Dual action of a dinoflagellate-derived precursor of Pacific ciguatoxins (P-CTX-4B) on voltage-dependent K(+) and Na(+) channels of single myelinated axons

The effects of Pacific ciguatoxin-4B (P-CTX-4B, also named gambiertoxin), extracted from toxic Gambierdiscus dinoflagellates, were assessed on nodal K(+) and Na(+) currents of frog myelinated axons, using a conventional voltage-clamp technique. P-CTX-4B decreased, within a few minutes, both K(+) and Na(+) currents in a dose-dependent manner, without inducing any marked change in current kinetics. The toxin was more effective in blocking K(+) than Na(+) channels. P-CTX-4B shifted the voltage-dependence of Na(+) conductance by about 14 mV towards more negative membrane potentials. This effect was reversed by increasing Ca(2+) in the external solution. A negative shift of about 16 mV in the steady-state Na(+) inactivation-voltage curve was also observed in the presence of the toxin. Unmodified and P-CTX-4B-modified Na(+) currents were similarly affected by the local anaesthetic lidocaine. The decrease of the two currents by lidocaine was dependent on both the concentration and the membrane potential during pre-pulses. In conclusion, P-CTX-4B appears about four times more effective than P-CTX-1B to affect K(+) channels, whereas it is about 50 times less efficient to affect Na(+) channels of axonal membranes. These actions may be related to subtle differences between the two chemical structures of molecules

Estimulación vagal en el tratamiento de la epilepsia

The vagal nerve stimulation is a new technique for the treatment of drug resistant epilepsies. DEVELOPMENT: In 1997, it was approved in United States by the FDA to be used in adults with refractory focal epilepsies not candidates for epilepsy surgery. Its mechanism of action is unknown. The results in the controlled studies indicated a decrease of 30 50% in the seizure frequency in around 50% of the patients. Although more experience is needed to corroborate these results, it seems reasonable as a treatment for patients with difficult epilepsies, especially when the response to the antiepileptic drugs is poor or they are producing secondary effects, and the resection of the focus is not possible

Trastornos específicos del desarrollo del lenguaje: bases neurobiológicas

Studies of twins, familial aggregates and particular phenotypic conditions have shown an inherited basis for some dysphasias or specific developmental language impairments (SLI). This predisposition is usually multifactorial but the analysis of some families allows to postulate an autosomal dominant transmission of deficits in specific modular aspects of linguistic competences. Moreover, neuroimaging studies have shown modifications of normal volumetric interhemispheric asymmetries, and in group of SLI with receptive prominent disorder coexist epileptiform activity in wakefulness and non-REM sleep EEG; in some of these cases, antiepileptic drugs, specially steroids, can significantly ameliorate the language processing. As many patients with SLI have a difficulty for discrimination of subtle temporal indices, a hypothesis can also be made of a dysfunction in various subcortical structures (thalamus, basal ganglia, cerebellum) modulating the cerebral cortex in phonological processing

Paresia poscrítica durante estudios de monitorización de vídeo-EEG

To know the frequency of Todd s paralysis during the video EEG monitoring studies, to investigate in its pathophysiology, and to confirm its value to localise the epileptic focus. PATIENTS AND METHODS: We reviewed 114 monitoring studies, in 102 patients. RESULTS: Sixty patients had epileptic seizures. An obvious paresis was noted in four seizures of two patients (3 and 1, respectively). Both patients had frontal epilepsy. During the paralysis, in the first patient the EEG showed ictal discharges on the contralateral centrotemporal area. In the second patient, the EEG demonstrated slow waves in the contralateral frontal region. The ictal onset was contralateral to the paresis in all cases. No patient with pseudoseizures had paralysis. CONCLUSIONS: Postconvulsive paralysis are not frequent in video EEG monitoring studies. However, if present it points out to a contralateral seizure onset. In our series it happened in patients with frontal seizures. The EEG may help to clarify if it correspond to a true postictal phenomenon or to a ictal paralysis

