Effects on plasma corticosterone levels and brain serotonin from interference with methamphetamine-induced corticosterone release in neonatal rats.

Methamphetamine (MA) induces multiple effects in rats including alterations to corticosterone (CORT) and adrenocorticotropic hormone (ACTH). This effect is age dependent showing a U-shaped function similar to that of other stressors during the stress hyporesponsive period. Neonatal MA treatment leads to adult learning and memory impairments, but whether these are related to MA-induced CORT release is unknown. Here in, four methods were tested in neonatal rats previously established in adult rats for inhibiting stress-induced CORT release: inhibiting synthesis (metyrapone (MET) or ketoconazole (KTZ)) or surgically by adrenalectomy or adrenal autotransplantation (ADXA). Pretreatment on postnatal day 11 with MET or KTZ prior to four doses of 10 mg/kg of MA initially suppressed MA-induced increases in plasma CORT, but 24 h later, even with additional inhibitor treatment, a large CORT increase was seen which exceeded that of MA alone. Adrenalectomy blocked MA-induced increases in CORT but caused a secondary effect on brain serotonin (5-HT) and dopamine (DA), causing greater reductions than those caused by MA alone. ADXA inhibited MA-induced CORT release without causing a 24-h CORT increase and did not produce additional effects on brain 5-HT or DA. Neonatal ADXA is a new model for developmental drug or stress experiments designed to test the role of CORT in mediating early effects on later outcomes.

The effect of amphetamine analogs on cleaved microtubule-associated protein-tau formation in the rat brain.

The present study quantified the cleaved form of the microtubule-associated protein tau (cleaved MAP-tau, C-tau), a previously demonstrated marker of CNS toxicity, following the administration of monoamine-depleting regimens of the psychostimulant drugs amphetamine (AMPH), methamphetamine (METH), +/-3,4-methylenedioxymethamphetamine (MDMA), or para-methoxyamphetamine (PMA) in an attempt to further characterize psychostimulant-induced toxicity. A dopamine (DA)-depleting regimen of AMPH produced an increase in C-tau immunoreactivity in the striatum, while a DA- and serotonin (5-HT)-depleting regimen of METH produced an increase in the number of C-tau immunoreactive cells in the striatum and CA2/CA3 and dentate gyrus regions of the hippocampus. MDMA and PMA, two psychostimulant drugs that produce selective 5-HT depletion in the striatum, had no effect on C-tau immunoreactivity in the striatum or hippocampus. Furthermore, 5,7-dihydroxytryptamine (5,7-DHT), an established 5-HT selective neurotoxin, did not produce an increase in C-tau immunoreactivity. Dual fluorescent immunocytochemistry with antibodies to glial fibrillary acidic protein (GFAP) and C-tau indicated that C-tau immunoreactivity was present in astrocytes, not neurons, suggesting that increased C-tau may be an alternative indicator of reactive gliosis. The present results are consistent with previous findings that the DA-depleting psychostimulants AMPH and METH produce reactive gliosis whereas the 5-HT-depleting drugs MDMA and PMA, as well as the known 5-HT selective neurotoxin 5,7-DHT, do not produce an appreciable glial response.

Phosphodiesterase 1B differentially modulates the effects of methamphetamine on locomotor activity and spatial learning through DARPP32-dependent pathways: evidence from PDE1B-DARPP32 double-knockout mice.

Mice lacking phosphodiesterase 1B (PDE1B) exhibit an exaggerated locomotor response to D-methamphetamine and increased in vitro phosphorylation of DARPP32 (dopamine- and cAMP-regulated phosphoprotein, M r 32 kDa) at Thr34 in striatal brain slices treated with the D1 receptor agonist, SKF81297. These results indicated a possible regulatory role for PDE1B in pathways involving DARPP32. Here, we generated PDE1B x DARPP32 double-knockout (double-KO) mice to test the role of PDE1B in DARPP32-dependent pathways in vivo. Analysis of the response to d-methamphetamine on locomotor activity showed that the hyperactivity experienced by PDE1B mutant mice was blocked in PDE1B-/- x DARPP32-/- double-KO mice, consistent with participation of PDE1B and DARPP32 in the same pathway. Further behavioral testing in the elevated zero-maze revealed that DARPP32-/- mice showed a less anxious phenotype that was nullified in double-mutant mice. In contrast, in the Morris water maze, double-KO mice showed deficits in spatial reversal learning not observed in either single mutant compared with wild-type mice. The data suggest a role for PDE1B in locomotor responses to psychostimulants through modulation of DARPP32-dependent pathways; however, this modulation does not necessarily impact other behaviors, such as anxiety or learning. Instead, the phenotype of double-KOs observed in these latter tasks may be mediated through independent pathways.

