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Biomedical subjects

A Alonso

Publications and source records attributed to A Alonso.

At least 217 records · Page 12Linked to original sources
PubMed1997

Chilling stress leads to increased cell membrane rigidity in roots of coffee (Coffea arabica L.) seedlings.

Tropical and sub-tropical higher plant species show marked growth inhibition when exposed to chilling temperatures. In root tip segments of coffee seedlings which were subjected for 6 days to temperatures of 10, 15, 20 and 25 degrees C, in darkness, we have detected an increased amount of malondialdehyde formed in the 10 degrees C treatment, accompanied by higher electrolyte leakage. The electron paramagnetic resonance (EPR) technique and the fatty acid spin probes 5-, 12- and 16-doxylstearic acid were used to assess cellular membrane fluidity. At the depth of the 5th and 16th carbon atom of the alkyl chains the nitroxide radical detected more rigid membranes in seedlings subjected to 10 degrees C compared with 15 and 25 degrees C. At the C-12 position of the chains the probe showed very restricted motion and was insensitive to chilling induced membrane alterations. EPR parameters for intact tissues and microsome preparations from root tips showed that the fluidity was essentially the same when evaluated at C-5 and C-16 positions of the chains, and was considerably more fluid for microsomal membranes in the region of the C-12 position of the bilayers. The rotational motion of the nitroxide at C-16 position of the chains experienced a phase transition at about 15 degrees C. The calculated energy barriers for reorientational motion of the probe 16-doxylstearic acid were higher at temperatures of 5-15 degrees C than in the interval of 15-25 degrees C, suggesting that below the phase transition the membrane lipids assume a more ordered and compacted array. Membrane rigidity induced by chilling was interpreted as due to lipid peroxidation that could have been facilitated by higher density of peroxidizable chains below the membrane phase transition.

Coffee↗
PubMed1997

Morphological characteristics of layer II projection neurons in the rat medial entorhinal cortex.

The entorhinal cortex receives inputs from a variety of neocortical regions. Neurons in layer II of the entorhinal cortex originate one component of the perforant path which conveys this information to the dentate gyrus and hippocampus. The current study extends our previous work on the electro-responsive properties of layer II neurons of the medial entorhinal cortex in which we distinguished two categories of layer II neurons based on their electrophysiological attributes (Alonso and Klink [1993] J Neurophysiol 70: 128-143). Here we report on the morphological features of layer II projection neurons, as revealed by in vitro intracellular injection of biocytin. We now report that the two electrophysiologically distinct types of neurons correspond to morphologically distinct types of cells. All neurons (65% of the total cells recorded) that developed sustained, subthreshold, sinusoidal membrane potential oscillations were found to have a stellate appearance. Neurons that did not exhibit oscillatory behavior had either a pyramidal-like (32%) or a horizontal cell morphology (3%). Stellate cells had multiple, thick, primary dendrites. Their widely diverging upper dendritic domain expanded mediolaterally over a distance of around 500 microns close to the pial surface. This mediolateral extent was more than double that of the pyramidal-like cells. Dendrites of stellate cells demonstrated long dendritic appendages, and their dendritic spines had a more complex morphology than those of nonstellates. The stellate cell axons emerged from a primary dendrite and were more than double the thickness (approximately 1.4 microns) of the axons of nonstellate cells. Recurrent axonal collaterization appeared more extensive in axons arising from stellate cells than from pyramidal-like cells.

Animals↗
PubMed1997

Detection of somatic mutations in the mitochondrial DNA control region of colorectal and gastric tumors by heteroduplex and single-strand conformation analysis.

Each entire hypervariable region of the mitochondrial DNA control region was screened for mutations from paired normal and tumor DNA corresponding to a group of 21 patients (13 colorectal and 8 gastric adenocarcinomas) using both heteroduplex analysis and single-strand conformation analysis. These two mutation scanning strategies allowed the identification of sequence alterations in 3/13 (23%) colorectal tumors and in 3/8 (37%) gastric tumors. Heteroduplex analysis showed the heteroplasmic state of the majority of these tumor mutations. Sequence analysis revealed two A:T/G:C transitions (nucleotide positions: 16241 and 16166) in hypervariable region 1 (HV1) and two C:G/T:A transitions (nucleotide positions: 76 and 312), one A:T/G:C transition (nucleotide position: 93), a 1-basepair C:G deletion (nucleotide position: 309), and a 2-base-pair CC:GG insertion (nucleotide position: 309) in the HV 2 region. A considerable proportion of these mutations was found in homopolymeric regions which are highly polymorphic among humans. Different mechanisms (clonal expansion, increased oxidative damage, and nuclear mutator mutations) were suggested to explain the increased mitochondrial DNA mutation rate observed in cancer.

