Histological and ultrastructural evidence that D-amphetamine causes degeneration in neostriatum and frontal cortex of rats

D-amphetamine maintenance therapy reduces cocaine use in female rats

RATIONALE

D-amphetamine maintenance therapy is a promising strategy to reduce drug use in cocaine use disorder (addiction). In both male rats and human cocaine users, d-amphetamine treatment reduces cocaine-taking and -seeking. However, this has not been examined systematically in female animals, even though cocaine addiction afflicts both sexes, and the sexes can differ in their response to cocaine.

OBJECTIVES

We determined how d-amphetamine maintenance therapy during cocaine self-administration influences cocaine use in female rats.

METHODS

In experiment 1, two groups of female rats received 14 intermittent access (IntA) cocaine self-administration sessions. One group received concomitant d-amphetamine maintenance treatment (COC + A rats; 5 mg/kg/day, via minipump), the other group did not (COC rats). After discontinuing d-amphetamine treatment, we measured responding for cocaine under a progressive ratio schedule, responding under extinction, and cocaine-primed reinstatement of drug-seeking. In experiment 2, we assessed the effects of d-amphetamine maintenance on these measures in already IntA cocaine-experienced rats. Thus, rats first received 14 IntA cocaine self-administration sessions without d-amphetamine. They then received 14 more IntA sessions, now either with (COC/COC + A rats) or without (COC/COC rats) concomitant d-amphetamine treatment.

RESULTS

In both experiments, d-amphetamine treatment did not significantly influence ongoing cocaine self-administration behaviour. After d-amphetamine treatment cessation, cocaine-primed reinstatement of cocaine-seeking was also unchanged. However, after d-amphetamine treatment cessation, rats responded less for cocaine both under progressive ratio and extinction conditions.

CONCLUSIONS

D-amphetamine treatment can both prevent and reverse increases in the motivation to take and seek cocaine in female animals.

Single Dose of Amphetamine Induces Delayed Subregional Attenuation of Cholinergic Interneuron Activity in the Striatum

Psychostimulants such as amphetamine (AMPH) target dopamine (DA) neuron synapses to engender drug-induced plasticity. While DA neurons modulate the activity of striatal (Str) cholinergic interneurons (ChIs) with regional heterogeneity, how AMPH affects ChI activity has not been elucidated. Here, we applied quantitative fluorescence imaging approaches to map the dose-dependent effects of a single dose of AMPH on ChI activity at 2.5 and 24 h after injection across the mouse Str using the activity-dependent marker phosphorylated ribosomal protein S6 (p-rpS6240/244). AMPH did not affect the distribution or morphology of ChIs in any Str subregion. While AMPH at either dose had no effect on ChI activity after 2.5 h, ChI activity was dose dependently reduced after 24 h specifically in the ventral Str/nucleus accumbens (NAc), a critical site of psychostimulant action. AMPH at either dose did not affect the spontaneous firing of ChIs. Altogether this work demonstrates that a single dose of AMPH has delayed regionally heterogeneous effects on ChI activity, which most likely involves extra-Str synaptic input.

Is Attention-Deficit/Hyperactivity Disorder a Risk Syndrome for Parkinson's Disease?

Recent epidemiological evidence indicates that diagnosis of attention-deficit/hyperactivity disorder (ADHD) is associated with increased risk for diseases of the basal ganglia and cerebellum, including Parkinson's disease (PD). The evidence reviewed here indicates that deficits in striatal dopamine are a shared component of the causal chains that produce these disorders. Neuropsychological studies of adult ADHD, prodromal PD, and early-stage PD reveal similar deficits in executive functions, memory, attention, and inhibition that are mediated by similar neural substrates. These and other findings are consistent with the possibility that ADHD may be part of the PD prodrome. The mechanisms that may mediate the association between PD and ADHD include neurotoxic effects of stimulants, other environmental exposures, and Lewy pathology. Understanding the nature of the association between PD and ADHD may provide insight into the etiology and pathogenesis of both disorders. The possible contribution of stimulants to this association may have important clinical and public health implications.

Animal models of drug addiction: Where do we go from here?

Compulsion and impulsivity are both primary features of drug addiction. Based on decades of animal research, we have a detailed understanding of the factors (both environmental and physiological) that influence compulsive drug use, but still know relatively little about the impulsive aspects of drug addiction. This review outlines our current knowledge of the relationship between impulsivity and drug addiction, focusing on cognitive and motor impulsivity, which are particularly relevant to this disorder. Topics to be discussed include the influence of chronic drug administration on impulsivity, the mechanisms that may explain drug-induced impulsivity, and the role of individual differences in the development of impulsive drug use. In addition, the manner in which contemporary theories of drug addiction conceptualize the relationship between impulsivity and compulsion is examined. Most importantly, this review emphasizes a critical role for animal research in understanding the role of impulsivity in the development and maintenance of drug addiction.

