Infant brain responses associated with reading-related skills before school and at school age.

INTRODUCTION: In Jyväskylä Longitudinal Study of Dyslexia, we have investigated neurocognitive processes related to phonology and other risk factors of later reading problems. Here we review studies in which we have investigated whether dyslexic children with familial risk background would show atypical auditory/speech processing at birth, at six months and later before school and at school age as measured by brain event-related potentials (ERPs), and how infant ERPs are related to later pre-reading cognitive skills and literacy outcome. PATIENTS AND METHODS: One half of the children came from families with at least one dyslexic parent (the at-risk group), while the other half belonged to the control group without any familial background of dyslexia. RESULTS: Early ERPs were correlated to kindergarten age phonological processing and letter-naming skills as well as phoneme duration perception, reading and writing skills at school age. The correlations were, in general, more consistent among at-risk children. Those at-risk children who became poor readers also differed from typical readers in the infant ERP measures at the group level. ERPs measured before school and at the 3rd grade also differed between dyslexic and typical readers. Further, speech perception at behavioural level differed between dyslexic and typical readers, but not in all dyslexic readers. CONCLUSIONS: These findings suggest persisting developmental differences in the organization of the neural networks sub-serving auditory and speech perception, with cascading effects on later reading related skills, in children with familial background for dyslexia. However, atypical auditory/speech processing is not likely a sufficient reason by itself for dyslexia but rather one endophenotype or risk factor.

Polyunsaturated fatty acids stimulate phosphatidylcholine synthesis in PC12 cells.

The synthesis of phospholipids in mammalian cells is regulated by the availability of three critical precursor pools: those of choline, cytidine triphosphate and diacylglycerol. Diacylglycerols containing polyunsaturated fatty acids (PUFAs) apparently are preferentially utilized for phosphatide synthesis. PUFAs are known to play an important role in the development and function of mammalian brains. We therefore studied the effects of unsaturated, monounsaturated and polyunsaturated fatty acids on the overall rates of phospholipid biosynthesis in PC12 rat pheochromocytoma cells. Docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (AA, 20:4n-6) all significantly stimulated the incorporation of (14)C-choline into total cellular phospholipids. In contrast, monounsaturated oleic acid (OA) and the saturated palmitic (PA) and stearic (SA) acids did not have this effect. The action of DHA was concentration-dependent between 5 and 50 microM; it became statistically significant by 3 h after DHA treatment and then increased over the ensuing 3 h. DHA was preferentially incorporated into phosphatidylethanolamine (PE) and phosphatidylserine (PS), while AA predominated in phosphatidylcholine (PC).

Early development of children at familial risk for dyslexia--follow-up from birth to school age.

We review the main findings of the Jyväskylä Longitudinal study of Dyslexia (JLD) which follows the development of children at familial risk for dyslexia (N = 107) and their controls (N = 93). We will illustrate the development of these two groups of children at ages from birth to school entry in the skill domains that have been connected to reading and reading disability in the prior literature. At school entry, the highest score on the decoding task among the poorer half (median) of the at risk children--i.e. of those presumably being most likely genetically affected--is 1 SD below the mean of the control group. Thus, the familial risk for dyslexia shows expected consequences. Among the earliest measures in which group differences as well as significant predictive associations with the first steps in reading have emerged, are indices of speech processing in infancy. Likewise, various measures of early language including pronunciation accuracy, phonological, and morphological skills (but not performance IQ) show both group differences and predictive correlations, the majority of which become stronger as the reliability of the measures increases by age. Predictive relationships tend to be strong in general but higher in the at risk group because of its larger variance in both the predictor variables and in the dependent measures, such as early acquisition of reading. The results are thus promising in increasing our understanding needed for early identification and prevention of dyslexia.

Stimulation of CDP-choline synthesis by uridine or cytidine in PC12 rat pheochromocytoma cells.

