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G De Filippi

Publications and source records attributed to G De Filippi.

At least 19 recordsLinked to original sources
PubMed2004

Physiological roles of neuronal nicotinic receptor subtypes: new insights on the nicotinic modulation of neurotransmitter release, synaptic transmission and plasticity.

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in the mammalian central nervous system (CNS). Despite this, very little was known, until recently, about their physiological role. In the periphery, nicotinic receptors mediate vital excitatory fast synaptic cholinergic transmission at both the neuromuscular junction and ganglia. In the brain, this role has been mainly "delegated" to glutamate receptors. The very broad cholinergic innervations of most brain areas, including the cortex, have implicated this system, and brain nicotinic receptors in particular, in a unique "modulatory" role of other transmitters systems. Recent evidence confirms, on one hand, that brain nicotinic receptors have a dominant "presynaptic" modulatory function, controlling the release of both acetylcholine (auto-receptors) and other neurotransmitters (hetero-receptors). On the other hand, more experimental data support the idea that a variable component of fast synaptic transmission in the brain can also be mediated by "postynaptic" nicotinic receptors, which, in turn, can control cell excitability. A challenging goal is to identify which one of the plethora of nicotinic receptor subtypes is mediating each effect in different brain areas, and which of these receptors and functions are lost or affected in different human neuro-psychiatric disorders. Needless to say, a better understanding of the physiological role of brain nicotinic receptors will drive our quest for more selective and efficacious nicotinic receptor targeted therapeutic agents.

Animals↗
PubMed2002

5-Hydroxyindole potentiates human alpha 7 nicotinic receptor-mediated responses and enhances acetylcholine-induced glutamate release in cerebellar slices.

The effects of 5-hydroxyindole (5-HI) have been investigated on human alpha 7 nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes and GH4 cells, on native alpha 7 nAChRs expressed by IMR-32 cells and on alpha 7 nAChR-mediated events in mossy fibre-granule cell synapses in rat cerebellar slices. In oocytes expressing alpha 7 nAChRs, 5-HI potentiated sub-maximal, 60 micro M ACh-induced ion currents in a concentration-dependent manner, the threshold effective concentration being 30 micro M. 5-HI itself did not act as an agonist on alpha 7 nAChRs. A maximum potentiation of 12 times the control was observed at 20 mM 5-HI. The effect of 1 mM 5-HI on the concentration-response curve for ACh revealed that 5-HI increased the potency as well as the efficacy of ACh on alpha 7 nAChRs. 5-HI also potentiated alpha 7-mediated increases in intracellular free calcium levels in both mammalian cells heterologously expressing human alpha 7 nAChRs and in human IMR-32 neuroblastoma cells expressing native alpha 7 nAChRs. At mossy fibre-granule cell synapses, application of 1 mM ACh induced glutamate-evoked excitatory post-synaptic currents (EPSCs). Co-application of 1 mM 5-HI with 1 mM ACh further increased the frequency of the EPSCs. The ACh-induced release, as well as the 5-HI-induced enhancement of release, were blocked by 1-10 nM methyllycaconitine or 200 nM alpha-bungarotoxin, demonstrating that both effects were mediated by presynaptic alpha 7 nAChRs. The results demonstrate that responses mediated by alpha 7 nAChRs are strongly potentiated by 5-HI.

Acetylcholine↗
PubMed2001

Evidence for nicotinic acetylcholine receptor activation in rat cerebellar slices.

Neuronal nicotinic ACh receptor (nAChR) activation is known to enhance glutamate and GABA release in different brain areas. Moreover, nAChRs play an important role in neuronal differentiation. By using the patch-clamp technique, we have investigated the presence of nAChRs in cerebellar granule cells in slices from P5-P14 rats. Application of ACh (1 mM) could elicit a variety of effects. Some cells did not respond at all. In other cells, a somatic current was activated. In a proportion of cells, postsynaptic currents (PSCs), with or without somatic current, were elicited. Somatic nAChRs are likely to be of the alpha(4)beta(2) subtype, but the presence of other subunit combinations (alpha(7)- or beta(4)-containing receptors) cannot be ruled out. The ACh-induced PSCs were glutamatergic in nature. Thus, in a reasonable proportion of cells, nicotinic receptors are present presynaptically. They are likely to be alpha(7) receptors whose activation elicits Glu release via a TTX-sensitive mechanism. Our experiments are the first electrophysiological evidence showing, in a native cerebellar preparation, the presence of nicotinic receptors at the mossy fibre-granule cell synapse at early developmental stages.