ROCK SURFACE CHARACTERIZATION BY IMMERSION CALORIMETRY: WETTABILITY AND SPECIFIC SURFACE AREA

ABSTRACT Petrophysical properties such as wettability and surface area control hydrocarbon storage and transport properties. In the work being reported in this paper, we present the theoretical aspects as well as experimental technique and results of testing and validating a proposed calorimetry technique for specific surface area and wettability characterization. Identical immersion calorimetry experiments with slightly different initial conditions of the sample are analyzed to obtain these two properties of a core sample. Validation of the experimental technique is an important step, which is performed in this work by comparing the surface areas of the samples obtained by the proposed technique with the surface area obtained by the well-known Brunauer-EmmettTaylor (BET) gas-adsorption technique. Surface area measurements are performed on a set of core plugs and reference samples, including hydrophilic and hydrophobic powders of pure substances, minerals, and clays

Africa’s single aviation market: The progress so far

To promote the development of air transport at the continental level, several policies were introduced, leading to the Yamoussoukro Decision (YD) in late 1999, which had the liberalisation of the intra-African aviation spaces as its main objective. Even though notable progress has been achieved towards more market-oriented aviation policies, at the pan-African level some markets are still restrictive and inconsistent with the YD, particularly with respect to the granting of 5th freedom rights. This paper aims to examine recent developments in the aviation sector in Africa, with a focus on the implementation of the YD. The obstacles to liberalisation are discussed and several measures for facilitating Africa’s move towards multilateral open skies are investigated. These include, among others, a greater collaboration and co-operation among African airlines, as well as between African airlines and foreign ones; redefinition of the role and responsibilities of different institutions which are instrumental in implementing the YD and some further issues such as ownership guidelines

Second primary malignancies in thyroid cancer patients

The late health effects associated with radioiodine ((131)I) given as treatment for thyroid cancer are difficult to assess since the number of thyroid cancer patients treated at each centre is limited. The risk of second primary malignancies (SPMs) was evaluated in a European cohort of thyroid cancer patients. A common database was obtained by pooling the 2-year survivors of the three major Swedish, Italian, and French cohorts of papillary and follicular thyroid cancer patients. A time-dependent analysis using external comparison was performed. The study concerned 6841 thyroid cancer patients, diagnosed during the period 1934-1995, at a mean age of 44 years. In all, 17% were treated with external radiotherapy and 62% received (131)I. In total, 576 patients were diagnosed with a SPM. Compared to the general population of each of the three countries, an overall significantly increased risk of SPM of 27% (95% CI: 15-40) was seen in the European cohort. An increased risk of both solid tumours and leukaemias was found with increasing cumulative activity of (131)I administered, with an excess absolute risk of 14.4 solid cancers and of 0.8 leukaemias per GBq of (131)I and 10(5) person-years of follow-up. A relationship was found between (131)I administration and occurrence of bone and soft tissue, colorectal, and salivary gland cancers. These results strongly highlight the necessity to delineate the indications of (131)I treatment in thyroid cancer patients in order to restrict its use to patients in whom clinical benefits are expected

Petroleum generation kinetics: Single versus multiple heating- ramp open-system pyrolysis

A B S T R A C T Some recent publications promote one-run, open-system pyrolysis experiments using a single heating rate (ramp) and fixed frequency factor to determine the petroleum generation kinetics of source-rock samples because, compared to multiple-ramp experiments, the method is faster, less expensive, and presumably yields similar results. Some one-ramp pyrolysis experiments yield kinetic results similar to those from multiple-ramp experiments. However, our data for 52 worldwide source rocks containing types I, II, IIS, II/III, and III kerogen illustrate that one-ramp kinetics introduce the potential for significant error that can be avoided by using high-quality kinetic measurements and multiple-ramp experiments in which the frequency factor is optimized by the kinetic software rather than fixed at some universal value. The data show that kinetic modeling based on a discrete activation energy distribution and three different pyrolysis temperature ramps closely approximates that determined from additional runs, provided the three ramps span an appropriate range of heating rates. For some source rocks containing well-preserved kerogen and having narrow activation energy distributions, both single-and multiple-ramp discrete models are insufficient, and nucleation-growth models are necessary. Instrument design, thermocouple size or orientation, and sample weight likely influence the acceptable upper limit of pyrolysis heating rate. Caution is needed for ramps of 30-50°C/min, which can cause temperature errors due to impaired heat transfer between the oven, sample, and thermocouple. Compound volatility may inhibit pyrolyzate yield at the lowest heating rates, depending on the effectiveness of the gas sweep. We recommend at least three pyrolysis ramps that span at least a 20-fold variation of comparatively lower rates, such as 1, 5, and 25°C/min. The product of heating rate an