Evidence of developmental alterations in cortical and subcortical regions of children with attention-deficit/hyperactivity disorder: a multivoxel in vivo phosphorus 31 spectroscopy study

CONTEXT

There is mounting evidence of neurodevelopmental alterations implicating the prefrontal cortex (PFC) and basal ganglia in children with attention-deficit/hyperactivity disorder (ADHD). The brain undergoes substantive structural and functional changes with a differential timing between brain regions during development from childhood to adolescence. In vivo phosphorus 31 magnetic resonance spectroscopy ((31)P MRS) is a noninvasive neuroimaging approach that is sensitive in assessing developmental changes of overproducing/pruning of synapses.

OBJECTIVE

To provide support for a developmental mechanism targeting a bottom-up dysfunction of the basal ganglia impairing the fine-tuning of prefrontal functions in ADHD.

DESIGN

Cross-sectional study.

SETTING

Pittsburgh, Pennsylvania, and the surrounding areas.

PARTICIPANTS

Thirty-one psychostimulant-naive children with ADHD (mean [SD] age, 8.1 [1.2] years; range, 6.1-10.0 years) and 36 healthy control subjects (mean [SD] age, 8.1 [1.3] years; range, 6.1-10.4 years).

MAIN OUTCOME MEASURE

Membrane phospholipid (MPL) precursor levels (ie, phosphomonoesters that are anabolic metabolites of MPL) were assessed in the PFC and basal ganglia as well as in 4 other brain regions using in vivo (31)P MRS.

RESULTS

Lower bilateral MPL precursor levels in the basal ganglia and higher MPL precursor levels in the inferior parietal region (primarily right side) were noted in the children with ADHD as compared with healthy control children. There was a group x age interaction in the PFC and inferior parietal region, with relatively older psychostimulant-naive children with ADHD showing significantly lower PFC and higher inferior parietal MPL precursor levels. No differences between groups were noted in the superior temporal, posterior white matter, or occipital regions.

CONCLUSION

Though based on cross-sectional data, these results are suggestive of possible progressive, nonlinear, and sequential alterations implicating a bottom-up developmental dysfunction in parts of the cortico-striato-thalamo-cortical network in ADHD.

Regionally specific alterations in membrane phospholipids in children with ADHD: An in vivo 31P spectroscopy study

This multi-voxel, phosphorus magnetic resonance spectroscopy ((31)P MRS) study examined the prefrontal cortex (PFC), basal ganglia (BG) and superior temporal (ST) region in 10 children with attention-deficit/hyperactivity disorder (ADHD) and 15 healthy controls. ADHD patients had lower PFC and BG phosphomonoester (PME) levels compared to healthy children. No differences were noted in the ST. These deficits in membrane phospholipid (MPL) precursor levels suggest reduced mass of cellular MPLs due to a possible underdevelopment of neuronal processes and synapses in ADHD.

Effects of acetyl-L-carnitine and myo-inositol on high-energy phosphate and membrane phospholipid metabolism in zebra fish: a 31P-NMR-spectroscopy study

Acetyl-L-carnitine (ALCAR) and myo-inositol are reported to enhance motor activity in animal models; modulate membrane phospholipid metabolism (ALCAR and myo-inositol) and high-energy phosphate metabolism (ALCAR) back to normal; and be effective treatments of major depression in humans. Fish in general and zebra fish in particular present unique animal models for the in vivo study of high-energy phosphate and membrane phospholipid metabolism by noninvasive in vivo 31P NMR. This 31P NMR study of free-swimming zebra fish showed that both ALCAR and myo-inositol decreased levels of phosphodiesters and inorganic orthophosphate and increased levels of PCr in the fish. These findings demonstrate both ALCAR and myo-inositol modulate membrane phospholipid and high-energy phosphate metabolism in free-swimming zebra fish.

Effects of chronic lithium administration on rat brain phosphatidylinositol cycle constituents, membrane phospholipids and amino acids

OBJECTIVE

There is evidence linking affective disorders and their treatment to alterations in membrane phospholipid metabolism, the phosphatidylinositol (PtdIns) second messenger cycle and brain excitatory and inhibitory amino acids. This study examines lithium effects on rat brain metabolites associated with the above systems and their reversal by myo-inositol.