Psychostimulants As Cognitive Enhancers in Adolescents: More Risk than Reward?

Methylphenidate and other psychostimulants, originally developed to treat attention deficit-hyperactivity disorder, are increasingly abused by healthy adolescents and adults seeking an advantage in scholastic performance and work productivity. However, how these drugs may affect cognitive performance, especially in the young brain, remains unclear. Here, we review recent literature and emphasize the risks of abuse of psychostimulants in healthy adolescents and young adults. We conclude that while the desire for cognitive enhancement, particularly with rising costs of education and increasingly competitive nature of scholarship programs, is unlikely to diminish in the near future, it is crucial for the scientific community to thoroughly examine the efficacy and safety of these stimulants in healthy populations across development. The current dearth of knowledge on the dose–response curve, metabolism, and cognitive outcomes in adolescents following methylphenidate or other psychostimulant exposure may be perpetuating a perception of these drugs as “safe” when that might not be true for developing brains.

Brain dopamine neurone 'damage': methamphetamine users vs. Parkinson's disease - a critical assessment of the evidence

The objective of this review is to evaluate the evidence that recreational methamphetamine exposure might damage dopamine neurones in human brain, as predicted by experimental animal findings. Brain dopamine marker data in methamphetamine users can now be compared with those in Parkinson's disease, for which the Oleh Hornykiewicz discovery in Vienna of a brain dopamine deficiency is established. Whereas all examined striatal (caudate and putamen) dopamine neuronal markers are decreased in Parkinson's disease, levels of only some (dopamine, dopamine transporter) but not others (dopamine metabolites, synthetic enzymes, vesicular monoamine transporter 2) are below normal in methamphetamine users. This suggests that loss of dopamine neurones might not be characteristic of methamphetamine exposure in at least some human drug users. In methamphetamine users, dopamine loss was more marked in caudate than in putamen, whereas in Parkinson's disease, the putamen is distinctly more affected. Substantia nigra loss of dopamine-containing cell bodies is characteristic of Parkinson's disease, but similar neuropathological studies have yet to be conducted in methamphetamine users. Similarly, it is uncertain whether brain gliosis, a common feature of brain damage, occurs after methamphetamine exposure in humans. Preliminary epidemiological findings suggest that methamphetamine use might increase risk of subsequent development of Parkinson's disease. We conclude that the available literature is insufficient to indicate that recreational methamphetamine exposure likely causes loss of dopamine neurones in humans but does suggest presence of a striatal dopamine deficiency that, in principle, could be corrected by dopamine substitution medication if safety and subject selection considerations can be resolved.

PEGylation of a High-Affinity Anti-(+)Methamphetamine Single Chain Antibody Fragment Extends Functional Half-Life by Reducing Clearance

PURPOSE

Methamphetamine (METH) abuse is a worldwide drug problem, yet no FDA-approved pharmacological treatments are available for METH abuse. Therefore, we produced an anti-METH single chain antibody fragment (scFv7F9Cys) as a pharmacological treatment for METH abuse. ScFv's have a short half-life due to their small size, limiting their clinical use. Thus, we examined the pharmacokinetic effects of conjugating poly(ethylene) glycol (-PEG) to scFv7F9Cys to extend its functional half-life.

METHODS

The affinity of scFv7F9Cys and PEG conjugates to METH was determined in vitro via equilibrium dialysis saturation binding. Pharmacokinetic and parameters of scFv7F9Cys and scFv7F9Cys-PEG20K (30 mg/kg i.v. each) and their ability to bind METH in vivo were determined in male Sprague-Dawley rats receiving a subcutaneous infusion of METH (3.2 mg/kg/day).

RESULTS

Of three PEGylated conjugates, scFv7F9Cys-PEG20K was determined the most viable therapeutic candidate. PEGylation of scFv7F9Cys did not alter METH binding functionality in vitro, and produced a 27-fold increase in the in vivo half-life of the antibody fragment. Furthermore, total METH serum concentrations increased following scFv7F9Cys or scFv7F9Cys-PEG20K administration, with scFv7F9Cys-PEG20K producing significantly longer changes in METH distribution than scFv7F9Cys.

