Learning disability subtypes and the effects of auditory and visual priming on visual event-related potentials to words

Three learning-disability (LD) subtype groups and a normal control group of children were compared in their visual event-related potentials (ERPs) to primed and unprimed words. The LD subtypes were defined by deficient performance on tests of arithmetic (Group A), reading and spelling (Group RS), or both (Group RSA). The primed words were preceded by pictures or spoken words having a related meaning, while unprimed words were preceded by non-associated pictures or spoken words. For normal controls, N450 amplitude was greater to unprimed words than to words primed by pictures and spoken words. For Group A, N450 amplitude was reduced by spoken-word primes, but not by picture primes, an effect that demonstrates a deficit in processing visual-spatial information. For Group RS and Group RSA, neither picture nor spoken-word primes reduced N450 amplitude. These effects can be understood in terms of deficiencies in processing auditory-verbal information. Normal controls displayed a greater left- than right-hemispheric asymmetry in frontal N450 amplitude to unprimed words, an effect that is consistent with the association of skilled reading with hemispheric specialization. This asymmetry was absent in the ERPs of all the LD subtypes. The distinct ERP effects for the groups endorses the value of defining LD subtypes on the basis of patterns of deficits in arithmetic and reading and spelling.

Metabolic effects of the nocturnal rise in cortisol on carbohydrate metabolism in normal humans

Glucocorticoid concentrations vary throughout the day. To determine whether an increase in cortisol similar to that present during sleep is of physiologic significance in humans, we studied the disposition of a mixed meal when the nocturnal rise in cortisol was mimicked or prevented using metyrapone plus either a variable or constant hydrocortisone infusion. When glucose concentrations were matched with a glucose infusion, hepatic glucose release (2.6 +/- 0.2 vs. 1.5 +/- 0.4 nmol/kg per 6 h) was higher (P < 0.05) while glucose disappearance (5.9 +/- 0.3 vs. 7.3 +/- 0.9 mmol/kg per 6 h) and forearm arteriovenous glucose difference (64 +/- 24 vs. 231 +/- 62 mmol/dl per 6 h) were lower (P < 0.05) during the variable than basal infusion. The greater hepatic response during the variable cortisol infusion was mediated (at least in part) by inhibition of insulin and stimulation of glucagon secretion as reflected by lower (P < 0.05) C-peptide (0.29 +/- 0.01 vs. 0.38 +/- 0.04 mmol/liter per 6 h) and higher (P < 0.05) glucagon (42.7 +/- 2.0 vs. 39.3 +/- 1.8 ng/ml per 6 h) concentrations. In contrast, the decreased rates of glucose uptake appeared to result from a state of "physiologic" insulin resistance. The variable cortisol infusion also increased (P < 0.05) postprandial palmitate appearance as well as palmitate, beta-hydroxybutyrate, and alanine concentrations, suggesting stimulation of lipolysis, ketogenesis, and proteolysis. We conclude that the circadian variation in cortisol concentration is of physiologic significance in normal humans.

Tracer disequilibrium in CO2 compartments during NaH14CO3 infusion

The failure of labeled CO2 to equilibrate between extracellular and intracellular CO2 compartments may influence the accuracy of substrate oxidation measurements during infusion of carbon-labeled tracers because it may generate errors in estimate of fixation of labeled CO2 derived from control experiments in which labeled bicarbonate is infused. In this study, normal volunteers received a 14-hour overnight primed continuous infusion of NaH14CO3. Over the last 4 hours of the study, steady-state conditions were achieved in the specific activities (SAs) of expired 14CO2 and plasma urea, which was used as a probe for hepatic intracellular CO2 SA. Plasma urea SA was approximately 17% lower than expired CO2 SA (46.4 +/- 5.6 v 56.8 +/- 3.9 disintegrations per minute.mumol-1, P < .02). Fractional 14CO2 recovery was 94.8% +/- 0.8%; when corrected for failure to equilibrate with intracellular CO2, fractional recovery was 89.5% +/- 1.9%. These data indicate that compartmentalization of CO2 may occur in humans. The duration of our experiments, required because of the long half-life of plasma urea, may have minimized the apparent magnitude of compartmentalization. Furthermore, it is possible that compartmentalization in extrahepatic tissues could be of either lesser or greater magnitude than that which we observed in liver. Whether this phenomenon contributes to incomplete recovery of 14CO2 during NaH14CO3 infusion cannot be determined from our results. Additional studies using different experimental approaches will be required to better measure CO2 compartmentalization.

A radioimmunoassay for human urinary prealbumin

We describe a validated radioimmunoassay for prealbumin in urine. Using timed overnight urine samples, the normal reference range was less than 10-148 micrograms/L; or less than 1.8-9.6 micrograms/mmol creatinine, excretion in women being significantly greater than in men (P < 0.05); or less than 7.3-114 ng/min with no significant difference in excretion rate between the sexes. Urines exhibited loss of immunoreactivity after storage at -20 degrees C and thawing. No such loss occurred after storage for 4 weeks at 4 degrees C or room temperature. The urinary excretion of prealbumin was highly correlated with that of albumin (r = 0.85), and clearance relative to creatinine was 2 x 10(-6), the same order as that of albumin.

