies or nematosomes. Their relationship with the subsynaptic web and a cytoplasmic filamentous network.
-
Polarized compartmentalization of organelles in growth cones from developing optic tectum.
We have used computer-assisted reconstructions of continuous serial sections to study the cytoplasmic organization of growth cones in vivo. Optic tecta from 6.25-6.5-d-old chicken embryos were quick-frozen and then freeze-substituted in acetone-osmium tetroxide or, for comparison, prepared by conventional fixation. Images of eight freeze-substituted and two conventionally fixed growth cones were reconstructed from aligned serial micrographs. After freeze-substitution, numerous lumenless membrane-bound sacs arrayed in multilamellar stacks appear to replace the abundant smooth endoplasmic reticulum found after chemical fixation. Microtubule fascicles progressively diverge from their typical fascicular organization in the initial segment of the growth cone and are absent in the varicosity and the more distal segment. Mitochondria, in contrast, are concentrated in the proximal segment of the varicosity; multilamellar stacks and endosome-like vacuoles are in the distal segment; and coated pits and vesicles are concentrated near the terminal filopodium, which is the most distal and organelle-poor domain of the growth cone. These observations suggest that dilation and fusion of the lumenless, membrane-bound sacs that occurs during chemical fixation give rise to the network of smooth endoplasmic reticulum. The three-dimensional reconstructions show that the cytoplasmic components of growth cones, including the membrane-bound sacs and multilamellar stacks revealed by freeze substitution, are polarized along the axis of these growth cones, which suggests that they have a role in recycling of membrane during elongation of the growth cone.
-
Influence of melatonin and serotonin on the number of rat pineal "synaptic" ribbons and spherules in vitro.
Previous studies have shown that the "synaptic" ribbons (SR) and spherules (SS) of the mammalian pineal gland may respond differently under physiological and various experimental conditions. The aim of the present study was to gain insight into the mechanisms that may be responsible for the numerical changes of these organelles during a 24-h cycle. As the possibility exists that the structures are influenced by substances synthesized within the pinealocyte, rat pineal glands were cultured with and without added melatonin or serotonin, using an experimental protocol such that the addition of melatonin and serotonin mimicks the circadian changes of the respective substances within the pineal. The tissue was processed for electron microscopy and the numbers of SR and SS were counted in a unit area of pineal tissue. The results obtained indicate that melatonin added to the incubation medium increases the number of SR in the first half of the night; serotonin decreases SR numbers in the morning. SS numbers, by contrast, decrease following melatonin administration in the afternoon, and increase in the morning following serotonin administration. It thus appears that the numbers of SR and SS are influenced by melatonin and serotonin and that the two structures are regulated by differential, but nevertheless biochemically closely related mechanisms.
-
Ultrastructure of pinealocytes of the cotton rat, Sigmodon hispidus.
Fine structural features of pinealocytes of cotton rats (Sigmodon hispidus) were examined. Golgi complexes, mitochondria, endoplasmic reticulum and polysomes are usual organelles seen in the perikaryonal cytoplasm of pinealocytes. Many non-granulated vesicles (40 to 80 nm in diameter) and a few granulated vesicles (about 100 nm in diameter) are associated with the Golgi cisternae. Occasionally, the cisternae contain granular materials. The perikaryonal cytoplasm of pinealocytes is characterized by the presence of inclusion bodies. These bodies are usually round in shape, not bounded by a limiting membrane and composed of fine granular or filamentous materials of high electron-opacity, which are similar in appearance to the substance seen in the nucleolonema. Pinealocyte processes, filled with abundant non-granulated vesicles and some granulated vesicles, are mainly found within the parenchyma and occasionally in perivascular spaces.
-
Ultrastructure of rat pituitary LH gonadotrophs in relation to serum and pituitary LH levels following repeated LH-RH stimulation.
The effects of single and repeated LH-RH injections at 120 min intervals on female rat LH gonadotrophs and on pituitary and serum LH levels were investigated using electronmicroscopy and radioimmunoassay. A temporary stimulation of granule release, of protein and new granule synthesis and of the accumulation of lysosomal structures was found in LH cells after the first LH-RH injection. The temporary stimulations were massively enhanced after the second injection. These consecutive yet in their time-sequence overlapping processes account for the initial depletion of secretory granule content (3--15 min after LH-RH injection), for the subsequent regranulation and accumulation of granules above control levels (60--120 min after injection) and also for the reduction in the number of granules to control levels (150 min after LH-RH injection and thereafter). Increased polymorphic lysosomal structures are believed to be responsible for this reduction of excess granules. The amount of assayable pituitary and serum LH generally corresponds with the morphological changes observed in LH-gonadotrophs, thus further substantiating the above observations. A schema which summarizes the observed morphological and hormonal changes in their time-sequence in response to LH-RH stimulation depicts the short-term regulation of secretory processes in female gonadotrophs.
-
Changes in the fine structure of tanycytes during the annual reproductive cycle of the male little brown bat Myotis lucifugus lucifugus.
The hypothalamic arcuate nucleus in the male little brown bat Myotis lucifugus lucifugus was studied with the electron microscope. Animals were killed by intracardial perfusion at each season throughout the year so that the arcuate nucleus could be examined for seasonal variations in morphology. Striking seasonal changes in the fine structure of ependymal tanycytes lining the arcuate nucleus were observed. Tanycytes in animals collected in the fall and early winter exhibited pale processes characterized by a scant internal framework of microtubules and fine filaments. These processes, which were found throughout the arcuate nucleus, exhibited simple irregular shapes. In animals collected between January and June, tanycyte processes contained dense accumulations of fine filaments intermingled with microtubules, and projected long attenuated extensions that often formed multilamellar sheets around axodendritic terminals or other neuronal elements. Tanycyte processes of animals collected in July and August were densely packed with microtubules and fine filaments. The processes radiated elaborate multilamellar extensions that encapsulated axons, dendrites and even entire neuronal perikarya. Multilamellar sheets consisted of as many as 10 or 12 closely spaced gyres. The seasonal variations in tanycyte structure are suggestive of astrocyte-like behaviour. These changes are discussed with respect to seasonal changes in hypothalamic neuroendocrine activity.