A review of in vivo 1H magnetic resonance spectroscopy of cerebral ischemia in rats

Role of polyunsaturated fatty acids in human brain structure and function across the lifespan: An update on neuroimaging findings

There is a substantial body of evidence from animal studies implicating polyunsaturated fatty acids (PUFA) in neuroinflammatory, neurotrophic, and neuroprotective processes in brain. However, direct evidence for a role of PUFA in human brain structure and function has been lacking. Over the last decade there has been a notable increase in neuroimaging studies that have investigated the impact of PUFA intake and/or blood levels (i.e., biostatus) on brain structure, function, and pathology in human subjects. The majority of these studies specifically evaluated associations between omega-3 PUFA intake and/or biostatus and neuroimaging outcomes using a variety of experimental designs and imaging techniques. This review provides an updated overview of these studies in an effort to identify patterns to guide and inform future research. While the weight of evidence provides general support for a beneficial effect of a habitual diet consisting of higher omega-3 PUFA intake on cortical structure and function in healthy human subjects, additional research is needed to replicate and extend these findings as well as identify response mediators and clarify mechanistic pathways. Controlled intervention trials are also needed to determine whether increasing n-3 PUFA biostatus can prevent or attenuate neuropathological brain changes observed in patients with or at risk for psychiatric disorders and dementia.

Relationship between Proton Magnetic Resonance Spectroscopy of Frontoinsular Gray Matter and Neurodevelopmental Outcomes in Very Low Birth Weight Children at the Age of 4

Very low birth weight is associated with long term neurodevelopmental complications. Macroscopic brain abnormalities in prematurity survivors have been investigated in several studies. However, there is limited data regarding local cerebral metabolic status and neurodevelopmental outcomes. The purpose of this study was to characterize the relationship between proton magnetic resonance spectra in basal ganglia, frontal white matter and frontoinsular gray matter, neurodevelopmental outcomes assessed with the Leiter scale and the Developmental Test of Visual Perception and selected socioeconomic variables in a cohort of very low birth weight children at the age of four. Children were divided in three groups based on the severity of neurodevelopmental impairment. There were no differences in spectroscopy in basal ganglia and frontal white matter between the groups. Lower concentrations of N-acetylaspartate (NAA), choline (Cho) and myoinositol (mI) were observed in the frontoinsular cortex of the left hemisphere in children with neurodevelopmental impairment compared to children with normal neurodevelopmental outcomes. Higher parental education, daycare attendance and breastfeeding after birth were associated with more favorable neurodevelopmental prognosis, whereas rural residence was more prevalent in children with moderate and severe impairment. Our study demonstrates the role of long term neurometabolic disruption in the left frontoinsular cortex and selected socioeconomic variables in determination of neurodevelopmental prognosis in prematurity survivors.

Effects of fish oil supplementation on prefrontal metabolite concentrations in adolescents with major depressive disorder: a preliminary 1H MRS study

OBJECTIVE

To use proton magnetic resonance spectroscopy ((1)H MRS) to investigate the effects of fish oil (FO) supplementation on cortical metabolite concentrations in adolescents with major depressive disorder (MDD).

METHODS

Metabolite concentrations were determined by (1)H MRS in the anterior cingulate cortex and bilateral dorsolateral prefrontal cortex (DLPFC) of adolescents with MDD before and following 10-week open-label supplementation with low (2.4 g/day, n = 7) or high (16.2 g/day, n = 7) dose FO. Depressive symptom severity scores and erythrocyte fatty acid levels were also determined.

RESULTS

Baseline erythrocyte eicosapentaenoic acid (EPA) composition was positively correlated, and arachidonic acid (AA) and the AA/EPA ratio were inversely correlated, with choline (Cho) concentrations in the right DLPFC. Docosahexaenoic acid (DHA) composition was inversely correlated with myo-inositol (mI) concentrations in the left DLPFC. Erythrocyte EPA and DHA composition increased, and AA decreased, significantly following low-dose and high-dose FO supplementation. In the intent-to-treat sample, depressive symptom severity scores decreased significantly in the high-dose group (-40%, P < 0.0001) and there was a trend in the low-dose group (-20%, P = 0.06). There were no significant baseline-endpoint changes in metabolite levels in each voxel. In the low-dose group there were changes with large effect sizes, including a decrease in mI in the left DLPFC (-12%, P = 0.18, d = 0.8) and increases in glutamate + glutamine (Glx) (+12%, P = 0.19, d = 0.8) and Cho (+15%, P = 0.08, d = 1.2) in the right DLPFC. In the high-dose group, there was a trend for increases in Cho in the right DLPFC (+10%, P = 0.09, d = 1.2).

