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Biomedical subjects

R D'Ambrosio

Publications and source records attributed to R D'Ambrosio.

At least 19 recordsLinked to original sources
PubMed2003

Increased vascular endothelial growth factor mRNA expression in the heart of streptozotocin-induced diabetic rats.

The aim of the present study was to evaluate vascular endothelial growth factor (VEGF), fms-like tyrosine kinase 1 (flt-1), and fetal liver kinase (flk-1) expression in the heart of experimental diabetic rats. Ten young adult male Wistar rats (5 streptozotocin [STZ]-induced diabetic rats, without insulin treatment, and 5 controls) were studied. Ninety days after the induction of diabetes, semiquantitative reverse transcription (RT)-polymerase chain reaction (PCR) coamplification of VEGF/glyceraldehyde 3-phosphate dehydrogenase (GAPDH) transcription was performed. RT-PCR was also performed for VEGF receptors flk-1 and flt-1. VEGF mRNA expression, at 234 bp, was detectable in the heart of the rats and was significantly higher in those with diabetes. Densitometric analysis of PCR products showed that VEGF mRNA levels were meanly 4.8-fold higher in STZ-induced diabetic rats than controls (VEGF/GAPDH densitometric ratio, 3.46 +/- 0.20 v 0.74 +/- 0.10, P <.001). No significant difference was found in flt-1 and flk-1 amplification products between STZ-induced diabetic rats and controls (flt-1/GAPDH densitometric ratio, 0.58 +/- 0.01 v 0.64 +/- 0.05, P>.1; flk-1/GAPDH densitometric ratio, 0.66 +/- 0.10 v 0.7 +/- 0.06, P >.2). The increase in VEGF mRNA expression observed in this experimental diabetic model is in contrast with the typical impairment in collateral vessels of diabetic hearts. This apparent discrepancy might be explained by a resistance of cardiac tissue to VEGF. The lack of mRNA flt-1 and flk-1 overexpression in diabetic hearts could be one of the mechanisms for this resistance.

Animals↗
PubMed2001

[Peutz-Jeghers syndrome: case report and update on diagnosis and treatment].

Peutz-Jeghers syndrome is a rare autosomal dominantly inherited condition with an incidence of 1/120.000 liveborns, characterized by the presence of hamartomatous gastrointestinal polyps and mucocutaneous pigmentation. This syndrome predisposes to various clinical problems such as intussusception and cancer development in different loci (gastrointestinal tract, breast and ovary). For this reason, PJS patients should undergo a surveillance protocol of the genital and gastrointestinal apparatus. Therefore, the early diagnosis of PJS in at-risk family members is very important in preventing cancer development. Germline mutations within the LKB1 or Serine Threonine Kinase (STK11) gene, located on chromosome 19p13.3, are responsible for most cases of PJS so far studied. The existence of a second locus is suspected on chromosome 19q13.4 in a minority of families. The LKB1 gene, recently cloned, encodes the Serine Threonine Kinase LKB1 and is ubiquitously expressed. The identification of the disease-causing mutation in each family makes it possible to perform a presymptomatic diagnosis; therefore, only the mutation carriers will undergo the clinical surveillance program. In this paper, the case of a PJS patient who has been surgically treated is presented. The DNA screening of the LKB1 gene in this patient has led to the identification of the causing mutation. A critical review of the literature and is also presented as well as the proposal to establish an Italian Registry of PJS.

Adult↗
PubMed1999

Impaired K(+) homeostasis and altered electrophysiological properties of post-traumatic hippocampal glia.

