Non-invasive neurochemical analysis of focal excitotoxic lesions in models of neurodegenerative illness using spectroscopic imaging

Application of 1H NMR spectroscopy to the metabolic phenotyping of rodent brain extracts: A metabonomic study of gut microbial influence on host brain metabolism

¹H NMR Spectroscopy has been applied to determine the neurochemical profiles of brain extracts from the frontal cortex and hippocampal regions of germ free and normal mice and rats. The results revealed a number of differences between germ free (GF) and conventional (CV) rats or specific pathogen-free (SPF) mice with microbiome-associated metabolic variation found to be both species- and region-dependent. In the mouse, the GF frontal cortex contained lower amounts of creatine, N-acetyl-aspartate (NAA), glycerophosphocholine and lactate, but greater amounts of choline compared to that of specific pathogen free (SPF) mice. In the hippocampus, the GF mice had greater creatine, NAA, lactate and taurine content compared to those of the SPF animals, but lower relative quantities of succinate and an unidentified lipid-related component. The GF rat frontal cortex contained higher relative quantities of lactate, creatine and NAA compared to the CV animals whilst the GF hippocampus was characterized by higher taurine and phosphocholine concentrations and lower quantities of NAA, N-acetylaspartylglutamate and choline compared to the CV animals. Of note is that, in both rat and mouse brain extracts, concentrations of hippocampal taurine were found to be greater in the absence of an established microbiome. The results provide further evidence that brain biochemistry can be influenced by gut microbial status, specifically metabolites involved in energy metabolism demonstrating biochemical dialogue between the microbiome and brain.

Quantification of neurovascular protection following repetitive hypoxic preconditioning and transient middle cerebral artery occlusion in mice

Experimental animal models of stroke are invaluable tools for understanding stroke pathology and developing more effective treatment strategies. A 2 week protocol for repetitive hypoxic preconditioning (RHP) induces long-term protection against central nervous system (CNS) injury in a mouse model of focal ischemic stroke. RHP consists of 9 stochastic exposures to hypoxia that vary in both duration (2 or 4 hr) and intensity (8% and 11% O2). RHP reduces infarct volumes, blood-brain barrier (BBB) disruption, and the post-stroke inflammatory response for weeks following the last exposure to hypoxia, suggesting a long-term induction of an endogenous CNS-protective phenotype. The methodology for the dual quantification of infarct volume and BBB disruption is effective in assessing neurovascular protection in mice with RHP or other putative neuroprotectants. Adult male Swiss Webster mice were preconditioned by RHP or duration-equivalent exposures to 21% O2 (i.e. room air). A 60 min transient middle cerebral artery occlusion (tMCAo) was induced 2 weeks following the last hypoxic exposure. Both the occlusion and reperfusion were confirmed by transcranial laser Doppler flowmetry. Twenty-two hr after reperfusion, Evans Blue (EB) was intravenously administered through a tail vein injection. 2 hr later, animals were sacrificed by isoflurane overdose and brain sections were stained with 2,3,5- triphenyltetrazolium chloride (TTC). Infarcts volumes were then quantified. Next, EB was extracted from the tissue over 48 hr to determine BBB disruption after tMCAo. In summary, RHP is a simple protocol that can be replicated, with minimal cost, to induce long-term endogenous neurovascular protection from stroke injury in mice, with the translational potential for other CNS-based and systemic pro-inflammatory disease states.

The effects of aging, housing and ibuprofen treatment on brain neurochemistry in a triple transgene Alzheimer's disease mouse model using magnetic resonance spectroscopy and imaging

We investigated a triple transgene Alzheimer's disease (AD) mouse model that recapitulates many of the neurochemical, anatomic, pathologic and behavioral defects seen in human AD. We studied the mice as a function of age and brain region and investigated potential therapy with the non-steroidal anti-inflammatory drug ibuprofen. Magnetic resonance spectroscopy (MRS) showed alterations characteristic of AD (i.e. increased myo-inositol and decreased N-acetylaspartate (NAA)). Mice at 6 months of age showed an increase in myo-inositol in the hippocampus at a time when the Aβ is intracellular, but not in amygdala or cortex. Myo-inositol increased as a function of age in the amygdala, cortex and striatum while NAA decreased only in the hippocampus and cortex at 17-23 months of age. Ibuprofen protected the increase of myo-inositol at six months of age in the hippocampus, but had no effect at 17-23 months of age (a time when Aβ is extracellular). In vivo MRI and MRS showed that at 17-23 months of age there was a significant protective effect of ibuprofen on hippocampal volume and NAA loss. Together, these data show the following: the increase in myo-inositol occurs before the decrease in NAA in hippocampus but not cortex; the hippocampus shows earlier changes than does the amygdale or cortex consistent with earlier deposition of Aβ40-42 in the hippocampus and ibuprofen protects against multiple components of the AD pathology. These data also show a profound effect of housing on this particular mouse model.

Metabolic disturbances in diseases with neurological involvement

Degeneration of specific neuronal populations and progressive nervous system dysfunction characterize neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. These findings are also reported in inherited diseases such as phenylketonuria and glutaric aciduria type I. The involvement of mitochondrial dysfunction in these diseases was reported, elicited by genetic alterations, exogenous toxins or buildup of toxic metabolites. In this review we shall discuss some metabolic alterations related to the pathophysiology of diseases with neurological involvement and aging process. These findings may help identifying early disease biomarkers and lead to more effective therapies to improve the quality of life of the patients affected by these devastating illnesses.

An in vivo ultrahigh field 14.1 T (1) H-MRS study on 6-OHDA and α-synuclein-based rat models of Parkinson's disease: GABA as an early disease marker

The detection of Parkinson's disease (PD) in its preclinical stages prior to outright neurodegeneration is essential to the development of neuroprotective therapies and could reduce the number of misdiagnosed patients. However, early diagnosis is currently hampered by lack of reliable biomarkers. (1) H magnetic resonance spectroscopy (MRS) offers a noninvasive measure of brain metabolite levels that allows the identification of such potential biomarkers. This study aimed at using MRS on an ultrahigh field 14.1 T magnet to explore the striatal metabolic changes occurring in two different rat models of the disease. Rats lesioned by the injection of 6-hydroxydopamine (6-OHDA) in the medial-forebrain bundle were used to model a complete nigrostriatal lesion while a genetic model based on the nigral injection of an adeno-associated viral (AAV) vector coding for the human α-synuclein was used to model a progressive neurodegeneration and dopaminergic neuron dysfunction, thereby replicating conditions closer to early pathological stages of PD. MRS measurements in the striatum of the 6-OHDA rats revealed significant decreases in glutamate and N-acetyl-aspartate levels and a significant increase in GABA level in the ipsilateral hemisphere compared with the contralateral one, while the αSyn overexpressing rats showed a significant increase in the GABA striatal level only. Therefore, we conclude that MRS measurements of striatal GABA levels could allow for the detection of early nigrostriatal defects prior to outright neurodegeneration and, as such, offers great potential as a sensitive biomarker of presymptomatic PD.