DISCUSSION

These preliminary data suggest that increasing the LCn-3 fatty acid status of adolescent MDD patients is associated with subtle changes in Glx, mI, and Cho concentrations in the DLPFC that warrant further evaluation in a larger controlled trial.

Dynamic correlations between hemodynamic, metabolic, and neuronal responses to acute whole-brain ischemia

Cerebral ischemia sets off a cascade of neuronal and metabolic responses to preserve brain viability. An understanding of the temporal evolution of these changes during and after ischemia, and their correlation with hemodynamic changes, is essential. In this study, a 12-min whole-brain ischemia based on the four-blood-vessel occlusion model was employed in rats. Using a high-temporal-resolution simultaneous (1)H-(31)P MRS acquisition sequence at 9.4 T, we investigated dynamic occlusion and reperfusion responses in cerebral lactate (Lac), phosphocreatine (PCr), adenosine triphosphate (ATP), pH, and blood oxygenation level dependence (BOLD), together with changes in neuronal field potential activity. We reveal tightly coupled dynamics between hemodynamic, metabolic, and neuronal responses to ischemia. Neuronal activity, BOLD, PCr, Lac, and pH changed immediately following occlusion, indicating reduced energy substrates and consumption, and increased glycolysis to maintain cellular ATP levels, which started to decrease 2.2 min after the onset of occlusion. ATP stores were then gradually consumed to maintain a minimum housekeeping neuronal activity level. By correlating dynamic changes of brain activity, BOLD, and energy metabolism, new insights into the brain's survival ability and mechanisms during an acute ischemic attack from the perspectives of cerebral metabolism, neuroenergetics, and neuronal activity were gained.

Inhibition of Pediatric Glioblastoma Tumor Growth by the Anti-Cancer Agent OKN-007 in Orthotopic Mouse Xenografts

Pediatric glioblastomas (pGBM), although rare, are one of the leading causes of cancer-related deaths in children, with tumors essentially refractory to existing treatments. Here, we describe the use of conventional and advanced in vivo magnetic resonance imaging (MRI) techniques to assess a novel orthotopic xenograft pGBM mouse (IC-3752GBM patient-derived culture) model, and to monitor the effects of the anti-cancer agent OKN-007 as an inhibitor of pGBM tumor growth. Immunohistochemistry support data is also presented for cell proliferation and tumor growth signaling. OKN-007 was found to significantly decrease tumor volumes (p<0.05) and increase animal survival (p<0.05) in all OKN-007-treated mice compared to untreated animals. In a responsive cohort of treated animals, OKN-007 was able to significantly decrease tumor volumes (p<0.0001), increase survival (p<0.001), and increase diffusion (p<0.01) and perfusion rates (p<0.05). OKN-007 also significantly reduced lipid tumor metabolism in responsive animals [(Lip1.3 and Lip0.9)-to-creatine ratio (p<0.05)], as well as significantly decrease tumor cell proliferation (p<0.05) and microvessel density (p<0.05). Furthermore, in relationship to the PDGFRα pathway, OKN-007 was able to significantly decrease SULF2 (p<0.05) and PDGFR-α (platelet-derived growth factor receptor-α) (p<0.05) immunoexpression, and significantly increase decorin expression (p<0.05) in responsive mice. This study indicates that OKN-007 may be an effective anti-cancer agent for some patients with pGBMs by inhibiting cell proliferation and angiogenesis, possibly via the PDGFRα pathway, and could be considered as an additional therapy for pediatric brain tumor patients.