Adenocarcinoma↗
PubMed1997

Morphological changes induced by phospholipase C and by sphingomyelinase on large unilamellar vesicles: a cryo-transmission electron microscopy study of liposome fusion.

Cryo-transmission electron microscopy has been applied to the study of the changes induced by phospholipase C on large unilamellar vesicles containing phosphatidylcholine, as well as to the action of sphingomyelinase on vesicles containing sphingomyelin. In both cases vesicle aggregation occurs as the earliest detectable phenomenon; later, each system behaves differently. Phospholipase C induces vesicle fusion through an intermediate consisting of aggregated and closely packed vesicles (the "honeycomb structure") that finally transforms into large spherical vesicles. The same honeycomb structure is also observed in the absence of enzyme when diacylglycerols are mixed with the other lipids in organic solution, before hydration. In this case the sample then evolves toward a cubic phase. The fact that the same honeycomb intermediate can lead to vesicle fusion (with enzyme-generated diacylglycerol) or to a cubic phase (when diacylglycerol is premixed with the lipids) is taken in support of the hypothesis according to which a highly curved lipid structure ("stalk") would act as a structural intermediate in membrane fusion. Sphingomyelinase produces complete leakage of vesicle aqueous contents and an increase in size of about one-third of the vesicles. A mechanism of vesicle opening and reassembling is proposed in this case.

Biophysical Phenomena↗
PubMed1997

[Glucose metabolism in children undergoing extracorporeal circulation: its correlation with weight and the degree of hypothermia].

INTRODUCTION: A prospective study has been carried out in 33 children with congenital heart disease, aged 5 days to 16 years, operated on with the aid of cardiopulmonary bypass (CPB), in order to evaluate intra and postoperative glycemia in relation to children's weight and intra-CPB perfusion temperature. MATERIAL AND METHODS: Plasmatic levels of glucose, lactate, insulin, C-peptide, growth hormone (GH) and cortisol were measured at five different times, from pre-CPB up to 18 hours post-CPB. Thirteen children weighing less than 10 kilograms (group I) were compared to 20 children weighing more than 10 kilograms (group II), and 15 children operated on with perfusion temperature below 27 degrees C (group A) were compared to 18 with perfusion temperature above 27 degrees C. RESULTS: All the cases showed intraoperative hyperglycemia. In relation to weight, evolution of glycemia was similar in both groups but anaerobic glycolysis was significantly higher in group I. In relation to temperature, glycemia, lactic acidemia intra- and post-CPB and serum C-peptide post-CPB were significantly higher in group A. Intraoperative insulin was decreased and GH serum levels were also higher in group I and A, but fell drastically post-CPB in all groups. CONCLUSIONS: Perioperative control of glycemia is important in children operated on with the aid of CPB. Control of lactic acidemia is also expedient. Carbohydrates metabolism and its hormonal regulation are more disturbed in infants and in children operated on with low perfusion temperature.

Adolescent↗
PubMed1997

Electroresponsiveness of medial entorhinal cortex layer III neurons in vitro.

