Norbert Herschkowitz

Structural and neurobehavioral delay in postnatal brain development of preterm infants.

Postnatal brain development of healthy prematurely born infants was assessed to study possible influence of premature birth and early extrauterine environment on structural, biochemical, and functional brain development. Myelination and differentiation of gray and white matter were studied byin vivo magnetic resonance (MR) imaging (MRI), changes in cerebral metabolism by 1H MR spectroscopy (MRS), and changes in early human neurobehavior by the assessment of preterm infants behavior (APIB). The stage of intrauterine and extrauterine brain development in prematurely born infants at term was compared with the stage of mainly intrauterine brain development in a group of full-term infants. Eighteen preterm infants unremarkable with respect to neurologic and medical status were studied at approximately 2 wk of postnatal age [gestational age (GA) 1: 32.5 ± 1.2 wk] and again at term(GA 2: 40.0 ± 1.1 wk). For comparison a group of 13 full-term born infants (GA T: 40.6 ± 2.1 wk) were studied by MR and six by APIB. When GA 2 to GA 1 was compared, significant maturational changes were found with MRI in gray and white matter and myelination, with 1H MRS in the concentration of N-acetylaspartate and with all scores of APIB. In preterm infants at term (GA 2) compared with full-term infants (GA T) significantly less gray and white matter differentiation and myelination was observed as well as significantly poorer performance in four neurobehavioral parameters (autonomic reactivity, motoric reactivity, state organization, attentional availability). We conclude that MRI and 1H MRS can be used to study postnatal brain development in preterm infants. Structural and biochemical maturation is accompanied by functional maturation as shown with the neurobehavior assessment. Preterm infants at term compared with full-term infants show a structural as well as a functional delay in brain development assessed at 40 wk of postconceptional age.

Magnetic resonance in preterm and term newborns: 1H-spectroscopy in developing human brain.

ABSTRACT: Localized proton magnetic resonance spectra were recorded from human cerebellum in vivo with a 1.5-T magnet. The spectra from healthy adults and preterm and term babies showed resonances from N-acetylaspartate, creatine and phosphocreatine, choline-containing compounds such as phosphocholine and glycerophosphocholine, taurine, and inositol. The age-dependent changes of in vivo molar concentrations of N-acetylaspartate, choline, taurine, and inositol were estimated in preterm babies, babies at term, and adults. The range of postconceptional age in the studied babies was 31 to 45 wk. Taking the biochemically measured creatine concentrations in age-corresponding autopsy material as an internal standard, the in vivo concentrations of the other metabolites were calculated from the proton spectra. N-acetylaspartate showed an increase from 1.9 mM in preterm babies to 3.1 mM in term babies and to 6.5 mM in adult brain. Taurine was noted to increase from 1.1 mM in preterm infants to 2.3 mM in term infants and did not decrease significantly in adult brain. Choline and inositol concentrations did not change significantly throughout the studied age groups. These new data on in vivo, localized 1H-spectroscopy show that it is a sensitive method for studying early metabolic brain development in humans.

N-Acetyl-L-Aspartate is a Major Source of Acetyl Groups for Lipid Synthesis during Rat Brain Development

The function of N-acetyl-L-aspartate (NAA), a predominant substance in the CNS, has not yet been determined. To investigate the possible function of NAA as a lipid precursor [14C]-N-acetyl-L-aspartate (NAA) or [14C]-acetate (AcA) was injected intracerebrally into 8, 15- and 22-day-old rats. These time points were selected because NAA concentration and the activity of the NAA synthetizing enzyme L-aspartate-N-acetyltransferase (ANAT) were low in 8-day-old rats, intermediate in 15-day-old rats and high in 22-day-old rats. During an incubation period of 4 h the radioactive acetyl group of NAA is incorporated into the lipid fraction in amounts of 42.9 to 65.7% of recovered total radioactivity, increasing with the age of the rats. In contrast, radioactivity incorporated from AcA is constant for all three ages. With NAA as precursor only 7.2-9.4% of the recovered total radioactivity is incorporated into the protein fraction. With AcA as precursor 27.0-18.1% of recovered radioactivity is incorporated into the protein fraction, the amounts decreasing with age. Taking into account that in vivo NAA concentration in the brain is much higher than the AcA concentration, NAA is clearly the more efficient precursor for lipid synthesis than AcA. Further, we compared NAA and AcA as lipid precursors by analyzing the radioactivity in single lipid fractions, expressed as normalized specific incorporation or normalized incorporation. The measured differences between NAA and AcA in normalized specific and normalized incorporation of acetyl groups imply that NAA is not simply degraded to AcA before incorporated into lipids. We conclude that NAA is a major source of acetyl groups for lipid synthesis during rat brain development.

