Biomedical subjects

M M González

Publications and source records attributed to M M González.

8 recordsLinked to original sources

PubMed2003

A gamma-ray burst with a high-energy spectral component inconsistent with the synchrotron shock model.

Gamma-ray bursts are among the most powerful events in nature. These events release most of their energy as photons with energies in the range from 30 keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical, and soft X-ray afterglows. The data are in general agreement with a relativistic shock model, where the prompt and afterglow emissions correspond to synchrotron radiation from shock-accelerated electrons. Here we report an observation of a high-energy (multi-MeV) spectral component in the burst of 17 October 1994 that is distinct from the previously observed lower-energy gamma-ray component. The flux of the high-energy component decays more slowly and its fluence is greater than the lower-energy component; it is described by a power law of differential photon number index approximately -1 up to about 200 MeV. This observation is difficult to explain with the standard synchrotron shock model, suggesting the presence of new phenomena such as a different non-thermal electron process, or the interaction of relativistic protons with photons at the source.

Journal Article↗

PubMed2000

Continuous sorbent preconcentration for the electrothermal atomic absorption spectrometric determination of ultratrace amounts of cobalt in milled wheat fractions.

A method for the rapid determination of cobalt at ultratrace levels was applied in flour and flour byproducts (shorts and bran) obtained from various types of wheat that includes on-line preconcentration and electrothermal atomic absorption spectrometry is proposed. Solutions in 0.1 mol/L HNO(3) of milled wheat fractions subjected to wet ashing are preconcentrated in a straightforward flow-injection system by sorption on a RP-C(18) column following chelation. The eluent, ethanol, is carried by an air stream, and the chelate is eluted and collected in a 500 microL PTFE autosampler cup. The determination of cobalt features a precision (RSD) of 6% for a concentration of 0.2 ng/mL and a sensitivity (slope of the calibration graph) of 0.38 +/- 0.03 A s x ng/mL. The cobalt content in each type of wheat was found to be influenced by its geographical origin and texture. Also, it was found to depend on the amount of bran present in the milled wheat fraction. On the other hand, it is not significantly affected by the technological processes involved in wheat milling at a flour-producing factory.

Cobalt↗

PubMed1998

Noradrenaline neurotoxin DSP-4 effects on sleep and brain temperature in the rat.

N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) has a selective degenerative effect on noradrenergic fibers originating from locus coeruleus (LC) neurons. In the present study, we studied its effect on vigilance states and brain temperature by continuous recordings for periods of 1-5 days and 2-4 weeks following DSP-4 treatment. On the first day, paradoxical sleep duration was significantly decreased (-67%, P < 0.05), slow-wave sleep (SWS) duration increased (+16%, P < 0.05) up to 48 h after DSP-4 treatment (+8%, P < 0.05) and the wake period decreased (-8%, P < 0.05). The vigilance states returned to control values 4-5 days later. The brain temperature was decreased during the first night (-2 degrees C) and then recovered the control values. Two and 4 weeks after DSP-4 treatment, paradoxical sleep was still decreased (-18% and -23%, respectively, P < 0.05), while SWS was significantly increased only at night during the fourth week (+23%, P < 0.05). These results therefore provide evidence for a differential involvement of the noradrenergic LC system in sleep mechanisms depending on the light-dark cycle. Different hypotheses are proposed.

Adrenergic Agents↗

PubMed1998

Involvement of stress in the sleep rebound mechanism induced by sleep deprivation in the rat: use of alpha-helical CRH (9-41).

A previous study demonstrated the efficacy of the corticotropin-releasing hormone (CRH) receptor antagonist, alpha-helical CRH (9-41), in blocking the paradoxical sleep increase induced by stress. In the present study, this peptide was used to evaluate the involvement of the stress component of the sleep deprivation, in the paradoxical sleep rebound. Rats were subjected for 10 h to the classical water-tank sleep-deprivation technique and were given, every 2 h throughout the sleep deprivation period, intracerebroventricular injections of either 100 microg/5 microl of alpha-helical CRH (9-41) or vehicle alone. Continuous recordings showed that antagonist treatment decreased the PS rebound, but not the SWS rebound, following sleep deprivation. These findings suggest that, in the water-tank sleep deprivation method, stress, acting via CRH activation, is the main factor inducing the paradoxical sleep rebound.

Animals↗

PubMed1997

Effect of intracerebroventricular administration of alpha-helical CRH (9-41) on the sleep/waking cycle in rats under normal conditions or after subjection to an acute stressful stimulus.