Novel gradient echo sequence‑based amide proton transfer magnetic resonance imaging in hyperacute cerebral infarction

In the progression of ischemia, pH is important and is essential in elucidating the association between metabolic disruption, lactate formation, acidosis and tissue damage. Chemical exchange-dependent saturation transfer (CEST) imaging can be used to detect tissue pH and, in particular, a specific form of CEST magnetic resonance imaging (MRI), termed amide proton transfer (APT) MRI, which is sensitive to pH and can detect ischemic lesions, even prior to diffusion abnormalities. The critical parameter governing the ability of CEST to detect pH is the sequence. In the present study, a novel strategy was used, based on the gradient echo sequence (GRE), which involved the insertion of a magnetization transfer pulse in each repetition time (TR) and minimizing the TR for in vivo APT imaging. The proposed GRE-APT MRI method was initially verified using a tissue-like pH phantom and optimized MRI parameters for APT imaging. In order to assess the range of acute cerebral infarction, rats (n=4) were subjected to middle cerebral artery occlusion (MCAO) and MRI scanning at 7 telsa (T). Hyperacute ischemic tissue damage was characterized using multiparametric imaging techniques, including diffusion, APT and T₂-Weighted MRI. By using a magnetization transfer pulse and minimizing TR, GRE-APT provided high spatial resolution and a homogeneous signal, with clearly distinguished cerebral anatomy. The GRE-APT and diffusion MRI were significantly correlated with lactate content and the area of cerebral infarction in the APT and apparent diffusion coefficient (ADC) maps matched consistently during the hyperacute period. In addition, compared with the infarction area observed on the ADC MRI map, the APT map contained tissue, which had not yet been irreversibly damaged. Therefore, GRE-APT MRI waa able to detect ischemic lactic acidosis with sensitivity and spatiotemporal resolution, suggesting the potential use of pH MRI as a surrogate imaging marker of impaired tissue metabolism for the diagnosis and prognosis of hyperacute stroke.

Non-invasive diagnostic biomarkers for estimating the onset time of permanent cerebral ischemia

The treatments for ischemic stroke can only be administered in a narrow time-window. However, the ischemia onset time is unknown in ~30% of stroke patients (wake-up strokes). The objective of this study was to determine whether MR spectra of ischemic brains might allow the precise estimation of cerebral ischemia onset time. We modeled ischemic stroke in male ICR-CD1 mice using a permanent middle cerebral artery filament occlusion model with laser Doppler control of the regional cerebral blood flow. Mice were then subjected to repeated MRS measurements of ipsilateral striatum at 14.1 T. A striking initial increase in γ-aminobutyric acid (GABA) and no increase in glutamine were observed. A steady decline was observed for taurine (Tau), N-acetyl-aspartate (NAA) and similarly for the sum of NAA+Tau+glutamate that mimicked an exponential function. The estimation of the time of onset of permanent ischemia within 6 hours in a blinded experiment with mice showed an accuracy of 33±10 minutes. A plot of GABA, Tau, and neuronal marker concentrations against the ratio of acetate/NAA allowed precise separation of mice whose ischemia onset lay within arbitrarily chosen time-windows. We conclude that (1)H-MRS has the potential to detect the clinically relevant time of onset of ischemic stroke.

Low docosahexaenoic acid status is associated with reduced indices in cortical integrity in the anterior cingulate of healthy male children: a 1H MRS Study

Docosahexaenoic acid (DHA, 22:6n-3) is the principal omega-3 fatty acid in mammalian brain gray matter, and emerging preclinical evidence suggests that DHA has neurotrophic and neuroprotective properties. This study investigated relationships among DHA status, neurocognitive performance, and cortical metabolism measured with proton magnetic resonance spectroscopy (1H MRS) in healthy developing male children (aged 8-10 years, n = 38). Subjects were segregated into low-DHA (n = 19) and high-DHA (n = 19) status groups by a median split of erythrocyte DHA levels. Group differences in 1H MRS indices of cortical metabolism, including choline (Cho), creatine (Cr), glutamine + glutamate + γ-aminobutyric acid (Glx), myo-inositol (mI), and n-acetyl aspartate (NAA), were determined in the right and left dorsolateral prefrontal cortex (R/L-DLPFC, BA9) and bilateral anterior cingulate cortex (ACC, BA32/33). Group differences in neurocognitive performance were evaluated with the Kaufman Brief Intelligence Test and identical-pairs version of the continuous performance task (CPT-IP). Subjects in the low-DHA group consumed fish less frequently (P = 0.02), had slower reaction times on the CPT-IP (P = 0.007), and exhibited lower mI (P = 0.007), NAA (P = 0.007), Cho (P = 0.009), and Cr (P = 0.01) concentrations in the ACC compared with the high-DHA group. There were no group differences in ACC Glx or any metabolite in the L-DLPFC and R-DLPFC. These data indicate that low-DHA status is associated with reduced indices of metabolic function in the ACC and slower reaction time during sustained attention in developing male children.