Animals↗
PubMed1998

The weaver mutation causes a loss of inward rectifier current regulation in premigratory granule cells of the mouse cerebellum.

Considerable interest has recently focused on the weaver mutation, which causes inward rectifier channel alterations leading to profound impairment of neuronal differentiation and to severe motor dysfunction in mice (Hess, 1996). The principal targets of mutation are cerebellar granule cells, most of which fail to differentiate and degenerate in a premigratory position (Rakic and Sidman, 1973a,b). Two hypotheses have been put forward to explain the pathogenetic role of mutant inward rectifier channels: namely that inward rectifier channel activity is either lacking (Surmeier et al., 1996) or altered (Kofuji et al., 1996; Silverman et al., 1996; Slesinger et al., 1996). We have examined this question by recording inward rectifier currents from cerebellar granule cells in situ at different developmental stages in wild-type and weaver mutant mice. In wild-type mice, the inward rectifier current changed from a G-protein-dependent activation to a constitutive activation as granule cells developed from premigratory to postmigratory stages. In weaver mutant mice, G-protein-dependent inward rectifier currents were absent in premigratory granule cells. A population of putative granule cells in the postmigratory position expressed a constitutive inward rectifier current with properties compatible with mutated GIRK2 channels expressed in heterologous systems. Because granule cells degenerate at the premigratory stage (Smeyne and Goldowitz, 1989), the loss of inward rectifier current and its regulation of membrane potential are likely to play a key role in the pathogenesis of weaver neuronal degeneration.

Anesthetics, Local↗
PubMed1998

Ionic mechanism of electroresponsiveness in cerebellar granule cells implicates the action of a persistent sodium current.

Although substantial knowledge has been accumulated on cerebellar granule cell voltage-dependent currents, their role in regulating electroresponsiveness has remained speculative. In this paper, we have used patch-clamp recording techniques in acute slice preparations to investigate the ionic basis of electroresponsiveness of rat cerebellar granule cells at a mature developmental stage. The granule cell generated a Na+-dependent spike discharge resistant to voltage and time inactivation, showing a linear frequency increase with injected currents. Action potentials arose when subthreshold depolarizing potentials, which were driven by a persistent Na+ current, reached a critical threshold. The stability and linearity of the repetitive discharge was based on a complex mechanism involving a N-type Ca2+ current blocked by omega-CTx GVIA, and a Ca2+-dependent K+ current blocked by charibdotoxin and low tetraethylammonium (TEA; <1 mM); a voltage-dependent Ca2+-independent K+ current blocked by high TEA (>1 mM); and an A current blocked by 2 mM 4-aminopyridine. Weakening TEA-sensitive K+ currents switched the granule cell into a bursting mode sustained by the persistent Na+ current. A dynamic model is proposed in which the Na+ current-dependent action potential causes secondary Ca2+ current activation and feedback voltage- and Ca2+-dependent afterhyperpolarization. The afterhyperpolarization reprimes the channels inactivated in the spike, preventing adaptation and bursting and controlling the duration of the interspike interval and firing frequency. This result reveals complex dynamics behind repetitive spike discharge and suggests that a persistent Na+ current plays an important role in action potential initiation and in the regulation of mossy fiber-granule cells transmission.

2-Amino-5-phosphonovalerate↗
PubMed1997

Synaptic activation of Ca2+ action potentials in immature rat cerebellar granule cells in situ.

