Biomedical subjects

G Bernardi

Publications and source records attributed to G Bernardi.

At least 145 records · Page 8Linked to original sources

PubMed2001

Selective involvement of mGlu1 receptors in corticostriatal LTD.

Although metabotropic glutamate receptors (mGluRs) have been proposed to play a role in corticostriatal long-term depression (LTD), the specific receptor subtype required for this form of synaptic plasticity has not been characterized yet. Thus, we utilized a corticostriatal brain slice preparation and intracellular recordings from striatal spiny neurons to address this issue. We observed that both AIDA (100 microM) and LY 367385 (30 microM), two blockers of mGluR1s, were able to fully prevent the induction of this form of synaptic plasticity, whereas MPEP (30 microM), a selective antagonist of the mGluR5 subtype, did not significantly affect the amplitude and time-course of corticostriatal LTD. Both AIDA and LY 367385 were ineffective on LTD when applied after its induction. The critical role of mGluR1s in the formation of corticostriatal LTD was confirmed in experiments performed on mice lacking mGluR1s. In these mice, in fact, a significant reduction of the LTD amplitude was observed in comparison to the normal LTD measured in their wild-type counterparts. We found that neither acute pharmacological blockade of mGluR1s nor the genetic disruption of these receptors affected the presynaptic modulation of corticostriatal excitatory postsynapic potentials (EPSPs) exerted by DCG-IV and L-SOP, selective agonists of group II and III mGluRs, respectively. Our data show that the induction of corticostriatal LTD requires the activation of mGluR1 but not mGluR5. mGluR1-mediated control of this form of synaptic plasticity may play a role in the modulatory effect exerted by mGluRs in the basal ganglia-related motor activity.

Animals↗

PubMed2001

Hypoglycaemia-induced cell death: features of neuroprotection by the P2 receptor antagonist basilen blue.

Our previous work in neuronal cultures has shown that several antagonists of P2 ATP receptors prevent cell death evoked by hypoglycaemia, chemical hypoxia, mitochondria dysfunction, as well as glutamate-dependent excitotoxicity and low potassium-induced apoptosis. Experiments are now designed to examine which biological pathway contributes to cell death/survival under glucose starvation. We show here that, consequently to hypoglycaemic insults, cerebellar granule neurones undergo a combination of apoptosis and necrosis both inhibited by the P2 receptor antagonist basilen blue. This is demonstrated by morphological and biochemical features, such as TdT-mediated dUTP-biotin nick end-labelling, fluorescent staining of nuclear chromatin using Hoechst 33258, direct counting of intact viable nuclei and extracellular releasing of the cytosolic enzyme LDH. Furthermore, we show that hypoglycaemia induces outflow of cytochrome c from mitochondria and it up-regulates heat-shock proteins HSP70, but not HSP90, glucose-regulated proteins GRP75 and GRP78, as well as expression and activity of the enzyme caspase-2. Basilen blue can modulate only some of these effects. Our data contribute to dissect the role played by P2 receptor antagonism in sustaining neuroprotection against metabolic stresses.

Animals↗

PubMed2001

Glucose deprivation and chemical hypoxia: neuroprotection by P2 receptor antagonists.

In this work we investigate cell survival after glucose deprivation and/or chemical hypoxia and we analyse the neuroprotective properties of selected antagonists of P2 ATP receptors. We find that in rat cerebellar granule neurones, the antagonist basilen blue prevents neuronal death under hypoglycaemia. Basilen blue acts through a wide temporal range and it retains its efficacy under chemically induced hypoxic conditions, in the presence of the respiratory inhibitors of mitochondria electron transport chain complexes II (3-nitropropionic acid) and III (antimycin A). In spite of the presence of these compounds, basilen blue maintains normal intracellular ATP levels. It furthermore prevents neuronal death caused by agents blocking the mitochondrial calcium uptake (ruthenium red) or discharging the mitochondrial membrane potential (carbonyl cyanide m-chlorophenylhydrazone). Inhibition of poly (ADP-ribose) polymerase, modulation of the enzyme GAPDH and mitochondrial transport of mono-carboxylic acids are not conceivable targets for the action of basilen blue. Survival is sustained by basilen blue also in CNS primary cultures from hippocampus and in PNS sympathetic-like neurones. Partial neuroprotection is furthermore provided by three additional P2 receptor antagonists: suramin, pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid 4-sodium and 4,4'-diisothiocyanatostilbene-2,2'disulphonic acid. Our data suggest the exploitation of selected P2 receptor antagonists as potential neuroprotective agents.

