Measurement of regional N-acetylaspartate after transient global ischemia in gerbils with and without ischemic tolerance: an index of neuronal survival

Changes in brain metabolites related to stress resilience: Metabolomic analysis of the hippocampus in a rat model of depression

The ability to cope successfully with stress is known as 'resilience', and those with resilience are not prone to developing depression. One preclinical animal model for depression is the chronic mild stress (CMS) model. There are CMS-resilient (do not manifest anhedonia) and CMS-susceptible (manifest anhedonia) rats. This study aimed to investigate the differences in the profiles of hippocampal metabolites between susceptible and resilient rats, and to identify a biomarker that can distinguish the two. We divided stress-loaded rats into susceptible and resilient types based on their sucrose preference values. We then conducted brain-derived neurotrophic factor (BDNF) quantification and metabolomic analysis in the hippocampus. Compared to the controls, no significant differences were observed in the hippocampal BDNF levels of susceptible and resilient rats. However, the control rats were clearly distinguishable from the susceptible rats in terms of their brain metabolite profiles; the control rats were difficult to distinguish from the resilient rats. CMS model rats showed an increase in the levels of N-acetylaspartate and glutamate, and a decrease in the levels of aspartate and γ-aminobutyric acid in the hippocampus. Of the 12 metabolites measured in the present study, N-acetylaspartate was the only one that could differentiate the three types (control, susceptible, and resilient) of rats. Thus, brain metabolomic analyses can not only distinguish CMS model rats from control rats, but also indicate stress susceptibility. The variation in the levels of N-acetylaspartate in the hippocampus of control, resilient, and susceptible rats demonstrated that it could be a biomarker for stress susceptibility.

Brain ischemic preconditioning protects against moderate, not severe, transient global cerebral ischemic injury

Ischemic preconditioning (IPC) in the brain increases ischemic tolerance to subsequent ischemic insults. In this study, we examined whether IPC protects neurons and attenuates microgliosis or not in the hippocampus following severe transient global cerebral ischemia (TCI) in gerbils. Gerbils were assigned to 8 groups; 5- and 15-min sham operated groups, 5-min and 15-min TCI operated groups, IPC plus 5- and 15-min sham operated groups, and IPC plus 5- and 15-min TCI operated groups. IPC was induced by subjecting animals to 2-min transient ischemia 1 day before 5-min TCI for a typical transient ischemia and 15-min TCI for severe transient ischemia. Neuronal damage was examined by cresyl violet staining and Fluoro-Jade B histofluorescence staining. In addition, microglial activation was examined using immunohistochemistry for Iba-1 (a marker for microglia). Delayed neuronal death and microgliosis was found in the CA1 alone in the 5-min TCI operated group at 5 days post-ischemia, and, in the 15-min TCI operated group, neuronal death and microgliosis was shown in all CA areas (CA1-3) and the dentate gyrus. IPC displayed neuroprotection and attenuated microglial activation in the 5-min TCI operated group. However, in the 15-min TCI operated group, IPC did not show neuroprotection and not attenuate microglial activation. Our present findings indicate that IPC hardly protect against severe transient cerebral ischemic injury.

Akinetic mutism caused by HIV-associated progressive multifocal leukoencephalopathy was successfully treated with mefloquine: a serial multimodal MRI Study

We report a case of a patient with highly active anti-retroviral therapy-resistant human immunodeficiency virus (HIV)-associated progressive multifocal leukoencephalopathy (PML). The patient showed an improvement in imaging findings and clinical symptoms after mefloquine was introduced as an additional treatment. Serial assessment of white matter lesions was conducted by proton magnetic resonance spectroscopy ((1)H-MRS) and diffusion-weighted imaging (DWI). As the clinical symptoms improved, the N-acetylaspartate/creatine ratio increased, the choline/creatine ratio decreased, and the elevated ADC value decreased. These concomitant changes suggested that (1)H-MRS and DWI were useful for the assessment of the therapeutic effect on PML.

Central nervous system involvement in diabetic neuropathy

Diabetic neuropathy is a chronic and often disabling condition that affects a significant number of individuals with diabetes. Long considered a disease of the peripheral nervous system, there is now increasing evidence of central nervous system involvement. Recent advances in neuroimaging methods detailed in this review have led to a better understanding and refinement of how diabetic neuropathy affects the central nervous system. Recognition that diabetic neuropathy is, in part, a disease that affects the whole nervous system is resulting in a critical rethinking of this disorder, opening a new direction for further research.

Thalamic neuronal dysfunction and chronic sensorimotor distal symmetrical polyneuropathy in patients with type 1 diabetes mellitus

AIMS/HYPOTHESIS

Although clear peripheral nerve pathological abnormalities have been demonstrated in diabetic peripheral neuropathy (DPN), there is little information with regard to brain involvement. Our aim was to use in vivo proton magnetic resonance specroscopy (H-MRS) in patients with DPN in order to assess the neuro-chemical status of the thalamus, which acts as the gateway to the brain for somatosensory information.