Expression of antigenic markers during the development of oligodendrocytes in mouse brain cell cultures

The expression of myelin basic protein (MBP) and galactocerebroside (GC), two antigenic markers for oligodendrocytes, was checked on 7-, 14-, 21- and 28-day-old dissociated mouse brain cell cultures (BCC) by using the indirect immunofluorescence method with double staining. The number of GC positive cells increased between the 7th and the 14th day of culture before a steady state was reached. In contrast to this, the MBP-positive cells appeared only on the 14th day of culture, and their number increased with the age of the culture. In double staining, the serum produced against isolated oligodendrocytes shows the same picture as the anti-GC serum, while only a part of GC-positive cells showed also the presence of MBP. Our data suggest that the GC appears very early on the membrane of the oligodendrocytes during development while cells exhibiting both GC and MBP probably represent a more differentiated oligodendrocyte population.

Short echo time proton mr spectroscopic imaging

Proton spectroscopic imaging at short TEs (20-30 ms) in human brain requires volume preselection inside the brain to suppress overwhelming lipid and water signals from surrounding tissue. In this article we discuss limitations of conventional volume preselection using stimulated echoes that lead to spectral contamination from surrounding tissue. Improved volume preselection was obtained by adding a complete outer volume suppression (presaturation). The performance of the method is illustrated on normal volunteers and on clinical cases with brain tumors and multiple sclerosis (MS) plaques. In normal human brain, we detected resonances with short T2 values and complex J-coupling, including rather broad methyl/methylene resonances in the chemical shift range between 0 and 2 ppm. Spectroscopic images obtained on patients with intracranial tumors and on one patient with several MS plaques demonstrate the possibility of detecting regional distributions of increased methyl/methylene resonances between 0 and 2 ppm in brain lesions.

Brain development:1H magnetic resonance spectroscopy of rat brain extracts compared with chromatographic methods

We compared in vitro1H magnetic resonance spectroscopy (MRS) measurements of rat brain extracts (rats: 2–56 days old) with chromatographic measurements and in a further step also with results of in vivo MRS. The following substances can be reliably measured in brain extracts by in vitro MRS: N-acetylaspartate (NAA), total creatine (Cr), phosphorylethanoloamine (PE), taurine (Tau), glutamate (Glu), glutamine (Gln), γ-aminobutyrate (GABA) and alanine (Ala). Two different methods of MRS data evaluation compared with chromatographic data on Cr and NAA are shown. During development of the rat from day 2–56 brain concentrations of PE, Tau and Ala decrease, those of NAA, Cr, Glu and Gln increase, while GABA does not change. The developmental patterns of these substances are the same, whether measured by in vitro MRS or by chromatographic methods. Quantification of NAA, Cr, Tau, GABA and PE leads to the same results with both methods, while Glu, Gln and Ala concentrations determined by in vitro MRS are apparently lower than those measured chemically. The NAA/Cr ratios of 7 to 35-day-old rats were determined by in vivo1H MRS. These results correlate with chromatographic and in vitro data. Using appropriate methods in the in vivo and in vitro MR-technique, the obtained data compare well with the chromatographic results.

Regional Metabolic Assessment of Human Brain during Development by Proton Magnetic Resonance Spectroscopy In Vivo and by High-Performance Liquid Chromatography/Gas Chromatography in Autopsy Tissue

To study the course of regional metabolite concentrations during early brain development, we measured in vivo metabolites [N-acetyl-aspartate (NAA), choline-containing compounds, and myo-inositol (M-Ino)] in the precentral area of the cerebrum by short echo-time single volume proton magnetic resonance spectroscopy and compared in vivo established spectroscopic data with classic chromatographic data (HPLC) on age-corresponding autopsy tissue in different regions of the brain. In autopsy tissue, regional (frontal lobe, precentral area, basal ganglia, thalamus) and age-dependent differences of the concentration of creatine, NAA, and M-Ino were determined. In vivo measurement of NAA by proton magnetic resonance spectroscopy shows a significant increase of NAA by increasing postconceptional age. M-Ino shows a weak correlation and a nonsignificant decrease with increasing postconceptional age. Choline shows no age-dependent changes. Creatine concentrations measured by HPLC in different regions of the developing brain at autopsy showed an age-dependent increase that was identical for the left and right side and similar for the precentral area and frontal lobe and more pronounced for the basal ganglia and thalamus. Comparison of the results obtained by the two methods shows agreement for the age-dependent changes and the absolute concentration of M-Ino. NAA determined in autopsy tissue by HPLC is significantly lower than that measured in vivo by proton magnetic resonance spectroscopy. A comparison of the concentrations measured by HPLC in frontal lobe, basal ganglia, and thalamus with the results obtained from the precentral area showed significant regional differences in all measured metabolites. These results define important age-dependent changes detected with both methods and further indicate limitations of both methods that have to be considered when presenting absolute concentration values.