Kynurenic acid and kynurenine aminotransferases in retinal aging and neurodegeneration

The kynurenine aminotransferases (KATs) KAT I and KAT II are pivotal to the synthesis of kynurenic acid (KYNA), the only known endogenous glutamate receptor antagonist and neuroprotectant. KAT I and II have been found in avian, rodent, and human retina. Expression of KAT I in Müller cell endfeet and KAT II in retinal ganglion cells has been documented. Developmental changes in KAT expression and KYNA concentration in the avian and rodent retina have also been found. Studies of retinal neurodegeneration have shown alterations in KYNA synthesis in the retina in response to retinal ganglion cell loss. In DBA/2J mice, a model of ocular hypertension, an age-dependent decrease of retinal KYNA and KATs was found. In the corpora amylacea in the human retina intensive KAT I and II immunoreactivity was demonstrated. In summary, these findings point to the potential involvement of KYNA in the mechanisms of retinal aging and neurodegeneration.

Brief mitochondrial inhibition causes lasting changes in motor behavior and corticostriatal synaptic physiology in the Fischer 344 rat

The striatum is particularly vulnerable to mitochondrial dysfunction and this problem is linked to pathology created by environmental neurotoxins, stimulants like amphetamine, and metabolic disease and ischemia. We studied the course of recovery following a single systemic injection of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP) and found 3-NP caused lasting changes in motor behavior that were associated with altered activity-dependent plasticity at corticostriatal synapses in Fischer 344 rats. The changes in synapse behavior varied with the time after exposure to the 3-NP injection. The earliest time point studied, 24h after 3-NP, revealed 3-NP-induced an exaggeration of D1 Dopamine (DA) receptor dependent long-term potentiation (LTP) that reversed to normal by 48 h post-3-NP exposure. Thereafter, the likelihood and degree of inducing D2 DA receptor dependent long-term depression (LTD) gradually increased, relative to saline controls, peaking at 1 month after the 3-NP exposure. NMDA receptor binding did not change over the same post 3-NP time points. These data indicate even brief exposure to 3-NP can have lasting behavioral effects mediated by changes in the way DA and glutamate synapses interact.

Multinuclear magnetic resonance spectroscopy for in vivo assessment of mitochondrial dysfunction in Parkinson's disease

Parkinson's disease (PD) is a common and often devastating neurodegenerative disease affecting up to one million individuals in the United States alone. Multiple lines of evidence support mitochondrial dysfunction as a primary or secondary event in PD pathogenesis; a better understanding, therefore, of how mitochondrial function is altered in vivo in brain tissue in PD is a critical step toward developing potential PD biomarkers. In vivo study of mitochondrial metabolism in human subjects has previously been technically challenging. However, proton and phosphorus magnetic resonance spectroscopy ((1)H and (31)P MRS) are powerful noninvasive techniques that allow evaluation in vivo of lactate, a marker of anaerobic glycolysis, and high energy phosphates, such as adenosine triphosphate and phosphocreatine, directly reflecting mitochondrial function. This article reviews previous (1)H and (31)P MRS studies in PD, which demonstrate metabolic abnormalities consistent with mitochondrial dysfunction, and then presents recent (1)H MRS data revealing abnormally elevated lactate levels in PD subjects.

Huntington's disease and dentatorubral-pallidoluysian atrophy: proteins, pathogenesis and pathology

Each of the glutamine repeat neurodegenerative diseases has a particular pattern of pathology largely restricted to the CNS. However, there is considerable overlap among the regions affected, suggesting that the diseases share pathogenic mechanisms, presumably involving the glutamine repeats. We focus on Huntington's disease (HD) and Dentatorubral-pallidoluysian atrophy (DRPLA) as models for this family of diseases, since they have striking similarities and also notable differences in their clinical features and pathology. We review the pattern of pathology in adult and juvenile onset cases. Despite selective pathology, the disease genes and their protein products (huntingtin and atrophin-1) are widely expressed. This presents a central problem for all the glutamine repeat diseases-how do widely expressed gene products give rise to restricted pathology? The pathogenic effects are believed to occur via a "gain of function" mechanism at the protein level. Mechanisms of cell death may include excitotoxicity, metabolic toxicity, apoptosis, and free radical stress. Emerging data indicate that huntingtin and atrophin-1 may have distinct protein interactions. The specific interaction partners may help explain the selective pathology of these diseases.

Subfield-specific loss of hippocampal N-acetyl aspartate in temporal lobe epilepsy

PURPOSE

In patients with mesial temporal lobe epilepsy (MTLE) it remains an unresolved issue whether the interictal decrease in N-acetyl aspartate (NAA) detected by proton magnetic resonance spectroscopy ((1)H-MRS) reflects the epilepsy-associated loss of hippocampal pyramidal neurons or metabolic dysfunction.

METHODS

To address this problem, we applied high-resolution (1)H-MRS at 14.1 Tesla to measure metabolite concentrations in ex vivo tissue slices from three hippocampal subfields (CA1, CA3, dentate gyrus) as well as from the parahippocampal region of 12 patients with MTLE.

RESULTS

In contrast to four patients with lesion-caused MTLE, we found a large variance of NAA concentrations in the individual hippocampal regions of patients with Ammon's horn sclerosis (AHS). Specifically, in subfield CA3 of AHS patients despite of a moderate preservation of neuronal cell densities the concentration of NAA was significantly lowered, while the concentrations of lactate, glucose, and succinate were elevated. We suggest that these subfield-specific alterations of metabolite concentrations in AHS are very likely caused by impairment of mitochondrial function and not related to neuronal cell loss.

CONCLUSIONS

A subfield-specific impairment of energy metabolism is the probable cause for lowered NAA concentrations in sclerotic hippocampi of MTLE patients.

Application of MRS to mouse models of neurodegenerative illness

The rapid development of transgenic mouse models of neurodegenerative diseases, in parallel with the rapidly expanding growth of MR techniques for assessing in vivo, non-invasive, neurochemistry, offers the potential to develop novel markers of disease progression and therapy. In this review we discuss the interpretation and utility of MRS for the study of these transgenic mouse and rodent models of neurodegenerative diseases such as Alzheimer's (AD), Huntington's (HD) and Parkinson's disease (PD). MRS studies can provide a wealth of information on various facets of in vivo neurochemistry, including neuronal health, gliosis, osmoregulation, energy metabolism, neuronal-glial cycling, and molecular synthesis rates. These data provide information on the etiology, natural history and therapy of these diseases. Mouse models enable longitudinal studies with useful time frames for evaluation of neuroprotection and therapeutic interventions using many of the potential MRS markers. In addition, the ability to manipulate the genome in these models allows better mechanistic understanding of the roles of the observable neurochemicals, such as N-acetylaspartate, in the brain. The argument is made that use of MRS, combined with correlative histology and other MRI techniques, will enable objective markers with which potential therapies can be followed in a quantitative fashion.

