Papers by Vladimir Flores
Fertility and Sterility, 2018
Most clinics (79.7%) have a sperm quarantine policy, which range from 7 days to 12 months, though... more Most clinics (79.7%) have a sperm quarantine policy, which range from 7 days to 12 months, though most (85.1%) are 6 months. While 60 (42.0%) respondents permit no quarantine protocol deviation, 41 (28.7%) allow a complete waiver, and 16 (11.2%) allow shortening the duration. REI's views of quarantine varied widely: 47 (34.8%) see it as ''an absolutely necessary protection'', while 41 (30.4%) view it as a ''risk reduction option patients should be able to waive.'' Nearly half (47.4%) considered mandatory quarantine an undue burden, with doctors younger than 60yo (p¼0.02) and LGBT physicians (p¼ .04) more likely to think so. LGBT physicians were also more likely (p¼0.03) to treat donors participating in home inseminations as a SIP of the biological mother, though this was overall an uncommon (30.4%) view. CONCLUSIONS: The management of directed sperm donors varies greatly, as do physician views regarding length, flexibility and duration of quarantine. In particular, younger and self-identified LGBT physicians expressed concern that mandated quarantine would restrict patient autonomy, while older REIs focused on the benefits of risk reduction. Given these findings, further detailed study may allow for an updated consensus that balances patient safety with expansion of treatment options for patients using directed sperm donors.
Embriología humana. Bases moleculares y celulares de la histogénesis, la morfogénesis y las alteraciones del desarrollo, 2015, ISBN 978-950-06-0092-7, págs. 173-211, 2015
Embriología humana. Bases moleculares y celulares de la histogénesis, la morfogénesis y las alteraciones del desarrollo, 2015, ISBN 978-950-06-0092-7, págs. 53-91, 2015
Embriología humana. Bases moleculares y celulares de la histogénesis, la morfogénesis y las alteraciones del desarrollo, 2015, ISBN 978-950-06-0092-7, págs. 31-52, 2015
The 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society
This paper analyzes the dynamics of cell proliferation in the developing central nervous system. ... more This paper analyzes the dynamics of cell proliferation in the developing central nervous system. Three different algorithms, Fano factor, Allan factor and detrended fluctuations analysis, are used to estimate de scaling exponent of space numerical series obtained by recording the number and position of proliferating cells along the cephalic-caudal axis of the system. It can be concluded that the dynamics of proliferation involves two component: (a) a random noncorrelated stochastic component representing a basal proliferating activity uniformly distributed along the cephalic-caudal axis and (b) a deterministic nonstationary component that imposes a defined global trend to the process. The deterministic nonstationary trend can be interpreted as the effect of a controlling influence operating along the cephalic-caudal axis. This result indicates that the proliferative activity is spatially organized along the cephalic-caudal axis of the system.
Prensa médica argentina, 2003
A prospective study is undertaken applying a stochastic model based on long-term dependencies wit... more A prospective study is undertaken applying a stochastic model based on long-term dependencies with the ability to predict the temporal evolution of series of the hemogram. Temporal sequences referred to hematocrit values registered daily during 1,024 consecutive days, from sheeps maintained in biotherion, were analyzed as samples of a stochastic model. The methods that estimate the parameters characterizing the stochastic model are compared. The comparison between the empirical sequences of the hematocrit and their related predictions, using selected values of the model of the stochastic process, indicate a close correlation between themselves. The future characterization of other blood components could support significatively to the design of a theoretical model to predict if series of the hemogram evolve towards the normality or otherwise run in opposite appointment.