METHODS

Participants included 18 type 1 diabetic men (eight without DPN, ten with DPN) and six non-diabetic healthy volunteers, who all underwent detailed clinical and neurophysiological assessments yielding a Neuropathy Composite Score (NCS) derived from Neuropathy Impairment Score of the Lower Limbs plus seven tests of nerve function prior to investigation via a single-voxel H-MRS technique, which was used to sample ventral posterior thalamic parenchyma. Spectroscopic resonances including those due to N-acetyl aspartate (NAA) were assessed at both short and long echo-time, providing putative indicators of neuronal function and integrity, respectively.

RESULTS

At long echo-time we observed significantly lower NAA:creatine (p = 0.04) and NAA:choline (p = 0.02) ratios in DPN patients than in the other groups. No group differences were detected at short echo-time. We found a significant positive association between both sural amplitude (rho = 0.61, p = 0.004) and nerve conduction velocity (r = 0.58, p = 0.006) and NAA:creatine signal among participants with diabetes. Vibration detection threshold (rho = -0.70, p = 0.004) was significantly related to NAA:choline ratio. Heart rate variability with deep breathing (rho = -0.46, p = 0.05) and NCS (rho = -0.53, p = 0.03) were significantly related to NAA:creatine ratio.

CONCLUSIONS/INTERPRETATION

The significantly lower NAA:creatine ratio in DPN is suggestive of thalamic neuronal dysfunction, while the lack of difference in short echo-time between the groups does not suggest neuronal loss. Taken together with the observed correlations between NAA and neurophysiological assessments, these findings provide evidence for thalamic neuronal involvement in DPN.

Fluorescence determination of N-acetylaspartic acid in the rat cerebrum homogenate using high-performance liquid chromatography with pre-column fluorescence derivatization

N-acetyl-L-aspartic acid (NAA) is an endogenous compound, and its brain concentration is suggested to be altered in neurological disorders. In the present study, a fluorescence determination method for NAA was developed by employing reversed-phase high-performance liquid chromatography (HPLC) with pre-column fluorescence derivatization using 4-N,N-dimethylaminosulfonyl-7-N-(2-aminoethyl)amino-2,1,3-benzoxadiazole (DBD-ED). Using methylsuccinic acid as the internal standard, a linear calibration curve for NAA was constructed in the range 125-1000 microM (n=3). The detection limit on the column was approximately 5.0 fmol (signal-to-noise ratio 3). The proposed HPLC method was applied to determine NAA in the rat cerebrum homogenate. Cerebrum NAA was successfully determined using 10 microL of the homogenate, and the validation data for the proposed HPLC method demonstrated satisfactory results. Intra- and inter-day precision and accuracy were within 1.1-7.0 and -8.1-6.3%, respectively. The concentration of NAA in the male rat cerebrum (13 weeks old) was 84 +/-4.6 nmol/mg protein (n = 3) [corrected].

Prognostic value of high-field proton magnetic resonance spectroscopy in patients presenting with clinically isolated syndromes suggestive of multiple sclerosis

INTRODUCTION

The aim of this study was to determine the prognostic value of metabolic alterations in the normal-appearing white matter (NAWM) of patients presenting with clinically isolated syndromes (CIS) suggestive of multiple sclerosis (MS) with special regard to the prediction of conversion to definite MS.

METHODS

Using a 3T whole-body MR system, a multisequence conventional MRI protocol and single-voxel proton MR spectroscopy (PRESS, repetition time 2000 ms, echo times 38 ms and 140 ms) of the parietal NAWM were performed in 25 patients presenting with CIS at baseline and in 20 controls. Absolute concentrations of N-acetyl-aspartate (tNAA), myo-inositol (Ins), choline (Cho) and creatine (tCr) as well as metabolite ratios were determined. Follow-up including neurological assessment and conventional MRI was performed 3-4 and 6-7 months after the initial event.

RESULTS

Nine patients converted to definite MS during the follow-up period. Compared to controls, those patients who converted to MS also showed significantly lower tNAA concentrations in the NAWM (-13.4%, P = 0.002) whereas nonconverters (-6.5%, P = 0.052) did not. The Ins concentration was 20.2% higher in the converter group and 1.9% higher in the nonconverter group, but these differences did not reach significance. No significant differences could be observed for tCr and Cho in either patient group.

CONCLUSION

Axonal damage at baseline in patients presenting with CIS was more prominent in those who subsequently converted to definite MS in the short term follow-up, indicating that tNAA might be a sufficient prognostic marker for patients with a higher risk of conversion to early definite MS.