Adenosine Triphosphate↗

PubMed2001

Ionic mechanisms underlying differential vulnerability to ischemia in striatal neurons.

Brain cells express extremely different sensitivity to ischemic insults. The reason for this differential vulnerability is still largely unknown. Here we discuss the ionic bases underlying the physiological responses to in vitro ischemia in two neostriatal neuronal subtypes exhibiting respectively high sensitivity and high resistance to energy deprivation. Vulnerable neostriatal neurons respond to ischemia with a membrane depolarization. This membrane depolarization mainly depends on the increased permeability to Na+ ions. In contrast, resistant neostriatal neurons respond to ischemia with a membrane hyperpolarization due to the opening of K+ channels. Interestingly, in both neuronal subtypes the ischemia-dependent membrane potential changes can be significantly enhanced or attenuated by a variety of pharmacological agents interfering with intracellular Ca2+ entry, ATP-dependent K+ channels opening, and Na+/Ca2+ exchanger functioning. The understanding of the ionic mechanisms underlying the differential membrane responses to ischemia represents the basis for the development of rational neuroprotective treatments during acute cerebrovascular insults.

Animals↗

PubMed2001

Metabotropic glutamate receptor 5 mediates the potentiation of N-methyl-D-aspartate responses in medium spiny striatal neurons.

Medium spiny neurons were recorded from striatal slices obtained from mice lacking the group I metabotropic glutamate receptor (mGluR) subtype 1 or subtype 5. In wild-type animals, N-methyl-D-aspartate (NMDA)-induced membrane depolarization/inward currents were potentiated in the presence of both the group I mGluR agonist 3,5-dihydroxyphenylglycine (3,5-DHPG) and the mGluR5 selective agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG). Likewise, in mGluR1 knockout mice, both 3,5-DHPG and CHPG were able to potentiate NMDA responses. Conversely, in neurons recorded from mGluR5-deficient mice, the enhancement of NMDA responses by both 3,5-DHPG and CHPG was absent. Pharmacological analysis performed from rat slices confirmed the data obtained with mice. In the presence of the competitive mGluR1 antagonist LY367385, the NMDA responses were potentiated in the presence of CHPG, whereas the CHPG-induced enhancement was not observed in slices treated with the non-competitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine. As in wild-type mice, in neither of the mGluR1- and mGluR5-deficient mice did (2S,1'R,2'R,3'R)-2-(2,3-dicarboxylcyclopropyl)-glycine (1 microM), nor L-serine-O-phosphate (30 microM) (agonists for group II and III mGluRs, respectively) affect the NMDA-evoked responses. In striatal medium spiny neurons, NMDA responses are potentiated by endogenous acetylcholine via M1-like muscarinic receptors. Since the enhancement of NMDA responses by 3,5-DHPG and by M1-like muscarinic agonists was shown to share common post-receptor mechanisms, we verified whether the muscarinic potentiation of NMDA responses was affected in these group I mGluR-deficient mice. Both in mGluR1 and mGluR5 knockout animals, in the presence of either muscarine or the M1-like muscarinic receptor agonist McN-A-343, the positive modulation of the NMDA-induced membrane depolarization persisted.These results confirm the permissive role of group I mGluRs on NMDA responses in striatal neurons and reveal that this functional interplay occurs exclusively through the mGluR5 subtype. The NMDA-mGluR5 interaction might play an important modulatory role in the final excitatory drive from corticostriatal afferents and suggests that drugs acting at mGluR5 might prove useful for the treatment of movement disorders involving the striatum.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗

PubMed2001

Interaction between ATP and nerve growth factor signalling in the survival and neuritic outgrowth from PC12 cells.