The application of NMR-based metabonomics in neurological disorders

Advances in postgenomic technologies have radically changed the information output from complex biological systems, generating vast amounts of high complexity data that can be interpreted by means of chemometric and bioinformatic methods to achieve disease diagnosis and prognosis. High-resolution nuclear magnetic resonance (NMR) spectroscopy of biofluids such as plasma, cerebrospinal fluid (CSF), and urine can generate robust, interpretable metabolic fingerprints that contain latent information relating to physiological or pathological status. This technology has been successfully applied to both preclinical and clinical studies of neurodegenerative diseases such as Huntington's disease, muscular dystrophy, and cerebellar ataxia. An extension of this technology, (1)H magic-angle-spinning (HRMAS) NMR spectroscopy, can be used to generate metabolic information on small intact tissue samples, providing a metabolic link between metabolic profiling of biofluids and histology. In this review we provide a summary of high-resolution NMR studies in neurodegenerative disease and explore the potential of metabonomics in evaluating disease progression with respect to therapeutic intervention.

H MRS identifies lactate rise in the striatum of MPTP-treated C57BL/6 mice

Mitochondrial dysfunction has been implicated in the death of nigrostriatal dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated experimental models of Parkinson's disease (PD). Here we utilized proton magnetic resonance spectroscopy ((1)H MRS) to identify changes in energy metabolism in the striatum of MPTP-treated C57BL/6 mice. Remarkable increases in lactate/creatine (Lac/Cr) ratio were observed at 2 h and then quickly returned to about the basal level by 7 h after injection of MPTP. Neurochemical and Western blot analyses revealed that dopamine contents and protein levels of tyrosine hydroxylase and dopamine transporter in the striatum were profoundly decreased at 3 days after MPTP treatment. Pretreatment with deprenyl, a monoamine oxidase B inhibitor, or GBR-12909, a dopamine uptake inhibitor, almost completely attenuated both the increases in striatal Lac/Cr ratio and the subsequent loss of dopaminergic nerve terminals in MPTP-treated mice. The present study indicates that (1)H MRS is a sensitive measure of biochemical alterations of the brain in a mouse model of PD, and further shows that the increases in striatal Lac/Cr ratio induced by MPTP may be associated with mitochondrial energy crisis, followed by dopaminergic neurotoxicity.

Hypothesis of the postconcussive vulnerable brain: experimental evidence of its metabolic occurrence

OBJECTIVE

We evaluated the effects of two consecutive concussive injuries on brain energy metabolism and N-acetylaspartate (NAA) to investigate how the temporal interval between traumatic events influences overall injury severity.

METHODS

Rats were injured to induce diffuse traumatic brain injury (TBI) (mild, 450 g/1 m; severe, 450 g/2 m). In two groups, two mild TBIs were delivered in 3- or 5-day intervals. Three additional animal groups were used: single mild TBI, single severe TBI, and sham. All animals were killed 48 hours postinjury. Adenosine 5'-triphosphate (ATP), adenosine diphosphate, and NAA concentrations were analyzed with high-performance liquid chromatography on deproteinized whole brain extracts.

RESULTS

In control animals, the NAA concentration was 9.17 +/- 0.38 micromol/g wet weight, the ATP concentration was 2.25 +/- 0.21 micromol/g wet weight, and the ATP-to-adenosine diphosphate ratio was 9.38 +/- 1.23. These concentrations decreased to 6.68 +/- 1.12 micromol/g wet weight, 1.68 +/- 0.24 micromol/g wet weight, and 6.10 +/- 1.21 micromol/g wet weight, respectively, in rats that received two mild TBIs at a 5-day interval (P < 0.01; not different from results in rats with single mild TBI). When a second TBI was delivered after 3 days, the NAA concentration was 3.86 +/- 0.53 micromol/g wet weight, the ATP concentration was 1.11 +/- 0.18 micromol/g wet weight, and the ATP-to-adenosine diphosphate ratio was 2.64 +/- 0.43 (P < 0.001 versus both controls and 3-day interval; not different from rats receiving a single severe TBI).

CONCLUSION

The biochemical modification severity in double TBI is dependent on the interval between traumatic events, which demonstrates the metabolic state of the vulnerable brain after mild TBI. These data support the hypothesis of the application of proton magnetic resonance spectroscopy to measure NAA as a possible tool to monitor the full recovery of brain metabolic functions in the clinical setting, particularly in sports medicine.

Neurochemical and oedematous changes in 1,3-dinitrobenzene-induced astroglial injury in rat brain from a 1H-nuclear magnetic resonance perspective

1,3-Dinitrobenzene (1,3-DNB), an intermediate used in the chemical industry, has toxic effects in the brain and testes. It produces focal lesions with marked astroglial necrosis in the rat brain upon repeated administration. Astrocytic death occurs in parallel with elevated local blood flow and is followed by damage to the cerebral vasculature and neurones. (1)H-nuclear magnetic resonance spectroscopic analysis before the onset of astrocytic damage, showed a global elevation of lactate, whereas choline containing compounds increased in the non-vulnerable cerebral cortex, yet decreased in the vulnerable brainstem. Similarly, glutamate increased in the cerebral cortex, cerebellum and midbrain, but decreased in the susceptible brainstem. In vivo T2-weighted NMR imaging showed high signal intensities in brain nuclei shown to develop astroglial loss by conventional neuropathology at 24 hours after completion of dosing, but not at 6-10 hours. Hence the early neurochemical changes in susceptible areas contribute to the aetiology of degeneration, and those seen elsewhere may represent adaptive responses dependent on the particular phenotype of different cell groups and underlying metabolic relationships.

3-Nitropropionic acid: a mitochondrial toxin to uncover physiopathological mechanisms underlying striatal degeneration in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder caused by a mutation in the gene encoding Huntingtin. The mechanisms underlying the preferential degeneration of the striatum, the most striking neuropathological change in HD, are unknown. Of those probably involved, mitochondrial defects might play an important role. The behavioural and anatomical similarities found between HD and models using the mitochondrial toxin 3-nitropropionic acid (3NP) in rats and primates support this hypothesis. Here, we discuss the recently identified mechanisms of 3NP-induced striatal degeneration. Two types of important factor have been identified. The first are the 'executioner' components that have direct roles in cell death, such as c-Jun N-terminal kinase and Ca2+-activated protease calpains. The second are 'environmental' factors, such as glutamate, dopamine and adenosine, which modulate the striatal degeneration induced by 3NP. Interestingly, these recent studies support the hypothesis that 3NP and mutated Huntingtin have certain mechanisms of toxicity in common, suggesting that the use of 3NP might give new insights into the pathogenesis of HD. Research on 3NP provides additional proof that the neurochemical environment of a given neurone can determine its preferential vulnerability in neurodegenerative diseases.

