Biomedical subjects

M Lafarga

Publications and source records attributed to M Lafarga.

At least 55 records · Page 3Linked to original sources

PubMed1992

Osmotic stimulation induces changes in the expression of beta-adrenergic receptors and nuclear volume of astrocytes in supraoptic nucleus of the rat.

The influence of osmotic stimulation on the density of beta-adrenoceptor binding sites in the rat supraoptic nucleus (SON) was studied by quantitative autoradiography using 125I-cyanopindolol (ICYP). Increased density of beta-adrenoceptor binding sites was observed in osmotically stimulated rats and also after the suppression of neuronal activation by rehydration of animals. This was mainly due to a significant increase in the concentration of beta 2 binding sites. The overexpression of beta-adrenoceptors occurred concomitantly with nuclear expansion in SON astrocytes. Moreover, the higher concentration of beta-adrenoceptors observed in the ventral portion of the SON largely coincided with the area that showed intense GFAP-immunostaining. These results provide indirect evidence of an astrocytic location of beta-adrenoceptors and also of beta-adrenergic mediation in the structural and functional changes of SON astrocytes.

Animals↗

PubMed1992

Fos-like expression and nuclear size in osmotically stimulated supraoptic nucleus neurons.

This study has analysed by immunocytochemistry the pattern of expression of Fos-related proteins, as well as variations in nuclear size, after the osmotically induced activation of supraoptic nucleus neurons of the rat. In control rats most supraoptic nucleus neurons were Fos-like negative. After acute and chronic dehydration by salt-loading, the number of Fos-like positive neurons increased dramatically. The level of Fos-like immunoreactivity was higher in chronically stimulated rats, and also the neurons of the ventral region of the supraoptic nucleus were more intensely stained than those of the dorsal region. The karyometric analysis was made on electron micrographs. The mean nuclear profile area showed a significant increase in dehydrated rats with respect to the controls (73 +/- 16 microns 2 in those dehydrated for six days vs 54 +/- 13 in controls, mean +/- S.D.). However, no significant differences in this parameter were found when one-day and six-day dehydrated groups were compared. The invagination factor of the nuclear membrane, a nuclear shape indicator, decreased significantly in dehydrated rats, indicating a tendency towards spherical nuclei. It is noteworthy that the nuclear profile perimeter was constant, about 32 microns, in control and osmotically simulated rats. The higher nuclear accumulation of Fos-related antigens after six days of dehydration suggests that in chronically stimulated supraoptic nucleus neurons there is a sustained induction of cell-specific genes. Moreover, the transcription rate of the target genes containing the consensus DNA sequence TGAC/GTCA or c-AMP responsive elements recognition sites may depend upon the nuclear concentration of Fos-related antigens in supraoptic nucleus neurons. Our results also suggest that the initial Fos-related antigen expression and nuclear size increase are triggered concomitantly in supraoptic nucleus neurons after a short period of osmotic stimulation. On the other hand, we propose that nuclear envelope invaginations represent a reservoir of nuclear membrane which allows dynamic changes in nuclear size and shape depending on the metabolic status of the supraoptic nucleus neurons.

Animals↗

PubMed1991

Organization of nucleoli and nuclear bodies in osmotically stimulated supraoptic neurons of the rat.