In a previous study we used P2 receptor antagonists to inhibit diverse responses that nerve growth factor (NGF) promotes and coordinates in PC12 cells and we suggested that P2 receptors partake in the NGF signalling cascade. In this paper, we examine the direct role of extracellular P2 receptor agonists as neurotrophic factors. ATP and 2-Cl-ATP promote neurite regeneration after priming PC12 cells with NGF and the effect is dose-dependent, with an EC(50) of about 5 and 3 microM, respectively. The number of cell clumps bearing neurites was maximally induced in day 1 and it was maintained up to about one week by ATP, or up to at least 2 weeks by 2-Cl-ATP. The involvement of P1 receptors or intracellular inosine in these actions was excluded, whereas various antagonists of P2 receptors were inhibitory. Moreover, NGF and ATP caused a direct up-regulation of P2X(2), P2X(3), P2X(4) and P2Y(2), but not P2Y(4) receptor proteins under neurite-regenerating conditions, as well as extracellular signal-regulated kinase (Erk)1-2 tyrosine/threonine phosphorylation and activation. Finally, ATP, 2-Cl-ATP and ATPgammaS enhanced neurite initiation evoked by sub-optimal NGF concentrations and ATP and 2-Cl-ATP fully sustained survival of PC12 cells after serum deprivation. Our results establish that P2 receptor agonists can behave as neurotrophic factors for neuronal cells and suggest a potential interplay between ATP and NGF in the signalling pathways triggered on their target cells.

Adenosine Triphosphate↗

PubMed2001

The effects of gabapentin on different ligand- and voltage-gated currents in isolated cortical neurons.

A clear picture of the mechanisms of action of the anti-epileptic agent gabapentin is far from being accomplished. We have analyzed the effects of gabapentin on ligand- and voltage-gated currents in isolated adult rat cortical neurons. Gabapentin failed to modify glutamate currents and produced a slight reduction of GABA responses. Negligible inhibition of sodium, but consistent inhibition of high-voltage-activated calcium conductance was promoted by gabapentin. In addition, gabapentin reduced calcium current sensitivity to dihydropyridine agonist and antagonists. Interestingly, gabapentin also decreased a not-inactivating, cadmium-sensitive, potassium current. These unconventional effects might underlie its efficacy in a variety of diseases which involve periodic discharge patterns as neuropathic pain or essential tremor.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed2001

Compositional mapping of chicken chromosomes and identification of the gene-richest regions.

'Compositional chromosomal mapping', namely the assessment of the GC level of chromosomal bands, led to the identification, in the human chromosomes, of the GC-richest H3+ bands and of the GC-poorest L1+ bands, which were so called on the basis of the isochore family predominantly present in the bands. The isochore organization of the avian genome is very similar to those of most mammals, the only difference being the presence of an additional, GC-richest, H4 isochore family. In contrast, the avian karyotypes are very different from those of mammals, being characterized, in most species, by few macrochromosomes and by a large number of microchromosomes. The 'compositional mapping' of chicken mitotic and meiotic chromosomes by in-situ hybridization of isochore families showed that the chicken GC-richest isochores are localized not only on a large number of microchromosomes but also on almost all telomeric bands of macrochromosomes. On the other hand, the GC-poorest isochores are generally localized on the internal regions of macrochromosomes and are almost absent in microchromosomes. Thus, the distinct localization of the GC-richest and the GC-poorest bands observed on human chromosomes appears to be a general feature of chromosomes from warm-blooded vertebrates.

Animals↗

PubMed2001

Dopaminergic control of synaptic plasticity in the dorsal striatum.