Effect of coenzyme Q10 and vitamin E on brain energy metabolism in the animal model of Huntington's disease

The neuropathological and clinical symptoms of Huntington's disease (HD) can be simulated in animal model with systemic administration of 3-nitropropionic acid (3-NP). Energy defects in HD could be ameliorated by administration of coenzyme Q(10) (CoQ(10)), creatine, or nicotinamid. We studied the activity of creatine kinase (CK) and the function of mitochondrial respiratory chain in the brain of aged rats administered with 3-NP with and without previous application of antioxidants CoQ(10)+vitamin E. We used dynamic and steady-state methods of in vivo phosphorus magnetic resonance spectroscopy ((31)P MRS) for determination of the pseudo-first order rate constant (k(for)) of the forward CK reaction, the phosphocreatine (PCr) to adenosinetriphosphate (ATP) ratio, intracellular pH(i) and Mg(i)(2+) content in the brain. The respiratory chain function of isolated mitochondria was assessed polarographically; the concentration of CoQ(10) and alpha-tocopherol by HPLC. We found significant elevation of k(for) in brains of 3-NP rats, reflecting increased rate of CK reaction in cytosol. The function of respiratory chain in the presence of succinate was severely diminished. The activity of cytochromeoxidase and mitochondrial concentration of CoQ(10) was unaltered; tissue content of CoQ(10) was decreased in 3-NP rats. Antioxidants CoQ(10)+vitamin E prevented increase of k(for) and the decrease of CoQ(10) content in brain tissue, but were ineffective to prevent the decline of respiratory chain function. We suppose that increased activity of CK system could be compensatory to decreased mitochondrial ATP production, and CoQ(10)+vitamin E could prevent the increase of k(for) after 3-NP treatment likely by activity of CoQ(10) outside the mitochondria. Results of our experiments contributed to elucidation of mechanism of beneficial effect of CoQ(10) administration in HD and showed that the rate constant of CK is a sensitive indicator of brain energy disorder reflecting therapeutic effect of drugs that could be used as a new in vivo biomarker of neurodegenerative diseases.

Behavioral alterations in Lewis rats following two-day continuous 3-nitropropionic acid administration

The mitochondrial toxin, 3-nitropropionic acid (3-NP), produces motor dysfunction and striatal atrophy in rats. However, rat strain and method of administration may contribute to variability in the deficits caused by 3-NP toxicity. To evaluate this, changes in nocturnal spontaneous locomotor activity from chronic administration of 3-NP using an osmotic mini pump, were examined in the Lewis rats. Lewis rats were treated with 3-NP or saline for 2 days and behavior was tested daily for a 15 day period. Animals receiving 3-NP displayed significantly less spontaneous activity than animals in the saline group. 3-NP treated animals also weighed significantly less when compared to saline treated animals. These results demonstrate that even though there were no significant alterations in overt anatomical pathology, even short-term exposure to 3-NP produced significant effects. This short-term administration may present a potential paradigm for examination of sub-threshold neurotoxicity.

Age-dependent biphasic changes in ischemic sensitivity in the striatum of Huntington's disease R6/2 transgenic mice

We used the oxygen/glucose deprivation (OGD) model of ischemia in corticostriatal brain slices to test the hypothesis that metabolic deficiencies in R6/2 transgenic Huntington's disease (HD) mice will impair their recovery from an ischemic challenge. Corticostriatal extracellular field excitatory postsynaptic potentials (fEPSPs) were evoked in transgenic and wild-type (WT) mice in three age groups: 3-4 wk, before the overt behavioral phenotype develops; 5-9 wk, as overt behavioral symptoms begin; and 10-15 wk when symptoms were most severe. OGD for 8 min completely and reversibly inhibited fEPSPs. Although responses of 3-4 wk WTs showed a tolerance to ischemia and recovered rapidly, ischemic sensitivity developed progressively; at 5-9 and 10-15 wk, responses recovered more slowly from OGD. In contrast, although 3-4 wk R6/2 transgenic fEPSPs showed significantly more ischemic sensitivity than their WT counterparts, the R6/2 fEPSPs maintained a relative tolerance to ischemia at 5-9 and 10-15 wk. As a result, a "crossover" point occurred, roughly coinciding with the development of the overt behavioral phenotype (5-9 wk), after which time R6/2 fEPSPs were significantly more resistant to ischemia than WT responses. The increased ischemic sensitivity in 3-4 wk R6/2 responses was not due to excessive glutamate release during OGD as it persisted in the presence of the glutamate receptor antagonist kynurenic acid (1 mM). Although the mechanism for development of ischemic resistance in R6/2 transgenics remains unknown, it correlates with metabolic and biochemical changes described in this model and in HD patients.

The Protective Effect of Cyclosporin A upon N-Acetylaspartate and Mitochondrial Dysfunction following Experimental Diffuse Traumatic Brain Injury

Pre- and post-injury Cyclosporin A (CsA) administration has shown neuroprotective properties by ameliorating mitochondrial damage. The aim of this study was to assess the effect of CsA upon N-acetylaspartate (NAA) reduction and ATP loss, two sensitive markers of mitochondrial dysfunction and bioenergetic impairment. Adult male Sprague-Dawley rats were exposed to impact acceleration traumatic brain injury (2 m/450 g) and randomized into the following experimental groups: intrathecal CsA/vehicle treated (n = 12), intravenous CsA/vehicle treated (n = 18) and sham (n = 12). Intrathecal treatment consisted of post-injury (30 min) cisternal bolus of CsA or Vehicle (0.15 mL, 10 mg/kg). Intravenous administration consisted of 30 min post-injury continuous 1 hour infusion of either 20 or 35 mg/kg CsA or Vehicle. Quantitative HPLC analysis of whole brain samples was performed 6 h post-injury for levels of NAA and ATP. Following intrathecal delivery CsA demonstrated significant neuroprotection blunting a 30% NAA reduction (p < 0.001) and restoring 26% of the ATP loss (p < 0.005). The 20 mg/kg intravenous dose failed to ameliorate the biochemical damages while the 35 mg/kg dosage showed 36% NAA recovery and 39% ATP restoration (p < 0.001). In conclusion, CsA is capable of restoring ATP and blunting NAA reduction. Intravenous infusion of 35 mg/kg appears to be the optimal therapeutic strategy in this model. These findings contribute to the notion that CsA achieves neuroprotection, preserving mitochondrial function, and provides a rationale for the assessment of CsA in the clinical setting where MR spectroscopy can monitor NAA and ATP in brain-injured patients.

Cortical spreading depression augments kynurenate levels and reduces malonate toxicity in the rat cortex

Cortical spreading depression (CSD) is characterized by slowly propagating neuronal and astrocytic depolarization, resulting in transient, heightened resistance to subsequent neuronal injury. This study was designed to examine a possible role of the endogenous neuroprotective agent kynurenate (KYNA) in this phenomenon. Unilateral, consecutive CSDs, induced by topical application of 2 M KCl to the cortical surface of adult male rats, resulted in an ipsilateral increase (201-222% compared to controls) in KYNA levels, which was observed in the frontal, parietal and occipital cortex but not in other brain areas. This effect peaked on day 3 after CSD, and KYNA levels returned to normal on day 7. In separate rats, the lesion caused by an intracortical microinjection of the indirect excitotoxin malonate (500 nmol/0.5 microl) on days 1, 3 or 7 after CSD was reduced by 56-75% in the ipsilateral hemisphere. In normal rats, single or multiple injections of the kynurenine 3-hydroxylase inhibitor 4,5-dichlorobenzoylalanine (PNU 156561; 50 mg/kg, i.p.), which results in selective increases in brain KYNA levels, failed to protect cortical neurons against a focal malonate injection. Taken together, these findings indicate that the observed increase in brain KYNA is not responsible for CSD-induced tolerance to malonate-induced neuronal damage.