This study has analyzed variations in the number of nucleoli and nuclear bodies, as well as in their ultrastructural and cytochemical organization, after the osmotically induced activation of supraoptic nucleus (SON) neurons of the rat. The number of nucleoli and nuclear bodies and also the nucleolar size were determined on smear preparations of previously block-impregnated SON. The mean number of nucleoli per cell was 1.35 +/- 0.6 (mean +/- SDM) in control rats. No significant variations in this value were registered either in dehydrated or rehydrated rats. The mean nucleolar volume and the total nucleolar volume per cell showed a significant increase in dehydrated rats with respect to the controls, whereas these two parameters tended to return to control values in rats rehydrated after dehydration. The mean number of nuclear bodies per cell increased significantly from 0.56 +/- 0.50 (mean +/- SDM) in control rats to 1.54 +/- 1.1 after 6 days of dehydration. By electron microscopy, SON neurons displayed a reticulated nucleolar configuration. After the osmotically induced neuronal activation, there was an increase in the proportion of the total nucleolar area occupied by the granular component, and also a reduction in the mean fibrillar-center area. The most characteristic nucleolar features in rehydrated rats were the tendency for the granular component to be segregated and the occurrence of intranucleolar vacuoles. Ultrastructural cytochemistry with a specific silver method revealed a selective silver reaction on the coiled threads of the nuclear bodies--identified as "coiled bodies"--and on the nucleolar fibrillar components in all animal groups studied. Since nucleoli play a major role in ribosome biogenesis, a relationship between these nucleolar changes and the level of cellular activity of SON neurons is proposed. Furthermore, the response of nuclear "coiled bodies" to neuronal activation suggests their participation in the processing and transport of rRNA precursors.

Animals↗

PubMed1991

Influence of age on nuclear bodies and nuclear volume in pituicytes of the rat neurohypophysis.

This study has analyzed age-related changes in the nuclear organization of pituicytes of the rat. The cytological study of the cell nucleus and the quantitative analysis of nuclear bodies (NBs) were performed on ultrathin sections. Nuclear diameter, perimeter, and area were measured on semithin sections, and nuclear volume was estimated from these data. The nucleolus was mainly composed of a few large fibrillar centers with their associated dense fibrillar component, whereas the granular component tended to form large masses at the nucleolar periphery. The most frequent configuration of NBs was a globular inclusion composed of a fibrillar capsule with a core that contained a few electron-dense granules. Intranuclear glycogen was detected on rare occasions and only in old rats. The proportion of nuclear sections containing NBs increased significantly from 1.5% in 3-month-old rats to 8.6% in 18-month-old rats. A significant increase in the nuclear volume was detected in older rats with respect to the younger ones (157 +/- 69 vs. 98 +/- 43 microns 3, mean +/- S.D.). Our results suggest an age-related activation of nuclear metabolism in pituicytes resulting in a nuclear expansion and an increase in the frequency of appearance of NBs. This activation might be a reactive cellular event induced by the degenerative changes in neurosecretory nerve endings naturally occurring in older animals.

Aging↗

PubMed1991

Freeze-fracture organization of chromatin and cytoplasm in neurons and astroglia of rat cerebellar cortex.

The cytology of the cell nucleus and cytoplasm of neurons and astroglia of the rat cerebellar cortex has been investigated by freeze-fracture electron microscopy. The main differential characteristics in the cytoplasm of the several cell types of the cerebellar cortex were: (1) the organization of endoplasmic reticulum elements, including special configurations of lamellar bodies and hypolemmal complexes, (2) the polarity, extension and arrangement of Golgi cisterns and associated tubulovesicular elements; (3) the connection pattern among different membrane-bounded cellular compartments; and (4) the architecture of endomembranes (i.e. presence of pits and fenestrations). In the nucleus, the main differential features were the the three-dimensional view of the nuclear envelope, the distribution of nuclear pores and the aggregation pattern of chromatin, visualized as clusters of nuclear particles in cross-fractures. The quantitative analysis of chromatin revealed four peaks of nuclear particle sizes (8, 12, 17 and 21 nm) that may correspond to variable degrees of coiling of the polynucleosomal chain in the chromatin fibre. Significant differences were observed in the proportion, numerical density and size distribution of aggregated nuclear particles in heterochromatin domains among the different cell types of the cerebellar cortex. The percentage of nuclear particles in aggregates varied from 10% in Purkinje cells to 64% in granule cells. Astrocytes and Bergmann glia showed intermediate values (about 40%). The percentage of nuclear particles in aggregates showed a significant (P less than 0.05) negative linear correlation with the nuclear volume, the number of pores per unit nuclear volume and the total number of pores per nucleus. In granule cells and astroglia, heterochromatin domains had a greater percentage of large nuclear particles (greater than 10 nm) than did euchromatin domains, whereas in interneurons, Purkinje and Golgi cells heterochromatin and euchromatin showed a similar proportion of large particles. Nuclear particles in euchromatin exhibited a similar pattern of distribution in all cerebellar cells.

