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Biomedical subjects

F Conti

Publications and source records attributed to F Conti.

At least 91 records · Page 5Linked to original sources
PubMed1985

NMR imaging in transient cerebral ischemia.

NMR has proved useful in the detection of Acute Cerebrovascular Disorders (ACVD), providing information related either to the tissue signal intensity and relaxation times, or to the morphological aspects of cerebral structures. Eighteen patients suffering from ischemic Acute Cerebrovascular Disorders were studied. A comparison between NMR imaging and CT scan was performed. Ischemic lesions, presence of edema, presence of reactive gliosis and anatomical vascular anomalies were found.

Acute Disease↗
PubMed1984

Detection of phospholipid phase separation. A multifrequency phase fluorimetry study of 1,6-diphenyl-1,3,5-hexatriene fluorescence.

Using multifrequency phase and modulation fluorometry and a nonlinear least-squares analysis of lifetime data, we were able to determine the complex decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) in synthetic phospholipid bilayers. Our results showed a monoexponential decay of DPH in the pure isotropic solvents studied, over a wide temperature range, and a double-exponential decay of DPH in phospholipids, both above and below the transition. During the transition, and in mixed-phase phospholipids, a three-component analysis was successfully accomplished, and the pre-exponential factors of the two main components have been shown to be quantitatively representative of the gel and liquid-crystalline phases of the bilayer. The fractional intensity of the shorter lifetime component depends on the modalities of the sample preparation. The factors affecting this component are discussed. From the DPH fluorescence lifetime and from the anisotropy data in L-alpha-dimyristoyl-phosphatidylcholine/L-alpha-dipalmitoyl-phosphatidyl choline mixtures, a phase diagram was independently constructed. Conclusions about the sensitivity and the partition of the probe between gel and the liquid-crystalline phases of the bilayer are derived. Lifetime experiments on DPH in a L-alpha-dilauroyl-phosphatidylcholine/L-alpha-dipalmitoyl-phosphatidylch oline mixture suggested a general method for the determination and quantitation of the two different phases in the bilayer.

Dimyristoylphosphatidylcholine↗
PubMed1984

Fluorescence studies using synchrotron radiation on normal and differentiated cells labeled with parinaric acids.

Changes in membrane properties during the differentiation process in K562 cells have been investigated. A decrease of lectin-induced agglutination has been detected. The agglutination assay revealed to be an early and sensitive test to monitor the induced differentiation of the K562 cells. Naturally occurring fluorescent fatty acids (cis- and trans-parinaric acids) and the recently developed multifrequency phase and modulation technique were used to study cell membrane properties. Changes in fluorescence lifetime and polarization are clearly associated with cell differentiation, suggesting the involvement of the cellular plasma membrane in the differentiation process.

Cell Aggregation↗
PubMed1984

[Topography of the thalamo-cortical projections on trunk representation demonstrated by fluorescent neuro-tracers].

With the aim to study the detailed topography of the thalamo-cortical neurones projecting to the trunk representation zone of the first somatosensory area (SI), punctate injections of three different fluorescent tracers (Evans Blue, Nuclear Yellow and Fast Blue) were performed in the three physiologically defined subareas forming the trunk region of SI. These injections resulted in the labelling of three different cell aggregates, narrow in dorsoventral and mediolateral extent but elongated rostrocaudally, located in topographically distinct regions of the nucleus ventralis posterio-lateralis. The results suggest that the highly organized topography of the trunk representation of area SI is imposed by the thalamo-cortical input from VPL.

Amidines↗
PubMed1984

[Callosal connections of the somatosensory area in the primate: anatomical and electrophysiological studies].

In order to study the callosal connections of the hand sensory field of the second somatosensory area of the monkey, experiments were carried out by combining the method of retrograde neuronal tracing with microelectrode recording. In six monkeys, Macaca Irus, single or multiple (5-8) injections of horseradish peroxidase (HRP) were performed into the cortex of the parietal operculum of one side. Neurones retrogradely labelled with HRP (callosal neurones) were found in the post-central gyrus and in the parietal operculum of the contralateral hemisphere. Microelectrode recording from this hemisphere showed that the cortical zones of both the first and the second somatosensory area containing neurones excited by sensory stimulation of the contralateral hand also contained HRP-positive neurones.

Animals↗
PubMed1984

Drug-membrane interactions: silymarin, silibyn and microsomal membranes.

Silymarin and silibyn are extracted from the seeds of Silybum marianum and used as a liver protectant because of their free radical scavenging. When incorporated into rabbit liver microsomes they cause a small decrease in the flourescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) but not of 1-anilinononaphthalene-8-sulphonic acid (ANS), incorporated into the membranes. They do, however, reduce the fluorescence intensity of incorporated ANS without changing the wavelength of maximum intensity. These observations suggest that the drugs are incorporated into the hydrophobic-hydrophilic interface of the microsomal bilayer and perturb the structure by influencing the packing of the acyl chains.

