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Biomedical subjects

M Villegas

Publications and source records attributed to M Villegas.

At least 19 recordsLinked to original sources
PubMed2005

Interface double-exchange ferromagnetism in the Mn-Zn-O system: new class of biphase magnetism.

In this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn(3+) and Mn(4+) via a double-exchange mechanism. The presence of the ZnO around MnO(2) modifies the kinetics of MnO(2)-->Mn(2)O(3) reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples.

Journal Article↗
PubMed1998

Chondroitin sulfate proteoglycan specific to retinal horizontal neurons.

ABSTRACT Proteoglycans (PGs) are a diverse group of highly glycosylated macromolecules that are implicated in the development and maintenance of neuronal circuitry. With its highly ordered, layered structure, the retina ideally serves to define the synthesis, processing, and distribution of these molecules within a specific cellular subpopulation. In retinal sections, monoclonal antibody (MAb) 6A2 immunostained a horizontal cell-specific antigen. Antigen 6A2 was expressed within abundant processes in the outer plexiform layer and in rare neurites that extend across the inner nuclear layer to the inner plexiform layer. Ultrastructurally, the antigen was localized to cisternae within horizontal cell somata, along tubulovesicular structures in dendrites, and in the perisynaptic space encircling presynaptic terminals of the cone photoreceptor triad. These findings suggest that this PG is synthesized within the horizontal cells, transported to the terminals, and released into the extracellular spaces just proximal to the synapse. Based on the focal stain in the adjacent photoreceptor cell, it is possible that antigen is pinocytosed by this cell and is concentrated at the ribbon synapse. In Western immunoblots of retinal homogenates, MAb 6A2 recognized a heterogeneous chondroitin sulfate (CS) PG (CSPG) of approximately 400-500 kDa. After sequential enzymatic removal of CS glycosaminoglycans, a major broad band of 300-500 kDa was identified by MAb 1B5, which detects CSPGs that bear uronic acid linked to unsulfated N-acetylgalactosamine as the initial disaccharide in the CS chain. Localization of this PG around presynaptic terminals of the horizontal neuron and at the ribbon synapse suggests that it may play a modulatory and sustaining role at the synapse.

Animals↗
PubMed1997

Thoracoscopic partial pericardiectomy in the diagnosis and management of pericardial effusion.

BACKGROUND: An effort was made to present our experience with thoracoscopy in the diagnosis and management of pericardial effusions. METHODS: Twenty-two partial pericardiectomies were performed with the thoracoscopic approach in patients with pericardial effusions, the etiology of which was uremic (n = 7), neoplastic (n = 8), idiopathic (n = 5), septicemia (n = 1), and postpericardiotomy (n = 1). All cases had grade III-IV/IV radiological cardiomegaly and ultrasonographic confirmation of the effusion. We found hemodynamic compromise in 17 patients. The operation, requiring the insertion of three trocars, enabled us to remove a large part (approximately 6 x 10 cm) of the left anterolateral side of the pericardium and aspirate the effusion contents for diagnostic and therapeutic purposes. RESULTS: In five cases we found coexisting pleural effusions. The pericardial effusion had a mean volume of 817 ml, which was serous in 11 cases, hematic in six, serohematic in four, and purulent in one. Cytology of the pericardial effusion was positive for neoplasia in four cases (one pulmonary neoplasia, two breast carcinomas, and one lymphoma). We observed conversion to grade I/IV cardiomegaly in 16 cases and a return to normality in the other six, with the absence of ultrasonographic effusion in all cases. There was no recurrence during the mean follow-up period of 20.5 months (range: 2-47). CONCLUSIONS: The thoracoscopic management of pericardial effusions is a simple and effective technique that allows us to create a large pericardial window that drains the effusion definitively, determines its etiology, and explores and treats coexisting pleural lesions, all without recurrences.

Adolescent↗
PubMed1997

[Reperfusion arrhythmias in valvular patients undergoing extracorporeal surgery and pretreated with captopril].