METHODS

Thirty rats were treated for 14 days with i.p. lithium, saline or lithium plus myo-inositol. 1H, 31P and 7Li NMR were used to measure brain metabolites.

RESULTS

Lithium, administered alone or with myo-inositol, resulted in brain lithium concentrations of approximately 0.6 microM/gram brain tissue. Brain myo-inositol was unchanged when lithium was co-administered with myo-inositol. Lithium increased brain inositol-1-phosphate (I1P) by 98% compared with saline and this effect was not attenuated by the addition of myo-inositol. Lithium treatment decreased phosphatidylserine (PtdSer) and PtdIns by 3% and 8%, respectively. Lithium also decreased taurine levels by 8% and increased aspartate levels by 9%. The above effects of lithium on PtdSer, PtdIns and taurine were attenuated or abolished by the co-administration of myo-inositol.

CONCLUSIONS

Lithium alters levels of key membrane phospholipids and appears to affect the balance between inhibitory and excitatory amino acids in rat brain. Co-administration of myo-inositol attenuates some of these lithium effects on brain metabolites.

Brain membrane phospholipid alterations in Alzheimer's disease

Studies have demonstrated alterations in brain membrane phospholipid metabolite levels in Alzheimer's disease (AD). The changes in phospholipid metabolite levels correlate with neuropathological hallmarks of the disease and measures of cognitive decline. This 31P nuclear magnetic resonance (NMR) study of Folch extracts of autopsy material reveals significant reductions in AD brain levels of phosphatidylethanolamine (PtdEtn) and phosphatidylinositol (PtdIns), and elevations in sphingomyelin (SPH) and the plasmalogen derivative of PtdEtn. In the superior temporal gyrus, there were additional reductions in the levels of diphosphatidylglycerol (DPG) and phosphatidic acid (PtdA). The findings are present in 3/3 as well as 3/4 and 4/4 apolipoprotein E (apoE) genotypes. The AD findings do not appear to reflect non-specific neurodegeneration or the presence of gliosis. The present findings could possibly contribute to an abnormal membrane repair in AD brains which ultimately results in synaptic loss and the aggregation of A beta peptide.

Chronic myo-inositol increases rat brain phosphatidylethanolamine plasmalogen

BACKGROUND

Oral myo-inositol (12--18 g/day) has shown beneficial effect in placebo-controlled studies of major depression, panic disorder, and obsessive compulsive disorder, and preliminary data suggest it also may be effective in bipolar depression. Evidence linking antidepressant activity to membrane phospholipid alterations suggested the examination of acute and chronic myo-inositol effects on rat brain membrane phospholipid metabolism.

METHODS

With both (31)P nuclear magnetic resonance (NMR) and quantitative high-performance thin-layer chromatography (HPTLC; hydrolysis) methods, rat brain phospholipid levels were measured after acute (n = 20, each group) and chronic myo-inositol administration (n = 10, each group). With (31)P NMR, we measured myo-inositol rat brain levels after acute and chronic myo-inositol administration.

RESULTS

Brain myo-inositol increased by 17% after acute myo-inositol administration and by 5% after chronic administration, as compared with the control groups. Chronic myo-inositol administration increased brain phosphatidylethanolamine (PtdEtn) plasmalogen by 10% and decreased brain PtdEtn by 5%, thus increasing the ratio PtdEtn plasmalogen (PtdEtn-Plas)/PtdEtn by 15%. Phosphatidylethanolamine plasmalogen levels quantified by (31)P NMR and HPTLC were highly correlated. The validity and reliability of the (31)P NMR method for phospholipid analysis were demonstrated with phospholipid standards.

CONCLUSIONS

The observed alteration in the PtdEtn-Plas/PtdEtn ratio could provide insights into the therapeutic effect of myo-inositol in affective disorders.