Although numerous Ca2+ channels have been identified in cerebellar granule cells, their role in regulating excitability remained unclear. We therefore investigated the excitable response in granule cells using whole cell patch-clamp recordings in acute rat cerebellar slices throughout the time of development (P4-P21, n = 183), with the aim of identifying the role of Ca2+ channels and their activation mechanism. After depolarizing current injection, 46% of granule cells showed Ca2+ action potentials, whereas repetitive Na+ spikes were observed in an increasing proportion of granule cells from P4 to P21. Because Ca2+ action potentials were no longer observed after P21, they characterized an immature granule cell functional stage. Ca2+ action potentials consisted of an intermediate-threshold spike (ITS) activating at -60/-50 mV and sensitive to voltage inactivation and of a high-threshold spike (HTS), activating at above -30 mV and resistant to voltage inactivation. Both ITS and HTS comprised transient and protracted Ca2+ channel-dependent depolarizations. The Ca2+ action potentials could be activated synaptically by excitatory postsynaptic potentials, which were significantly slower and had a proportionately greater N-methyl-D-aspartate (NMDA) receptor-mediated component than those recorded in cells with fast repetitive Na+ spikes. The NMDA receptor current, by providing a sustained and regenerative current injection, was critical for activating the ITS, which was not self-regenerative. Moreover, NMDA receptors determined temporal summation of impulses during repetitive mossy fiber transmission, raising membrane potential into the range required for generating protracted Ca2+ channel-dependent depolarizations. The nature of Ca2+ action potentials was considered further using selective ion channel blockers. N-, L-, and P-type Ca2+ channels generated protracted depolarizations, whereas the ITS and HTS transient phase was generated by putative R-type channels (R(ITS) and R(HTS), respectively). R(HTS) channels had a higher activation threshold and were more resistant to voltage inactivation than R(ITS) channels. At a mature stage, most of the Ca2+-dependent effects depended on the N-type current, which promoted spike repolarization and regulated the Na+-dependent discharge frequency. These observations relate Ca2+ channel types with specific neuronal excitable properties and developmental states in situ. Synaptic NMDA receptor-dependent activation of Ca2+ action potentials provides a sophisticated mechanism for Ca2+ signaling, which might be involved in granule cell development and plasticity.

Action Potentials↗
PubMed1995

Synaptic excitation of individual rat cerebellar granule cells in situ: evidence for the role of NMDA receptors.

1. Current-clamp recordings were made in whole-cell patch-clamp configuration from ninety-one granule cells in parasagittal cerebellar slices obtained from 21- to 31-day-old rats. Recordings were performed at 30 degrees C. 2. Resting membrane potential was -58 +/- 6 mV (n = 43). The membrane voltage response to step current injection showed inward rectification consistent with increasing input resistance during membrane depolarization. Over -35 +/- 7 mV (n = 14) repetitive firing with little or no adaptation was activated. Spike frequency increased nearly linearly with injected current. 3. Unitary EPSPs obtained by stimulating the mossy fibre bundle had an amplitude of 11.4 +/- 2.1 mV (n = 22, holding potential = -75 mV). Synchronous activation of greater than one to two mossy fibres was needed to elicit action potentials. Antidromic stimulation elicited antidromic spikes and also EPSPs, presumably through a mossy fibre 'axon reflex'. 4. EPSPs were brought about by NMDA and non-NMDA receptor activation, accounting for about 70 and 30%, respectively, of peak amplitude at the holding potential of -70 mV. The EPSP decay conformed to passive membrane discharge after blocking the NMDA receptors. 5. No appreciable correlation was found between the time-to-peak and decay time constant of the EPSPs, consistent with the compact electrotonic structure of these neurons. 6. During membrane depolarization EPSP amplitude increased transiently, due to both a voltage-dependent increase of the NMDA component and inward rectification. In addition, EPSPs slowed down due to a slowdown of the NMDA component. 7. Temporal summation during high-frequency stimulation was sustained by NMDA receptors, whose contribution to depolarization tended to prevail over that of non-NMDA receptors during the trains. A block of the NMDA receptors resulted in reduced depolarization and output spike frequency. 8. This study, as well as extending previous knowledge to the intracellular level in vivo, provides evidence for a primary role of NMDA receptors in determining mossy fibre excitation of granule cells. It is suggested that the marked voltage dependence of the EPSP time course, which was mainly caused by voltage dependence in NMDA conductance, promotes the NMDA receptor-dependent enhancement of granule cell coding observed during repetitive mossy fibre activity.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

The relationship between synaptogenesis and expression of voltage-dependent currents in cerebellar granule cells in situ.

