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G Garreffa

Publications and source records attributed to G Garreffa.

7 recordsLinked to original sources
PubMed2003

Issues concerning the construction of a metabolic model for neuronal activation.

The metabolic events underlying neuronal activity still remain the object of intense debate, in spite of the considerable amount of information provided from different experimental techniques. Indeed, several attempts at linking the cellular metabolic phenomena with the macroscopic physiological changes have not yet attained foolproof conclusions. The difficulties in drawing definitive conclusions are due primarily to the heterogeneity of the experimental procedures used in different laboratories, and also given the impossibility of extrapolating the findings obtained under stationary conditions (prolonged stimulation) to dynamic and transient phenomena. Recently, lactate has received much attention, following its proposal by Pellerin and Magistretti (1994; Proc. Natl. Acad. Sci. USA 91:10625-10629), instead of glucose, as the main substrate for neurons during activity. Several challenging aspects suggest the return to a more conventional view of neuronal metabolism, in which neurons are able to metabolize ambient glucose directly as their major substrate, also during activation.

Animals↗
PubMed2003

The aerobic brain: lactate decrease at the onset of neural activity.

The metabolic events of neuronal energetics during functional activity are still partially unexplained. In particular, lactate (and not glucose) was recently proposed as the main substrate for neurons during activity. By means of proton magnetic resonance spectroscopy, lactate was reported to increase during the first minutes of prolonged stimulation, but the studies reported thus far suffered from low temporal resolution. In the present study we used a time-resolved proton magnetic resonance spectroscopy strategy in order to analyse the evolution of lactate during the early seconds following a brief visual stimulation (event-related design). A significant decrease in lactate concentration was observed 5 s after the stimulation, while a recovering of the baseline was observed at 12 s.

Adult↗
PubMed1999

[Rationale and limits of echo planar magnetic resonance imaging].

INTRODUCTION: The use of Echo Planar Imaging (EPI) techniques has extensively increased in the last few years. The technical improvements in new Magnetic Resonance Imaging (MRI) systems satisfy the instrumental requirements for these complex high-speed methods. The latest commercial systems are provided with standard EPI sequences. The increased data acquisition speed which characterizes EPI opens new and interesting perspectives, although the resolution is lower than the one typically achieved with conventional imaging. MATERIALS AND METHODS: The description of the data sampling process in terms of the k-space is a powerful tool for planning or understanding complex sequence diagrams like EPI. The basic concepts of the method are reported and discussed, pointing out the most noteworthy feature of the k-space, i.e., its Fourier inverse yield to the image. A generic pulse sequence has been considered to explain the sampling of k-space trajectories. Examples of ultrafast imaging techniques are subsequently considered and discussed. CONCLUSIONS: EPI improves the resolution time of MRI, which is an intrinsically slow imaging procedure. Images can be obtained in few tenth of a second so that MRI suits the short temporal range of many interesting physiological processes. Recently the main goal of functional Magnetic Resonance Imaging (fMRI) has been the study of brain activity related to local changes in brain hemodynamics. These changes cause MR signal intensity variations. In the last years, several brain activity studies have been performed by means of Positron Emission Tomography (PET) which involves the administration of radioactive substances; fMRI has the advantage that it is a noninvasive technique, although peripheral nerve stimulation effects should be considered.

Humans↗
PubMed1992

Partial cerebral ischemia assessed by "in vivo" 31P NMR spectroscopy in rats.

31P NMR spectroscopy was used to assess the cerebral ischemia status in rats by measuring the relative levels of phosphate metabolites. Partial cerebral ischemia was induced in 49 rats by reversible occlusion of the carotid arteries. Rats were intubated and mechanically ventilated on a hypoxic gas mixture. Physiological parameters such as temperature and arterial pressure were strictly controlled during the experiments. 31P spectra were acquired at 7 T during basal observation, for 15-20 min after the induction of ischemia, and for 1 hr after reperfusion. Depletion and increase in PCr and Pi levels, respectively, were already observable in the collected spectra within few minutes after the onset of ischemia. No appreciable changes were found in the ATP levels.

Animals↗
PubMed1992

Immiscible fluids permeability by T1 imaging.

Soil pollution by hydrocarbon compounds is an important part of the more general pollution problem. Some analogies with research problems encountered in studies of oil reservoirs in rocks suggested to us the opportunity to study the pollution dynamics by imaging the spatial distribution of the pollutant in a wet soil model by an NMR imaging technique. Some preliminary results using T1-weighted imaging are reported here.

Magnetic Resonance Spectroscopy↗
PubMed1989

Study of proton spin-lattice relaxation variation induced by paramagnetic antibodies.

A murine anti-human melanoma monoclonal antibody fragment was labeled with gadolinium and its proton relaxation efficiency compared to controls at frequencies ranging from 2 to 300 MHz. Relaxation time variations were about 30-40% in 10-15 microM solutions. The labeled fragment showed proton relaxation enhancement relative to free gadolinium, while preserving its immunoreactivity. A tentative labeling of a melanoma pellet by means of the fragment, just at the borderline of a minimum expected T1 variation, gave no detectable difference.

Animals↗