Traumatic brain injury (TBI) can be associated with memory impairment, cognitive deficits, or seizures, all of which can reflect altered hippocampal function. Whereas previous studies have focused on the involvement of neuronal loss in post-traumatic hippocampus, there has been relatively little understanding of changes in ionic homeostasis, failure of which can result in neuronal hyperexcitability and abnormal synchronization. Because glia play a crucial role in the homeostasis of the brain microenvironment, we investigated the effects of TBI on rat hippocampal glia. Using a fluid percussion injury (FPI) model and patch-clamp recordings from hippocampal slices, we have found impaired glial physiology 2 d after FPI. Electrophysiologically, we observed reduction in transient outward and inward K(+) currents. To assess the functional consequences of these glial changes, field potentials and extracellular K(+) activity were recorded in area CA3 during antidromic stimulation. An abnormal extracellular K(+) accumulation was observed in the post-traumatic hippocampal slices, accompanied by the appearance of CA3 afterdischarges. After pharmacological blockade of excitatory synapses and of K(+) inward currents, uninjured slices showed the same altered K(+) accumulation in the absence of abnormal neuronal activity. We suggest that TBI causes loss of K(+) conductance in hippocampal glia that results in the failure of glial K(+) homeostasis, which in turn promotes abnormal neuronal function. These findings provide a new potential mechanistic link between traumatic brain injury and subsequent development of disorders such as memory loss, cognitive decline, seizures, and epilepsy.

Animals↗
PubMed1999

Frequency-dependent changes in cerebral blood flow and evoked potentials during somatosensory stimulation in the rat.

Contrary to the concept of neuronal-vascular coupling, cortical evoked potentials do not always correlate with blood flow responses during somatosensory stimulation at changing stimulus rates. The goal of this study is to clarify the effects of stimulus frequency on the relationship between somatosensory evoked potentials (SEPs) and cerebral blood flow. In rats anesthetized with alpha-chloralose, we measured SEPs by signal-averaging field potentials recorded with an electrode placed on dura overlying the hindlimb somatosensory cortex. Regional blood flow was simultaneously assessed in the same region with a laser-Doppler flow (LDF) probe. The contralateral sciatic nerve was stimulated with 0.1 A pulses at the frequencies of 1, 2, 5, 10 and 20 Hz. SEPs (both P1 and N1 components) declined with increasing frequency regardless whether stimulus duration (20 s) or number (100) were kept constant, suggesting that frequency is an important determinant of neuronal activity. In contrast, LDF responses increased to a maximum at 5 Hz, and do not correlate with SEPs. Because CBF should reflect integrated neuronal activity, we computed the sum of SEPS (summation operatorSEP = SEP x stimulus frequency) as an index of total neuronal activity at each frequency. Summation operatorSEP indeed correlates positively (P<0.001) with LDF responses. Thus, during somatosensory stimulation at various frequencies, cerebral blood flow is coupled to integrated neuronal activity but not to averaged evoked potentials.

Animals↗
PubMed1999

Extracellular chloride and the maintenance of spontaneous epileptiform activity in rat hippocampal slices.

Previous studies showed that furosemide blocks spontaneous epileptiform activity without diminishing synaptic transmission or reducing hyperexcited field responses to electrical stimuli. We now test the hypothesis that the antiepileptic effects of furosemide are mediated through its blockade of the Na+,K+,2Cl- cotransporter and thus should be mimicked by a reduction of extracellular chloride ([Cl-]o). In the first set of experiments, field recordings from the CA1 cell body layer of hippocampal slices showed that spontaneous bursting developed within 10-20 min in slices perfused with low-[Cl-]o (7 mM) medium but that this spontaneous epileptiform activity ceased after a further 10-20 min. Intracellular recordings from CA1 pyramidal cells showed that normal action potential discharge could be elicited by membrane depolarization, even after the tissue was perfused with low-[Cl-]o medium for >2 h. In a second set of experiments, spontaneous bursting activity was induced in slices by perfusion with high-[K+]o (10 mM), bicuculline (100 microM), or 4-aminopyridine (100 microM). In each case, recordings from the CA1 region showed that reduction of [Cl-]o to 21 mM reversibly blocked the bursting within 1 h. Similar to previous observations with furosemide treatment, low-[Cl-]o medium blocked spontaneous hypersynchronous discharges without reducing synaptic hyperexcitability (i.e., hyperexcitable field responses evoked by electrical stimulation). In a third set of experiments, prolonged exposure (>1 h after spontaneous bursting ceased) of slices to systematically varied [Cl-]o and [K+]o resulted in one of three types of events: 1) spontaneous, long-lasting, and repetitive negative field potential shifts (7 mM [Cl-]o; 3 mM [K+]o); 2) oscillations consisting of 5- to 10-mV negative shifts in the field potential, with a period of approximately 1 cycle/40 s (16 mM [Cl-]o; 12 mM [K+]o); and 3) shorter, infrequently occurring negative field shifts lasting 20-40 s (21 mM [Cl-]o; 3 mM [K+]o). Our observations indicate that the effects of low [Cl-]o on neuronal synchronization and spontaneous discharge are time dependent. Similar effects were seen with furosemide and low [Cl-]o, consistent with the hypothesis that the antiepileptic effect of furosemide is mediated by the drug's effect on chloride transporters. Finally, the results of altering extracellular potassium along with chloride suggest that blockade of the Na+, K+,2Cl- cotransporter, which normally transports chloride from the extracellular space into glial cells, is key to these antiepileptic effects.

