Biomedical subjects

A Flores

Publications and source records attributed to A Flores.

At least 19 recordsLinked to original sources

PubMed2006

Phantom reflexes: muscle contractions at a frequency not physically present in the input stimuli.

In the motor system, the periodic stimulation of one Ia-afferent input produces reflex muscle contractions at the input frequency. However, we observed that when two Ia monosynaptic reflex-afferent inputs are involved the periodic muscle contractions may occur at a frequency physically not present in the afferent inputs even when these inputs are sub-threshold. How can the muscles respond with such phantom reflex contractions at a frequency physically absent in the sub-threshold Ia-afferent input stimuli? Here we provide an explanation for this phenomenon in the cat spinal cord, that we termed "ghost motor response". We recorded monosynaptic reflexes in the L7 ventral root, intracellular potentials in the motoneurons, and the associated muscular contractions elicited by stimulation of the lateral and medial gastrocnemius nerves. By stimulating with periodic pulses of sub-threshold intensities and distinct frequencies of 2 and 3 Hz the lateral and medial gastrocnemius nerves, respectively, we observed monosynaptic responses and phantom reflex muscle contractions occurring at the fundamental frequency (1 Hz), which was absent in the input stimuli. Thus we observed a reflex ghost motor response at a frequency not physically present in the inputs. We additionally studied the inharmonic case for sub-threshold stimuli and observed muscular contractions occurring at much lower frequencies, which were also conspicuously absent in the inputs. This is the first experimental evidence of a phantom reflex response in the nervous system. The observed behavior was modeled by numerical simulations of a pool of neurons subjected to two different input pulses.

Animals↗

PubMed2006

Identification of a calcium-dependent matrix metalloproteinase complex in rat chorioallantoid membranes during labour.

The induction of the expression of matrix metalloproteinases (MMPs) and their extracellular activation are key processes in connective tissue degradation in the chorioallantoid membrane during rat labour. However, the regulatory mechanisms remain largely unknown. Here, we report the identification of a calcium-dependent high molecular weight complex composed of MMP-9, MMP-3, MMP-2, tissue inhibitor of metalloproteinase 1 (TIMP-1) and TIMP-2, identified by zymography and western blotting. Molecular sieve chromatography confirmed the presence of a complex of MMPs and TIMPs with an exclusion volume >670 kDa. Differential scanning calorimetry of the complex confirmed the existence of a macromolecular complex that unfolds with a broad transition; it is denatured over a wide range of temperatures and has a T(m) of 72 degrees C in the presence of Ca(2+). When denatured in the absence of Ca(2+), there were at least eight transitions with T(m)s that corresponded to pro-MMP-9, MMP-9, pro-MMP-3, MMP-3, pro-MMP-2, MMP-2, TIMP-1 and TIMP-2. Co-localization of the same molecular components was demonstrated by confocal microscopy using cell-depleted chorioallantoid membranes. The assembly and disassembly of the complex can be reproduced at physiological concentrations of Ca(2+). This complex provides a potential mechanism for the enzymatic regulation of MMPs, which may participate in connective tissue degradation leading to the rupture of the fetal membranes during labour.

Animals↗

PubMed2006

Paradoxical antagonism of PACAP receptor signaling by VIP in Xenopus oocytes via the type-C natriuretic peptide receptor.

Atrial natriuretic peptide (ANP) and the closely-related peptides BNP and CNP are highly conserved cardiovascular hormones. They bind to single transmembrane-spanning receptors, triggering receptor-intrinsic guanylyl cyclase activity. The "truncated" type-C natriuretic peptide receptor (NPR-C) has long been called a clearance receptor because it lacks the intracellular guanylyl cyclase domain, though data suggest it might negatively couple to adenylyl cyclase via G(i). Here we report the molecular cloning and characterization of the Xenopus laevis type-C natriuretic peptide receptor (XNPR-C). Analysis confirms the presence of a short intracellular C-terminus, as well as a high similarity to fish and mammalian NPR-C. Injection of XNPR-C mRNA into Xenopus oocytes resulted in expression of high affinity [(125)I]ANP binding sites that were competitively and completely displaced by natriuretic analogs and the unrelated neuropeptide vasoactive intestinal peptide (VIP). Measurement of cAMP levels in mRNA-injected oocytes revealed that XNPR-C is negatively coupled to adenylyl cyclase in a pertussis toxin-sensitive manner. When XNPR-C was co-expressed with PAC(1) receptors for pituitary adenylyl cyclase-activating polypeptide (PACAP), VIP and natriuretic peptides counteracted the cAMP induction by PACAP. These results suggest that VIP and natriuretic peptides can potentially modulate the action of PACAP in cells where these receptors are co-expressed.