Subclinical cerebral edema in children with diabetic ketoacidosis randomized to 2 different rehydration protocols

OBJECTIVE

Previous studies show that vasogenic cerebral edema (CE) occurs during diabetic ketoacidosis (DKA) treatment in children, but the role of intravenous fluids in contributing to CE is unclear. We used magnetic resonance diffusion weighted imaging to quantify subclinical CE in children with DKA randomized to 2 intravenous fluid regimens.

METHODS

Children with DKA were randomized to receive fluids at a more rapid rate (n = 8) or a slower rate (n = 10), with all other aspects of DKA treatment kept identical. Children underwent diffusion weighted imaging 3 to 6 hours and 9 to 12 hours after beginning DKA treatment and after recovery from DKA (≥ 72 hours after beginning treatment). We calculated brain apparent diffusion coefficient (ADC) values as the average of measurements in the basal ganglia, thalamus, frontal white matter, and hippocampus and determined the mean brain ADC value during DKA treatment by averaging data from the 3- to 6-hour and 9- to 12-hour measurements. The difference in mean brain ADC between DKA treatment and postrecovery was used as an index of the severity of CE during DKA treatment.

RESULTS

Mean brain ADC values during DKA treatment were significantly higher than postrecovery values, consistent with vasogenic CE (842 ± 38 vs 800 ± 41 × 10(-6) mm(2)/second, P = .002). We did not detect significant differences in ADC elevation in children treated with more rapid versus slower rehydration (β coefficient 0.11 for 1 SD change in ADC, 95% confidence interval: -0.91 to 1.13).

CONCLUSIONS

ADC changes during DKA treatment (reflective of vasogenic CE) do not appear to be substantially affected by the rate of intravenous fluid administration.

Magnetic resonance spectroscopy reveals N-acetylaspartate reduction in hippocampus and cingulate cortex after fear conditioning

The fear conditioning in rodents provides a valuable translational tool to investigate the neural basis of learning and memory and potentially the neurobiology of post-traumatic stress disorder (PTSD). Neurobiological changes induced by fear conditioning have largely been examined ex vivo while progressive 'real-time' changes in vivo remain under-explored. Single voxel proton magnetic resonance spectroscopy (1H MRS) of the hippocampus, cingulate cortex and thalamus of adult male C57BL/6N mice (N=12) was performed at 1 day before, 1 day and 1 week after, fear conditioning training using a 7T scanner. N-acetylaspartate (NAA), a marker for neuronal integrity and viability, significantly decreased in the hippocampus at 1 day and 1 week post-conditioning. Significant NAA reduction was also observed in the cingulate cortex at 1 day post-conditioning. These findings of hippocampal NAA decrease indicate reduced neuronal dysfunction and/or neuronal integrity, contributing to the trauma-related PTSD-like symptoms. The neurochemical changes characterized by 1H MRS can shed light on the biochemical mechanisms of learning and memory. Moreover, such information can potentially facilitate prompt intervention for patients with psychiatric disorders.

Reversible loss of N-acetylaspartate after 15-min transient middle cerebral artery occlusion in rat: a longitudinal study with in vivo proton magnetic resonance spectroscopy

It is generally accepted that N-acetylaspartate (NAA) can be used a biochemical marker for assessing neuronal viability/integrity after cerebral ischemia. However, this view has recently been questioned based on observations showing that after a photothrombotic permanent ischemia the acute decline of NAA in the infracted regions, where massive neuronal loss persists, is reversible over time. In this study, we measured the longitudinal changes of NAA and total creatine (Cr) in ischemic rat brain after a 15-min transient middle cerebral artery occlusion (MCAO) by in vivo (1)H magnetic resonance spectroscopy. The results showed that the levels of NAA and total Cr in the ischemic lesion decrease significantly at 1 day post-ichemia, followed by spontaneous recovery to the control levels by 2 weeks and remained stable thereafter up to 16 weeks. The normalization of NAA and total Cr levels was associated histologically with persisted neuronal loss up to 90 % in the ischemic core, and accompanied by marked reactive astrocytic responses occurring with a similar time course. The absolute T(2) relaxation time in the ischemic lesion increased during acute phase, and declined afterwards during subacute and chronic phases of 15-min MCAO. The delayed decreases of T(2) in the ischemic lesion might be associated with deposition of paramagnetic species, such as manganese and iron originated from chronic inflammation, vascular degradation and/or hemorrhagic transformation. The results of this study give further support to the hypothesis that the recovery of NAA after cerebral ischemia might have contributions from reactive glia cells, and caution the use of NAA as a specific neuronal marker during the chronic stage of cerebral ischemia.

