Neuronal maturation and N-acetyl-L-aspartic acid development in human fetal and child brains

Changes in brain metabolite levels across childhood

Metabolites play important roles in brain development and their levels change rapidly in the prenatal period and during infancy. Metabolite levels are thought to stabilize during childhood, but the development of neurochemistry across early-middle childhood remains understudied. We examined the developmental changes of key metabolites (total N-acetylaspartate, tNAA; total choline, tCho; total creatine, tCr; glutamate+glutamine, Glx; and myo-inositol, mI) using short echo-time magnetic resonance spectroscopy (MRS) in the anterior cingulate cortex (ACC) and the left temporo-parietal cortex (LTP) using a mixed cross-sectional/longitudinal design in children aged 2-11 years (ACC: N=101 children, 112 observations; LTP: N=95 children, 318 observations). We found age-related effects for all metabolites. tNAA increased with age in both regions, while tCho decreased with age in both regions. tCr increased with age in the LTP only, and mI decreased with age in the ACC only. Glx did not show linear age effects in either region, but a follow-up analysis in only participants with ≥3 datapoints in the LTP revealed a quadratic effect of age following an inverted U-shape. These substantial changes in neurochemistry throughout childhood likely underlie various processes of structural and functional brain development.

Development of a fast and robust liquid chromatography-mass spectrometry-based metabolomics analysis method for neonatal dried blood spots

Dried blood spot (DBS) samples have been widely used in many fields including newborn screening, with the advantages in transportation, storage and non-invasiveness. The DBS metabolomics research of neonatal congenital diseases will greatly expand the understanding of the disease. In this study, we developed a liquid chromatography-mass spectrometry-based method for neonatal metabolomics analysis of DBS. The influences of blood volume and chromatographic effects on the filter paper on metabolite levels were studied. The levels of 11.11 % metabolites were different between 75 μL and 35 μL of blood volumes used for DBS preparation. Chromatographic effects on the filter paper occurred in DBS prepared with 75 μL whole blood and 6.67 % metabolites had different MS responses when central disks were compared with outer disks. The DBS storage stability study showed that compared with - 80 °C storage, storing at 4 °C for 1 year had obvious influences on more than half metabolites. Storing at 4 °C and - 20 °C for short term (< 14 days) and - 20 °C for longer term (1 year) had less influences on amino acids, acyl-carnitines and sphingomyelins, but greater influences on partial phospholipids. Method validation showed that this method has a good repeatability, intra-day and inter-day precision and linearity. Finally, this method was applied to investigate metabolic disruptions of congenital hypothyroidism (CH), metabolic changes of CH newborns were mainly involved in amino acid metabolism and lipid metabolism.

Neurometabolite mapping highlights elevated myo-inositol profiles within the developing brain in down syndrome

The neurodevelopmental phenotype in Down Syndrome (DS), or Trisomy 21, is variable including a wide spectrum of cognitive impairment and a high risk of early-onset Alzheimer's disease (AD). A key metabolite of interest within the brain in DS is Myo-inositol (mIns). The NA+/mIns co-transporter is located on human chromosome 21 and is overexpressed in DS. In adults with DS, elevated brain mIns was previously associated with cognitive impairment and proposed as a risk marker for progression to AD. However, it is unknown if brain mIns is increased earlier in development. The aim of this study was to estimate mIns concentration levels and key brain metabolites [N-acetylaspartate (NAA), Choline (Cho) and Creatine (Cr)] in the developing brain in DS and aged-matched controls. We used in vivo magnetic resonance spectroscopy (MRS) in neonates with DS (n = 12) and age-matched controls (n = 26) scanned just after birth (36-45 weeks postmenstrual age). Moreover, we used Mass Spectrometry in early (10-20 weeks post conception) ex vivo fetal brain tissue samples from DS (n = 14) and control (n = 30) cases. Relative to [Cho] and [Cr], we report elevated ratios of [mIns] in vivo in the basal ganglia/thalamus, in neonates with DS, when compared to age-matched typically developing controls. Glycine concentration ratios [Gly]/[Cr] and [Cho]/[Cr] also appear elevated. We observed elevated [mIns] in the ex vivo fetal cortical brain tissue in DS compared with controls. In conclusion, a higher level of brain mIns was evident as early as 10 weeks post conception and was measurable in vivo from 36 weeks post-menstrual age. Future work will determine if this early difference in metabolites is linked to cognitive outcomes in childhood or has utility as a potential treatment biomarker for early intervention.

Changes in metabolites in the brain of patients with fibromyalgia after treatment with an NMDA receptor antagonist

The aims of this work were to evaluate whether the treatment of patients with fibromyalgia with memantine is associated with significant changes in metabolite concentrations in the brain, and to explore any changes in clinical outcome measures. Magnetic resonance spectroscopy was performed of the right anterior and posterior insula, both hippocampi and the posterior cingulate cortex. Questionnaires on pain, anxiety, depression, global function, quality of life and cognitive impairment were used. Ten patients were studied at baseline and after three months of treatment with memantine. Significant increases were observed in the following areas: N-acetylaspartate (4.47 at baseline vs. 4.71 at three months, p = 0.02) and N-acetylaspartate+N-acetylaspartate glutamate in the left hippocampus (5.89 vs. 5.98; p = 0.007); N-acetylaspartate+N-acetylaspartate glutamate in the right hippocampus (5.31 vs 5.79; p = 0.01) and the anterior insula (7.56 vs. 7.70; p = 0.033); glutamate+glutamine/creatine ratio in the anterior insula (2.03 vs. 2.17; p = 0.022) and the posterior insula (1.77 vs. 2.00; p = 0.004); choline/creatine ratio in the posterior cingulate (0.18 vs. 0.19; p = 0.023); and creatine in the right hippocampus (3.60 vs. 3.85; p = 0.007). At the three-month follow-up, memantine improved cognitive function assessed by the Cognition Mini-Exam (31.50, SD = 2.95 vs. 34.40, SD = 0.6; p = 0.005), depression measured by the Hamilton Depression Scale (7.70, SD = 0.81 vs. 7.56, SD = 0.68; p = 0.042) and severity of illness measured by the Clinical Global Impression severity scale (5.79, SD = 0.96 vs. 5.31, SD = 1.12; p = 0.007). Depression, clinical global impression and cognitive function showed improvement with memantine. Magnetic resonance spectroscopy could be useful in monitoring response to the pharmacological treatment of fibromyalgia.

From fetus to older age: A review of brain metabolic changes across the lifespan

INTRODUCTION

The knowledge of metabolic changes across the lifespan is poorly understood. Thus we systematically reviewed the available literature to determine the changes in brain biochemical composition from fetus to older age and tried to explain them in the context of neural, cognitive, and behavioural changes.