Adenylyl Cyclases↗

PubMed2006

Pattern formation and morphology evolution in Langmuir monolayers.

We present a study of how patterns formed by Langmuir monolayer domains of a stable phase, usually solid or liquid condensed, propagate into a metastable one, usually liquid expanded. During this propagation, the interface between the two phases moves as the metastable phase is transformed into the more stable one. The interface becomes unstable and forms patterns as a result of the competition between a chemical potential gradient that destabilizes the interface on one hand and line tension that stabilizes the interface on the other. During domain growth, we found a morphology transition from tip splitting to side branching; doublons were also found. These morphological features were observed with Brewster angle microscopy in three different monolayers at the water/air interface: dioctadecylamine, ethyl palmitate, and ethyl stearate. In addition, we observed the onset of the instability in round domains when an abrupt lateral pressure jump is made on the monolayer. Frequency histograms of unstable wavelengths are consistent with the linear-instability dispersion relation of classical free-boundary models. For the case of dendritic morphologies, we measured the radius of the dendrite tip as a function of the dendrite length as well as the spacing of the side branches along a dendrite. Finally, a possible explanation of why Langmuir monolayers present this kind of nonequilibrium growth patterns is presented. In the steady state, the growth behavior is determined by Laplace's equation in the particle density with specific boundary conditions. These equations are equivalent to those used in the theory of morphology diagrams for two-dimensional diffusional growth, where morphological transitions of the kind observed here have been predicted.

Journal Article↗

PubMed2006

Phosphorylation of neurofibromin by PKC is a possible molecular switch in EGF receptor signaling in neural cells.

Children with neurofibromatosis (NF1) typically develop central nervous system (CNS) abnormalities, including aberrant proliferation of astrocytes and formation of benign astrocytomas. The NF1 gene encodes neurofibromin, a Ras-GAP, highly expressed in developing neural cells; the mechanism of regulation of neurofibromin as a Ras-GAP, remains however unknown. We now show that, in response to EGF, neurofibromin is in vivo phosphorylated on serine residues by PKC-alpha, in human, rat, and avian CNS cells and cell lines. EGF-induced PKC phosphorylation was prominent in the cysteine/serine-rich domain (CSRD) of neurofibromin, which lies in the N-terminus and upstream of the Ras-GAP domain (GRD), and this modification significantly increased the association of neurofibromin with actin in co-immunoprecipitations. In addition, we show that Ras activation in response to EGF was significantly lowered when C62B cells overexpressed a construct encoding both CSRD + GRD. Moreover, when PKC-alpha was downregulated, the Ras-GAP activity of CSRD + GRD was significantly diminished, whereas overexpressed GRD alone acted as a weaker GAP and in a PKC-independent manner. Most importantly, functional Ras inhibition and EGF signaling shifts were established at the single cell level in C6-derived cell lines stably overexpressing CSRD + GRD, when transient co-overexpression of Ras and PKC-depletion prior to stimulation with EGF-induced mitosis. Taken together, these data provide the first evidence of a functional, allosteric regulation of GRD by CSRD, which requires neurofibromin phosphorylation by PKC and association with the actin cytoskeleton. Our data may suggest a novel mechanism for regulating biological responses to EGF and provide a new aspect for the understanding of the aberrant proliferation seen in the CNS of children with NF1.

Animals↗

PubMed2005

Mpg1, a fission yeast protein required for proper septum structure, is involved in cell cycle progression through cell-size checkpoint.