In this work we consider the ontogenetic changes of membrane currents and their relationship with synaptogenesis in cerebellar granule cells. Recordings were performed in whole-cell patch-clamp configuration from cerebellar slices obtained from 4 to 31-day-old rats. Granule cells in the external granular layer, and non-connected granule cells in the internal granular layer expressed outward currents, and inconstantly also small Ca2+ currents, but no fast Na+ currents. Most connected granule cells expressed Ca2+ and Na+ currents. These data indicate that Ca2+ and Na+ current development occurs after synapse formation, while outward (K+) currents begin their development before. Mixed NMDA/non-NMDA synaptic currents were observed at all stages, while synaptic currents with a prominent NMDA component were observed exclusively at immature stages. At P4, ie 1-2 days after the arrival of the first granule cells in the internal granular layer, some granule cells already expressed mature synaptic and voltage-dependent currents, suggesting that establishment of mossy fibre synapses and development of membrane properties takes just 1-2 days to complete. Starting at P4, the probability of activating mossy fibre currents, and sizeable Ca2+ and Na+ currents increased at a similar rate, attaining a plateau level around P20. Average amplitude of Na+ and outward currents decreased until P10 and then increased attaining plateau soon beyond P20. Average amplitude of Ca2+ currents increased monotonically. The time courses of probability and average current amplitude curves are likely explained by changes in the rate of accumulation of migrating granule cells in the internal granular layer, and by changes in granule cell membrane surface extension. These data suggest a relevant role for the process of synapse formation in inducing the expression of new channels in the developing granule cells, which may involve Ca2+ influx through the NMDA channel.

Animals↗
PubMed1994

Carbon monoxide-diffusing capacity in intravenous drug abusers: the effect of cigarette smoking and HIV infection.

A reduction in the Dco has been frequently found in intravenous drug addicts (IVDAs) and in subjects with HIV infection. Since also cigarette smoking decreases Dco, we studied a group of street IVDAs, who did not show respiratory symptoms and/or infiltrates on chest x-ray film. Sixty-two patients were presently smoking, 2 had never smoked. Twenty-seven were HIV-negative and 37 HIV-positive. Mean values for Dco (percent of predicted values) were 78 +/- 16.4 in HIV-positives compared to 97.9 +/- 17.6 in HIV-negatives (p < 0.0001) using smoking specific equations and 71.8 +/- 15.4 in HIV-positives compared to 80.7 +/- 13.4 (p < 0.0001) using non-smokers equations. Dco was < 80 percent in 19 of 35 (54.3%) HIV-positive subjects and in 4 of 26 (15.4%) HIV-negative subjects (p < 0.009) using predicted values for smokers, and in 28 of 35 (80%) HIV-positive subjects and in 6 of 26 (23.1%) HIV-negative subjects (p < 0.0001) using predicted values for non-smokers. These data suggest that Dco alterations observed in HIV-positive subjects are due, in absence of respiratory symptoms and/or chest x-ray abnormalities, to an interstitial pneumopathy due to HIV or to a subclinical pulmonary disease. We conclude that the knowing of smoking in IVDAs is useful, but the knowing of seropositivity is much more important, since a marked reduction of Dco in these subjects suggests an HIV-related lymphocytic alveolitis, an opportunistic infection or a malignancy.

Adolescent↗
PubMed1992

Abdominal placement of tube thoracostomy due to lack of recognition of paralysis of hemidiaphragm.

Tube thoracostomy is an invasive procedure that carries a risk of complications. We report a patient with liver cirrhosis, ascites and large left-sided pleural effusion, in whom a trocar type chest tube was inserted at the seventh left intercostal space in the midaxillary line. Chest roentgenogram revealed that the drainage tube was placed into the abdominal cavity because of a misrecognized elevation of the left hemidiaphragm. This case demonstrates that the placement of a tube thoracostomy requires caution in the identification of possible abnormalities which can lead to dangerous complications.