Treatment with trimethyltin promotes the formation of cleaved tau in the rat brain.

Trimethyltin (TMT) is a well-documented neurotoxin that affects primarily limbic system structures. Most previous studies have relied on histological approaches to examine TMT neurotoxicity, so the aim of this study was to employ the novel biomarker cleaved MAP-tau (C-tau) to assess TMT-induced CNS injury both quantitatively and qualitatively. Immunoblot studies indicated that cleaved MAP-tau proteins with molecular weights of 45-50 kD were present in the hippocampus of rats treated with TMT but not vehicle 21 days after treatment. Quantitative ELISA revealed that C-tau concentration in rats treated with TMT was greatest at 14 and 21 days in the piriform cortex and hippocampus, respectively; TMT did not significantly increase C-tau concentration in the mesencephalon. C-tau immunocytochemistry demonstrated the greatest TMT-induced damage in the hippocampus and piriform cortex. Additional studies utilizing dual immunocytochemistry revealed that C-tau-labeled cells were also glial fibrillary acidic protein-positive, leading to identification of these cells as astrocytes. Although the origin of C-tau in astrocytes of rats treated with TMT is currently unknown, increased C-tau concentration and the presence of C-tau positive cells in limbic system structures of TMT-treated rats further supports the view that C-tau is a reliable marker of CNS toxicity.

Effect of a serotonin depleting regimen of 3,4-methylenedioxymethamphetamine (MDMA) on the subsequent stimulation of acetylcholine release in the rat prefrontal cortex.

The amphetamine analog 3,4-methylenedioxymethamphetamine (MDMA) is considered to be selectively neurotoxic to serotonergic nerve terminals. Although the long term effects of MDMA on serotonin (5-HT) terminals have been well studied, other potential neurochemical consequences associated with MDMA-induced 5-HT depletion have been less well investigated. In view of the cognitive impairments in human MDMA abusers and the role of acetylcholine (ACh) in learning and memory, it was of interest to determine the influence of a 5-HT depleting regimen of MDMA on subsequent stimulation of ACh release in the prefrontal cortex (PFC). Male rats received vehicle or MDMA (10 mg/kg, i.p. every 2 h for four injections) and underwent in vivo microdialysis 7 days later to assess the subsequent drug- (e.g., MDMA, 5-HT1A agonist) or stress- (e.g., tail pinch, presence of an intruder rat) induced stimulation of ACh release. The increase in the extracellular concentration of ACh in the PFC produced by MDMA (10 mg/kg, i.p.) was significantly less in rats previously exposed to the neurotoxic regimen of MDMA than that in control animals. In contrast, there was no difference in the magnitude of the stimulation of cortical ACh release elicited by the 5-HT1A agonist, 8-hydroxy-2-(di-n-propyl-amino)tetralin (8-OH-DPAT, 0.3mg/kg, s.c.), tail pinch (30 min) or the presence of an intruder rat (40 min) between control animals and animals previously exposed to a neurotoxic regimen of MDMA. These results suggest that although MDMA-induced 5-HT depletion diminishes subsequent MDMA-induced ACh release, there is little impact on cortical ACh release elicited by the stress of pain or the novelty of an environmental intruder.

Quantification and localization of kainic acid-induced neurotoxicity employing a new biomarker of cell death: cleaved microtubule-associated protein-tau (C-tau).

