PubMed Health⌕ Search

Biomedical subjects

G Bernardi

Publications and source records attributed to G Bernardi.

At least 19 recordsLinked to original sources
PubMed1992

Large-scale methylation patterns in the nuclear genomes of plants.

Methylation was investigated in compositional fractions of nuclear DNA preparations (50-100 kb in size) from five plants (onion, maize, rye, pea and tobacco), and was found to increase from GC-poor to GC-rich fractions. This methylation gradient showed different patterns in different plants and appears, therefore, to represent a novel, characteristic genome feature which concerns the noncoding, intergenic sequences that make up the bulk of the plant genomes investigated and mainly consist of repetitive sequences. The structural and functional implications of these results are discussed.

5-Methylcytosine↗
PubMed1992

Compositional mapping of the human dystrophin-encoding gene.

The genomes of warm-blooded vertebrates are mosaics of long DNA segments (> 300 kb, on the average), the isochores, homogeneous in GC levels, which belong to a small number of compositional families. In the present work, the human dystrophin-encoding gene, spanning more than 2.3 Mb in Giemsa band Xp21 (on the short arm of the X chromosome), was analyzed in its isochore organization by hybridizing cDNA probes, corresponding to eight contiguous segments of the coding sequence, on compositional fractions from human DNA. Five DNA regions of uniform (+/- 0.5%) GC content, separated by compositional discontinuities of about 2% GC, were found, so providing the first high-resolution compositional map obtained for a human genome locus and the first direct estimate of isochore size (360 kb to more than 770 kb, in the locus under consideration). One of the isochores contains 71% and another one 21% of deletion breakpoints found in patients suffering from Duchenne's and Becker's muscular dystrophies.

Computer Simulation↗
PubMed1992

The mosaic organization of the mitochondrial introns of Saccharomyces cerevisiae: features and evolutionary origins.

The introns of three genes (oxi3, cob and 21S) from the mitochondrial (mt) genome of Saccharomyces cerevisiae contain closed reading frames (CRFs). In the present work, we have analyzed these sequences in their oligodeoxyribonucleotide (oligo; isostich) patterns. We have shown that the relative amounts of di- to hexanucleotides, when compared to random sequences having the same sizes and compositions, exhibit the same deviations as the intergenic noncoding sequences of the mt genome (except for the CRFs from 21S intron). In contrast, intronic open reading frames (ORFs) showed oligo patterns which were generally quite distinct from those of CRFs, although some similarities could be detected in some cases (especially for aI5 alpha). The mt introns of yeast, therefore, are endowed with a mosaic structure, in which CRFs derive from mt intergenic sequences, whereas ORFs have a different origin (indicated as exogenous by other evidences) yet show, in some cases, the effects of 'sequence assimilation' with CRFs.

Base Composition↗
PubMed1992

A voltage-clamp analysis of NMDA-induced responses on dopaminergic neurons of the rat substantia nigra zona compacta and ventral tegmental area.

The effects of NMDA-receptor activation on dopaminergic neurons of the rat substantia nigra zona compacta and ventral tegmental area were studied by using in vitro intracellular electrophysiological recordings (current and voltage-clamp). NMDA depolarized the membrane and increased the firing activity. A voltage-dependent inward current and a reduction of the apparent input conductance were observed in voltage-clamp experiments. Interestingly, the peak amplitude of the inward current occurred at approximately -60 mV. The NMDA-induced responses were reduced by the application of DL-2-amino-5-phosphonovaleric acid (APV). The NMDA-induced current was unaffected by potassium channel blockers, was present in low-sodium solutions or in solutions treated with TTX; but was reduced or blocked in low-calcium solutions containing cobalt. In addition, no reduction of the apparent input conductance was observed either in the solutions without magnesium or in those with low-sodium. Our data indicate that the activation of NMDA receptors produces a powerful excitatory stimulus on the dopaminergic neurons of the ventral mesencephalon and this may be primarily the result of a voltage-dependent influx of calcium ions. The degeneration of the dopaminergic cells after application of neurotoxins may be explained by their peculiar response to NMDA.

2-Amino-5-phosphonovalerate↗
PubMed1992

Compositional bimodality and evolution of retroviral genomes.