METHODS

The search identified 1262 articles regarding proton magnetic resonance spectroscopy (1H MRS) examinations through December 2017. The following data was extracted: age range of the subjects, number of subjects studied, brain regions studied, MRS sequence used, echo time, MR system, method of statistical analysis, metabolites analyzed, significant differences in metabolites concentrations with age as well as the way of presentation of the results.

RESULTS

82 studies that described brain metabolite changes with age were identified. Reports on metabolic changes related to healthy aging were analyzed and discussed among six basic age groups: fetuses, infants, children, adolescents, adults, and the elderly as well as between groups and during the whole lifetime.

DISCUSSION

The results presented in the reviewed papers provide evidence that normal aging is associated with a number of metabolic changes characteristic for every period of life. Therefore, it can be concluded that the age matching is essential for comparative studies of disease states using 1H MRS.

Longitudinal investigation of the metabolome of 3D aggregating brain cell cultures at different maturation stages by 1H HR-MAS NMR

The aim of the present study was to establish the developmental profile of metabolic changes of 3D aggregating brain cell cultures by ¹H high-resolution magic angle spinning (HR-MAS) NMR spectroscopy. The histotypic 3D brain aggregate, containing all brain cell types, is an excellent model for mechanistic studies including OMICS analysis; however, their metabolic profile has not been yet fully investigated. Chemometric analysis revealed a clear separation of samples from the different maturation time points. Metabolite concentration evolutions could be followed and revealed strong and various metabolic alterations. The strong metabolite evolution emphasizes the brain modeling complexity during maturation, possibly reflecting physiological processes of brain tissue development. The small observed intra- and inter-experimental variabilities show the robustness of the combination of ¹H-HR-MAS NMR and 3D brain aggregates, making it useful to investigate mechanisms of toxicity that will ultimately contribute to improve predictive neurotoxicology. Graphical Abstract ᅟ.

Noninvasive Tracking of Anesthesia Neurotoxicity in the Developing Rodent Brain

BACKGROUND

Potential deleterious effect of multiple anesthesia exposures on the developing brain remains a clinical concern. We hypothesized that multiple neonatal anesthesia exposures are more detrimental to brain maturation than an equivalent single exposure, with more pronounced long-term behavioral consequences. We designed a translational approach using proton magnetic resonance spectroscopy in rodents, noninvasively tracking the neuronal marker N-acetyl-aspartate, in addition to tracking behavioral outcomes.

METHODS

Trajectories of N-acetyl-aspartate in anesthesia naïve rats (n = 62, postnatal day 5 to 35) were determined using proton magnetic resonance spectroscopy, creating an "N-acetyl-aspartate growth chart." This chart was used to compare the effects of a single 6-h sevoflurane exposure (postnatal day 7) to three 2-h exposures (postnatal days 5, 7, 10). Long-term effects on behavior were separately examined utilizing novel object recognition, open field testing, and Barnes maze tasks.

RESULTS

Utilizing the N-acetyl-aspartate growth chart, deviations from the normal trajectory were documented in both single and multiple exposure groups, with z-scores (mean ± SD) of -0.80 ± 0.58 (P = 0.003) and -1.87 ± 0.58 (P = 0.002), respectively. Behavioral testing revealed that, in comparison with unexposed and single-exposed, multiple-exposed animals spent the least time with the novel object in novel object recognition (F(2,44) = 4.65, P = 0.015), traveled the least distance in open field testing (F(2,57) = 4.44, P = 0.016), but exhibited no learning deficits in the Barnes maze.

CONCLUSIONS

Our data demonstrate the feasibility of using the biomarker N-acetyl-aspartate, measured noninvasively using proton magnetic resonance spectroscopy, for longitudinally monitoring anesthesia-induced neurotoxicity. These results also indicate that the neonatal rodent brain is more vulnerable to multiple anesthesia exposures than to a single exposure of the same cumulative duration.

Temporal brain metabolite changes in preterm infants with normal development

OBJECTIVE

Preterm infants are at high risk for developmental delay, epilepsy, and autism spectrum disorders. Some reports have described associations between these conditions and gamma-aminobutyric acid (GABA) dysfunction; however, no study has evaluated temporal changes in GABA in preterm infants. Therefore, we assessed temporal changes in brain metabolites including GABA using single-voxel 3-Tesla (T) proton magnetic resonance spectroscopy (¹H-MRS) in preterm infants with normal development.

METHODS

We performed 3T ¹H-MRS at 37-46 postmenstrual weeks (PMWs, period A) and 64-73PMWs (period B). GABA was assessed with the MEGA-PRESS method. N-acetyl aspartate (NAA), glutamate-glutamine complex (Glx), creatine (Cr), choline (Cho), and myo-inositol (Ins) were assessed with the PRESS method. Metabolite concentrations were automatically calculated using LCModel.

RESULTS

Data were collected from 20 preterm infants for periods A and B (medians [ranges], 30 [24-34] gestational weeks, 1281 [486-2030]g birth weight). GABA/Cr ratio decreased significantly in period B (p=0.03), but there was no significant difference in GABA/Cho ratios (p=0.58) between the two periods. In period B, NAA/Cr, Glx/Cr, NAA/Cho, and Glx/Cho ratios were significantly increased (p<0.01), whereas Cho/Cr, Ins/Cr, and Ins/Cho ratios were significantly decreased (p<0.01). There was no significant difference for GABA or Cho concentrations (p=0.52, p=0.22, respectively). NAA, Glx, and Cr concentrations were significantly increased (p<0.01), whereas Ins was significantly decreased (p<0.01).

CONCLUSIONS

Our results provide new information on normative values of brain metabolites in preterm infants.

The Effect of Single Dose Methylphenidate on Neurometabolites according to COMT Gene Val158Met Polymorphism in the Patient with Attention Deficit Hyperactivity Disorder: A Study Using Magnetic Resonance Spectroscopy

OBJECTIVE

Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder. Thus, the present study aimed to determine the effects of a single dose of methylphenidate (Mph) on neurometabolite levels according to polymorphisms of the catechol-O-methyltransferase (COMT) gene.

METHODS

This study evaluated the neurometabolite levels including N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) of ADHD patients, before and after treatment with Mph (10 mg) according to the presence of COMT polymorphisms. The spectra were obtained from the dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), cerebellum, and striatum.

