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J M Alonso

Publications and source records attributed to J M Alonso.

At least 73 records · Page 4Linked to original sources
PubMed1998

Functional connectivity between simple cells and complex cells in cat striate cortex.

In the cat primary visual cortex, neurons are classified into the two main categories of simple cells and complex cells based on their response properties. According to the hierarchical model, complex receptive fields derive from convergent inputs of simple cells with similar orientation preferences. This model received strong support from anatomical studies showing that many complex cells lie within the range of layer IV simple-cell axons but outside the range of most thalamic axons. Physiological evidence for the model, however, has remained elusive. Here we demonstrate that layer IV simple cells and layer II and III complex cells show correlated firing consistent with monosynaptic connections. As expected from the hierarchical model, all connections were in the direction from the simple cell to the complex cell, most frequently between cells with similar orientation preferences.

Animals↗
PubMed1998

Coding of visual information by precisely correlated spikes in the lateral geniculate nucleus.

Correlated firing among neurons is widespread in the nervous system. Precisely correlated spiking, occurring on a millisecond time scale, has recently been observed among neurons in the lateral geniculate nucleus with overlapping receptive fields. We have used an information-theoretic analysis to examine the role of these correlations in visual coding. Considerably more information can be extracted from two cells if temporal correlations between them are considered. The percentage increase in information depends on the degree of correlation; the average increase is approximately 20% for strongly correlated pairs. Thus, precise temporal correlation could be used as an additional information channel from thalamus to visual cortex.

Action Potentials↗
PubMed1998

Effective prophylaxis of influenza A virus pneumonia in mice by topical passive immunotherapy with polyvalent human immunoglobulins or F(ab')2 fragments.

The effectiveness of polyvalent plasma-derived human immunoglobulins (IVIG) in passive immunotherapy of influenza virus pneumonia was assessed, using the Strain Scotland (A/Scotland/74 (H3N2)) adapted to BALB/c mice by repeated lung passages. Haemagglutinin antibodies in two batches of IVIG at 10 mg/ml had a titre of 1/16. Intravenous injection of 1000-5000 microg of IVIG, 3 h after infection, gave 60-70% protection, whereas intranasal injection of 25-50 microg protected 90% of mice infected with a lethal dose of influenza virus. F(ab')2 fragments were at least as protective as intact IVIG, suggesting that complement or Fcgamma receptor-bearing cells were not required. Topical passive immunotherapy with IVIG or F(ab')2 gave protection up to 8 h after infection, but not at 24 h, suggesting that anti-influenza A antibodies in IVIG, delivered locally, are only effective at early stages of the infectious process. The potential value of topical administration of IVIG or F(ab')2 fragments for influenza A pneumonia prophylaxis was further demonstrated by the protective effects of their intranasal administration 24 h before challenge.

Animals↗
PubMed1998

Kinetics of Chlamydia trachomatis clearance in patients with azithromycin, as assessed by first void urine testing by PCR and transcription-mediated amplification.

METHODS: Test-of-cure of 19 patients with Chlamydia trachomatis genital infection was assessed by daily collection of first void urine for 7 days just after treatment by azithromycin single-dose. RESULTS: Detection by PCR and TMA of C. trachomatis showed a good correlation between both methods. The observation that post-therapy chlamydial nucleic acid detection is associated to bacterial clearance suggests that all the patients were cured.

Anti-Bacterial Agents↗
PubMed1998

Evaluation of a new competitive immunoassay (BioElisa Syphilis) for screening for Treponema pallidum antibodies at various stages of syphilis.

The BioElisa Syphilis, a new competitive enzyme immunoassay (EIA) for Treponema pallidum whole antigen that uses specific human immunoglobulin G (IgG) antibodies as the competitor, was evaluated for potential use in screening for syphilis at various stages. The results obtained by this competitive EIA were compared with those obtained by the fluorescent treponemal antibody absorption (FTA-abs) test and the T. pallidum hemagglutination assay (TPHA). Serum samples from 434 patients with positive TPHA and FTA-abs test results, including patients with primary, latent, secondary, and tertiary syphilis and neurosyphilis, were investigated. Two samples tested negative by competitive EIA but were weakly reactive by the TPHA and the FTA-abs test. Sixteen serum samples from patients with clinically documented active syphilis, including several patients infected with human immunodeficiency virus, tested positive by the competitive EIA. There was a direct inverse correlation between EIA indices and titers in the TPHA and the FTA-abs test for all samples that tested positive. Specificity was assessed by testing 358 serum samples which tested negative for syphilis by TPHA and the FTA-abs test, including 100 serum samples from patients with documented infectious or autoimmune diseases. Only two serum samples gave a weakly positive EIA result. Thus, competitive EIA had a sensitivity of 99.5% and a specificity of 99.4% relative to the results of the FTA-abs test and TPHA. Our evaluation shows that BioElisa Syphilis is a sensitive, specific, and simple assay for screening for syphilis.

