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R V Mendoza

Publications and source records attributed to R V Mendoza.

17 recordsLinked to original sources
PubMed1995

Development of the neurogliohemal complex in the mouse neurohypophysis.

The mouse neurohypophysis was studied at different ages of development in order to analyse the ultrastructural changes that lead to the maturation of the neurogliohemal complex and to determine the existence of permeability between the blood capillaries and the neurohypophysial channels. In all the studies ages, two groups of 5 animals each were intravenously injected with different tracer solutions: to one group, 10 microliters of cationized ferritin were used and to the other, 10 microliters of ferrous fumarate were applied. For the ultrastructural studies the tissue samples were processed using the conventional techniques for electron microscopy. At day 17 of prenatal age, some hypothalamic axons (10 axonic profiles/20 microns2) were already seen within the neurohypophysis, increasing threefold (26 to 30 axonic profiles/20 microns2) at prenatal day 19. In these axons terminals, the first neurosecretory vesicles began to appear. At this early age, the glial cells formed few prolongations. Between postnatal days 1 and 9, numerous axon terminals containing dense neurosecretory vesicles composed the neuropile areas. After day 9, there was a broadening of the intercellular space, which we have termed as neurohypophysial channels; these were actually expansions of the existing extracellular space in the neurohypophysis. Between days 9 and 21, the population of axon terminals showing a higher density of neurosecretory vesicles continued to increase in number. Some of these axon terminals were separated by irregular neurohypophysial channels. The glial cells showed scarce cytoplasm and formed numerous lamellar prolongations, which became increasingly finer surrounding bundles of individual axons.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1994

Cerebral implants of histotypic hypothalamic cultures.

In the present report, the implantation of hypothalamic histotypic cultures within the cerebral hemisphere is described. The cultures were prepared from 10-day-old mice and rotary incubated during 6 or 10 days. When the cells reached their phenotypic characteristics at the end of the incubation period, the cultures were implanted in the posterior area of the lateral ventricle. 30 days postoperatively, the whole implanted area was removed and processed for light and electron microscopy observations. The implanted cultures completed maturation in the host tissue and no rejection signs were noticed; on the contrary, we were able to observe a favorable reaction from the host tissue, such as the formation of secondary blood vessels which penetrated the mass of the implanted culture. Well-developed magno- and parvocellular neurons were seen to contain neurosecretory vesicles in their terminals, and the neuroglial relationships established within these implants were homologable to those normally found.

Animals↗
PubMed1992

Release of neurotransmitters and neurosecretory substances during in vitro maturation of mouse hypothalamic cultures.

The maturation of the neurosecretory activity of a hypothalamic nerve cell population grown in vitro, prepared from 10-day-old mice and cultured for 6 days, has been demonstrated in the present report. A low-molecular weight polypeptide of 30-kD was found to be released into the culture media during the 6-day period of incubation, as analyzed by SDS-polyacrylamide gel electrophoresis. Comparative electrophoresis of the in situ hypothalamic, neurohypophysis and cerebral cortex homogenates revealed the presence of a 30-kD protein component in both the hypothalamus and neurohypophysis but not in the cerebral cortex. The release of the 30-kD polypeptide into the incubation media indicates an expression of the neurosecretory activity of the peptidergic neurons of the hypothalamus during in vitro maturation. On the other hand, high pressure liquid chromatography with electrochemical detection showed appreciable quantities of released dopamine (DA), epinephrine and serotonin (5-HT) in the incubation media in which the neurons were allowed to differentiate. There was a steady release of DA during the 6-day incubation period, varying from 0.21 +/- 0.02 to 0.49 +/- 0.05 ng/mg protein. The epinephrine level increased progressively from day 1 to 6 of culture, from 3.73 +/- 0.57 to 12.08 +/- 1.81 ng/mg protein, respectively. The measured 5-HT level was 0.07 +/- 0.001 on day 2 and increased to 0.38 +/- 0.05 ng/mg protein on day 6 of culture. These data demonstrate the functional maturation of catecholaminergic, serotoninergic and peptidergic neurons in these rotary histotypic cultures of the mouse hypothalamus.

Animals↗
PubMed1991

In vitro hypothalamic neurogenesis: morphological maturation of mouse hypothalamic cultures and in vitro versus in situ biochemical analysis.