Using a yeast two-hybrid screen we isolated a gene from Schizosaccharomyces pombe which corresponds to the previously uncharacterized ORF SPCC1906.01. We have designated this gene as mpg1, based on the putative function of its product as a mannose-1-phosphatase guanyltransferase. Mpg1 shows strong similarity to other GDP-mannose-1-phosphate guanyltransferases involved in the maintenance of cell wall integrity and/or glycosylation. This homology, together with the protein's localization pattern demonstrated in this work, strongly suggests that Mpg1 is involved in cell wall and septum synthesis. Moreover, cells lacking Mpg1 present a defect in glycosylation, are more sensitive to Lyticase, and show an aberrant septum structure from the start of its deposition, indicating that the Mpg1 function is necessary for the correct assembly of the septum. Interestingly, lack of Mpg1 clearly affects cell cycle progression: mpg1 null mutants arrest as septated and bi-nucleated 4C cells, without an actomyosin ring. Wee1 is required for the G2/M arrest induced in the absence of Mpg1, since the blockade is circumvented when Wee1 is inactivated. Wee1 is part of a cell-size checkpoint that prevents entry into mitosis before cells reach a critical size. The results presented in this work demonstrate that the G2/M arrest induced in the absence of Mpg1 is mediated by this cell size checkpoint, since oversized mutant cells enter mitosis. The mpg1 loss-of-function mutant, therefore, provides a good model in which to study how cells coordinate cell growth and cell division.

Amino Acid Sequence↗

PubMed2004

Gene encoding the group B streptococcal protein R4, its presence in clinical reference laboratory isolates & R4 protein pepsin sensitivity.

BACKGROUND & OBJECTIVES: R proteins were first identified by Lancefield in group B Streptococcus (GBS) as resistant to trypsin at pH8 and sensitive to pepsin at pH2. The R4 protein found predominantly in type III and some type II and V invasive isolates conforms to these criteria. The Rib protein, although structurally and epidemiologically similar to R4, was reported as resistant to both proteases. We report here the gene encoding the R4 protein from a type III group B streptococcal isolate (76-043) well characterized in our laboratory. METHODS: Trypsin extracted GBS proteins were assayed for protease sensitivities by double-diffusion Ouchterlony using varying conditions for the enzyme pepsin. Standard haemoglobin assay was used to examine pepsin enzymatic activity. Thirty clinical isolates of varying protein profiles identified by double-diffusion from our reference strain laboratory were screened by PCR and Southern technique. SDS-PAGE gel purified R4 amino acid sequences were determined and used to design oligonucleotide primers for screening a 76-043 genomic library. RESULTS: R4 was sensitive to pepsin at pH2 but appeared resistant at pH4, the reported pH used for Rib. By standard haemoglobin assay and trypsin extract studies of R4 protein, pepsin was shown to be active at pH2, yet easily inactivated; assays of GBS surface proteins are critical at pH2. Of the amino acids initially sequenced from R4, 88 per cent (61/69) showed identity to Rib; the r4 nucleotide sequence was identical to that of rib. All isolates with strong positive protein reactions for R4 were positive in both PCR and Southern technique, whereas isolates expressing alpha, beta, R1/R4, and R5 (BPS) protein profiles were not. INTERPRETATION & CONCLUSION: Sequenced PCR products aligned with identity to the R4 and Rib nucleotide sequences and confirmed the identity of these proteins and their molecular sequences.

Amino Acid Sequence↗

PubMed2003

CXCR4 and SDF-1 expression in B-cell chronic lymphocytic leukemia and stage of the disease.

The pathogenesis of B-cell chronic lymphocytic leukemia (B-CLL) has been linked to an overexpression of the chemokine receptor CXCR4 and increased in vitro functional response to its natural ligand CXCL12 (SDF-1). The CXCR4/SDF-1 system appears to be important for tissue localization and increased survival of B-CLL cells. The aim of our study was to examine if CXCR4 expression and SDF-1 blood levels were correlated to clinical and pathological stage of B-CLL. Flow cytometry and enzyme-linked immunosorbent assay (ELISA) techniques were used to determine CXCR4 expression and SDF-1 plasma levels, respectively, in a cohort of 51 patients diagnosed with B-CLL to correlate these measurements with several parameters that define the clinical stage of the disease. We confirmed that CXCR4 was consistently expressed on circulating B-CLL cells with a fluorescence intensity that was five-fold greater than in cells from healthy volunteers. There was a correlation between CXCR4 expression and leukocyte count ( r: 0.55, p<0.01), and CD19(+)/CD5(+ )cells ( r: 0.63, p<0.01). Interestingly, the group of B-CLL patients showed lower SDF-1 plasma levels compared to the control group. However, there was no correlation between CXCR4 or SDF-1 expression and the clinical stage of disease or the pattern of bone marrow infiltration. The results obtained suggest that other factors, and not only alteration in the SDF-1/CXCR4 chemokine system, must account for marrow infiltration of neoplastic cells observed in B-CLL and that CXCR4 could be involved in other features that exhibit malignant B cells, such as increased survival, rather than in their homing or migration to the bone marrow.