Cortical glutamatergic and nigral dopaminergic afferents impinge on projection spiny neurons of the striatum, providing the most significant inputs to this structure. Isolated activation of glutamate or dopamine (DA) receptors produces short-term effects on striatal neurons, whereas the combined stimulation of both glutamate and DA receptors is able to induce long-lasting modifications of synaptic excitability. Repetitive stimulation of corticostriatal fibres causes a massive release of both glutamate and DA in the striatum and, depending on the glutamate receptor subtype preferentially activated, produces either long-term depression (LTD) or long-term potentiation (LTP) of excitatory synaptic transmission. D1-like and D2-like DA receptors interact synergistically to allow LTD formation, while they operate in opposition during the induction phase of LTP. Corticostriatal synaptic plasticity is severely impaired after chronic DA denervation and requires the stimulation of DARPP-32, a small protein expressed in dopaminoceptive spiny neurons which acts as a potent inhibitor of protein phosphatase-1. In addition, the formation of LTD and LTP requires the activation of PKG and PKA, respectively, in striatal projection neurons. These kinases appear to be stimulated by the activation of D1-like receptors in distinct neuronal populations.

Animals↗

PubMed2001

Glutamate receptor stimulation induces a persistent rhythmicity of the GABAergic inputs to rat midbrain dopaminergic neurons.

The substantia nigra pars compacta and the ventral tegmental area are part of a complex network in the basal ganglia involved in behaviours as diverse as motor planning, generation of pleasure and drug addiction. Here we report that in the dopaminergic neurons of the rat ventral midbrain a brief coactivation of group I metabotropic and NMDA glutamate receptors may transform a temporally dispersed synaptic GABAergic input into a rhythmic pattern (range 4.5-22.5 Hz), probably through a mechanism involving electrotonic couplings. The plastic and long-lasting modification in the temporal code of the inhibitory synaptic activity induced by glutamate may be a key element in determining the function of midbrain dopaminergic neurons in both normal and pathological behaviour.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2001

Resistance to NMDA toxicity correlates with appearance of nuclear inclusions, behavioural deficits and changes in calcium homeostasis in mice transgenic for exon 1 of the huntington gene.

Transgenic Huntington's disease (HD) mice, expressing exon 1 of the human HD gene (lines R6/1 and R6/2), are totally resistant to striatal lesions caused by the NMDA receptor agonist quinolinic acid (QA). Here we show that this resistance develops gradually over time in both R6/1 and R6/2 mice, and that it occurred earlier in R6/2 (CAG-155) than in R6/1 (CAG-115) mice. The development of the resistance coincided with the appearance of nuclear inclusions and with the onset of motor deficits. In the HD mice, hippocampal neurons were also resistant to QA, especially in the CA1 region. Importantly, there was no change in susceptibility to QA in transgenic mice with a normal CAG repeat (CAG-18). R6/1 mice were also resistant to NMDA-, but not to AMPA-induced striatal damage. Interestingly, QA-induced current and calcium influx in striatal R6/2 neurons were not decreased. However, R6/2 neurons had a better capacity to handle cytoplasmic calcium ([Ca2+]c) overload following QA and could avoid [Ca2+]c deregulation and cell lysis. In addition, basal [Ca2+]c levels were increased five-fold in striatal R6/2 neurons. This might cause an adaptation of R6 neurons to excitotoxic stress resulting in an up-regulation of defense mechanisms, including an increased capacity to handle [Ca2+]c overload. However, the increased level of basal [Ca2+]c in the HD mice might also disturb intracellular signalling in striatal neurons and thereby cause neuronal dysfunction and behavioural deficits.

Aging↗

PubMed2001

Bilateral GPi DBS is useful to reduce abnormal involuntary movements in advanced Parkinson's disease patients, but its action is related to modality and site of stimulation.