Antibodies, Bacterial↗
PubMed1998

[Epidemiology and epizootiology of plague: the major role of the surveillance of reservoir populations of wild rodents in the control of permanent foci].

Plague is a bacterial infection, due to Yersinia pestis. It is essentially a zoonosis of rodents, communicable from rodent to rodent and from rodent to man by flea bite. From the first human case, acquired from rodents, interhuman transmission occurs by means of flea bite (bubonic plague) or is airborne (primary pulmonary plague). Long term implantation of plague amongst wild rodents populations after the third pandemic (1894 to present), created inveterate foci in all continents, except Europe. Those wild rodents settlements in arid biotopes, preserved from human activities, represent the main reservoir of plague. Their determination is mandatory for the surveillance of epizootics and the prevention of epidemics.

Animals↗
PubMed1997

Cutaneous hyalohyphomycosis caused by Fusarium solani in a loggerhead sea turtle (Caretta caretta L.).

Fusarium solani was reported as the agent of a cutaneous infection in an injured sea turtle collected in the Mediterranean Sea. The turtle was treated with both a topical 10% solution of iodine in alcohol and ketoconazole. The source of the causal agent was traced to the sand in the tank in which the turtle was maintained. The strain was only sensitive in vitro to amphotericin B and was resistant to 5-fluorocytosine, fluconazole, itraconazole, and ketoconazole.

Administration, Topical↗
PubMed1997

Clinical and molecular study of Corynebacterium diphtheriae systemic infections in France. Coryne Study Group.

Diphtheria is a disease with a long history that almost completely disappeared from developed countries. In addition, until 1987, systemic infections involving Corynebacterium diphtheriae were rare. However, in 1990, an epidemic occurred in Russia. These two circumstances have provided the stimulus to gain insight into the situation in France. In fact, between 1987 and 1993, a total of 59 C. diphtheriae strains were isolated. Epidemiological data were collected for patients from whom 40 strains were isolated from normally sterile sites, including 34 from blood cultures, and half of the bacteremic patients developed endocarditis. Osteoarticular involvement was noted in 11 of these 40 patients, including 5 bacteremic patients. The fatality rate following bacteremia was 36%, despite specific antibiotic treatment (beta-lactams and aminoglycosides). The mean age of the participants was 38 years, with half of the patients subsisting under low socioeconomic conditions and suffering from homelessness or alcoholism. Apparently, the skin turned out to be the major route of transmission in this reemerging disease. Eighty-eight percent of the isolates belonged to the C. diphtheriae biotype mitis. These were found predominantly in the Paris area, and most were of the same ribotype. Those isolates originating from the overseas territories (Guyana and New Caledonia) belonged to C. diphtheriae biotype gravis. No strains were positive for the tox gene by PCR. This study attests to the persistent circulation in France of C. diphtheriae in the form of systemic infections. The matter is especially significant since these strains are nontoxigenic and are of a unique ribotype. The strains are, however, sensitive to most antibiotics, although 20% are rifampin resistant.

Adolescent↗
PubMed1997

[Role of macrophages in papillomavirus infections].

Papillomaviruses have naturally a strict tropism to epithelial cells in which they replicate during the cell differentiation. There is no histological evidence of any inflammatory reaction. No leucocyte recruitment is observed and thus, the role of macrophages during the early infectious process in the epithelium remains unknown. This silent, subacute or chronic infectious disease is characterized fundamentally by a dual pathogenic process, including an infectious process leading to the production of infective virus particles during the differentiation of infected epithelial cells, on the one hand, and an oncogenic process due to interactions of viral oncogenes with host cell regulatory proteins after integration of the virus to the cellular genome. The role of activated macrophages on the oncogenic process is clearly established. They contribute to regulate negatively the transcription of the non structural E6 E7 viral oncogenes and have cytotoxic effects to transformed cells by a direct intercellular contact without evidence of an effect due to a soluble factor such as tumor-necrotizing factor (TNF). Macrophages have, hence, a prominent role as cellular effectors of protective immunity against lesions due to papillomaviruses and particularly against the oncogenic process complicating these infections.