Stability of CSF metabolites measured by proton NMR

Analysis of cerebrospinal fluid (CSF) metabolites can provide data regarding CNS involvement in neurologic and psychiatric illness. However, there is lack of research into the effect of processing and storage of CSF specimens on the levels of metabolites analyzed. CSF specimens from 10 depressed patients were analyzed by proton NMR before and after 72 hours exposure to room temperature. No effect of exposure was found on myoinositol, glucose, acetate, and alanine CSF levels and there was a substantial decrease of citrate (>50%) and increase in lactate, glutamine, creatine, and creatinine levels.

Brain metabolic effects of acute nicotine

(-)Nicotine acetylcholine receptors are located on both nerve cell bodies and synaptic terminals, are permeable to calcium, and function perhaps predominantly by facilitating the release of neurotransmitters and neuropeptides. The behavioral rewards from (-)nicotine and perhaps addiction appear to be related to dopamine release. 31P NMR analysis reveals subcutaneously administered (-)nicotine produces acute alterations in brain membrane phospholipid and high-energy phosphate metabolism of Fischer 344 rats. These metabolic responses to (-)nicotine could contribute to nicotine's behavioral effects.

Molecular insights into neurodevelopmental and neurodegenerative diseases

Magnetic resonance spectroscopy (MRS) is a non-invasive physical technique that is routinely used to determine the quantity and structure of organic molecules in solution. Technical advances that have expanded the usefulness of this technique include: (1) high resolution MRS to identify and quantify individual molecules present in complex mixtures of tissue extracts; (2) in vivo MRS techniques to non-invasively monitor metabolites in humans; (3) structure determination of proteins of moderate size; and (4) improved structure characterization of solids and liquid crystals, such as the detection of phase changes in membranes. The focus of this review is on the first two technical advances mentioned above. The strengths of MRS as a research tool to investigate molecular alterations in disease states include ease of sample preparation, minimum sample manipulation, avoidance of the preparation of derivatives, and the ability to analyze an unfractionated sample. The strengths of MRS in the clinic are its ability to measure neuronal metabolite levels non-invasively in humans and its potential for disease diagnosis, monitoring disease progression, and assessing the efficacy of experimental therapies.

Increased cerebrospinal fluid glutamine levels in depressed patients

BACKGROUND

There is increasing evidence for an association between alterations of brain glutamatergic neurotransmission and the pathophysiology of affective disorders.

METHODS

We studied the association between cerebrospinal fluid (CSF) metabolites, including glutamine, in unipolar and bipolar depressed patients versus control subjects using a proton magnetic resonance spectroscopy technique. Cerebrospinal fluid samples were obtained from 18 hospitalized patients with acute unmedicated severe depression without medical problems and compared with those of 22 control subjects.

RESULTS

Compared with the control group, the depressed patient group had significantly higher CSF glutamine concentrations, which correlated positively with CSF magnesium levels.

CONCLUSIONS

These findings suggest an abnormality of the brain glial-neuronal glutamine/glutamate cycle associated with N-methyl-D-aspartate receptor systems in patients with depression.

Metabolic alterations in postmortem Alzheimer's disease brain are exaggerated by Apo-E4

Alterations in phospholipid metabolites are a characteristic abnormality of Alzheimer's disease (AD). Many of these alterations have been demonstrated by magnetic resonance spectroscopy (MRS) studies of postmortem tissue. Phosphodiesters appear to be elevated late in the disease and phosphomonoesters appear to be elevated early in the disease and then decrease. Second to aging, the most robust risk factor for AD identified to date is the presence of the E4 allele of apolipoprotein-E (Apo-E). Because apolipoproteins are intimately involved in lipid metabolism, this study was performed to determine if the presence of the Apo-E4 allele affects the abnormalities in phospholipid metabolites in AD brain. Perchloric acid extracts from 12 Apo-E 3/3, 31 3/4, 6 4/4 AD brains and 5 Apo-E 3/3 control brains were studied by both proton magnetic resonance spectroscopy and phosphorus-31 magnetic resonance spectroscopy. When the E4-positive AD samples were compared with the 3/3 AD samples, an exaggeration in both phosphomonoester and phosphodiester abnormalities was observed. The decrease in N-acetyl-L-aspartate (NAA) was also exaggerated. These results suggest membrane phospholipid metabolite alterations observed in AD are more severe in the presence of the Apo-E4 allele.