INTRODUCTION AND OBJECTIVES: After the ischemia-reperfusion process in extracorporeal cardiac surgery there are, among several phenomena, some reperfusion arrhythmias which are influenced by a varied series of mechanisms. These arrhythmias have been related to the release of oxygen-derived free radicals during the first moments of reperfusion. Thus, a previous administration of free-radical scavengers might be beneficial, among which captopril has been included with good results in human studies in vitro and in animals in vivo. The aim of this study was to evaluate the influence of pretreatment with captopril on the prevention of reperfusion arrhythmias in patients undergoing valvular cardiac surgery. METHODS: 30 patients were randomly allocated to pretreatment with either captopril (CTP group, n = 15) or without captopril (CON group, n = 15). Exclusion criteria (left ventricular ejection fraction < 40%, evidence of angiographic coronary disease, prior myocardial infarction and preoperatory myocardial infarction). The dose of captopril administered was 12.5 mg every 8 hours orally, from 24 hours before surgery. A Holter register was used to analyze the ventricular arrhythmias (extrasystoles, salvos, tachycardia and fibrillation) during the first hour of reperfusion. The need for cardioversion was examined and the number of shocks needed. These events were related to changes in blood analyses from coronary sinus samples to determine creatine phosphokinase, activity of the angiotensin converting enzyme and cyclic adenosine monophosphate, before aortic clamping and after the heart was rewarmed. RESULTS: No significant differences were found in the number of ventricular arrhythmias. 60% of the patients with captopril and only 40% of the patients without it (non significant) had spontaneous defibrillation without electric shock; in those cases in which it was necessary, the number of shocks was less in the captopril group (p < 0.05). Excepting the significant correlation (p < 0.01) that we have found between ventricular fibrillation and the cyclic adenosine monophosphate increase, there is no significant correlation between the other arrhythmias and the analytical data studied. CONCLUSIONS: These data suggest that captopril, given before cardiac surgery, has little or no protector effect on reperfusion ventricular arrhythmias in extracorporeal cardiac surgery, though in patients treated with captopril there is a greater possibility of spontaneous defibrillation and fewer shocks necessary for defibrillation, without negative effects.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Acute treatment with the N-methyl-D-aspartate receptor antagonist MK-801: effect of concurrent administration of haloperidol or scopolamine on preproenkephalin mRNA levels of the striatum and nucleus accumbens of the rat brain.

We injected rats three times at 3 h intervals (from 0900 h to 1500 h) with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 at 0.1 or 0.5 mg/kg of body weight. Three hours after the last injection, animals were sacrificed and the brains were processed for in situ hybridization histochemistry. Preproenkephalin (PPE) mRNA levels were significantly decreased throughout the caudate-putamen (CPu) and nucleus accumbens (NAc) at the lower dose. The higher dose produced significant decreases only in anterior CPu (aCPu) and NAc. Concurrent administration of the muscarinic cholinergic receptor antagonist scopolamine at 2 or 5 mg/kg neither potentiated nor prevented the effect of MK-801 on PPE mRNA levels in the neostriatum. In contrast, co-administration of haloperidol (dopamine receptor antagonist) with MK-801 blocked the effect of the latter in the NAc, and elevated PPE mRNA levels throughout the CPu. The data demonstrate that the acute effects of glutamate receptor activity on striatal and accumbal PPE mRNA expression via the NMDA receptor can be modulated by the dopaminergic system in the brain of the rat.

Animals↗
PubMed1996

Restraint stress reversibly enhances spatial memory performance.

The effects of restraint stress on performance of a spatial memory task, the eight arm radial maze, was examined in rats. When stress was given for 6 h/day for 7 days and performance evaluated days 10-13 post stress, no effect on performance was noted; however, daily restraint stress for 13 days caused a small, but significant, enhancement of performance days 10-13 post stress. Stressed rats performed better than controls: their number of correct choices in the first 8 visits was higher than the controls, and stressed rats took fewer total choices to finish the maze than controls. Stress-dependent, enhanced performance does not appear permanent since further maze testing on days 14 and 15 post stress showed no differences between the groups. Performance of the stressed rats significantly correlated with their stress-induced, serum corticosterone levels measured after 6 h of restraint on the last day of restraint, day 13 (r = -0.63, P < 0.05); rats with higher levels of CORT took fewer choices to finish the task. Examination of hippocampal CA3c pyramidal neurons with Golgi techniques showed no effect of stress on the basal or apical dendritic arbors. Since our previous study showed that 21 days of restraint stress is associated with impaired spatial memory performance (10), these results suggest that the duration of stress may differentially affect learning/memory with shorter periods of stress serving an adaptive function while longer durations causing maladaptive changes.

Animals↗
PubMed1996

Reversed shunting across the ductus arteriosus or atrial septum in utero heralds severe congenital heart disease.

