Usefulness of direct fluorescent in buffy coat in the diagnosis of Candida sepsis in neonates.

OBJECTIVE: The objective of this study is to assess the clinical utility of direct fluorescent assay in buffy coat in the diagnosis of Candida sepsis (CS) in neonates. STUDY DESIGN: A cross-sectional study was conducted in a Neonatal Intensive Care Unit and 22 neonates with suspected CS were enrolled. Fungus isolation from blood cultures and direct fluorescent tests in buffy coat were performed and validity parameters were estimated. RESULTS: Candida was isolated in 13/22 (59%) blood cultures. The direct fluorescent test was positive in 12/13 and 1/9 cases with positive and negative blood culture as corresponding. Estimated sensitivity, specificity, positive predictive value, negative predictive value, positive likehood ratio and negative likehood ratio were 92%, 89%, 92%, 89%, 8.31 and 0.09, respectively. CONCLUSION: The direct fluorescent assay in buffy coat might be useful to support early and accurate diagnosis of CS in neonates.

Theoretical aspects of the neurobiological integration of memory.

Whenever a peripheral structure like the visual system captures information, the input signal reverberates in circuits of neurons, which send it thereafter towards: (a) the motor system, triggering a specific response, evoked by a short-term memory mechanism; and (b) the hippocampus, to produce long-term potentiation or depression. Two different processes regulate short-term memory: (1) Homosynaptic depression that inhibits neurotransmitter release by means of a decrease in Ca++ inflow, and an increase in calmodulin affinity for synaptic vesicles; and (2) Heterosynaptic facilitation that triggers neurotransmitter release, whenever serotonin activates a proteinkinase A. Besides carrying out a brief review on the matter, we support two different physiological explanations with regard to: (a) ion exchange process and the interstitial pH during habituation; and (b) the possibility of a sensitive presynaptic neuron interaction within the habituated reverberant circuit, to trigger dishabituation. We also propose the term 'time-mediated stimulatory action dependent' to name those serotonin receptors that may lead to a rapid or a delayed postsynaptic onset responses.

Hb D-Los Angeles associated with Hb S or beta-thalassemia in four Mexican Mestizo families.

Twenty-five individuals were studied from four unrelated Mexican Mestizo families with Hb D-Los Angeles. We observed five compound heterozygotes: four for Hb S and Hb D, and one for Hb D and beta-thalassemia (beta(0) 39 nonsense mutation); 16 heterozygotes: four for Hb S, seven for Hb D, and five for beta-thalassemia, while the remaining four were normal. The four Hb S/Hb D patients had severe hemolytic anemia, while in the Hb D/beta-thalassemia patient, the anemia was similar to that of a beta-thalassemia heterozygote; therefore, Hb D is clinically harmful when it is associated with Hb S. The beta(S) chromosomes were associated with the Benin haplotype in two families and Bantu in one family, while the beta(D) and beta(0) 39 mutations were associated with haplotype 1 [+ - - - - + +]. The Bantu and Benin haplotypes have been found with high frequency in Hb S individuals from the East Coast and Northwestern Mexico. The beta(D) chromosomes from Italy were also shown to be associated with haplotype 1, the most frequently observed haplotype in the world; there are no haplotype studies on beta(D) chromosomes from India or China where Hb D-Los Angeles is most common. Thus, the true origin of this mutation observed in these Mestizo families remains to be elucidated.

Frequency-dependent effects of 4-aminopyridine and almokalant on action-potential duration of adult and neonatal rabbit ventricular muscle.

The effects of 4-aminopyridine (1 mM) and almokalant (1 microM) on action-potential duration of neonatal and adult rabbit ventricular multicellular preparations and plateau membrane currents of single ventricular myocytes were studied. In adult ventricular preparations, 4-aminopyridine increased action-potential duration in a frequency-dependent manner, with a greater effect at low stimulation frequencies ("reverse" use dependence). In neonatal preparations, the increase in action-potential duration by 4-aminopyridine was significantly smaller than in adults, and the effect was frequency independent. Almokalant increased the action-potential duration more in neonatal than in adult myocytes. The effect of almokalant was frequency independent between 0.5 and 2 Hz. The block of transient outward current and delayed rectifier current in single myocytes was quantitatively similar. We propose that differences in the kinetic behavior of the transient outward current between adult and neonatal ventricular preparations, slower inactivation, and recovery from inactivation in adults determine differences in the frequency-dependent changes induced by 4-aminopyridine and almokalant on action-potential duration.

Alpha-thalassemia in a selected population of Mexico.

OBJECTIVE: To identify by molecular biology the alleles of alpha-Thal in selected hospital populations. METHODS: Eighteen propositi with hematological and biochemical data suggestive of alpha-thalassemia, selected from 356 patients of four hospitals in two cities with probable hemoglobinopathy were investigated for six common alpha-Thal alleles. Molecular studies were done by PCR and digestion with specific restriction enzymes. RESULTS: The alpha 3.7 allele was identified in two cases and the family study revealed the same allele in the mother; HbS heterozigocity was also detected in one of them. An analysis with Apa I demonstrated a class I deletion in both patients. The present study showed 2/356 (0.6%) of alpha 3.71 carriers which is a low frequency as compared with other countries. As no other common alpha-thalassemia alleles were found, we suspect that alpha-Thal in Mexico is as heterogeneous at a molecular level as beta-Thal.

Receptors, photoreception and brain perception. New insights.

Once photons have activated photosensitive cell receptors, a biochemical process mediated by G-proteins transforms the initial signal into nerve potentials. The generated impulses transmit the information through ganglion cells, after a complex interaction with other neurons by means of different neurotransmitters. Since visual function is processed in parallel, ganglion cells are divided into M-neurons which are in charge of capturing large objects, P-neurons capable of analyzing fine details and colors, and non-M, non-P neurons which are sensitive to changes in light intensity. Retina, bipolar and ganglion cells share circular receptive fields with an antagonistic surround whereas the lateral geniculate nucleus possesses rectangular receptive fields. Thus, when central cones are stimulated, ON-center cells depolarize, while OFF-center cells hyperpolarize. At the brain cortex, the magnocellular layers lead to orientation and achromatic perception, the parvocellular layers perform color vision in the blobs and achromatic contrast and orientation in the interblobs, and eventually, binocular perception is the result of multiple disparities phenomenon. On these bases, patients with agnosia for form and pattern or for depth and movement have been described. Likewise, color blindness is another disease that could be the result of photoreceptor dysfunctions or brain perception defects.

Differences in outward currents between neonatal and adult rabbit ventricular cells.

In adult rabbit ventricular preparations, action potential duration is significantly increased when stimulation frequency is increased from 0.1 to 1.0 Hz. In neonatal preparations, a similar change in stimulation frequency produced no significant increase in action potential duration. To identify the ionic basis for this difference, we studied different outward currents in single myocytes from papillary muscle and from epicardial tissue of adult and neonatal rabbits. The densities of the outward currents in neonatal cells were about one-half of the current density in adult cells. The density of the voltage-activated transient outward current (I(to1)) was smaller in cells from papillary muscle than in cells from epicardium in adult and newborn rabbits. We found major differences in the kinetic behavior of I(to1) between adult and neonatal cells: 1) the rate of apparent inactivation was faster in neonatal cells, and 2) the recovery from inactivation was significantly faster in neonatal cells, with a time constant of 113 vs. 1,356 ms. We propose that this marked difference in the recovery from inactivation of I(to1) is the basis for the difference in frequency dependence of action potential duration.