Magnetic resonance imaging and spectroscopy in assessing 3-nitropropionic acid-induced brain lesions: an animal model of Huntington’s disease

Huntington's disease (HD) is an inherited neurodegenerative disease, in which there is progressive motor and cognitive deterioration, and for which the pathogenesis of neuronal death remains controversial. Mitochondrial toxins like 3-nitropropionic acid (3-NP) and malonate, functioning as the inhibitors of the complex II of mitochondrial respiratory chain, have been found to effectively induce specific behavioral changes and selective striatal lesions in rats and non-human primates mimicking those in HD. Furthermore, several kinds of transgenic mouse models of HD have been recently developed, and used in the development and assessment of novel treatments for HD. In the past, most studies evaluating the animal models for HD were based on histological changes or in vitro neuronal cultures. With the emergence of advanced magnetic resonance technologies, non-invasive magnetic resonance imaging (MRI) and spectroscopy provide more detail of cerebral alterations, including the changes of cerebral structure, function and metabolites. These studies support the hypothesis that mitochondrial dysfunction with increased excitation of N-methyl-D-aspartate (NMDA) receptors can replicate the neurobehavioral changes, selective brain injury and neurochemical alterations in HD. The present review focuses on our work as well as that of others regarding 3-NP-induced neurotoxicity and other animal models of HD. Using both conventional and advanced MRI and spectroscopy, we summarize the pathogenesis and possible therapeutic strategies in chemical and transgenic models of HD. The results show magnetic resonance techniques to be powerful techniques in the evaluation of pathogenesis and therapeutic intervention for both chemical and transgenic models of HD.

Type I glutaric aciduria, part 2: a model of acute striatal necrosis

Type I glutaric aciduria (GA1) is an inborn error of organic acid metabolism that is associated with acute neurological crises, typically precipitated by an infectious illness. The neurological crisis coincides with swelling, metabolic depression, and necrosis of basal ganglia gray matter, especially the putamina and can be visualized as focal, stroke-like, signal hyperintensity on MRI. Here we focus on the stroke-like nature of striatal necrosis and its similarity to brain injury that occurs in infants after hypoxia-ischemia or systemic intoxication with 3-nitropropionic acid (NPA). These conditions share several features including abrupt onset, preferential effect in the striatum and age-specific susceptibility. The pathophysiology of the conditions is reviewed and a model proposed herein. We encourage investigators to test this model in an appropriate experimental system.

In vivo NMR studies of neurodegenerative diseases in transgenic and rodent models

In vivo magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) provide unique quality to attain neurochemical, physiological, anatomical, and functional information non-invasively. These techniques have been increasingly applied to biomedical research and clinical usage in diagnosis and prognosis of diseases. The ability of MRS to detect early yet subtle changes of neurochemicals in vivo permits the use of this technology for the study of cerebral metabolism in physiological and pathological conditions. Recent advances in MR technology have further extended its use to assess the etiology and progression of neurodegeneration. This review focuses on the current technical advances and the applications of MRS and MRI in the study of neurodegenerative disease animal models including amyotrophic lateral sclerosis, Alzheimer's, Huntington's, and Parkinson's diseases. Enhanced MR measurable neurochemical parameters in vivo are described in regard to their importance in neurodegenerative disorders and their investigation into the metabolic alterations accompanying the pathogenesis of neurodegeneration.

The adenosine A1 receptor agonist adenosine amine congener exerts a neuroprotective effect against the development of striatal lesions and motor impairments in the 3-nitropropionic acid model of neurotoxicity

Huntington's disease is a genetic neurodegenerative disorder characterized clinically by both motor and cognitive impairments and striatal lesions. At present, there are no pharmacological treatments able to prevent or slow its development. In the present study, we report the neuroprotective effect of adenosine amine congener (ADAC), a specific A1 receptor agonist known to be devoid of any of the side effects that usually impair the clinical use of such compounds. Remarkably, in a rat model of Huntington's disease generated by subcutaneous infusion of the mitochondrial inhibitor 3-nitropropionic acid (3NP), we have observed that an acute treatment with ADAC (100 microg x kg(-1) x d(-1)) not only strongly reduces the size of the striatal lesion (-40%) and the remaining ongoing striatal degeneration (-30%), but also prevents the development of severe dystonia of hindlimbs. Electrophysiological recording on corticostriatal brain slices demonstrated that ADAC strongly decreases the field EPSP amplitude by 70%, whereas it has no protective effect up to 1 microm against the 3NP-induced neuronal death in primary striatal cultures. This suggests that ADAC protective effects may be mediated presynaptically by the modulation of the energetic impairment-induced striatal excitotoxicity. Altogether, our results indicate that A1 receptor agonists deserve further experimental evaluation in animal models of Huntington's disease.

Decreased TCA cycle rate in the rat brain after acute 3-NP treatment measured by in vivo 1H-[13C] NMR spectroscopy

Inhibition of succinate dehydrogenase (SDH) by the mitochondrial toxin 3-nitropropionic acid (3-NP) has gained acceptance as an animal model of Huntington's disease. In this study 13C NMR spectroscopy was used to measure the tricarboxylic acid (TCA) cycle rate in the rat brain after 3-NP treatment. The time course of both glutamate C4 and C3 13C labelling was monitored in vivo during an infusion of [1-13C]glucose. Data were fitted by a mathematical model to yield the TCA cycle rate (Vtca) and the exchange rate between alpha-ketoglutarate and glutamate (Vx). 3-NP treatment induced a 18% decrease in Vtca from 0.71 +/- 0.02 micro mol/g/min in the control group to 0.58 +/- 0.02 micro mol/g/min in the 3-NP group (p < 0.001). Vx increased from 0.88 +/- 0.08 micro mol/g/min in the control group to 1.33 +/- 0.24 micro mol/g/min in the 3-NP group (p < 0.07). Fitting the C4 glutamate time course alone under the assumption that Vx is much higher than Vtca yielded Vtca=0.43 micro mol/g/min in both groups. These results suggest that both Vtca and Vx are altered during 3-NP treatment, and that both glutamate C4 and C3 labelling time courses are necessary to obtain a reliable measurement of Vtca.

Effects of middle cerebral artery occlusion on spontaneous activity and cognitive function in rats

The middle cerebral artery occlusion (MCAO) in the rat is a commonly used model to evaluate new therapeutic strategies for the treatment of ischemic stroke. However, many such studies rely on short-term neurological examination and infarct volume as endpoint measures while neglecting more long-term functional assessments. In this study, we examined whether there were changes in passive avoidance behavior, spontaneous behavioral patterns across the light-dark cycle, and motor coordination as measured on the rotorod test 1 month after Sprague-Dawley rats had undergone MCAO. Compared to age-matched controls, fewer animals in the MCAO group remained on the platform during the passive avoidance retention test (p < .03). Significant differences between the groups were observed in the spontaneous activity during the initial portions of both the light and dark testing periods, when the test situation was new (p < .01 to .05, depending on the variable examined). Any differences on the rotorod test failed to gain statistical significance. These results suggest that at least the passive avoidance test and measures of spontaneous activity are sensitive to ischemia-induced damage over a more prolonged survival period and therefore may be appropriate measures for long-term effectiveness of new treatments.

