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V Castellani

Publications and source records attributed to V Castellani.

At least 19 recordsLinked to original sources
PubMed2000

The RR Lyrae Star U Comae as a Test for Nonlinear Pulsation Models.

We use high-precision multiband photometric data of the first-overtone RR Lyrae star U Comae to investigate the predictive capability of full-amplitude, nonlinear, convective hydrodynamical models. The main outcome of this investigation is that theoretical predictions properly account for the luminosity variations along a full pulsation cycle. Moreover, we find that this approach, because of the strong dependence of this observable and of the pulsation period on stellar parameters, supplies tight constraints on stellar mass, effective temperature, and distance modulus. Pulsational estimates of these parameters appear in good agreement with empirical ones. Finally, a well-defined bump just before the luminosity maximum gave the unique opportunity to calibrate the turbulent convection model adopted for handling the coupling between pulsation and convection.

Journal Article↗
PubMed1999

Opposing roles for neurotrophin-3 in targeting and collateral formation of distinct sets of developing cortical neurons.

Neurotrophin-3 and its receptor TrkC are expressed during the development of the mammalian cerebral cortex. To examine whether neurotrophin-3 might play a role in the elaboration of layer-specific cortical circuits, slices of layer 6 and layers 2/3 neurons were cultured in the presence of exogenously applied neurotrophin-3. Results indicate that neurotrophin-3 promotes axonal branching of layer 6 axons, which target neurotrophin-3-expressing layers in vivo, and that it inhibits branching of layers 2/3 axons, which avoid neurotrophin-3-expressing layers. Such opposing effects of neurotrophin-3 on axonal branching were also observed with embryonic cortical neurons, indicating that the response to neurotrophin-3 is specified at early developmental stages, prior to cell migration. In addition to its effects on fiber branching, axonal guidance assays also indicate that neurotrophin-3 is an attractive signal for layer 6 axons and a repellent guidance cue for layers 2/3 axons. Experiments with specific antibodies to neutralize neurotrophin-3 in cortical membranes revealed that endogenous levels of neurotrophin-3 are sufficient to regulate branching and targeting of cortical axons. These opposing effects of neurotrophin-3 on specific populations of axons demonstrate that it could serve as one of the signals for the elaboration of local cortical circuits.

Animals↗
PubMed1998

Dual action of a ligand for Eph receptor tyrosine kinases on specific populations of axons during the development of cortical circuits.

The structural basis of cortical columns are radially oriented axon collaterals that form precise connections between distinct cortical layers. During development, these connections are highly specified from the initial outgrowth of collateral branches. Our previous work provided evidence for positional cues confined to individual layers that induce and/or prevent the formation of axon collaterals in specific populations of cortical neurons. Here we demonstrated with in situ hybridization techniques that mRNA of the Eph receptor tyrosine kinase EphA5 and one of its ligands, ephrin-A5, are present in distinct cortical layers, at a time when intrinsic connections are being formed in the cortex. Axonal guidance assays indicate that ephrin-A5 is a repellent signal for a populations of axons that in vivo avoid the cortical layer expressing ephrin-A5. In contrast to its established role as a repulsive axonal guidance signal, ephrin-A5 specifically mediates sprouting of those cortical axons that target the ephrin-A5-expressing layer in vivo. These results identify a novel function of ephrin-A5 on axonal arbor formation. The laminar distribution and the dual action on specific populations of axons suggest that ephrin-A5 plays a role in the assembly of local cortical circuits.

Aging↗
PubMed1997

Membrane-associated molecules regulate the formation of layer-specific cortical circuits.

The columnar organization of the mammalian neocortex is based on radially oriented axon collaterals which precisely link cells from distinct cortical layers. During development, these interlaminar connections are specific from their initial outgrowth: collaterals form only in the target layers and there are no transient axonal collaterals in the nontarget layers. To examine whether positional cues within individual cortical layers regulate the laminar specificity of collateral formation, explants of cells destined for different cortical layers were cultured on membranes prepared from target and nontarget layers. Axonal growth and branching were examined on homogeneous membrane substrates and on alternating stripes of membranes from different layers. Results show that axons branch preferentially on membrane substrates from those layers that they would target in vivo. In addition, when cortical axons were given a choice to grow on membranes from either their target or their nontarget layer, they exhibited a clear preference for the target layers. This indicates that membrane-associated cues confined to individual layers regulate the formation of collaterals of cortical axons and restrict their growth to their target layers. Heat inactivation of membranes from target layers resulted in reduced axonal branching. The same manipulation of membranes from nontarget layers increased axonal branching for one population of cortical neurons. Taken together, these results suggest that membrane-associated molecules confined to individual layers induce and prevent the formation of axon collaterals in distinct populations of cortical neurons. Thus, the expression of layer-specific cues provides important constraints for the remodeling of local circuits during cortical development.