Analysis of a Chinese hamster ovary cell mutant with defective mobilization of cholesterol from the plasma membrane to the endoplasmic reticulum

The factors involved in shuttling cholesterol among cellular membranes have not been defined. Using amphotericin B selection, we previously isolated Chinese hamster ovary cell mutants expressing defects in intracellular cholesterol transport. Complementation analysis among seven mutants identified one cell line, mutant 3-6, with a unique defect. The present analysis revealed three key features of mutant 3-6. First, the movement of cholesterol both from the endoplasmic reticulum and through lysosomes to the plasma membrane was normal. However, when intact 3-6 cells were treated with sphingomyelinase, movement of plasma membrane cholesterol to acyl CoA:cholesterol acyltransferase in the endoplasmic reticulum was defective. Cellular cholesterol was mobilized to this enzyme upon activation by 25-hydroxycholesterol. Second, mutant 3-6 did not utilize endogenously synthesized sterol or low density lipoprotein-derived cholesterol for growth as effectively as parental Chinese hamster ovary cells. Finally, despite normal movement of cholesterol to the plasma membrane, mutant 3-6 was amphotericin B resistant. The plasma membrane cholesterol content was normal as assessed by cholesterol oxidase treatment and Semliki Forest virus fusion, which suggests that the 3-6 mutation alters the organization of cholesterol in the plasma membrane. Our characterization of this mutant cell line should facilitate the identification of gene(s) required for this transport pathway.

Magnetic resonance spectroscopic changes in Alzheimer's disease

In vitro and in vivo 31P magnetic resonance (MR) spectroscopy studies of Alzheimer's disease (AD) brain have revealed alterations in membrane phospholipid metabolism and high-energy phosphate metabolism. Mildly demented AD patients compared with control subjects have increased levels of phosphomonoesters, decreased levels of phosphocreatine and probably adenosine diphosphate and an increased oxidative metabolic rate. As the dementia worsens, levels of phosphomonoesters decrease and levels of phosphocreatine and adenosine di-phosphate increase. The changes in oxidative metabolic rate suggest that the AD brain is under energetic stress. The phosphomonoester findings support our in vitro findings and implicate basic defects in membrane metabolism in AD brain. MR spectroscopy provides new diagnostic insights and a noninvasive method to follow the progression of the disease and the metabolic response to therapeutic interventions.

Aggregation of beta-amyloid peptide is promoted by membrane phospholipid metabolites elevated in Alzheimer's disease brain

Increased amounts of beta-amyloid (A beta) peptide deposits are found in Alzheimer's disease brain. These amyloid deposits have been implicated in the pathophysiology of this common dementing illness. A beta peptides have been shown to be toxic to neurons in cell culture, and this toxicity is critically dependent on the aggregation of the peptide into cross-beta-pleated sheet fibrils. Also, in vivo and postmortem NMR studies have shown changes in certain brain membrane phospholipid metabolites in normal aging and more extensive alterations in patients with Alzheimer's disease. The finding that membrane phospholipids affect the aggregation of A beta suggests that the abnormalities in membrane metabolism found in Alzheimer's disease could affect the deposition of A beta in vivo. Therefore, we examined the effect of membrane phospholipid metabolites that are altered in Alzheimer's disease brain on the aggregation of A beta(1-40) using a light scattering method. Certain metabolites (glycerophosphocholine, glycerophosphoethanolamine, and alpha-glycerophosphate) augment the aggregation of A beta. Other membrane phospholipid metabolites (phosphocholine, phosphoethanolamine, and inositol-1-phosphate) have no effect. We conclude that increased membrane phospholipid metabolite concentrations may play a role in the deposition of A beta seen in normal aging and the even greater deposition of A beta observed in Alzheimer's disease.

