PubMed Health⌕ Search

Biomedical subjects

Mariella De Biasi

Publications and source records attributed to Mariella De Biasi.

13 recordsLinked to original sources
PubMed2006

Mice with the R176Q cardiac ryanodine receptor mutation exhibit catecholamine-induced ventricular tachycardia and cardiomyopathy.

Mutations in the cardiac ryanodine receptor 2 (RyR2) have been associated with catecholaminergic polymorphic ventricular tachycardia and a form of arrhythmogenic right ventricular dysplasia. To study the relationship between RyR2 function and these phenotypes, we developed knockin mice with the human disease-associated RyR2 mutation R176Q. Histologic analysis of hearts from RyR2(R176Q/+) mice revealed no evidence of fibrofatty infiltration or structural abnormalities characteristic of arrhythmogenic right ventricular dysplasia, but right ventricular end-diastolic volume was decreased in RyR2(R176Q/+) mice compared with controls, indicating subtle functional impairment due to the presence of a single mutant allele. Ventricular tachycardia (VT) was observed after caffeine and epinephrine injection in RyR2(R176Q/+), but not in WT, mice. Intracardiac electrophysiology studies with programmed stimulation also elicited VT in RyR2(R176Q/+) mice. Isoproterenol administration during programmed stimulation increased both the number and duration of VT episodes in RyR2(R176Q/+) mice, but not in controls. Isolated cardiomyocytes from RyR2(R176Q/+) mice exhibited a higher incidence of spontaneous Ca(2+) oscillations in the absence and presence of isoproterenol compared with controls. Our results suggest that the R176Q mutation in RyR2 predisposes the heart to catecholamine-induced oscillatory calcium-release events that trigger a calcium-dependent ventricular arrhythmia.

Animals↗
PubMed2005

Corelease of dopamine and serotonin from striatal dopamine terminals.

The striatum receives rich dopaminergic and more moderate serotonergic innervation. After vesicular release, dopamine and serotonin (5-hydroxytryptamine, 5-HT) signaling is controlled by transporter-mediated reuptake. Dopamine is taken up by dopamine transporters (DATs), which are expressed at the highest density in the striatum. Although DATs also display a low affinity for 5-HT, that neurotransmitter is normally efficiently taken up by the 5-HT transporters. We found that when extracellular 5-HT is elevated by exogenous application or by using antidepressants (e.g., fluoxetine) to inhibit the 5-HT transporters, the extremely dense striatal DATs uptake 5-HT into dopamine terminals. Immunohistochemical results and measurements using fast cyclic voltammetry showed that elevated 5-HT is taken up by DATs into striatal dopamine terminals that subsequently release 5-HT and dopamine together. These results suggest that antidepressants that block serotonin transporters or other factors that elevate extracellular 5-HT alter the temporal and spatial relationship between dopamine and 5-HT signaling in the striatum.

Animals↗
PubMed2004

Functional polymorphisms in the human beta4 subunit of nicotinic acetylcholine receptors.

Human nicotinic acetylcholine receptor (nAChR) polymorphisms occur in different ethnic populations and may result in differences in nAChR ion channel properties. We have identified four nAChR beta 4 subunit (beta4) nucleotide variants: 392C-->T, 526C-->T, 538A-->G, and 1519A-->G. Their corresponding amino acid substitutions are: Thr to Ile at codon 91 (T91I), Arg to Trp at codon 136 (R136W), Ser to Gly at codon 140 (S140G), and Met to Val at codon 467 (M467V), respectively. The nAChR ion channel properties of these variants were studied and compared with the more-common (wild-type) allele as wild-types. The nAChRs (alpha4beta4 channels) were expressed heterologously in Xenopus oocytes and studied using the two-electrode voltage clamp technique to reveal functional differences between the wild-type and the variants. The receptors containing the R136W and M467V mutations (or variants) had a higher sensitivity to acetylcholine and lower EC50 than the wild-type. The T91I mutation had lower sensitivity to acetylcholine and the EC50 was larger than in wild-type nAChRs. The S140G mutation had a dose-response relationship that was similar to the wild-type. The T91I, R136W, and M467V mutations (or variants) also showed a slightly greater degree of steady-state desensitization than the wild-type in response to a 30-min exposure to one tenth of their EC50. The present results demonstrate that human beta4 nAChR DNA polymorphisms result in functional changes, and suggest that certain individuals with those variants may be more or less sensitive to cholinergic drugs or to dysfunctions associated with nicotinic cholinergic systems.