Animals↗

PubMed1991

Cytology and organization of reactive astroglia in human cerebellar cortex with severe loss of granule cells: a study on the ataxic form of Creutzfeldt-Jakob disease.

In order to investigate the cellular basis of human astrogliosis, we have selected the cerebellar cortex because it provides a relatively simple and geometrical organization of both neuronal and glial populations. A pathological system with severe and progressive loss of granule cells was studied: the ataxic form of Creutzfeldt-Jakob disease, where the tissue geometry is minimally disturbed. The quantitative study revealed a drastic reduction in the numerical density of granule cells in the Creutzfeldt-Jakob disease cerebellum, and a significant increase in the numerical density of astrocytes. Karyometric analysis showed that the nuclear area was significantly greater in reactive astroglial cells than in normal astroglia. Glial fibrillary acidic protein immunocytochemistry revealed astroglial hypertrophy, but the geometry and spatial domains of astroglial subtypes were strictly preserved. Vimentin expression was detected in Bergmann glia and in certain astrocytes of the granular layer. Ultrastructural analysis showed that reactive astroglia had large nuclei, with expanded interchromatinic regions which contained clusters of interchromatin granules and nuclear bodies, and prominent reticulate nucleoli. In the cytoplasm, hypertrophied bundles of intermediate filaments were observed, some of them associated with the nuclear envelope. Numerous adhering and gap junctions were also found among reactive astroglial cells. Perivascular glial processes showed a terminal web of intermediate filaments and a conspicuous plasmalemmal undercoat. Interendothelial tight junctions were preserved. Our results suggest that the severe loss of granule cells induces a highly ordered astroglial response which tends to preserve the geometry of the astroglial scaffold, the domains of each astroglial subtype, the neuronal microenvironmental conditions and the efficiency of the blood brain barrier, in order to promote neuron survival.

Astrocytes↗

PubMed1990

Interactions between astroglia and ectopic granule cells in the cerebellar cortex of normal adult rats: a morphological and cytochemical study.

The cytology and organization of astroglial cells associated with ectopic granule cells (EGCs) have been studied in the cerebellar cortex of normal adult rats, using Golgi preparations, immunohistochemistry against the glial fibrillary acidic protein (GFAP) and ultrastructural analysis. Elongated perikarya of EGCs scattered in the molecular layer were usually attached to radial Bergmann fibers, which exhibited a normal morphology. A second configuration of EGCs consisted of intrafissural colonies of ectopic neurons. The molecular layer that surrounded these ectopic colonies showed disorientation of both Bergmann fibers and parallel fibers. Within the ectopic tissue, typical velate astrocytes were commonly observed. They formed homologous associations with EGC perikarya and cerebellar glomeruli. However, a restricted astroglial plasticity was detected in the form of heterologous interactions between astrocytes and Purkinje cell dendrites, including their associated synapses with parallel fibers. In spite of this astroglial plasticity, our results suggest that in the physiological systems of granule cell ectopia studied here, the different specific interactions of Bergmann glia and astrocytes with neurons tend to be conserved.

Animals↗

PubMed1990

Creutzfeldt-Jakob disease with severe involvement of cerebral white matter and cerebellum.

We describe a patient with Creutzfeldt-Jakob disease (CJD) of the ataxic and panencephalopathic type. Postmortem examination revealed the characteristic lesions of CJD in the grey matter and profound white matter involvement was seen with immunocytochemical techniques. Ultrastructural white matter lesions were identical to those described in experimentally transmitted CJD. There was marked loss of cerebellar granule cells with virtual disappearance of parallel fibres, but Purkinje cells were only slightly reduced. Electron microscopic studies revealed extensive degenerative changes including cytoplasmic vacuoles in both cell types. Silver methods disclosed massive impregnation of white matter and striking abnormalities of Purkinje cells consisting of hypertrophy and flattening of thick dendritic branches, reduction in the number of terminal branchlets, segmentary loss of spines and polymorphic spines. These findings show the extensive involvement of all three cerebellar cortical layers and the reactive plasticity of Purkinje cells to deafferentiation. They favour the hypothesis that demyelination represents a primary lesion of the white matter.