Cytotoxicity, Immunologic↗
PubMed1996

Precisely correlated firing in cells of the lateral geniculate nucleus.

Simple cells within layer IV of the cat primary visual cortex are selective for lines of a specific orientation. It has been proposed that their receptive-field properties are established by the pattern of connections that they receive from the lateral geniculate nucleus (LGN) of the thalamus. Thalamic inputs, however, represent only a small proportion of the synapses made onto simple cells, and others have argued that corticocortical connections are likely to be important in shaping simple-cell response properties. Here we describe a mechanism that might be involved in selectively strengthening the effect of thalamic inputs. We show that neighbouring geniculate neurons with overlapping receptive fields of the same type (on-centre or off-centre) often fire spikes that are synchronized to within 1 millisecond. Moreover, these neurons often project to a common cortical target neuron where synchronous spikes are more effective in evoking a postsynaptic response. We propose that precisely correlated firing within a group of geniculate neurons could serve to reinforce the thalamic input to cortical simple cells.

Action Potentials↗
PubMed1996

Neisseria gonorrhoeae RNA/DNA hybridization and culture for screening of gonococcal infections in a low-prevalence population.

Gonorrhea is still a major sexually transmitted disease (STD) worldwide. Its etiologic diagnosis is based on identification of the causative agent, Neisseria gonorrhoeae, by culture of genital secretions, which is often hampered by difficulties of sample collection and transport. Alternatively, nucleic acid hybridization techniques for routine diagnosis of N. gonorrhoeae appear to be useful by eliminating problems associated with bacterial viability, particularly for surveillance of low-prevalence populations. Our study among 1,508 outpatients undergoing routine examination for common STDs used RNA/DNA hybridization with a DNA probe specific for N. gonorrhoeae (Gen Probe Pace 2) and classical culture. Of the 1,750 specimens tested, 12 were positive by DNA probe and culture. In 8 cases, only DNA probe was positive while culture was negative. In 3 of these discrepant cases clinical and epidemiological data suggested true N. gonorrhoeae infection. Thus, DNA probe assay for N. gonorrhoeae may greatly improve screening of N. gonorrhoeae among low-prevalence populations. However, culture remains mandatory for testing antimicrobial resistance of these highly communicable infectious agents.

Acridines↗
PubMed1996

The processing and encoding of information in the visual cortex.

Our knowledge of the response properties of visual cortical neurons has increased steadily since the original studies of Hubel and Wiesel in the 1960s. By comparison, an understanding of the neural mechanisms responsible for these properties has proved more elusive. Models for the mechanisms involved in even the most basic responses, such as the orientation tuning of simple cells in the primary visual cortex of the cat, remain controversial. Recent studies, however, are providing further support for a simple model (first suggested by Hubel and Wiesel), in which it is hypothesized that the response properties of simple cells in layer 4 of the cortex are dominated by the convergence of highly specific thalamic inputs.

Animals↗
PubMed1996

Passive and active immunotherapy for experimental pneumococcal pneumonia by polyvalent human immunoglobulin or F(ab')2 fragments administered intranasally.

Experimental pneumococcal pneumonia in leukopenic BALB/c mice enabled evaluation of passive immunotherapy with human polyvalent intravenous immune globulin (IVIG) given intravenously or intranasally and with F(ab')2 fragments administered intranasally. For intravenous and intranasal IVIG, the respective effective doses were < 5 but > 0.5 mg/kg and < 250 but > 2.5 micrograms/kg. For F(ab')2 fragments, the effective dose was < 500 but > 2.5 micrograms/kg. Assessment of the acquired immune responses of passively protected mice and convalescing controls 3 weeks after primary infection showed that antibody responses to whole bacteria were serotype-specific in all mice. Mice protected with IVIG and F(ab')2 fragments had more antibodies to pneumolysin than did controls. In addition, treated mice acquired greater resistance to reinfection than untreated survivors. Thus, local passive immunotherapy may be an effective means of treating pneumococcal pneumonia and may promote acquired resistance to reinfection.