Amino Acid Substitution↗
PubMed2004

Decreased signs of nicotine withdrawal in mice null for the beta4 nicotinic acetylcholine receptor subunit.

Withdrawal from chronic exposure to nicotine, the main addictive component of tobacco, produces distinctive symptoms in humans. The appearance of these symptoms is a major deterrent when people try to quit smoking. To study which type of nicotine receptor is relevant for the onset of the withdrawal syndrome, we used a mouse model of nicotine withdrawal. Wild-type mice and mice null for the beta4 (beta4-/-) or the beta2 (beta2-/-) nicotinic acetylcholine receptor subunits were implanted with osmotic minipumps delivering 24 mg x kg(-1) x d(-1) nicotine for 13 d. Subsequently, a single intraperitoneal injection of the nicotinic receptor antagonist mecamylamine induced behavioral symptoms of withdrawal measured as increased grooming, chewing, scratching, and shaking, plus the appearance of some unique behaviors such as jumping, leg tremors, and cage scratching. Mecamylamine injection triggered comparable withdrawal signs in wild-type and in beta2-/- mice, whereas the beta4-/- mice displayed significantly milder somatic symptoms. In addition, nicotine withdrawal produced hyperalgesia in wild-type but not beta4-/- mice. Finally, chronic nicotine produced an increase in epibatidine binding in several areas of the brain in both wild-type and in beta4-/- mice, but such receptor upregulation did not correlate with the severity of withdrawal signs. Our results demonstrate a major role for beta4-containing nicotinic acetylcholine receptors in the appearance of nicotine withdrawal symptoms. In contrast, the beta2 subunit does not seem to greatly influence this phenomenon. We also show that the upregulation of epibatidine binding sites attributable to chronic nicotine, an effect associated with beta2-containing receptors, is probably not related to the mechanisms underlying withdrawal.

Animals↗
PubMed2004

The alpha3 and beta4 nicotinic acetylcholine receptor subunits are necessary for nicotine-induced seizures and hypolocomotion in mice.

Binding of nicotine to nicotinic acetylcholine receptors (nAChRs) elicits a series of dose-dependent behaviors that go from altered exploration, sedation, and tremors, to seizures and death. nAChRs are pentameric ion channels usually composed of alpha and beta subunits. A gene cluster comprises the alpha3, alpha5 and beta4 subunits, which coassemble to form functional receptors. We examined the role of the beta4 subunits in nicotine-induced seizures and hypolocomotion in beta4 homozygous null (beta4 -/-) and alpha3 heterozygous (+/-) mice. beta4 -/- mice were less sensitive to the effects of nicotine both at low doses, measured as decreased exploration in an open field, and at high doses, measured as sensitivity to nicotine-induced seizures. Using in situ hybridization probes for the alpha3 and alpha5 subunits, we showed that alpha5 mRNA levels are unchanged, whereas alpha3 mRNA levels are selectively decreased in the mitral cell layer of the olfactory bulb, and the inferior and the superior colliculus of beta4 -/- brains. alpha3 +/- mice were partially resistant to nicotine-induced seizures when compared to wild-type littermates. mRNA levels for the alpha5 and the beta4 subunits were unchanged in alpha3 +/- brains. Together, these results suggest that the beta4 and the alpha3 subunits are mediators of nicotine-induced seizures and hypolocomotion.

Analysis of Variance↗
PubMed2003

Altered anxiety-related responses in mutant mice lacking the beta4 subunit of the nicotinic receptor.

