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To clarify the role of oxygen free radicals in expression of the c-fos protooncogene, the distribution of c-fos mRNA was investigated in CuZn-superoxide dismutase (SOD-1) transgenic (Tg) mice compared to control nontransgenic (nTg) littermates after a mild (i.e. 10 min) focal cerebral ischemia. c-fos mRNA expression occurred at 1 to 6 h after reperfusion in the ipsilateral hippocampus and thalamus in Tg mice, whereas it did only at i h in the same regions in nTg mice. In the ipsilateral cortex, there were no significant differences in the pattern of the expression between nTg and Tg mice. These results suggest that oxygen radicals may suppress the expression of c-fos in the hippocampus and thalamus, the areas known to be without blood supply from the middle cerebral artery, following a mild focal cerebral ischemia and reperfusion.

We have used female and male transgenic (Tg) mice that carry the complete sequence of the human copper-zinc (CuZn) superoxide dismutase (SOD) gene in order to assess the lethal effects of methylenedioxyamphetamine (MDA) and methylenedioxymethamphetamine (MDMA). In contrast to non-Tg mice, both heterozygous and homozygous SOD-Tg mice showed resistance to the lethal effects of both drugs. Females of both SOD-Tg and non-Tg strains were somewhat more resistant to the effects of these drugs in comparison to males. In general, homozygous animals show greater resistance to the effects of the two drugs. These results suggest that the acute lethal effects of amphetamine-substituted analogs might involve the intracellular overproduction of the superoxide radicals secondary to hypoxic injury. The gender differences suggest that there might be hormonal-free radical scavenger interactions that offer better protection to female mice. This might be related both to the lifespan of and to the lower prevalence of Parkinson's disease in women. Future studies will need to address these issues further.

Studies of neuronal injury and death after cerebral ischemia and various neurodegenerative diseases have increasingly focused on the interactions between mitochondrial function, reactive oxygen species (ROS) production and glutamate neurotoxicity. Recent findings suggest that increased mitochondrial ROS production precedes neuronal death after glutamate treatment. It is hypothesized that under pathological conditions when mitochondrial function is compromised, extracellular glutamate may exacerbate neuronal injury. In the present study, we focus on the relationship between mitochondrial superoxide production and glutamate neurotoxicity in cultured cortical neurons with normal or reduced levels of manganese-superoxide dismutase (MnSOD) activity. Our results demonstrate that neurons with reduced MnSOD activity are significantly more sensitive to transient exposure to extracellular glutamate. The increased sensitivity of cultured cortical neurons with reduced MnSOD activity is characteristically subject only to treatment by glutamate but not to other glutamate receptor agonists, such as N-methyl-d-aspartate, kainate and quisqualate. We suggest that the reduced MnSOD activity in neurons may exacerbate glutamate neurotoxicity via a mechanism independent of receptor activation.

We examined hsp70 mRNA expression in the brains of transgenic (Tg) mice overexpressing CuZn-superoxide dismutase and in wild-type (Wt) littermates after 3 min of bilateral common carotid artery occlusion. Significant induction of hsp70 mRNA occurred in the hippocampus, the cortex, and other brain regions of the Tg mice 4 h after ischemia compared to the Wt mice. However, there was no histological damage in the brains of Tg and Wt mice as assessed by both Cresyl violet staining and by TUNEL staining for DNA fragmentation. These data suggest that high levels of CuZn-superoxide dismutase activity increase hsp70 mRNA expression and that intense hsp70 mRNA expression does not predict neuronal damage, even in vulnerable hippocampal CA1 neurons.