Axonal damage but no increased glial cell activity in the normal-appearing white matter of patients with clinically isolated syndromes suggestive of multiple sclerosis using high-field magnetic resonance spectroscopy

BACKGROUND AND PURPOSE

Proton MR spectroscopy ((1)H-MR spectroscopy) is a well-established method for the in vivo investigation of the normal-appearing white matter (NAWM) in patients with multiple sclerosis (MS). Metabolic changes in NAWM are of special interest in patients with clinically isolated syndromes (CIS) suggestive of MS regarding further prognostic classifications. The purpose of this study was to investigate metabolic alterations in NAWM in patients with CIS with use of high-field (1)H-MR spectroscopy and to compare the results to those in patients with an early course of MS.

MATERIALS AND METHODS

With use of a 3T whole-body MR imaging system, single-voxel (1)H-MR spectroscopy (PRESS; TR: 2000 ms; TE: 38 ms and 140 ms) of the parietal NAWM was performed in 20 control subjects, 36 patients with CIS, and 12 patients with MS. Metabolite ratios and concentrations of N-acetylaspartate (tNAA), myo-inositol (mIns), choline, and total creatine (tCr) were determined.

RESULTS

Compared with the control group, mean NAWM mIns concentrations were significantly elevated in the MS group (4.56 mmol/L versus 3.75 mmol/L, P = .02) but not in the CIS group (4.04 mmol/L, P = .44). The higher concentration of mIns in the MS group was also reflected in the increased Ins/tCr ratio (P = .02). The mean NAWM tNAA was significantly decreased in both patient groups compared with the control group (CIS, 13.42 mmol/L, P = .02; MS, 12.77 mmol/L versus 14.51 mmol/L, P = .008).

CONCLUSIONS

A significant increase of the activity of the glial cells can only be observed in patients with an established diagnosis of MS but not in patients with CIS. Axonal damage occurs already during the first demyelinating episode in patients with CIS as well as in patients with definite MS.

Effect of seizure on hippocampus in mesial temporal lobe epilepsy and neocortical epilepsy: an MRS study

This study was performed to evaluate the effect of seizures on the bilateral hippocampus in mesial temporal lobe epilepsy (mTLE) and neocortical epilepsy by single voxel proton magnetic resonance spectroscopy (MRS). Forty-one patients with mTLE having unilateral hippocampal sclerosis and 43 patients with a neocortical epilepsy who underwent subsequent epilepsy surgery were recruited. Ninety-five percent confidence intervals of N-acetyl aspartate/choline (NAA/Cho) and NAA/creatine (NAA/Cr) ratios in 20 healthy control subjects were used as threshold values to determine abnormal NAA/Cho and NAA/Cr. NAA/Cho and NAA/Cr were significantly lower in the ipsilateral hippocampus of mTLE and neocortical epilepsy. Using asymmetry indices for patients with bilaterally abnormal ratios of NAA/Cho and NAA/Cr in addition to using unilateral abnormal ratio, the seizure focus was correctly lateralized in 65.9% of patients with mTLE and 48.8% of neocortical epilepsy patients. Bilateral NAA/Cho abnormality was significantly related to a poor surgical outcome in mTLE. No significant relationship was found between the results of NAA/Cho or NAA/Cr and surgical outcome in neocortical epilepsy. The mean contralateral NAA/Cr ratio of the hippocampus in mTLE was significantly lower in patients with a history of secondary generalized tonic-clonic seizure (SGTCS) than in those without. Our results demonstrate effects of seizures on the hippocampi in neocortical epilepsy and the relation between SGTCS and NAA/Cr of the contralateral hippocampus in mTLE. This proves the presence of a seizure effect on the hippocampus in neocortical epilepsy as well as in mTLE.

Reduced prefrontal N-acetylaspartate in stroke patients with apathy

BACKGROUND

Although substantial numbers of stroke patients suffer from apathy, its causes are still poorly understood. Previous studies suggest that dysfunction of the frontal lobes is implicated in the pathophysiology of motivation. Our aim was to investigate the association between proton magnetic resonance spectroscopy (H1-MRS) measurements in unaffected frontal lobes and apathy in a group of first-time stroke patients.

METHODS

31 patients with a first-time ischemic stroke located outside the frontal lobes and 20 healthy subjects were included in the study. The authors performed single voxel H1-MRS in order to measure the N-acetylaspartate/creatine (NAA)/Cr, glutamate+glutamine (Glx)/Cr, choline (Cho)/Cr and myo-inositol (mI)/Cr ratios in the frontal lobes. Patients were assessed between days 7 and 12 post stroke. Diagnosis of apathy was made on the basis of clinical observation, interview and Apathy Scale.