Abdomen↗
PubMed1992

False positivity of tumor markers in pleural fluid of traumatic hemothorax.

Various biochemical parameters of pleural fluid have been employed to identify malignant effusions. However, many of them are also elevated in patients with nonmalignant conditions. We report on a patient with traumatic hemothorax, showing high pleural fluid concentrations of ferritin, tissue polypeptide antigen, and cancer antigen 125. This patient's pleural fluid also contained high levels of bilirubin and many macrophages containing phagocytized red blood cells, suggesting a local metabolism of hemoglobin. Our case confirms that some tumoral markers can give false positive results and suggests that their significance must be evaluated differently in bloody pleural effusions as compared with non-bloody pleural effusions.

Adult↗
PubMed1991

[Naloxone and naltrexone in the therapy of advanced COPD].

We report a patient with COPD and bullous emphysema treated with narcotic antagonists (naloxone and naltrexone) for severe respiratory failure, with hypoxemia and hypercapnia, non responding to traditional medical therapy. According to previous reports, this treatment was started while waiting for lung transplantation, and it improved clinical pattern and arterial blood gas levels. Though the patient died for left ventricular failure fifteen days after the beginning of therapy, we think that narcotic antagonists can be successfully administered in some patients with advanced stage COPD.

Humans↗
PubMed1991

Terlipressin-induced metabolic acidosis.

Vasopressin and its analogue terlipressin are potent vasoconstrictors which reduce mesenteric blood flow and have been used in the therapy of variceal hemorrhage. This vasoconstrictor effect applies on vascular beds throughout the body. Since in literature vasopressin is rarely described to determine lactic acidosis, we report of a patient in whom a severe metabolic (probably lactic) acidosis appeared, associated with terlipressin administration for bleeding esophageal varices. By exclusion, the temporal sequence with terlipressin therapy, the contemporary increase of arterial blood pressure and autoptic data in the case presented make likely a diagnosis of terlipressin-induced lactic acidosis. Because of the seriousness of metabolic acidosis observed in our patient we suggest a careful monitoring of acid-base parameters in patients under treatment with vasopressin analogues.

Acidosis↗
PubMed1990

Malignant pleural effusions: meaning of pleural-fluid pH determination.

In 36 patients with malignant pleural effusions, we determined the pH and the glucose concentration of the pleural fluid. Twenty-one of 36 patients (58.3%) had a low pH (less than 7.30) and 15 had a normal pH (greater than or equal to 7.30; 7.13 +/- 0.12 vs. 7.37 +/- 0.05; p less than 0.0005). The patients with low pH had significantly lower glucose concentrations than those with normal pH (2.7 +/- 1.4 vs. 6.3 +/- 2.9 mmol/l; p less than 0.0005). Twenty-one of 34 patients (61.7%) had a glucose concentration lower than a cut-off value of 4.4 mmol/l; of these, 17 (81%) had a low pH. The mean survival in the low-pH group was 4.8 +/- 4.4 months, whereas the mean survival in the normal-pH group was 5 +/- 8 months (p greater than 0.4). Twelve of 36 patients (33.3%) were treated with intrapleural Corynebacterium parvum (CBP) injections. Fourteen of 21 low-pH patients (66.6%) survived more than 2 months, and 4 of them are still alive. Six of 15 normal-pH patients (40%) survived more than 2 months, and 1 of them is still alive. Three of the 5 living patients were treated with CBP (2 in the low-pH group and 1 in the normal-pH groups). Our results confirm that pH and glucose concentrations in the pleural fluid of patients with malignant effusions are frequently low. However, the survival and the response to CBP pleurodesis in patients with low-pH malignant effusions are the same as those in patients with normal-pH malignant effusions.

Adolescent↗
PubMed1989

Angiotensin-converting enzyme as a possible marker for lung toxicity in amiodarone-treated patients.