Brain↗

PubMed1990

A morphometric ultrastructural study of the nucleus of cerebellar granule cells.

A quantitative approach to the nuclear ultrastructure of cerebellar granule cells is described here. The study was made using conventional electron microscopy from cerebellar cortices of adult rats by means of a semiautomatic image analyzer. The basic observation is that the nuclei of mature granule cells constitute a homogeneous population in terms of morphometric and stereologic data; in fact, the volume density of condensed chromatin within the nuclei remains practically constant in all nuclear sections. These results seem to indicate the existence of a cell-specific nuclear morphometric phenotype which might be considered as an effective criterion for the typification of this cellular lineage.

Animals↗

PubMed1989

Distribution of nuclear pores and chromatin organization in neurons and glial cells of the rat cerebellar cortex.

Nuclear pores were assessed on freeze-fracture replicas from different neuronal and glial cell types of the rat cerebellar cortex. Nuclear diameter and perimeter were measured on semithin sections, and nuclear surface area and volume were calculated from these data. The proportion of inner nuclear membrane in apposition to condensed chromatin was measured on thin sections. The values of nuclear pore numerical density (number/micron2) were as follows (mean +/- S.D.): Purkinje cells, 22 +/- 3; Golgi cells 17 +/- 3; granule cells, 6 +/- 4; stellate and basket cells, 6 +/- 1; protoplasmic astrocytes, 11 +/- 1; Bergmann glia, 10 +/- 1; oligodendrocytes, 6 +/- 1. The total number of nuclear pores per nucleus varied from 18,451 +/- 2,336 (Purkinje cells) to 621 +/- 394 (granule cells) among neurons, and from 1,782 +/- 162 (protoplasmic astrocytes) to 402 +/- 67 (oligodendrocytes) among glial cells. The number of nuclear pores per unit nuclear volume (number/micron3), a parameter related to nucleocytoplasmic transport capacity, varied from 15 +/- 2 in Purkinje cells to 6 +/- 4 in granule cells. The proportion of nuclear membrane free of condensed chromatin was significantly (P less than 0.01) correlated to pore numerical density and total number of pores per nucleus. Some nuclear pores were associated in clusters of two or more pores. The amount of pore clustering was measured by counting the proportion of pores associated in clusters. This proportion varied among the different cell types from 82% in Purkinje cells to 44% in stellate and basket cells. The amount of pore clustering showed a positive linear correlation to pore numerical density and pore number per nucleus. However, the proportion of pores in clusters was not significantly correlated with the amount of condensed chromatin applied against the inner nuclear membrane.

Animals↗

PubMed1989

Nucleolar organization in granule cell neurons of the rat cerebellum.

The present light and electron microscopic study deals with the morphology and cytochemical properties of the nucleolus in mature granule cells of the rat cerebellum. Nucleolar organization has been examined by several different methodological approaches: (a) determination of the number of nucleoli per cell from smear preparations, (b) morphometric estimation of nucleolar size, and (c) ultrastructural and cytochemical characterization of nucleolar components. The mean number of nucleoli per cell was found to be 1.46 +/- 0.02 (mean +/- SEM). The morphometric measurement of the nucleolar area showed an average value of 0.359 +/- 0.07 microns 2 (mean +/- SDM). At the electron microscope level, most granule cell nucleoli displayed a fine texture which does not differ substantially from the 'ring-shaped' configuration usually found in cells with low levels of protein synthesis activity; i.e., a large round fibrillar centre surrounded by the dense fibrillar component, and small masses of granular component segregated from the preceding constituents. The meaning of this nucleolar configuration is discussed in the light of recent ultrastructural and biochemical data on nucleolar function. A relationship between this pattern of nucleolar organization and metabolic characteristics of the granule cells is suggested.