Oral administration of CDP-choline to rats raises plasma and brain cytidine levels and increases brain levels of phosphatidylcholine (PC). In contrast, in humans oral CDP-choline increases plasma levels of uridine. To determine whether uridine can also enhance PC synthesis, we developed an assay for CDP-choline, an immediate and rate-limiting precursor in PC synthesis, and measured this intermediate in clonal PC12 rat pheochromocytoma cells incubated with various concentrations of uridine or cytidine. Addition of uridine (50-100 microM) to the incubation medium caused significant elevations in UTP, CT, USAP and CDP-choline levels in PC12 cells. Uridine had no effect on the synthesis of diacylglycerol (DAG) or the activity of the phosphotransferase which catalyzes the synthesis of PC from DAG and CDP-choline. Hence uridine treatment was unlikely to inhibit the conversion of endogenous CDP-choline to PC. These results suggest the possibility that uridine may also enhance PC synthesis in intact brain.

Event-related potentials and consonant differentiation in newborns with familial risk for dyslexia.

We measured event-related potentials (ERPs) to synthetic consonant-vowel syllables (/ba/, /da/, /ga/) from 26 newborns with familial risk for dyslexia and 23 control infants participating in the Jyväskylä Longitudinal Study of Dyslexia. The syllables were presented with equal probability and with interstimulus intervals ranging from 3,010 to 7,285 ms. Analyses of averaged ERPs from the latencies identified on the basis of principal component analysis (PCA) revealed significant group differences in stop-consonant processing in several latency ranges. At the latencies of 50-170 ms and 540-630 ms, the responses to /ga/ were larger and more positive than those to /ba/ and /da/ in the right hemisphere in the at-risk group. Between 740 and 940 ms, the responses to /ba/ and /da/ differed between anterior and posterior electrode sites in the control group. These results indicate that the cortical electric activation evoked by speech elements differs between children with and without risk for dyslexia even immediately after birth. Group-related effects at early and late latency ranges of ERPs suggest differences both in the early sound processing based on activation of afferent elements and in later phases of syllable encoding.

Developmental pathways of children with and without familial risk for dyslexia during the first years of life.

Comparisons of the developmental pathways of the first 5 years of life for children with (N = 107) and without (N = 93) familial risk for dyslexia observed in the Jyväskylä Longitudinal study of Dyslexia are reviewed. The earliest differences between groups were found at the ages of a few days and at 6 months in brain event-related potential responses to speech sounds and in head-turn responses (at 6 months), conditioned to reflect categorical perception of speech stimuli. The development of vocalization and motor behavior, based on parental report of the time of reaching significant milestones, or the growth of vocabulary (using the MacArthur Communicative Development Inventories) failed to reveal differences before age 2. Similarly, no group differences were found in cognitive and language development assessed by the Bayley Scales of Infant Development and the Reynell Developmental Language Scales before age 2.5. The earliest language measure that showed lower scores among the at-risk group was maximum sentence length at age 2. Early gross motor development had higher correlation to later language skills among the at-risk group rather than the control children. The most consistent predictor of differential development between groups was the onset of talking. Children who were identified as late talkers at age 2 were still delayed at the age 3.5 in most features of language-related skills-but only if they belonged to the group at familial risk for dyslexia. Several phonological and naming measures known to correlate with reading from preschool age differentiated the groups consistently from age 3.5. Our findings imply that a marked proportion of children at familial risk for dyslexia follow atypical neurodevelopmental paths. The signs listed previously comprise a pool of candidates for early predictors and precursors of dyslexia, which await validation.

Auditory event-related potentials (ERP) reflect temporal changes in speech stimuli.

We studied the brain's reactions to deviations in the duration of a stop consonant using event-related potentials in an oddball paradigm. A naturally produced nonsense word was used as a frequent standard stimulus which differed from two infrequently presented deviant stimuli only by the duration of the silence period inside the stop, making the consonant sound longer. Evoked responses to the deviant stimuli showed sharply rising negativity after the unexpected prolongation of the silence and a later negativity, the duration of which was related to the timing of the beginning of the second part of the deviant sound. This later negativity is, at least partly, elicited by a mismatch process to the omission of a sound at the expected latency.

Cerebrospinal fluid levels of amyloid beta-protein in Alzheimer's disease: inverse correlation with severity of dementia and effect of apolipoprotein E genotype.