RESULTS

The NAA levels of the val/val and val genotype carriers (val/val and val/met genotypes) increased in the DLPFC and ACC, respectively, following Mph treatment. The NAA/Cr ratio was lower in the DLPFC of val carriers than in the met/met genotype carriers prior to Mph administration. The Cho levels of the val/met genotype and val carriers increased in the striatum following Mph treatment. Following Mph treatment, the Cr levels of the met/met genotype carriers were higher than those of the val/met genotype and val carriers. Additionally, after Mph treatment, there was a significant increase in Cr levels in the DLPFC of the met/met genotype carriers but a significant decrease in such levels in the striatum of val/val genotype carriers.

CONCLUSION

These findings suggest that polymorphisms of the COMT gene can account for individual differences in neurochemical responses to Mph among ADHD patients. Therefore, further studies are needed to fully characterize the effects of the Val158met polymorphism of the COMT gene on treatment outcomes in patients with ADHD.

Normal development

Numerous events are involved in brain development, some of which are detected by neuroimaging. Major changes in brain morphology are depicted by brain imaging during the fetal period while changes in brain composition can be demonstrated in both pre- and postnatal periods. Although ultrasonography and computed tomography can show changes in brain morphology, these techniques are insensitive to myelination that is one of the most important events occurring during brain maturation. Magnetic resonance imaging (MRI) is therefore the method of choice to evaluate brain maturation. MRI also gives insight into the microstructure of brain tissue through diffusion-weighted imaging and diffusion tensor imaging. Metabolic changes are also part of brain maturation and are assessed by proton magnetic resonance spectroscopy. Understanding and knowledge of the different steps in brain development are required to be able to detect morphologic and structural changes on neuroimaging. Consequently alterations in normal development can be depicted.

Brain maturation in neonatal rodents is impeded by sevoflurane anesthesia

BACKGROUND

A wealth of data shows neuronal demise after general anesthesia in the very young rodent brain. Herein, the authors apply proton magnetic resonance spectroscopy (1HMRS), testing the hypothesis that neurotoxic exposure during peak synaptogenesis can be tracked via changes in neuronal metabolites.

METHODS

1HMRS spectra were acquired in the brain (thalamus) of neonatal rat pups 24 and 48 h after sevoflurane exposure on postnatal day (PND) 7 and 15 and in unexposed, sham controls. A repeated measure ANOVA was performed to examine whether changes in metabolites were different between exposed and unexposed groups. Sevoflurane-induced neurotoxicity on PND7 was confirmed by immunohistochemistry.

RESULTS

In unexposed PND7 pups (N = 21), concentration of N-acetylaspartate (NAA; [NAA]) increased by 16% from PND8 to PND9, whereas in exposed PND7 pups (N = 19), [NAA] did not change and concentration of glycerophosphorylcholine and phosphorylcholine ([GPC + PCh]) decreased by 25%. In PND15 rats, [NAA] increased from PND16 to PND17 for both the exposed (N = 14) and the unexposed (N = 16) groups. Two-way ANOVA for PND7 pups demonstrated that changes over time observed in [NAA] (P = 0.031) and [GPC + PCh] (P = 0.024) were different between those two groups.

CONCLUSIONS

The authors demonstrated that normal [NAA] increase from PND8 to PND9 was impeded in sevoflurane-exposed rats when exposed at PND7; however, not impeded when exposed on PND15. Furthermore, the authors showed that noninvasive 1HMRS is sufficiently sensitive to detect subtle differences in developmental time trajectory of [NAA]. This is potentially clinically relevant because 1HMRS can be applied across species and may be useful in providing evidence of neurotoxicity in the human neonatal brain.

Assessing Temporal Brain Metabolite Changes in Preterm Infants Using Multivoxel Magnetic Resonance Spectroscopy

PURPOSE

To investigate temporal changes in brain metabolites during the first year of life in preterm infants using multivoxel proton magnetic resonance spectroscopy ((1)H-MRS).

METHODS

Seventeen infants born at 29 (25-33) gestational week (median, range) weighing 1104 (628-1836) g underwent 1.5-T multivoxel (1)H-MRS at 42 postconceptional week (PCW) and at 3, 6, 9, and 12 months after. We measured N-acetyl aspartate (NAA)/creatine (Cr), choline (Cho)/Cr, myo-inositol (Ins)/Cr, NAA/Cho, and Ins/Cho ratios in the frontal lobe (FL) and basal ganglia and thalamus (BG + Th). Linear regression analyses were performed to identify longitudinal changes in infants showing normal imaging findings and normal development. We also evaluated ratios of subjects with abnormal imaging findings and/or development using the 95% confidence intervals (CIs) of regression equations in normal subjects.

RESULTS

In the 13 infants with normal development, NAA/Cr and NAA/Cho ratios showed significant positive correlations with PCWs in the FL (r = 0.64 and 0.83, respectively, both P < 0.01) and BG + Th (r = 0.79 and 0.87, respectively, both P < 0.01), while Cho/Cr and Ins/Cr ratios revealed significant negative correlations with PCWs in the FL (r =-0.69 and -0.58, respectively, both P < 0.01) and BG + Th (r =-0.74 and -0.72, respectively, both P < 0.01). Ins/Cho ratios in the FL did not significantly correlate with PCWs (r =-0.19, P = 0.18), while those in the BG + Th showed significant negative correlation with PCWs (r =-0.44, P < 0.01). The metrics in the abnormal group were within the normal group 95% CIs in all periods except a few exceptions.

CONCLUSIONS

Longitudinal multivoxel MRS is able to detect temporal changes in major brain metabolites during the first year of life in preterm infants.

NMR Based Cerebrum Metabonomic Analysis Reveals Simultaneous Interconnected Changes during Chick Embryo Incubation

To find out if content changes of the major functional cerebrum metabolites are interconnected and formed a network during the brain development, we obtained high-resolution magic-angle-spinning (HR-MAS) 1H NMR spectra of cerebrum tissues of chick embryo aged from incubation day 10 to 20, and postnatal day 1, and analyzed the data with principal component analysis (PCA). Within the examined time window, 26 biological important molecules were identified and 12 of them changed their relative concentration significantly in a time-dependent manner. These metabolites are generally belonged to three categories, neurotransmitters, nutrition sources, and neuronal or glial markers. The relative concentration changes of the metabolites were interconnected among/between the categories, and, more interestingly, associated with the number and size of Nissl-positive neurons. These results provided valuable biochemical and neurochemical information to understand the development of the embryonic brain.

Longitudinal study of the substantia nigra in Parkinson disease: A high-field (1) H-MR spectroscopy imaging study

INTRODUCTION

The value of biomarkers in early diagnosis and development of therapeutics in Parkinson's disease (PD) is well established.

METHODS

We used proton magnetic resonance spectroscopy in a prospective, longitudinal study of 23 patients with early PD, naïve to dopaminergic therapy, and six age-matched healthy controls to examine the temporal changes in metabolic profile of substantia nigra over a period of 3 months.

