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Biomedical subjects

R Rivera

Publications and source records attributed to R Rivera.

At least 73 records · Page 4Linked to original sources
PubMed1994

Parvalbumin and calbindin-D28k immunocytochemistry in human neocortical epileptic foci.

Serial sections of cortical resection of 30 patients suffering from drug-resistant epilepsy were processed for parvalbumin and calbindin-D28k immunocytochemistry to determine local circuit neuron populations. Our findings indicate that there is not a simple mechanism to explain neocortical epileptic foci. On the basis of the present results it can be suggested that: (1) reduced percentage of local circuit neurons in the vicinity of neoplasms may account for a decreased intracortical inhibition. (2) Abnormal morphology and distribution of local circuit neurons may result in abnormal cortical inhibition in patients with focal cortical dysplasia, and, probably, in other focal migrational disorders, including neuronal nests in the white matter. (3) Increased percentages of immunoreactive local circuit neurons and fibers in focal neocortical necrosis (cavernous angiomas), diffuse hypoxic encephalopathy, and hippocampus in patients with temporal lobe epilepsy due to mesial sclerosis, may play a role in epilepsy. These neurons can be activated by reduced excitatory inputs, or they may establish abnormal synaptic contacts with other inhibitory neurons. (4) Lack of consistent morphologic abnormalities in the neocortex of patients with temporal lobe epilepsy, and in patients with cryptogenetic frontal lobe epilepsy, suggests that electrically abnormal neocortical foci in these cases are probably epiphenomena.

Adolescent↗
PubMed1993

Parvalbumin-immunoreactive dystrophic neurites and aberrant sprouts in the cerebral cortex of patients with Alzheimer's disease.

Parvalbumin-immunoreactive dystrophic neurites and aberrant terminal sprouts associated with senile plaques, together with preserved density of parvalbumin-immunoreactive neurons, were found in the cerebral cortex of two patients with Alzheimer's disease, one of them familiar, in which a biopsy of the left frontal lobe was carried out for diagnostic and counselling purposes. These findings suggest that, although parvalbumin-immunoreactive cells are relatively resistant to degeneration in Alzheimer's disease, parvalbumin-immunoreactive neuronal processes can degenerate in some cases of Alzheimer's disease.

Aged↗
PubMed1993

Parvalbumin-immunoreactive cortical neurons in Creutzfeldt-Jakob disease.

Massive abnormalities of parvalbumin-immunoreactive cortical neurons were observed in the cerebral biopsy samples of 3 patients with Creutzfeldt-Jakob disease. Immunoreactive cells had reduced and short, often fragmented, dendrites, and large numbers of dendritic varicosities were observed. Since parvalbumin-immunoreactive neurons are the most important inhibitory cells in the cerebral cortex, the damage to these neurons may account, in part, for the impaired cortical function, and may play a role in the appearance of myoclonus and electroencephalographic patterns in patients with Creutzfeldt-Jakob disease.

Cerebral Cortex↗
PubMed1993

Radiosensitive populations and recovery in X-ray-induced apoptosis in the developing cerebellum.

Sprague-Dawley rats received a single dose of 2 Gy X-rays at the age of 1 or 3 days and were killed at different intervals. Dying cells with the morphological characteristics of apoptosis appeared in the external and internal granular layers (EGL and IGL) and white matter (WM) of the cerebellum, mainly 3-6 h after irradiation, and decreased thereafter to reach normal values between 48 h and 5 days later. This process was curbed by the injection of cycloheximide at a dose of 1 microgram/g body weight. In addition, the number of mitoses in EGL rapidly decreased after irradiation and did not reach normal values until a few days later. Proliferating cell nuclear antigen (PCNA)-immunoreactive cells, which were chiefly found in EGL but also in IGL and WM, dramatically decreased in number from 3 to 48 h after irradiation. PCNA-immunoreactive cells reappeared and reached age-matched values in the following days. Hu (considered as an early neuronal marker) and vimentin immunocytochemistry disclosed that Hu-nonreactive cells in the upper level of EGL, Hu-immunoreactive cells in the inner level of EGL, Bergmann glia and many astrocytes in WM, as well as many non-typified cells in WM, were radiosensitive populations, whereas Purkinje cells were not. The present results indicate that irradiation at P1 or P3 blocks mitosis in EGL and kills sensitive cells mainly in the late G1 and S phases of the cell cycle, probably by apoptosis through a protein synthesis-mediated process. Radiosensitive cells are germinal cells and neuroblasts in EGL, Bergmann glia, astrocytes in WM, and non-typified cells, probably glial cell precursors, in WM. Surviving cells in EGL and PCNA-immunoreactive cells in other cortical layers and white matter reconstitute the cerebellum following a single dose of X-rays.