The compositional distributions of genomes, genes (and their third codon positions) and long terminal repeats from retroviruses of warm-blooded vertebrates are characterized by a striking bimodality which is accompanied by a remarkable compositional homogeneity within each retroviral genome. A first, major class of retroviral genomes is GC-rich, whereas a second, minor class is GC-poor. Representative expressed viral genomes from the two classes integrate in GC-rich and GC-poor isochores, respectively, of host genomes. The first class comprises all oncoviruses (except B-types and some D-types), the second, lentiviruses, spumaviruses, as well as B-type and some D-type oncoviruses (e.g., mouse mammary tumor virus and simian retroviruses type D, respectively). The compositional bimodal distribution of retroviral genomes and the accompanying compositional homogeneity within each retroviral genome appear to be the result of the compositional evolution of retroviral genomes in their integrated form.

Animals↗
PubMed1992

A-current in rat globus pallidus: a whole-cell voltage clamp study on acutely dissociated neurons.

Globus pallidus neurons were dissociated from adult rats and recorded in whole-cell voltage-clamp mode. In tetrodotoxin- and cadmium-added bath, outward potassium conductances were evaluated. Depolarization activated large and predominantly sustained currents, with little inactivation. The transient outward current was isolated through its voltage-dependency, kinetics and pharmacology. A-like current activated around -45 mV and decayed exponentially with a time-constant of about 50 ms at 0 mV. Steady-state half-inactivation voltage was about -60 mV, suggesting that A-current was not fully inactivated at rest. 4-Aminopyridine sensitivity of the transient outward current was in the low millimolar range. A-current might play a relevant role in shaping firing properties of pallidal neurons.

4-Aminopyridine↗
PubMed1992

Coactivation of D1 and D2 dopamine receptors is required for long-term synaptic depression in the striatum.

Long-term changes of synaptic transmission following brief trains of high-frequency stimulation of excitatory pathways in the brain have attracted attention as a possible correlate of memory. In the cerebellum, concurrent activation of parallel fibers and climbing fibers leads to a long-term depression (LTD) of synaptic transmission, which may be the cellular substrate of motor learning in this structure. We report here for the first time that high-frequency stimulation of corticostriatal glutamatergic fibers in the striatum, another brain structure strongly involved in motor control, also induces LTD of synaptic transmission. Induction of striatal LTD is blocked either by SCH 23390, a D1 dopamine (DA) receptor antagonist or by L-sulpiride, a D2 DA receptor antagonist. The lesion of the nigrostriatal DAergic pathway abolishes LTD. After DA depletion, LTD can be restored by the application of exogenous DA. LTD can also be restored by coadministration of D1 and D2 DA receptor agonists, but not by the application of a single class of DA agonists alone. Our data show that coactivation of D1 and D2 DA receptors is required for LTD in the striatum. D1/D2 receptor cooperation in the induction of LTD may play a crucial role in the behavioural function of DA and in the therapeutic effects of DA agonists in Parkinson's disease.

Animals↗
PubMed1992

An electrophysiological study of D2 dopaminergic actions in normal human retina: a tool in Parkinson's disease.

A peculiar deficit of electrophysiological retinal responses to pattern reversal grating stimuli has been reported in Parkinson's disease (PD) patients. A similar abnormality has been reproduced by means of non-selective dopaminergic antagonists in normal humans. Aim of this study was to verify, by means of a selective D2 antagonist (sulpiride) administered to normal subjects, whether a D2 blockade affects the visual electrophysiological performances with the same trend as observed in PD patients. Patterns electroretinogram (PERG) responses to 1 cycle per degree (c/d) of spatial frequency at 1 (transient) and 7.5 (steady state) Hz of temporal modulation of a square-wave grating pattern reversal have been recorded in 19 healthy volunteers before and after the administration of 100 mg i.m. of sulpiride. The data are consistent for the following conclusion: a selective D2 antagonist reduces steady state and delays transient retinal responses as expected for a PD mimicking agent.

Adult↗
PubMed1992

The highest gene concentrations in the human genome are in telomeric bands of metaphase chromosomes.

Chromosome in situ suppression hybridization has been carried out on human metaphase chromosomes to localize the G+C-richest human DNA fraction (which only represents 3.5% of the genome), as isolated by preparative equilibrium centrifugation in Cs2SO4/3,6-bis(acetatomercurimethyl)-1,4-dioxane density gradient. This fraction essentially corresponds to isochore family H3. The rationale for carrying out this experiment is that this isochore family has, by far, the highest gene concentration, the highest concentration in CpG islands, the highest transcriptional and recombinational activity, and a distinct chromatin structure. The in situ hybridization results obtained show that the H3 isochore family is localized in two coincident sets of bands of human metaphase chromosomes: telomeric bands and chromomycin A3-positive 4',6-diamidino-2-phenylindole-negative bands. This result is the first step toward a complete compositional map of the human karyotype. Because the G+C gradient across isochore families is paralleled by a gene concentration gradient, such a map has structural, functional, and evolutionary relevance.