Embriología humana. Bases moleculares y celulares de la histogénesis, la morfogénesis y las alteraciones del desarrollo, 2015, ISBN 978-950-06-0092-7, págs. 371-401, 2015
International Journal of Developmental Neuroscience, 2018
The present article summarizes the main events involved in the isthmic organizer and optic tectum... more The present article summarizes the main events involved in the isthmic organizer and optic tectum determination and analyses how optic tectum patterning is translated, by the organized operation of several specific cell behaviors, into the terminally differentiated optic tectum. The paper proposes that this assembling of temporally/spatially organized cell behaviors could be incorporated into a wider notion of patterning and that, given the asymmetric organization of the developing optic tectum, the notion of "sensitive period" does not capture the whole complexity of midbrain development and the pathogenesis of congenital disorders. The cell behaviors involved in the optic tectum development are organized in time and space by the isthmic organizer. A comprehensive description of the normal optic tectum development, and also its alterations, should consider both domains. Significantly, the identity of each neuronal cohort depends critically on its "time and place of birth". Both parameters must be considered at once to explain how the structural and functional organization of the optic tectum is elaborated. The notion of "patterning" applies only to the early events of the optic tectum development. Besides, the notion of "sensitive period" considers only a temporal domain and disregards the asymmetric organization of the developing optic tectum. The present paper proposes that these notions might be redefined: (a) a wider meaning of the term patterning and (b) a replacement of the term "sensitive period" by a more precise concept of "sensitive temporal/spatial window". of the time. Organizers function as "spatial reference systems" on the basis of which body regions, systems, apparatus, organs, tissues and cells acquire defined identities and occupy defined positions within the organism. These processes of spatially organized commitments or determinations are designated as "patterning". Organizers secrete diffusible morphogens whose concentrations decrease gradually, as a function of the distance, generating morphogenetic fields of defined extension within their adjacent competent tissues (Wolpert, 1998; Freeman and Gurdon, 2002; Green, 2002). Competent cell populations submitted to different concentrations of the morphogen, receive different positional information, undergo different irreversible epigenetic reprogramming of their genome-determination or commitment-, express different combinations of cell-type specific transcription factors and acquire different identities. This spatially organized process of cell determination constitutes the specific-"sensu stricto"-notion of patterning and corresponds to the earlier
Estimates of scaling indexes are being increasingly used since the last ten years for revealing o... more Estimates of scaling indexes are being increasingly used since the last ten years for revealing organization in processes seemingly at random. The range of application fields is extensive: seismology, economy, biology, internet connections; just to name a few. Radical differences among the analyzed phenomena impel interpreting mathematical results in the specific context; however, wide common ground is found on the
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Advances in biochemical psychopharmacology, 1986
1. Adv Biochem Psychopharmacol. 1986;42:25-38. GABA receptors in the developingchick visual syste... more 1. Adv Biochem Psychopharmacol. 1986;42:25-38. GABA receptors in the developingchick visual system: influence of light and darkness. Fiszer de Plazas S, Flores V, Ríos H. PMID: 3020898 [PubMed - indexed for MEDLINE]. MeSH Terms. ...
Tissue and Cell, 1988
Septate junctions are almost ubiquitous in the tissues of invertebrates hut arc never found in th... more Septate junctions are almost ubiquitous in the tissues of invertebrates hut arc never found in those of vertebrates. In spite of their widespread occurrence and hence ohwoua importance to the invertebrates, their prewe function has remained elusive although they have been variously considered to be regions of cell-cell coupling, permeability barriers or adhesion sites. This report demonstrates that elements of the cytoskeletal system insert into the cvtoplasmic face of septate junctions. Actin filaments. identified by virtue of their capacity to bmd the S, subfragment of rabbit myosin, are associated with the membranes of septate junctions. Cytochalasin D, an actin depolymerizer, leads to disorganization of the intramrmhrane components of these junctions. These data suggest that a primary role of septate junctions could he to maintain intercellular cohesion and hence tissue integrity. The assembly and localization of these junctions may be mediated. directly or indirectly, by the cytoplasmic actin filaments aswciatcd with their lateral membranes
Neurochemical Research, 1995
Determinations of plaminogen activator (PA) activity are usually performed in Triton X-100-treate... more Determinations of plaminogen activator (PA) activity are usually performed in Triton X-100-treated tissue homogenates or crude membrane fractions. Such preparations usually involve a single Triton X-100 treatment. In the present paper we describe the pattern of variability of PA activity measured in different fractions obtained from the developing chick CNS by a repetitive procedure of Triton X-100 treatment and ultracentrifugation. To further characterize this PA activity we have also performed zymographic analyses during the embryonic development and the early postnatal life. Our results show that: a) a single Triton X-100 treatment does not completely extract the enzyme and this lead to an underestimation of the total PA activity; b) the PA activity is associated with the particulate component of the total tissue homogenate requiring its complete solubilization more drastic Triton X-100 treatments; c) better estimations of total and specific activities are obtained by using soluble fractions derived by ultracentrifugation from Triton X-100-treated membrane fractions; d) the developing chick optic lobe expresses only one kind of PA molecule along the entire development; e) the level of PA activity vary characteristically during the ontogeny and the early postnatal life indicating the existence of a developmentally regulated mechanism of PA expression.