Animals↗
PubMed1993

Primary central white matter degeneration in old dogs.

Degeneration of the central white matter is described in old dogs. The presence of ubiquitin-immunoreactive free granules and intracytoplasmic globules in glial cells and macrophages, together with galacerebroside-immunoreactive precipitates and lipofusion storage, point to the likelihood of a primary myelin degeneration with deposits of non-degraded ubiquitin-protein conjugates and complex galactolipids.

Aging↗
PubMed1993

Fructose-1,6-bisphosphate fails to ameliorate delayed neuronal death in the CA1 area after transient forebrain ischaemia in gerbils.

Fructose-1,6-bisphosphate has been shown to reduce ischaemic-induced brain damage in rabbits and gerbils. In view of these findings, we investigated the effects of fructose-1,6-bisphosphate on delayed neuronal death, following bilateral forebrain ischaemia, in the gerbil hippocampus at the fourth day of reperfusion. We subjected gerbils to bilateral forebrain ischaemia for 20 min. Fructose-1,6-bisphosphate was administered: intraperitoneally at a dose of 1 g/kg in saline in hr before the occlusion or at a dose of 1 g/kg 1 hr before the occlusion and every 24 hr for 3 days; or intraventricularly at a dose of 0.1 g/kg just after the carotid occlusion. No significant differences in the number of dying cells in the CA1 area were found between each group of treated animals when compared with controls. This study suggests that fructose-1,6-bisphosphate, administered according to these three different schedules, fails to ameliorate delayed neuronal death after 20 min of bilateral forebrain ischaemia in the CA1 area of the gerbil hippocampus.

Animals↗
PubMed1993

Midazolam in the treatment of status epilepticus in children.

OBJECTIVE: To determine the efficacy and safety of midazolam given as a continuous infusion in the treatment of status epilepticus in children. DESIGN: Prospective, open study. SETTING: Pediatric intensive care unit. PATIENTS: Twenty-four children with seizures, in whom three repeated intravenous doses of 0.3 mg/kg of diazepam, 20 mg/kg of phenobarbital, and 20 mg/kg of phenytoin failed to bring the episode under control. INTERVENTIONS: All patients received a bolus of midazolam (0.15 mg/kg iv) followed by a continuous infusion at 1 microgram/kg/min. The dose was increased every 15 mins until the episode of seizure was brought under control. Time to control seizures, infusion rate, and side-effects were monitored. MEASUREMENTS AND MAIN RESULTS: The mean age of the patient population was 2.2 yrs (range 2 months to 12 yrs; 14 female and 10 male). In all patients, seizures were controlled in a mean time of 0.78 hrs (range 15 mins to 4.5 hrs). The mean infusion rate was 2.3 micrograms/kg/min (range 1 to 18). None of the patients had clinically important changes in blood pressure, heart rate, oxygen saturation, or respiratory status attributable to the use of midazolam. The mean time to full consciousness for patients after stopping the infusion was 4.2 hrs (range 2 to 8.5). CONCLUSION: Midazolam is an effective and safe drug to control refractory seizures in children with status epilepticus.

Child↗
PubMed1993

Contact lenses affect corneal stromal pH.

Recent studies suggest that corneal acidosis may alter corneal structure and function. We determined whether the range of oxygen transmissibility (Dk/L) provided by a hydrogel lens could affect corneal stromal pH. Stromal pH was measured using a noninvasive fluorometric technique under both open- and closed-eye conditions on subjects who wore hydrogel lenses made of the same material but with different lens powers. Under closed-eye lens wearing conditions, central stromal pH was reduced substantially and there was no relation between degree of acidosis and lens Dk/L. Under open-eye lens wearing conditions, central stromal pH was also reduced but the degree of acidosis was dependent on lens Dk/L. These results suggest extended wear of hydrogel lenses can produce marked decreases in stromal pH which could remain reduced even after the eyes are opened.