CONCLUSIONS

PEGylation of scFv7F9Cys significantly increase the functional half-life of scFv7F9Cys, suggesting it may be a long-lasting pharmacological treatment option for METH abuse.

Glutamatergic neurometabolites during early abstinence from chronic methamphetamine abuse

BACKGROUND

The acute phase of abstinence from methamphetamine abuse is critical for rehabilitation success. Proton magnetic resonance spectroscopy has detected below-normal levels of glutamate+glutamine in anterior middle cingulate of chronic methamphetamine abusers during early abstinence, attributed to abstinence-induced downregulation of the glutamatergic systems in the brain. This study further explored this phenomenon.

METHODS

We measured glutamate+glutamine in additional cortical regions (midline posterior cingulate, midline precuneus, and bilateral inferior frontal cortex) putatively affected by methamphetamine. We examined the relationship between glutamate+glutamine in each region with duration of methamphetamine abuse as well as the depressive symptoms of early abstinence. Magnetic resonance spectroscopic imaging was acquired at 1.5 T from a methamphetamine group of 44 adults who had chronically abused methamphetamine and a control group of 23 age-, sex-, and tobacco smoking-matched healthy volunteers. Participants in the methamphetamine group were studied as inpatients during the first week of abstinence from the drug and were not receiving treatment.

RESULTS

In the methamphetamine group, small but significant (5-15%, P<.05) decrements (vs control) in glutamate+glutamine were observed in posterior cingulate, precuneus, and right inferior frontal cortex; glutamate+glutamine in posterior cingulate was negatively correlated (P<.05) with years of methamphetamine abuse. The Beck Depression Inventory score was negatively correlated (P<.005) with glutamate+glutamine in right inferior frontal cortex.

CONCLUSIONS

Our findings support the idea that glutamatergic metabolism is downregulated in early abstinence in multiple cortical regions. The extent of downregulation may vary with length of abuse and may be associated with severity of depressive symptoms emergent in early recovery.

Chronic D-amphetamine administered from childhood to adulthood dose-dependently increases the survival of new neurons in the hippocampus of male C57BL/6J mice

Adderall is widely prescribed for attention deficit hyperactivity disorder (ADHD) though long term neurological effects of the main ingredient d-amphetamine are not well understood. The purpose of this study was to examine effects of clinically prescribed doses of d-amphetamine and one abuse dose administered from childhood to adulthood on adult hippocampal neurogenesis and activation of the granule layer of the dentate gyrus. Beginning in early adolescence (age 28 days) to adulthood (age 71), male C57BL/6J mice were administered twice daily i.p. injections of vehicle, 0.25, 0.5 or 2mg/kg d-amphetamine. Locomotor activity was measured in home cages by video tracking. At age 53-56, mice received bromodeoxyuridine (BrdU) injections to label dividing cells. Immunohistochemical detection of BrdU, neuronal nuclear protein (NeuN), doublecortin (DCX) and Ki67 was used to measure neurogenesis and cell proliferation at age 71. ΔFosB was measured as an indicator of repeated neuronal activation. An additional cohort of mice was treated similarly except euthanized at age 58 to measure activation of granule neurons from d-amphetamine (by detection of c-Fos) and cell proliferation (Ki67) at a time when the fate of BrdU cells would have been determined in the first cohort. d-Amphetamine dose-dependently increased survival and differentiation of BrdU cells into neurons and increased number of DCX cells without affecting the number of Ki67 cells. Low doses of d-amphetamine decreased c-Fos and ΔFosB in the granule layer. Only the high dose induced substantial locomotor stimulation and sensitization. Results suggest both therapeutic and abuse doses of d-amphetamine increase the number of new neurons in the hippocampus when administered from adolescence to adulthood by increasing survival and differentiation of cells into neurons not by increasing progenitor cell proliferation. Mechanisms for amphetamine-induced neurogenesis are unknown but appear activity independent. Results suggest part of the beneficial effects of therapeutic doses of d-amphetamine for ADHD could be via increased hippocampal neurogenesis.

Increased risk of Parkinson's disease in individuals hospitalized with conditions related to the use of methamphetamine or other amphetamine-type drugs

BACKGROUND

Since methamphetamine and other amphetamine-type stimulants (meth/amphetamine) can damage dopaminergic neurons, researchers have long speculated that these drugs may predispose users to develop Parkinson's disease (PD), a dopamine deficiency neurological disorder.