In Parkinson's disease (PD) patients, internal globus pallidus (GPi) stimulation has been reported to produce good effects on abnormal involuntary movements (AIM); less improvement has been observed in extrapyramidal symptoms. We assessed the effect of monopolar dorsal (uppermost), ventral (lowest) and bipolar (uppermost vs. lowest) bilateral globus pallidus stimulation by quadripolar electrode on extrapyramidal symptoms and AIM induced by a dose of apomorphine. Six PD patients were studied in OFF therapy condition after surgery without stimulation (STIM OFF) and during stimulation (STIM ON) with the three different modalities. All patients were evaluated by the unified Parkinson's disease rating scale, section III (UPDRS) and by the AIM. Our results show that all three bilateral GPi stimulation modalities reduce the UPDRS score (between 49.7 and 31.5%), although the bipolar and lowest stimulation are the most effective. Similarly, bipolar and lowest stimulation were also the most effective in reducing the occurrence and intensity of the apomorphine-induced AIM. On the contrary, uppermost stimulation (UP ON) produced an AIM occurrence similar to that observed in the OFF stimulus condition. We suggest that bilateral GPi stimulation is an useful procedure to ameliorate extrapyramidal signs of advanced PD patients; however, it produces an antidyskinetic effect only if the ventral or the entire GPi is stimulated. On the contrary, the UP ON, most probably located in the external globus pallidus (GPe), does not modify the AIM occurrence.

Aged↗

PubMed2001

Levetiracetam does not modulate neuronal voltage-gated Na+ and T-type Ca2+ currents.

This study investigated whether the mechanism of action of levetiracetam (LEV) is related to effects on neuronal voltage-gated Na+ or T-type Ca2+currents. Rat neocortical neurones in culture were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study voltage-gated Na+ current. Additionally, visually identified pyramidal neurones in the CA1 area of rat hippocampal slices were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study low-voltage-gated (T-type) Ca2+ current. LEV (10 microM-1 mM) did not modify the Na+ current amplitude and did not change (200 microM) the steady-state activation and inactivation, the time to peak, the fast kinetics of the inactivation and the recovery from the steady-state inactivation of the Na+ current. Likewise, LEV (32-100 microM) did not modify the amplitude and did not change the steady-state activation and inactivation, the time to peak, the fast kinetics of the inactivation and the recovery from the steady-state inactivation of the T-type Ca2+current. In conclusion, neuronal voltage-gated Na+ channels do not appear directly involved in the antiepileptic mechanism of action of LEV, and LEV was devoid of effect on the low-voltage-gated (T-type) Ca2+ current in hippocampal neurones.

Animals↗

PubMed2001

Adenosine-mediated inhibition of striatal GABAergic synaptic transmission during in vitro ischaemia.

Several reports have shown that energy deprivation, as a result of hypoxia, hypoglycaemia or ischaemia, depresses excitatory synaptic transmission in virtually all brain areas. How this pathological condition affects inhibitory synaptic transmission is still unclear. In the present in vitro study, we coupled whole-cell patch clamp recordings from striatal neurones with focal stimulation of GABAergic nerve terminals in order to characterize the electrophysiological effects of combined oxygen and glucose deprivation (in vitro ischaemia) on inhibitory postsynaptic currents (IPSCs) in this brain area. We found that brief periods (2-5 min) of in vitro ischaemia invariably caused a marked depression of IPSC amplitude. This inhibitory effect was fully reversible on removal of the ischaemic challenge. It was coupled with an increased paired-pulse facilitation, suggesting the involvement of presynaptic mechanisms. Accordingly, the ischaemic inhibition of striatal GABAergic IPSCs was not caused by a shift in the reversal potential of GABA(A)-receptor mediated synaptic currents, and was independ- ent of postsynaptic ATP concentrations. Endogenous adenosine, acting on A1 receptors, appeared responsible for this presynaptic action as the ischaemic depression of IPSCs was prevented by CPT [8-(4-chlorophenylthio) adenosine] and DPCPX, two adenosine A1 receptor antagonists, and mimicked by the application of adenosine in the bathing solution. Conversely, ATP-sensitive potassium channels were not involved in the inhibition of IPSCs by ischaemia, as demonstrated by the fact that tolbutamide and glipizide, two blockers of these channels, were ineffective in preventing this electrophysiological effect. The early depression of GABA-mediated synaptic transmission might play a role in the development of irreversible neuronal injury in the course of brain ischaemia.