Adult↗

PubMed2002

Absence of coherence between cervical and lumbar spinal cord dorsal surface potentials in the anaesthetized cat.

Recordings of spontaneous cord dorsum potentials (CDPs) along the longitudinal axis of the spinal cord were made. These recordings were obtained from the surface of the dorsal horn at different points along the spinal cord caudally and cranially in relation to the point giving spontaneous potentials of maximal amplitude. We found two curves (lumbar and cervical) for the longitudinal distribution of the area of the power spectra of these recordings. Each of these curves had a symmetrical decrement on both sides of the position of the point for the maximal area of power. Such points were discovered on the L5-L7 and C3-C4 spinal segments. Spectral analysis of the spontaneous CDPs simultaneously recorded in both regions indicates no evidence of coherence, thus suggesting that the spontaneous CDPs recorded in the lumbar and cervical regions of the pentobarbitone-anaesthetized cat are generated by two independent populations of neurones not functionally interconnected between them.

Action Potentials↗

PubMed2002

Internal stochastic resonance in the coherence between spinal and cortical neuronal ensembles in the cat.

Internal stochastic resonance is a phenomenon in which the coherence of a non-linear system is enhanced by the presence of a particular, non-zero level of noise generated by internal or external sources without a periodic input signal. The aim of this study was to demonstrate the experimental occurrence of internal stochastic resonance in the coherence between spinal and cortical neuronal ensembles. Simultaneous recordings of spinal and cortical evoked potentials were made in the somatosensory system of the anaesthetized cat. Evoked potentials were produced by input noise introduced in the tactile stimulation of the hindpaw skin. Coherence between the spinal and cortical evoked activity recorded during different levels of input noise was calculated. All animals showed distinct internal stochastic resonance like behavior. We found that the mean coherence was an inverted U-like function of the level of input noise with a mean coherence peak of 0.43. To our knowledge, this is the first documented evidence of such phenomenon in an in vivo preparation of the central nervous system.

Animals↗

PubMed2002

Stochastic resonance in human electroencephalographic activity elicited by mechanical tactile stimuli.

Stochastic resonance (SR) is a phenomenon in which the response of a non-linear system to a weak input signal is optimized by the presence of noise. The aim of this study was to demonstrate the experimental occurrence of SR in electroencephalographic (EEG) activity elicited by mechanical tactile stimuli. Our experiments show that EEG responses evoked by mechanical tactile stimuli in the region overlying the somatosensory cortical area were optimized by the addition of certain noise amplitudes. All subjects showed distinct SR behavior. The signal-to-noise ratio (SNR) of the response evoked by mechanical indentations of the skin was an inverted U-like function of the input noise. As the noise amplitude increased, SNR values became larger. A maximum value was reached with a particular noise amplitude value. Beyond such peak, with higher noise amplitudes, the curve subsided gradually. To our knowledge, this is the first documented evidence that such remarkable phenomenon embodies electrical processes of the human brain. Such behavior might explain related findings described in psychophysical studies.

Adolescent↗

PubMed2002

Amplitude of somatosensory cortical evoked potentials is correlated with spontaneous activity of spinal neurones in the cat.