Alzheimer's disease (AD) is characterized by formation in brain of neurofibrillary tangles and of amyloid deposits. The major protein component of the former is tau, while the latter are composed of amyloid beta-peptides (A beta), which are derived by proteolytic cleavage of the amyloid beta-protein precursor (APP). Both tau and various secretory APP derivatives including A beta and APPS are present in human cerebrospinal fluid (CSF). To investigate whether clinical signs of AD are paralleled by changes in CSF levels of these proteins, we correlated quantitative measures of dementia severity with CSF concentrations of A beta, of APPS, and of tau. We found that levels of A beta in CSF of AD patients were inversely correlated both to cognitive and to functional measures of dementia severity. In contrast, levels of APPS and of tau did not correlate with dementia severity. Apolipoprotein E (apoE) genotype did not influence CSF levels of A beta, APPS, or tau, which were similar among AD patients with Apo E epsilon 3/3, epsilon 3/4, and epsilon 4/4 alleles. These data indicate that CSF levels of A beta decrease with advancing severity of dementia in AD and suggest that they are independent of a patient's Apo E genotype.

Dioctanoylglycerol stimulates accumulation of [methyl-14C]choline and its incorporation into acetylcholine and phosphatidylcholine in a human cholinergic neuroblastoma cell line.

Dioctanoylglycerol, a synthetic diacylglycerol, stimulated [14C]choline uptake in cultured human neuroblastoma (LA-N-2) cells. As this effect has not, to our knowledge, been reported before, it was of interest to characterize it in more detail. In the presence of 500 microM dioctanoylglycerol the levels of [14C]choline attained during a 2 hour labeling period were elevated by 78 +/- 12%, while [14C]acetylcholine and long fatty acyl chain [14C]phosphatidylcholine levels increased by 26 +/- 2% and 19 +/- 5%, respectively (mean +/- S.E.M.). Total (long chain plus dioctanoyl-) [14C]phosphatidylcholine was increased by 198 +/- 33%. Kinetic analysis showed that dioctanoylglycerol reduced the apparent Km for choline uptake to 56 +/- 9% of control (n = 4). The Vmax was not significantly altered. The stimulation of [14C]choline accumulation by dioctanoylglycerol was not dependent on protein kinase C activation; the effect was not mimicked by phorbol ester or by 1-oleoyl-2-acetylglycerol, and was not inhibited by the protein kinase C inhibitors H-7 or staurosporine, or by prolonged pretreatment with phorbol 12-myristate 13-acetate. The effect of dioctanoylglycerol was slightly (but not significantly) reduced by EGTA and strongly inhibited by the cell-permeant calcium chelator bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl)ester. Although these results implicate elevated intracellular calcium in the response, dioctanoylglycerol did not increase phosphatidylinositol hydrolysis in LA-N-2 cells, and its effect was not inhibited by the diacylglycerol kinase inhibitor R 59 022 (which blocks the conversion of diacylglycerol to phosphatidic acid, a known stimulator of phosphatidylinositol hydrolysis).(ABSTRACT TRUNCATED AT 250 WORDS)

Base-exchange and cell growth in 3T6 mouse fibroblasts.

Synthesis of phosphatidyl serine by base-exchange and DNA synthesis both declined rapidly in mouse fibroblast cultures upon withdrawal of serum from nutrient medium. Base-exchange returned to control levels within 3 h after the addition of serum, while DNA synthesis lagged by 10 h. Phosphatidyl serine synthesis is thus an early response of 3T6 cells to mitogenic signals.

Relationship between pituitary ACTH content and hypothalamic catecholamines in the rat.

Hypothalamic concentrations of epinephrine and norepinephrine were determined in rats following 6-hydroxydopamine lesions of the locus coeruleus and subcoeruleus system and following sham-operation. These concentrations were correlated with pituitary ACTH content. While the lesion procedure did not have a major effect on hypothalamic monoamine levels, we were able to demonstrate a strong negative correlation between hypothalamic epinephrine and pituitary ACTH content independent of the experimental condition. Only a weak negative correlation was observed for hypothalamic norepinephrine and pituitary ACTH. Our recent and previous data suggest a tonic and phasic inhibition of ACTH release by hypothalamic monoamines.

Acetylcholine synthesis and secretion by LA-N-2 human neuroblastoma cells.