METHODS

We employed a retrospective population-based cohort study using all linked statewide California inpatient hospital episodes and death records from January 1, 1990 through December 31, 2005. Patients at least 30 years of age were followed for up to 16 years. Competing risks analysis was used to determine whether the meth/amphetamine cohort had elevated risk of developing PD (ICD-9 332.0; ICD-10 G20) in comparison to a matched population-proxy appendicitis group and a matched cocaine drug control group. Individuals admitted to hospital with meth/amphetamine-related conditions (n=40,472; ICD-9 codes 304.4, 305.7, 969.7, E854.2) were matched on age, race, sex, date of index admission, and patterns of hospital admission with patients with appendicitis conditions (n=207,831; ICD-9 codes 540-542) and also individuals with cocaine-use disorders (n=35,335; ICD-9 codes 304.2, 305.6, 968.5).

RESULTS

The meth/amphetamine cohort showed increased risk of PD compared to both that of the matched appendicitis group [hazard ratio (HR)=1.76, 95% CI: 1.12-2.75, p=0.017] and the matched cocaine group [HR=2.44, 95% CI: 1.32-4.41, p=0.004]. The cocaine group did not show elevated hazard of PD compared to the matched appendicitis group [HR=1.04, 95% CI: 0.56-1.93, p=0.80].

CONCLUSION

These data provide evidence that meth/amphetamine users have above-normal risk for developing PD.

The Basal Ganglia as a Substrate for the Multiple Actions of Amphetamines

Amphetamines are psychostimulant drugs with high abuse potential. Acute and chronic doses of amphetamines affect dopamine (DA) neurotransmission in the basal ganglia. The basal ganglia are a group of subcortical nuclei that are anatomically positioned to integrate cognitive, motor and sensorimotor inputs from the cortex. Amphetamines can differentially alter the functioning of specific BG circuits to produce neurochemical changes that affect cognition, movement, and drug seeking behavior through their effects on DA neurotransmission. This review focuses on how alterations in dopaminergic neurotransmission within distinct basal ganglia pathways can modify their functional output to predict and explain the acute and long term behavioral consequences of amphetamine exposure.

Methamphetamine induces striatal neurokinin-1 receptor endocytosis primarily in somatostatin/NPY/NOS interneurons and the role of dopamine receptors in mice

Methamphetamine (METH) is a psychostimulant that induces long-term deficits of dopamine terminal markers and apoptotic cell death in the striatum. Our laboratory demonstrated that pharmacological blockade of the neurokinin-1 receptor attenuated the METH-induced damage to the striatal dopamine terminals and the apoptotic cell death of some striatal neurons. Here, we used histological methods to assess the effect of METH on neurokinin-1 receptor trafficking in the striatum as an indirect index of signaling by the neuropeptide substance P (natural ligand for this receptor). Male mice received a single injection of METH (30 mg/kg, i.p.) and were sacrificed 30 min later. Immunohistofluorescence confocal microscopy confirmed that the neurokinin-1 receptor is located on cholinergic and somatostatin interneurons of the striatum. METH induced the trafficking of the neurokinin-1 receptor from the membrane into cytoplasmic endosomes primarily in the somatostatin/NPY/NOS interneurons, and this phenomenon was attenuated by antagonists of the dopamine D1 (SCH-23390), D2 (raclopride), or neurokinin-1 (WIN-51,708) receptors. These data demonstrate that METH induces the trafficking of the striatal neurokinin-1 receptors principally in the somatostatin/NPY/NOS interneurons and that this phenomenon is dependent on the activity of dopamine D1 and D2 receptors.

Ultrastructural characterization of tryptophan hydroxylase 2-specific cortical serotonergic fibers and dorsal raphe neuronal cell bodies after MDMA treatment in rat

RATIONALE

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") is a widely used recreational drug known to cause selective long-term serotonergic damage.

OBJECTIVES

The aim of this study was to characterize the ultrastructure of serotonergic pericarya and proximal neurites in the dorsal raphe nucleus as well as the ultrastructure of serotonergic axons in the frontal cortex of adolescent Dark Agouti rats 3 days after treatment with 15 mg/kg i.p. MDMA.

METHODS

Light microscopic immunohistochemistry and pre-embedding immunoelectron microscopy with a novel tryptophan hydroxylase-2 (Tph2) specific antibody, as a marker of serotonergic structures.

RESULTS

Light microscopic analysis showed reduced serotonergic axon density and aberrant swollen varicosities in the frontal cortex of MDMA-treated animals. According to the electron microscopic analysis, Tph2 exhibited diffuse cytoplasmic immunolocalization in dorsal raphe neuronal cell bodies. The ultrastructural-morphometric analysis of these cell bodies did not indicate pathological changes or significant alteration in the cross-sectional areal density of any examined organelles. Proximal serotonergic neurites in the dorsal raphe exhibited no ultrastructural alteration. However, in the frontal cortex among intact fibers, numerous serotonergic axons with destructed microtubules were found. Most of their mitochondria were intact, albeit some injured axons also contained degenerating mitochondria; moreover, a few of them comprised confluent membrane whorls only.