RESULTS

13 out of 31 patients (42%) demonstrated apathy. Patients with apathy had lower NAA/Cr ratios in the right frontal lobe than non-apathetic subjects. The patient group was divided into two subgroups: Those with left hemisphere strokes, and those with right hemisphere strokes. Of these subjects, significantly lowered NAA/Cr ratios were found in the right hemispheres of apathetic patients in the subgroup with left-sided brain lesions.

CONCLUSIONS

These findings point to the association between apathy and frontal lobe integrity, suggest different reactions of the hemispheres and indicate that changes in the NAA/Cr ratio are related to the apathy.

1H-MR-Spektroskopie

Techniques and methods of clinical (1)H-MR spectroscopy are described in this manuscript. The role of (1)H-MRS in the multimodal focus analysis of temporal lobe epilepsy (TLE) is illustrated with special respect to focus lateralization and differentiation between mesial and lateral (neocortical) TLE. Additionally the application of (1)H-MRS for evaluating postoperative outcome and monitoring conservative antiepileptic treatment schedules is summarized.

Time course of NAA T2 and ADCw in ischaemic stroke patients: 1H MRS imaging and diffusion-weighted MRI

BACKGROUND AND PURPOSE

Proton spectroscopy and quantitative diffusion-weighted imaging (DWI) were used to investigate the pertinence of N-acetyl aspartate (NAA) as a reliable marker of neuronal density in human stroke.

METHODS

The time courses of tissue water apparent diffusion coefficient (ADC(w)) and metabolite T2 were investigated on a plane corresponding to the largest area of cerebral infarction, within and outside the site of infarction in 71 patients with a large cortical middle cerebral artery territory infarction.

RESULTS

Significant reductions are seen in NAA T2 deep within the infarction during the period comprised between 5 and 20 days postinfarction; the relaxation times appearing to normalise several months after stroke. After an acute reduction in ADC(w), the pseudonormalisation of ADC(w) occurs at 8-12 days after the ischaemic insult. The minimum in N-acetyl aspartate T2 relaxation times and the pseudonormalisation of ADC(w) appear to coincide.

CONCLUSIONS

The data suggest that modifications in the behaviour of the observed proton metabolites occur during the period when the vasogenic oedema is formed and cell membrane integrity is lost. For this reason, NAA may not be a reliable marker of neuronal density during this period.

Magnetic resonance spectroscopy in cognitive research

The neurophysiological basis of cognition is relatively unexplained, with most studies reporting weak relationships between cognition and measures of brain function, such as event-related potentials, brain size and cerebral blood flow. Magnetic resonance spectroscopy (MRS) is an in vivo method used to detect neurochemicals within the brain that are relevant to certain brain processes. The most widely used methods are 1H-MRS and 31P-MRS, which detect compounds that contain hydrogen and phosphorus, respectively. Recent studies have shown that the absolute concentrations or ratios of these neurochemicals, in particular N-acetyl aspartate (NAA), which is associated with neuronal viability, correlate with performance on neuropsychological tests or other measures of cognitive function in normal subjects. Many studies in adults and children have shown a relationship between neurometabolite values and cognitive status or extent of cognitive dysfunction in various neurological and neuropsychiatric disorders. We review these studies and conclude that MRS has potential applications for the study of cognitive processes in health and disease and may be used clinically for differential diagnosis, the early detection of pathology and the examination of longitudinal change.

Regional N-acetyl-aspartate level and immunohistochemical damage in the hippocampus after transient forebrain ischemia in gerbils

We investigated changes in regional N-acetyl-aspartate (NAA) levels in the vulnerable CA1 and resistant CA3 areas of the hippocampus after transient forebrain ischemia in gerbils. Under light ether anesthesia, bilateral common carotid arteries of adult male Mongolian gerbils (60-80 g) were occluded for 5 min and reperfused for 7 days. Brains from experimental and control gerbils (n = 4 each) were frozen in situ, and frozen sections (20 microm) were prepared using cryostat (-20 degrees C). After overnight lyophilization, the CA1 and CA3 areas were dissected out separately, weighed (50-200 microg), and the supernatant of the perchloric acid extract was used for assay of NAA using HPLC. Adjacent 10 microm-thick sections were used for immunohistochemical analysis using antiserum against microtubule-associated protein I and II. The preischemic NAA levels were not significantly different between CA1 and CA3 areas. After transient ischemia, a significant (P < 0.01) decrease in the NAA level was observed in the CAI area, but not in the CA3 area of the hippocampus. Immunohistochemical ischemic damage evolved only in the CA1 area. Thus, the decrease of the regional NAA level was associated with development of immunohistochemical neuronal damage.

