Biomedical subjects

Luis Hernandez

Publications and source records attributed to Luis Hernandez.

11 recordsLinked to original sources

PubMed2006

Toxoplasma gondii infection lower anxiety as measured in the plus-maze and social interaction tests in rats A behavioral analysis.

It has been suggested that the parasite Toxoplasma gondii reduces the fear of rodents toward their feline predators, which may lead to an augmented rate of predation and multiplication of the parasite through an increased number of life cycles. To investigate whether T. gondii infection induces selective effects on behavior associated with anxiety, Wistar rats were inoculated i.p. with several doses of T. gondii tachyzoites and tested in two animal tests of anxiety. In the third week following inoculation, rats infected with 100 and 1000 tachyzoites increased plus-maze open arm exploration in a dose-related manner. However, no effect was detected in either social interaction levels or motor activity measures. In the seventh week after inoculation, rats infected with 100 and 1000 tachyzoites showed increased open arm exploration and social investigation without change on any motor activity measures. However, rats infected with a higher dose (1500 tachyzoites) showed a drop in locomotion. These data support the hypothesis that T. gondii impairs mechanism of warning as a function of reduced anxiety. The pattern of brain colonization by the parasite and the host immune response suggests that the predominant invasion to limbic areas works as a natural anxiolytic mechanism.

Animals↗

PubMed2006

Analysis of security problems in a medical image encryption system.

Recently, a new system for the secure transmission and efficient storage of medical images interleaved with patient information has been proposed in 2003 by Rajendra Acharya et al. In this paper, we analyse the security of this system, showing how to improve it to obtain a truly secure system.

Algorithms↗

PubMed2005

Accounting for nonlinear BOLD effects in fMRI: parameter estimates and a model for prediction in rapid event-related studies.

Nonlinear effects in fMRI BOLD data may substantially influence estimates of task-related activations, particularly in rapid event-related designs. If the BOLD response to each stimulus is assumed to be independent of the stimulation history, nonlinear interactions create a prediction error that may reduce sensitivity. When stimulus density differs among conditions, nonlinear effects can cause artifactual differences in activation. This situation can occur in rapid event-related designs or when comparing blocks of unequal lengths. We present data showing substantial nonlinear history effects for stimuli 1 s apart and use estimates of nonlinearities in response magnitude, onset time, and time to peak to form a low-dimensional parameterization of these nonlinear effects. Our estimates of nonlinearity appear relatively consistent throughout the brain, and these estimates can be used to form adjusted linear predictors for future rapid event-related fMRI studies. Adjusting the linear model for these known nonlinear effects results in a substantially better model fit. The biggest advantages to using predictors adjusted for known nonlinear effects are (1) higher sensitivity at the individual subject level of analysis, (2) better control of confounds related to nonlinear effects, and (3) more accurate estimates of design efficiency in experimental fMRI design.

Adolescent↗

PubMed2004

Tonic and phasic alteration in amygdala 5-HT, glutamate and GABA transmission after prefrontal cortex damage in rats.

The relationship between the ventromedial prefrontal cortex and the amygdala during the presentation of an unconditioned fear stimulus was assessed. Rats underwent bilateral ibotenic acid or vehicle administration into the ventromedial prefrontal cortex. Five weeks later, the behavior as well as the neurochemical changes in the amygdala was evaluated before and after a brief cat presentation. Lesioned animal freezing behavior increased 10 times when compared to controls. In the right basolateral amygdala, basal concentrations of 5-HT, 5-HIAA, glutamate and serine were elevated but basal level of GABA was diminished in lesioned animals relative to controls. Sham but not lesioned animals increased 5-HT and decreased GABA and serine levels after cat presentation. Phasic changes in glutamate were not detected either in lesioned or shams but the difference in amygdala glutamate between lesioned and shams persisted after cat presentation. These data show that increased serotonin and glutamate tone and decreased gabaergic tone in the amygdala correlate to elevated fear and anxiety after prefrontal cortex ibotenic acid lesion. The lesion also seems to produce a failure of adaptive changes in neurotransmitter systems revealing lost of control of the ventromedial prefrontal cortex over the amygdala in frightening situations.