OBJECTIVES: This study was performed to define the significance of Doppler color flow mapping in demonstrating reversal of the direction of the normal physiologic flow across the atrial septum and ductus arteriosus in the human fetus. BACKGROUND: Reversal of the physiologic shunting across the ductus arteriosus or atrial septum in utero (i.e., left to right) can be readily identified by Doppler color flow mapping, complemented by pulsed and continuous wave Doppler information. METHODS: We reviewed echocardiograms recorded at our three institutions from 1988 to 1993, which displayed reversal of flow by Doppler color flow in 53 fetuses of gestational age 18 weeks to term. The diagnoses were confirmed by postnatal echocardiography, operation or autopsy. Reversal of shunting was consistently associated with severe heart disease. RESULTS: Reversed atrial shunting was found with severe left heart obstructive lesions, including 19 with hypoplastic left heart syndrome, 3 with critical aortic stenosis, 2 with double-outlet right ventricle and 1 each with an interrupted aortic arch, atrioventricular septal defect and severe left ventricular dysfunction due to dilated cardiomyopathy. Reversed ductus arteriosus shunting was found with severe right heart obstructive lesions, including nine fetuses with pulmonary atresia, six with severe obstructive tricuspid valve abnormalities, five with severe tetralogy of Fallot, four with Ebstein's anomaly and two with single ventricle and pulmonary stenosis. Associated cardiac lesions were common in both groups. Only 3 of the 15 infants who were delivered alive from the reverse ductus arteriosus shunt group and 4 of 12 from the reverse atrial shunt group still survive. CONCLUSIONS: The finding of reversed flow by Doppler color flow mapping during fetal life provides a key to subsequent accurate diagnosis and denotes a spectrum of diseases with a very poor prognosis.

Ductus Arteriosus↗
PubMed1996

Analysis of partial sequences of genes coding for 16S rRNA of actinomycetes isolated from Casuarina equisetifolia nodules in Mexico.

Filamentous bacteria isolated from surface-sterilized nodules of Casuarina equisetifolia trees in México were capable of reducing acetylene, a diagnostic test for nitrogenase, but were unable to nodulate their host. Analysis of partial 16S rRNA gene sequences suggests that the Mexican isolates are not Frankia strains but members of a novel clade.

Actinomycetales↗
PubMed1995

Attenuation of neostriatal preproenkephalin and preprotachykinin mRNA abundance by chronic treatment with the kainate/quisqualate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione in the rat brain.

The present investigation assessed the effect of chronic blockade of kainate/quisqualate binding sites with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on preproenkephalin (PPE) and preprotachykinin (PPT) mRNA abundance in the neostriatum of the rat brain. Daily injection of CNQX for seven consecutive days decreased PPE mRNA abundance approximately 25% below vehicle-injected controls in dorsolateral, dorsomedial, anterior caudate-putamen (dlCPu, dmCPu and aCPu, respectively) and nucleus accumbens (NAc). Similarly, PPT mRNA abundance was significantly decreased in dlCPu, dmCPu and aCPu but not in the accumbens. The data demonstrate that non-NMDA receptor activity modulates basal levels of expression of PPE and PPT mRNAs in the neostriatum of the rat brain.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Ventricular function during liver reperfusion in hepatic transplantation. A transesophageal echocardiographic study.

Postreperfusion syndrome (PRS) is the most dramatic and acute hemodynamic alteration that occurs in OLT. Our aim was to determine heart function by hemodynamic monitoring and transesophageal echocardiography during PRS. We studied 24 nonconsecutive patients allocated to 2 groups: group A (n = 8), patients with PRS, and group B (n = 16), patients without PRS. Usual hemodynamic data were obtained simultaneously with transesophageal echocardiography recording of the left ventricular imaging in 4 different stages: after induction of anesthesia, 5 min before the end of the anhepatic phase, between 2 and 5 min after reperfusion, and 5 min after graft reperfusion. The hemodynamic and echocardiographic findings during reperfusion were (group A vs. group B patients): mean arterial pressure, 50.0 +/- 15.2 vs. 74.7 +/- 13.9 mmHg (P < 0.01); pulmonary capillary wedge pressure, 12.7 +/- 6.1 vs. 13.9 +/- 5.7 mmHg (NS); left ventricular ejection fraction, 79.6 +/- 9.3 vs. 83.4 +/- 9.4% (NS); left ventricular end diastolic volume index, 35.5 +/- 12.7 vs. 54.7 +/- 21.3 ml/m2 (P < 0.05); and stroke volume index, 27.9 +/- 8.9 vs. 45.5 +/- 15.9 ml/m2 (P < 0.01). There was a mild decrease in left ventricular compliance in group A. We found no alteration in left ventricular function that can justify PRS. The hemodynamic changes during PRS seemed to be caused by an insufficient increase in preload after unclamping.

Diastole↗
PubMed1994

Repeated stress causes reversible impairments of spatial memory performance.