Induced hippocampal neuron protection in an optimized gerbil ischemia model: insult thresholds for tolerance induction and altered gene expression defined by ischemic depolarization

Preconditioning of hippocampal CA1 neurons was evaluated in a gerbil model of transient global ischemia using extracellular recording of DC potential shifts characteristic of ischemic depolarization to precisely define the duration of both priming and test insults. Brief ischemia resulting in depolarizations of 2.5 to 3.5 minutes consistently induced maximal tolerance (95% protection) against subsequent challenges 2 days later with an approximate doubling of the insult duration required for complete CA1 neuron loss from 6 to 12 minutes depolarization when evaluated 1 week after the test insult. Significant protection persisted at 2 months survival, although the apparent injury threshold regressed to approximately 8 minutes, indicating delayed progression of injury after longer test insults. In situ hybridization was used to evaluate depolarization thresholds for induction of mRNAs encoding the 70 kDa heat shock/stress protein, hsp72, as well as several immediate-early genes (c-fos, c-jun, junB, and junD). Immediate-early genes were prominently expressed after short insults inducing tolerance, whereas appreciable hsp72 induction only occurred after insults approaching the threshold for neuron injury. These results establish an ischemic preconditioning model with the predictability needed for mechanistic studies and demonstrate that prior transcriptional activation of the postischemic heat shock response is not required for expression of delayed tolerance.

N-acetylaspartate to total creatine ratio in the hippocampal CA1 sector after transient cerebral ischemia in gerbils: influence of neuronal elements, reactive gliosis, and tissue atrophy

The authors compared temporal profiles of N-acetylaspartate (NAA) and the NAA/total creatine ratio with neuronal and astrocytic densities and with tissue atrophy in the hippocampal CA1 sector of gerbils after 5-minute bilateral forebrain ischemia and subsequent reperfusion for up to 6 months. The CA1 sector was dissected from 20- micro m lyophilized sections (n = 5) for NAA, phosphocreatine, and creatine assays using high-performance liquid chromatography. Adjacent 10- micro m sections were used for immunohistochemical analysis to follow neuronal and astrocytic responses. The NAA concentration was significantly (P<0.01) decreased after 7 days but leveled off thereafter. The NAA/total creatine (phosphocreatine + creatine) ratio was significantly decreased after 7 days and further decreased (P<0.05) after 6 months. Extensive neuronal damage developed beyond 7 days, while reactive astrogliosis progressed throughout the observation period. There was a good linear correlation (P<0.01) between astroglial density and the NAA/total creatine ratio beyond 7 days. The thickness of the CA1 sector was significantly reduced after 1 month and further reduced after 6 months. Although both NAA level and the NAA/total creatine ratio seemed to be indicators of neuronal damage, the latter could be influenced by reactive astrogliosis with progression of tissue atrophy.

Proton magnetic resonance spectroscopic imaging suggests progressive neuronal damage in human temporal lobe epilepsy

Whether temporal lobe epilepsy (TLE) is the result of an isolated, early injury or whether there is ongoing neuronal damage due to seizures is often debated. We attempted to examine the long-term effect of seizures using proton magnetic resonance spectroscopic imaging (1H-MRSI), which can quantify neuronal loss or dysfunction based on reduced signals from the neuronal marker N-acetylaspartate (NAA). We performed 1H-MRSI in 82 consecutive patients with medically intractable, non-foreign-tissue TLE to determine whether there was a correlation between seizure frequency, type or duration of epilepsy and NAA to creatine ratios (NAA/Cr). Spectroscopic resonance intensities were categorized as to whether they were measured from the temporal lobe ipsilateral or contralateral to the predominant EEG focus. Ipsilateral and contralateral NAA/Cr was negatively correlated with duration of epilepsy. Furthermore, patients with frequent generalized tonic-clonic seizures had lower NAA/Cr than patients with no or rare generalized tonic-clonic seizures. The results suggest that although an early injury may cause asymmetric temporal lobe damage that is present at the onset of epilepsy, generalized seizures may induce additional neuronal damage that progresses over the course of the disease.

[Magnetic resonance imaging in the diagnosis and understanding of the nature of pathologic changes in multiple sclerosis]

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N-Acetylaspartate, a marker of both cellular dysfunction and neuronal loss: its relevance to studies of acute brain injury

To evaluate the contribution of cellular dysfunction and neuronal loss to brain N-acetylaspartate (NAA) depletion, NAA was measured in brain tissue by HPLC and UV detection in rats subjected to cerebral injury, associated or not with cell death. When lesion was induced by intracarotid injection of microspheres, the fall in NAA was related to the degree of embolization and to the severity of brain oedema. When striatal lesion was induced by local injection of malonate, the larger the lesion volume, the higher the NAA depletion. However, reduction of brain oedema and striatal lesion by treatment with the lipophilic iron chelator dipyridyl (20 mg/kg, 1 h before and every 8 h after embolization) and the inducible nitric oxide synthase inhibitor aminoguanidine (100 mg/kg given 1 h before malonate and then every 9 h), respectively, failed to ameliorate the fall in NAA. Moreover, after systemic administration of 3-nitropropionic acid, a marked reversible fall in NAA striatal content was observed despite the lack of tissue necrosis. Overall results show that cellular dysfunction can cause higher reductions in NAA level than neuronal loss, thus making of NAA quantification a potential tool for visualizing the penumbra area in stroke patients.