RESULTS

N-acetyl aspartate to creatine ratio at month 3 was compared with baseline values in the PD and control groups, as well as the side-to-side difference of the ratio at baseline. By month 3, n-acetyl aspartate to creatine ratio had decreased by 4.4% in patients with PD (P = 0.024), without a concomitant change in healthy controls. The side-to-side asymmetry was significantly higher in the PD group (16.7%) vs. healthy controls (1.6%, P = 0.0024).

CONCLUSION

Estimation of change in the n-acetyl aspartate to creatine ratio appears to be a fast, quantifiable, and reliable marker of dopaminergic neuronal viability in PD.

MR spectroscopy of the fetal brain: is it possible without sedation?

BACKGROUND AND PURPOSE

The quality of spectroscopic studies may be limited because of unrestricted fetal movement. Sedation is recommended to avoid motion artefacts. However, sedation involves side effects. The aim of this study was to assess the feasibility and quality of brain (1)H-MR spectroscopy in unsedated fetuses and to evaluate whether quality is dependent on the type of spectra, fetal presentation, GA, and/or fetal pathology.

MATERIALS AND METHODS

Seventy-five single-voxel spectroscopic studies of the fetal brain, performed at gestational weeks 19-38 at 1.5T, were evaluated retrospectively. A PRESS (TE = 144 or 35 ms) was used. Fetal presentation, GA, and kind of pathology were recorded. The quality of the spectra was assessed by reviewing the spectral appearance (line width, signal-to-noise) of the creatine resonance obtained relative to concentrations (ratios-to-creatine) of choline, myo-inositol, and NAA.

RESULTS

Of 75 studies, 50 (66.6%) were rated as readable: short TE = 17/50 (34%), long TE = 33/50 (66%), cephalic presentation in 36/50 (72%) studies, breech in 10/50 (20%) studies, and "other" presentation in 4/50 (8%) studies (mean GA, 31.0 weeks). Twenty-eight of 50 fetuses (56%) showed normal development (short TE = 12/28, long TE = 16/28), and 22/50 (44%) showed pathology. Of the 75 studies, 25 (33.3%) were not readable: short TE = 14/25 (56%), long TE = 11/25 (44%), cephalic presentation in 20/25 (80%) studies, breech in 4/25 (16%) studies, and other presentation in 1 study (4%) (mean GA, 30.1 week). Thirteen of 25 fetuses (52%) showed normal development; 12/25 (48%) showed pathology. Statistical analysis revealed no impact of the different parameters on the quality of spectra.

CONCLUSIONS

Single-voxel spectroscopy can be performed in approximately two-thirds of unsedated fetuses, regardless of the type of spectra, fetal presentation, GA, and pathology.

Magnetic resonance methods in fetal neurology

Fetal magnetic resonance imaging (MRI) has become an established clinical adjunct for the in-vivo evaluation of human brain development. Normal fetal brain maturation can be studied with MRI from the 18th week of gestation to term and relies primarily on T2-weighted sequences. Recently diffusion-weighted sequences have gained importance in the structural assessment of the fetal brain. Diffusion-weighted imaging provides quantitative information about water motion and tissue microstructure and has applications for both developmental and destructive brain processes. Advanced magnetic resonance techniques, such as spectroscopy, might be used to demonstrate metabolites that are involved in brain maturation, though their development is still in the early stages. Using fetal MRI in addition to prenatal ultrasound, morphological, metabolic, and functional assessment of the fetus can be achieved. The latter is not only based on observation of fetal movements as an indirect sign of activity of the fetal brain but also on direct visualization of fetal brain activity, adding a new component to fetal neurology. This article provides an overview of the MRI methods used for fetal neurologic evaluation, focusing on normal and abnormal early brain development.

Maturation of limbic regions in Asperger syndrome: a preliminary study using proton magnetic resonance spectroscopy and structural magnetic resonance imaging

People with autistic spectrum disorders (ASD, including Asperger syndrome) may have developmental abnormalities in the amygdala-hippocampal complex (AHC). However, in vivo, age-related comparisons of both volume and neuronal integrity of the AHC have not yet been carried out in people with Asperger syndrome (AS) versus controls. We compared structure and metabolic activity of the right AHC of 22 individuals with AS and 22 healthy controls aged 10-50 years and examined the effects of age between groups. We used structural magnetic resonance imaging (sMRI) to measure the volume of the AHC, and magnetic resonance spectroscopy ((1)H-MRS) to measure concentrations of N-acetyl aspartate (NAA), creatine+phosphocreatine (Cr+PCr), myo-inositol (mI) and choline (Cho). The bulk volume of the amygdala and the hippocampus did not differ significantly between groups, but there was a significant difference in the effect of age on the hippocampus in controls. Compared with controls, young (but not older) people with AS had a significantly higher AHC concentration of NAA and a significantly higher NAA/Cr ratio. People with AS, but not controls, had a significant age-related reduction in NAA and the NAA/Cr ratio. Also, in people with AS, but not controls, there was a significant relationship between concentrations of choline and age so that choline concentrations reduced with age. We therefore suggest that people with AS have significant differences in neuronal and lipid membrane integrity and maturation of the AHC.

Human fetal brain chemistry as detected by proton magnetic resonance spectroscopy

Magnetic resonance spectroscopy represents an invaluable tool for the in vivo study of brain development at the chemistry level. Whereas magnetic resonance spectroscopy has received wide attention in pediatric and adult settings, only a few studies were performed on the human fetal brain. They revealed changes occurring throughout gestation in the levels of the main metabolites detected by proton magnetic resonance spectroscopy (N-acetylaspartate, choline, myo-inositol, creatine, and glutamate), providing a reference for the normal metabolic brain development. Throughout the third trimester of gestation, N-acetylaspartate gradually increases, whereas choline undergoes a slow reduction during the process of myelination. Less clear are the modifications in creatine, myo-inositol, and glutamate levels. Under conditions of fetal distress, the meaning of lactate detection is unclear, and further studies are needed. Another field for investigation involves the possibility of early detection of glutamate levels in fetuses at risk for hypoxic-ischemic encephalopathy, because the role of glutamate excitotoxicity in this context is well-established. Because metabolic modifications may precede functional or morphologic changes in the central nervous system, magnetic resonance spectroscopy may likely serve as a powerful, noninvasive tool for the early diagnosis and prognosis of different pathologic conditions.