Association between pH-weighted endogenous amide proton chemical exchange saturation transfer MRI and tissue lactic acidosis during acute ischemic stroke

The ischemic tissue becomes acidic after initiation of anaerobic respiration, which may result in impaired tissue metabolism and, ultimately, in severe tissue damage. Although changes in the major cerebral metabolites can be studied using magnetic resonance (MR) spectroscopy (MRS)-based techniques, their spatiotemporal resolution is often not sufficient for routine examination of fast-evolving and heterogeneous acute stroke lesions. Recently, pH-weighted MR imaging (MRI) has been proposed as a means to assess tissue acidosis by probing the pH-dependent chemical exchange of amide protons from endogenous proteins and peptides. In this study, we characterized acute ischemic tissue damage using localized proton MRS and multiparametric imaging techniques that included perfusion, diffusion, pH, and relaxation MRI. Our study showed that pH-weighted MRI can detect ischemic lesions and strongly correlates with tissue lactate content measured by (1)H MRS, indicating lactic acidosis. Our results also confirmed the correlation between apparent diffusion coefficient and lactate; however, no significant relationship was found for perfusion, T(1), and T(2). In summary, our study showed that optimized endogenous pH-weighted MRI, by sensitizing to local tissue pH, remains a promising tool for providing a surrogate imaging marker of lactic acidosis and altered tissue metabolism, and augments conventional techniques for stroke diagnosis.

Neuronal and axonal degeneration in experimental spinal cord injury: in vivo proton magnetic resonance spectroscopy and histology

Longitudinal in vivo proton magnetic resonance spectroscopy (1H-MRS) and immunohistochemistry were performed to investigate the tissue degeneration in traumatically injured rat spinal cord rostral and caudal to the lesion epicenter. On 1H-MRS significant decreases in N-acetyl aspartate (NAA) and total creatine (Cr) levels in the rostral, epicenter, and caudal segments were observed by 14 days, and levels remained depressed up to 56 days post-injury (PI). In contrast, the total choline (Cho) levels increased significantly in all three segments by 14 days PI, but recovered in the epicenter and caudal, but not the rostral region, at 56 days PI. Immunohistochemistry demonstrated neuronal cell death in the gray matter, and reactive astrocytes and axonal degeneration in the dorsal, lateral, and ventral white-matter columns. These results suggest delayed tissue degeneration in regions both rostrally and caudally from the epicenter in the injured spinal cord tissue. A rostral-caudal asymmetry in tissue recovery was seen both on MRI-observed hyperintense lesion volume and the Cho, but not NAA and Cr, levels at 56 days PI. These studies suggest that dynamic metabolic changes take place in regions away from the epicenter in injured spinal cord.

Cerebral metabolic alterations in rats with diabetic ketoacidosis: effects of treatment with insulin and intravenous fluids and effects of bumetanide

OBJECTIVE

Cerebral edema is a life-threatening complication of diabetic ketoacidosis (DKA) in children. Recent data suggest that cerebral hypoperfusion and activation of cerebral ion transporters may be involved, but data describing cerebral metabolic alterations during DKA are lacking.

RESEARCH DESIGN AND METHODS

We evaluated 50 juvenile rats with DKA and 21 normal control rats using proton and phosphorus magnetic resonance spectroscopy (MRS). MRS measured cerebral intracellular pH and ratios of metabolites including ATP/inorganic phosphate (Pi), phosphocreatine (PCr)/Pi, N-acetyl aspartate (NAA)/creatine (Cr), and lactate/Cr before and during DKA treatment. We determined the effects of treatment with insulin and intravenous saline with or without bumetanide, an inhibitor of Na-K-2Cl cotransport, using ANCOVA with a 2 x 2 factorial study design.