Acidosis↗
PubMed1993

Study and introduction of family planning methods in developing countries.

Research in developing countries is essential for the evaluation of the safety, efficacy and acceptability of both new and already available contraceptives. Research conducted by scientists in developing countries has also played an essential role in the development of new contraceptives. The continuous delivery of progestin at a low dose, copper IUDs, contraceptive implants, monthly injectables and vaginal rings are examples of new methods developed with the input of research conducted largely in developing countries. When research in developing countries is funded or coordinated by international agencies, local scientists have to be involved not only in its implementation, but in the planning, analysis and dissemination of such research. The World Health Organization, the Population Council and Family Health International have played an important role in supporting collaborative studies for the development, introduction and evaluation of family planning methods in developing countries.

Developing Countries↗
PubMed1993

The intrauterine device in the present and future.

Good counseling and better selection of candidates would result in the intrauterine device's (IUD) safer use. Age and parity of the IUD acceptor do not seem to be associated with an increased risk of pelvic inflammatory disease (PID). The newer generation of copper- and hormone-releasing IUDs are associated with improved safety and efficacy.

Aftercare↗
PubMed1992

Influence of age and parity on the development of the human breast.

Breast cancer is heavily influenced by the reproductive history of the individual. Pregnancy has a protective effect which is attributed to differences in the degree of differentiation of the breast. The purpose of this work was to determine whether the quantity and the type of parenchymal structures present in the human breast were related to the age and parity history of a woman. Fifty-one human breast samples were obtained from bilateral or unilateral reduction mammoplasties performed in 40 parous women ranging in age from 18 to 57 years, and 11 nulliparous women ranging in age from 14 to 54 years. An average of 100 grams of tissue/specimen were processed for whole mount. A total of 650 slides were examined and 31,222 structures were classified and counted under the light microscope. The following mammary structures were identified: terminal structures (TS), and lobules (LOB) type 1, 2, and 3. Results were plotted for the total patient population and separately for nulliparous and parous women against age. The total patient population contained similar proportions of LOb1, 2, and 3 between ages 14-18, with a reduction of percentage of Lob1 and increase in Lob3 between ages 23 to the middle forties, when Lob3 decreased and Lob1 increased to 70%. Lob2 and TS did not exhibit significant changes throughout the period of life analyzed. When analyzed separately it was found that the breasts of nulliparous women were predominantly composed of Lob1, fewer Lob2, with Lob3 almost completely absent, whereas parous women had a high frequency of Lob3, which were the predominant structures until the fourth decade of life.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Evaluating the readability of informed consent forms used in contraceptive clinical trials.

The readability level of informed consent forms used in clinical trials on contraceptives was determined. Three different formulas for measuring readability were used. Some forms received relatively high scores by all three methods. The most common problems associated with high readability scores were the use of 'unfamiliar' words, long words and long sentences. At present all forms used must be readable, using the SMOG formula, at a grade 6 level or less.

Clinical Trials as Topic↗
PubMed1992

Interactions between intrauterine contraceptive device use and breast-feeding status at time of intrauterine contraceptive device insertion: analysis of TCu-380A acceptors in developing countries.

OBJECTIVE: This paper is a reassessment of earlier findings from a preliminary analysis of data from a multicenter international trial regimen on breast-feeding and non-breast-feeding women in which events related to insertion, expulsion, and removal of the TCu-380A intrauterine contraceptive device (ParaGard 380) were investigated. STUDY DESIGN: Performance of the TCu-380A through 12 months after insertion was compared with life-table rate analysis, chi 2, Fisher exact test, or Student's t test. Variables were events reported during intrauterine contraceptive device insertion and events throughout the 12 months of study participation by breast-feeding status. RESULTS: Breast-feeding among intrauterine contraceptive device users was associated with fewer insertion-related complaints and lower removal rates for bleeding and pain. No uterine perforations were reported throughout the study. CONCLUSION: Differences in the performance of the TCu-380A intrauterine contraceptive device suggest physiologic effects associated with lactational amenorrhea. The TCu-380A intrauterine contraceptive device is a viable option for women breast-feeding at the time of intrauterine contraceptive device insertion.

