Non-Invasive Neurochemical Analysis of Focal Excitotoxic Lesions in Models of Neurodegenerative Illness Using Spectroscopic Imaging

Abstract

Water-suppressed chemical shift magnetic resonance imaging was used to detect neurochemical alterations in vivo in neurotoxin-induced rat models of Huntington's and Parkinson's disease. The toxins were: N-methyl-4-phenylpyridinium (MPP+), aminooxyacetic acid (AOAA), 3-nitropropionic acid (3-NP), malonate, and azide. Local or systemic injection of these compounds caused secondary excitotoxic lesions by selective inhibition of mitochondrial respiration that gave rise to elevated lactate concentrations in the striatum. In addition, decreased N-acetylaspartate (NAA) concentrations were noted at the lesion site over time. Measurements of lactate washout kinetics demonstrated that t1/2 followed the order: 3-NP approximately MPP+ >> AOAA approximately malonate, which parallels the expected lifetimes of the neurotoxins based on their mechanisms of action. Further increases in lactate were also caused by intravenous infusion of glucose. At least part of the excitotoxicity is mediated through indirect glutamate pathways because lactate production and lesion size were diminished using unilateral decortectomies (blockade of glutamatergic input) or glutamate antagonists (MK-801). Lesion size and lactate were also diminished by energy repletion with ubiquinone and nicotinamide. Lactate measurements determined by magnetic resonance agreed with biochemical measurements made using freeze clamp techniques. Lesion size as measured with MR, although larger by 30%, agreed well with lesion size determined histologically. These experiments provide evidence for impairment of intracellular energy metabolism leading to indirect excitotoxicity for all the compounds mentioned before and demonstrate the feasibility of small-volume metabolite imaging for in vivo neurochemical analysis.

The neurochemical profile quantified by in vivo 1H NMR spectroscopy

“…In accordance with the expected mitochondrial impairment, the inhibitor of the respiratory chain 3-NP leads to increased striatal lactate concentration (e.g. Jenkins et al, 1996;Lee and Chang, 2004;Tsai et al, 1997). …”

“…Reduced NAA and increased lactate levels were observed in the striatum or substantia nigra of mouse (Boska et al, 2005;Koga et al, 2006), rat (Jenkins et al, 1996;Storey et al, 1992), feline (Podell et al, 2003), canine (Choi et al, 2011) or primate (Brownell et al, 1998) MPTP/ MPP + -intoxicated models, suggesting neuronal loss and mitochondrial dysfunction. GABA was suggested to be either increased (Chassain et al, 2008(Chassain et al, , 2010 of reduced (Storey et al, 1992) after MPTP/MPP + treatment.…”

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

“…In vivo NMR spectroscopy is a non-invasive method, which does not require substrates with isotope labeling. Only a limited number of metabolites, such as N-acetylaspertate, creatine, and lactate, however, has been quantified with in vivo NMR spectroscopic techniques in excitotoxic lesions (Jenkins et al, 1996;Strauss et al, 1997;Matthews et al, 1998b;Lee et al, 2000). Recent developments in high field in vivo 1 H NMR spectroscopy (Gruetter et al, 1998b) have resulted in the ability to quantify up to 18 metabolites simultaneously and noninvasively (Pfeuffer et al, 1999a;Tkáč, et al, 1999).…”

Quantification of Neurovascular Protection Following Repetitive Hypoxic Preconditioning and Transient Middle Cerebral Artery Occlusion in Mice

“…Furthermore, the neuroprotection induced by RHP may extend to improved BBB integrity in mouse models of Alzheimer's, which could be analyzed with the EB. 45 The dual TTC and EB analysis would be even more useful in Parkinson's model as it induces striatal lesions 46 and BBB disruption, 47 which can be quantified with TTC 48 and EB, 49 respectively. Overall RHP is a simple, powerful form of preconditioning with great translational potential as it uniquely induces long-term, anti-inflammatory, and neuroprotective effects.…”