4-Aminopyridine↗
PubMed1998

Functional specialization and topographic segregation of hippocampal astrocytes.

Astrocytes have been suggested to play several roles in the complex control of brain microenvironment. However, they have been generally considered to constitute a homogeneous population of cells. Here we show that at least three electrophysiologically distinct types of astrocytes can be found in the mature hippocampus. These subpopulations of glia were characterized by expression of different ion currents. In astrocytes exposed to elevated K+, Cs+ prevented influx of K+ only in cells with inwardly rectifying currents (IIR). The topographic distribution of glia with Cs+-sensitive inward rectifying currents (involved in K+ buffering) was nonuniform. Cs+-sensitive astrocytes were predominantly found in CA3 radiatum, whereas most CA1 astrocytes were Cs+-insensitive. Functional significance of the spatial segregation of glial cells with inward rectification was addressed in slices that were bathed in Cs+-containing media. Under these conditions, neuronal stimulation induced spontaneous epileptiform activity, which first appeared in CA3 and was then synaptically propagated to CA1. Intracellular labeling of astrocytes with biocytin revealed that CA1 astrocytes are characterized by a high degree of cell-to-cell coupling; in contrast, cell labeling in CA3 revealed smaller groups and occasionally individual cells. Three individual biocytin-labeled cells had electrophysiological properties indistinguishable from Cs+-sensitive astrocytes but had morphology typical of oligodendroglia. These results provide evidence for a role of K+ uptake via IIR into astrocytes. The segregated expression of potassium channels in a subpopulation of astrocytes suggests that functionally specialized cell types are involved in K+ homeostasis.

Animals↗
PubMed1998

Selective loss of hippocampal long-term potentiation, but not depression, following fluid percussion injury.

We investigated the early effects of in vivo fluid percussion injury (FPI) on hippocampal synaptic potentials and excitability. In vitro field potential recordings and immunocytochemistry were performed in the CA1 region in slices from naïve, post-FPI, or sham-operated rats. The following electrophysiological and morphological parameters were affected following FPI: (1) threshold for population spike generation was increased suggesting that post-FPI neurons were hypoexcitable; (2) long-term potentiation (LTP) could not be induced in injured hippocampi; (3) GFAP and inducible NO synthase (iNOS) immunoreactivity were enhanced post-FPI; and (4) following injury, synaptophysin immunoreactivity was enhanced in CA1 stratum radiatum. The effects of FPI on synaptic plasticity were LTP-specific, since long-term depression (LTD) could be equally induced and maintained in post-FPI, sham-operated and control slices. Sham-operated slices were characterized by synaptic excitability indistinguishable from naïve controls, but displayed decreased ability for LTP production and expressed high levels of iNOS. We conclude that FPI causes a selective loss of LTP, possibly due to a previous potentiation induced by trauma as reflected by the increased expression of synaptic proteins. Sham surgical procedures were, however, not without effects on long-term potentiation itself; the latter effects appear to be mediated by an increased production of NO. Our study demonstrates for the first time that hippocampal slices can be used to investigate the correlates of in vivo FPI. Furthermore, we describe LTP-specific deficits in post-traumatic brain injury, suggesting that FPI can selectively erase one of the two main NMDA-dependent forms of synaptic plasticity in the hippocampus.