Nicotine, acting at nicotinic acetylcholine receptors (nAChRs), is the primary addictive component of tobacco. Smokers often report an anxiolytic effect of cigarettes. This relief of anxiety, attributed to nicotine, is an important contributor to relapse when smokers try to quit. Hence, the study of the anxiolytic effects of nicotine is important for understanding the mechanisms underlying nicotine addiction. Mammalian nAChRs are pentameric ion channels usually composed of alpha andbeta subunits. Taking advantage of beta4-homozygous-null mice (beta4-/-), we examined the role of the nAChR beta4 subunit in anxiety-related behaviors. The beta4-/- mice behaved as though they were less anxious than wild-type littermates on the elevated-plus and staircase mazes, tests that measure anxiety-related behaviors. To obtain an independent, physiological indication of the stress produced by several tests, we measured changes in heart rate using telemetry. Consistently with the behavioral phenotype, beta4-/- mice had a smaller heart rate increase in the elevated-plus maze than did wild-type littermates. In contrast, during social isolation, a separate test for anxiety,beta4-/- mice exhibited a greater increase in heart rate than did wild-type littermates. Finally, beta4-/- mice were indistinguishable from their wild-type littermates in the open field, the light/dark box, and the mirrored chamber. The overall results demonstrate that beta4-containing (beta4*) nAChRs influence behavioral responses during anxiety-related tests, and that this effect depends on the type of anxiety-provoking experience. Through their influence on anxiety-related behavior, beta4* nAChRs might influence both tobacco consumption and smoking relapse.

Animals↗
PubMed2003

The nicotinic acetylcholine receptor subunit alpha 5 mediates short-term effects of nicotine in vivo.

Nicotine, acting at pentameric neuronal nicotinic acetylcholine receptors (nAChRs), is the primary addictive component in tobacco. At low doses, it affects attention, learning, memory, anxiety, cardiovascular responses, thermoregulation, and nociception. At high doses, nicotine produces more drastic behaviors and eventually induces tonic-clonic seizures in rodents. In mammals, several subunits of the nAChRs have been cloned, including eight alpha and three beta subunits. To study the physiological role of the alpha 5 subunit, we have generated alpha 5-deficient mice. These mice have a generally healthy appearance and are normal in a standard battery of behavioral tests. However, the sensitivity of alpha 5 mutant mice to nicotine-induced behaviors and seizures is dramatically reduced compared with their wild-type littermates. These animals have a normal brain anatomy and normal levels of mRNA for other nAChR subunits, namely alpha 4, alpha 6, alpha 7, beta 2, and beta 4. In addition, (125)I-epibatidine and [(125)I]alpha-bungarotoxin binding in the brains of alpha 5-deficient mice is normal. Together, these results suggest a direct involvement of the alpha 5 subunit in the observed phenotypes.

Animals↗
PubMed2002

Absence of alpha7-containing neuronal nicotinic acetylcholine receptors does not prevent nicotine-induced seizures.

Nicotine is the primary addictive component in tobacco, and at relatively low doses it affects cardiovascular responses, locomotor activity, thermoregulation, learning, memory, and attention. At higher doses nicotine produces seizures. The mechanisms underlying the convulsive effects of nicotine are not known, but studies conducted on a number of inbred strains of mice have indicated a positive correlation between the number of alpha-bungarotoxin (alpha-BTX) binding sites in the hippocampus and the sensitivity to nicotine-induced seizures. Because alpha7-containing neuronal nicotinic acetylcholine receptors (nAChRs) represent the major binding site for alpha-BTX, mice lacking the alpha7 nAChR subunit were predicted to be less sensitive to the convulsive effects of nicotine. To test this hypothesis, we injected nicotine intraperitoneally in alpha7 mutant mice and found that the dose-response curve for nicotine-induced seizures was similar in the alpha7 +/+, alpha7 +/- and alpha7 -/- mice. The retained sensitivity to the convulsant effects of nicotine could not be explained by the presence of cholinergic compensatory mechanisms such as increases in mRNA levels for other nAChR subunits, or changes in binding levels or affinity for nicotinic ligands such as epibatidine and nicotine. These findings indicate that alpha7 may not be necessary for the mechanisms underlying nicotine-induced seizures.

Animals↗
PubMed2002

Nicotinic mechanisms in the autonomic control of organ systems.

Most visceral organs are under the control of the autonomic nervous system (ANS). Information on the state and function of these organs is constantly relayed to the central nervous system (CNS) by sensory afferent fibers. The CNS integrates the sensory inputs and sends neural commands back to the organ through the ANS. The autonomic ganglia are the final site for the integration of the message traveling from the CNS. Nicotinic acetylcholine receptors (nAChRs) are the main mediators of fast synaptic transmission in ganglia, and therefore, are key molecules for the processing of neural information in the ANS. This review focuses on the role of nAChRs in the control of organ systems such as heart, gut, and bladder. The autonomic control of these organ systems is discussed in the light of the results obtained from the analysis of mice carrying mutations targeted to nAChR subunits expressed in the ANS.