Amygdala↗

PubMed2004

Pilot study of fixed-infusion rate gemcitabine with Cisplatin and dexamethasone in patients with relapsed or refractory lymphoma.

Management of patients with multiple-relapsed lymphoma meets with little success. The optimal use of available drugs in this situation is often unknown. Gemcitabine has documented efficacy in this setting. Pharmacodynamic data suggest that the optimal use may involve a fixed-rate infusion and coadministration with platinum compounds. In this study we explored the use of gemcitabine starting at a dose of 800 mg/m(2) administered at a fixed infusion rate of 10 mg/m(2) per minute with cisplatin 35 mg/m(2) intravenously, both given on day 1, and dexamethasone 20 mg daily for 4 days; the treatment was given every 2 weeks (days 1 and 15 of a 28-day cycle) for the treatment of relapsed Hodgkin's and non-Hodgkin's lymphoma. Dose escalation of gemcitabine was allowed according to phase I criteria. Twenty-two patients with a median of 4 prior treatments were enrolled (Hodgkin's lymphoma, n = 7; B-cell non-Hodgkin's lymphoma, n = 9; T-cell non-Hodgkin's lymphoma, n = 6). Ten patients had relapsed after prior autologous transplantation. Grade 4 thrombocytopenia and neutropenia were the dose-limiting toxicities and occurred in 9 patients (41%) and 4 patients (18%), respectively. Initial dose escalation of gemcitabine was not possible. Responses were observed in 45% of the patients: 2 of 5 with T-cell non-Hodgkin's lymphoma (1 patient withdrew after first treatment and was evaluable only for toxicity), 4 of 7 with Hodgkin's lymphoma, and 4 of 9 with B-cell non-Hodgkin's lymphoma. The coadministration of gemcitabine 800 mg over 80 minutes with low-dose cisplatin and dexamethasone is feasible and sufficiently active in a heavily pretreated patient population with lymphoma.

Adult↗

PubMed2003

Anxiolysis followed by anxiogenesis relates to coping and corticosterone after medial prefrontal cortical damage in rats.

Medial prefrontal cortex (MPFC) damage causes profound behavioral and neuroendocrine alterations. However, many reports have been inconsistent regarding the direction of these effects. We hypothesized that the lesion recovery stage might be a key factor generating discrepancies. To examine changes over time following ibotenic acid lesion in the ventral part of the MPFC, behavioral and endocrine testing was conducted on the second and the fifth week after lesioning. On the second post-lesion week, bilaterally lesioned animals increased social interaction and swimming scores and their corticosterone response to restraint was exaggerated as compared with shams. On the fifth post-lesion week, social interaction and swimming scores were diminished in bilaterally lesioned animals; their basal plasma corticosterone was enhanced, while their corticosterone increase under restraint was blunted relative to shams. These results reveal that the emotional and endocrine responses to stress vary as a function of time following MPFC lesion, which may help to reconcile conflicting reports on effect direction. The role of the MPFC in anxiety, ability to cope with stress and adrenal regulation is also discussed.

Animals↗

PubMed2003

Switching attention and resolving interference: fMRI measures of executive functions.

Is there a single executive process or are there multiple executive processes that work together towards the same goal in some task? In these experiments, we use counter switching and response inhibition tasks to examine the neural underpinnings of two cognitive processes that have often been identified as potential executive processes: the switching of attention between tasks, and the resolution of interference between competing task responses. Using functional magnetic resonance imaging (fMRI), for both event-related and blocked design tasks, we find evidence for common neural areas across both tasks in bilateral parietal cortex (BA 40), left dorsolateral prefrontal cortex (DLPFC; BA 9), premotor cortex (BA 6) and medial frontal cortex (BA 6/32). However, we also find areas preferentially involved in the switching of attention between mental counts (BA 7, BA 18) and the inhibition of a prepotent motor response (BA 6, BA 10), respectively. These findings provide evidence for the separability of cognitive processes underlying executive control.

Adolescent↗

PubMed2003

Extracellular glutamate increases in the lateral hypothalamus during meal initiation, and GABA peaks during satiation: microdialysis measurements every 30 s.

