Endogenous dopamine enhances the neurotoxicity of 3-nitropropionic acid in the striatum through the increase of mitochondrial respiratory inhibition and free radicals production Ruth F. Villara ´n a , M. Toma ´s-Camardiel a , Rocı ´o M. de Pablos a , Marti Santiago a , Antonio J. Herrera a , Ana Navarro b , Alberto Machado a , Josefina Cano a, * a Departamento de Bioquı ´mica, Bromatologı ´a, Toxicologı ´a y Medicina Legal, Facultad de Farmacia, Universidad de Sevilla, C/Profesor Garcı ´a Gonza ´lez, 2, 41012-Sevilla, Spain b Departamento de Bioquı ´mica y Biologı ´a Molecular, Facultad de Medicina, Universidad de Ca ´diz, Spain Received 27 July 2007; accepted 7 November 2007 Available online 17 November 2007 Abstract 3-Nitropropionic acid (3-NP), an inhibitor of the mitochondrial enzyme succinate dehydrogenase, induces neuronal degeneration in the striatum. It is known that dopamine (DA) enhances this toxic effect. In this work, we study how the increase of DA influences the toxic effect of 3- NP on DAergic terminals, GABAergic neurons, astroglia and microglia in the striatum. We increased the content of DA through the inhibition of its uptake by nomifensine or the inhibition of its catabolism by deprenyl. We found that although nomifensine and deprenyl enhanced the DA overflow produced by 3-NP perfusion, they protected against the damage induced by 3-NP in the DAergic terminals and the GABAergic neurons in the striatum. Moreover, there was a decrease of apoptotic cells, astrogliosis and activation of microglia as index of damage. We also found that depletion of DA by reserpine and alpha-methyl-p-tyrosine produced a significant reduction of the inhibition of the respiratory rate and of the production of superoxide radical induced by 3-NP in synaptosomes from the striatum. All these results suggest that endogenous dopamine within the dopaminergic terminals of the striatum enhances the mitochondrial production of radical oxygen species along with the respiratory inhibition produced by 3-NP and thus increases the toxicity produced by 3-NP in the striatum. # 2007 Elsevier Inc. All rights reserved. Keywords: 3-Nitropropionic acid; The striatum; Neurodegeneration; Endogenous dopamine; Nomifensine; Deprenyl 1. Introduction 3-Nitropropionic acid (3-NP) is an inhibitor of the mitochondrial enzyme succinate dehydrogenase (SDH), a part of complex II that links the tricarboxylic acid cycle to the respiratory electron transport chain. 3-NP has been described as responsible for the neuronal degeneration caused in human brain by the ingestion of sugar cane, corn and peanuts contaminated by fungi (Ludolph et al., 1991; He et al., 1995; Brouillet et al., 2005); it has also been used in a model of Huntington’s disease (Brouillet et al., 1999; Lee and Chang, 2004). A generally admitted hypothesis to account for the degeneration induced for 3-NP in the striatum is that depletion of ATP levels produced by a deficit in energy metabolism can lead to membrane depolarization and produce NMDA toxicity through the relief of a voltage-dependent Mg 2+ block (Beal et al., 1993; Zeevalk et al., 1995; Greene et al., 1998; Gabrielson et al., 2001). On the other hand, impaired energy metabolism can produce oxidative stress as well as formation of reactive oxygen and nitrogen species (Lipton and Rosenberg, 1994; Schulz et al., 1995; Andreassen et al., 2001; Kim and Chan, 2001), which are suspected to be critically involved in neuronal death. GABAergic neurons seem to be the main target for the neurotoxic action of 3-NP among neurotransmitter systems. Studies using 13 C magnetic resonance spectroscopy showed that 3-NP preferentially inhibited oxidative metabolism in GABAergic neurons in vivo, whereas astrocyte metabolism was spared (Hassel and Sonnewald, 1995). 3-NP is also toxic for striatal dopaminergic terminals (Beal et al., 1993). The effect on dopaminergic terminals is consistent Available online at www.sciencedirect.com NeuroToxicology 29 (2008) 244–258 * Corresponding author. Tel.: +34 954556751; fax: +34 954556752. E-mail address: josefina@us.es (J. Cano). 0161-813X/$ – see front matter # 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.neuro.2007.11.001