Elevated phosphocholine and phosphatidylcholine following rat entorhinal cortex lesions

At early stages of Alzheimer's disease, phosphomonoesters (PMEs) including phosphocholine (P-choline) are present at elevated levels. PMEs also are elevated in the developing brain during the period of neurite extension. To determine if the elevation of PMEs in AD could reflect neuritic sprouting, 31P-NMR was used to examine phospholipid metabolites and membrane phospholipids at various times following unilateral lesions of the entorhinal cortex, a well-defined model of neuritic sprouting. Two to 7 days postlesion, P-choline levels were elevated 48% in the hippocampus ipsilateral to the entorhinal cortex lesion, but not in the contralateral hippocampus or cerebral cortex. P-choline levels declined by day 15, and reached control levels 45 days following the lesion. The lesion-induced elevation in P-choline could result from increased P-choline synthesis via choline kinase, decreased activity of CTP:phosphocholine cytidylyltransferase, or breakdown of phosphatidylcholine (PC). To distinguish between these possibilities, the membrane phospholipids PC and phosphatidylethanolamine (PE) were measured. Both phospholipids were maintained at or above control levels at each of the postlesion time points, arguing against membrane breakdown or decreased PC synthesis contributing to the elevation of P-choline levels. Other alterations included a widespread elevation in inositol phosphate 2 days postlesion, but not at later time points. The alterations in phospholipid metabolites observed in the rat hippocampus following entorhinal cortex lesions closely resemble those observed in the human brain in the early stages of AD.

Quantitative 1H and 31P MRS of PCA extracts of postmortem Alzheimer's disease brain

Several previous studies have shown metabolic abnormalities in perchloric acid extracts of postmortem Alzheimer's disease (AD) brain by both proton (1H) and phosphorus-31 (31P) magnetic resonance spectroscopy (MRS). In all of these studies the results were expressed in relative terms, in units of mol percent. The results of this study, expressed in the absolute units of mumol/g wet weight, verify the previous 1H and 31P MRS studies. Absolute increases were found for myo-inositol, aspartate, L-glutamate, alanine, phosphocholine, and the phosphodiesters,. Absolute decreases were found for phosphoethanolamine and N-acetyl-l-aspartate. Many of these changes also were observed in non-AD dementia brain extracts, but changes in myo-inositol, inositol-l-phosphate, aspartate, and L-glutamate appeared to be more specific for AD in extracts of many brain areas. These results suggest that compounds related to membrane degradation and excitatory neuro-transmission increase in Alzheimer's disease while compounds related to neuronal integrity and inhibitory neurotransmission are decreased.

Changes in brain membrane phospholipid and high-energy phosphate metabolism precede dementia

A 52-year-old Caucasian male was followed with Mattis and 31P MRS examinations every 6 months for 33 months. At entry into the study, the subject had a normal clinical examination and normal Mattis scores but had alterations in MRS measures of membrane phospholipid and high-energy phosphate metabolism indistinguishable from those previously reported in mildly demented AD patients. After 33 months of follow-up, the subject had clinical and Mattis findings suggestive of possible incipient dementia and after 46 months of follow-up there was sufficient cognitive decline to make the diagnosis of dementia with a frontal lobe preponderance. The findings in this subject support the contention that alterations in brain membrane phospholipid and high-energy metabolism can be noninvasively detected by 31P MRS years before any clinical manifestations of the disease.

Magnetic resonance spectroscopy and its application to aging and Alzheimer's disease

This is a review of magnetic resonance (MR) spectroscopy and its application to aging and Alzheimer's disease (AD). Examinations of perchloric acid extracts of AD brain tissue by MR spectroscopy reveal elevated levels of phosphomonoesters, phosphodiesters, and glutamate accompanied by reduced levels of N-acetyl-L-aspartate compared with extracts from controls. These metabolicalterations may be an indication of accelerated membrane phospholipid metabolism, glutamate neurotoxicity, and neuronal loss in AD brain that is not seen in normal aging. In vivo 31P MR spectroscopy studies of AD indicate that levels of phosphomonoesters are elevated early in the course of AD, which may be a causative molecular neuropathologic event. In vivo MR spectroscopy is a powerful technique to investigate the molecular neuropathology of the disease, to follow the progression of AD, and to assess the efficacy of experimental therapies.