Animals↗
PubMed2002

Increased sensitivity to nicotine-induced seizures in mice expressing the L250T alpha 7 nicotinic acetylcholine receptor mutation.

High doses of nicotine, the addictive component of tobacco, induce clonic-tonic seizures in animals. Pharmacological and biochemical data have suggested that alpha 7-containing neuronal nicotinic receptors (nAChRs) contribute to these seizures. To study potential alpha 7 contributions, we examined alpha 7 subunits with a Leu250-to-Thr substitution in the channel domain, which creates a gain-of-function mutation. Previous studies have shown that mice homozygous for the alpha 7 L250T mutation (T/T) die shortly after birth, but animals heterozygous for the mutation (+/T) are viable and grow to adulthood. Hippocampal neurons from the +/T mice exhibited altered alpha 7-type currents with increased amplitudes and slower desensitization kinetics, confirming a partial gain of function for the alpha 7 nAChR. We found that +/T mice were more sensitive to the convulsant effects of nicotine compared with their wild-type (+/+) littermates. Furthermore, although their behavior was normal in basal conditions, +/T mice showed a unique nicotine-induced phenotype, consisting of head-bobbing and paw-tapping movements. Increased sensitivity to nicotine-induced seizures occurred despite a 60% decline in brain alpha 7 nAChR protein levels. There were no changes in the levels of alpha 4, alpha 5, alpha 6, alpha 7, beta 2, and beta 4 mRNA, or in [(125)I]epibatidine and [(3)H]nicotine binding between +/T and +/+ mice. Recent data from our laboratory show that alpha 7-null mice maintain normal sensitivity to nicotine-induced seizures. Hence, these present findings suggest that alterations in the properties rather than absence of alpha 7 nAChRs might affect the mechanisms underlying the convulsive properties of nicotine.

Amino Acid Substitution↗
PubMed2002

Urocortin-deficient mice display normal stress-induced anxiety behavior and autonomic control but an impaired acoustic startle response.

Corticotropin-releasing hormone (Crh) plays an important role in modulating physiological and behavioral responses to stress. Its actions are mediated through two receptors, Crhr1 and Crhr2. Urocortin (Ucn), a Crh-related neuropeptide and the postulated endogenous ligand for Crhr2, is a potential mediator of stress responses. We generated Ucn-deficient mice using embryonic stem cell technology to determine its role in stress-induced behavioral and autonomic responses. Unlike Crhr1- or Crhr2-deficient mice, Ucn-deficient mice exhibit normal anxiety-like behavior as well as autonomic regulation in response to stress. However, the mutant mice display an impaired acoustic startle response that is not due to an obvious hearing defect. Thus, our results suggest that Ucn does not play an essential role in stress-induced behavioral and autonomic responses. Ucn may modulate the acoustic startle response through the Ucn-expressing neuron projections from the region of the Edinger-Westphal nucleus.

Alleles↗
PubMed2002

Nicotinic receptor mutant mice in the study of autonomic function.

Nicotinic acetylcholine receptors (nAChRs) have been implicated in Alzheimer's disease, Parkinson's disease, epilepsy, nicotine addiction, schizophrenia, and autonomic dysfunctions. Although nicotine may be used therapeutically either alone or in association with other drugs, its beneficial effects are limited by its addictive properties and a number of other side effects. A deeper understanding of nicotinic cholinergic mechanisms is necessary to develop nAChR ligands that are more selective, less toxic, and more therapeutically effective than nicotine. Although there has been significant progress identifying the nAChR subunits that form functional nAChRs, there is limited information associating the location and function of nAChR subtypes in the nervous system. Several groups have genetically engineered mice in which one or more genes encoding nAChR subunits has been deleted or altered. Mice with nAChR mutations targeted to subunits that are highly expressed in the CNS have brought insight into the nAChR mechanisms involved in nicotine addiction, analgesia, aging, and nicotine-induced behaviors. Mutations targeted to nAChR subunits that are highly expressed in the peripheral nervous system have opened a window on the complex mechanisms governing autonomic control of peripheral organs. This review examines nAChRs in the autonomic control of peripheral organ systems as gleaned from studies of nAChR mutant mice.

Animals↗