Search PubMed⌕ Search

Biomedical subjects

S Cocco

Publications and source records attributed to S Cocco.

17 recordsLinked to original sources
PubMed2001

Force and kinetic barriers to unzipping of the DNA double helix.

A theory of the unzipping of double-stranded DNA is presented and is compared to recent micromanipulation experiments. It is shown that the interactions that stabilize the double helix and the elastic rigidity of single strands simply determine the sequence-dependent approximately 12-pN force threshold for DNA strand separation. Using a semimicroscopic model of the binding between nucleotide strands, we show that the greater rigidity of the strands when formed into double-stranded DNA, relative to that of isolated strands, gives rise to a potential barrier to unzipping. The effects of this barrier are derived analytically. The force to keep the extremities of the molecule at a fixed distance, the kinetic rates for strand unpairing at fixed applied force, and the rupture force as a function of loading rate are calculated. The dependence of the kinetics and of the rupture force on molecule length is also analyzed.

DNA↗
PubMed2001

Trajectories in phase diagrams, growth processes, and computational complexity: how search algorithms solve the 3-satisfiability problem.

Decision and optimization problems typically fall into one of two categories for any particular solving algorithm. The problem is either solved quickly (easy) or demands an impractically long computational effort (hard). Here we show that some characteristic parameters of problems can be tracked during a run of the algorithm defining a trajectory through the parameter space. Focusing on 3-satisfiability, a recognized representative of hard problems, we analyze trajectories generated by search algorithms. These trajectories can cross well-defined phases, corresponding to domains of easy or hard instances, and allow one to successfully predict the times of resolution.

Journal Article↗
PubMed2000

Hippocampal acetylcholine release correlates with spatial learning performance in freely moving rats.

To assess the activity of septohippocampal cholinergic neurons during the learning of a radial-arm maze task we measured changes in extracellular acetylcholine levels in the hippocampus by means of the vertical microdialysis technique. During the 12 days spent learning the spatial task the extracellular concentration of acetylcholine in the hippocampus was monitored while rats performed the test. One week before radial-arm maze training a guide cannula was implanted unilaterally in the hippocampus. On each day of testing a removable microdialysis probe was inserted through the guide cannula and the dialysate was collected during the test performance. The concentration of acetylcholine in the dialysate was detected by means of a high-performance liquid chromatograph coupled to an electrochemical detector. We found that hippocampal acetylcholine release progressively increased from 139% to 245% during the 12 days of radial-maze learning and the magnitude of change in acetylcholine output was positively correlated with spatial memory performance, thus suggesting that changes in the functioning of these neurons are involved in learning.

Acetylcholine↗
PubMed2000

A tryptophan-free diet markedly reduces frontocortical 5-HT release, but fails to modify ethanol preference in alcohol-preferring (sP) and non-preferring (sNP) rats.

It has been hypothesised that rat lines genetically selected for their alcohol preference consume large amounts of ethanol because they have a low 5-HT content. Since brain tryptophan (TRP) availability controls the rate at which neurons synthesise and release serotonin (5-HT), we assessed whether the administration of a TRP-supplemented or TRP-free diet for 3 consecutive days influenced alcohol intake in alcohol-preferring and non-preferring sP and sNP rats, respectively. In the same animals extracellular 5-HT concentration was monitored by microdialysis in the frontal cortex. A TRP-free diet progressively and markedly decreased cortical extracellular 5-HT in sP and sNP rats during the treatment period with respect to a balanced diet. However, the TRP-free diet failed to modify alcohol consumption and preference in sP and sNP rats. The TRP-supplemented diet also failed to alter the intake of alcohol in either group of rats. Therefore, these results do not support a specific role of 5-HT transmission in ethanol intake and preference in sP and sNP rats.

Animals↗
PubMed2000

A physiological method to selectively decrease brain serotonin release.