Clinical and neurochemical effects of acetyl-L-carnitine in Alzheimer's disease

In a double-blind, placebo study, acetyl-L-carnitine was administered to 7 probable Alzheimer's disease patients who were then compared by clinical and 31P magnetic resonance spectroscopic measures to 5 placebo-treated probable AD patients and 21 age-matched healthy controls over the course of 1 year. Compared to AD patients on placebo, acetyl-L-carnitine-treated patients showed significantly less deterioration in their Mini-Mental Status and Alzheimer's Disease Assessment Scale test scores. Furthermore, the decrease in phosphomonoester levels observed in both the acetyl-L-carnitine and placebo AD groups at entry was normalized in the acetyl-L-carnitine-treated but not in the placebo-treated patients. Similar normalization of high-energy phosphate levels was observed in the acetyl-L-carnitine-treated but not in the placebo-treated patients. This is the first direct in vivo demonstration of a beneficial effect of a drug on both clinical and CNS neurochemical parameters in AD.

Analysis of magnetic resonance spectra by mole percent: comparison to absolute units

A variety of metabolites present in perchloric acid extracts of brain tissue were measured by 1H and 31P magnetic resonance spectroscopy (MRS) and HPLC in the same tissue sample and the MRS results were expressed both in terms of mole % and mumole/g based on an internal standard. The levels of 16 metabolites were compared by linear regression analysis and the mole % results were found to correlate very well with the results expressed as mumole/g. To compare the two units under typical experimental conditions, the percent change in metabolites in a group of Alzheimer's disease brains was compared to a control group using both units. The results were essentially identical for the mole % and mumole/g methods. We conclude that the use of the mole % method of expressing MRS data yields results which are equivalent to those expressed in absolute units and suggest that, for in vivo MRS studies, use of the mole % method is preferable because fewer artifacts, such as partial volume effects, are introduced.

Alterations of cerebral metabolism in probable Alzheimer's disease: a preliminary study

Previous in vitro and in vivo 31P MRS studies of Alzheimer's disease patients have revealed alterations in membrane phospholipid metabolism and PET studies have shown alterations in glucose and oxidative metabolism. This study of probable Alzheimer's disease patients demonstrates severity dependent alterations in measures of both high-energy phosphate and membrane phospholipid metabolism. Mildly demented Alzheimer's patients compared to the controls, have increases in the levels of phosphomonoesters, decreases in the levels of phosphocreatine and probably adenosine diphosphate, and an increased oxidative metabolic rate. As the dementia worsens, the levels of phosphocreatine and adenosine diphosphate increase, the levels of phosphomonoesters decrease, and the oxidative metabolic rate decreases. The phosphomonoester findings replicate previous findings and provide a new dimension to the molecular pathology of Alzheimer's disease, implicating basic defects in membrane metabolism. The changes in oxidative metabolic rate suggest the AD brain is under energetic stress. The changes in energy metabolites with increasing dementia could be a consequence of nerve terminal degeneration and are consistent with previous PET findings. 31P MRS provides new diagnostic and metabolic insights into this disease and would be a noninvasive method to follow the progression of the disease and the metabolic response to therapeutic interventions.

A preliminary 31P MRS study of autism: evidence for undersynthesis and increased degradation of brain membranes

In this pilot study, brain high energy phosphate and membrane phospholipid metabolism were investigated in the dorsal prefrontal cortex of 11 high-functioning autistic adolescent and young adult men (the age range is 12-36 years) and 11 age-, gender-, IQ, race- and socioeconomic status-matched normal controls using in vivo 31P nuclear magnetic resonance spectroscopy (MRS). The autistic group had decreased levels of phosphocreatine and esterified ends (alpha ATP + alpha ADP + dinucleotides + diphosphosugars) compared to the controls. When the metabolite levels were compared within each subject group with neuropsychologic and language test scores, a common pattern of correlations was observed across measures in the autistic group, but not in the control group. As test performance declined in the autistic subjects, levels of the most labile high energy phosphate compound and of membrane building blocks decreased, and levels of membrane breakdown products increased. No significant correlations were present with age in either group or with IQ in the control group, suggesting that these findings were not the consequence of age or IQ effects. This pilot study provides tentative evidence of alterations in brain energy and phospholipid metabolism in autism that correlate with the neuropsychologic and language deficits. The findings are consistent with a hypermetabolic energy state and undersynthesis of brain membranes and may relate to the neurophysiologic and neuropathologic abnormalities in autism.