Evaluation of CA1 damage using single-voxel 1H-MRS and un-biased stereology: Can non-invasive measures of N-acetyl-asparate following global ischemia be used as a reliable measure of neuronal damage?

Global brain ischemia provoked by transient occlusion of the carotid arteries (2VO) in gerbils results in a severe loss of neurons in the hippocampal CA1 region. We measured the concentration of the neuron specific N-acetyl-aspartate, [NAA], in the gerbil dorsal hippocampus by proton MR spectroscopy (1H-MRS) in situ, and HPLC, 4 days after global ischemia. The [NAA] was correlated with graded hippocampus damage scoring and stereologically determined neuronal density. A basal hippocampal [NAA] of 8.37+/-0.10 and 9.81+/-0.44 mmol/l were found from HPLC and 1H-MRS, respectively. HPLC measurements of [NAA] obtained from hippocampus 4 days after 2VO showed a 20% reduction in the [NAA] following 4 min of ischemia (P<0.001). 1H-MRS measurements on gerbils subjected to 4 or 8 min of ischemia showed a similar 24% decline in the [NAA] (P<0.05). Thus, there was correlation between the HPLC and 1H-MRS determined NAA decline. There was also a significant correlation between 1H-MRS [NAA] and the corresponding reduction in CA1 neuronal density (P<0.004). In summary our findings show that single voxel 1H-MRS can be used as a supplement to histological evaluation of neuronal injury in studies after global brain ischemia. Accordingly, volume selective spectroscopy has a potential for assessment of neuroprotective therapeutic compounds/strategies with respect to neuronal rescue for delayed ischemic brain damage.

The significance of bilateral CSI changes for the postoperative outcome in temporal lobe epilepsy

PURPOSE

In a prospective study, we evaluated the significance of preoperative bilateral chemical shift spectroscopy imaging (CSI) changes for the prognosis of postoperative seizure outcome in the surgical treatment of patients with temporal lobe epilepsy (TLE).

METHOD

CSI using multivoxel spectroscopy was performed. Twenty-six consecutive TLE patients scheduled for epilepsy surgery were included. To evaluate the value of the CSI with respect to postoperative seizure outcome, discriminant analysis with ipsilateral and contralateral CSI was performed.

RESULTS

The discriminant analysis showed that the contralateral metabolic changes alone are able to predict seizure outcome whereby 92.3% of cases were correctly classified. Upon comparison of the two groups of seizure-free and non-seizure-free patients with respect to contralateral metabolic changes, the difference proved to be highly significant (paired t test: t = -6.3, df = 24, p < 0.001).

CONCLUSION

Bilateral metabolic CSI changes have a predictive value for the postoperative outcome in patients with TLE. In patients with severe bilateral metabolic changes, poor seizure outcome is a likely result.

Chronic lithium and sodium valproate both decrease the concentration of myo-inositol and increase the concentration of inositol monophosphates in rat brain

One of the mechanisms underlying lithium's efficacy as a mood stabilizer in bipolar disorder has been proposed to be via its effects on the phosphoinositol cycle (PI-cycle), where it is an inhibitor of the enzyme converting inositol monophosphates to myo-inositol. In contrast, sodium valproate, another commonly used mood stabilizer, appears to have no direct effects on this enzyme and was thus believed to have a different mechanism of action. In the present study, high resolution nuclear magnetic resonance (NMR) spectroscopy was used to study the chronic effects of both lithium and sodium valproate on the concentrations of myo-inositol and inositol monophosphates in rat brain. As predicted, lithium-treated rats exhibited a significant increase in the concentration of inositol monophosphates and a significant decrease in myo-inositol concentration compared to saline-treated controls. However, unexpectedly, sodium valproate administration produced exactly the same results as lithium administration. These novel findings suggest that both lithium and sodium valproate may share a common mechanism of action in the treatment of bipolar disorder via actions on the PI-cycle.

Proton magnetic resonance spectroscopic imaging studies in patients with newly diagnosed partial epilepsy

PURPOSE

To assess whether the N-acetyl aspartate (NAA) to creatine ratio (NAA/Cr) is abnormally low at the onset of epilepsy and whether successful treatment of seizures with antiepileptic drugs is sufficient for normalization of NAA/Cr.

PATIENTS AND METHODS

Proton magnetic resonance spectroscopic imaging (1H-MRSI) was used to measure NAA/Cr in temporal lobes of eight patients with newly diagnosed epilepsy before or soon after starting medication. Six patients had follow-up 1H-MRSI examinations 7 months later. Clinical pattern of the seizures and the EEG findings suggested partial seizures in all and TLE in five patients. None of the patients had lesional epilepsy according to magnetic resonance imaging.