Animals↗
PubMed1997

Heterogeneity of astrocyte resting membrane potentials and intercellular coupling revealed by whole-cell and gramicidin-perforated patch recordings from cultured neocortical and hippocampal slice astrocytes.

Astrocytes are thought to regulate the extracellular potassium concentration by mechanisms involving both voltage-dependent and transport-mediated ion fluxes combined with intercellular communication via gap junctions. Mechanisms regulating resting membrane potential (RMP) play a fundamental role in determining glial contribution to buffering of extracellular potassium and uptake of potentially toxic neurotransmitters. We have investigated the passive electrophysiological properties of cultured neocortical astrocytes and astrocytes recorded in hippocampal slices from 18-25 d postnatal rats. These experiments revealed a wide range of astrocyte RMPs that were independent of developmental factors, length of culturing, cellular morphology, the electrophysiological techniques used (whole-cell vs perforated recording), cell-specific expression of Na+/2HCO3- co-transporters, or voltage-dependent Na+ channels. Exposure of cultured astrocytes to differentiation-inducing factors (such as cAMP) or inhibition of proliferation (by serum deprivation) did not significantly influence RMP. Expression of ATP-sensitive potassium channels was absent in these glia; thus, K(ATP)-related mechanisms did not contribute to cell resting potential. In both cultured and slice astrocytes, spontaneous electrophysiological changes were commonly observed. These reversible events, which resulted in differential sensitivity to potassium channel blockers (cesium and barium) and sudden current-voltage profile changes, were attributable to dynamic changes in cell-to-cell coupling, as confirmed by recordings from isolated pairs of cells. We conclude that the heterogeneity of astrocytic RMP and intercellular coupling both in culture and in situ are intrinsic properties of glia that may contribute to transcellular transport of potassium. We propose a model in which spatial buffering may be facilitated by heterogeneous mechanisms controlling glial RMP in combination with dynamic changes in intercellular coupling.

ATP-Binding Cassette Transporters↗
PubMed1997

Reduction of K+ uptake in glia prevents long-term depression maintenance and causes epileptiform activity.

Extracellular cesium causes synchronous, interictal-like bursting and prevents maintenance of long-term depression (LTD) in the CA1 hippocampal region. We have investigated the cellular mechanisms underlying cesium actions. Whole-cell recordings showed that brief (2 min) bath exposures to cesium caused pyramidal cell hyperpolarization associated with decreased membrane conductance attributable to blockade of an inward h-type current. After prolonged (>2 min) exposures, a late depolarizing response was observed; this effect was not associated with changes in cell membrane conductance. Recordings from interneurons revealed that Ih is expressed in a subpopulation of cells and that cesium effects on interneurons expressing Ih are comparable to those observed in pyramidal cells. Consistent with this effect, cesium decreased the early component of the IPSP recorded in pyramidal cells. Interneurons lacking Ih were not affected by cesium but developed a depolarizing response when drug applications were paired to orthodromic stimulation. We concluded that cesium actions on LTD and cesium-induced epileptiform activity were not attributable exclusively to its direct effects on neurons. Recordings from hippocampal slice astrocytes revealed that cesium interfered with glial electrical responses during LTD induction. Cesium blocked glial inwardly rectifying potassium channels and increased the amplitude and duration of stimulation-evoked [K+]out increases. Thus, the effects of cesium on CA1 synchronization and synaptic plasticity appear to be mediated predominantly by blockade of glial voltage-dependent potassium uptake.

Afferent Pathways↗
PubMed1997

Radioimmunoassay of zidovudine: extended use and potential application.