The entorhinal cortex funnels sensory information from the entire cortical mantle into the hippocampal formation via the perforant path. A major component of this pathway originates from the stellate cells in layer II and terminates on the dentate granule cells to activate the hippocampal trisynaptic circuit. In addition, there is also a significant, albeit less characterized, component of the perforant path that originates in entorhinal layer III pyramidal cells and terminates directly in area CA1. As a step in understanding the functional role of this monosynaptic component of the perforant path, we undertook the electrophysiological characterization of entorhinal layer III neurons in an in vitro rat brain slice preparation using intracellular recording techniques with sharp micropipettes and under current-clamp conditions. Cells were also intracellularly injected with biocytin to assess their pyramidal cell morphology. Layer III pyramidal cells did not display either the rhythmic subthreshold membrane potential oscillations nor spike-cluster discharge that characterizes the spiny stellate cells from layer II. In contrast, layer III pyramidal cells displayed a robust tendency towards spontaneous activity in the form of regular tonic discharge. Analysis of the voltage-current relations also demonstrated, in these neurons, a rather linear membrane voltage behaviour in the subthreshold range with the exception of pronounced inward rectification in the depolarizing direction. Depolarizing inward rectification was unaffected by Ca(2+)-conductance block with but was abolished by voltage-gated Na(+)-conductance block with tetrodotoxin, suggesting that a persistent Na(+)-conductance provides much of the inward current sustaining tonic discharge. In addition, in the presence of tetrodotoxin, an intermediate threshold (approximately -50 mV) Ca(2+)-dependent rebound potential was also observed which could constitute another pacemaker mechanism. A high-threshold Ca(2+)-conductance was also found to contribute to the action potential as judged by the decrease in spike duration towards the peak observed during Ca(2+)-conductance block. On the other hand, Ca(2+)-conductance block increase spike duration at the base and abolished the monophasic spike afterhyperpolarization. Analysis of the input-output relations revealed firing properties similar to those of regularly spiking neocortical cells. Current-pulse driven spike trains displayed moderate adaptation and were followed by a Ca(2+)-dependent slow afterhyperpolarization. In summary, the intrinsic electroresponsiveness of entorhinal layer III pyramidal cells suggest that these neurons may perform a rather high-fidelity transfer function of incoming neocortical sensory information directly to the CA1 hippocampal subfield. The pronounced excitability of layer III cells, due to both Na+ and Ca2+ conductances, may also be related to their tendency towards degeneration in epilepsy.

Animals↗
PubMed1997

Inhibitory effect of dipyridamole and its derivatives on lipid peroxidation in mitochondria.

Dipyridamole (DIP), 2,6-bis(diethanolamino)-4,8-dipiperidino-[5,4-d] pyrimidine, is a coronary vasodilator widely used in clinics. It has also been reported to have coactivator activity for a number of antitumour drugs and antioxidant activity in membrane systems. In recent years we have been studying the spectroscopic properties of this drug and several of its derivatives as well as their interaction with charged micelles and phospholipid monolayers. A strong interaction of DIP and DIP derivatives with these model membrane systems and a dependence of the strength of the interaction upon the chemical structure of the DIP derivative was observed. Here, the antioxidant effect of DIP and the derivatives, RA14, RA47, and RA25, was compared. We observed that although it strongly inhibits the iron-induced lipoperoxidation on mitochondria (IC50 = 1 microM), it shows no protection against an organic oxidant, cumene hydroperoxide. The order of hydrophobicity of the DIP derivatives, DIP > RA14 > RA47 > RA25, correlates very well with both the values of the association constants of these derivatives to micelles, their localization in the micelles, and phospholipid films and their antioxidant effect on mitochondria. So, a very good correlation of the structure of the drug in regarded to the nature of its substituents with the biological activity is observed. Essentially the same result was observed either measuring the lipid peroxidation or the membrane fluidity by ESR, suggesting that the effect of DIP and DIP derivatives is probably associated to their binding to the lipid bilayer and not to interaction with membrane proteins.

Animals↗
PubMed1997

Reliability of a new recombinant immunoblot assay (RIBA HIV-1/HIV-2 SIA) as a supplemental (confirmatory) test for HIV-1 and HIV-2 infections.

The diagnosis of HIV infection is usually determined using serological methods. Positive results in a screening test should be confirmed with more specific supplementary assays, and the Western blot (WB) is the most frequently used. However, problems of WB, particularly in regard to the significance of indeterminate results, still remain. We evaluate a new recombinant HIV-1/2 antigen-based immunoblot (RIBA) as confirmatory assay in a panel of 190 clinical samples. The RIBA was much more sensitive and specific than WB. In particular, the test allows for a significant reduction in the number of indeterminate results and for more accurate distinction between HIV-1 and/or HIV-2 infections. Thus, these results make tests such as the RIBA instead of WB particularly attractive for validating anti-HIV EIA reactivity.

HIV Infections↗
PubMed1997

Sexual behavior regulated (paced) by the female induces conditioned place preference.