RESULTS

Cerebral intracellular pH was decreased during DKA compared with control (mean +/- SE difference -0.13 +/- 0.03; P < 0.001), and lactate/Cr was elevated (0.09 +/- 0.02; P < 0.001). DKA rats had lower ATP/Pi and NAA/Cr (-0.32 +/- 0.10, P = 0.003, and -0.14 +/- 0.04, P < 0.001, respectively) compared with controls, but PCr/Pi was not significantly decreased. During 2-h treatment with insulin/saline, ATP/Pi, PCr/Pi, and NAA/Cr declined significantly despite an increase in intracellular pH. Bumetanide treatment increased ATP/Pi and PCr/Pi and ameliorated the declines in these values with insulin/saline treatment.

CONCLUSIONS

These data demonstrate that cerebral metabolism is significantly compromised during DKA and that further deterioration occurs during early DKA treatment--consistent with possible effects of cerebral hypoperfusion and reperfusion injury. Treatment with bumetanide may help diminish the adverse effects of initial treatment with insulin/saline.

Evolution of the neurochemical profile after transient focal cerebral ischemia in the mouse brain

Evolution of the neurochemical profile consisting of 19 metabolites after 30 mins of middle cerebral artery occlusion was longitudinally assessed at 3, 8 and 24 h in 6 to 8 microL volumes in the striatum using localized 1H-magnetic resonance spectroscopy at 14.1 T. Profound changes were detected as early as 3 h after ischemia, which include elevated lactate levels in the presence of significant glucose concentrations, decreases in glutamate and a transient twofold glutamine increase, likely to be linked to the excitotoxic release of glutamate and conversion into glial glutamine. Interestingly, decreases in N-acetyl-aspartate (NAA), as well as in taurine, exceeded those in neuronal glutamate, suggesting that the putative neuronal marker NAA is rather a sensitive marker of neuronal viability. With further ischemia evolution, additional, more profound concentration decreases were detected, reflecting a disruption of cellular functions. We conclude that early changes in markers of energy metabolism, glutamate excitotoxicity and neuronal viability can be detected with high precision non-invasively in mice after stroke. Such investigations should lead to a better understanding and insight into the sequential early changes in the brain parenchyma after ischemia, which could be used for identifying new targets for neuroprotection.

Neuroimaging as a basis for rational stem cell therapy

Neonatal global or focal hypoxic-ischemic brain injury remains a frequent and devastating condition, with serious long-term sequelae. An important issue in any neonatal clinical trial of neuroprotective agents relates to developing accurate measures of injury severity and also suitable measures of the response to treatment. Advanced magnetic resonance imaging techniques can acquire serial and noninvasive data about brain structure, metabolic activity, and the response to injury or treatment. These imaging methods need validation in appropriate animal models for translational research studies in human newborns. This review describes several approaches that use imaging as well as proton magnetic resonance spectroscopy to assess the severity of ischemic injury (e.g., for possible candidate selection) and for monitoring the progression and evolution of injury over time and as an indicator of recovery or response to treatment. Preliminary data are presented on how imaging can be used after neural stem cell implantation to characterize the migration rate, the magnitude of stem cell proliferation, and their final location. Imaging has the potential to allow monitoring of many dimensions of neuroprotective treatments and can be expected to contribute to efficacy and safety when clinical trials using neural stem cells or other neuroprotective agents become available.

Proton magnetic resonance spectroscopy: clinical applications in patients with brain lesions

CONTEXT

Proton spectroscopy has been recognized as a safe and noninvasive diagnostic method that, coupled with magnetic resonance imaging techniques, allows for the correlation of anatomical and physiological changes in the metabolic and biochemical processes occurring within previously-determined volumes in the brain. There are two methods of proton magnetic resonance spectroscopy: single voxel and chemical shift imaging.

OBJECTIVE

The present work focused on the clinical applications of proton magnetic resonance spectroscopy in patients with brain lesions.

CONCLUSIONS

In vivo proton spectroscopy allows the detection of certain metabolites in brain tissue, such as N-acetyl aspartate, creatine, choline, myoinositol, amino acids and lipids, among others. N-acetyl aspartate is a neuronal marker and, as such, its concentration will decrease in the presence of aggression to the brain. Choline increase is the main indicator of neoplastic diseases. Myoinositol is raised in patients with Alzheimer's disease. Amino acids are encountered in brain abscesses. The presence of lipids is related to necrotic processes.