When first approved, the dosing regimens for zidovudine were 1,200-1,500 mg/day; however, because toxicity developed, the daily dose had to be reduced to 500-600 mg/day. At these lower doses, plasma concentrations for a considerable segment of the dosing interval are often below the assay sensitivity for the high-performance liquid chromatography (HPLC) method. Although commonly used, the zidovudine radioimmunoassay has had minimal documentation for the quantitative analysis of clinical samples, especially at current doses. The authors' findings indicate that plasma, urine treated with phosphate buffer, and cerebrospinal fluid samples may be assayed using a commercially available radioimmunoassay. A good correlation was found for clinical samples measured by radioimmunoassay and HPLC (R2 = 0.85). The greater assay sensitivity, ability to process multiple specimens, and the relatively rapid turnaround time suggest that the zidovudine radioimmunoassay may have an important role in clinical trials evaluating zidovudine pharmacokinetics. This report summarizes the authors' experience with the zidovudine radioimmunoassay and focuses on its potential use in studying the role of therapeutic drug monitoring for zidovudine.

Chromatography, High Pressure Liquid↗
PubMed1996

In vitro protein-binding characteristics of delavirdine and its N-dealkylated metabolite.

This study was performed to determine delavirdine protein-binding characteristics as well as those of its N-dealkylated metabolite (N-DLV). Initial studies of 36 microM delavirdine and 30 microM N-DLV in solutions of plasma, albumin 4 g%, alpha-1-acid glycoprotein (AAG) 100 mg% or immune globulin (IVIG) 5 g% were conducted. Delavirdine (12, 36 and 73 microM) and N-DLV (10, 30 and 60 microM) were then studied alone and in combination in plasma and various concentrations of albumin. Studies were done in triplicate using equilibrium dialysis. The mean delavirdine fraction unbound (fu) in plasma, albumin, IVIG and AAG was 0.013, 0.033, 0.752 and 0.912 while the mean fu of N-DLV in these same protein solutions was 0.139, 0.195, 0.329 and 0.359. In plasma and albumin, a greater fu was observed at higher delavirdine concentrations and no significant changes in fu were noted with the addition of N-DLV. An increase in delavirdine fu was noted as the albumin concentrations decreased. The fu of N-DLV increased significantly as the concentration of albumin decreased as well as with decreasing N-DLV concentration. The potential implications of extensive delavirdine binding to plasma proteins, primarily albumin, are discussed.

Anti-HIV Agents↗
PubMed1996

Didanosine measurement by radioimmunoassay.

Didanosine is commonly prescribed as monotherapy or as part of a combination regimen for patients with human immunodeficiency virus infection. The use of lower doses, either as part of a combination regimen or as a result of dose reduction secondary to clinical intolerance, requires that a sensitive assay method be available for either traditional or population-based pharmacokinetic evaluations. We evaluated a radioimmunoassay technique with a standard curve range of 0 to 100 ng/ml in human plasma, urine, and cerebrospinal fluid and assessed its accuracy and precision for use in pharmacokinetic studies.

Antiviral Agents↗
PubMed1996

[The washout in emergency surgery of the colon. A technical note].

The authors report their experience in the treatment of 179 cases of colonic neoplasm between January 1985 and August 1992. Particularly, they emphasize the advantages of one-stage colectomy with anastomosis because of an obstructing carcinoma of the left colon, used on 41 cases. This treatment can be practicable by using the intraoperative "wash-out" technique. The one-stage colectomy with anastomosis can be advisable because the long survival can be compared to that deriving from the non obstructing carcinoma. Moreover this technique offers several advantages such as the one-stage treatment, the absence of colostomy, the improvement of the cost-benefit relationship, etc. On 41 cases treated by this technique, the authors lament only one decease caused by a total dehiscence of the anastomosis, notwithstanding reintervention. Moreover, 9 cases of partial dehiscence were treated by NPT (Total Parenteral Nutrition) except one which demanded a reintervention.

Adult↗
PubMed1996

[Acute appendicitis in pregnancy. Our experience].