Animals↗

PubMed1988

Nucleoli numbers and neuronal growth in supraoptic nucleus neurons during postnatal development in the rat.

We present a quantitative study of the variations in the number of nucleoli in supraoptic nucleus neurons during the postnatal period, as well as a morphometric and stereological analysis of the nuclear and cytoplasmic volume changes of these maturing neurons. The mean number of nucleoli per cell was 1.59 +/- 0.28 (mean +/- S.D.) at P1; it then began to decrease until P14 (1.32 +/- 0.67) at which age the adult pattern in the number of nucleoli was attained. The mean nuclear volume increased steadily from 214.56 +/- 6.48 microns 3 (mean +/- S.E.) at P1 to 326.1 +/- 10.93 microns 3 at P14 where it remained constant. The average cytoplasmic volume underwent a remarkable increase during postnatal period from 256.38 +/- 12.66 microns 3 at P1 to 3791.18 +/- 204.88 microns 3 at P90. It is noteworthy that the stabilization of the number of nucleoli coincides with the termination of the nuclear growth phase of supraoptic neurons. We suggest that these nuclear and nucleolar changes reflect the attainment of the fully-differentiated state of the protein synthesis machinery in these neurosecretory neurons.

Aging↗

PubMed1988

Colony-forming ectopic granule cells in the cerebellar primary fissure of normal adult rats: a morphologic and morphometric study.

The morphology and degree of maturation of intrafissural colony-forming ectopic granule cells (EGCs) were investigated in the cerebella of normal adult rats. These EGCs exhibit a notable degree of morphological maturity, with 2-5 short dendrites radiating from a globular soma, typical dendritic claw-like terminals and descending axons. The EGCs receive the afferent input of mossy fiber terminals and their axons also establish homologous synapses with the postsynaptic dendritic spines of the Purkinje cells. Although these EGCs exhibit the typical morphology of mature granule cells, the morphometric analysis shows, however, a significant reduction in the number of dendrites (mean 3.30 +/- 0.60) and 'claws' (mean 3.66 +/- 0.12) in the EGCs with respect to the controls (mean 3.85 +/- 0.73 and 4.53 +/- 0.13, respectively). These differences may be indicative of a slight numerical mismatching between EGCs and afferent mossy fibers, which limit the input that the ectopic neurons receive. The karyometric study also showed that the average nuclear area in EGCs was significantly smaller (mean 19.38 +/- 0.24 micron2) than in controls (mean 21.88 +/- 0.24 micron2), suggesting a positive correlation between nuclear size and the number of postsynaptic dendritic terminals available in the granule cells. The influence of some morphogenetic factors on the degree of maturity attained by these ectopic neurons is discussed, particularly the interactions of mossy fibers and astrocytes with maturing EGCs.

Animals↗

PubMed1987

Cajal-Smirnow ansiform fibers in the molecular layer of the rat cerebellar cortex.

The present light and electron microscopic study deals with the morphology and organization of Cajal-Smirnow ansiform fibers (AFs) in the molecular layer of the cerebellar cortex. The cerebella of normal adult rats were processed with Cajal's reduced silver method and conventional electron microscopy. With the silver method AFs appear as isolated elements or, more frequently, as small bundles of myelinated fibers, which emerge from the medullary rays, ascend through the granular, Purkinje cell and molecular layers and curve back to reenter the granular layer or cerebellar white matter. They traced an arciform trajectory of variable width and height in the molecular layer. Relatively large bundles of AFs were rarely found. The occurrence of AFs was confirmed in semithin sections as myelinated fibers of variable diameter ranging from 1 to 6 micron. Oligodendrocytes were often observed near AFs. At the ultrastructural level, the most common type of AF is large, with a relatively thin myelin sheath and a moderately dense axoplasm. Nodal or terminal synaptic differentiations were not observed. We suggest that AFs are misoriented cerebellar mossy fibers and their occurrence may be the consequence of a small-scale error in the axonal guidance of growing mossy fibers.