Adult↗
PubMed1992

Field tests of an acephate baiting system designed for eradicating undesirable honey bees (Hymenoptera: Apidae).

Field evaluations were made of a baiting system designed for use by regulatory agencies in suppressing populations of undesirable feral honey bees, Apis mellifera L. (e.g., bees posing hazards [especially Africanized bees] and colonies infested with parasitic mites). Bees from feral or simulated feral (hived) colonies were lured with honey and Nasonov pheromone components to feeders dispensing sucrose-honey syrup. After 1-3 wk of passive training to feeders, colonies were treated during active foraging by replacing untreated syrup with syrup containing 500 ppm (mg/liter) acephate (Orthene 75 S). In four trials using hived colonies on Grant Terre Island, LA., 21 of 29 colonies foraged actively enough at baits to be treated, and 20 of the 22 treated were destroyed. In the lower Rio Grande Valley of Texas (two trials at each of two trials), treatments killed 11 of 16 colonies (6 of 10 hived; 50 of 6 feral). Overall results showed that all 11 colonies that collected greater than 25 mg acephate died, whereas 3 of 10 colonies receiving less than 25 mg survived. Delivering adequate doses required a minimum of approximately 100 bees per target colony simultaneously collecting treated syrup. The system destroyed target colonies located up to nearly 700 m away from baits. Major factors limiting efficacy were conditions inhibiting foraging at baits (e.g., competing natural nectar sources and temperatures and winds that restricted bee flight).

Animals↗
PubMed1992

Complications of endotracheal intubation and mechanical ventilation in infants and children.

OBJECTIVE: To assess the frequency of complications of endotracheal intubation and mechanical ventilation. DESIGN: Prospective cohort study. SETTING: Pediatric tertiary multidisciplinary ICU. PATIENTS: Eight hundred sixty-nine serial patients, of whom 500 were endotracheally intubated and 431 were mechanically ventilated. INTERVENTIONS: Daily clinical observation. MAIN OUTCOME MEASURES: Age, diagnosis, endotracheal tube size, type of ventilator and humidification, duration of intubation and mechanical ventilation, ventilatory settings, and complications (accidental extubation, tissue damage, endobronchial intubation, postintubation stridor, endotracheal tube blockage, pulmonary airleak, bronchopulmonary dysplasia, pulmonary atelectasis) were recorded. RESULTS: The median patient age was 10 months (25th and 75th quartiles: 1 month and 15 yrs). The median duration of endotracheal intubation and mechanical ventilation was 4 days and 2 days, respectively. A total of 186 complications were recorded in 119 (24%) patients. No deaths were due to intubation or ventilation. The overall frequency of accidental extubation was 3.2% of patients at a rate of 1.26 extubations/100 intubation days. In nonventilated, unsedated patients with croup or epiglottitis, the frequency of accidental extubation was 23% at a rate of 11.83 extubations/100 intubation days. Lung atelectasis occurred in 7.8%, airleak in 6.8%, and infection in 2.3% of patients. Other complications included tissue damage (3.4%), endobronchial intubation (2.4%), postintubation stridor (2.4%), bronchopulmonary dysplasia (2.3%), and endobronchial tube blockage (0.8%). CONCLUSIONS: Complications were related to the duration of intubation and mechanical ventilation.

Adolescent↗
PubMed1992

[Clinical course characteristics of gastric cancer 1958-1990].

The clinical, surgical and histopathologic characteristics of patients with gastric cancer were compared among 3 consecutive periods from 1958 to 1990. A significant increase in the frequency of location at the upper third of the stomach, a greater proportion of resectable lesions, an increasing tendency towards extended total gastrectomy and a significant increase in the frequency of undifferentiated or diffuse carcinoma were observed. A change in pathogenetic factors along the years may be involved in the differences described.

Adult↗