In this protocol the effect of both an acute and chronic tryptophan (TRP)-free diet on brain serotonin (5-HT) release was studied in rats. Extracellular levels of cortical 5-HT, assessed by in vivo microdialysis, revealed a decrease in the release of this monoamine. Indeed, 120 min after the acute administration of a TRP-free diet, cortical 5-HT release decreased significantly by about 40% with respect to a balanced diet and the decrease persisted for more than 6 h. The chronic intake of a TRP-free diet induced a gradual reduction in 5-HT release. Five days after the diet consumption, our HPLC system detected no 5-HT in cortical dialysate. On the contrary, the acute or chronic administration of the TRP-free diet made no significant change in extracellular noradrenaline content in the frontal cortex, suggesting a specific action of the diet on the serotonergic system. Therefore, the administration of a TRP-free amino acid diet offers a non-pharmacological means for effectively decreasing brain 5-HT release. This diet can be used to study the physiological and behavioral effects of reduced brain 5-HT function.

Animals↗
PubMed1999

Long-term voluntary ethanol consumption affects neither spatial nor passive avoidance learning, nor hippocampal acetylcholine release in alcohol-preferring rats.

Long-term ethanol consumption in humans and laboratory animals is associated with morphological and functional alterations of brain structures involved in cognitive processes. In the present experiments, we assessed whether voluntary long-term consumption of ethanol by alcohol-preferring (sP) rats under free choice condition with water (also) caused alterations in memory performance and hippocampal acetylcholine (ACh) release in vivo. A group of sP rats were offered a 10% v/v ethanol solution in a free choice with water for 36 weeks; controls had only tap water available. After withdrawal of ethanol, rats were tested in one trial passive avoidance test and thereafter were trained in a food-reinforced radial arm maze task for 12 days. One day after the last session in the radial-arm maze, rats were implanted with a microdialysis probe in the dorsal hippocampus and dialysate concentrations of ACh were measured. No significant differences were observed between sP drinking and control rats in retention latencies in the passive avoidance test, in radial arm-maze performance or in basal levels of hippocampal ACh release. These results show that long-term ethanol consumption by sP rats is not associated with cognitive impairments or with alterations in the hippocampal cholinergic function. To the extent that chronic ethanol intoxication can be considered a causal factor in the development of memory and neurochemical alterations, these results suggest that sP rats self-regulate ethanol consumption so as to avoid intoxication. These findings may challenge the notion that sP rat lines can be considered a valid model of human alcoholism.

Acetylcholine↗
PubMed1999

Serotonin and acetylcholine release response in the rat hippocampus during a spatial memory task.

By using in vivo microdialysis we monitored the extracellular levels of acetylcholine and serotonin in the hippocampus of rats performing a spatial memory task. After rats were trained for 10 consecutive days to master a food-reinforced radial-arm maze task, they were implanted with a microdialysis probe in the dorsal hippocampus. On day 12, rats were tested in the maze and acetylcholine and serotonin outputs were monitored before the test, during the waiting phase and while performing the trials. In trained, food-rewarded rats, hippocampal acetylcholine levels increased during the waiting period (181 +/- 90 of baseline) and further increased during the radial-maze performance to 236 +/- 13% of baseline values, while serotonin levels did not change during the waiting period but increased to 142 +/- 3% during the maze performance. To discriminate whether the increase of acetylcholine and serotonin levels during the testing was associated with memory performance or with food consumption, we monitored hippocampal acetylcholine and serotonin release in rats that were trained, but not food rewarded, or in rats that were not trained, but rewarded only on the test day. In the trained, non-rewarded group, acetylcholine release increased during the waiting phase to 168 +/- 6%, but did not increase further during the task performance. In contrast, no change in serotonin release was observed in this group in any phase of the test. In rats which were not trained, but food rewarded, acetylcholine increased only during the maze period (150 +/- 5%). Serotonin increased gradually and become significant at the end of the trials. (130 +/- 3%). While both neurotransmitters could be implicated in feeding behaviour, only activation of cholinergic neurotransmission appears to be associated with memory function. Our results support the following hypotheses: (i) hippocampal acetylcholine could be involved in attentional and cognitive functions underlying motivational processes; (ii) serotonin could be implicated in non-cognitive processes (i.e. in the control of motor and feeding behaviour). Since serotonin and acetylcholine neurotransmission is simultaneously activated during the spatial memory task, this suggests that these neurotransmitter systems regulate behavioural and cognitive functions.