Anilino Naphthalenesulfonates↗
PubMed1984

Topography and receptive field organization of the body midline representation in the ventrobasal complex of the cat.

The topography and receptive field (RF) organization of neurones in the trunk zone of the thalamic ventrobasal complex (VB) projecting to the homologous zone of the ipsilateral first somatosensory area (SI) were studied in the cat by performing experiments of retrograde neuronal tracing and microelectrode recording. Punctate cortical injections of small amounts of either horseradish peroxidase or fluorescent tracers (Evans Blue, Nuclear Yellow and Fast Blue) retrogradely labelled cell aggregates lying in the dorsal half of a VB region interposed between subnucleus VPL1 and VPLm. Aggregates of labelled cells were narrow in dorsoventral and mediolateral extent and elongated rostrocaudally. The distribution of VB cells projecting to the cortical subareas representing the dorsal midline, lateral trunk and ventral midline of the body in area SI, was established by injecting a different fluorescent marker into a physiologically defined site in each subarea. These injections resulted in labelling of three different cell aggregates located in topographically distinct regions of the VB trunk zone. Each aggregate of labelled cells only projected to one cortical subarea. Microelectrode analysis of cell populations of the VB trunk zone showed that neurones lying in regions projecting to dorsal and ventral midline zones of area SI had bilateral RFs, straddling the dorsal and the ventral midline of the body respectively. Neurones lying in the region projecting to the lateral trunk representation of area SI had contralateral RFs located on the lateral surface of the trunk. The results suggest that the detailed topography of the trunk map in the area SI and the bilaterality of the cortical representation of the body midlines, described in previous experiments, is imposed by the thalamocortical input from the VB.

Animals↗
PubMed1984

Extrinsic charge movement in the squid axon membrane. Effect of pressure and temperature.

The absorption of the lipophilic anions dipicrylamine (DPA-) and tetraphenylborate (TPhB-) by the lipid matrix of the squid axon membrane, and the kinetics of their translocation, were studied by the charge pulse relaxation technique. The axons were treated with tetrodotoxin (TTX) and 4-aminopyridine to block the ionic currents responsible for nerve excitation. At high enough concentrations of absorbed ions (approximately 10(-12) mol/cm2) the membrane voltage relaxation following a brief current pulse consisted mainly of two exponential components, whose time constants and relative amplitudes were used for estimating the translocation rate constant, K, and the density of absorbed ions, N. These measurements were performed at different hydrostatic pressures in the range 1-100 MPa (approximately 1,000 atm), and at different temperatures in the range 5 degrees C-20 degrees C. Both K and N were found to be little affected by pressure. The pressure dependence of K indicated that the translocation of lipophilic ions across the nerve membrane involves activation volumes of the order of 5 cm3/mol. In all experiments the passive membrane resistance was little affected by pressures up to 80 MPa. However, above 100 MPa it fell dramatically to low values, presumably because of phase separation phenomena between the membrane components. The temperature dependence of K, both for DPa- and TPhB-, implied an activation energy for ion translocation of the order of 60 kJ/mol, close to that measured in artificial lipid bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Pressure dependence of sodium gating currents in the squid giant axon.

Asymmetric displacement currents, Ig, were measured in squid axons at different hydrostatic pressures, P, up to 60 MPa. Potassium and sodium currents were abolished by intracellular Cs+ and TEA+, by extracellular Tetrodotoxin (TTX), and by Na+ substitution with Tris+. The time course of Ig became progressively slower with increasing pressure, and the amplitude decreased. With appropriate scaling in time and amplitude, Ig records at any given P could be made to superimpose very well with those obtained at atmospheric pressure. The same scaling factors yielded a good superposition of all records obtained for voltage steps to membrane potentials in the range -30 to +42 mV. The ratio between the amplitude and time factors was larger than unity and increased with P, indicating a progressive decrease (up to 35% at 60 MPa) of the total charge displaced, Q, with no significant change in its voltage dependence. The time-scaling factor increased exponentially with P, as expected if all the steps involved in the opening of a sodium channel, and producing a major charge redistribution, have the same activation volume, delta V not equal to g approximately 17 cm3/mol. This value is roughly one-half of that characterizing the pressure dependence of sodium current activation, suggesting that some late, rate-limiting step in the opening of sodium channels has a large activation volume without being accompanied by an easily detected charge movement. Part of the decrease of Q with pressure could be attributed to an increase in sodium inactivation. However, we cannot exclude the possibility that there is a reversible reduction in the number of fast activating sodium channels, similar to the phenomenon that has been reported to occur at low temperatures (Matteson and Armstrong 1982).

Animals↗
PubMed1984

Callosal mechanism for the interhemispheric transfer of hand somatosensory information in the monkey.