The morphological and biochemical changes that occur during in vitro neurogenesis of the mouse hypothalamus were studied in rotary cultures prepared from mice between 4 and 16 days of postnatal age. After 6 days of in vitro growth, histotypic cultures with a high degree of morphological differentiation were obtained in cultures prepared from 8- to 10-day-old mice. Before day 8, the cultures showed immature neurons, while after day 12 most of them exhibited an undesired number of degenerated cells. Light-microscopic, Golgi and ultrastructural studies clearly showed the stages of development of the neurosecretory cells in culture. The particular organization of the hypothalamic cells in these cultures can be homologized to its equivalent region in vivo, as demonstrated by their morphological similarities as well as by the fact that the majority of the neurons orient their axons toward the external part of the culture in order to release the neurosecretory material outside the in vitro grown neuronal population, as is the case in situ since hypothalamic neurons release their neurosecretory products at the vascular system. Biochemical parameters such as DNA, RNA and protein contents were determined during the period of in situ development used for the preparation of histotypic cultures and compared to the biochemical changes that occurred during in vitro maturation. The changes in the in vitro DNA and protein contents showed the same variation pattern as in situ. The DNA/protein and RNA/protein ratios also had comparable characteristics, having peak values at days 10 and 16 in situ and in the histotypic cultures prepared from 10-day-old mice. These studies have demonstrated the correlation between the in vitro biochemical and morphological development and the significance of the critical period during hypothalamic neurogenesis for successful organotypic preparations.

Animals↗
PubMed1988

Dendritic RNA and postsynaptic density formation in chick cerebellar synaptogenesis.

In order to investigate the ribosomal origin of the postsynaptic densities during chick cerebellar maturation, a new procedure for synaptosomal preparation was implemented. Samples from embryonic chick cerebellar cortex, from 14 to 20 days of development and young adult chicks, were initially mechanically dissociated after treatment with 1.25% trypsin for 10 min; with this procedure we were able to obtain a dendritic suspension from which an enriched synaptosomal fraction was prepared in a discontinuous Ficoll sucrose gradient. RNA and protein values determined from the synaptosomal fractions showed the following variations: from 46.3 ng RNA/mg of wet weight at day 14 to 616.7 ng RNA/mg of wet weight at day 18; in young adult chicks, the average was 242 ng RNA/mg of wet weight. RNA/protein ratio varied from 78.9 micrograms RNA/mg protein at day 16 to 329.8 micrograms RNA/mg protein at day 18; in the young adult chick, this ratio decreased to 68.4 micrograms RNA/mg protein. The highest value of RNA was obtained at day 18 of chick embryo development coinciding with the maximum period of synaptic formation and consequently of the PSDs. These results seem to reinforce the hypothesis of the ribosomal origin of the PSDs.

Animals↗
PubMed1987

Clinical, histochemical, and ultrastructural correlation in septal endomyocardial biopsies from chronic chagasic patients: detection of early myocardial damage.

In order to recognize early signs of myocardial damage, histologic, histochemical, and ultrastructural studies were performed on septal endomyocardial biopsy tissue obtained from 79 chronic chagasic patients and from 18 patients with atypical chest pain (control group). Abnormal biopsy findings were recognized in 9 of 16 (60%) chagasic patients with no clinical evidence of myocardial damage. In cases of segmental asynergy only, biopsies were abnormal in 18 of 19 patients. When signs of advanced myocardial damage were evidenced by clinical examination or ECGs, all biopsies were abnormal. Mitochondrial, nuclear, and cell membrane irregularities were consistent findings. A peculiar dilatation and filling of the T tubule system with a glycoprotein-like substance and a remarkable increase in monoamine oxidase activity were observed early in the disease and progressed in magnitude and frequency as myocardial damage became more evident by other diagnostic methods. Septal endomyocardial biopsy is a sensitive method for detection of early myocardial damage in chronic chagasic patients. Based on these findings, a modification of the currently used classification is proposed.

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PubMed1983

Morphological changes in neuromuscular junctions during exercise.

Long lasting exercise produces several morphological changes in teleostean neuromuscular junctions (NJs), consisting of progressive synaptic vesicles (SVs) depletion and lamellar branching of the nerve endings. Exercised fishes kept swimming during 1 hr against a 3.5 1/min flow of oxygenated water in spite of the fact that the number of SVs was reduced in about 70% after 10 min of exercise. This observation indicates that the SVs formation fails to restore their original number and consequently, under such circumstances, the transmitter release may occur by a different mechanism.

