Title

 

Authors

G. Bazzu¹, G. Calia², G. Rocchitta¹, R. Migheli¹, M.S. Desole¹, P.A. Serra^1
 
1Dept. of Neuroscience, Medical School, University of Sassari, Italy 
²Dept. of Biomedical Sciences, Medical School, University of Sassari, Italy 

 

Abstract

A prerequisite of many neurological studies is an accurate and continuous monitoring of in vivo concentrations of substances in the brain extracellular space and the combination of microdialysis with highly sensitive analytical techniques allows the measurement of a lot of neuroactive compounds (Di Chiara, 1990). In this study we propose an innovative microdialysis approach for the simultaneous monitoring of striatal dopamine (DA) and energy substrates in freely moving animals using asymmetric perfusion flow rates on a dual microdialysis probe. Catecholamines and their related compounds have been implicated in neurochemistry and physiology of mental diseases and neurological disorders. A significant reduction of striatal content of DA is a hallmark in Parkinson’s disease (Bazzu et al., 2010). Under normal physiological conditions, glucose is the major source of energy for the mammalian brain (Siesjö, 1978) and is actively involved in ATP synthesis. Increased brain levels of pyruvate and lactate/pyruvate ratio reflect respectively an increase in brain metabolic activity and a relative increase in anaerobic metabolism (Darbin et al., 2006). MPP⁺, produced during MPTP metabolism, acts as a potent inhibitor of mitochondrial electron transport chain resulting in mitochondrial impairment and depletion of dopaminergic neurons. Adult male Wistar rats (280-330 g) were used in this study. A dual-microdialysis probe was stereotaxically inserted in the right striatum and experiments, started 24 h after surgery, were repeated for three consecutive days. Systemic MPTP was administered as follows: 25 mg/Kg (day 1), 15 mg/Kg (day 2), 10 mg/Kg (day 3). D-amphetamine (2 mg/Kg/day i.p. for 3 days) was intraperitoneally administered to a second group of animals. Control animals received only vehicle (2.5 ml). Striatal levels of dopamine (DA) were evaluated using a HPLC-EC, while levels of glucose lactate, pyruvate and L/P ratio were evaluated using a spectrophotometric method (CMA Iscus Analyzer). The first MPTP dose (day 1) induced an increase in all studied neurochemicals. On day 2 and 3, MPTP injections showed a progressive reduction of DA, glucose and pyruvate levels with a concomitant further increase of lactate and L/P ratio. The first systemic administration of d-amphetamine increased DA and decreased its acidic metabolite levels in striatal dialysate while a statistically significant increase of glucose, lactate and pyruvate levels, but not in L/P ratio, was observed. On day 2 and 3, d-amphetamine injections resulted in a progressive reduction of DA release and its striatal metabolites, a smaller increase in glucose, lactate and pyruvate extracellular concentrations with a stable L/P ratio.These in-vivo results are suggestive of physiological(and reversible) striatal activation after d-amphetamine administration while MPTP inducedenergetic impairment consequent to mitochondrial damage (Serra et al., 2002).The simultaneous monitoring of striatal dopamine changes and brain bioenergetics could be useful in toxin-induced animal models of Parkinson’s disease.
 
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