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Biomedical subjects

M Ramírez

Publications and source records attributed to M Ramírez.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

[Determination of verotoxins in strains of Escherichia coli O157:H7].

We performed an study to find out the main virulence factor in verotoxigenic Escherichia coli: the production of verotoxins in 50 non sorbitol-fermenting Escherichia coli strains (possible enterohemorrhage) which were isolated from children with acute diarrheas in the City of Havana and referred to the National Reference Laboratory for acute diarrheal diseases in "Pedro Kourí" Institute. By using the agglutination technique with latex particles of E. coli O157:H7, we determined whether the verotoxins belonged to this serotype, we also researched the production of verotoxins in Vero cell culture. Ninety-six percent of the total number of strains were positive in the qualitative determination of this factor which was more frequently observed after 24 hours.

Bacterial Toxins↗
PubMedDate not supplied

[Aminoglycoside antibiotics neomycin and kanamycin inhibit the increase of of pyroglutamyl aminopeptidase activity by depolarizing synaptosomes of the frontal cortex of the rate].

INTRODUCTION: Thyrotrophin releasing hormone (TRH) has emerging in the last few years as a neuropeptide with important functions, not only as neurohormone into the hypothalamus-pituitary axis, but as neurotransmitter in several areas of the nervous system. Although little is known about its extra-endocrine functions, TRH has been related with several types of psychiatric disorders. Pyroglutamyl aminopeptidase (pGluAP) is the enzyme involved in the degradation of TRH. OBJECTIVES: The present research studies the levels of pGluAP activity under basal (resting) and KCl-stimulated (depolarized) conditions. The role of intracellular free calcium homeostasis, by means of the aminoglycoside antibiotics neomycin and kanamycin as voltage-dependent calcium channels blockers, is also studied. MATERIAL AND METHODS: Both pGluAP activity and intracellular free calcium concentration were analyzed in synaptosomes obtained from the frontal cortex of rats. Synaptosomes were incubated in artificial cerebrospinal fluid, under basal (resting) or KCl-stimulated (depolarized) conditions, with of without neomycin or kanamycin at different concentrations. RESULTS: Depolarization increases significantly pGluAP activity, which is completely abolished by neomycin and kanamycin at the lower concentrations used. On the contrary, aminoglycoside antibiotics do not block completely the increase on intracellular free calcium concentration induced by depolarization. Under basal conditions, no changes were found on pGluAP activity nor intracellular free calcium. CONCLUSIONS: pGluAP activity could regulate the neurotransmitter/neuromodulatory functions of TRH trough intracellular free calcium movements through aminoglycoside-sensitive voltage-dependent calcium channels. A role for inositol 4,5-bisphosphate breakdown products is also suggested.

Animals↗
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[Plesiomonas shigelloides, a Vibrionaceae to be taken into account].

The antigenic structure and antimicrobial susceptibility were studied in 99 strains isolated from patients with acute diarrhea (6 strains from an outbreak of digestive transmission disease in Santiago de Cuba) and a strain isolated from a patient who died from infections neurological syndrome (INS, meningitis). Four new serotypes (093, 994, 095, 096), which had not been described in the world classification, were identified from the Cuban isolated strains and were included in the International Serotyping Scheme by the International Reference Center located in Prague, Czech Republic. For the first time in Cuba, the circulation of serotypes 017:H11, 011: H2, 023. H1alc, 057: H3 which show cross reaction to Shiguella species was proved. Those strains from the outbreak of digestive disease belonged to serotype 050: H11 and had a thermostable toxin. The first case of infectious neurologic syndrome with Plesionomas shigelloides etiology reported in Cuba was described; the strain corresponded to serotype 050: H11. The worldwide reported pattern of antimicrobial resistance was demonstrated.

Acute Disease↗
PubMedDate not supplied

[Toxigenic Vibrio cholerae non-01].

The antimicrobial susceptibility and the presence of a heat-stable toxin were researched into 100 non-01 Vibrio cholerae strains sent by 7 different health centers to the National Reference Laboratory of Acute Diarrheal Diseases in "Pedro Kourí" Tropical Medicine Institute. The presence of 20% toxigenic non-01 Vibrio cholerae was detected, a figure substantially higher than that reported in other geographic areas, except for endemic areas. This result will make it possible to set epidemiological alert in Cuba because these strains can be infected by CTX phages (element transporting genes that encode for choleric toxin) which will give such strains an epidemic potential similar to that of the etiologic agent of cholera. The identified strains could be studied as possible cholera vaccine candidates.