Animals↗
PubMed1983

In vitro and in situ formation of neuron-glia junctions.

The formation of neuron-glia junctions during neurogenesis has been considered as an error of the neuronal specificity mechanism or as a consequence of the artificial conditions when observed in central nervous system tissue culture. We report the demonstration of the regular existence of synaptic-like junctions in tissue cultures prepared from different regions of chick central nervous system as well as the occurrence of such intercellular contacts in the cerebellum of adult and normal frogs. The formation of neuron-glia junctions in tissue culture during normal neurogenesis and their presence in adult frogs seem to indicate that those types of neuron-glia relationships are not a simple biologic error. Rather, we propose that they may represent a primitive, but normal neuron-glia interaction.

Animals↗
PubMed1982

In vitro development of chick hypothalamic neurosecretory cells.

The in vitro maturation of chick hypothalamic neurosecretory cells has been studied by the Golgi method and electron microscopy. Rotary cultures prepared from chick embryos aged 6, 8 and 10 days of development fail to assemble histotypic cultures; however, cultures prepared from older embryos, i.e. 12, 14 and 16 days of development, progressively exhibited more neurosecretory characteristics. It is interesting to point out that cultures prepared from 12-, 14- and 16-day-old chick embryos form complex surfaces composed of patches of glioepithelial cells alternating with zones containing neurosecretory nerve endings partially surrounded by glial processes. This particular distribution of the nerve endings seems to indicate that cytotypic hypothalamic neurons in rotary cultures deliver their products to the incubation medium; this interpretation is further reinforced by the observed exocytosis of the neurosecretory material within the external neuropile of histotypic cultures. Details of the neurosecretory cell maturation are given in the text.

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PubMed1981

Synaptogenetic mechanisms during chick cerebellar cortex development.

Chick embryo cerebellar cortex development was analyzed in an attempt to visualize the fine ultrastructural changed involved in cortical synaptogenesis. Three major stages of synapses formation were detected during days 13 to 18 of maturation: intermembranous adherence, cytoplasmic recognition, and definitive synaptic formation period. The more primitive morphological event indicative of synaptic onset was the occurrence of external plaques; these plaques must have a negative charge since they accumulated cationized electron-dense tracers. These plaques favor the adhesions between parallel fibers and Purkinje cell dendrites. Once axonal and dendritic membranes adhered to form an adhesion contact, the dendritic half of this contact forms a pinocytic vesicle that incorporates part of the membrane of the axonic half of the contact. This particular pinosome delivers its content to different cytoplasmic organelles including the nucleus. At day 15 Purkinje cells significantly increase the number of dendritic-forming pinocytic vesicles; this phenomenon means that during this day a large amount of parallel fiber membrane is passed into the Purkinje cell cytoplasm. From day 15 to 16 postsynaptic densities begin to appear; ribosomes associated to these structures seem to be the origin of a progressively accumulated amorphous material composing the rare primitive postsynaptic densities. Some other morphological details related to these processes are given in the text.

Animals↗
PubMed1979

In vitro formation of neuroglial synapses.

Neuroglial synapses have been systematically observed in histotypical cerebellar rotary tissue cultures. These axoglial contacts appear as excitatory-like synapses in which the presynaptic element contains rounded synaptic vesicles accumulated at the presynaptic active zone. The post-synaptic structures were always the somata as well as processes of astrocytic glial cells. The axoglial contacts appear in these cultures when they are prepared from 16-day-old chick embryos cerebellum and cultivated during 6 days. To explain these neuroglial interrelationship it has been suggested as a working hypothesis that glial and nerve cells develop plastic capacities in order to establish synaptic contact in the in vitro conditions.

Animals↗
PubMed1976

In vitro vs in situ development of Purkinje cells.

Analysis of in vitro vs in situ development of Purkinje cells was undertaken in order to compare the transitory morphology of Purkinje cells grown in situ with their differentiation in vitro. Purkinje cells in rotary cultures developed their basic morphological pattern only when the cultures were prepared from 16-day chick embryos, indicating the existence of a critical period during their normal differentiation, which lasted approximately 24 hr between days 14 and 15 embryonic development.

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