Effects of acute and chronic amphetamine intoxication on brain catecholamines in the guinea pig

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.

Ascorbic acid-deficient condition alters central effects of methamphetamine

Effects of multiple doses of methamphetamine (METH) were examined in normal and ascorbic acid-deficient (scorbutic) guinea pigs. METH-induced decreases of striatal serotonin concentrations were completely antagonized in scorbutic animals. Elevations of nigral substance P-like immunoreactivity also differed significantly in METH-treated scorbutic compared to METH-treated normal animals. Various lines of evidence indicate that dopamine is an essential mediator of METH-induced effects in both serotonergic and substance P systems in the brain areas examined; however, results from the present study indicate that, along with dopamine, ascorbic acid also plays a role in mediating the effects of METH in the central nervous system.

Methamphetamine-induced changes in brain catecholamines in rats and guinea pigs

Repeated administration of methamphetamine was found to cause long-term changes in caudate dopamine levels in the rat and guinea pig. Methamphetamine was administered twice a day for thirty days. Two weeks following the last injection, the animals were killed and brains assayed for catecholamine content. These long-term depletions of dopamine, when combined with similar observations previously reported in rhesus monkeys, indicate a species generality of the effects of methamphetamine on caudate dopamine levels.

Tolerance to amphetamine in two species (rat and guinea pig) that metabolize it differently

It has been proposed that p-hydroxynorephedrine, a metabolite of amphetamine, is responsible for the tolerance that occurs to this drug. To test this idea, the development of tolerance to amphetamine has been examined in two species, the rat and the guinea pig, the former of which produces p-hydroxynorephedrine from amphetamine while the latter does not. In both species, tolerance develops to the anorectic and hyperthermic actions of amphetamine, and similar changes in the pattern of behavioural stimulation are seen.

Amphetamine tachyphylaxis in the pithed guinea-pig

A single dose of (+)-amphetamine (8 mg kg-1, i.p.) administered 4 h before experimentation, reduced the pressor and positive chronotropic effects elicited by this drug (0-6 mg kg-1, i.v.) and augmented the rate of the development of tachyphylaxis to these responses in the pithed guinea-pig preparation. Amphetamine pretreatment reduced the pressor and positive chronotropic effects of phenylephrine (0-1 mg kg-1, i.v.) and the positive chronotropic effects of angiotensin (30 mug kg-1, i.v.). The rate of the development of tachyphylaxis to the cardiovascular responses elicited by phenylephrine and angiotensin was augmented by amphetamine pretreatment. The results suggest that an indirect mechanism (noradrenaline) may in part mediate the cardiovascular effects of these 3 drugs and/or that amphetamine may act as a competitive antagonist at adrenoceptor sites.

Supersensitivity to d-amphetamine- and apomorphine-induced stereotyped behavior induced by chronic d-amphetamine administration

Guinea pigs exhibit an increased sensitivity to both d-amphetamine- and apomorphine-induced stereotyped behavior following chronic pretreatment with d-amphetamine. This chronic agonist or "innervation" supersensitivity is believed to be a reflection of an increased sensitivity of dopamine receptor sites within the corpus striatum to dopaminergic agonists. The appearance of dyskinetic movement disorders in humans following the chronic use of levodopa or amphetamine may be a manifestation of similarly increased dopamine receptor site sensitivity within the striatum. It is suggested that the animal model of "innervation" supersensitivity may be useful in the investigation of these human movement disorders.

The role of p-hydroxylation of amphetamine in its peripheral mode of action

Desipramine completely abolished the blood pressure response to (+) amphetamine in the rat, whereas the tricyclic antidepressant iprindole did not reduce this response. Since both tricyclic drugs inhibit the aromatic hydroxylation of amphetamine, these studies do not support the hypothesis that hydroxylated metabolites of amphetamine, p-hydroxyamphetamine and p-hydroxynorephedrine are essential for the peripheral sympathomimetic effects of amphetamine.