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B Valenzuela

Publications and source records attributed to B Valenzuela.

12 recordsLinked to original sources
PubMed1992

Structural organization of chromatin during the cell cycle of Entamoeba histolytica trophozoites.

The nuclear division of E. histolytica trophozoites was analyzed by using specific stains for DNA, with the aim to define the sequential changes of chromatin during its life cycle. Furthermore, we characterized the internal structural arrangements of microtubules in the microtubular organizing center (MTOC) and determined the number of chromosomes and its association with the spindle. The MTOC is formed by multiple microtubule-nucleating centers, that are involved in the displacement of DNA during nuclear division. We found the existence of a single MTOC in one pole of the nucleus at early anaphase. Our results lead us to propose a new hypothesis in which it is suggested that metaphase corresponds to the arrangement of condensed DNA bodies, or "chromosomes" around the MTOC and, through the assembly of microtubules, one set of uncondensed chromatin is displaced to the opposite pole of the nucleus, while the other remains condensed and associated to the original MTOC. We observed six chromosomes in our preparations, corroborating previous observations (2,3). Whether or not a new MTOC is formed during nuclear division remains to be clarified.

Animals↗
PubMed1988

The early development of the atrioventricular node and bundle of His in the embryonic chick heart. An electrophysiological and morphological study.

The development of the atrioventricular node and bundle of His of embryonic chick hearts was studied by electrophysiological and morphological techniques. The dorsal wall of the AV canal and the interatrial septum were explored to determine if they contribute to the formation of the AV node and bundle of His. The resting membrane and action potentials of the interatrial septum cells were systematically analyzed and found to undergo progressive differentiation with development. The earliest identification of the AV node and upper bundle of His group of cells was achieved at 5 1/2-6 days of development by the electrical recording of their corresponding characteristic action potentials, from a circumscribed area located in the lowest and dorsal segment of the interatrial septum. The morphological and anatomical characterization of the cells was made following electrical recording and labelling with charcoal particles. The earlier AV node and bundle of His responses had similar characteristics to those of the adult heart. It is concluded that the AV node and upper bundle of His cells derive from the low interatrial septum. The possibility that AV canal cells contribute to this event was discarded. The functional relationship of the Av node and bundle of His with other cardiac tissues during the early development of the heart is discussed.

Animals↗
PubMed1986

Electrophysiological and ultrastructural study of the atrioventricular canal during the development of the chick embryo.

The development of the atrioventricular canal (A-V canal) of embryonic chick hearts (35 to 120 h) was studied by morphological and electrophysiological techniques. The earliest identification of the A-V canal action potentials was at 45 to 49 h of incubation coinciding with the atrium formation and the appearance of its corresponding distinctive action potential. At that time the first atrioventricular delay was recorded and its action potentials showed a low rate of rise, particularly at the initiation of the upstroke and a long duration. The conduction velocity was the lowest in the A-V canal. As the development proceeded from 45 to 120 h, the cardiac cells of the A-V canal showed scanty membrane to membrane contacts and large intercellular spaces filled with abundant extracellular matrix components, in striking contrast to the paucity of these components in the atrium and ventricle. The morphological and electrophysiological characteristics described for the A-V canal cells, could help to explain their slow conduction properties and the atrioventricular delay.

Animals↗
PubMed1971

[Flail chest].

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Accidents, Traffic↗
PubMedDate not supplied

[Juvenile myoclonic epilepsy. Life difficulties and response to treatment].

Juvenile myoclonic epilepsy (JME) may have different forms of clinical expression and produces different kinds of life difficulties. Both eventualities have not been sufficiently described in the literature. Treatment with valproic acid is useful but requires strict compliance of medical instructions. Thirty two patients with this disease, are presented in order to describe their presenting forms, associated life handicaps and the results of their treatment. The disease may first present as tonic-clonic, complex absence or complex partial seizures, followed months or years later, by typical myoclonic crisis or as JME to which other kinds of epileptic crisis may or not be added after some time. Twenty four (75%) patients had 38 life difficulties, these being, mainly, objects dropped from hand, burns and parental aggression. Eighteen (56.25%) patients had relapses during treatment. In 14 cases (77.77%) relapses were due to noncompliance, 8 (57.19%) patients couldn't afford the cost of valproic acid. Knowledge of the presenting forms of the disease may favor opportune diagnosis and treatment, which would prevent life difficulties. Relapses are mainly due to noncompliance and economic reasons.

Adolescent↗
PubMedDate not supplied

[Follow-up of infants with birth weight under 1,500 g].

A prospective study of 199 children with birth weight less than 1,500 g was done. 86 boys and 113 girls, 141 (71%) adequate for gestational age and 58 (29%) small for gestational age. At follow-up 43 (21.6%) infants were lost to control, 17 (7%) moved to other places and 7 (3.5%) died in the first year of life. In the first year of life, infants whose birthweights were adequate for gestational age had been hospitalized more frequently and the small for dates showed higher percentage of undernutrition. After the second year of life, it was possible to know the impairment. It was found 7.4% of cerebral palsy, 2.9% of hipoacusia and 2.2% of retinopathy of prematurity, these diagnosis were most frequent in children that were adequate for gestational age. We concluded that small for dates infants are at risk of undernutrition and that those adequate for gestational age are at risk of permanent sequelae.

Birth Weight↗
PubMedDate not supplied

[Neurologic development in children with birth weight under 1,000 grams].

A follow up study of 27 children with birth weight less than 1,000 g was done. Their mean birth weight was 881.2 g +/- 102.2 g and gestational age 27.2 +/- 1.8 weeks. One child died at four months of age and four children were lost to follow up. Twenty two patients were followed for 43.6 months, range 2 to 6 years. At follow up seven children (31.8%) showed evidence of neurologic sequelae, six with spastic signs and one with cicatricial retrolental fibroplasia. All children with neurological sequelae had evidence of intracranial hemorrhage. Fifteen of 22 children under effective follow up are apparently normal.

Birth Weight↗
PubMedDate not supplied

[Juvenile myoclonic epilepsy: Janz' syndrome].

Thirty two patients with juvenile myoclonic epilepsy are described. The most relevant aspects of the disease are the following: it starts at nearly 12 years of age or before; it is frequently associated with generalized tonic-clonic seizures; myoclonic and tonic-clonic seizures occur at time of awaking or shortly after; no pathological findings occur at the central nervous system; a large number of relatives show generalized seizures and the interictal electroencephalogram is usually disturbed by generalized epileptic activity. Valproic acid, preferably alone, is probably the treatment of choice for these patients.

Adolescent↗