Evidence that POB1, a Saccharomyces cerevisiae protein that binds to DNA polymerase alpha, acts in DNA metabolism in vivo

Potential DNA replication accessory factors from the yeast Saccharomyces cerevisiae have previously been identified by their ability to bind to DNA polymerase alpha protein affinity matrices (J. Miles and T. Formosa, Proc. Natl. Acad. Sci. USA 89:1276-1280, 1992). We have now used genetic methods to characterize the gene encoding one of these DNA polymerase alpha-binding proteins (POB1) to determine whether it plays a role in DNA replication in vivo. We find that yeast cells lacking POB1 are viable but display a constellation of phenotypes indicating defective DNA metabolism. Populations of cells lacking POB1 accumulate abnormally high numbers of enlarged large-budded cells with a single nucleus at the neck of the bud. The average DNA content in a population of cells lacking POB1 is shifted toward the G2 value. These two phenotypes indicate that while the bulk of DNA replication is completed without POB1, mitosis is delayed. Deleting POB1 also causes elevated levels of both chromosome loss and genetic recombination, enhances the temperature sensitivity of cells with mutant DNA polymerase alpha genes, causes increased sensitivity to UV radiation in cells lacking a functional RAD9 checkpoint gene, and causes an increased probability of death in cells carrying a mutation in the MEC1 checkpoint gene. The sequence of the POB1 gene indicates that it is identical to the CTF4 (CHL15) gene identified previously in screens for mutations that diminish the fidelity of chromosome transmission. These phenotypes are consistent with defective DNA metabolism in cells lacking POB1 and strongly suggest that this DNA polymerase alpha-binding protein plays a role in accurately duplicating the genome in vivo.

Protein affinity chromatography with purified yeast DNA polymerase alpha detects proteins that bind to DNA polymerase

We have overexpressed the POL1 gene of the yeast Saccharomyces cerevisiae and purified the resulting DNA polymerase alpha polypeptide in an apparently intact form. We attached the purified DNA polymerase covalently to an agarose matrix and used this matrix to chromatograph extracts prepared from yeast cells. At least six proteins bound to the yeast DNA polymerase alpha matrix that did not bind to a control matrix. We speculate that these proteins might be DNA polymerase alpha accessory proteins. Consistent with this interpretation, one of the binding proteins, which we have named POB1 (polymerase one binding), is required for normal chromosome transmission. Mutations in this gene cause increased chromosome loss and an abnormal cell morphology, phenotypes that also occur in the presence of mutations in the yeast alpha or delta polymerase genes. These results suggest that the interactions detected by polymerase affinity chromatography are biologically relevant and may help to illuminate the architecture of the eukaryotic DNA replication machinery.

Measurement of plasma acetate kinetics using high-performance liquid chromatography

Previous studies suggest that plasma acetate may be an important fuel in man, accounting for approximately 10% of energy expenditure. Available methods for the determination of plasma acetate kinetics are difficult and time consuming. We describe here a procedure for the determination of plasma acetate concentration and specific activity using automated high-performance liquid chromatography that is precise and sensitive and accommodates large numbers of samples. The procedure involves extraction from plasma with diethyl ether, derivatization with bromoacetophenone, and separation on a C-18 reversed-phase column. The specific activities of D-beta-hydroxybutyrate and lactate can also be determined. Acetate turnover was measured in four dogs and was similar to that previously reported in sheep and humans. Transport of [14C]acetate into red blood cells was negligible.

The effect of picture priming on event-related potentials of normal and disabled readers during a word recognition memory task

Normal and one subtype of disabled readers were compared in their visual event-related potentials (ERPs) that were elicited by primed and unprimed words during a recognition memory task. The primed words were preceded by a picture having the same denotative meaning, while unprimed words were preceded by a picture having a non-associated meaning. Normal readers exhibited consistently greater amplitude than the disabled readers to unprimed words with a negative wave at 455 ms (N400). For the disabled readers, this N400 was evident, though somewhat smaller, than for controls, at fronto-central placements, but absent at the lateral parietal and occipital sites. Priming a word with a picture reduced N400 amplitude for both the normal and disabled readers. There were no remarkable differences between groups in their ERPs to the pictures. The pattern of ERP results obtained seems to reflect a failure of this subtype of disabled readers to engage long-term, semantic memory, while their short-term linguistic processing is intact.

Intractable complex partial seizures associated with occult temporal lobe encephalocele and meningoangiomatosis: a case report

Occult congenital temporal lobe encephalocele has rarely been reported in association with medically intractable complex partial seizures. The four previously reported cases were unsuspected preoperatively. We present the case of an 18-year-old woman with intractable complex partial seizures since age 13. Seizure onset was electrically localized to the right temporal lobe. Preoperative neuroimaging studies revealed a middle fossa defect and inferior herniation of the right temporal lobe. Pathologic examination of the resected encephalocele revealed prominent features of meningoangiomatosis. We believe this to be the first case of temporal lobe encephalocele and epilepsy to be diagnosed preoperatively, and the first case also to be associated with meningoangiomatosis. The relevant literature on meningoangiomatosis and on temporal lobe encephalocele as a cause of epilepsy is reviewed.

Helping people prepare. Catholic healthcare facilities can give patients advice on advance directives

Although state courts have tended recently to allow surrogates to make healthcare treatment decisions for incompetent patients, the Missouri Supreme Court went against the trend by denying Nancy Cruzan's family the right to withdraw her artificial nutrition and hydration. The U.S. Supreme Court upheld the Missouri decision. At the same time, however, the Court's opinions strongly implied that it would uphold other state courts' decisions affirming the right of surrogates to make treatment decisions for incompetent patients. In his majority opinion, moreover, Chief Justice William Rehnquist upheld a competent person's liberty interest in refusing medical treatment, including artificial nutrition and hydration. Catholic healthcare facilities should be prepared to provide information to the many patients and long-term care residents seeking advice on advance directives as a result of the Court's ruling. Because living wills are proving to be less effective than many at first thought they would be, providers can best help individuals by giving them information on preparing proxy documents.