Animals↗
PubMed1997

How do wiring molecules specify cortical connections?

The laminar and columnar organization of the cortex is reflected in the projections to and from the cortex and in the intracortical connections. During development of the cerebral cortex, growing axons are able to distinguish between the different cortical layers, and cortical axons originating from different laminae respond to different layer-specific signals. Here we consider some experimental systems for identifying mechanisms that contribute to the elaboration of layer-specific cortical connections.

Animals↗
PubMed1996

Specification of layer-specific connections in the developing cortex.

One of the basic tasks of neurobiology is to understand how the precision and specificity of neuronal connections is achieved during development. In this paper we reviewed some recent in vitro studies on the developing mammalian cerebral cortex that have been made towards this end. The results of these experiments provided evidence that membrane-associated molecules are instrumental for the formation of specific afferent and efferent cortical projections. Substrate-bound molecules guide growing axons towards their target, regulate the timing of thalamocortical innervation and mediate target cell recognition. Moreover, a newly described glycoprotein, defined by a monoclonal antibody, revealed a molecular heterogeneity in the developing white matter. Since this molecule has opposite effects on thalamic and cortical axons, it might play a role in the segregation of axons running to and from the cortex. Substrate-bound cues are important during the formation of local cortical circuits. In vitro assays demonstrated that molecular components confined to individual cortical layers control the laminar specificity of cortical axon branching. This suggests that similar developmental strategies contribute to the laminar specification of extrinsic and intrinsic cortical circuits. Thus substrate-bound molecules might provide the framework for subsequent activity-dependent mechanisms that control the elaboration of precise connections between the cortical columns. A major challenge ahead is to identify the factors that mediate these processes and to determine their mode of action. Recently, two families of proteins, the netrins and the semaphorins/collapsins, have been identified as growth cone signals in the developing spinal cord (reviewed in Goodman, 1994; Colamarino and Tessier-Lavigne, 1995a; Dodd and Schuchardt, 1995; Kennedy and Tessier-Lavigne, 1995). Semaphorins/collapsins appear to regulate axonal guidance by repelling growth cones and by inhibiting axonal branching and synapse formation. Originally, netrins have been purified as diffusible chemoattractants for commissural axons of the dorsal spinal cord, but it is now well established that they can also function as chemorepellent factors for other classes of neurons. Since netrins are related to extracellular matrix components and since they can bind to the cell surface, they might also act as local guidance cues. A possible role of netrins and semaphorins/collapsins in the development of cortical connections is likely to be resolved in the near future. The identification of the factors that regulate specific branching patterns of cortical neurons might provide a better understanding of cortical development, but it might also be relevant to some aspects of plasticity and repair in the adult cortex.

Afferent Pathways↗
PubMed1996

Developmental strategies underlying the elaboration of cortical circuits.

The mammalian cerebral cortex is organized in layers and columns, which are reflected in the local intrinsic connections and in the projections to and from the cortex. It is well established that the development of the columnar architecture is under the influence of neuronal activity, but little is known about the mechanisms that control the laminar specificity of cortical circuits. Here we review some recent studies which show that diffusible and membrane-associated molecules provide sufficient information to reconstruct layer-specific intrinsic and extrinsic cortical circuits under in vitro conditions.

Animals↗
PubMed1992

Comparison of ST segment changes on standard and Holter electrocardiogram during exercise testing.

In order to compare the ST segment changes recorded simultaneously on Holter (Del Mar Avionics 445B recorder and DCG VII Scanner) and standard electrocardiogram, 22 patients with chest discomfort and normal resting ECG were evaluated during exercise testing. The conventional ECG was recorded using chest lead V5 and a modified lead II. The Holter recording was done using the bipolar chest lead CM5 and the same modified lead II. Bifurcating electrodes permitted simultaneous recording of electrocardiogram on both systems from the same electrode sites. Seven of the 22 patients had a positive test and 15 had a negative test by both systems. In 7 positive cases the amplitude of ST segment depression was compared. The Holter lead CM5 showed higher amplitude of ST segment depressions in 6 cases compared to the conventional lead V5: 3 cases by 0.5 mm; 2 cases by 1 mm and 1 case by 2.5 mm. In 1 case it was identical. The amplitude of ST segment depression in lead CM5 ranged from 1 to 3.5 mm (mean 2.2 +/- 0.6 mm) and in lead V5 from 1 to 2.5 mm (mean 1.5 +/- 0.6 mm). Thus the amplitude of ST depression was higher in lead CM5 by a mean of 0.7 mm compared to the lead V5. ST segment depression was present only in 6 cases in the modified lead II. ST segment depressions were reproduced faithfully in 3 patients and within the variation of 0.5 mm in other 3 cases by the Holter system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Acromegalic cardiomyopathy. An echocardiographic study.