We have investigated the rates of acetylcholine (ACh) synthesis and release in LA-N-2 cells in order to characterize them as a potential model of cholinergic neurons. When grown in a serum-containing medium the cells extend few neurites. In the absence of serum most cells develop processes. ACh content of the cells (determined by a radioenzymatic assay) varies with extracellular choline concentration in a saturable fashion, reaching a maximum of approximately 25 nmol/mg protein. Radiolabeled choline is taken up by the cell and converted to ACh or phosphocholine, as determined by purification from cell extracts by HPLC, in a saturable manner which is described by a single rectangular hyperbola. Hemicholinium-3 (100 microM) inhibits this uptake. The cells release ACh spontaneously and this release is enhanced upon depolarization with potassium or veratridine (the latter effect is blocked by tetrodotoxin). The data demonstrate that LA-N-2 cells exhibit some properties similar to cholinergic neurons and may therefore be useful for studies of ACh synthesis and release.

Synthesis of acetylcholine from choline derived from phosphatidylcholine in a human neuronal cell line.

Cholinergic neurons are unique among cells since they alone utilize choline not only as a component of major membrane phospholipids, such as phosphatidylcholine (Ptd-Cho), but also as a precursor of their neurotransmitter acetylcholine (AcCho). It has been hypothesized that choline-phospholipids might serve as a storage pool of choline for AcCho synthesis. The selective vulnerability of cholinergic neurons in certain neurodegenerative diseases (e.g., Alzheimer disease, motor neuron disorders) might result from the abnormally accelerated liberation of choline (to be used as precursor of AcCho) from membrane phospholipids, resulting in altered membrane composition and function and compromised neuronal viability. However, the proposed metabolic link between membrane turnover and AcCho synthesis has been difficult to demonstrate because of the heterogeneity of the preparations used. Here we used a population of purely cholinergic cells (human neuroblastoma, LA-N-2), incubated in the presence of [methyl-3H]methionine to selectively label PtdCho synthesized by methylation of phosphatidylethanolamine, the only pathway of de novo choline synthesis. PtdCho, purified by thin-layer chromatography, contained 90% of the label incorporated into lipids, demonstrating that LA-N-2 cells contained phosphatidylethanolamine N-methyltransferase. Three peaks of radioactive material that cochromatographed with authentic Ac-Cho, choline, and phosphocholine were observed when the water-soluble metabolites of the [3H]PtdCho were purified by high-performance liquid chromatography. Their identities were ascertained by subjecting them to enzymatic modifications with acetylcholinesterase, choline oxidase, and alkaline phosphatase, respectively. The results demonstrate that AcCho can be synthesized from choline derived from the degradation of endogenous PtdCho formed de novo by methylation of phosphatidylethanolamine.

Phosphatidylcholine as a precursor of choline for acetylcholine synthesis.

It has been hypothesized that the selective vulnerability of certain brain cholinergic neurons in Alzheimer's disease may reflect the unique way that choline is utilized by these neurons, i.e. not only as a component of major membrane phospholipids, e.g. phosphatidylcholine (PC), but also as a precursor of their neurotransmitter, acetylcholine (ACh). A prolonged utilization of choline liberated from PC, for ACh production, without adequate resynthesis of this lipid, might result in a net loss of the phosphatide followed by an impairment of membrane function and loss of cellular viability. Studies described in this paper, performed on electrically stimulated striatal slices and on cholinergic cell lines, test this hypothesis. 1) Electrically-stimulated striatal slices continue to release ACh, and sustain their free choline and ACh levels, even when perfused with a choline-free medium. Striatal levels of PC decline under these circumstances, and this decline can be blocked by adding tetrodotoxin (which blocks neuronal depolarization) or choline to the medium. The other major membrane phospholipids, phosphatidylserine and phosphatidylethanolamine, also decline proportionately to PC when slices are stimulated in the absence of choline. 2) In a population of purely cholinergic cells (human neuroblastoma, LA-N-2), ACh can be synthesized from choline derived from degradation of endogenous PC formed de novo by methylation of phosphatidylethanolamine. 3) PC content of cells in culture (neuroblastoma X glioma hybrid, NG 108-15) can be altered by adding various amounts of choline to the growth media. The proportion of PC in the cells apparently affects cellular survival and rate of growth. Taken together these data demonstrate that cholinergic neurons utilize the choline stored in PC to synthesize ACh; that this process may lead to a depletion in membrane phospholipids (when choline supply is inadequate); and that the resulting changes in neuronal membrane composition might adversely affect cellular viability.