MR imaging methods for assessing fetal brain development

Fetal magnetic resonance imaging provides an ideal tool for investigating growth and development of the brain in vivo. Current imaging methods have been hampered by fetal motion but recent advances in image acquisition can produce high signal to noise, high resolution 3-dimensional datasets suitable for objective quantification by state of the art post acquisition computer programs. Continuing development of imaging techniques will allow a unique insight into the developing brain, more specifically process of cell migration, axonal pathway formation, and cortical maturation. Accurate quantification of these developmental processes in the normal fetus will allow us to identify subtle deviations from normal during the second and third trimester of pregnancy either in the compromised fetus or in infants born prematurely.

MR imaging of brain maturation

Magnetic resonance imaging (MRI) is the imaging tool of choice to evaluate brain maturation and especially brain myelination. Magnetic resonance imaging also provides functional insight through diffusion images and proton spectroscopy. In this review the MRI techniques are analyzed for both pre- and postnatal periods. The origin of MR signal changes is also detailed in order to understand normal myelination evolution and the consequences on brain maturation of the different pathologies encountered prior and after birth. Because MRI is "blind" in terms of signal on conventional sequences after 2 years of age, a particular attention is given to diffusion images and proton spectroscopy of the developing brain.

Evidence of brain dysfunction in attention deficit-hyperactivity disorder: a controlled study with proton magnetic resonance spectroscopy

RATIONALE AND OBJECTIVES

Attention deficit-hyperactivity disorder (ADHD) is a socially disabling condition whose pathophysiology is mostly unknown. Previous magnetic resonance imaging (MRI)-based reports have shown structural abnormalities in the prefrontal region and the striatum, but with inconsistencies across the studies with regard to right/left specificity of changes. Our study is aimed at finding evidence of dysfunction with more refined MRI techniques such as diffusion-weighted MRI and spectroscopy.

MATERIALS AND METHODS

We enrolled 22 ADHD children (mean age 9; SD 2.91) and 8 healthy children (mean age 7.5; SD 3). All of them underwent diffusion-weighted MRI in several areas of the brain bilaterally: prefrontal, lentiform nucleus, posterior cingulate, and centrum semiovale; and single-voxel proton magnetic resonance spectroscopy in the left centrum semiovale and right prefrontal region.

RESULTS

We did not see either apparent structural abnormalities of the brain in conventional MRI or differences in the apparent-diffusion coefficients in any of the areas studied. However, we observed significant differences in the N-acetyl-aspartate/creatine ratios in relation to controls in the right prefrontal corticosubcortical region: 1.58 (SD 0.09) versus 1.47 (0.08), P = .01); and in the left centrum semiovale: 2.02 (0.13) versus 1.79 (0.13), P = .0003. This finding is consistent with a published report on eight ADHD children in whom N-acetyl-aspartate/creatine ratios were also elevated.

CONCLUSIONS

Given these results, we hypothesize that a biochemical dysfunction might underlie in the brain of ADHD children. The N-acetyl-aspartate/creatine ratio may be regarded as a potential marker of the disease.

Assessment of normal fetal brain maturation in utero by proton magnetic resonance spectroscopy

Cerebral maturation in the normal human fetal brain was investigated by in utero localized proton MR spectroscopy ((1)H MRS). Fifty-eight subjects at 22-39 weeks of gestational age (GA) were explored. A combination of anterior body phased-array coils (four elements) and posterior spinal coils (two to three elements) was used. Four sequences were performed (point-resolved spectroscopy (PRESS) sequence with short and long TEs (30 and 135 ms), with and without water saturation). A significant reduction in myo-inositol (myo-Ins) and choline (Cho) levels, and an increase in N-acetylaspartate (NAA) and creatine (Cr) content were observed with progressing age. A new finding is the detection of NAA as early as 22 weeks of GA. This result is probably related to the fact that oligodendrocytes (whether mature or not) express NAA, as demonstrated by in vitro studies. Cho and myo-inositol were the predominant resonances from 22 to 30 weeks and decreased gradually, probably reflecting the variations in substrate needed for membrane synthesis and myelination. The normal MRS data for the second trimester of gestation (when fetal MRI is usually performed) reported here can help determine whether brain metabolism is altered or not, especially when subtle anatomic changes are observed on conventional images.

Prenatal Cord Clamping in Newborn Macaca nemestrina: A Model of Perinatal Asphyxia

Our objective was to establish a nonhuman primate model of perinatal asphyxia appropriate for preclinical evaluation of neuroprotective treatment strategies under conditions that closely resemble human neonatal emergencies, and to begin testing the safety and efficacy of erythropoietin neuroprotective treatment. Prior to delivery by hysterotomy, the umbilical cords of near term Macaca nemestrina (n = 8) were clamped for times ranging between 12 and 15 min. Animals received erythropoietin (5,000 U/kg/dose x 2 i.v., n = 3), or vehicle (n = 5) after resuscitation. We assessed physiologic parameters, continuous electroencephalogram, magnetic resonance imaging/spectroscopy, safety parameters and behavior. Animals were euthanized at 4 months of age. Mean birth weight was 507 +/- 62 g. Initial arterial pH ranged from 6.75 to 7.12, with base deficits of 17-25 mEq. Animals were flaccid at birth, with attenuated electroencephalograms, and seizures occurred in 3 of 8 animals. We demonstrated magnetic resonance imaging/spectroscopy changes consistent with hypoxia (elevated lactate levels were present in some animals), significant motor and behavioral abnormalities (particularly with 15 min of cord clamping), and evidence of gliosis at the time of death. We have established a reproducible model of moderate to severe perinatal hypoxic-ischemic injury in M. nemestrina newborns. This model, which combines structural, biochemical, and behavioral assessments over time can be used to assess the safety and efficacy of neuroprotective strategies.

Response variability in Attention-Deficit/Hyperactivity Disorder: a neuronal and glial energetics hypothesis

BACKGROUND

Current concepts of Attention-Deficit/Hyperactivity Disorder (ADHD) emphasize the role of higher-order cognitive functions and reinforcement processes attributed to structural and biochemical anomalies in cortical and limbic neural networks innervated by the monoamines, dopamine, noradrenaline and serotonin. However, these explanations do not account for the ubiquitous findings in ADHD of intra-individual performance variability, particularly on tasks that require continual responses to rapid, externally-paced stimuli. Nor do they consider attention as a temporal process dependent upon a continuous energy supply for efficient and consistent function. A consideration of this feature of intra-individual response variability, which is not unique to ADHD but is also found in other disorders, leads to a new perspective on the causes and potential remedies of specific aspects of ADHD.