Previous studies of neuronal degeneration induced by the neurotoxin, kainic acid, employed silver stain techniques that are non-quantitative or ELISA measurement of the non-neuronal protein, glial fibrillary acidic protein. As previous studies employed biomarkers that were either non-quantitative or non-neuronal, the present study employed a new neuronally localized biomaker of neuronal damage, cleaved microtubule-associated protein (MAP)-tau (C-tau). The time course of kainate neurotoxicity was quantitatively determined in several brain regions in the present study employing a C-tau specific ELISA. Differences in ELISA determined regional brain levels of C-tau were compared with the density of somatodendritic C-tau labeling qualitatively determined in immunohistochemical anatomical mapping studies of kainic acid-treated animals. Immunoblot studies revealed that the C-tau antibodies employed in the present study were highly specific for proteolytic cleaved C-tau. Immunolabeling of 45 kD-50 kD C-tau proteins was observed only in brain samples from kainic acid-treated but not vehicle-treated rats. Time course studies revealed that C-tau levels determined by ELISA were maximal 3 days after kainic acid with C-tau levels increasing 26-fold in hippocampus, 16-fold in cortex and four-fold in both striatum and hypothalamus. These statistical differences in maximal C-tau levels observed in the ELISA studies were similar to differences qualitatively observed in C-tau immunohistochemical studies. C-tau immunohistochemistry revealed extensive damage in hippocampal regions CA1 and 3, moderate damage in several cortical regions and mild damage in striatum and hypothalamus. Similar cleavage of rat MAP-tau to C-tau has been reported after neuronal degeneration induced by neurotoxic doses of methamphetamine and neuronal degeneration resulting from bacterial meningitis. In humans, C-tau proteolysis has been demonstrated to be a reliable biomarker of neuronal damage in traumatic brain injury and stroke where cerebrospinal C-tau levels are correlated with patient clinical outcome. These data suggest that C-tau proteolysis may prove a reliable species independent biomarker of neuronal degeneration regardless of source of injury.

Methamphetamine enhances the cleavage of the cytoskeletal protein tau in the rat brain.

The view that methamphetamine is neurotoxic to dopaminergic and serotonergic axon terminals has been based largely on biochemical and histological studies. In the present study, methamphetamine-induced structural damage to axons was quantified using a sensitive sandwich enzyme-linked immunosorbent assay developed for the detection of the cleaved form of the cytoskeletal protein tau. The administration of a monoamine-depleting regimen of methamphetamine (4 x 10 mg/kg, i.p. every 2 hours for a total of four injections) produced a time-dependent increase in the concentration of cleaved tau in the striatum. Maximal concentrations of cleaved tau were detected 3 days following methamphetamine administration. Cleaved tau concentrations also were significantly elevated in the dorsal hippocampus and, to a lesser extent, in the prefrontal cortex of methamphetamine-treated rats. Maintenance of rats in a cold (4 degrees C) environment not only prevented the methamphetamine-induced depletion of striatal dopamine and serotonin but also prevented the methamphetamine-induced increase in striatal cleaved tau concentrations. The novel findings from this study are supportive of the view that methamphetamine produces acute structural damage to neurons that may lead to the long-term neurotoxic effects of repeated, high-dose administration of the drug and that cleaved tau reliably quantifies the time-dependent neurotoxic effects of methamphetamine.

Impaired spatial and sequential learning in rats treated neonatally with D-fenfluramine.

D-Fenfluramine, a serotonin releaser, was administered to neonatal rats on postnatal days 11-20 (a stage of hippocampal development analogous to third trimester human ontogeny). As adults, the D-fenfluramine-treated offspring exhibited dose-related impairments of sequential and spatial learning and reference memory in the absence of sensorimotor impairments. Procedures to minimize stress and to control for other performance effects prior to testing for spatial learning demonstrated that nonspecific factors did not account for the selective effects of D-fenfluramine on learning and memory. Developmental D-fenfluramine-induced spatial and sequential learning deficits are similar to previous findings with developmental MDMA treatment. By contrast, recent findings with developmental D-methamphetamine treatment showed spatial learning deficits while sparing sequential learning. The spatial learning effects common to all three drugs suggest that they may share a common mechanism of action, however, the effects are not related to long-lasting changes in hippocampal 5-HT levels as no differences were found in adulthood. Whether the cognitive deficits are related to the effects of substituted amphetamines on corticosteroids, other aspects of the 5-HT system, or some unidentified neuronal substrates is not known, but the data demonstrate that these drugs are all capable of inducing long-term adverse effects on learning.