Administration, Intranasal↗
PubMed1996

Assessment of two penicillins plus beta-lactamase inhibitors versus cefotaxime in treatment of murine Klebsiella pneumoniae infections.

The in vivo efficacies of piperacillin, piperacillin plus tazobactam, ticarcillin, ticarcillin plus clavulanic acid, piperacillin plus clavulanic acid, and cefotaxime were compared in a mouse model of pneumonia induced by the SHV-1 beta-lactamase-producer Klebsiella pneumoniae. Each antibiotic was injected either once intraperitoneally at 24 h postinfection or at repeated times during 24 h. The efficacies of the drugs and therapeutic protocols were assessed by counting viable bacteria recovered from the lungs of mice sacrificed at selected times. No emergence of beta-lactam-resistant organisms was detected. Ticarcillin at 300 mg/kg was ineffective. Repeated injections of piperacillin at 300 mg/kg, either alone or in combination with tazobactam (8:1), led to a significant decrease in bacterial counts, but this was followed by bacterial regrowth. The pharmacokinetic analysis demonstrated that this short-lasting antibacterial effect was not due to a failure of piperacillin and/or tazobactam to penetrate the lungs. The combinations of ticarcillin at 300 mg/kg plus clavulanic acid (15:1) and piperacillin at 300 mg/kg plus tazobactam (4:1) were proven to be effective in that they decreased the bacterial burden in the lungs from 10(5) to < 10(3) CFU. This dose effect of tazobactam can be explained by its dose-dependent penetration in the lungs. Cefotaxime at 100 mg/kg and the combination of piperacillin (slightly hydrolyzed by SHV-1) at 300 mg/kg plus clavulanic acid (15:1) led to the best efficacy. Both of these treatments induced a decrease in bacterial counts of nearly 4 log10 units. The survival rates correlated with the quantitative measurements of in vivo bacterial killing. These experimental results obtained from the restricted animal model used here may help in the design of further protocols for clinical trials.

Animals↗
PubMed1996

Receptive field asymmetries and sensitivity to random dot stereograms.

The differences between the two monocular receptive fields of cortical cells were measured and compared to their disparity tuning in the awake behaving monkey. Several receptive field properties (direction selectivity, orientation preference, eye preference and response modulation) were determined for each eye using sweeping bright bars. The disparity sensitivity of these cells was also assessed by plotting their response profile, determined for each cell under strictly binocular cyclopean stimulation (dynamic random dot stereograms, RDS). We have found that large differences between the two monocular receptive fields were infrequent and, apparently, not related with the disparity sensitivity profile. We conclude that the monocular asymmetries tested in this study and the sensitivity to positional binocular disparities present in RDS, might be linked to different mechanisms involved in depth perception in the visual system.

Animals↗
PubMed1995

Visually evoked calcium action potentials in cat striate cortex.

Early intracellular studies of cerebral cortical neurons indicated that synaptic input evokes dendritic action potentials that convey information towards the soma. Subsequent work in vitro established that neocortical neurons produce dendritic Ca2+ action potentials. To determine whether natural stimuli elicit Ca2+ spikes, we combined the techniques of whole-cell recording, pharmacology and quantitative receptive field mapping. Our findings show that visual stimulation routinely evoked Ca2+ spikes in distinct functional and anatomical classes of cells in different layers of the cat striate cortex. Hence regenerative Ca2+ potentials appear to play a role in both the initial and later stages of cortical sensory processing.

Action Potentials↗
PubMed1995

Specificity of monosynaptic connections from thalamus to visual cortex.

In cortical area 17 of the cat, simple receptive fields are arranged in elongated subregions that respond best to bright (on) or dark (off) oriented contours, whereas the receptive fields of their thalamic inputs have a concentric on and off organization. This dramatic transformation suggests that there are specific rules governing the connections made between thalamic and cortical neurons (see ref. 4). Here we report a study of these rules in which we recorded from thalamic (lateral geniculate nucleus; LGN) and cortical neurons simultaneously and related their receptive fields to their connectivity, as measured by cross-correlation analysis. The probability of finding a monosynaptic connection was high when a geniculate receptive field was superimposed anywhere over an elongated simple-cell subregion of the same signature (on or off). However, 'inappropriate' connections from geniculate cells of the opposite receptive field signature were extremely rare. Together, these findings imply that the outline of the elongated, simple receptive field, and thus of cortical orientation selectivity, is laid down at the level of the first synapse from the thalamic afferents.

Animals↗