Animals↗
PubMedDate not supplied

[Dietary cholesterol modifies pyroglutamyl aminopeptidase activity in mouse frontal cortex. Sexual differences].

INTRODUCTION: Pyroglutamyl aminopeptidase (pGluAP) is an omega peptidase widely distributed in fluid and tissues, which hydrolyses biological active peptides including thyrotropin-releasing-hormone (TRH). In the last years, different endocrine and extraendocrine functions have been attributed to TRH. OBJECTIVES: The aim of present work is to study the influence of high dietary cholesterol on soluble and membrane bound pGluAP activity in frontal cortex of male and female mice. Material and methods. Soluble and membrane bound pGluAP activities of frontal cortex of mice feeding during 15 days, a standard diet enriched with cholesterol (1%) and cholic acid (0.5%) were measured using fluorimetric assays. RESULTS: Significant increases were observed in membrane bound pGluAP activity in males and females. No changes were detected in soluble pGluAP activity in frontal cortex of females but a significant increase was observed in this enzymatic activity in males. CONCLUSIONS: High dietary cholesterol induces a significant increase in tissue pGluAP activity. These increases may produce changes in TRH metabolism which may be related with alterations in its neuromodulatory functions and with the possible relationship between TRH and other neurotransmitter systems.

Animals↗
PubMedDate not supplied

[Influence of alcohol on brain aminopeptidases. An in vitro study].

INTRODUCTION: It is well known the depressor effect of alcohol on several inhibitory nervous centres. This can be due to the inhibition that induces in the release of different type of neurotransmitters, and because alcohol can increase the membrane fluidity and changes the function of proteins inserted in the membrane. Several aminopeptidases (AP) have been described as enzymes that regulate the activity of peptide neurotransmitters. In the present work, the influence of alcohol (25, 50 and 100 mM) on several aminopeptidase activities (alanyl AP, arginyl AP, cystinyl AP, leucyl AP and tyrosyl AP) has been determined in synaptosomes obtained from the cortex of mouse, under basal and K+ stimulated conditions and their calcium dependence, in a non toxic in vitro model. MATERIAL AND METHODS: AP activities were determined using aminoacyl ? naphthylamides as substrates. Non toxic in vitro model were demonstrated analyzing free radical generation, lipid peroxidation and oxidation of synaptosomal proteins. In addition, the bioenergetic behavior of synaptosomes was determined under different experimental protocols. RESULTS: In basal conditions, alcohol produces a dose related inhibition of alanyl AP activity. The rest of activities show a biphasic behavior. In this way, depending on the concentration of alcohol used, aminopeptidases are inhibited or stimulated. Depolarization with K+ 25 mM leads to a decrease of alanyl AP and tyrosyl AP activities but does not change the rest of activities. The presence of alcohol under stimulated conditions produces the inhibition of all the enzymatic activities, specially with the highest concentrations used. CONCLUSIONS: Alcohol modifies several aminopeptidase activities from synaptosomes of the cortex of mouse, acting in different ways under basal or stimulated conditions. These effects seem not to be related with degenerative events induced by alcohol. Therefore, a specific effect of this substance on the neurotransmisory/neuromodulatory systems mediated by neuropeptides must exist, modifying the enzymes that are responsible of their degradation.

Aminopeptidases↗
PubMedDate not supplied

[Influence of estradiol on pyroglutamyl aminopeptidase activity in the frontal cortex of ovariectomized mice].

INTRODUCTION: Pyroglutamyl aminopeptidase (pGluAP) is an omega peptidase widely distributed in fluid and tissues which hydrolyses biological active peptides including thyrotropin releasing hormone (TRH). OBJECTIVES. The aim of present work is to study the influence of estradiol on soluble and membrane bound pGluAP activity in the frontal cortex of female mice. MATERIAL AND METHODS: Soluble and membrane bound pGluAP activities in frontal cortex of ovariectomized mice and ovariectomized mice injected with different doses of estradiol were measured using espectrophotometric assays. RESULTS: Soluble pGluAP activity in frontal cortex did not change after ovariectomy or after the administration of the different doses of estradiol. However, membrane bound pGluAP activity showed a significant increase after ovariectomy. After the administration of the lower dose of estradiol, membrane bond pGluAP activity returned to the same levels detected before the ovariectomy. CONCLUSION: Estradiol modifies membrane bound pGluAP activity which is the principal enzyme involved in the hydrolysis of TRH. Therefore, misregulation of estradiol levels may produce modifications in the neuromodulatory functions of TRH.