N-acetyl-L-aspartate and other amino acid metabolites in Alzheimer's disease brain: A preliminary proton nuclear magnetic resonance study

We used proton nuclear magnetic resonance spectroscopy in this preliminary study of perchloric acid extracts of 12 Alzheimer's disease (AD) and five control brain samples to measure the relative levels of taurine, aspartate, glutamine, glutamate, gamma-aminobutyric acid (GABA), and the putative neuronal marker, N-acetyl-L-aspartate (NAA). We found no significant changes in taurine, aspartate, or glutamine. NAA was lower in AD compared with control, and this decrease correlated with the number of senile plaques and neurofibrillary tangles in adjacent tissue sections. GABA levels also were lower in AD brain. Glutamate levels were greater in AD than control and showed a close, inverse correlation with NAA levels. These findings suggest that the decrease in NAA reflects neuronal loss and that remaining neurons could be exposed to a relative excess of glutamate and a relative lack of GABA. If present in the neurotransmitter pool, this imbalance could result in neurotoxic cell damage. This hypothesis is further supported by in vitro and in vivo phosphorus 31 nuclear magnetic resonance findings.

Actions of phosphomonoesters on CA1 hippocampal neurons as revealed by a combined electrophysiological and nuclear magnetic resonance study

Phosphomonoesters (PMEs), precursors of membrane phospholipids, are found in high levels in the developing brain and Alzheimer's disease brain. The present study details the neurophysiological and metabolic effects of acute PME elevation on the Fisher 344 rat in vitro hippocampal slice. Two abundant PMEs, phosphoethanolamine (PE) and L-phosphoserine (PS), reliably altered properties of synaptic transmission at the Schaffer collateral/commissural-CA1 cell synapse. Specifically, PE reversibly depressed the amplitude of population EPSPs at millimolar concentrations but had no effect at micromolar concentrations. PS had biphasic effects on population EPSPs, inducing first a reduction followed by an enhancement of response amplitude. In contrast to PE, the effects of PS were not reversible; population EPSPs were augmented during the wash of PS, and the CA3 region generated evoked (but not spontaneous) epileptiform discharges. 31P nuclear magnetic resonance spectroscopy revealed enhanced slice uptake of PS compared to PE. There was no significant effect of PE on slice high-energy phosphates but incubation with PS significantly lowered slice phosphocreatine (PCr) and ATP concentrations. These observations indicate that the slice uptake of PS could be energy requiring and the enhanced response amplitude observed at 5 mM PS also could produce a drain on high-energy phosphates. Possible modes of PME action on hippocampal physiology are discussed.

Al-ATP as an intracellular carrier of Al(III) ion

1. Using 27Al and 31P NMR spectroscopy in conjunction with an Al lactate aqueous reagent at pH 7.2, Al complexes of ATP and of phospholipids were characterized in synthetic-aqueous and organic-phospholipid chemical systems and in the intact human red blood cell. 2. The observed 31P NMR chemical shifts of the Al-ATP complex in aqueous laboratory preparations or the intact human red blood cell were, respectively, alpha phosphate, -11.53 delta; beta phosphate, -22.65 delta; and gamma phosphate, -10.95 delta. 3. The observed complexed 27Al chemical shift was -2.22 delta. 4. The relative affinities for Al of the phospholipids determined from 31P NMR spectroscopic titrations were PA much greater than Cl much greater than PS greater than PG approximately equal to PI greater than PE plus approximately equal to PE much greater than SPH greater than PC.