The authors' aim is to review the medical literature dealing with diagnostic and therapeutical problems, after observations in pregnancy because of acute appendicitis in 9 cases. Diagnosis is difficult because of the aspecificity and the alterations both of the site of symptoms and clinical manifestations, particularly during the last period of gestation. As there is an upward displacement of the viscus by the pregnant uterine. Notwithstanding the use of some not invasive methods, such as graded-compression sonography, the diagnosis is always effected by the clinical examination. Surgical treatment is always possible in the presence of acute appendicitis, as pregnancy isn't a reason for delay. The maternal mortality is at a zero level, the fetal one varies from 2% to 43% in cases of perforated appendicitis.

Acute Disease↗
PubMed1994

Fifteen years of operation of a high-performance liquid chromatographic assay for prednisolone, cortisol and prednisone in plasma.

A high-performance liquid chromatographic (HPLC) assay first described in 1979 has been modified and revalidated for the simultaneous determination of prednisone, cortisol and prednisolone in human plasma using betamethasone as an internal standard. Revisions include: mobile phase composition; use of a precolumn, automated injector, integrator, and computer software; improved sensitivity and quantitation; thorough investigation of stability, variation, and specimen type; and inclusion of suggested quality control criteria. Plasma-based drug standards are extracted with methylene chloride and washed with sodium hydroxide followed by a water wash. After evaporation of solvent and reconstitution with mobile phase, the extracts are then injected onto a silica gel column (Zorbax SIL) for chromatography with UV absorbance at 254 nm. Calculated limits of quantitation are 10 ng/ml and limits of detection are less than 5 ng/ml. Intra- and inter-day coefficients of variation for quality control samples for all three corticosteroids are less than 11.2%. Recovery and stability data are also provided. Several drugs that may be coadministered do not interfere with the analysis.

Chromatography, High Pressure Liquid↗
PubMed1994

Multicenter comparison of tacrolimus (FK 506) whole blood concentrations as measured by the Abbott IMX analyzer and enzyme immunoassay with methylene chloride extraction.

A multicenter comparison was made between the Abbott IMX and enzyme-linked immunosorbent assay (ELISA) procedures for analysis of tacrolimus (FK 506) in whole blood. Proficiency samples and 853 patient specimens obtained after various organ transplantations were assayed by 13 laboratories. Both groups of test samples yielded slightly lower (7 and 13%) values by the IMX method, but the difference is not clinically meaningful. The type of organ transplant was not a factor that contributed to assay variation. The Abbott IMX results were essentially equivalent to ELISA and considerably facilitates monitoring of FK 506 therapy.

Enzyme-Linked Immunosorbent Assay↗
PubMed1994

[Strangulated laparoceles. Our experience].

The authors present their own experience of emergency in strangulated laparoceles. Between January 1984 and June 1992 they treated at the Division of Emergency Surgery of the Hospital "A. Cardarelli" in Naples 133 cases of laparocele, 63 of which were strangulated. 48 of the 63 cases were treated by simply vertical or transversal laparoplasty ("waistcoat"); in 4 cases a direct plastic surgery; was executed in 11 cases a synthetic patch was used: in 2 cases a Teflon prosthesis was used; in one case a double prosthesis: a reabsorbable Vicryl patch internally and an external Marlex reticulated; in 8 cases a Marlex prosthesis. Moreover in most cases, before the laparoplasty of the abdominal wall operations of viscerolysis, were carried out intestinal and/or epiploon resection because of ischemia, colostomy, a Hartmann (one case). Of the 11 patients treated with synthetic patches, only 4 presented local complications: a seroma, two suppurations of the wound and a skin necrosis. These complications were treated with a medical therapy. In no case it was necessary to remove the prosthesis, as there were no general complications or deaths. We have to underline that notwithstanding the great advances both in surgery and in prosthesis' materials, the problem of the strangulated laparocele still represent a great engagement for the surgeon. The main reasons are: concomitant pathologies ("eventration disease"') and complications. The complications may be local (infection of the wound) or general (cardiocirculatory and respiratory problems due the viscus reduction in the original abdominal cavity).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