Acetylcholine↗
PubMed1998

Large-scale analysis of hepatitis C virus serological typing assay: effectiveness and limits.

The HCV (hepatitis C virus) Serotyping 1-6 Assay (Murex Laboratories) was evaluated on 303 French HCV-infected patients. Serological typing results were compared to the genotypes obtained from sequence analyses of the 5' noncoding regions of the virus genome from 46 HCV-infected patients, and assay specificity was found to be high (97.6%). The serological typing assay, run in 257 consecutive HCV-infected patients, yielded an assay sensitivity lower (70.6%) than that previously reported. This finding was attributed mainly to nonreactive sera from human immunodeficiency virus (HIV)-positive patients (P < 0.001) and perhaps reflected cryoglobulin positivity in others. No anti-type 6 reactivity was detected, and the overall serological type distribution values for types 1 to 5 were 67.3, 7.9, 16.4, 6.6, and 0.9%, respectively. A higher prevalence of type 4 was noted among HIV-infected patients (P < 0.001). In addition, serotype 2 was significantly more frequent in cryoglobulinemia positive than in cryoglobulinemia-negative patients (P < 0.05). Although an initial high level (7%) of mixed serological typing reactivities was found, after predilution of serum only two mixed infections could be confirmed (0.9%). It is suggested, therefore, that mixed reactivities have to be interpreted carefully and retested with prediluted serum, particularly when the optical density of the reactivity is > 2.5 or remains > 0.4 after competition with all type-specific peptides. The high specificity and relatively good sensitivity even in immunocompromised patients obtained with this assay indicate that it can be used routinely. Because response to treatment is linked to HCV type, this assay could be used to identify HCV serotype to guide therapeutic decisions.

Case-Control Studies↗
PubMed1997

The decrease of serotonin release induced by a tryptophan-free amino acid diet does not affect spatial and passive avoidance learning.

We assessed whether consumption of a diet lacking in tryptophan (TRP) resulted in alteration in learning and memory performance and hippocampal 5-HT release in rats. Two hours after the acute administration of TRP-free (T) and balanced (B) diet rats were trained in a one-trial passive avoidance task. The two groups of rats showed no significant difference in retention latencies. Two other groups of rats, fed with the above diets during the acquisition of a radial-arm maze task, showed no difference in baseline performance. The acute ingestion of the T diet produced a significant and long lasting decrease of hippocampal and cortical 5-HT release in rats when compared to the B diet, while the 12th day of the T diet, 5-HT was not detectable in the dialysate. These data indicate that the diminished brain release of 5-HT induced by a T diet is not sufficient to impair cognitive processes.

Animals↗
PubMed1997

Acute administration of a tryptophan-free amino acid mixture decreases 5-HT release in rat hippocampus in vivo.

The effect of oral administration of a tryptophan-free amino acid mixture or the same mixture containing tryptophan (Trp) on hippocampal serotonin (5-HT) extracellular levels was studied using in vivo brain microdialysis of freely moving rats. During chloral hydrate anesthesia rats were implanted with dialysis probes in the dorsal hippocampus, and experiments were performed 24 h later. In vehicle-treated rats, the extracellular levels of 5-hydroxyindolacetic acid (5-HIAA) and 5-HT did not change during 240 min after ingestion. Oral administration of the Trp-free amino acid mixture significantly decreased basal 5-HT and 5-HIAA output 100 min after ingestion (65 and 81% of basal value, respectively) and remained at this level for another 140 min. The amino acid mixture containing Trp failed to significantly change basal extracellular levels of 5-HT, but enhanced that of 5-HIAA by approximately 134%. Moreover, in rats receiving the Trp-free amino acid mixture, the increase of hippocampal 5-HT release induced by d-fenfluramine (206%) was smaller than that released by the same drug in rats receiving the nutritionally balanced amino acid mixture (271%). Thus these results show that removal of Trp from the balanced amino acid mixture decreases spontaneous and d-fenfluramine-induced release of 5-HT in the hippocampus. In conclusion, our study supports the hypothesis that the mood-lowering effect observed in man after ingestion of a Trp-free amino acid mixture is associated with diminished 5-HT release in the brain.