Since it has been observed that in vitro amiodarone induces morphological alterations in endothelial cells similar to those observed in patients with lung toxicity and that the angiotensin-converting enzyme (ACE) seems to be a marker for perturbation of the alveolar-capillary membrane, serum ACE concentrations have been determined in 44 patients, 23 treated with amiodarone (group A) and 21 treated with other anti-arrhythmic drugs (group B), before the beginning of treatment and after 7, 15, 30, 60 and 180 days. Serum ACE concentrations in group A were lower than the basal values (15.8 +/- 5.9 mU/ml) on day 7 (12.7 +/- 4.5 mU/ml) and were higher on day 60 (17.9 +/- 3.8 mU/ml), then returned to basal values by day 180 (15.9 +/- 5.5 mU/ml), but none of the differences were statistically significant. In group B, serum ACE concentrations were significantly higher than basal values (15.2 +/- 4.0 versus 14.2 +/- 3.5 mU/ml, p less than 0.05) only on day 15. In group A serum ACE concentrations were significantly higher than in group B only on day 60 (17.9 +/- 3.8 versus 14.7 +/- 4.5 mU/ml, p less than 0.025). During the period of the study none of the patients showed any clinical or radiological signs of lung toxicity or reduction of lung diffusion capacity for carbon monoxide (DLCO). Serum ACE levels were normal even in three patients who developed pulmonary fibrosis and in four whose DLCO was reduced by more than 20% from the basal values after the study was completed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

[Aortic regurgitation: evaluation by pulsed Doppler echocardiography].

Ninety-one consecutive patients with aortic regurgitation, either isolated (23 subjects) or associated with other valvular diseases (68 subjects), were studied with pulsed Doppler echocardiography and subsequent aortography, and the results were compared in order to assess the value of the noninvasive technique for a semiquantitative evaluation of the degree of the aortic regurgitation. Both the noninvasive and invasive estimations were graded on a four-point scale. In the long-axis parasternal view, the outflow tract of the left ventricle was divided in four areas going from the aortic valve to the apex. Echo-Doppler grading (from + 1 to +4) was obtained by assessing the area where the abnormal diastolic flow could still be recorded. In the group as a whole, concordant degrees of the aortic insufficiency were obtained in 73 of 91 patients (r = .93; p less than .001); the degree of the aortic regurgitation was overestimated in 8 cases (9%) and underestimated in 10 cases (11%). Most of the discrepancies between the Doppler and the aortographic evaluation were found in patients with intermediate degree (+2, +3) of aortic regurgitation; the degree of discordance was never more than +1 or -1. Correlation between Doppler and aortography was higher in the subjects with pure aortic regurgitation (r = .94, p less than .001) and lower in the subgroup of the subjects with associated mitral stenosis (r = .87, p less than .001). Two-dimensional pulsed Doppler echocardiography is a simple and little time consuming technique that in selected groups of patients can be relied upon for the semiquantitated evaluation of the degree of aortic regurgitation.

Adolescent↗
PubMed1985

[Fetal echocardiography: diagnosis of congenital cardiomyopathies in a population at risk].

2-Dimensional and M-mode Echocardiography were performed in 142 fetuses at specific risk for congenital heart disease between 16 and 40 weeks of gestational age. In 105 cases the diagnosis was checked at delivery; prevalence of cardiac malformations was 5.7%. In 5 cases out of 7 the malformation was correctly diagnosed at Echocardiographic examination: ectopia cordis of thoracic type with tetralogy of Fallot, ectopia cordis of abdominal type with normal intracardiac anatomy, atrio-ventricular canal, left atrial membrane, single heart in jointed twins. There were 3 diagnostic errors: two false negative (a case of pulmonary atresia and a case of univentricular heart) and one false positive (a case of suspected transposition of the great vessels in a normal heart). The sensitivity of the test was 71.4%, the specificity was 98.9%, the predictive value of the positive test was 83.3%. M-mode Echo was particularly useful in cases of arrhythmias. 3 cases of benign rhythm disorders were identified: 2 cases of conducted and blocked atrial ectopic beats and one case of transient 2:1 A-V block. In 5 cases there was a wide variability of the sinus rhythm. 2-D Echocardiogram seems a reliable method for the diagnosis of fetal heart diseases in a population at risk. Its clinical usefulness to guide therapeutic decisions in our population was limited by the coexistence of multiple malformations.

Arrhythmias, Cardiac↗