Reversible loss of N-acetyl-aspartate in rats subjected to long-term focal cerebral ischemia

To evaluate the true meaning of N-acetyl-aspartate (NAA) measurements in ischemic stroke, the authors followed the temporal changes in brain NAA content in rats subjected to permanent focal ischemia. Ischemia was induced by photothrombotic cortical occlusion. At 1, 3, 8, and 30 d after onset of ischemia, NAA was measured in the infarct by high-performance liquid chromatography coupled to ultraviolet detection and histologic damage was examined. Cerebral content of NAA was markedly reduced in the lesioned tissue, reaching -90% after 3 d, a time at which viable neurons were no longer detected. N-Acetyl-aspartate concentrations after 8 and 30 d were higher than that observed after 3 d. This metabolic change coincided with an important microglial and astroglial activation. The results of this study raise questions regarding the use of NAA as a specific neuronal marker in chronic stage of stroke.

Chronic ischemic stroke model in cynomolgus monkeys: behavioral, neuroimaging and anatomical study

Previous nonhuman primate stroke models have employed temporary occlusion of arteries, had limited behavioral testing and imaging, and focused on the short-term outcome. Our goals were 1. to develop a stable model of chronic stroke in the nonhuman primate, 2. to study in vivo the long-term biochemical changes in the area adjacent to the infarct, using proton magnetic resonance spectroscopy (H MRS), and 3. evaluate these changes in relation to the histopathological effects of stroke. Four adult cynomologous monkeys had an occlusion of the M1 segment of the right MCA. Behavioral tests included a clinical rating scale, motor planning task, fine motor task, and activity monitoring. Eight months afterwards, MRI and 1H MRS were performed. Following the imaging studies the monkeys were perfused transcardially, their brains extracted and processed. Nissl staining and immunohistochemistry for neuronal markers (NeuN) were performed and used to measure the lesion volume and neuronal optical density (OD). All animals developed a left hemiparesis and were unable to perform a fine motor task with the left hand. There was a significant (31%) decline in the motor planning ability with the nonparetic extremity. Monkeys displayed a stooped posture, episodes of rotation to the side of the lesion, partial left hemianopsia, and transient changes in activity. The clinical signs improved over the first 6-8 weeks but the deficits remained stable for the remaining six months of follow up. MRI demonstrated a subcortical and cortical infarction in the right MCA distribution. 1H MRS data detected a significant decrease in the N-acetyl-aspartate (NAA)/creatine (Cr) ratio in the area adjacent to the infarction (VOl-St) compared to a mirror area in the contralateral hemisphere (VOl-Co). Histopathological measurements revealed a significant decline in neuronal cross-sectional area and neuronal optical density in the region of the VOl-St. We established a stable and reproducible model of chronic stroke in the MCA distribution, in the macaque monkey. Our data indicate that NAA detected by 1H MRS can be used to measure neuronal loss in vivo and help target this area for intervention. Our model may be particularly suitable for studies testing the effects of therapeutic strategies involving neural or stem cell transplantation, trophic factors or gene therapy.

Molecular aspects of magnetic resonance imaging and spectroscopy

Magnetic resonance imaging (MRI) is a well known diagnostic tool in radiology that produces unsurpassed images of the human body, in particular of soft tissue. However, the medical community is often not aware that MRI is an important yet limited segment of magnetic resonance (MR) or nuclear magnetic resonance (NMR) as this method is called in basic science. The tremendous morphological information of MR images sometimes conceal the fact that MR signals in general contain much more information, especially on processes on the molecular level. NMR is successfully used in physics, chemistry, and biology to explore and characterize chemical reactions, molecular conformations, biochemical pathways, solid state material, and many other applications that elucidate invisible characteristics of matter and tissue. In medical applications, knowledge of the molecular background of MRI and in particular MR spectroscopy (MRS) is an inevitable basis to understand molecular phenomenon leading to macroscopic effects visible in diagnostic images or spectra. This review shall provide the necessary background to comprehend molecular aspects of magnetic resonance applications in medicine. An introduction into the physical basics aims at an understanding of some of the molecular mechanisms without extended mathematical treatment. The MR typical terminology is explained such that reading of original MR publications could be facilitated for non-MR experts. Applications in MRI and MRS are intended to illustrate the consequences of molecular effects on images and spectra.