THE HYPOTHESIS

We propose that in ADHD, astrocyte function is insufficient, particularly in terms of its formation and supply of lactate. This insufficiency has implications both for performance and development: H1) In rapidly firing neurons there is deficient ATP production, slow restoration of ionic gradients across neuronal membranes and delayed neuronal firing; H2) In oligodendrocytes insufficient lactate supply impairs fatty acid synthesis and myelination of axons during development. These effects occur over vastly different time scales: those due to deficient ATP (H1) occur over milliseconds, whereas those due to deficient myelination (H2) occur over months and years. Collectively the neural outcomes of impaired astrocytic release of lactate manifest behaviourally as inefficient and inconsistent performance (variable response times across the lifespan, especially during activities that require sustained speeded responses and complex information processing).

TESTING THE HYPOTHESIS

Multi-level and multi-method approaches are required. These include: 1) Use of dynamic strategies to evaluate cognitive performance under conditions that vary in duration, complexity, speed, and reinforcement; 2) Use of sensitive neuroimaging techniques such as diffusion tensor imaging, magnetic resonance spectroscopy, electroencephalography or magnetoencephalopathy to quantify developmental changes in myelination in ADHD as a potential basis for the delayed maturation of brain function and coordination, and 3) Investigation of the prevalence of genetic markers for factors that regulate energy metabolism (lactate, glutamate, glucose transporters, glycogen synthase, glycogen phosphorylase, glycolytic enzymes), release of glutamate from synaptic terminals and glutamate-stimulated lactate production (SNAP25, glutamate receptors, adenosine receptors, neurexins, intracellular Ca2+), as well as astrocyte function (alpha1, alpha2 and beta-adrenoceptors, dopamine D1 receptors) and myelin synthesis (lactate transporter, Lingo-1, Quaking homolog, leukemia inhibitory factor, and Transferrin).

IMPLICATIONS OF THE HYPOTHESIS

The hypothesis extends existing theories of ADHD by proposing a physiological basis for specific aspects of the ADHD phenotype - namely frequent, transient and impairing fluctuations in functioning, particularly during performance of speeded, effortful tasks. The immediate effects of deficient ATP production and slow restoration of ionic gradients across membranes of rapidly firing neurons have implications for daily functioning: For individuals with ADHD, performance efficacy would be enhanced if repetitive and lengthy effortful tasks were segmented to reduce concurrent demands for speed and accuracy of response (introduction of breaks into lengthy/effortful activities such as examinations, motorway driving, assembly-line production). Also, variations in task or modality and the use of self- rather than system-paced schedules would be helpful. This would enable energetic demands to be distributed to alternate neural resources, and energy reserves to be re-established. Longer-term effects may manifest as reduction in regional brain volumes since brain areas with the highest energy demand will be most affected by a restricted energy supply and may be reduced in size. Novel forms of therapeutic agent and delivery system could be based on factors that regulate energy production and myelin synthesis. Since the phenomena and our proposed basis for it are not unique to ADHD but also manifests in other disorders, the implications of our hypotheses may be relevant to understanding and remediating these other conditions as well.

Canavan disease: studies on the knockout mouse

Canavan disease (CD) is an autosomal recessive disorder, characterized by spongy degeneration of the brain. Patients with CD have aspartoacylase (ASPA) deficiency, which results accumulation of N-acetylaspartic acid (NAA) in the brain and elevated excretion of urinary NAA. Clinically, patients with CD have macrocephaly, mental retardation and hypotonia. A knockout mouse for CD which was engineered, also has ASPA deficiency and elevated NAA. Molecular studies of the mouse brain showed abnormal expression of multiple genes in addition to ASPA deficiency. Adenoassociated virus mediated gene transfer and stem cell therapy in the knockout mouse are the latest attempts to alter pathophysiology in the CD mouse.

MRS of normal and impaired fetal brain development

Cerebral maturation in the human fetal brain was investigated by in utero localized proton magnetic resonance spectroscopy (MRS). Spectra were acquired on a clinical MR system operating at 1.5 T. Body phased array coils (four coils) were used in combination with spinal coils (two coils). The size of the nominal volume of interest (VOI) was 4.5 cm(3) (20 mm x 15 mm x 15 mm). The MRS acquisitions were performed using a spin echo sequence at short and long echo times (TE = 30 ms and 135 ms) with a VOI located within the cerebral hemisphere at the level of the centrum semiovale. A significant reduction in myo-inositol and choline and an increase in N-acetylaspartate were observed with progressive age. The normal MR spectroscopy data reported here will help to determine whether brain metabolism is altered, especially when subtle anatomic changes are observed on conventional images. Some examples of impaired fetal brain development studied by MRS are illustrated.

Canavan disease: A white matter disorder

Breakdown of oligodendrocyte-neuron interactions in white matter (WM), such as the loss of myelin, results in axonal dysfunction and hence a disruption of information processing between brain regions. The major feature of leukodystrophies is the lack of proper myelin formation during early development or the onset of myelin loss late in life. These early childhood WM diseases are described as hypomyelination or dysmyelination arising from a primary block in normal myelin synthesis because of a genetic mutation expressed in oligodendrocytes, or failure in myelination secondary to neuronal or astroglial dysfunctions (van der Knaap 2001 Dev. Med. Child Neurol. 43:705-712). Here, we describe the pathophysiological parameters of Canavan disease (CD), caused by genetic mutations of the aspartoacylase (ASPA) gene, a metabolic enzyme restricted in the central nervous system (CNS) to oligodendrocytes. CD presents pathophysiological dysfunctions similar to diseases caused by myelin gene mutations, such as Pelizaeus-Merzbacher disease (PMD) and several animal models, such as myelin deficient rat (md), jimpy (jp), shiverer (sh), and quaking (qk viable) mutant mice. These single gene mutations have pleiotropic effects, whereby the alteration of one myelin gene expression disrupts functional expression of other oligodendrocyte genes with an outcome of hypomyelination/dysmyelination. Among all of the known leukodystrophies, CD is the first disorder, which was approved and tested for the adeno-associated virus vector (AAV)-ASPA gene therapy (Leone et al. 2000 Ann. Neurol. 48:27-38; Janson et al. 2001 Trends Neurosci. 24:706-712) without much success following the first two attempts. ASPA gene delivery attempts in animal models have shown a lowering of N-acetyl L-aspartate and a change in motor functions, while sponginess of the WM, a characteristic of CD remained unchanged (Matalon et al. 2003 Mol. Ther. 7 (5, Part 1):580-587; McPhee et al. 2005 Brain Res. Mol. Brain Res. 135:112-121) even with better viral serotype and delivery of the gene during early phase of development (Klugmann et al. 2005 Mol. Ther. 11:745-753). While different approaches are being sought for the success of gene therapy, there are pivotal developmental questions to address regarding the specific regions of the CNS and cell lineages that become the target for the onset and progression of CD symptoms from early to late stages of development.