Enhancement of 3,4-methylenedioxymethamphetamine neurotoxicity by the energy inhibitor malonate.

The acute and long-term effects of the local perfusion of 3,4-methylenedioxymethamphetamine (MDMA) and the interaction with the mitochondrial inhibitor malonate (MAL) were examined in the rat striatum. MDMA, MAL or the combination of MAL with MDMA was reverse dialyzed into the striatum for 8 h via a microdialysis probe while extracellular dopamine (DA) and serotonin (5-HT) were measured. One week later, tissue immediately surrounding the probe was assayed for DA and 5-HT tissue content. Local perfusion of MDMA increased DA and 5-HT release but did not produce long-term depletion of DA or 5-HT in tissue. Malonate also increased both DA and 5-HT release but, in contrast to MDMA, produced only long-term depletion of DA. The combined perfusion of MDMA/MAL synergistically increased the release of DA and 5-HT and produced long-term depletion of both DA and 5-HT in tissue. These results support the conclusion that DA, compared with 5-HT, neurons are more susceptible to mitochondrial inhibition. Moreover, MDMA, which does not normally produce DA depletion in the rat, exacerbated MAL-induced DA depletions. The effect of MDMA in combination with MAL to produce 5-HT depletion suggests a role for bio-energetic stress in MDMA-induced toxicity to 5-HT neurons. Overall, these results highlight the importance of energy balance to the function of DA and 5-HT neurons and to the toxic effects of MDMA.

Effects of lubeluzole on the methamphetamine-induced increase in extracellular glutamate and the long-term depletion of striatal dopamine.

The administration of a neurotoxic regimen of methamphetamine (MA) produces an acute elevation in the extracellular concentrations of dopamine and glutamate in the striatum and a long-term depletion of striatal dopamine content in rats. The intent of the present study was to determine whether attenuation of the MA-induced increase in extracellular glutamate would prevent the depletion of striatal dopamine. Male rats were treated with MA (10 mg/kg, i.p.) or vehicle every 2 h for four injections and concomitantly perfused intrastriatally with either artificial cerebrospinal fluid or lubeluzole (300 microM), a novel neuroprotectant that has been shown to prevent the increase in extracellular glutamate after the induction of neocortical infarct in rats. Lubeluzole significantly attenuated the MA-induced increase in extracellular glutamate in the striatum without affecting the MA-induced increase in extracellular dopamine or the MA-induced hyperthermic response. Nevertheless, lubeluzole did not prevent the long-term depletion of striatal dopamine produced by a neurotoxic regimen of MA. These results suggest that the MA-induced depletion of striatal dopamine may not be dependent on the increased extracellular concentration of striatal glutamate.

Alterations in diurnal and nocturnal locomotor activity in rats treated with a monoamine-depleting regimen of methamphetamine or 3,4-methylenedioxymethamphetamine.

RATIONALE: The long-term neurochemical effects produced by the repeated administration of methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA) are well documented; however, the functional consequences have not been clearly defined. OBJECTIVE: The present study was designed to investigate whether rats treated with a monoamine-depleting regimen of MA or MDMA exhibit disturbances in locomotor activity during the diurnal and nocturnal cycles. METHODS: Rats were treated with the vehicle or a monoamine-depleting regimen of MA or MDMA (10 mg/kg, IP, every 2 h for four injections on a single day). One week after drug treatment, the rats were placed in residential activity chambers and their locomotor activity was monitored for the next 7-day/night cycles. RESULTS: MA-treated rats exhibited depletions of striatal dopamine and serotonin content of approximately 70%, whereas MDMA-treated rats showed depletions of striatal serotonin content of approximately 50%. Rats treated with MA demonstrated a significant reduction in diurnal, but not nocturnal, locomotor activity, whereas MDMA-treated rats exhibited significant reductions in both diurnal and nocturnal locomotor activity. Analysis of the difference in activity between the nocturnal and diurnal cycles revealed that MA-treated animals exhibited a significantly greater change in activity as compared to that observed in vehicle- and MDMA-treated rats. CONCLUSIONS: Although it is unknown whether the adaptations in locomotor activity observed in MA- and MDMA-treated rats are due to the loss of dopamine and/or serotonin, these data suggest that the administration of a monoamine-depleting regimen of MA or MDMA results in alterations in light-cycle-dependent locomotor activity.

