Cesarean section and maternal age in low-risk nulliparas.

The relationship between maternal age and cesarean section in low-risk nulliparas was analysed in 7454 perinatal clinical records selected from eleven databases of Latin American institutions obtained with a comprehensive perinatal information system. The risk of cesarean section in nulliparas between 29 and 49 years of age was found to be three times higher than that corresponding to pregnant women of lesser age. This clearly more aggressive obstetrical conduct could not be explained by the main indications for cesarean section.     

Phosphatidylglycerol determination in the amniotic fluid from a PAD placed over the vulva: a method for diagnosis of fetal lung maturity in cases of premature ruptured membranes.

Four hundred and forty seven pregnant women with ruptured membranes, were prospectively studied in order to assess the diagnostic capacity of Phosphatidylglycerol (PhG) determination in amniotic fluid recovered from vulval pads in the diagnosis of Hyaline Membrane Disease (HMD). The identification of PhG was performed using one dimensional silica gel thin layer chromatography. The sensitivity of PhG determination in the diagnosis of HMD in newborns of the total population was found to be 88.2%, with a specificity of 76.9%. In the study population, the incidence of HMD was 7.6%, the negative predictive value was 98.8% and, the positive predictive value was 24.0%. When the 265 newborns of the gestational age group of less than or equal to 34 weeks is considered, we observed an incidence of HMD of 12.1%. The diagnostic capacity of PhG in this group was shown by a sensitivity of 87.5%, a specificity of 76.4%, a positive predictive value of 33.7% and a negative predictive value of 97.8%. This method of assessment of fetal lung maturity has a diagnostic capability similar to that described by other authors, who used amniotic fluid obtained vaginally or transabdominally. The procedure described here of amniotic fluid collection is non-invasive, harmless to the mother and fetus and simple to perform. The characteristics of this method, allow serial studies of the amniotic fluid to be carried out.     

Afferents to the seizure-sensitive neurons in layer III of the medial entorhinal area: a tracing study in the rat

Neurons in layer III of the medial entorhinal area (MEA) in the rat are extremely vulnerable to local injections of amino-oxyacetic acid and to exprimentally induced limbic seizures. A comparable specific pathology has been noted in surgical specimens from patients with temporal lobe epilepsy. Efforts to understand this preferential neuronal vulnerability led us to study the neural input to this layer in the rat. Iontophoretic injection of the retrograde tracer fast blue, aimed at layer III of the MEA, resulted in retrogradely labeled neurons in the presubiculum in all the injected hemispheres. The nucleus reuniens thalami, the anteromedial thalamic nucleus, the ventral portion of the claustrum (endopiriform nucleus), the dorsomedial parts of the anteroventral thalamic nucleus, and the septum-diagonal band complex were labeled less frequently. In only one experiment, retrogradely labeled neurons were observed in the ventrolateral hypothalamus and in the brainstem nucleus raphe dorsalis. Since projections from claustrum to the entorhinal cortex has not been studied in the rat with modern sensitive anterograde tracing techniques, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were placed into the ventral portion of the claustrum. Anterogradely labeled fibers in the entorhinal area proved not to be confined to the MEA, since a prominent projection distributed to the lateral entorhinal area as well. In both areas, the densest terminal labeling was present in layers IV–VI, whereas layer III appeared to be only sparsely labeled. The present data indicate that of all potential afferents only those from the presubiculum distribute preferentially to layer III of the MEA. This, in turn, suggests a potentially important role of the presubiculum in the seizure-related degeneration of neurons in layer III of the MEA.     

Substrate utilization in boys during exercise with [13C]-glucose ingestion

The influence of glucose ingestion on substrate utilization during prolonged exercise in children and adolescents is currently unknown. In the present study we determined the effect of intermittent exogenous glucose (GLUexo) ingestion on substrate utilization during prolonged exercise, in adolescent boys ages 13 17 years. Healthy untrained volunteers performed four 30-min exercise bouts on a cycle ergometer, separated by 5-min rest periods (approximately equal to 60% maximum O2 consumption), on two occasions spaced 1-4 weeks apart. Two trials were performed, a control trial (CT), in which subjects ingested water intermittently during the exercise, and a glucose trial (GT), in which subjects ingested a 13C-enriched GLUexo drink (approximately egual to glucose kg body mass(-1)), also intermittently during the exercise. Total free fatty acids (FATtotal), glucose (GLUtotal) and carbohydrate (CHOtotal) oxidation was determined from indirect calorimetry, while GLUexo oxidation was calculated from the 13C/12C ratio in expired air after 5-10 min and 25-30 min of exercise in each bout. Heart rate and rating of perceived exertion (RPE) were determined at the same time intervals. The oxidation of CHOtotal was 169.1 (12.9) g x 120 min(-1) and 203.1 (15.9) g x 120 min(-1) (P < 0.01) and that of FATtotal was 31.0 (4.2) g x 120 min(-1) and 17.1 (2.5) g x 120 min(-1) (P < 0.01) in CT and GT, respectively. GLUexo oxidation in GT was 57.8 (4.3) g x 120 min(-1), or 34.2 (2.2)% of that ingested. Endogenous glucose oxidation was 169.1 (12.9) g x 120 min(-1) and 145.3 (11.9) g x 120 min(-1) (P < 0.01) in CT and GT, respectively. Insulin and glucose concentrations were higher in GT than in CT by 226% and 37%, respectively (both P < 0.05). Free fatty acids and glycerol concentrations were lower in GT than in CT, by 27% and 79%, respectively (both P < 0.05). Heart rate was similar between trials, but RPE was lower in GT vs CT at both 115 and 135 min. Thus, under these experimental conditions, GLUexo intake spares endogenous carbohydrate and fat by 16% and 45%, respectively, contributes to approximately 25% of the total energy demand of exercise, and lowers the RPE.     