Eighteen acromegalic patients (A) and 18 controls without clinical evidence of cardiac involvement and/or endocrine disease (C), matched for sex, age, body surface area, and blood pressure (BP), were investigated by M-mode (2-D derived) echocardiography, to clarify the prevalence and the possible determinants of left ventricular hypertrophy (LVH). Seven patients in each group were hypertensive (BP greater than 160/95 mmHg). Left ventricular mass (LVM) was 183.1 +/- 60.0 g/m2 in A and 130 +/- 25.9 g/m2 in C. A LVM above 140 g/m2 (that is the upper normal range in our laboratory) was found in 15/18 A and 2/18 C. The LVH was concentric (h/r greater than 0.45) in 12/15 A and 1/2 C. Systolic function indexes (% FS, end-systolic stress/end-systolic volume), cardiac index and total peripheral resistance index (as determined by echo) were within the normal range and similar in both groups. No correlation was found between LVM and BP, LVM and GH plasma levels, LVM and Sm-C levels. A significant correlation was found between LVM and duration of the disease (r 0.44; p less than 0.05). Our data confirm that LVH is an early and frequent finding in acromegaly. Its prevalence is not entirely accounted for by such factors as body size, BP or increased cardiac output. Metabolic factors may play a major role, and a long lasting exposition to increased GH levels seems the most relevant determinant of LVH.

Acromegaly↗
PubMed1987

Hemispheric TIA and amaurosis fugax: what is their relation to stenotic lesions of internal carotid artery?

We evaluated the correlation of clinical and echo-Doppler findings from the internal carotid artery (ICA) in 17 patients with amaurosis fugax (AF) and in 68 patients with hemispheric TIA (H-TIA). In the study population as a whole, moderate stenoses (20%-49% diameter reduction) were the most prevalent finding in the symptomatic ICA, being detectable in 51.6% of cases. Total occlusions were found in an unexpectedly high percentage (7.5%). Asymptomatic ICAs, that were contralateral to the symptoms, showed the same degree of atherosclerotic involvement as the symptomatic ICAs. When we compared AF with H-TIA, we found a significantly higher prevalence of severe hemodynamically significant stenoses in the former (52.6% vs. 18.8%, chi-square test 10.85, P less than 0.05). Thus, we conclude that in the vast majority of patients with transient neurological symptoms a bilateral ICA involvement is to be expected. The side on which the symptoms occur does not indicate which ICA is more severely stenotic except in AF, where a severe involvement of the ipsilateral ICA is most likely.

Aged↗
PubMed1987

Prevalence of atherosclerotic involvement of the internal carotid artery in hypertensive patients.

The prevalence of atherosclerotic involvement of the internal carotid arteries, as diagnosed through an echo-Doppler imaging system with pulsed Doppler spectral analysis was evaluated in 49 hypertensives who had a negative history for neurological symptoms and 49 matched controls. The prevalence was 24.5% in the hypertensive group and 10.2% in the controls with a statistically significant difference (chi-square = 6.07, P less than 0.01). Two hypertensives had severe stenosis (above 50% diameter reduction) and 7 had potentially embolic lesions (irregular surface, inhomogeneous appearance). No one of the matched controls was as severely involved. We conclude that arterial hypertension can account for enhanced prevalence of carotid artery disease in asymptomatic patients.

Adult↗
PubMed1987

Prospective evaluation of combined carotid and coronary surgery.

In order to evaluate the effectiveness of combined carotid and coronary surgery in reducing the incidence of neurological disturbances after coronary artery bypass grafting (CABG), 144 consecutive candidates for CABG (group I) were screened for carotid disease noninvasively with Doppler ultrasonography (duplex). Twenty-six (18%) were considered at risk for stroke because of a severe (above 50% diameter reduction) stenosis; 20 (4 symptomatic and 16 asymptomatic) underwent combined surgery. Forty-seven other patients (group II) underwent CABG surgery without previous Doppler investigation. Only three patients (1.5% of the survivors) developed transient neurological disturbances after surgery; two who had normal internal carotid arteries belonged to group I, and one to group II. None of the six patients at risk for stroke who underwent only CABG developed neurological symptoms. The incidence of intra- and postoperative cardiac complications of the group who had CABG only compared to that of the group with combined surgery. We conclude that, although safe, combined surgery is not to be performed systematically on candidates for CABG with a significant internal carotid artery stenosis.

Brain Ischemia↗
PubMed1987

[Prevalence, characteristics and clinical correlates of left ventricular hypertrophy in stable hypertension. Echocardiographic study].