Base Composition↗
PubMed1992

Activation of quisqualate metabotropic receptors reduces glutamate and GABA-mediated synaptic potentials in the rat striatum.

The role of quisqualate (QUIS) metabotropic receptors in the synaptic transmission in the striatum was investigated using the cortico-striatal slice preparation. Low concentrations (1-30 microM) of trans-1-amino-cyclopentyl-1,3- dicarboxylic acid (t-ACPD), a selective agonist of QUIS metabotropic receptors, decreased glutamate-mediated synaptic potentials (EPSPs) evoked in the striatum by the stimulation of cortico-striatal fibers. This agonist decreased also GABA-mediated depolarizing synaptic potentials evoked by intrastriatal stimulation in the presence of 6-cyano-7-nitro-quinoxaline-2,3- dione (CNQX); this effect was less potent than the action of t-ACPD on glutamate-mediated potentials. Low concentrations of t-ACPD did not affect the intrinsic membrane properties of striatal neurons and their postsynaptic responses to exogenous glutamate and GABA. Higher concentrations (50-100 microM) to t-ACPD caused membrane depolarizations and inward currents in several neurons. Our data suggest that low concentrations of t-ACPD selectively reduce synaptic transmission while higher concentrations of this agonist may cause a direct excitatory action on striatal neurons.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

A universal compositional correlation among codon positions.

We have investigated the compositional distributions of third codon positions of genes from the 16 prokaryotes and seven eukaryotes for which the largest numbers of coding sequences are available in data banks. In prokaryotes, both narrow and broad distributions were found. In eukaryotes, distributions were very broad (except for Saccharomyces cerevisiae) and remarkably different for different genomes. In low-GC genomes, third codon positions were lower in GC than first + second codon positions and trailed towards high GC; the opposite situation was found for high-GC genomes. In all genomes, first codon positions were higher in GC than second codon positions. We then investigated the compositional correlations between third and first + second codon positions in prokaryotic genomes (the 16 mentioned above plus 87 additional ones) and in genome compartments of eukaryotes. A general, common relationship was found, which also holds within the same (heterogeneous) genomes. This universal correlation is due to the fact that the relative effects of compositional constraints on different codon positions are the same, on the average, whatever the genome under consideration.

Animals↗
PubMed1992

Chronic neuroleptic treatment: D2 dopamine receptor supersensitivity and striatal glutamatergic transmission.

We studied the in vitro electrical activity of rat neostriatal neurons following chronic neuroleptic treatment. In haloperidol-treated rats, unlike naive animals, activation of neostriatal D2 dopamine receptors induced a potent presynaptic inhibition of glutamate-mediated excitatory synaptic potentials. Haloperidol treatment did not affect the intrinsic membrane properties of the neostriatal neurons. Pre- and postsynaptic physiological responses to direct and indirect gamma-aminobutyric acid (GABA)-ergic and cholinergic agonists were not affected by chronic haloperidol treatment. These findings suggest that movement disorders induced by chronic neuroleptic treatment may result, at least in part, from a hypersensitivity of presynaptic D2 dopamine receptors regulating the release of glutamate.

Aging↗
PubMed1992

Active muscle length reduction progressively damages soleus in hindlimb-suspended rabbits.

This study describes the morphologic changes in rabbit soleus muscle following hindlimb suspension (HS) for 1 to 4 weeks (group A); or following HS with hindfeet passively dorsiflexed, by means of an elastic band, for 1 to 2 weeks (group B). In the latter, elastic band use allowed phasic contractions of foot extensor muscles against resistance and prevented 35% chronic soleus shortening, which occurred in group A animals. In group A, the soleus revealed progressive muscle atrophy and myofibrillar damage. Myofibrils underwent dissolution, muscle regeneration was ineffective, and adipose tissue developed from about 2-week suspension onward. Conversely, passive dorsiflexion of unloaded hindfeet was essential in maintaining mass and structural muscle integrity in the soleus of group B. It is hereby demonstrated that HS-induced soleus damage in the rabbit is progressive, and can be prevented, avoiding long-term shortening of soleus and its phasic unloaded contractions. Soleus sensitivity to unloading conditions, such as HS, tenotomy, and hypogravity, may depend on the particular physiology of this tonic antigravity muscle, engaged mainly in developing long-lasting isometric contractions in a stretched length.