Administration, Oral↗
PubMed1995

Isolation of a differentially regulated splicing isoform of human NF-E2.

The transcription factor NF-E2 (nuclear factor erythroid 2), interacting via DNA motifs within regulatory regions of several hematopoietic genes, is thought to mediate the enhancer activity of the globin locus control regions. By screening a human fetal liver cDNA library with probes derived from mouse NF-E2, we have isolated a splicing variant of the NF-E2 gene (fNF-E2) that differs in the 5' untranslated region from the previously reported cDNA (aNF-E2). The fNF-E2 isoform is transcribed from an alternative promoter located in the 3' end of the first intron and joined by alternative splicing to the second and third exons, which are shared by both RNA isoforms. Although the two forms produce the same protein, they are expressed in different ratios during development. fNF-E2 is more abundant in the fetal liver and less abundant in the adult bone marrow compared to the previously described form. Their distribution apparently follows the differential expression of fetal and adult hemoglobins.

Alternative Splicing↗
PubMed1994

Repeated PCR in CML during IFN-alpha therapy.

Repeated PCR analysis was performed on bone marrow and/or peripheral blood samples from 4 CML patients in complete cytogenetic remission during treatment with IFN-alpha. Two patients became PCR-negative. One was negative for the analyses carried out from the 9th to the 30th months, but reverted to PCR positivity 10 months after IFN was reduced from 1.5 x 10(6) IU/day to 1 x 10(6) IU and given on alternate days. Although the dose was again raised to 3 x 10(6) IU/day, 8 months later her peripheral blood cells were still PCR-positive, but remained persistently Ph'-negative. Another patient became PCR-negative at the 42nd month and remained so at the last analysis performed 3 months later. Two patients were persistently PCR-positive. Cytogenetic relapse was documented in both, in one while still on full therapy. Ph'-positive metaphases reappeared in the other patient 7 months after discontinuing IFN-alpha therapy.

Adult↗
PubMed1992

HbH disease in Sardinia: molecular, hematological and clinical aspects.

In this study we have defined the molecular basis and correlated the clinical phenotype with the alpha-globin genotype in a large series of patients of Sardinian descent with HbH disease. The most prevalent molecular defect was the deletion of 3 alpha-globin structural genes most commonly the (--/-alpha 3.7) genotype (83.6%) and rarely the (--/-alpha 4.2) genotype (1.4%), followed in decreasing order of incidence by the combination of deletion alpha zero-thalassemia and initiation codon mutation of the alpha 2-gene (--/alpha NcoI alpha = 9.8%), deletion alpha zero-thalassemia and pentanucleotide deletion of IVS-I of the alpha 2-globin gene, (--/alpha HphI alpha = 3.3%) deletion alpha zero-thalassemia and initiation codon mutation of the alpha 1-gene (--/alpha alpha NcoI = 1.3%), a homozygous state for initiation codon mutation of the alpha 2-gene (alpha Nco alpha/alpha NcoI alpha = 0.7%). Patients with the (--/alpha thal alpha) genotypes showed severer clinical and hematological features as compared to those with the (--/-alpha) or those with the (--/alpha alpha thal) genotypes. The single patient with the (alpha Nco alpha/alpha Nco alpha) genotype had a clinical phenotype intermediate between HbH disease and the alpha-thalassemia carrier status. This heterogeneity depends on the fact that the alpha 2-globin gene produces 2-3 times alpha-globin chains than the alpha 1-gene and the single remaining alpha 1-like globin gene in the -alpha 3.7 chromosome has a compensatory increase in the alpha-globin chain output. alpha-Globin gene mapping of HbH disease patients may be useful for predicting the clinical outcome and to improve genetic counseling.

Adult↗