Simultaneous recordings of cortical evoked potentials in the posterior sigmoid gyrus, and spontaneous negative cord dorsum potentials (CDPs) of the L6 lumbar spinal segment, were made in the anaesthetised cat. The electrodes were positioned in cortical and spinal somatosensory regions where the largest spontaneous and evoked negative potentials were detected. Evoked potentials were produced by electrical stimulation to cutaneous nerves or by mechanical stimulation of the hindpaw skin. We found that both electrically and mechanically cortical evoked potentials were facilitated during the spontaneous negative CDPs. The magnitude of such facilitation was proportional to the amplitude of the 'conditioning' spontaneous negative CDPs. This led to a high positive correlation between amplitude fluctuations of spontaneous negative CDPs and fluctuations of the cortical evoked potentials. This observation suggests that transmission of cutaneous sensory information in ascending pathways could be facilitated when dorsal horn spinal neurones are active.

Action Potentials↗

PubMed2002

Cortical neuronal ensembles driven by dorsal horn spinal neurones with spontaneous activity in the cat.

Simultaneous recordings of cortical activity, recorded as the cortical local field potential (CLFP) in the contralateral posterior sigmoid gyrus, and the spinal activity, recorded as the cord dorsum potential (CDP) of the L6 lumbar segment, were made in the anaesthetized cat. The electrodes were positioned in somatosensory regions where the largest spontaneous negative CLFPs and CDPs were recorded. We found that spontaneous negative CLFPs were preceded by spontaneous negative CDPs with a mean latency of 14.4+/-3.5 ms. Amplitude of these spontaneous negative CLFPs was abolished after section of the dorsal columns and ipsilateral dorsolateral funiculus. It is concluded that the neurones of the primary somatosensory cortex can be driven by dorsal horn spinal neurones producing the spontaneous negative CDPs. This suggests very strongly that spontaneous neuronal activity in somatosensory regions of the brain is generated not only by ongoing activity of neurones located at supraspinal sites, but also by ongoing activity of spinal neurones.

Action Potentials↗

PubMed2002

Treatment of childhood Wilms' tumor without radiotherapy in Nicaragua.

BACKGROUND: Recent trends in therapeutic strategies for Wilms' tumor are based on an attempt to reduce or omit radiotherapy (RT) in a sizable fraction of patients. We report here the clinical and histological features as well as the results obtained in 37 children (23 males, 14 females; median age at diagnosis 3 years, range 0.8-8 years) diagnosed between 1991 and 1996, and treated with chemotherapy (CT) and surgery at La Mascota Hospital, Managua, Nicaragua. PATIENTS AND METHODS: Patients were grouped as follows: those who underwent surgery at diagnosis (group A, n = 4), patients who received preoperative CT because of large tumor size (group B, n = 27), lung metastases (n = 5) or bilateral disease (n = 1) (group C, n = 6). Treatment consisted of vincristine (VCR) and actinomycin-D (ACTD) for 24 weeks in group A, and of VCR, ACTD and adriamycin for 68 weeks in groups B and C. Histology was classified as favorable in 30 patients (81%), unfavorable in six patients (all of group B) and unknown in one. RESULTS: With a median follow-up time of 6.4 years the event-free survival for the whole group was 80.1%+/-6.8 (SE). No event occurred beyond 5 years of diagnosis. CONCLUSIONS: These results suggest that RT does not appear necessary for the majority of patients, and that an excellent surgical approach associated with an intensive CT schedule can control the disease, even in the absence of adequate information on the intra-abdominal tumor extent.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2001

NO donor SIN-1 potentiates monosynaptic reflexes in the cat spinal cord.

The effect produced by the nitric oxide donor SIN-1 on monosynaptic reflexes was examined. Experiments were performed on anesthetized, paralyzed and spinalized cats. Lumbar monosynaptic reflexes were produced by stimulation of Ia afferents. I.v. application of SIN-1 (500 microg/kg) produced a mean marked potentiation of 704% of pre-drug control (100%) in the amplitude of monosynaptic reflexes. In addition, in other experiments a concentration-dependent effect on the amplitude of monosynaptic reflexes was observed after microinjections of SIN-1 into the ventral horn (1 microl; 10(-12) - 10(-3) M), with a mean facilitatory effect of 355%. In both cases, the potentiation was reversible 45 min after i.v. or local application of SIN-1. These results provide the first evidence that monosynaptic reflexes can be potentiated by nitric oxide.

Animals↗

PubMed2001

In vivo hydroxyl radical formation after quinolinic acid infusion into rat corpus striatum.