Animals↗

PubMed1986

An improved cytological silver staining method for the demonstration of neuronal nuclear bodies.

A simple cytological method for the selective impregnation of neuronal "nuclear bodies" is described. This procedure involves glutaraldehyde fixation, pretreatment with methanol-acetic acid, impregnation in a 1.5% colloidal solution of silver nitrate containing gelatin, and pyrogallic reduction of whole tissue blocks. After block staining the material was either dehydrated and embedded in araldite for light and electron microscopy studies, or processed for the elaboration of neuronal smear preparations, which were used for the quantitative analysis of nuclear bodies. By light microscopy, nuclear bodies appear as conspicuous, intensely impregnated inclusions, 0.3-0.9 micron in diameter. Both the nucleoli and cytoplasmic Nissl bodies can be counterstained with Toluidine blue. Overimpregnation produces an additional staining of the nucleolar fibrillar component.

Animals↗

PubMed1986

Ectopic Purkinje cells in the cerebellar white matter of normal adult rodents: a Golgi study.

In Golgi/Río-Hortega preparations of rat and rabbit cerebellar vermis we have occasionally found isolated ectopic Purkinje cells in the white matter. They were located beneath the bases of the folia and their dendritic branches extended within the confines of the white matter without penetrating into the overlying cortical layers. The general morphology of these ectopic cells was variable, particularly in the extension and shape of the dendritic trees, but all of them exhibited a lower density of dendritic branches than normal Purkinje cells. The less-developed ectopic neurons had multipolar dendritic trees with nonplanar branches irregularly studded with spines. The well-developed ones displayed a more extensive arborization of their processes and they usually preserved some morphological features of normal cortical Purkinje cells: distal dendritic branches studded with numerous spines, a pear-shaped soma, clearly defined morphological polarity and a tendency to display planar arrangement of the dendritic arbors. In semithin sections these neurons also showed cytological features of normal Purkinje cells, such as the Nissl substance forming a nuclear cap oriented toward the dendritic pole. We suggest that the abnormal location of the neurons results from a disorder of Purkinje cell migration which occurs naturally during the prenatal development of the cerebellum. The possible morphogenetic mechanisms involved in the migration and differentiation of these ectopic neurons are also discussed.

Animals↗

PubMed1986

Microcolonies of hemopoietic cells in the rat choroid plexus during the neonatal period.

Microcolonies of hemopoietic cells have occasionally been found in the choroidal stroma of the rat myelencephalic choroid plexus during neonatal life. These hemopoietic foci are mixed colonies mainly composed of erythroblasts and maturing megakaryocytes; granulocyte precursors were not identified. The morphological data indicate that both erythro- and magakaryopoiesis occur in these microcolonies. With respect to their origin, we suggest that circulating pluripotential stem cells may colonize the choroidal stroma and produce erythro- and megakaryocyte cell lines.

Animals↗

PubMed1986

Laminated cytoplasmic bodies in Schwann cells and phagocytes: an ultrastructural and cytochemical study in the normal and lead-damaged peripheral nervous system of the rat.

We studied the distribution and cytochemical characteristics of laminated bodies (LBs) in the peripheral nervous system of normal and lead-intoxicated rats. In normal rats, LBs were exclusively present in myelin-forming Schwann cells (SCs). Nerves from lead-intoxicated animals showed extensive demyelination and remyelination. In these nerves we found an increase of LBs in the SC cytoplasm, and also within phagocytes involved in myelin removal, but not in remyelinating SCs. Cytochemical studies revealed that LBs were positive for acid phosphatase, thus demonstrating the lysosomal nature of such inclusions. Taken together, these data suggest that LBs are autophagolysosomes derived from myelin catabolism, which may be enhanced in the lead-induced demyelinating neuropathy of the rat. The possible mechanisms underlying this phenomenon and their pathological relevance are discussed.

Acid Phosphatase↗