It has been shown in a previous study that specific lesioning of the noradrenergic system of the locus coeruleus abolished the sleep increase induced by immobilization stress. Given the fact that brain corticotropin-releasing hormone (CRH) acts as a neurotransmitter in the locus coeruleus under stress conditions, the present study was designed to investigate the involvement of CRH in the sleep increase seen after immobilization stress and on the spontaneous wake/sleep cycle. One hundred micrograms of the specific CRH receptor antagonist alpha-helical CRH (9-41), or vehicle alone was injected into the right lateral ventricle 30 min either before subjecting the animals to immobilization stress or before the spontaneous sleep-waking recordings onset. A single intracerebroventricular (i.c.v.) injection of alpha-helical CRH (9-41) had no effect on spontaneous paradoxical sleep but abolished the stress-induced increase, while wakefulness and slow-wave sleep were unchanged under both normal and stressful conditions. We therefore report that the involvement of endogenous CRH in the paradoxical sleep mechanism is dependent on the environmental conditions and suggest that, while the paradoxical sleep increase induced by immobilization stress may be mediated by endogenous corticotropin-releasing hormone, other mechanisms, either CRH-independent or situated at a distance from antagonist activity, may be involved in spontaneous paradoxical sleep. These results show, for the first time, that endogenous CRH may be involved in sleep-waking mechanisms only under stressful conditions and, in particular, as a fundamental component of the paradoxical sleep increase.

Animals↗

PubMed1996

Role of the locus coeruleus in the sleep rebound following two different sleep deprivation methods in the rat.

The aim of the present study was to assess the involvement of the locus coeruleus in the paradoxical sleep rebound following sleep deprivation in the rat. Animals were sleep-deprived for 10 h before, and after, specific N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) lesioning of the noradrenergic-locus coeruleus system. Sleep deprivation was produced using either an instrumental (water tank) or pharmacological (methylamphetamine) method. After lesioning, the rats submitted to the instrumental method showed a significant decrease in the paradoxical and slow-wave sleep rebounds (-54% and -78%, respectively), while animals receiving metamphetamine did not. Our results suggest that the noradrenergic system of the locus coeruleus is a relevant component of the sleep rebound mechanisms. However, the extent of involvement is dependent on the sleep deprivation method used.

Adrenergic Agents↗

PubMedDate not supplied

Slurry atomization of wheat-milled fractions for electrothermal atomic absorption spectrometric determination of nickel and chromium.

A slurry electrothermal atomic absorption spectrometric technique was used to determine Ni and Cr in wheat flour and its by-products. Slurries (3%, w/v) were prepared in a mixture of 15% HNO3-10% H2O2 as suspended medium. Differences in Ni and Cr contents due to origin and texture of the wheat and to the effects of the milling process were studied. Ni and Cr levels were more markedly influenced by the geographical origin of the wheat than by its texture. Both metals were related to the amount of bran present in each milled fraction and varied over the ranges of 212-298 ng/g (Ni) and 34-85 ng/g (Cr) in flours (with minimal bran contents); 297-460 ng/g (Ni) and 67-118 ng/g (Cr) in shorts; and 424-723 ng/g (Ni) and 106-165 ng/g (Cr) in brans. The Ni and Cr contents were not significantly affected by the technological processes typically performed in a flour-producing factory.

Chromium↗

PubMedDate not supplied

[Changes in gastric mucosa in acute malaria].

A high incidence rate of Malaria is observed at Bolívar state (Venezuela) and, beside classic acute symptomatology, we have observed gastric symptoms like epigastralgia, anorexia, nausea and vomits. The scope of this study is to establish changes of gastric mucosa related to Plasmodium infection, using macro and microscopic technics. One hundred both sex patients with Malaria diagnosis done with thick drop technic and gastric symptomatology were studied in our department from March 1990 to February 1991. The esophagus, stomach and duodenum of all patients were evaluated with upper digestive tract endoscopy and still photographs, and biopsies of fundus, body and antrum were taken, fixed in 10% formaldehyde and stained with hematoxylin-eosine method. P. falciparum was found in 52 cases, P. vivax in 39 and 9 infected with both, most of patients complained of shivering fever, epigastralgia (76%), nausea and vomits (72%), tartness (25%) and burning pain (21%). Mucosal edema and congestion (gastritis) were the endoscopic findings in 88% of cases, usually located at antrum (67%) and fundus (33%). The microscopic findings were: mucosal edema (90%), superficial bleeding (87%), microthrombosis (60%), gastric atrophy (40%) and intestinal metaplasia (8%). Acute gastric symptomatology we have observed in patients with acute malaria my be due to microthrombosis and arteriolar occlusion, leading to ischemic changes and mucosal edema. These pathophysiological changes explain most of upper digestive tract symptoms in acute malaria, particularly when agent is P. falciparum. We have not found related papers in bibliography.

Acute Disease↗