Elsevier

Neuropharmacology

Volume 48, Issue 7, June 2005, Pages 965-974
Neuropharmacology

Acute or repeated cocaine administration generates reactive oxygen species and induces antioxidant enzyme activity in dopaminergic rat brain structures

https://doi.org/10.1016/j.neuropharm.2005.01.018Get rights and content

Abstract

Either a single (acute) or repeated daily (chronic) injections (1 injection/day) of 20 mg/kg cocaine for 10 days to rats was found to increase reactive oxygen species production in two dopaminergic brain structures, the frontal cortex and the striatum. We found that the mitochondrial genome was down-regulated after acute cocaine injection. Hydroperoxide and lipid peroxide generation was correlated with an increase in mitochondrial hydrogen peroxide generation and with a reduced functioning of mitochondrial complex I in response to cocaine. As judged from the measurement of caspase-3 activity and TUNEL labeling, neither acute nor chronic cocaine treatment has been found to induce apoptosis in any of the structures examined. This differs dramatically from what has been described for methamphetamine. Cocaine-induced radical formation was accompanied by the induction of the antioxidant enzymes superoxide dismutase and glutathione peroxidase, after both acute and chronic cocaine treatment. In addition, proteasome chymotrypsin-like activity was enhanced following a single cocaine injection in both cortex and striatum. It is proposed that the compensatory mechanisms to oxidative stress occurring in response to cocaine were effective in scavenging reactive oxygen species and in preventing subsequent cellular damage, thus explaining why no significant cell death was found in these brain structures.

Introduction

Cocaine and methamphetamine (METH) are psychostimulants abused by man, that eventually lead to drug dependence. They both increase extracellular level of the monoamines dopamine, serotonin and noradrenaline, although by distinct mechanisms. Cocaine binds with high affinity to transporter sites for the monoamines and inhibits monoamine uptake into presynaptic neurons (Ritz et al., 1990, Ross and Renyi, 1969). METH induces the release of even greater amounts of the monoamines from vesicles to the cytoplasm and extracellular space. Increase in neurotransmitter concentrations in the synaptic cleft subsequently results in the over-stimulation of the corresponding receptors. METH administration to rodents has been shown to provoke significant neurotoxicity in vitro (Cubells et al., 1994) and in vivo (Cadet et al., 2003, Fumagalli et al., 1999). Neurotoxicity of amphetamines is thought to result essentially from reactive oxygen species (ROS) that are formed by the oxidation of dopamine. Toxicity involves dopaminergic nerve terminal degeneration, as assessed by reductions in dopamine, dopamine transporter and tyrosine hydroxylase, and is accompanied by reactive gliosis. However, little information on the effect of cocaine on ROS production and neurotoxicity in the brain is currently available.

In order to identify the molecular events underlying neuro-adaptations occurring in rat cingulate cortex in response to cocaine administration, we recently searched for genes, the expression of which is modified in this dopaminergic projection area by this drug. Using the differential display technique, we found that acute administration of cocaine down-regulated several transcripts encoded by the mitochondrial genome, including NADH dehydrogenase subunits and cytochrome c oxidase subunits (Dietrich et al., 2004). Given the well documented role of mitochondria in ROS formation, this mitochondria dysfunction we characterized prompted us to study the effect of cocaine on the expression of ROS in dopaminergic rat brain structures. The study was conducted after both single and repeated cocaine administration. We also investigated whether cocaine induced neuronal apoptosis, as has been described for METH. Furthermore, we measured the effect of cocaine on the activity of antioxidant enzymes such as glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), and also on the activity of the proteasome.

Section snippets

Animals

Male Wistar rats (250–300 g) were housed with a fixed 12-h light–dark cycle and free access to food and water. All experiments were conducted in conformity with the European Community Council guidelines. Rats were injected intraperitoneally (i.p.) with either 20 mg/kg cocaine hydrochloride (Sigma, St Louis, MO) or an equivalent volume of saline (NaCl 0.9%). For chronic treatment, rats were injected with the same dose for 10 days (1 injection/day). d-amphetamine (5 mg/kg) was administered i.p. for 3

Cocaine reduces mitochondrial ND4 gene expression

Using the differential display technique, we previously showed that several transcripts encoded by the mitochondrial genome were down-regulated in rat cingulate cortex following a single cocaine administration (Dietrich et al., 2004). Table 1 shows a real-time PCR quantification of NADH dehydrogenase subunit 4 (ND4) in frontal cortex 15 h after an acute cocaine injection. ND4 mRNA level was found to be reduced by 44% in response to cocaine administration, thus confirming that this mitochondrial

Discussion

We report here that administration of cocaine to rats was found to increase the formation of hydrogen peroxide in mitochondria prepared from frontal cortex. Either acute or repeated injection of cocaine was also found to increase hydroperoxide and lipid peroxide production in frontal cortex and striatum, two brain structures that contain numerous dopaminergic nerve terminals. It is well known that the mitochondrial respiratory chain produces ROS as by-products of normal respiration (Boveris et

Acknowledgements

We thank Dr. L. Caumont for help with immunohistological techniques, and Dr. K. Langley for critical reading of the manuscript.

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