Adenosine↗

PubMed2001

Translational selection on codon usage in Xenopus laevis.

A correspondence analysis of codon usage in Xenopus laevis revealed that the first axis is strongly correlated with the base composition at third codon positions. The second axis discriminates between putatively highly expressed genes and the other coding sequences, with expression levels being confirmed by the analysis of Expressed sequence tag frequencies. The comparison of codon usage of the sequences displaying the extreme values on the second axis indicates that several codons are statistically more frequent among the highly expressed (mainly housekeeping) genes. Translational selection appears, therefore, to influence synonymous codon usage in Xenopus.

Amino Acids↗

PubMed2001

A method based on DIMOND quality criteria to evaluate imaging in diagnostic and interventional cardiology.

Image quality criteria (IQC) for cine-angiography were recently settled. The aim of this study was to test whether these criteria allow a measurement of the quality of cine-angiograms. A questionnaire was derived from IQC where a binary response was required regarding the degree of visibility of anatomic or pathologic structures. Scores were given on a ranking scale. Two quality scores were defined (total score and minimum score) and standard deviation (SD) was assumed to be an indicator of the method's reproducibility. Data of the total score are presented for the first nine angiograms. Six experts obtained thirty-nine readings. The total scores ranged between 83 and 99% (SD 0.8-18.7%); 89% of the readings were within 4% of SD. This preliminary experience indicates that quality criteria can be translated into a scoring system that yields reproducible data in most instances. The analysis of the remaining angiograms will help in understanding how to improve these results.

Cardiology↗

PubMed2001

Patient dose related to the complexity of interventional cardiology procedures.

In interventional cardiology (IC) the PTCA (percutaneous transluminal coronary angioplasty) procedure is the most frequent procedure with the highest dose to the patient. The procedure is usually performed by cardiologists having, in general, insufficient knowledge of radiation physics, radiation technology and radiation protection. The need for radiation protection is of paramount importance in this field of interventional radiology. Correlation between the complexity of PTCA procedure and irradiation parameters (fluoroscopy time, number of images and dose-area product--DAP) has been demonstrated. The presence of severe tortuosity and occlusion of > or = 3 months play a major role. Fluoroscopy time is better correlated with technical factors than DAP, which also includes the influence of patient size, collimation, operation modes, and X ray beam orientation. The number of acquired images is less correlated with the complexity of the PTCA procedure. A complexity index was conceived and procedures were divided into three groups, defined as: simple, medium and complex, which were significantly different in terms of patient dose.

Angioplasty, Balloon, Coronary↗

PubMed2001

New high-performance liquid chromatographic method for plasma/serum analysis of lamotrigine.

Lamotrigine is an anticonvulsant drug recently approved in Italy for clinical use. Therapeutic monitoring of lamotrigine is relevant for patient management and avoidance of toxicity. The authors describe a simple, sensitive, and highly selective high-performance liquid chromatography method that does not involved extraction for analysis of serum lamotrigine. Serum (20 microL) with internal standard (BW 725 C) was injected directly into a column (25 cm x 4.6 mm) with an internal surface reversed phase (ISRP). The mobile phase consisted of 0.01 mol/L potassium phosphate bibasic (pH 6.0) and acetonitrile (82:18), the flow rate was 1.0 mL/min, and UV detection was optimized at 330 nm. The overall between-run coefficient of variance ranged from 1.89% to 3.25% and the lowest limit of detection was 0.05 mg/L. High linearity (r = 0.9996) in a wide range of concentrations (0.1-20.0 mg/L) and no interference with other antiepileptic drugs, benzodiazepines, and tricyclic antidepressants were the other characteristics of the method. The innovation of this method is the use of ISRP column and the choice of detection wavelength, which allow a shorter analysis time (5-6 minutes). The possibility of direct injection of plasma samples into the column permits a reduction in reagent consumption and in analytic steps, and hence in analytic error.

Anticonvulsants↗