RESULTS

Initial 1H-MRSI of the temporal lobes showed significantly low NAA/Cr values in five of eight patients. Five of six patients who had follow-up 1H-MRSI were seizure-free after using medication; the remaining patient did not take medication and continued to experience occasional auras. Wilcoxon rank sign comparison of NAA/Cr on initial 1H-MRSI examination and follow-up 1H-MRSIs showed no significant difference (Z = 135, p = 0.893, 2-tailed) for five seizure-free patients.

CONCLUSIONS

Neuronal dysfunction is present at an early stage of the epileptic process. NAA/Cr recovery in seizure-free patients controlled with antiepileptic drugs is less evident, compared with successful surgical treatment. Thus, absence of seizures is not necessarily coupled with NAA/Cr improvement and observed variable response warrants further investigation.

Preconditioning the Brain and Heart: Implications for Cardiac Surgery

Despite many recent advances in emboli detection, aortic imaging, myocardial preservation, and perfusion equipment, ischemic injury to the heart and brain remains a serious complications after cardiac surgery. Hypoperfusion (particularly in the heart) and microem boli (particularly in the brain) during cardiopulmonary bypass constitute the etiology of ischemia. Although hypothermia has traditionally been the mainstay for systemic protection from transient ischemia, there has been a general trend to accept warmer heart and core temperatures during bypass, which increases the poten tial for ischemic injury to various organs. This article discusses recent advances in the understanding of myocardial and brain preconditioning and their poten tial role to provide additional protection during cardiac surgery.

Spatial extent of neuronal metabolic dysfunction measured by proton MR spectroscopic imaging in patients with localization-related epilepsy

PURPOSE

To assess the spatial extent of the decrease in the neuronal marker N-acetyl-aspartate (NAA) relative to creatine (Cr) in patients with localization-related epilepsy, and to assess clinical differences between patients with and without widespread NAA/Cr reduction.

METHODS

We studied 51 patients with localization-related epilepsy. Patients were divided into three groups according to the EEG investigation: (a) temporal lobe epilepsy (TLE, n = 21), (b) extratemporal lobe epilepsy (extra-TLE, n = 20), and (c) multilobar epilepsy (patients with a wider epileptogenic zone, n = 10). We acquired proton magnetic resonance (MR) spectrocopic imaging (1H-MRSI) of temporal and frontocentroparietal regions in separate examinations for both patients and controls. NAA/Cr values 2 standard deviations below the mean of normal controls were considered abnormal.

RESULTS

Twenty-three (45%) patients including 12 with TLE had normal MR imaging including volumetric studies of the hippocampus. Forty-nine (96%) patients had low NAA/Cr, indicating neuronal dysfunction in either temporal and/or extratemporal 1H-MRSIs; 38% of patients with TLE and 50% of patients with extra-TLE also had NAA/Cr reduction outside the clinical and EEG-defined primary epileptogenic area. The NAA/Cr reduction was more often widespread in the multilobar group [six (60%) of 10] than in temporal or extratemporal groups [five (31%) of 16]. Nonparametric tests of (a) seizure duration, (b) seizure frequency, and (c) lifetime estimated seizures showed no statistically significant difference (p > 0.05) for TLE and extra-TLE patients with or without NAA/Cr reduction outside the seizure focus.

CONCLUSIONS

Of patients with localization-related epilepsy, 40-50% have neuronal metabolic dysfunction that extends beyond the epileptogenic zone defined by clinical-EEG and/or the structural abnormality defined by MRI.

Correlation between N-acetylaspartate levels and histopathologic changes in cortical infarcts of mice after middle cerebral artery occlusion

The aim of the present study was to evaluate the use of the endogenous neuronal compound N-acetylaspartate (NAA) as a marker of neuronal damage after focal cerebral ischemia in mice. After occlusion of the middle cerebral artery (MCAO) the ischemic cortex was sampled, guided by 2,3,5-triphenyltetrazolium chloride (TTC) staining, and the NAA concentration was measured by high-pressure liquid chromatography (HPLC). Conventional histology and immunohistological methods using antibodies against neuron-specific enolase (NSE), neurofilaments (NF), synaptophysin, glial fibrillary acidic protein (GFAP), and carbodiamide-linked NAA and N-acetylaspartylglutamate (NAAG). The level of NAA rapidly declined to 50% and 20% of control levels in infarcted tissue after 6 hours and 24 hours, respectively. No further decrease was observed during the observation period of 1 week. Within the first 6 hours the number of normal-appearing neurons in the infarcted cortical tissue decreased to 70% of control, of which the majority were eosinophilic. After 24 hours almost no normal-appearing neurons were seen. The number of eosinophilic neurons decreased steadily to virtually zero after 7 days. The number of immunopositive cells in the NSE, NF, and synaptophysin staining within the infarct was progressively reduced, and after 3 to 7 days the immunoreactions were confined to discrete granulomatous structures in the center of the infarct, which otherwise was infested with macrophages. This granulomatous material also stained positive for NAA. The number of cells with positive GFAP immunoreactions progressively increased in the circumference of the infarct. They also showed increased immunoreaction against NAA and NSE. The study shows that the level of NAA 7 days after ischemia does not decline to zero but remains at 10% to 20% of control values. The fact NAA is trapped in cell debris and NAA immunoreactivity is observed in the peri-infarct areas restricts its use as a marker of neuronal density.

