Ascorbic acid-deficient condition alters central effects of methamphetamine

L-ascorbate attenuates methamphetamine neurotoxicity through enhancing the induction of endogenous heme oxygenase-1

Methamphetamine (METH) is a drug of abuse which causes neurotoxicity and increased risk of developing neurodegenerative diseases. We previously found that METH induces heme oxygenase (HO)-1 expression in neurons and glial cells, and this offers partial protection against METH toxicity. In this study, we investigated the effects of l-ascorbate (vitamin C, Vit. C) on METH toxicity and HO-1 expression in neuronal/glial cocultures. Cell viability and damage were evaluated by 3-(4,5-dimethylthianol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) release, respectively. Neuronal and glial localization of HO-1 were identified by double immunofluorescence staining. Reactive oxygen species (ROS) production was measured using the fluorochrome 2',7'-dichlorofluorescin diacetate. HO-1 mRNA and protein expression were examined by RT-qPCR and Western blotting, respectively. Results show that Vit. C induced HO-1 mRNA and protein expressions in time- and concentration-dependent manners. Inhibition of p38 mitogen-activated protein kinase (MAPK) but not extracellular signal-regulated kinase (ERK) significantly blocked induction of HO-1 by Vit. C. HO-1 mRNA and protein expressions were significantly elevated by a combination of Vit. C and METH, compared to either Vit. C or METH alone. Pretreatment with Vit. C enhanced METH-induced HO-1 expression and attenuated METH-induced ROS production and neurotoxicity. Pharmacological inhibition of HO activity abolished suppressive effects of Vit. C on METH-induced ROS production and attenuated neurotoxicity. We conclude that induction of HO-1 expression contributes to the attenuation of METH-induced ROS production and neurotoxicity by Vit. C. We suggest that HO-1 induction by Vit. C may serve as a strategy to alleviate METH neurotoxicity.

Behavioral sensitization to cocaine is not associated with changes in serotonin (5-HT) fiber immunoreactivity in rat forebrain

We investigated whether cocaine-induced behavioral sensitization is associated with changes in serotonin (5-HT) immunoreactivity. Male Sprague-Dawley rats were injected with either cocaine (15 mg/kg, IP) or saline twice daily for seven days. Their behavior was observed and rated for locomotor activation and stereotypy. One day after the final injection, the brains were processed for 5-HT immunohistochemistry. The intensity of 5-HT immunoreactive staining of 5-HT axons and terminal varicosities was blindly rated in cocaine-sensitized rats and found not to differ from saline-treated rats. The results support the hypothesis that unlike some amphetamine derivatives, repeated cocaine administration which results in behavioral sensitization is not neurotoxic to 5-HT axons and terminals in the forebrain.

Effects of high-dose methamphetamine administration on serotonin uptake sites in rat brain measured using [3H]cyanoimipramine autoradiography

Repeated administration of high doses of methamphetamine (15 mg/kg given for 5 doses over 24 h) resulted in long-term decreases in the binding of [3H]cyanoimipramine ([3H]CN-IMI) to serotonin uptake sites measured using quantitative autoradiography. Seven days after termination of drug administration decreases were seen in 23 of 28 regions examined. This is consistent with previous studies indicating that methamphetamine and related amphetamines are neurotoxic to serotonin neurons. Significant decreases were still present in many brain areas on the same dosage schedule 30 days after drug administration. However, the number of areas affected was considerably less, consistent with some regrowth of serotonin neurons. At a lower dosage (7.5 mg/kg on the same schedule) no effects on [3H]CN-IMI binding were seen. The results of this study provide support for the serotonergic neurotoxicity of repeated methamphetamine administration in rats. They also show that the neurotoxicity is highly regional and dose dependent.

Effects of methamphetamine on central monoaminergic systems in normal and ascorbic acid-deficient guinea pigs

Repeated injections (s.c.) of methamphetamine (METH) were administered to normal and ascorbic acid-deficient (scorbutic) guinea pigs to assess a potential role for ascorbic acid in the METH-induced effects in central monoaminergic systems. The ascorbic acid-deficient condition differentially influenced the METH-induced responses of dopaminergic and serotonergic variables in the striatum: drug-induced changes in dopaminergic variables were identical in normal and scorbutic animals; METH-induced decreases in serotonergic variables [tryptophan hydroxylase activity, serotonin (5-HT) and 5-hydroxyindoleacetic acid concentrations], however, were prevented in scorbutic animals. The scorbutic condition did not alter significantly the distribution of METH in the brain, nor were striatal concentrations of dopamine (DA) or 5-HT affected. In vitro, ascorbic acid increased significantly DA-mediated [3H]5-HT release from striatal slices, thus suggesting a potential role for ascorbate in DA-mediated actions of METH on serotonergic systems. Although supplemental ascorbate failed to restore the METH-induced serotonergic effects in scorbutic guinea pigs, these data suggest that, in a normal animal, the effects of multiple injections of METH, on serotonergic systems, involve ascorbic acid.