Ascorbic acid prevents 3,4-methylenedioxymethamphetamine (MDMA)-induced hydroxyl radical formation and the behavioral and neurochemical consequences of the depletion of brain 5-HT.

MDMA-induced 5-HT neurotoxicity has been proposed to involve oxidative stress due to increased formation of hydroxyl radicals. Recently, MDMA-induced 5-HT neurotoxicity has been shown to be accompanied by a suppression of behavioral and neurochemical responses to a subsequent injection of MDMA. The intent of the present study was to examine whether suppression of the MDMA-induced formation of hydroxyl radicals by an antioxidant, ascorbic acid, attenuates both the MDMA-induced depletion of 5-HT and the functional consequences associated with this depletion. Treatment of rats with ascorbic acid suppressed the generation of hydroxyl radicals, as evidenced by the production of 2,3-dihydroxybenzoic acid from salicylic acid, in the striatum during the administration of a neurotoxic regimen of MDMA. Ascorbic acid also attenuated the MDMA-induced depletion of striatal 5-HT content. In rats treated with a neurotoxic regimen of MDMA, the ability of a subsequent injection of MDMA to increase the extracellular concentration of 5-HT in the striatum, elicit the 5-HT behavioral syndrome, and produce hyperthermia was markedly reduced compared to the responses in control rats. The concomitant administration of ascorbic acid with the neurotoxic regimen of MDMA prevented the diminished neurochemical and behavioral responses to a subsequent injection of MDMA. Finally, a neurotoxic regimen of MDMA produced significant reductions in the concentrations of vitamin E and ascorbic acid in the striatum and hippocampus. Thus, the MDMA-induced depletion of brain 5-HT and the functional consequences thereof appear to involve the induction of oxidative stress resulting from an increased generation of free radicals and diminished antioxidant capacity of the brain.

Neurotoxic regimen of methamphetamine produces evidence of behavioral sensitization in the rat.

A neurotoxic regimen of methamphetamine (MA) produces long-term depletions in neostriatal dopamine and serotonin concentrations. In addition to evidence of dopaminergic and serotonergic neurotoxicity, there is evidence of MA-induced behavioral changes. In this regard, stereotypic behavior elicited by MA is greater in rats treated previously with a neurotoxic regimen of MA than in control animals. The present study was designed to determine whether the enhanced stereotypy observed in MA-treated rats is due to the MA-induced loss of dopamine (neurotoxicity) or to the repeated exposure to MA (sensitization). Rats were treated with MA (10 mg/kg every 2 h for four injections) or vehicle at either a normal (24 degrees C) room temperature or a cold (4 degrees C) room temperature, which has been shown to attenuate the MA-induced loss of dopamine. Stereotypy was assessed 7 days after treatment. Rats that had received a neurotoxic regimen of MA at 24 degrees C exhibited 49% and 45% reductions in neostriatal dopamine and serotonin concentrations, respectively, whereas rats treated with MA at 4 degrees C had no significant neurochemical depletions. Stereotypy elicited by MA (5.0 mg/kg) was significantly greater in rats treated with a neurotoxic regimen of MA regardless of the initial treatment temperature. In addition, an injection of apomorphine (0.5 mg/kg) elicited an enhanced stereotypic response in MA-treated rats. These data suggest that the augmented stereotypic behavior observed in rats treated with a neurotoxic regimen of MA is not due to the loss of dopamine, but rather the manifestation of behavioral sensitization, possibly due to an increase in dopamine receptor sensitivity.

Methamphetamine selectively alters brain glutathione.

