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Abstract
Methamphetamine (meth) is an illicit psychostimulant that is abused throughout the world. Repeated passive injections of the drug given in a single day or over a few days cause significant and long-term depletion of dopamine and serotonin in the mammalian brain. Because meth self-administration may better mimic some aspects of human drug-taking behaviors, we examined to what extent this pattern of drug treatment might also result in damage to monoaminergic systems in the brain. Rats were allowed to intravenously self-administer meth (yoked control rats received vehicle) 15 hours per day for 8 days before being euthanized at either 24 hours or at 7 and 14 days after cessation of drug taking. Meth self-administration by the rats was associated with a progressive escalation of daily drug intake to 14 mg/kg per day. Animals that self-administered meth exhibited dose-dependent decreases in striatal dopamine levels during the period of observation. In addition, there were significant reductions in the levels of striatal dopamine transporter and tyrosine hydroxylase proteins. There were also significant decreases in the levels of dopamine, dopamine transporter, and tyrosine hydroxylase in the cortex. In contrast, meth self-administration caused only transient decreases in norepinephrine and serotonin levels in the two brain regions, with these values returning to normal at seven days after cessation of drug taking. Importantly, meth self-administration was associated with significant dose-dependent increases in glial fibrillary acidic protein in both striatum and cortex, with these changes being of greater magnitude in the striatum. These results suggest that meth self-administration by rats is associated with long-term biochemical changes that are reminiscent of those observed in post-mortem brain tissues of chronic meth abusers.
Highlights
Methamphetamine (METH) is a highly addictive psychostimulant drug whose abuse has reached epidemic proportions in the USA and worldwide [1,2,3,4]
The present experiments demonstrated that (1) extended access to METH self-administration was associated with a progressive escalation of drug intake by rats and significant decreases in their body weights; (2) this pattern of METH intake resulted in persistent dose-dependent depletion of striatal and cortical DA levels measured at various times after cessation of drug treatment; (3) METH self-administration caused decreases in the expression of striatal and cortical tyrosine hydroxylase (TH) and dopamine transporters (DAT) proteins; and (4) METH induced dose-dependent increases in GFAP expression in both, striatum and cortex
Our results are in agreement with findings from post-mortem studies that have reported decreased DA levels and reduced TH and DAT protein expression in the striata of human METH addicts [16,17,18]
Summary
Methamphetamine (METH) is a highly addictive psychostimulant drug whose abuse has reached epidemic proportions in the USA and worldwide [1,2,3,4]. This presents a serious public concern because chronic METH abuse is associated with major health problems including anxiety, depression, psychosis and psychomotor dysfunctions in humans [5,6]. Cognitive studies of chronic METH users have found deficits consistent with impaired functions of striatal and cortical systems These include deficits in attention, learning, working memory, and decision making [7,8,9,10,11].
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