251 in stable hypertensives were studied with M-Mode and two-dimensional echocardiography, in order to evaluate the prevalence of left ventricular hypertrophy (LVH), its patterns and clinical correlates. 54 subjects (21%) had been treated previously with antihypertensive drugs while the remaining 197 (79%) had not. A normal left ventricle was found in 69 subjects (27.1%; group A); a concentric LVH (h/r greater than or equal to 0.45) was found in 99 (39.4%; group B), while an eccentric LVH (left ventricular myocardial mass index greater than 140 g/m2, h/r less than 0.45) in 83 (43.1%; group C). An asymmetric LVH (septum to posterior wall thickness ratio greater than or equal to 1.3) was found in 33 subjects (3 did not fulfill the criteria for LVH, 21 had a concentric, and 10 an eccentric LVH). Mean age was significantly higher in group B as compared to groups A and C. The body mass index was comparable in all groups. Mean systolic blood pressure was significantly higher in groups B and C as compared to A. The duration and the severity of hypertension did not differ among the three groups. W.H.O. stage III was absent in group A, but no differences were found between group B and C as for W.H.O. stage distribution. We conclude that such factors as BMI, duration and severity of hypertension poorly correlate with the occurrence of LVH and its patterns. The fact that group B hypertensives were older than the others on average is against the hypothesis that eccentric hypertrophy follows the concentric pattern. Whether these two patterns represent separate entities in relation to different hemodynamic profiles deserves further investigation.

Adult↗
PubMed1986

Echocardiographic evaluation of the dimensions and systolic properties of the left ventricle in freshman athletes during physical training.

The purpose of the study was to evaluate the early anatomic and functional changes of the left ventricles in junior freshman non-professional athletes just beginning specific regular training programs for 6 different types of sport. Forty-nine males (mean age 20 +/- 6 years) and 9 sedentary controls were studied by means of sequential M-mode echocardiograms, before and after a 10 to 12 week training period: 13 athletes started bicycle-riding (aerobic category), 6 sprint (anaerobic category), 6 weight-lifting (strength category), 13 soccer (mixed category), 11 rifle-shooting (manual dexterity category). Resting heart rate, blood pressure, left ventricular diameter (LVID), left ventricular posterior wall and interventricular septum thickness (LVPWT, IVST), left ventricular mass (LVMI), relative wall thickness (h/r ratio) and fractional shortening (FS%) of the LVID, cardiac index (CI) and stroke volume (SV) were comparable in all groups initially. After the training period, the cyclists, the sprinters and the soccer-players showed an increased LVID, LVMI and FS%. The cyclists and the soccer players also showed a decreased h/r ratio. The weight-lifters showed a slight increase of their LVMI, with an increased h/r ratio. We have, thus, documented that even after a relatively short non-strenuous training period, specific anatomical and functional changes occurred in the hearts of young athletes practising sports for recreational purposes, according to the type of sport.

Adolescent↗
PubMed1986

The echo-Doppler (duplex) system for the detection of vertebral artery occlusive disease: comparison with angiography.

The reliability of the echo-Doppler (duplex) system for the visualization of the vertebral arteries was evaluated in 304 patients, in which 588 vertebral arteries had been investigated. Of these, 545 (92.69 per cent) arteries, either normal or diseased, were successfully visualized. However, the origin of the vertebral artery from the subclavian artery was localized in only 354 vessels (60 per cent of those visualized). Angiography was available for comparison in 33 arteries. The overall accuracy and the sensitivity of the duplex were 63.64 per cent and 38.46 per cent, respectively; they attained 86.67 per cent and 83.33 per cent in the vertebral arteries visualized from their origin, (a site early and most commonly involved by the atherosclerotic process). As the vertebral arteries can be visualized with a 92 per cent success rate, their examination should become a routine part of the duplex cerebrovascular study. In order to accurately detect diseased vertebral arteries, their origin from the subclavian artery should be localized.

Aged↗
PubMed1986

[Prevalence of atherosclerotic lesions of the carotid bifurcation found with echo-doppler (duplex) technic in patient candidates for aortocoronary bypass].

The association of an overt coronary artery disease with a cerebrovascular disease is frequently reported. However the real prevalence of atherosclerotic lesions at the carotid bifurcation in coronary patients is not well established. The aim of our study was to evaluate the prevalence of atherosclerotic involvement of the extracranial carotid arteries in a group of 141 patients undergoing coronary artery by-pass graft (CABG) and to verify whether any correlations between coronary and carotid artery disease exist. The extracranial carotid arteries have been studied by means of an echo-doppler (duplex) system, which combines a B-mode images with a pulsed doppler. A high prevalence (17.02%) of patients with a severe (greater than 50% diameter reduction) carotid involvement was detected (Tab. II). However, no correlations between the coronary and the carotid disease were found in terms of extension and severity (Tab. V). In conclusion, a systematic evaluation of the carotid arteries is recommendable in the coronary patients, candidates to CABG, even in the absence of cerebrovascular symptoms.

Adult↗