Methamphetamine (METH) has long-lasting neurotoxic effects on the nigrostriatal dopamine (DA) system of rodents. METH-induced neurotoxicity is thought to involve release of DA in presynaptic DA terminals, which is associated with increased formation of oxygen-based free radicals. We have recently shown that METH-induced striatal DA depletion is attenuated in transgenic (Tg) mice that express the human CuZn-superoxide dismutase (SOD) enzyme. That study did not specifically address the issue of loss of DA terminals. In the present study, we have used receptor autoradiographic studies of [ 125 I]RTI-121-labeled DA uptake sites to evaluate the effects of several doses of METH on striatal DA terminals of Non-Tg as well as of heterozygous and homozygous SOD-Tg mice. In Non-Tg mice, METH caused decreases in striatal DA uptake sites in a dose-dependent fashion. The loss of DA terminals was more prominent in the lateral region than in the medial subdivisions of the striatum. In SOD-Tg mice, the loss of DA terminals caused by METH was attenuated in a gene dosage-dependent fashion, with the homozygous mice showing the greatest protection. Female mice were somewhat more resistant than male mice against these deleterious effects of METH. These results provide further evidence for a role of superoxide radicals in the long-term effects of METH. They also suggest the notion of a gender-specific handling of oxidative stress.

Methamphetamine (METH) causes deleterious effects in brain monoaminergic systems. Evidence has accumulated to suggest that these effects may be mediated via the overproduction of the superoxide radicals. We have recently shown that METH-induced dopamine (DA) depletion is attenuated in copper-zinc superoxide dismutase (CuZnSOD) transgenic (Tg) mice. In the present study, we have used receptor autoradiographic studies of [ 125 I]RTI-55 labeled serotonin (5-HT) uptake sites to evaluate the effect of a two dosing schedule (5 mg/kg or 10 mg/kg×4) of METH on striatal 5-HT uptake sites in nontransgenic (Non-Tg), heterozygous (Hetero) and homozygous (Homo) SOD-Tg mice. The low dose caused no significant changes in striatal 5-HT uptake sites in any of the groups. The high dose caused marked decreases (−74%) in striatal 5-HT uptake sites in Non-Tg mice. In contrast, 5-HT uptake sites showed only a 31% decrease in homozygous SOD-Tg mice whereas heterozygous SOD-Tg mice showed 63% depletion. These results show that increased SOD activity can protect against METH-induced neurotoxicity in striatal serotonergic terminals. These data provide further evidence for a role of oxidative stress in the neurotoxic effects of METH.

Our recent whole cell patch-pipette studies have shown that human trisomy 21 (Down syndrome) cultured fetal dorsal root ganglion (DRG) neurons have accelerated rates of action potential depolarization and repolarization, with reduced spike duration, compared to control neurons. Similar observations were made using DRG neurons from the trisomy 16 mouse, an animal model of trisomy 21. In this study we have used transgenic mice in order to investigate the relationship between excess gene dosage and neurophysiological abnormalities. DRG neurons which possessed additional copies of the gene for human superoxide dismutase-1 (SOD), a gene from the Down syndrome region of chromosome 21, were compared to normal neurons. No electrophysiological differences were found between the two groups of neurons, indicating that increased dosage of the SOD gene alone is not causal to action potential dysfunction found in trisomy 21 and trisomy 16 neurons.

Current and voltage clamp recordings were made with a patch-clamp technique from large, light, dorsal root ganglia (DRG) neurons in tissue culture, derived from trisomy 16 and normal fetal mice. In a Na gradient of [52 mM]o/[28 mM]i, the action potential was accelerated, depolarization and repolarization were faster and the total Na conductance was higher in trisomic neurons. A tetrodotoxin (TTX)-sensitive, fast Na current was demonstrated, about 0.9 nA in trisomic and 0.3 nA in control neurons. The calculated mean specific membrane conductances were 0.74 mS/cm2 and 0.28 mS/cm2, respectively. A TTX-insensitive, slow Na conductance, 3-4 times the fast Na conductance and sensitive to Cd, also was demonstrated, with a 2-fold greater current density and conductance in trisomic as compared with control neurons, of 2.22 +/- 0.54 mS/cm2 and 1.26 +/- 0.09 mS/cm2, respectively. The voltage-dependence and kinetics of the TTX-insensitive, slow, Na current were similar in the two neuronal groups. The results indicate that depolarization during the action potential, in fetal mouse DRG neurons in culture, is mediated by this slow TTX-insensitive Na current. Further, acceleration of depolarization in trisomy 16 neurons is caused by a 2-fold increase in the density of the slow Na current.