The possibility that female-paced coital behavior induces a reward state of sufficient intensity and duration to induce conditioning was evaluated by the conditioned-place-preference paradigm. Ovariectomized female rats, treated with estradiol benzoate and progesterone, regulated (paced) their coital interactions with a stud male through a 2-compartment chamber in which only the female could freely move from one compartment to the other. The females that paced their coital interactions showed a clear place preference. In contrast, no change in preference was observed in the females that could not pace their coital contacts. The change in preference in the females that paced their coital interactions was similar to that produced by an injection of morphine (1 mg/kg). These results suggest that coital interactions in females can induce a reward state when the females can control the pace of the sexual interaction.

Animals↗
PubMed1997

Hepatocellular carcinoma in a non-cirrhotic coal miner with secondary haemochromatosis.

We report a case of hepatocarcinoma in a non-cirrhotic patient with secondary haemochromatosis. A 61-year-old man, who had been a coal miner for 36 years, presented with a well differentiated hepatocarcinoma without cirrhosis. The patient had a haemochromatosis with no family history of liver disease and a normal genetic study. Right hepatectomy was performed and 15 months later there has been no recurrence. This case confirms the possibility of hepatocarcinoma occurring in haemochromatosis patients without cirrhosis. The recognition of populations at risk of haemochromatosis is a necessity, and this should include coal miners.

Abdominal Pain↗
PubMed1997

Multiple antibiotic resistance in Stenotrophomonas maltophilia.

A cryptic multidrug resistance (MDR) system in Stenotrophomonas maltophilia, the expression of which is selectable by tetracycline, is described. Tetracycline resistance was the consequence of active efflux of the antibiotic, and it was associated with resistance to quinolones and chloramphenicol, but not to aminoglycosides or beta-lactam antibiotics. MDR is linked to the expression of an outer membrane protein (OMP54) both in a model system and in multidrug-resistant clinical isolates.

Aminoglycosides↗
PubMed1997

Muscarinic modulation of the oscillatory and repetitive firing properties of entorhinal cortex layer II neurons.

Neurons in layer II of the entorhinal cortex (EC) are key elements in the temporal lobe memory system because they integrate and transfer into the hippocampal formation convergent sensory input from the entire cortical mantle. EC layer II also receives a profuse cholinergic innervation from the basal forebrain that promotes oscillatory dynamics in the EC network and may also implement memory function. To understand the cellular basis of cholinergic actions in EC, we investigated by intracellular recording in an in vitro rat brain slice preparation the muscarinic modulation of the electroresponsive properties of the two distinct classes of medial EC layer II projection neurons, the stellate cells (SCs) and non-SCs. In both SCs and non-SCs, muscarinic receptor activation with carbachol (CCh, 10-50 microM) caused atropine-sensitive (300 nM) membrane depolarization. In SCs, the CCh-induced membrane depolarization was associated with subthreshold membrane potential oscillations and "spike cluster" discharge, which are typically expressed by these cells on depolarization. CCh, however, caused a decrease of the dominant frequency of the membrane potential oscillations from 9.2 +/- 1.1 (SD) Hz to 6.3 +/- 1.1 Hz, as well as a decrease of the intracluster firing frequency from 18.1 +/- 1.7 Hz to 13.6 +/- 1.3 Hz. In addition, spike cluster discharge was less robust, and the cells tended to shift into tonic firing during CCh. In contrast to SCs, in non-SCs, CCh drastically affected firing behavior by promoting the development of voltage-dependent, long-duration (1-5 s) slow bursts of action potentials that could repeat rhythmically at slow frequencies (0.2-0.5 Hz). Concomitantly, the slow afterhyperpolarization (sAHP) was replaced by long-lasting plateau postdepolarizations. In both SCs and non-SCs, CCh also produced conspicuous changes on the action potential waveform and its afterpotentials. Notably, CCh significantly decreased spike amplitude and rate of rise, which suggests muscarinic modulation of a voltage-dependent Na+ conductance. Finally, we also observed that whereas CCh abolished the sAHP in both SCs and non-SCs, the membrane-permeant analogues of adenosine 3',5'-cyclic monophosphate, 8-(4-chlorophenylthio)-adenosine-cyclic monophosphate and 8-bromo-adenosine-cyclic-monophosphate, abolished the sAHP in SCs but not in non-SCs. The data demonstrate that cholinergic modulation further differentiates the intrinsic electroresponsiveness of SCs and non-SCs, and add support to the presence of two parallel processing systems in medial EC layer II that could thereby differentially influence their hippocampal targets. The results also indicate an important role for the cholinergic system in tuning the oscillatory dynamics of entorhinal neurons.

Action Potentials↗