The retrograde transport of horseradish peroxidase (HRP) was combined with extracellular microelectrode recording from single and multiple-neurones to study the anatomical and functional organization of the callosal connections of the hand sensory projection field in the parietal operculum of monkeys (Macaca Irus). In 3 animals anaesthetized with ketamine, a single injection of HRP (0.5 microliter) was delivered into the cortex forming the upper bank of the sylvian sulcus at a site where neuronal responses to somatic sensory stimulation of the hand were recorded. In the ipsilateral hemisphere, retrogradely HRP-labelled cells were found in the cortex of the post-central gyrus and in the thalamic nuclei ventralis posteroinferior and pulvinar oralis. In the contralateral hemisphere HRP-labelled neurones were present in the opercular cortex lying dorsal, and slightly caudal, to the posterior pole of the insula. Few scattered callosal neurones were also found in the post-central gyrus. In 3 other animals, multiple injections (5-8; 0.5 microliter each) of HRP were performed in the parietal operculum. In the ipsilateral hemisphere, retrogradely labelled cells were present in the post-central gyrus and in the following thalamic nuclei: ventralis posteroinferior, pulvinar oralis and medialis, ventralis posteromedialis and posterior complex. Few labelled cells were also present in the ventral part of the nucleus ventralis posterolateralis. In the contralateral hemisphere, numerous callosal cells were labelled with HRP. These cells were found, with regional variations in density, in wide regions of the buried and exposed cortex of the parietal operculum and in the post-central gyrus. These 3 monkeys were subjected to microelectrode mapping experiments (N2O and halothane anaesthesia) to explore the peripheral receptive fields of neurones in the parietal operculum and post-central gyrus contralateral to the injected side. HRP labelled callosal neurones were found in regions of the second and first somatosensory cortical areas which also contained units driven from the contralateral hand.

Animals↗
PubMed1984

Non-stationary fluctuations of the potassium conductance at the node of ranvier of the frog.

Potassium currents were recorded from voltage-clamped nodes of isolated, myelinated axons of Rana pipiens. Nodes were maintained in a modified Ringer solution containing tetrodotoxin to block sodium current and 47.5 mM-potassium to minimize effects of extracellular potassium accumulation. Voltage protocols included depolarizing pulses lasting a few milliseconds to several seconds. Fluctuations about the ensemble average of the current were characterized in terms of non-stationary variance and autocovariance. The fluctuations had a Gaussian amplitude distribution and were virtually free of contaminations from systematic variations of the membrane current. Corrections for background noise were based on measurements done while potassium current was blocked with tetraethylammonium, and on simulations of extrinsic current fluctuations expected to arise from noise in the actual membrane voltage. The fluctuations were attributed to variations of nodal potassium conductance, since they were absent at the reversal potential of the potassium current and at membrane voltages that do not activate potassium current. Covariances indicated that voltage steps that reversed a macroscopic potassium current also reversed the sign of the fluctuation. Plots of the conductance variance versus the mean potassium conductance were generated from both the activation and deactivation (tail) phases of the potassium currents at various voltages between -80 and +70 mV. When the current was activated by a small depolarization (-50 mV) the trajectories from both phases were indistinguishable and were fitted by the parabola expected for a single population of channels with only one open-channel conductance. Apparent single-channel conductance from the early activation phase averaged 24 pS and was not significantly voltage dependent. In contrast, experiments with large depolarizations (+10 to +70 mV) gave significantly different variance--mean trajectories during activation and deactivation and these trajectories were poorly fitted by parabola. This result indicates that the fluctuations reflect several populations of channels and/or a population of channels that can have several levels of non-zero conductance. Projections of the fluctuation covariance showed long correlations, as well as the rapidly decaying component expected from the activation gating of channels. A slow fluctuation arose at a time slightly later than the rise of potassium current, spanned the entire length of brief depolarizations, and extended up to 880 ms during long depolarizations.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1982

Axonal branching in the periaqueductal gray projections to the thalamus: a fluorescent retrograde double-labeling study in the cat.

The double-labeling technique based on the retrograde axonal transport of fluorescent tracers (Evans blue, EB; Fast blue, FB; Nuclear yellow, NY) was used in the cat in order to investigate the occurrence of axonal branching in the periaqueductal gray (PAG) projections to some thalamic nuclei (n. ventralis postero-lateralis, VPL; n. ventralis postero-medialis, VPM; n. parafascicularis, Pf). In a first group of cats, FB and EB were injected, respectively, within the right and left VPM. In another two groups of cats, FB injections into Pf were combined with either EB or NY injections within VPL or VPM. Double-labeled neurons were found within the PAG only in the animals of the first group. The present results show that some PAG neurons project bilaterally to VPM by means of axons collaterals.

Animals↗