The effects of intrahippocampal ibotenic acid and their blockade by (−) 2-amino-7-phosphonoheptanoic acid: Morphological and electroencephalographical analysis

Intrahippocampal injections of the excitotoxin ibotenic acid caused a biphasic behavioral pattern in rats. Both the immediate induction of hyperactivity and stereotypical behaviors and a secondary phase of progressively decreasing behavioral activities beginning 15-20 min after ibotenate administration, were accompanied by characteristic seizures measured by bilateral recordings in hippocampus and cortex. Typically, EEG changes consisted of high voltage spiking in all leads. The phase of behavioral depression was accompanied by episodic, short (5-30 s) seizures. In addition, cortical slow waves very similar to those elicited by intrahippocampal muscimol were observed during this period. Attempts were made to correlate occurrence and severity of seizures with the extent of neuronal degeneration. While a trend in favor of such a correlation existed, a firm causal relationship could not be established; some animals could display seizure activity with only marginal concomitant nerve cell loss and vice versa. Intrahippocampal co- and post-administration of ibotenate with (-) 2-amino-7-phosphonoheptanoic acid entirely prevented or stopped the occurrence of both EEG changes and neuronal degeneration. Ibotenate-induced seizures and lesions and their specific blockade by a selective antagonist may constitute valuable experimental paradigms for the investigation of seizure disorders.     

“Dark” (compacted) neurons may not die through the necrotic pathway

Dark neurons were produced in the cortex of the rat brain by hypoglycemic convulsions. In the somatodendritic domain of each affected neuron, the ultrastructural elements, except for disturbed mitochondria, were remarkably preserved during the acute stage, but the distances between them were reduced dramatically (ultrastructural compaction). Following a 1-min convulsion period, only a few neurons were involved and their environment appeared undamaged. In contrast, 1-h convulsions affected many neurons and caused swelling of astrocytic processes and neuronal dendrites (excitotoxic neuropil). A proportion of dark neurons recovered the normal structure in 2 days. The non-recovering dark neurons were removed from the brain cortex through two entirely different pathways. In the case of 1-h convulsions, their organelles swelled, then disintegrated and finally dispersed into the neuropil through large gaps in the plasma membrane (necrotic-like removal). Following a 1-min convulsion period, the non-recovering dark neurons fell apart into membrane-bound fragments that retained the compacted interior even after being engulfed by astrocytes or microglial cells (apoptotic-like removal). Consequently, in contrast to what is generally accepted, the dark neurons produced by 1-min hypoglycemic convulsions do not die as a consequence of necrosis. As regards the case of 1-h convulsions, it is assumed that a necrotic-like removal process is imposed, by an excitotoxic environment, on dark neurons that previously died through a non-necrotic pathway. Apoptotic neurons were produced in the hippocampal dentate gyrus by intraventricularly administered colchicine. After the biochemical processes had been completed and the chromatin condensation in the nucleus had reached an advanced phase, the ultrastructural elements in the somatodendritic cytoplasm of the affected cells became compacted. If present in an apparently undamaged environment such apoptotic neurons were removed from the dentate gyrus through the apoptotic sequence of morphological changes, whereas those present in an impaired environment were removed through a necrotic-like sequence of morphological changes. This suggests that the removal pathway may depend on the environment and not on the death pathway, as also assumed in the case of the dark neurons produced by hypoglycemic convulsions.     

Identification of quinolinic acid in rat and human brain tissue

An analytical technique for the determination of the excitotoxic compound quinolinic acid (2,3-pyridine dicarboxylic acid) in brain tissue has been developed. Following sample prepurification by ion exchange and high pressure liquid chromatography, quinolinic acid is converted to the dihexafluoroisopropyl ester and the derivative is analyzed by mass fragmentography. Using the present technique quinolinic acid has been identified in both rat and human brain tissue.     