Effect of chloroquine on cultured fibroblasts: release of lysosomal hydrolases and inhibition of their uptake.

Abstract Incubation of normal human fibroblasts with 1–5 μM chloroquine at physiological pH for 8 hr produces granular cytoplasmic inclusions, release of lysosomal enzymes into the medium and decrease of intracellular lysosomal enzyme activities. The effects are dose dependent and reversible. The uptake of arylsulfatase A into fibroblasts genetically deficient in arylsulfatase A (grown from skin biopsies of patients with metachromatic leukodystrophy) is completely inhibited by pretreating the cells with 5 μM chloroquine. Arylsulfatase A, which has been taken up as exogenous enzyme from the medium into the cells, is partially released into the culture medium upon incubation with chloroquine. The data suggest that chloroquine competes with the binding of lysosomal enzymes to the cell membrane and to the membranes of pinocytotic vacuoles and causes release of previously internalized exogenous enzyme.

In Vivo Measurement of Phenylalanine in Human Brain by Proton Nuclear Magnetic Resonance Spectroscopy

Disorders of the CNS are the major causes of morbidity and mortality observed in untreated subjects with phenylketonuria (PKU). A method to measure cerebral concentrations of phenylalanine (Phe) in vivo would greatly enhance the ability to investigate both the pathophysiology and the efficacy of therapy of this aminoacidopathy. Twelve image-guided localized proton nuclear magnetic resonance spectroscopic studies were performed in seven subjects with PKU using pulse sequences optimized to detect the aromatic protons of Phe. Ten control studies were also performed using a 2.1-Tesla Bruker Biospec spectrometer. Plasma Phe was measured at the time of the spectroscopic examination in the PKU patients. A Phe signal was observed in all 12 studies performed on the group with PKU, and in five studies cerebral Phe concentrations were measured to be 480 to 780 μmol/g. Plasma Phe concentrations were 0.7 to 3.3 mM (10.8 to 54.8 mg/dL) in the subjects with PKU. Human cerebral Phe concentrations can be measured noninvasively using proton nuclear magnetic resonance spectroscopy. A simultaneous measure of Phe and several other cerebral metabolites is obtained with this innovative technology. Adaptations of this technique can be used to investigate PKU and other neurometabolic disorders with modifications of current clinical magnetic resonance imaging systems.

Selective uptake of neuroactive amino acids by both oligodendrocytes and astrocytes in primary dissociated culture: A posssible role for oligodendrocytes in neurotransmitter metabolism

CNS glia may be involved in the modulation of neuronal excitability through their capacity to accumulate and metabolize neuroactive amino acids. To investigate the possible role of oligodendrocytes in amino acid neurotransmitter metabolism, we have used light microscopic autoradiography, following the uptake of 3H-labelled amino acids by dissociated cultures of neonatal mouse brain, characterized immunocytochemically using cell-type specific markers. Oligodendrocytes, recognized by their characteristic galactocerebroside membrane staining, rapidly accumulated [3H] gamma-aminobutyric acid (GABA), becoming intensely labelled over cell body and processes after short incubations. In contrast, oligodendrocytes became only lightly labelled with [3H]L-glutamate and aspartate, which preferentially labelled astrocytes. [3H]D-aspartate, a non-metabolized analogue of L-glutamate, was avidly accumulated by oligodendrocytes, labelling cell bodies and processes after short incubations, to a similar extent as GABA. Thus, oligodendrocytes possess a transport mechanism for these excitatory amino acids, but rapidly metabolize them and release the metabolites. Not only the GC-positive cells but also the GC-negative undifferentiated oligodendrocyte precursors accumulated both GABA and D-aspartate, suggesting that this may be a function expressed early in the differentiation of oligodendrocytes. Net uptake of [3H] beta-alanine and [3H]glycine by oligodendrocytes was not observed under any conditions tested. A small number of oligodendrocytes were labelled with [3H]taurine after longer incubations. The uptake of certain neuroactive amino acids is thus a property shared by astrocytes and oligodendrocytes, the latter acting in a protective fashion around neuronal perikarya and axons.