Changes in brain energy and phospholipid metabolism during development and aging in the Fischer 344 rat

The effects of brain development and aging on high-energy phosphate and membrane phospholipid metabolism were studied from birth to senescence in the Fischer 344 rat using 31P nuclear magnetic resonance spectroscopy. Marked developmental and smaller aging-related changes were observed in brain high-energy phosphates, phospholipid precursors and phospholipid breakdown products. The biochemical changes correlate with known histological and electrophysiological changes occurring in the brain during development (neuritic sprouting and onset of brain electrical activity) and aging (loss of dendritic processes). These findings provide a framework for interpreting the effects of physiological insults during different developmental and aging periods.

Correlation of phosphorus-31 magnetic resonance spectroscopy and morphologic findings in Alzheimer's disease

Senile plaques (SPs), especially, and neurofibrillary tangles are important pathologic markers for the diagnosis of Alzheimer's disease (AD), but neither is pathognomonic for AD. We hypothesize that elevations in levels of phosphomonoesters, precursors of membrane phospholipids, occur early in the pathogenesis of AD and precede the appearance of SPs. In contrast, elevations in levels of phosphodiesters, breakdown products of phospholipids, reflect degeneration of neural membranes and will correlate with the appearance of SPs. Correlative phosphorus-31 magnetic resonance spectroscopy and morphologic studies conducted to test this hypothesis disclosed that elevations in levels of phosphomonoesters had a negative correlation with the numbers of SPs, and elevations in levels of phosphodiesters had a positive correlation with the numbers of SPs. No correlations were observed for either membrane parameter and neurofibrillary tangles. These findings support our hypothesis and suggest that aberrations in the synthesis of membrane phospholipids are early metabolic events in the pathogenesis of AD.

31P nuclear magnetic resonance study of the brain in Alzheimer's disease

The histopathological hallmarks of Alzheimer's disease have long been considered to be neurofibrillary tangles (NFT) and neuritic (senile) plaques (SP). Neither of these structures, however, are unique to Alzheimer's disease, and both probably represent end-stage markers of the disorder. NFT have been demonstrated in many disorders; SP occur in small numbers with normal aging. Evidence is presented for elevation of phosphomonoesters (PME) in Alzheimer's brain compared to non-Alzheimer's diseased controls and normal controls. The PME detected by 31P nuclear magnetic resonance (NMR) spectroscopy of autopsy brain are predominantly anabolic precursors of membrane phospholipids. Elevated PME could be secondary to a metabolic block at the rate-limiting enzyme in membrane phospholipid synthesis, which is cytidine triphosphate (CTP): phosphocholine (or phosphoethanolamine) cytidyltransferase (EC 2.7.7.15). Elevated PME could also be secondary to decreased breakdown of PME by phospholipase D activity. Since CTP: phosphocholine cytidyltransferase is inactivated by phosphorylation and since there is independent evidence for hyperphosphorylation of tau and MAP-2 proteins in AD brain, enhanced protein kinase activity could be a common factor. Preliminary evidence suggests that PME could interact with N-methyl-D-aspartate receptors and potentially act as false neurotransmitters. Further studies will be needed to investigate these possibilities.

Considerations for brain pH assessment by 31P NMR

Recently in vivo NMR spectroscopy has been used to measure brain pH non-invasively. Both the inorganic orthophosphate (Pi) chemical shift (delta) and the difference between the chemical shifts of phosphocreatine (PCr) and Pi(delta delta PCr-Pi) have been proposed as indicators of brain pH. However, the precise delta of Pi may be difficult to determine under normoxic conditions as is the delta of PCr under hypoxic/ischemic conditions. Ideally one needs a NMR delta parameter that: (1) linearly changes between pH 6.0-8.0, (2) is either relatively unaffected or predictably affected by cations (e.g., Mg2+) other than H+, and that (3) comes from readily observable 31P NMR resonances whose delta's can be accurately assessed under all physiological conditions. Therefore, we undertook a systematic 31P NMR study of the pH and Mg2+ titration curves for 16 phosphorus-containing metabolites observed in brain by 31P NMR. On the basis of the titration curves, the delta delta's for PCr-Pi, phosphoethanolamine (PE)-Pi, and PCr-PE fulfill criteria (1) and (2), but not criterion (3). However, the delta delta of ATP gamma-alpha fulfills all three criteria and potentially provides information on the intracellular Mg2+ concentration.