3-Hydroxyanthranilic acid accumulation following administration of the 3-hydroxyanthranilic acid 3,4-dioxygenase inhibitor NCR-631

In the kynurenine pathway of tryptophan metabolism, 3-hydroxyanthranilic acid is the substrate for formation of the excitotoxin quinolinic acid by 3-hydroxyanthranilic acid 3, 4-dioxygenase. This study was designed to characterize the effects on 3-hydroxyanthranilic acid after treatment with the 3-hydroxyanthranilic acid 3,4-dioxygenase inhibitor 4, 6-di-bromo-3-hydroxyanthranilic acid (NCR-631) in Sprague-Dawley rats. The blood plasma and brain concentrations of 3-hydroxyanthranilic acid were found to increase rapidly in a dose-dependent manner after gavage administration of NCR-631. However, the effect was relatively transient, with a decline in 3-hydroxyanthranilic acid levels already at 1h after NCR-631 treatment. Similar increases in plasma levels of 3-hydroxyanthranilic acid were observed following either gavage or parenteral (i.v. or s.c.) administration of NCR-631 (25 mg/kg). Only a minor enhancement of the NCR-631-induced increase in plasma 3-hydroxyanthranilic acid levels was found after sub-chronic treatment (25 mg/kg by gavage; 7 days, b.i.d.), suggesting a low propensity for altered 3-hydroxyanthranilic acid 3,4-dioxygenase activity following repeated inhibition. Administration of [14C]NCR-631 suggested 20 min initial plasma half life and an oral absorption around 50%. A dose of 250 mg/kg [14C]NCR-631 given by gavage provided plasma levels of almost 2 micromol/ml and a brain concentration of approximately 16 nmol/g, when analyzed 15 min after administration. Neither acute nor sub-chronic administration of NCR-631 caused any substantial effects on quinolinic acid levels in plasma or brain. Also, the plasma levels of kynurenic acid, another neuroactive kynurenine pathway metabolite, were unaffected by acute NCR-631 treatment. Moreover, the brain levels of the major cerebral tryptophan metabolites 5-hydroxytryptamine and 5-hydroxyindoleacetic acid remained unchanged following administration of NCR-631. Although reversible inhibition of 3-hydroxyanthranilic acid 3, 4-dioxygenase with NCR-631 in normal rats is insufficient to cause substantial changes in the levels of quinolinic acid or other important tryptophan metabolites, it causes a major accumulation of the substrate 3-hydroxyanthranilic acid.     

Disruption of inhibition in area CA1 of the hippocampus in a rat model of temporal lobe epilepsy.

Previous studies have revealed a loss of neurons in layer III of the entorhinal cortex (EC) in patients with temporal lobe epilepsy. These neurons project to the hippocampus and may activate inhibitory interneurons, so that their loss could disrupt inhibitory function in the hippocampus. The present study evaluates this hypothesis in a rat model in which layer III neurons were selectively destroyed by focal injections of the indirect excitotoxin, aminooxyacetic acid (AOAA). Inhibitory function in the hippocampus was assessed by evaluating the discharge of CA1 neurons in response to stimulation of afferent pathways in vivo. In control animals, stimulation of the temporo-ammonic pathway leads to heterosynaptic inhibition of population spikes generated by subsequent stimulation of the commissural projection to CA1. This heterosynaptic inhibition was substantially reduced in animals that had received AOAA injections 1 mo previously. Stimulation of the commissural projection also elicited multiple population spikes in CA1 in AOAA-injected animals, and homosynaptic inhibition in response to paired-pulse stimulation of the commissural projection was dramatically diminished. These results suggest a disruption of inhibitory function in CA1 in AOAA-injected animals. To determine whether the disruption of inhibition occurred selectively in CA1, we assessed paired-pulse inhibition in the dentate gyrus. Both homosynaptic inhibition generated by paired-pulse stimulation of the perforant path, and heterosynaptic inhibition produced by activation of the commissural projection to the dentate gyrus appeared largely comparable in AOAA-injected and control animals; thus abnormalities in inhibitory function following AOAA injections occurred relatively selectively in CA1. Electrolytic lesions of the EC did not cause the same loss of inhibition as seen in animals with AOAA injections, indicating that the loss of inhibition in CA1 is not due to the loss of excitatory driving of inhibitory interneurons. Also, electrolytic lesions of the EC in animals that had been injected previously with AOAA had little effect on the abnormal physiological responses in CA1, suggesting that most alterations in inhibition in CA1 are not due to circuit abnormalities within the EC. Comparisons of control and AOAA-injected animals in a hippocampal kindling paradigm revealed that the duration of afterdischarges elicited by high-frequency stimulation of CA3, and the number of stimulations required to elicit kindled seizures were comparable. Taken together, our results reveal that the selective loss of layer III neurons induced by AOAA disrupts inhibitory function in CA1, but this does not create a circuit that is more prone to at least one form of kindling.