Metabolic changes in quinolinic acid-lesioned rat striatum detected non-invasively by in vivo (1)H NMR spectroscopy

Intrastriatal injection of quinolinic acid (QA) provides an animal model of Huntington disease. In vivo (1)H NMR spectroscopy was used to measure the neurochemical profile non-invasively in seven animals 5 days after unilateral injection of 150 nmol of QA. Concentration changes of 16 metabolites were measured from 22 microl volume at 9.4 T. The increase of glutamine ((+25 +/- 14)%, mean +/- SD, n = 7) and decrease of glutamate (-12 +/- 5)%, N-acetylaspartate (-17 +/- 6)%, taurine (-14 +/- 6)% and total creatine (-9 +/- 3%) were discernible in each individual animal (P < 0.005, paired t-test). Metabolite concentrations in control striata were in excellent agreement with biochemical literature. The change in glutamate plus glutamine was not significant, implying a shift in the glutamate-glutamine interconversion, consistent with a metabolic defect at the level of neuronal-glial metabolic trafficking. The most significant indicator of the lesion, however, were the changes in glutathione ((-19 +/- 9)%, P < 0.002)), consistent with oxidative stress. From a comparison with biochemical literature we conclude that high-resolution in vivo (1)H NMR spectroscopy accurately reflects the neurochemical changes induced by a relatively modest dose of QA, which permits one to longitudinally follow mitochondrial function, oxidative stress and glial-neuronal metabolic trafficking as well as the effects of treatment in this model of Huntington disease.

Early degenerative changes in transgenic mice expressing mutant huntingtin involve dendritic abnormalities but no impairment of mitochondrial energy production

Mitochondrial defects, which occur in the brain of late-stage Huntington's disease (HD) patients, have been proposed to underlie the selective neuronal loss in the disease. To shed light on the possible role of mitochondrial energy impairment in the early phases of HD pathophysiology, we carried out Golgi impregnation and quantitative histochemical/biochemical studies in HD full-length cDNA transgenic mice that were symptomatic but had not developed to a stage in which neuronal loss could be documented. Golgi staining showed morphologic abnormalities that included a significant decrease in the number of dendritic spines and a thickening of proximal dendrites in striatal and cortical neurons. In contrast, measurements of mitochondrial electron transport Complexes I-IV did not reveal changes in the striatum and cerebral cortex in these mice. Examination of the neostriatum and cerebral cortex in human presymptomatic and pathological Grade 1 HD cases also showed no change in the activity of mitochondrial Complexes I-IV. These data suggest that dendritic alterations precede irreversible cell loss in HD, and that mitochondrial energy impairment is a consequence, rather than a cause, of early neuropathological changes.

A fMRI study of brain activations during non-noxious and noxious electrical stimulation of the sciatic nerve of rats

An acute pain animal model for fMRI study would provide useful spatial and temporal information for studying the supraspinal nociceptive neuronal responses. The aim of the present study was to investigate whether the nociceptive responses in different brain areas can be differentiated by using functional magnetic resonance imaging (fMRI) in anesthetized rats. Functional changes in brain regions activated by noxious or non-noxious stimuli of the sciatic nerve were investigated using fMRI in a 4.7 T MR system in alpha-chloralose anaesthetized rats. To determine the electrical intensity for noxious and non-noxious stimuli, compound action potential recording was employed to reveal the type of fibers activated by graded electrical stimulation of sciatic nerve. It showed that innocuous A-beta fibers were excited by two times the muscle twitch threshold and nociceptive A-delta and C fibers were recruited and excited by 10 and 20 times threshold, respectively. A series of four-slice gradient echo images were acquired during innocuous (two times threshold) and noxious (10 and 20 times threshold) stimuli in a 4.7 T MR system. Contralateral somatosensory cortex was the most prominent brain area activated by innocuous stimuli. Both signal intensity and activated areas were significantly increased in the somatosensory cortex, cingulate cortex, medial thalamus and hypothalamus during noxious stimuli. These four brain areas activated by noxious stimuli were significantly suppressed by prior intravenous injection of morphine (5 mg/kg). The present findings demonstrated that the difference of the innocuous and nociceptive responses in the brain could be detected and localized by an in vivo spatial map using fMRI. Results suggest that fMRI may be an invaluable tool for studying pain in anesthetized animals.

MRI studies of the neurotoxic effects of l -2-chloropropionic acid on rat brain

L-2-Chloropropionic acid (L-CPA) is selectively toxic to rat cerebellar granule cells; necrosis is first observed about 36 hours after administration of L-CPA (750 mg/kg p.o.) becoming more marked by 48 h. Parallel to the onset of cell death an increase in cerebellar water content and sodium concentration has been reported suggesting an oedematous reaction. In this study T(2)-weighted (T(2)WI) and diffusion weighted (DWI) imaging were used to detect the development of neuronal damage in the cerebellum of rats as a result of exposure to L-CPA. T(2)WI and DWI were not able to detect cerebellar abnormalities at 37 h post-dosing except for a slight swelling of the cerebellum. However, at 48 h post-dosing when cerebellar swelling and granule cell necrosis were marked, T(2)WI and DWI hyperintensities were observed in the cerebellum. Therefore, under the conditions of this study, MRI was not able to detect abnormalities in the cerebellum prior to the onset of the clinical signs of neurotoxicity or at the time of early histological changes. T(2)WI also suggested a marked increase in the amount of fluid in the ventricular system of rats 37 and 48 h after dosing; fluid accumulation was observed in all animals studied whether or not necrosis was detected. The occurrence of T(2)WI hyperintensity in the forebrain lead us to discover a new lesion in the habenular nucleus.

Temporal changes of cerebral metabolites and striatal lesions in acute 3-nitropropionic acid intoxication in the rat

To investigate the mechanisms of neuronal death in neurodegeneration, in vivo localized proton magnetic resonance spectroscopy ((1)H-MRS) and diffusion-weighted MRI (DWI) were used to evaluate temporal changes in rat striata after administration of 3-nitropropionic acid. It was found that N-acetylaspartate (NAA) reduction, with nearly simultaneous evidence of striatal lesions in DWI, was preceded by a significant and progressive increase of acetate. Shortly before the NAA levels decreased to the lowest point, acetate levels peaked and began to gradually decline toward the control levels. These results suggest that acetate increase may arise from fatty acid degradation, inhibition of succinate dehydrogenase and possible NAA hydrolysis. The elevated acetate may provide a source of acetyl group for membrane repair during excitotoxic brain injury. Magn Reson Med 44:29-34, 2000.