Glutamate injected into the lateral hypothalamus can initiate eating, and gamma-aminobutyric acid (GABA) can stop it. This leads to the hypothesis that glutamate inputs are active at the beginning of a meal, and GABA is released at the end. To test this theory, the authors used microdialysis to sample glutamate and GABA simultaneously before, during, and after a meal. Food-deprived rats ate a meal of chow. Glutamate increased during the first third of the meal, then decreased to below baseline while the rats were still eating. GABA also increased at the start of the meal but continued rising and peaked during the last third of the meal. Glutamate may drive a hypothalamic system for eating, and GABA may oppose it.

Animals↗

PubMed2002

Endobronchial hamartoma.

OBJECTIVES: To describe clinical, endoscopic, radiographic, and follow-up characteristics of a series of patients in whom endobronchial hamartoma (EH) had been diagnosed. METHODS: Retrospective study of all cases of hamartoma diagnosed by bronchial biopsy between 1974 and 1997 in a tertiary referral hospital in Madrid, Spain. RESULTS: EH was diagnosed 47 patients during the study period. Four patients were excluded from the study because no clinical history was available. We analyzed the cases of 43 patients (37 men and 6 women), with a mean (+/- SD) age of 62 +/- 12 years. Seven patients had a concurrent lung neoplasm, and the EH was an incidental endoscopic finding. Among the other 36 patients, 31 had a new onset of respiratory symptoms, most commonly, recurrent respiratory infections in 16 patients (44%) and hemoptysis in a further 12 patients (33.4%). Chest radiograph findings were abnormal in 38 of 43 patients. At bronchoscopy, the lesions were equally distributed throughout the right and left lungs with no clear lobar predilection. Endobronchial obstruction was evident in 26 patients (72.2%) without concurrent neoplasm, 17 of whom underwent resection with a rigid bronchoscope and laser, with total resolution in 13 patients. Partial resolution was achieved in four patients, two of whom needed a second endoscopic procedure. Five patients were treated with open lung surgery. Clinical and endoscopic follow-up was performed in 23 patients at 1 to 73 months (mean, 17 months), and recurrence was found in 4 patients. CONCLUSION: EH frequently produces respiratory complaints and radiographic abnormalities. Patients with endobronchial obstructions had satisfactory responses to endoscopic therapy.

Adult↗

PubMed2002

Temporal sensitivity of event-related fMRI.

The temporal resolution of event-related fMRI is limited by the low sampling rate of typical MR whole brain protocols and by the slow rate of the BOLD response. Within the assumptions of the General Linear Model, we explore the tolerance of regression analyses of fMRI data to errors in the timing of the model relative to the experimental data under a number of circumstances. Given the sensitivity of the analysis to temporal shifts of the model relative to the data, one can search for the time a neuronal event occurs with temporal resolution on the order of a few hundred milliseconds with 95% confidence. This confidence level is strongly dependent on the signal-to-noise ratio of the observed BOLD responses (approximately +/-200 ms in our example of visual stimulation data collected at 1.5 T).

Algorithms↗

PubMed2000

Noxious stimulation increases glutamate and arginine in the periaqueductal gray matter in rats: a microdialysis study.

The periaqueductal gray matter (PAG) is an important center in the modulation of behavioral responses during nociception and stress. In the present experiment, extracellular excitatory amino acid overflow in the PAG was measured every 30 s during noxious stimulation. A combination of in vivo brain microdialysis in freely moving rats and capillary zone electrophoresis with laser induced-fluorescence detection allowed us to detect short lasting changes of excitatory amino acid in dialysates. A formalin injection in the hindpaw of the rat increased glutamate, arginine and aspartate concentration in PAG dialysates. This increase was calcium and nerve impulse-dependent, suggesting neuronal and glial origin of glutamate and arginine, respectively. Handling, pinching or saline injection in the hind paw did not increase glutamate showing that this neurochemical phenomenon is related to painful and persistent noxious stimulation. The results suggest that a rapid excitation of the PAG occurs during noxious stimulation. The role of glutamate and arginine in analgesia is discussed.

Animals↗