We studied the effect of an acute infusion of quinolinic acid (QUIN) on in vivo hydroxyl radical (.OH) formation in the striatum of awake rats. Using the microdialysis technique, the generation of.OH was assessed through electrochemical detection of the salicylate hydroxylation product 2,3-dihydroxybenzoic acid (2,3-DHBA). The .OH extracellular levels increased up to 30 times over basal levels after QUIN infusion (240 nmol/microl), returning to the baseline 2 h later. This response was attenuated, but not abolished, by pretreatment with the NMDA receptor antagonist MK-801 (10 mg/kg, i.p.) 60 min before QUIN infusion. The mitochondrial toxin 3-nitropropionic acid (3-NPA, 500 nmol/microl) had stronger effects than QUIN on .OH generation, as well as on other markers of oxidative stress explored as potential consequences of .OH increased levels. These results support the hypothesis that early .OH generation contributes to the pattern of toxicity elicited by QUIN. The partial protection by MK-801 suggests that QUIN neurotoxicity is not completely explained through NMDA receptor overactivation, but it may also involve intrinsic QUIN oxidative properties.

Animals↗

PubMed2001

Nitric oxide modulates spontaneous cord dorsum potentials in the cat spinal cord.

A previous study has shown that lumbar spontaneous cord dorsum potentials (CDPs) are produced by background activity of a neuronal ensemble located in the dorsal horn. Here, the effects produced by intravenous application of the nitric oxide synthase inhibitor L-N(G)-nitro arginine (L-NOARG, 100 microg/kg) and of the nitric oxide donor 3-morpholinosydnonimine hydrochloride (SIN-1, 500 microg/kg) on spontaneous CDPs were examined. Experiments were performed on pentobarbitally anesthetized, paralyzed and spinalized cats. The amplitude of spontaneous CDPs increased after L-NOARG, however, decreased after SIN-1. These observations suggest that electrical activity of dorsal horn neurones generating spontaneous CDPs is dependent on nitric oxide production.

Action Potentials↗

PubMed2001

[Pneumonia in patients with chronic lymphocytic leukemia. Study of 30 episodes].

BACKGROUND: To analyse the etiology, diagnostic methods and response to therapy in 30 episodes of pneumonia diagnosed in 17 patients with chronic lymphocytic leukemia (CLL) between 1995 and 2000. PATIENTS AND METHOD: In each episode of pneumonia the following data were analysed: age, gender, treatment of CLL, antiinfectious prophylaxis, granulocytopenia, CD4/CD8 lymphocytes ratio, hipogammaglobulinemia, origin of pneumonia (nosocomial or community-acquired), localisation, respiratory insufficiency, need for mechanical ventilation, antimicrobial therapy and response. Diagnostic methods included blood and sputum cultures, fiberoptic bronchoscopy and search for antigens in urine (Legionella pneumophila serogroup 1, galactomannan, and Streptococcus pneumoniae). RESULTS: Median age of the series was 60 yr. (range 50-86) and 12 patients were male. Chlorambucil and prednisone were used in 13 cases and fludarabine in 8. Granulocytopenia was present in 14 episodes, hypogammaglobulinemia was seen in 22 and CD4/CD8 ratio was lower than 1 in 8 out of 14 evaluable cases. Etiology of pneumonia was established in 16 episodes (53%). Fiberoptic bronchoscopy was the most useful technique (83% of positive diagnoses) followed by blood cultures (38%). Two patients were diagnosed of aspergillosis at autopsy. Pneumococcus was the most frequent agent (5 cases) followed by Pseudomonas aeruginosa (4), Pneumocystis carinii (2) and Aspergillus fumigatus (2). One out of the two patients with P. carinii pneumonia had received fludarabin and the remaining was treated with prednisone for long time. Ten patients (30%) had died: P. aeruginosa (3 cases), P. carinii (2), A. fumigatus (2), Mycobacterium xenopi (1), and unknown microorganism (2). CONCLUSIONS: In this series of CLL patients the frequency of etiologic diagnosis of pneumonias was good. Pneumococcus was the most frequent microorganism. Pneumonias caused by opportunistic microorganisms were associated to the treatment with fludarabin or prednisone and were associated to a high mortality rate.

Aged↗