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To determine whether behavioral sensitization produced by prolonged D-amphetamine administration affects susceptibility of nigrostriatal dopaminergic neurons to the neurotoxic actions of 6-hydroxydopamine (6-OHDA), rats were treated daily from the 23 rd day after birth for 11 consecutive days with D-amphetamine (1.0 mg/kg s.c.) or saline. On the last day of treatment, one group primed with D-amphetamine and one control group of rats were tested to confirm behavioral sensitization development. The remaining animals were additionally treated on the 34 th day (one day after the last D-amphetamine injection) with 6-OHDA HBr (300 µg in 10 µl i.c.v., salt form, half in each lateral ventricle) or its vehicle. Four weeks later the levels of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-metoxytyramine (3-MT), as well as 5-hydroxytrypatmine (5-HT) and its metabolite 5-hydroxyindoleacteic acid (5-HIAA) were assayed in the striatum, by HPLC/ED. In rats with behavioral sensitization, 6-OHDA reduced endogenous dopamine and its metabolites content to a comparable degree in comparison to controls. This finding indicates that presumed up-regulation of the dopamine transporter in the behaviorially sensitized rats did not increase the neurotoxicity of a high dose of 6-OHDA.
Pregnant Wistar rats received 50 ppm of zinc (ZnSO4 • 7H2O) in their drinking water for the entire duration of pregnancy. On the day of delivery zinc was removed from the drinking water. Another group, dams, received 50 ppm of zinc in drinking water during the suckling period (from delivery until the 21st day of postnatal life). Their offspring were weaned on the 21st day, at which time zinc was removed from the drinking water. The control group drank tap water only. In 8-12-week-old offspring of all three groups the DA, DOPAC, HVA, 3-MT, 5-HT, 5-HIAA, NA, and MOPEG synthesis rate in the brain was estimated by HPLC/ED technique. Independent behavioral exam were performed such as locomotor and exploratory activity, irritability, yawning and oral activity, stereotype behavior, catalepsy and others. For the above, cen­tral DA receptor agonists (quinpirole, SKF 38393, apomorphine, 7-OH-DPAT) or antagonists (haloperidol, SCH 23390) were used. It was found that exposure to zinc during early stages of ontogenic development produce changes in the central dopaminergic system activity of adult offspring. From the above we con­cluded that uncontrolled supplementation with zinc during pregnancy or lactation can induce disturbance of the central dopaminergic system in adult mammal.
On the morning of the first day of pregnancy, Wistar rats were administered a single IP injection of either zinc sulfate (10.0 mg/kg) or saline. For the remainder of pregnancy, half the rats in each group then consumed filtered tap water while the other half consumed filtered tap water with 50 ppm of cadmium (CdCl₂ ). At eight weeks after birth, the behavioral profile of male offspring was assessed in the following way: Apomorphine (non-selective dopamine receptor agonist), (+)-7-hydroxy-2-(di-n-propylamino) tetralin (7-OH-DPAT) (D₃ agonist) and (+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol (SKF 38393) (D₁ agonist) were used to evaluate stereotyped behavior, yawning activity and oral movements – indices for these respective agonists. In addition, two dopamine receptor antagonists, haloperidol (D₂ antagonist) and 7-chloro-8-hydroxy3-methyl-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzapine (SCH 23390) (D₁ antagonist) were used to evaluate cataleptogenic activity. Additional behavioral parameters studied were locomotor activity, irritability and reaction to a painful stimulus. Dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT) were quantified in the striatum, hippocampus and in the frontal cortex of the brain by means of HPLC/ED technique. In addition, cadmium levels were analyzed in the brain, liver, kidney and bone of newborn rats. Our results indicate that prenatal exposure of pregnant rats to cadmium produced alterations in the reactivity of central dopamine receptors and modulated the level of dopamine and its metabolites in the offsprings’ brains. A single injection of zinc, preceding cadmium consumption, attenuated some of the effects of cadmium on the offsprings’ dopaminergic system. Zinc also reduced cadmium deposition in the brain, kidney and bone, but enhanced its accumulation in liver. In summary, zinc may exert some neuroprotective effects against cadmium neurotoxicity.
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