Journal of Neurochemistry, 2008
Glutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number... more Glutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number of tissues such as kidney, prostate and brain. The brain form of GCPII (also known as N-acetylated-a-linked-acidic dipeptidase, NAALADase) cleaves N-acetyl-aspartyl glutamate to yield free glutamate. Animal model experiments show that inhibition of GCPII prevents neuronal cell death during experimental ischaemia. GCPII thus represents an important target for the treatment of neuronal damage caused by excess glutamate. We report the mapping of the entire coding region of GCPII and identification of the region sufficient and necessary for the production of active recombinant protein. Extracellular portion of human glutamate carboxypeptidase II (amino acids 44-750) was expressed in Drosophila Schneider's cells and purified to homogeneity. A novel assay for hydrolytic activity of GCPII, based on fluorimetric detection of released alpha-amino groups was established, and used for enzymological characterization of GCPII. The potential of this assay for high-throughput inhibitor testing was evaluated and pH dependence for the enzymatic activity have been analysed. Using a complete set of protected dipeptides, substrate specificity of recombinant GCPII was elucidated. Ac-Glu-Met, Ac-Asp-Met and surprisingly Ac-Ala-Met were identified as novel substrates for GCPII. The glycosylation has been found indispensable for the activity of the enzyme. A series of point mutants of the enzyme has been expressed and purified and the glycosylation sites critical for the proteolytic activity have been identified.
Journal of Neurobiology, 1983
The electroretinographic responses of regenerated eyes of snails (C. aspersa) were studied by mea... more The electroretinographic responses of regenerated eyes of snails (C. aspersa) were studied by means of suction electrodes and single or repetitive flash stimulation. The eyes were fixed and observed under light and electron microscopy. The results indicate that the electroretinographic response of regenerated eyes does not differ from control eyes after dark adaptation. However, the repetitive stimulation of the regenerated eyes induced an earlier fatigue of the response, evident after the fifth stimulus. This fatigue is a function of light intensity. Ultrastructural features of the regenerated eyes are similar to those of the control eyes but regenerated eyes show smaller rhabdomeres, fewer photic vesicles, and fewer paracrystalline bodies. It is suggested that the regenerated eye lability to the repetitive stimulation might be due to the decrease in the amount of photic vesicles and paracrystalline bodies, to the decrease in membrane surface of the rhabdomeres, or to some other metabolic failure not distinguished at electron microscopic level, like the membrane ionic regulation. The appearance of photic vesicles in the axon cones of regenerated and stimulated cells also suggests a possible failure in the mechanism of transport of vesicles.
Cell proliferation (CP) is a specific developmental cell behavior. The simplest result of cell pr... more Cell proliferation (CP) is a specific developmental cell behavior. The simplest result of cell proliferation is the increase in the number of cells of a giving system. It also plays primary roles in morphogenesis and generation of complexity. Current methods to estimate and analyse cell proliferation do not take into account the spatial relationships between proliferating cells. The present paper postulates that quantification of the proliferative activity as a spatial series recorded along a defined intrinsic spatial references axis can be mathematically treated a signal representing a stochastic point process.
Prensa Med Argent, Sep 1, 2006
The present work is devoted to describe a set of rules explaining the discriminating versus non-d... more The present work is devoted to describe a set of rules explaining the discriminating versus non-discriminating behavior of the di-basic stages and to characterize the role of each base in determining such a behavior. Bases are analyze as dual entities characterized by its chemical type and the number of H bonds involved in the codon-anticodon interaction. A codon is characterized
International Journal of Developmental Neuroscience, 1995
Several ontogenetic studies have been devoted to the structural organization of the developing te... more Several ontogenetic studies have been devoted to the structural organization of the developing tectum opticum. They disagree in many respects because they are based on histological preparations performed with differently oriented planes of section. According to our results the differences found in the literature mainly result from the fact that the developmental gradient axis undergoes remarkable positional changes with respect to both optic lobe and neural tube longitudinal anatomical axes during the early stages of development. The present work is a dynamic description of the tectum opticum lamination based on sections coinciding with the developmental gradient. Since this latter displays a curved disposition, several slightly modified planes of section had to be used to obtain a complete picture along the developmental gradient. The development of the tectal architecture proceeds from a relatively simple organization through increasingly complex multilaminated patterns. A dynamic interpretation of successive images of a particular region observed at increasing developmental stages or of images observed at a particular stage along the entire length of the developmental gradient axis, allows us to propose that embryonic laminae are only transient spatial arrangements of cells actively migrating from the sites where they were generated to those where they will definitively reside. These considerations led us to define a nomenclature that establishes clear correlations between the early transient organizations and the definitive one of the fully developed optic tectum. This type of nomenclature could be usefully applied to describe dynamically the development of structures displaying multilaminated patterns such as other cortical zones of the central nervous system.
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Papers by Vladimir Flores