Nonlinear decrease over time in N-acetyl aspartate levels in the absence of neuronal loss and increases in glutamine and glucose in transgenic Huntington's disease mice

Mice transgenic for exon I of mutant huntingtin, with 141 CAG repeats, exhibit a profound symptomatology characterized by weight loss, motor disorders, and early death. We performed longitudinal analysis of metabolite levels in these mice using NMR spectroscopy in vivo and in vitro. These mice exhibited a large (53%), nonlinear drop in in vivo N-acetyl aspartate (NAA) levels over time, commencing at approximately 6 weeks of age, coincident with onset of symptoms. These drops in NAA levels occurred in the absence of neuronal death as measured by postmortem Nissl staining and neuronal counting but in the presence of nuclear inclusion bodies. In addition to decreased NAA, these mice showed a large elevation of glucose in the brain (600%) consistent with a diabetic profile and elevations in blood glucose levels both before and after glucose loading. In vitro NMR analysis revealed significant increases in glutamine (100%), taurine (95%) cholines (200%), and scyllo-inositol (333%) and decreases in glutamate (24%) and succinate (47%). These results lead to two conclusions. NAA is reflective of the health of neurons and thus is a noninvasive marker, with a temporal progression similar to nuclear inclusion bodies and symptoms, of neuronal dysfunction in transgenic mice. Second, the presence of elevated glutamine is evidence of a profound metabolic defect. We present arguments that the elevated glutamine results from a decrease in neuronal-glial glutamate-glutamine cycling and a decrease in glutaminase activity.

An integrated strategy for evaluation of metabolic and oxidative defects in neurodegenerative illness using magnetic resonance techniques

The number of physiologic and metabolic phenomena amenable to analysis using magnetic resonance (MR) techniques is increasing every year. MR techniques can now evaluate tissue parameters relevant to TCA cyclemetabolism, anerobic glycolysis, ATP levels, blood-brain barrier permeability, macrophage infiltration, cytotoxic edema, spreading depression, cerebral blood flow and volume, and neurotransmitter function. The paramagnetic nature of certain oxidation states of iron leads to the ability to map out brain function using deoxyhemoglobin as an endogenous contrast agent, and also allows for mapping of local tissue iron concentrations. In addition to these metabolic parameters, the number of ways to generate anatomic contrast using MR is also expanding; and in addition to conventional anatomic scans, mapping of axonal fiber tracts can also be performed using the anisotropy of water diffusion. A strategy for integration of these multifarious parameters in a comprehensive neurofunctional exam in neurodegenerative illness is outlined in this paper. The goals of the integrated exam, as applied to a given neurodegenerative illness, can be subdivided into three categories: etiology, natural history, and therapeutic end points. The consequences of oxidative stress and/or mitochondrial dysfunction are explored in the context of the various parameters that can be measured using the integrated MR exam.

Neuroprotective effect of lamotrigine and MK-801 on rat brain lesions induced by 3-nitropropionic acid: evaluation by magnetic resonance imaging and in vivo proton magnetic resonance spectroscopy

Magnetic resonance imaging and in vivo proton magnetic resonance spectroscopy were used to evaluate the therapeutic effect of lamotrigine and MK-801 on rat brain lesions induced by 3-nitropropionic acid. Systemic administration of 3-nitropropionic acid (15 mg/kg per day) to two-month-old Sprague-Dawley rats (n = 10 for each group) for five consecutive days induced selective striatal and hippocampal lesions and specific behavioral change. Pretreatment with lamotrigine (10 mg/kg or 20 mg/kg per day) or MK-801 (2 mg/kg per day) attenuated the lesions and behavioral change. There were no significant differences in T2 values of the striatum and hippocampus among rats pretreated with MK-801, lamotrigine (20 mg/kg) and sham controls. Significant elevations of succinate/creatine and lactate/creatine ratios and decreases of N-acetylaspartate/creatine and choline/creatine ratios were observed after 3-nitropropionic acid injections (P < 0.001). The changes were nearly prevented after pretreatment with lamotrigine (20 mg/kg). However, the N-acetylaspartate/creatine in rats pretreated with lamotrigine (10 mg/kg) (P < 0.01) and MK-801 (P < 0.05) still showed significant reduction as compared with sham controls. Thus we conclude that both lamotrigine and MK-801 are effective in attenuation of brain lesions induced by 3-nitropropionic acid. A higher dose of lamotrigine provides a better neuroprotective effect than MK-801. With a better therapeutic effect and fewer side effects, lamotrigine is more promising for potential clinical application.

Respiratory chain inhibition induces tolerance to focal cerebral ischemia

The authors show that the inhibitor of the succinate dehydrogenase, 3-nitroproprionic acid (3-NPA), which in high doses and with chronic administration is a neurotoxin, can induce profound tolerance to focal cerebral ischemia in the rat when administered in a single dose (20 mg/kg) 3 days before ischemia. Infarcts were approximately 70% and 35% smaller in the 3-NPA preconditioned groups of permanent and transient focal cerebral ischemia, respectively. This regimen of 3-NPA preconditioning neither induced necrosis, apoptosis, or any other histologically detectable damage to the brain, nor did it affect behavior of the animals. 3-NPA led to an immediate (1-hour) and long-lasting (3-day) decrease in succinate dehydrogenase activity (30% reduction) throughout the brain, whereas only a short metabolic impairment occurred (ATP decrease of 35% within 30 minutes, recovery within 2 hours). The authors found that 3-NPA induces a burst of reactive oxygen species and the free radical scavenger dimethylthiourea, when administered shortly before the 3-NPA stimulus, completely blocked preconditioning. Inhibition of protein synthesis with cycloheximide given at the time of 3-NPA administration completely inhibited preconditioning. The authors were unsuccessful in showing upregulation of mRNA for the manganese superoxide dismutase, and did not detect increased activities of the copper-zinc and manganese superoxide dismutases, prototypical oxygen free radicals scavenging enzymes, after 3-NPA preconditioning. The authors conclude that it is possible to pharmacologically precondition the brain against focal cerebral ischemia, a strategy that may in principal have clinical relevance. The data show the relevance of protein synthesis for tolerance, and suggests that oxygen free radicals may be critical signals in preconditioning.

Temporal evolution of 3-nitropropionic acid-induced neurodegeneration in the rat brain by T2-weighted, diffusion-weighted, and perfusion magnetic resonance imaging

An appropriate detecting technique is necessary for the early detection of neurodegenerative diseases. 3-Nitropropionic acid-intoxicated rats serve as the animal model for one neurodegenerative disease, Huntington's disease. Non-invasive diffusion- and T2-weighted magnetic resonance imaging were applied to study temporal evolution and spatial distribution of brain lesions which were produced by intravenous injection of 3-nitropropionic acid in rats. Lesions in the striatum, hippocampus, and corpus callosum but not in the cortex were observed 3 and 4.5 h after 3-nitropropionic acid injection (30 mg/kg) on the diffusion- and T2-weighted images, respectively (n = 6). The results demonstrated that the diffusion-weighted imaging is not only superior to T2-weighted imaging in detecting onset of 3-nitropropionic acid-induced excitotoxic brain damage but also differentiates lesion and non-lesion areas with better spatial resolution than T2-weighted imaging. Additionally, to correlate structural alterations with pathophysiological conditions, dynamic susceptibility contrast magnetic resonance imaging was performed before and 4 h after 3-nitropropionic acid administration (n = 8). The relative cerebral blood volume was significantly elevated in the striatum (P < 0.001) but not in the cortex after 3-nitropropionic acid administration. The changes in regional relative cerebral blood volume were well correlated to the changes in signal intensities in the corresponding areas on the diffusion- and T2-weighted images. The combined structural and functional information in this study may provide new insights and therapeutic strategies in treating neurodegenerative diseases.