Animals↗
PubMedDate not supplied

[The neurobiology of developmental dyslexia: a survey].

One of the most common disorders affecting the ability to read is developmental dyslexia, which, unlike the alexia related to a loss of the capacity to read associated with brain damage, refers to a specific disorder in the acquisition of reading skills and becomes apparent in reiterated persistent difficulties in learning to read. A number of studies have attempted to detect structural and functional abnormalities that might be the origin of problems in learning to read. The use of functional neuroimaging techniques such as positron emission tomography (PET), spectroscopic magnetic resonance imaging (SMRI) and functional magnetic resonance imaging (fMRI) enables us to measure changes in the metabolic activity associated with alterations in the neuronal networks involved in the reading process. In this review, different studies are analysed in an attempt to identify alterations in the cortico subcortical regions which could be the origin of the developmental dyslexia. Results show that in dyslexics there is a temporoparietooccipital disconnection, and a disconnection with the left frontal cortex as regards the demands for fast auditory processing, as well as abnormalities in the connections between the temporoparietal cortex and the cerebellum with other regions of the brain. Such findings suggest that the altered areas of the brain do not only show a characteristic pattern of hypoactivation, but also that these alterations could be the cause of this malady. We highlight the importance of these findings in the diagnosis and rehabilitation of this population.

Dyslexia↗
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[Comparative study of bilateral lesions in the entorhinal cortex and in the fimbria fornix].

INTRODUCTION: Numerous reports show that lesions to hippocampus afferents, such as the entorhinal cortex (EC) and the fimbria fornix (FF), exert an effect on memory in rodents. There are, however, no long term comparative studies that show which of these lesions could be most useful as a model for studies into neuroplasticity. MATERIAL AND METHODS: Young male Sprague Dawley rats were used. Bilateral electrolytic lesion was caused to the EC or the FF was damaged by transection. One, four or 12 weeks later the animals were evaluated in a Morris water maze, first with an invisible platform and then with the platform within view. The results from the two groups were compared to each other and to those obtained from healthy controls and subjects with false lesions by means of a variance analysis. RESULTS: In the test with an invisible platform, both types of lesion gave rise to serious, irreparable involvement of the spatial memory of the animals, at least up to 12 weeks after the lesion. The test with the visible platform revealed significant differences between animals with lesion to the EC evaluated at 12 weeks, which suggests the development of some visual or motor deterioration in these animals. CONCLUSIONS: Although both lesions gave rise to behavioural deterioration that was irreversible in the long term in rodents, the lesion to the FF seems to be a better model for evaluating specific effects on learning and memory, since the lesion to the EC apparently triggers additional sensory and motor involvement.

Animals↗
PubMedDate not supplied

[Recent advances in rehabilitation technology: a review of the brain-computer interface].

INTRODUCTION AND AIMS: In this work we review some of the options available in rehabilitation technology that are used to aid people with severe neuromuscular disorders, and which take electrophysiological activity as a source of biological signals with which to design interfaces. DEVELOPMENT: A number of different researchers have generated a novel communication and control system that utilises the electrical activity of the brain as a signal that represents the messages or commands an individual sends to the outside world, without using the normal output pathways of the brain, such as peripheral nerves and muscles; instead, this is achieved through an artificial system that extracts, encodes and applies them, called a brain-computer interface (BCI). The electrophysiological activity for a BCI can be obtained by means of superficial or implanted electrodes, and may therefore be classified as invasive or non-invasive. Five types of brain signals have been explored for use with a BCI: visual evoked potentials, slow cortical potentials, cortical neuronal activity, beta and mu rhythms, and event-related potentials. CONCLUSIONS: Thanks to recent improvements and developments in prototypes, this technology is sure to open up new possibilities of communication and control for the affected population; it also represents a valuable field of multidisciplinary research with numerous interesting applications in areas beyond the sphere of health care.

Brain↗
PubMedDate not supplied

[Semantic verbal fluency in Spanish-speaking people: a comparative analysis].