Comparative study of cerebral white matter in autism and attention-deficit/hyperactivity disorder by means of magnetic resonance spectroscopy

RATIONALE AND OBJECTIVES

Autism and attention-deficit/hyperactivity disorder (ADHD) are neurodevelopmental disorders whose pathophysiology is mostly unknown. As far as the symptoms are different and, in some aspects, opposed, we hypothesize that there must be biochemical differences in the brain of the afflicted children. The aim of the study is to analyze comparatively the metabolite concentration of the cerebral white matter in autism, in ADHD, and in a control group of healthy children to test the hypothesis that N-acetyl aspartate (NAA) is decreased in autism and increased in ADHD.

PATIENTS AND METHODS

We included 21 autistic children according to DSM-IV criteria, 8 children with ADHD meeting the respective criteria of DSM-IV, and 12 healthy controls of similar age. Single-voxel proton magnetic resonance spectroscopy was performed on all of them with an echo time of 30 milliseconds and a repetition time of 2500 milliseconds. The voxel was placed in the left centrum semiovale. Metabolite ratios relative to creatine were reported for NAA, choline, and myoinositol.

RESULTS

Although we did not observe differences between autistic children and controls, we found a mean higher concentration of NAA in the left centrum semiovale of ADHD children (2.2; SD, 0.21) than that found in autistic children (1.88; SD, 0.18) and controls (1.91; SD, 0.01), which was significant (P = .01 in parametric and in nonparametric test).

CONCLUSION

We conclude that white matter of autistic children does not present alterations on MRS. We hypothesize that the higher concentration of NAA in the white matter of ADHD points to mitochondrial hypermetabolism. This may constitute a new substrate in the pathophysiology and merits further research.

Assessment of cortical maturation with prenatal MRI. Part I: Normal cortical maturation

Cortical maturation, especially gyral formation, follows a temporospatial schedule and is a good marker of fetal maturation. Although ultrasonography is still the imaging method of choice to evaluate fetal anatomy, MRI has an increasingly important role in the detection of brain abnormalities, especially of cortical development. Knowledge of MRI techniques in utero with the advantages and disadvantages of some sequences is necessary, in order to try to optimize the different magnetic resonance sequences to be able to make an early diagnosis. The different steps of cortical maturation known from histology represent the background necessary for the understanding of maturation in order to be then able to evaluate brain maturation through neuroimaging. Illustrations of the normal cortical maturation are given for each step accessible to MRI for both the cerebral hemispheres and the posterior fossa.

Brain magnetic resonance imaging in 23 patients with mucopolysaccharidoses and the effect of bone marrow transplantation

A longitudinal study of cranial magnetic resonance imaging (MRI) was carried out in 23 patients with mucopolysaccharidoses (MPS); 1 each of types IH, VI, and VII; 2 of type IS; 10 of type II; and 4 each of types IIIB and IVA. Six types of distinct abnormalities were 1) cribriform changes or spotty changes in the corpus callosum, basal ganglia, and white matter; 2) high-intensity signal in the white matter on T2-weighted image; 3) ventriculomegaly; 4) diffuse cerebral cortical atrophy; 5) spinal cord compression; and 6) megacisterna magna. The cribriform changes that corresponded to dilated perivascular spaces were found in the patients with MPS IS, II, and VI. The patchy and diffuse intensity changes were found in the patient with MPS II and IIIB, respectively. MPS IH and the severe type of MPS II showed marked ventriculomegaly. Marked cerebral atrophy was observed in all MPS IIIB patients and in the severe type of MPS II patients. Spinal cord compression was a feature usually observed in MPS IH, IVA, VI, and VII. Megacisterna magna was frequent in the patients with MPS II (6/10). In two of five patients, the therapeutic effect of bone marrow transplantation (BMT) was remarkable. Both the cribriform changes and the intensity change of the white matter in a MPS VI patient disappeared eight years after the BMT. Slight improvement of cribriform change was noted in one patient with MPS II three years after the BMT. MRS was not sufficient to estimate the accumulation of glycosaminoglycans but was useful for evaluating neuronal damages.

Increased thalamic N-acetylaspartate in male patients with familial bipolar I disorder

N-Acetylaspartate (NAA) in the anterior and mediodorsal thalamic regions was measured using proton magnetic resonance spectroscopic imaging (1H-MRSI) in 15 euthymic male patients with familial bipolar I disorder and compared to values in 15 male control subjects to determine if there was evidence for altered neuronal/axonal integrity. MRI tissue segmentation methods were also utilized to obtain tissue-contribution estimates for each MRSI voxel. Relative to the comparison group, the patients with bipolar I disorder demonstrated significantly higher NAA and creatine in both the right and left thalamus. NAA was also significantly higher in the left thalamus compared to the right in both bipolar I patients and controls. There were no group or lateralized differences in the percentages of different tissue types within the MRSI voxels, suggesting that the thalamic NAA and creatine alterations were not an artifact of variations in tissue type percentages in the MRSI voxels. There was also no significant association between NAA or creatine and illness duration. The findings of increased thalamic NAA bilaterally may represent neuronal hypertrophy or hyperplasia, reduced glial cell density, or abnormal synaptic and dendritic pruning. Increased thalamic creatine bilaterally may represent altered cellular energy metabolism and is consistent with prior studies demonstrating changes in thalamic metabolism in mood disorders.

MRI of disseminated developmental dysmyelination in Fukuyama type of CMD

Whether the pathologic origin of white matter lesions in Fukuyama type of congenital muscular dystrophy (FCMD) is delayed myelination or dysmyelination is a controversial issue. This study investigated pathologic distribution in white matter with heavily T(2)-weighted images using fluid-attenuated inversion recovery (FLAIR) pulse sequence. For detection of abnormal white matter lesions, FLAIR images were approximately twice as sensitive as T(2)-weighted images and five times as sensitive as T(1)-weighted images of spin echo sequence. The distribution of the white matter lesions was disseminated and not correlated with cortical disarrangement. The distribution was not consistent with delayed myelination. These findings support the evidence found using in vitro proton-NMR spectroscopy that the pathologic origin of white matter lesions is dysmyelination. When conventional magnetic resonance imaging is used, masked white matter lesions are easy to misidentify as delayed myelination instead of disseminated developmental dysmyelination. The lesions in the white matter of FCMD are masked because of brain development.

Prefrontal and medial temporal correlates of repetitive violence to self and others

BACKGROUND

The neurobiological basis for violence in humans is poorly understood, yet violent behavior (to self or others) is associated with large social and healthcare costs in some groups of patients (e.g., the mentally retarded). The prefrontal cortex and amygdalo-hippocampal complex (AHC) are implicated in the control aggression, therefore we examined the neural integrity of these regions in violent patients with mild mental retardation and nonviolent control subjects.