Restraint stress, 6 h/day for 21 days, caused an impairment, during acquisition, of the performance of a spatial memory task, the eight-arm radial maze. The impairment was reversible, temporally limited and blocked by phenytoin, a blocker of excitatory amino acid action, or tianeptine, an antidepressant, which lowers extracellular serotonin. These effects on behavior parallel the reversible stress-induced atrophy of dendrites of hippocampal CA3 neurons that are also blocked by the drugs.

Animals↗
PubMed1993

Pulmonary arterial hypertension and cor pulmonale associated with chronic domestic woodsmoke inhalation.

We describe the clinical, radiologic, functional, and pulmonary hemodynamic characteristics of a group of 30 nonsmoking patients with a lung disease that may be related to intense, long-standing indoor wood-smoke exposure. The endoscopic and some of the pathologic findings are also presented. Intense and prolonged wood-smoke inhalation may produce a chronic pulmonary disease that is similar in many aspects to other forms of inorganic dust-exposure interstitial lung disease. It affects mostly country women in their 60s, and severe dyspnea and cough are the outstanding complaints. The chest roentgenograms show a diffuse, bilateral, reticulonodular pattern, combined with normalized or hyperinflated lungs, as well as indirect signs of pulmonary arterial hypertension (PAH). On the pulmonary function test the patients show a mixed restrictive-obstructive pattern with severe hypoxemia and variable degrees of hypercapnia. Endoscopic findings are those of acute and chronic bronchitis and intense anthracotic staining of the airways appears to be quite characteristic. Fibrous and inflammatory focal thickening of the alveolar septa as well as diffuse parenchymal anthracotic deposits are the most prominent pathologic findings, although inflammatory changes of the bronchial epithelium are also present. The patients had severe PAH in which, as in other chronic lung diseases, chronic alveolar hypoxia may play the main pathogenetic role. However, PAH in wood-smoke inhalation-associated lung disease (WSIALD) appears to be more severe than in other forms of interstitial lung disease and tobacco-related COPD. The patients we studied are a selected group and they may represent one end of the spectrum of the WSIALD.

Blood Pressure↗
PubMed1993

Cardiac ultrasonography in structural abnormalities and arrhythmias. Recognition and treatment.

Fetal cardiac ultrasonography has become an important tool in the evaluation of fetuses at risk for cardiac anomalies. It can both guide prenatal treatment and assist the management and timing of delivery. We recommend that a fetal echocardiogram be done when there is a family history of congenital heart disease; maternal disease that may affect the fetus; a history of maternal drug use, either therapeutic or illegal; evidence of other fetal abnormalities; or evidence of fetal hydrops. The optimal timing of evaluation is 18 to 22 weeks' gestation. An entire range of structural cardiac defects can be visualized prenatally, including atrioventricular septal defect, ventricular septal defect, cardiomyopathy, ventricular outlet obstruction, and complex cardiac defects. The outcome for a fetus with a recognized abnormality is unfavourable, with less than 50% surviving the neonatal period. Fetal cardiac arrhythmias are also a common occurrence, 15% in the series described here. Premature atrial or ventricular contractions are most commonly seen and usually require no treatment. Supraventricular tachycardia can result in hydrops and require in utero treatment to prevent fetal demise. Complete heart block, particularly in association with structural heart disease, has a poor prognosis for fetal survival.

Arrhythmias, Cardiac↗
PubMed1992

Cardiac dimensions determined by cross-sectional echocardiography in the normal human fetus from 18 weeks to term.

Assessment of cardiac dimensions of the chambers, great arteries and veins in the human fetus is important to distinguish abnormal dimensions from normal. This study establishes normal values based on cross-sectional echocardiographic measurements over the gestational period where these measurements may be clinically useful. Ventricular and atrial dimensions were measured from the 4-chamber view, the short-axis dimension immediately below the mitral and tricuspid valve leaflets in diastole, and the long axis from the closed apposed atrioventricular valves to their respective apices. The ventricular walls and septum were measured at the level at which cavity dimensions in diastole were measured, defining both the left and right ventricular wall thickness, as well as that of the ventricular septum. Furthermore, the long axis of the right and left atria was measured from the center of the apposed atrioventricular valve leaflets to the posterior atrial wall, and the sizes of the atrial chambers were defined using their widths at the prospective broadest points through the area of foramen ovale. From a variety of views, diameters were measured at maximal expansion of the main, left and right pulmonary arteries, the ductus arteriosus, and the superior and inferior venae cavae. The data were evaluated longitudinally from 18 weeks to term, and regression analysis was performed using the best fit of a linear or polynomial equation. The data provide a means for evaluating the normal sizes and dimensions of the fetal heart chambers, as well as the thickness of the ventricular walls and septum.

Aorta↗