Animals↗
PubMed1992

EEG changes induced by carbamazepine therapy at rest and during mental processes.

The effects of carbamazepine (CBZ) on EEG background activity have been studied, at rest and during mental processes, in 18 epileptic patients suffering from focal epilepsy and starting antiepileptic treatment for the first time. The EEGs were recorded before and after CBZ therapy, at rest with eyes closed (EC), during blocking reaction (BR), fixation (FIX) and mental arithmetic (MA) tasks, and then evaluated by spectral analysis. All data underwent statistical evaluation utilizing the ANOVA and correlation coefficient. The following parameters were evaluated: mean absolute and relative power and mean frequency. The results have shown that CBZ induced a significant increase of slow activity at rest with EC, which was represented by delta potentials, and was correlated with CBZ plasma levels. In evaluating the different cortical activation patterns, a decrease of the alpha reactivity was noted during BR and FIX, while a significant increase of beta activity was observed during the performance of all tasks. The relationship between the increased beta power, possibly reflecting an increase of cognitive activity for processing information, and the lack of a significant decrease of alpha activity are discussed.

Adolescent↗
PubMed1992

The electrophysiological actions of dopamine and dopaminergic drugs on neurons of the substantia nigra pars compacta and ventral tegmental area.

The dopaminergic neurons of the substantia nigra pars compacta and ventral tegmental area play a crucial role in regulating movement and cognition respectively. Several lines of evidence suggest that a degeneration of dopaminergic cells in the substantia nigra produces the symptoms of Parkinson's disease. On the other hand, a hyperactivity of the dopaminergic transmission in the brain induces dyskinesia, dystonia and psychosis. It is also well established that the euphoric and rewarding responses evoked by drugs of addiction, such as amphetamine and cocaine, are mediated by central dopamine systems. Electrophysiological experiments which study the activity of single dopaminergic neurons in the ventral mesencephalon have shown that dopamine and dopaminergic drugs reduce the firing frequency of these cells. This is due to the stimulation of D2-D3 autoreceptors and to a hyperpolarization of the membrane produced by an increase in potassium conductance. In addition, substances which increase the release (amphetamine), the synthesis (levodopa) or block the uptake (cocaine, nomifensine, amineptine) of dopamine in the brain inhibit the firing activity of the dopaminergic cells throughout dopamine-mediated mechanisms. In this review, we will briefly examine the literature concerning the physiological and behavioural responses caused by dopamine and dopaminergic agents on the dopaminergic neurons of the ventral mesencephalon. Our conclusion suggests that the electrophysiological actions of dopamine and dopamine-related drugs on dopaminergic cells in the ventral mesencephalon might be indicative of the pharmacological effects of these agents on the brain.

Animals↗
PubMed1992

Molecular phylogeny of the prickly shark, Echinorhinus cookei, based on a nuclear (18S rRNA) and a mitochondrial (cytochrome b) gene.

The classification of the sharks is unclear. This is particularly true for the superorder Squalomorphii. The relationships between the squalomorphs and other superorders of sharks and the relationships between the different orders within the squalomorphs are a matter of debate. Here, we report a molecular phylogeny for a little known member of this superorder, the genus Echinorhinus. Echinorhinus is most commonly classified in either the family Echinorhinidae (Squaliformes) or the family Squalidae (Squaliformes). However, some authors have suggested a closer relationship to the order Hexanchiformes. In an attempt to shed light on this controversy, we have cloned, sequenced, and compared two genes widely used in molecular phylogeny studies, the cytochrome b and the 18S rRNA from the rare prickly shark, Echinorhinus cookei, and two potential relatives, the spiny dogfish Squalus acanthias (Squaliformes), and the sevengill shark, Notorynchus cepedianus (Hexanchiformes). The sequences of these genes for the prickly shark, the dogfish, and the sevengill shark were found to be equally divergent, suggesting that the prickly shark is no closer to the order Squaliformes than to the order Hexanchiformes.

Animals↗
PubMed1992

Migraine with aura-like syndrome due to arteriovenous malformation. The clinical value of transcranial Doppler in early diagnosis.

Arteriovenous malformations are an acknowledged cause of migraine that can long constitute the only clinical manifestation before bleeding. We describe two cases of patients suffering from symptoms like migraine with aura in whom arteriovenous malformations were detected by transcranial Doppler examination. We suggest that a screening of migraine patients to prevent bleeding from a possible underlying unruptured arteriovenous malformation could be performed by using transcranial Doppler, a non-invasive and low cost examination.

Adult↗