As methamphetamine-induced neurotoxicity has been proposed to involve oxidative stress, reduced and oxidized glutathione (GSH and GSSG, respectively), vitamin E and ascorbate were measured in the striata of rats killed 2 or 24 h after a neurotoxic regimen of methamphetamine. At 2 h, methamphetamine increased GSH and GSSG (32. 5% and 43.7%, respectively) compared to controls at 2 h. No difference was seen in glutathione at 24 h, and in vitamin E and ascorbate at either time point. These findings indicate selectivity of methamphetamine for the glutathione system and a role for methamphetamine in inducing oxidative stress.

Rapid and transient inhibition of mitochondrial function following methamphetamine or 3,4-methylenedioxymethamphetamine administration.

Metabolic mapping of discrete brain regions using cytochrome oxidase histochemistry was used as a marker for alterations in mitochondrial function and cytochrome oxidase enzymatic activity in response to high doses of amphetamine derivatives. The activity of cytochrome oxidase, complex IV of the electron transport chain, was determined at three different time-points following administration of high doses of methamphetamine or 3,4-methylenedioxymethamphetamine (MDMA) (four injections of 10-15 mg/kg administered over 8 h). There was a rapid decrease in cytochrome oxidase staining in the striatum (23-29%), nucleus accumbens (29-30%) and substantia nigra (31-43%), 2 h following administration of either methamphetamine and MDMA. This decrease in cytochrome oxidase activity was transient and returned to control levels within 24 h. Since the methamphetamine and MDMA-induced decrease in cytochrome oxidase activity was localized to dopamine-rich regions, increased extracellular concentrations of dopamine may contribute to the inhibition of metabolic function via its metabolism to form quinones or other reactive oxygen species. These results support previous studies demonstrating that psychostimulants induce a rapid and transient decrease in striatal ATP stores and provide further evidence that these drugs of abuse can disrupt mitochondrial function.

A neurotoxic regimen of MDMA suppresses behavioral, thermal and neurochemical responses to subsequent MDMA administration.

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA) produces a long-term depletion of serotonin (5-HT) in the rat brain; this depletion may have some functional consequences. OBJECTIVE: The aim of the present study was to evaluate the acute effects of MDMA on the extracellular concentrations of dopamine and 5-HT, body temperature and the 5-HT behavioral syndrome in rats 7 days following a neurotoxic regimen of MDMA. METHODS: One week after the rats were treated with a neurotoxic regimen of MDMA (10 mg/kg, i.p., every 2 h for a total of four injections), the rats were injected with a subsequent injection of MDMA. In vivo microdialysis combined with HPLC was utilized to measure the extracellular concentration of 5-HT and dopamine in the striatum. The increase in body temperature was determined by rectal temperature measurements, and the 5-HT behavioral syndrome was scored using a rating scale following the administration of MDMA. RESULTS: The neurotoxic regimen produced a 45% reduction in brain 5-HT concentrations. The magnitude of the MDMA-induced increase in the extracellular concentration of 5-HT, but not dopamine, in the striatum produced by an acute injection of MDMA (7.5 mg/kg, i.p.) was reduced in rats treated previously with the neurotoxic regimen of MDMA when compared with that in control animals. In addition, the magnitude of the 5-HT behavioral syndrome, as well as the hyperthermic response, produced by MDMA was markedly diminished in rats that had previously received the neurotoxic regimen of MDMA. CONCLUSIONS: It is concluded that the long-term depletion of brain 5-HT produced by MDMA is accompanied by impairments in 5-HT function, as evidenced by the deficits in the neurochemical, thermal and behavioral responses to subsequent MDMA administration.

Biphasic effect of sigma receptor ligands on the extracellular concentration of dopamine in the striatum of the rat.

The extracellular concentration of dopamine in the striatum of the rat was determined following the intrastriatal infusion of sigma ligands. The administration of (+)-pentazocine (0.3 and 1.0 mM) through a microdialysis probe for 120 min resulted in a biphasic effect on the extracellular concentration of dopamine: a brief increase of approximately 70% followed by a prolonged decrease of approximately 65%. A similar effect on dopamine release was elicited by the (-)-isomer of pentazocine, as well as by di-o-tolylguanidine. In addition, the infusion of the NMDA antagonist 3-(2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP) (100 microM) through the dialysis probe significantly attenuated the initial increase but not the subsequent decrease in dopamine release produced by the intrastriatal infusion of (+)-pentazocine. These data are suggestive that dopamine release in the striatum may be modulated by multiple sigma receptor subtypes and that NMDA receptors may mediate the stimulatory effect of sigma ligands on dopamine release in the striatum.