NG108-15 hybrid cells take up but do not synthesize serotonin.

The mouse neuroblastoma x rat glioma hybrid cell line, NG108-15, does not synthesize serotonin from tryptophan, although the cells take up tryptophan and serotonin in a saturable manner from serum-supplemented incubation medium. Since serum commonly used to supplement the growth medium contains serotonin, it is concluded that appreciable levels of serotonin found in NG108-15 cells are attributable to uptake of serotonin from the serum-supplemented medium.

Multiple classes of calcium channels in mouse pituitary tumor cells.

Synthetic corticotropin-releasing factor (CRF) is a potent adrenocorticotropin (ACTH) secretagogue in the mouse pituitary tumor cell strain AtT20/D16v (D16). In the absence of added calcium in the incubation medium a dose of 5 nM CRF stimulates ACTH secretion 2-fold over control values while at medium calcium concentrations greater than 1 mM the same dose of CRF elicits a 3-fold stimulation. In the presence of EGTA or of the calcium antagonists verapamil, cobalt, or lanthanum the CRF effect is abolished. Depolarizing concentrations of extracellular K+ lead to a rapid increase in cell-associated calcium, a response which is inhibited by the dihydropyridine calcium antagonist nimodipine. Although treatment with CRF does not alter the concentration of cell-associated calcium in D16 cells, ACTH secretion stimulated by both CRF and elevated medium K+ are inhibited by nimodipine in a dose-related manner. The results indicate that D16 cells possess both voltage-sensitive and CRF-activated calcium channels.

ACTH secretion in mouse pituitary tumor cells in culture: inhibition of CRF-stimulated hormone release by somatostatin.

Synthetic corticotropin-releasing factor (CRF) stimulates ACTH secretion in the clonal mouse pituitary cell strain AtT20/D16v (D16) in a dose-dependent manner with a half-maximal effect at 2X10(-9)M. A single dose of 5X10(-9)M CRF maximally stimulates the rate of ACTH secretion during the initial two hrs of treatment. During the period of maximal CRF stimulation intracellular hormone concentration declines progressively to a nadir at 4 hrs. During the ensuing 24 hrs of incubation intracellular hormone levels in CRF-stimulated cells increase gradually toward control values. Somatostatin (SRIF) inhibits the secretory response to CRF. This action of SRIF is dose-dependent with a half-maximal effect at 1X10(-9)M and results in decreased maximal ACTH secretion with little effect on the ED50 for CRF.

Adrenocorticotropin secretion by mouse pituitary tumor cells in culture: the role of Ca+2 in stimulated and somatostatin-inhibited secretion.

SRIF inhibits ACTH secretion by AtT20/D16v (D16) mouse pituitary cells stimulated by high (50 mM) extracellular concentrations of K+ or by divalent cation ionophores. Although stimulation of ACTH secretion by K+ requires extracellular Ca+2, the response is invariant over medium Ca+2 concentrations of 0.003-1 mM; with Ca+2 concentrations from 1-5 mM there is a dramatic amplification of the secretory response. SRIF at concentrations of 10(-8) M completely inhibits the secretory response to K+ at Ca+2 concentrations between 0.2 and 1 mM; with increasing medium Ca+2 above 1 mM there is a progressive attenuation of SRIF-inhibition. At concentrations of 5 mM, Ca+2 alone can serve as an ACTH secretagogue. The ionophore ionomycin stimulates ACTH secretion in a Ca+2-dependent manner with a half-maximal effect at 5 X 10(-6) M ionomycin. The secretory response to ionomycin and to X537A is inhibited by at least 50% by SRIF. The secretory response to K+ is accompanied by a rapid and sustained increase in 45Ca+2 uptake, whereas the ionophores ionomycin, X537A, and A23187 increase Ca+2 efflux. SRIF does not affect Ca+2 movement across D16 cell membranes in response to either K+ or ionophores. These results show that an increase in intracellular Ca+2 is an effective stimulus to ACTH secretion by D16 cells and inhibition of ACTH secretion by SRIF is not effected by interference with the stimulus-elicited increase in intracellular Ca+2.