Dopamine imaging markers and predictive mathematical models for progressive degeneration in Parkinson's disease

We conducted PET imaging studies of modulation of dopamine transporter function and MRS studies of neurochemicals in idiopathic primate Parkinson's disease (PD) model induced by long-term, low-dose administration of MPTP. MR spectra showed striking similarities of the control spectrum of the primate and human striatum as well as MPTP-treated primate (six months after cessation of MPTP), and Parkinson's disease patient striatum (68 year old male; Hoehn-Yahr scale II; 510 mg/d L-DOPA). The choline/creatine ratio was similar in the MPTP model and human parkinsonism, suggesting a possible glial abnormality. The progressive degeneration of dopamine re-uptake sites observed in our PD model can be expressed by a time dependent exponential equation N(t) = N0 exp (-(0.072 +/- 0.016) t), where N0 represents intact entities (dopamine re-uptake sites before MPTP) and 0.072 per month is the rate of degeneration. When the signs of PD appear, N(t) is about 0.3-0.4 times N0. Interestingly, this biological degenerative phenomena has similar progression to that observed in cell survival theory. According to this theory and calculated degeneration rate, predictive models can be produced for regeneration and protective treatments.

Pathogenesis of neurodegenerative diseases associated with expanded glutamine repeats: new answers, new questions

Eight diseases are now known to be caused by an expansion mutation of the trinucleotide repeat CAG encoding glutamine. Each disease is caused by a CAG expansion in a different gene, and the genes bear no similarity to each other except for the presence of the repeat. Nonetheless, the essential feature of all of these disorders is neurodegeneration in a set of overlapping cortical and subcortical regions. Disease age of onset, and in some cases severity, is correlated with repeat length. These and other observations have led to the hypothesis that CAG expansion causes disease by a toxic gain-of-function of the encoded stretch of polyglutamine residues. Expansion-induced abnormalities of cytoskeletal function or neuronal signalling processes may contribute to the pathogenic process. In addition, theoretical and experimental analysis of the chemistry of uninterrupted stretches of glutamine residues suggest that polyglutamine-containing proteins or protein fragments may aggregate, via a "polar zipper", into beta pleated sheets. Recent findings have now established the presence of such aggregates in selected regions of brain from affected individuals, in transgenic mice expressing expanded repeats, and in isolated cells transfected with expanded repeats. The aggregates are most prominently manifest as neuronal intranuclear inclusion bodies. As the investigation of the link between these inclusions and cell dysfunction and death continues, it is possible that new avenues for therapeutic intervention will emerge.

Combined PET/MRS brain studies show dynamic and long-term physiological changes in a primate model of Parkinson disease

We used brain imaging to study long-term neurodegenerative and bioadaptive neurochemical changes in a primate model of Parkinson disease. We gradually induced a selective loss of nigrostriatal dopamine neurons, similar to that of Parkinson disease, by creating oxidative stress through infusion of the mitochondrial complex 1 inhibitor MPTP for 14+/-5 months. Repeated evaluations over 3 years by positron emission tomography (PET) demonstrated progressive and persistent loss of neuronal dopamine pre-synaptic re-uptake sites; repeated magnetic resonance spectroscopy (MRS) studies indicated a 23-fold increase in lactate and macromolecules in the striatum region of the brain for up to 10 months after the last administration of MPTP. By 2 years after the MPTP infusions, these MRS striatal lactate and macromolecule values had returned to normal levels. In contrast, there were persistent increases in striatal choline and decreases in N-acetylaspartate. Thus, these combined PET/MRS studies demonstrate patterns of neurochemical changes that are both dynamic and persistent long after selective dopaminergic degeneration.

Reduced MPTP neurotoxicity in striatum of the mutant mouse tottering

The effects of MPTP treatment (4 x 10 mg/kg, 2-h intervals) on in vivo striatal binding of (+)-alpha-[3H]dihydrotetrabenazine ((+)-[3H]DTBZ) to the vesicular monoamine transporter type 2 (VMAT2) were examined in wild type (+,+) and tottering (tg/tg) mice of the C57BL/6J strain. The tottering mutant has been previously characterized as having hyperinnervation of noradrenergic terminals in the brain, with increased concentrations of norepinephrine and increased numbers of VMAT2 binding sites. In wild-type mice, MPTP caused a significant decrease in specific striatal (+)-[3H]DTBZ binding in both males (-71%) and females (-57%), consistent with dopaminergic terminal losses. In the tottering mice, the neurotoxic effects of MPTP were diminished, with smaller losses of (+)-[3H]DTBZ binding observed both in males (-45%) and females (-26%). These results are consistent with the hypothesis that vesicular storage (as a result of hyperinnervation) offers neuroprotection toward MPTP toxicity, although the confounding effects of increases in norepinephrine concentrations or changes in calcium ion channel function (both also characteristics of the tottering mutant) cannot be ruled out. The tottering mutant does, however, offer another animal model to examine the biochemical features responsible for MPTP toxicity.

Is NADH effective in the treatment of Parkinson's disease?

Most Parkinson's disease (PD) treatments palliate symptoms by increasing nigrostriatal dopaminergic tone. A unique strategy for accomplishing this pharmacological end-point proposes using reduced nicotinamide adenine dinucleotide (NADH) to boost endogenous dopamine production, since NADH indirectly supplies reducing equivalents to the rate-limiting, tyrosine hydroxylase-catalysed step of dopamine synthesis. Support for using NADH in PD treatment includes claims that NADH stimulates tyrosine hydroxylase and dopamine biosynthesis in tissue culture and humans, as well as case series associating intravenous and oral NADH administration with PD rating scale improvements. Theoretical and practical arguments against NADH include underlying NADH disposal impairment in PD and failure of a placebo-controlled trial to show any clear benefit. While NADH may yet prove to ameliorate parkinsonism, recommendations for its use in PD are premature.

Neuroprotective effects of creatine and cyclocreatine in animal models of Huntington's disease

The gene defect in Huntington's disease (HD) may result in an impairment of energy metabolism. Malonate and 3-nitropropionic acid (3-NP) are inhibitors of succinate dehydrogenase that produce energy depletion and lesions that closely resemble those of HD. Oral supplementation with creatine or cyclocreatine, which are substrates for the enzyme creatine kinase, may increase phosphocreatine (PCr) or phosphocyclocreatine (PCCr) levels and ATP generation and thereby may exert neuroprotective effects. We found that oral supplementation with either creatine or cyclocreatine produced significant protection against malonate lesions, and that creatine but not cyclocreatine supplementation significantly protected against 3-NP neurotoxicity. Creatine and cyclocreatine increased brain concentrations of PCr and PCCr, respectively, and creatine protected against depletions of PCr and ATP produced by 3-NP. Creatine supplementation protected against 3-NP induced increases in striatal lactate concentrations in vivo as assessed by 1H magnetic resonance spectroscopy. Creatine and cyclocreatine protected against malonate-induced increases in the conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid, biochemical markers of hydroxyl radical generation. Creatine administration protected against 3-NP-induced increases in 3-nitrotyrosine concentrations, a marker of peroxynitrite-mediated oxidative injury. Oral supplementation with creatine or cyclocreatine results in neuroprotective effects in vivo, which may represent a novel therapeutic strategy for HD and other neurodegenerative diseases.