METHODS

We used (1)H-magnetic resonance spectroscopy (MRS) to measure 1) concentrations and ratios of N-acetyl aspartate (NAA), creatine phosphocreatine (Cr+PCr), and choline-related compounds (Cho) in prefrontal lobe of 10 violent inpatients and 8 control subjects; 2) ratios of NAA, Cr+PCr, and Cho in the AHC of 13 inpatients and 14 control subjects; and 3) frequency and severity of violence in patients.

RESULTS

Compared to control subjects, violent patients had significantly (p <.05, analysis of covariance-age and IQ as confounding covariates) lower prefrontal concentrations of NAA and Cr+PCr, and a lower ratio of NAA/Cr+PCr in the AHC. Within the violent patient group, frequency of observed violence to others correlated significantly with prefrontal lobe NAA concentration (r = -0.72, p <.05).

CONCLUSIONS

NAA concentration indicates neuronal density, and Cr+PCr concentration high-energy phosphate metabolism. Our findings suggest that violent patients with mild mental retardation have reduced neuronal density, and abnormal phosphate metabolism in prefrontal lobe and AHC compared to nonviolent control subjects. Further studies are needed, however, to determine if these findings are regionally specific, or generalize to other groups of violent individuals.

In vitro expression of N-acetyl aspartate by oligodendrocytes: implications for proton magnetic resonance spectroscopy signal in vivo

Magnetic resonance spectroscopy (MRS) provides a noninvasive means of assessing in vivo tissue biochemistry. N-Acetyl aspartate (NAA) is a major brain metabolite, and its presence is used increasingly in clinical and experimental MRS studies as a putative neuronal marker. A reduction in NAA levels as assessed by in vivo 1H MRS has been suggested to be indicative of neuronal viability. However, temporal observations of brain pathologies such as multiple sclerosis, mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS), and hypothyroidism have shown reversibility in NAA levels, possibly reflecting recovery of neuronal function. A knowledge of the cellular localisation of NAA is critical in interpreting these findings. The assumption that NAA is specific to neurones is based on previous immunohistochemical studies on whole brain using NAA-specific antibodies. The neuronal localisation was further substantiated by cell culture experiments in which its presence in the oligodendrocyte-type 2 astrocyte progenitors and immature oligodendrocytes, but not in the mature oligodendrocytes, was observed. More recently, studies on oligodendrocyte biology have revealed the requirement for trophic factors to promote the generation, maturation, and survival of oligodendrocytes in vitro. Here, we have used this new information to implement a more pertinent cell cultivation procedure and demonstrate that mature oligodendrocytes can express NAA in vitro. This observation brings into question whether the NAA changes observed in clinical in vivo 1H MRS studies reflect neuronal function alone. The data presented here support the hypothesis that oligodendrocytes may express NAA in vivo and contribute to the NAA signal observed by 1H MRS.

Cerebral intracellular lactic alkalosis persisting months after neonatal encephalopathy measured by magnetic resonance spectroscopy

We have found that cerebral lactate can be detected later than 1 month of age after neonatal encephalopathy (NE) in infants with severe neurodevelopmental impairment at 1 y. Our hypothesis was that persisting lactate after NE is associated with alkalosis and a decreased cell phosphorylation potential. Forty-three infants with NE underwent proton and phosphorus-31 magnetic resonance spectroscopy at 0.2-56 wk postnatal age. Seventy-seven examinations were obtained: 25 aged <2 wk, 16 aged > or = 2 to < or = 4 wk, 25 aged > 4 to < or = 30 wk, and 11 aged > 30 wk. Neurodevelopmental outcome was assessed at 1 y of age: 17 infants had a normal outcome and 26 infants had an abnormal outcome. Using univariate linear regression, we determined that increased lactate/creatine plus phosphocreatine (Cr) was associated with an alkaline intracellular pH (pHi) (p < 0.001) and increased inorganic phosphate/phosphocreatine (Pi/PCr) (p < 0.001). This relationship was significant, irrespective of outcome group or age at time of study. Between outcome groups, there were significant differences for lactate/Cr measured at < 2 wk (p = 0.005) and > 4 to < or = 30 wk (p = 0.01); Pi/PCr measured at < 2 wk (p < 0.001); pHi measured at < 2 wk (p < 0.001), > or = 2 to < or = 4 wk (p = 0.02) and > 4 to < or = 30 wk (p = 0.03); and for N-acetylaspartate/Cr measured at > or = 2 to < or = 4 wk (p = 0.03) and > 4 to < or = 30 wk (p = 0.01). Possible mechanisms leading to this persisting cerebral lactic alkalosis are a prolonged change in redox state within neuronal cells, the presence of phagocytic cells, the proliferation of glial cells, or altered buffering mechanisms. These findings may have implications for therapeutic intervention.

PET in child psychiatry: the risks and benefits of studying normal healthy children

1. Inclusion of children, particularly healthy control children, is a continuing debate. 2. Why involve children in PET research? The assumption is that the knowledge gained from such studies is critical for the advance of prevention and treatment of psychiatric illnesses. 3. What are the risks of PET procedures? Radiation exposure poses the most difficult problem. The assessment of this risk needs to separate the emotional reaction at the mention of "radiation" from the consideration of objective data of large studies of health hazards associated with low-level radiation exposure. 4. The assessment of the benefit/risk ratio is critical to the conduct of research, and requires the evaluation of risks according to the ambiguous definition of "minimal risk".

In vivo spectroscopic quantification of the N-acetyl moiety, creatine, and choline from large volumes of brain gray and white matter: effects of normal aging

Volumetric proton magnetic resonance spectroscopic imaging (MRSI) was used to generate brain metabolite maps in 15 young and 19 elderly adult volunteers. All subjects also had structural MR scans, and a model, which took into account the underlying structural composition of the brain contributing to each metabolite voxel, was developed and used to estimate the concentration of the N-acetyl-moiety (NAc), creatine (Cr), and choline (Cho) in gray matter and white matter. NAc concentration (signal intensity per unit volume of brain) was higher in gray than white matter and did not differ between young and old subjects despite significant gray matter volume deficits in the older subjects. To the extent that NAc is an index of neuronal integrity, the available gray matter appears to be intact in these older healthy adults. Cr concentrations were much higher in gray than white matter and significantly higher in the old than young subjects. Cho concentration in gray matter was also significantly higher in old than young subjects. Independent determination of metabolite values rather than use of ratios is essential for characterizing age-related changes in brain MRS metabolites.