INTRODUCTION: Semantic verbal fluency (SVF) is the most commonly used test in the evaluation of normal and pathological functioning, whether it be clinically or experimentally. Several studies have suggested that the age, schooling and culture of the subject all affect performance in this test. To date no research has been conducted that proves whether there are differences between subjects who speak the same language but who come from different countries. PATIENTS AND METHODS: Data from the 'animals' category of the SVF in adult Spanish-speaking subjects and also the influence exerted by culture, age and schooling on the outcomes in this test were both submitted to analysis. The aforementioned variables were compared with the data reported by five research groups. RESULTS: The SVF test yields similar data from one Spanish-speaking country to another, provided that the subjects' age and schooling are taken into account. The differences found in this study may be due to variations in the way the tests are administered and scored rather than any cultural effect. We propose a standardised method of applying the test, so as to allow these variables to be unified in the future. CONCLUSION: Age and schooling are factors that determine performance in the SVF, although this is not true of culture.

Adolescent↗
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[Subcellular distribution of soluble and membrane-bound aminopeptidase in the left and right hemispheres of young and adult rats].

The levels of soluble and membrane-bound aminopeptidase activities were assayed in subcellular fractions from young (1 month old) and adult (5 month old) left and right rat brains, using Leu-, Arg- and Asp-2-naphthylamide as substrates. Both soluble Leu- and Arg-aminopeptidase activities showed the highest levels in the synaptosomal fraction in the two groups of rats. The highest levels of membrane-bound Leu- and Arg-aminopeptidase activities were found in the microsomal fraction of the two ages studied. There were no differences between the two ages in soluble Leu- and Arg- aminopeptidase activities. However, a significant decrease in both membrane-bound activities was evidenced in the synaptosomal fraction of adult rats. The young rats showed the highest soluble and membrane-bound levels of Asp-aminopeptidase activity in the microsomal fraction but no differences among fractions were found at 5 months of age. The soluble Asp-aminopeptidase activity of the homogenate and the mitochondrial fraction was significantly increased in adult animals when compared to that of younger ones. Finally, no differences between left and right brains, in soluble or membrane-bound activities, were found neither in young animals nor in the adult ones.

Aging↗
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[Interhemispherical study of the activities of aminopeptidases, lactate dehydrogenase and glutamate-oxaloacetate transaminase in the rat brain].

Aminopeptidase activity has been assayed from both soluble and membrane bound fractions in eleven regions of the left and right hemispheres of the rat brain, using L-leucine-2-naphthylamide as substrate. Two other metabolic enzymes, lactate dehydrogenase and glutamate-oxalacetate aminotransferase activities were simultaneously determined in the same areas. When individual zones of the left hemisphere were compared with its corresponding right zones, soluble aminopeptidase activities were significantly higher in left frontal cortex and left hypothalamus than in right frontal cortex and right hypothalamus, respectively. No other significant differences were found neither in the remaining areas nor for the other enzymatic activities between both brain hemispheres.

Aminopeptidases↗
PubMedDate not supplied

[A fluorimetric method for the determination of brain aminopeptidases].

A fluorometric method adapted to the determination of brain aminopeptidase activities has been developed in our laboratory. This method is based in the fluorescence produced by 2-naphthylamine when it is released from aminoacyl-2-naphthylamides under the hydrolytic action of these enzymes. Values of enzymatic activities and kinetic constants are similar to those previously described in the literature.

Aminopeptidases↗
PubMedDate not supplied

[Acute non-bacterial interstitial tubular nephritis].

With the idea in mind to review the etiologic characteristics and evolution of nonbacterial acute tubulointerstitial nephritis, 29 cases seen at the Hospital Infantil de México between 1972 and 1978 were studied. The ages of patients fluctuated from 3 months to 14 years; 18 of them were males. The disease was associated with the administration of nephrotoxic agents, fundamentally antibiotics, being in order of frequency; gentamicin, kanamycin, ampicillin and streptomycin. The main initial manifestations were hematuria and oliguria. At the onset of the disease, acute renal failure was found in 5 of the patients. Two patients developed chronic renal failure, which in one of them was caused by diphenylhydantoin and was reversible on discontinuance of the drug. There were 3 deaths which in 2 cases followed infectious complication and in 1, renal failure. Considerations are made on the pathogenesis of the disease which is predominantly immunologic of following direct toxic action.

Acute Disease↗