Hypothermia-induced ischemic tolerance

Delayed resistance to ischemic injury can be induced by a variety of conditioning stimuli. This phenomenon, known as delayed ischemic tolerance, is initiated over several hours or a day, and can persist for up to a week or more. The present paper describes recent experiments in which transient hypothermia was used as a conditioning stimulus to induce ischemic tolerance. A brief period of hypothermia administered 6 to 48 hours prior to focal ischemia reduces subsequent cerebral infarction. Hypothermia-induced ischemic tolerance is reversed by 7 days postconditioning, and is blocked by the protein synthesis inhibitor anisomycin. Electrophysiological studies utilizing in vitro brain slices demonstrate that hypoxic damage to synaptic responses is reduced in slices prepared from hypothermia-preconditioned animals. Taken together, these findings indicate that transient hypothermia induces tolerance in the brain parenchyma, and that increased expression of one or more gene products contributes to this phenomenon. Inasmuch as hypothermia is already an approved clinical procedure for intraischemic and postischemic therapy, it is possible that hypothermia could provide a clinically useful conditioning stimulus for limiting injury elicited by anticipated periods of ischemia.

Characterization of tissue damage in multiple sclerosis by nuclear magnetic resonance

Nuclear magnetic resonance (NMR) imaging is an established diagnostic medium to diagnose multiple sclerosis (MS). In clinically stable MS patients, NMR detects silent disease activity, which is the reason why it is being used to monitor treatment trials, in which it serves as a secondary outcome parameter. The absence of a clear correlation with clinical disability, the so-called 'clinico-radiological' paradox, and the poor predictive value of NMR prohibit the use of NMR as a primary outcome parameter in clinical trials. This is--among others--a result of the limited histopathological specificity of conventional, or 'T2-weighted' imaging, the most commonly used NMR technique. In this paper we review additional NMR techniques with higher tissue specificity, most of which show marked heterogeneity within NMR-visible lesions, reflecting histopathological heterogeneity. Gadolinium enhancement identifies the early inflammatory phase of lesion development, with active phagocytosis by macrophages. Persistently hypointense lesions on T1-weighted images ('black holes') relate to axonal loss and matrix destruction, and show a better correlation with clinical disability. Marked prolongation of T1 relaxation time correlates with enlargement of the extracellular space, which occurs as a result of axonal loss or oedema. Axonal viability can also be measured using the concentration of N-acetyl aspartate (NAA) using NMR spectroscopy; this technique is also capable of showing lactate and mobile lipids in lesions with active macrophages. The multi-exponential behaviour of T2 relaxation time in brain white matter provides a tool to monitor the myelin water component in MS lesions (short T2 component) as well as the expansion of the extracellular space (long T2 component). Chemical exchange with macromolecules (e.g. myelin) can be measured using magnetization transfer imaging, and correlates with demyelination, axonal loss and matrix destruction. Increased water diffusion has been found in MS lesions (relating to oedema and an expanded extracellular space) and a loss of anisotropy may indicate a loss of fibre orientation (compatible with demyelination). Apart from the histopathological heterogeneity within focal MS lesions, the normal-appearing white matter shows definite abnormalities with all quantifiable NMR techniques. A decrease in the concentration of NAA, decreased magnetization transfer values and prolonged T1 relaxation time values are probably all related to microscopic abnormalities, including axonal damage. This 'invisible' lesion load may constitute a significant proportion of the total lesion load but is not visible on conventional NMR. Similarly, mechanisms for clinical recovery exist, which are not distinguished using MR imaging. Therefore, it is highly unlikely that the clinico-radiological paradox will ever be solved completely. However, NMR provides an opportunity to sequentially measure tissue changes in vivo. Using MR parameters with (presumed) histopathological specificity, the development of (irreversible) tissue damage can be monitored, which perhaps allows the identification of factors that determine lesional outcome in MS. Since the absence of severe tissue destruction is prognostically favourable, NMR monitoring of the extent to which such changes can be prevented by treatment will ultimately benefit the selection of future treatment strategies.