Involvement of the serotonin transporter in the formation of hydroxyl radicals induced by 3,4-methylenedioxymethamphetamine.

The mechanism of 3,4-methylenedioxymethamphetamine (MDMA)-induced depletion of brain serotonin (5-hydroxytryptamine, 5-HT) has been proposed to involve the generation of reactive oxygen species. In the present study, quantification of the extracellular concentration of 2,3-dihydroxybenzoic acid (2,3-DHBA) from salicylic acid was used as an index of hydroxyl radical generation. Although both MDMA and D-amphetamine markedly increased the extracellular concentration of dopamine in the striatum, only MDMA increased the extracellular concentration of 2,3-DHBA. Treatment with fluoxetine either 1 h prior to or 4 h following the administration of MDMA reduced the MDMA-induced formation of 2,3-DHBA and also attenuated the MDMA-induced depletion of 5-HT in the striatum. These results are supportive of the view that the MDMA-induced generation of hydroxyl radicals and, ultimately, the long-term depletion of 5-HT, is dependent, in part, on the activation of the 5-HT transporter.

Methamphetamine-induced neurotoxicity alters locomotor activity, stereotypic behavior, and stimulated dopamine release in the rat.

The neurochemical evidence of methamphetamine (MA)-induced toxicity to dopaminergic nerve terminals is well documented; however, the functional consequences are not clearly defined. The present study was designed to investigate whether MA-induced dopamine depletions affect locomotor activity, stereotypic behavior, and/or extracellular dopamine concentrations in the neostriatum. Male rats were treated with a neurotoxic regimen of MA (10 mg/kg, i.p., every 2 hr for four injections) or vehicle and tested for functional effects 1 week later. Animals that had received the neurotoxic regimen of MA showed a reduction in both caudate nucleus and nucleus accumbens dopamine contents of 56 and 30%, respectively. Furthermore, MA-treated rats exhibited a significant attenuation in spontaneous activity, as well as a significant diminution in MA (low dose)-stimulated locomotor activity as compared to vehicle-treated rats. However, there were no differences in the MA (low dose)-induced increases in extracellular dopamine concentrations in the caudate nucleus or the nucleus accumbens core of either group. Interestingly, the acute administration of higher doses of MA elicited a significantly augmented stereotypic response and a significantly attenuated increase in the extracellular concentration of dopamine in the caudate nucleus of rats treated with a neurotoxic regimen of MA as compared to vehicle-treated animals. These data indicate that MA-induced neurotoxicity results in abnormal dopamine-mediated behaviors, as well as a brain region-specific impairment in stimulated dopamine release.

Mazindol attenuates the 3,4-methylenedioxymethamphetamine-induced formation of hydroxyl radicals and long-term depletion of serotonin in the striatum.

The formation of hydroxyl radicals following the systemic administration of 3,4-methylenedioxymethamphetamine (MDMA) was studied in the striatum of the rat by quantifying the stable adducts of salicylic acid and D-phenylalanine, namely, 2,3-dihydroxybenzoic acid (2,3-DHBA) and p-tyrosine, respectively. The repeated administration of MDMA produced a sustained increase in the extracellular concentration of 2,3-DHBA and p-tyrosine, as well as dopamine. The MDMA-induced increase in the extracellular concentration of both dopamine and 2,3-DHBA was suppressed in rats treated with mazindol, a dopamine uptake inhibitor. Mazindol also attenuated the long-term depletion of serotonin (5-HT) in the striatum produced by MDMA without altering the acute hyperthermic response to MDMA. These results are supportive of the view that MDMA produces a dopamine-dependent increase in the formation of hydroxyl radicals in the striatum that may contribute to the mechanism whereby MDMA produces a long-term depletion of brain 5-HT content.