CONCLUSIONS

Our treatment protocol does not lead to ultrastructural alteration in the serotonergic dorsal raphe cell bodies and in their proximal neurites but causes impairment in cortical serotonergic axons. In these, the main ultrastructural alteration is the destruction of microtubules although a smaller portion of these axons probably undergo an irreversible damage.

Acute quetiapine dose-dependently exacerbates anhedonia induced by withdrawal from escalating doses of d-amphetamine

Recent clinical studies show that the atypical antipsychotic medication, quetiapine, may be beneficial in the treatment of substance abuse by alleviating the withdrawal-negative affect stage of addiction. Since the effect of quetiapine on central reward function is largely unknown we studied its effects on brain stimulation reward in animals under withdrawal from escalating doses of d-amphetamine. Male Sprague-Dawley rats were trained to produce an operant response to receive a short train of electrical stimulation to the lateral hypothalamus. Measures of reward threshold were determined with the curve-shift method in different groups of rats before, and during four days after treatment with escalating doses (1 to 10mg/kg, i.p.) of d-amphetamine or its vehicle. At 24h of withdrawal, the effects of two doses of quetiapine (2 and 10mg/kg i.p.) were tested. Animals treated with d-amphetamine showed a 25% reward deficit at 24h of withdrawal, an effect that decreased progressively over the next three days. Quetiapine attenuated reward in the vehicle-control animals, and amplified the anhedonia at the moderate, but not the low, dose in the animals under withdrawal. These results show that acute treatment with clinically relevant doses of quetiapine for the treatment of schizophrenia may exacerbate anhedonia induced by amphetamine withdrawal. Further research should investigate whether repeated treatment with quetiapine has the ability to reverse amphetamine withdrawal-induced anhedonia.

Medial prefrontal gray matter volume reductions in users of amphetamine-type stimulants revealed by combined tract-based spatial statistics and voxel-based morphometry

Amphetamine-type stimulants (ATS) refer to a group of drugs whose principal members include amphetamine, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA). Worldwide, ATS are among the most common illicit drugs. Therefore, understanding whether and to what extent ATS exposure affects brain structure and functioning in recreational users has become a critical public health issue. We studied gray and white matter densities in 20 experienced users of ATS (more than 100 units MDMA and/or 50 g of amphetamine lifetime dose), 42 low exposure users with very limited ATS experience (less than 5 units lifetime dose) and 16 drug-naive controls. A tract-based spatial statistics (TBSS) analysis of fractional anisotropy images was applied to diffusion magnetic resonance imaging (MRI) data. Furthermore, alignment invariant white matter tract representations acquired from the TBSS analysis were used as a reference for inter-subject brain registrations in a voxel-based morphometry (VBM) analysis of gray matter volume, reducing characteristic alignment inaccuracies associated with this voxel-wise gray matter investigation approach. Between-group white matter comparison revealed no significant results. However, compared to low exposure users, experienced users showed several regions of lower gray matter volume in medial frontal regions, in particular the orbital and medial frontal cortex. Differences are likely to reflect effects of repeated ATS exposure even in recreational users. However, differences in pre-existing or confounding factors might also account for between-group differences.

Neuroprotective strategies in drug abuse-evoked encephalopathy

Encephalopathy is evidenced as an altered mental state with various neurological symptoms, such as memory and cognitive problems. The type of a substance-evoked encephalopathy will depend on the drug, substance, or combination being abused. The categories into which we could place the various abused substances could be tentatively divided into stimulants, amphetamines, hallucinogens, narcotics, inhalants, anesthetics, anabolic steroids, and antipsychotics/antidepressants. Other factors that may underlie encephalopathy, such as infectious agents, environmental, and other factors have also to be taken into account. Drugs of abuse can be highly toxic to the CNS following acute, but more so in chronic exposure, and can produce significant damage to other organs, such as the heart, lungs, liver, and kidneys. The damage to these organs may be at least partially reversible when drug abuse is stopped but CNS damage from repeated or prolonged abuse is often irreversible. The major pathways for the organ and CNS toxicity could be related to ischemic events as well as increased cell damage due to metabolic or mitochondrial dysfunction resulting in increased excitotoxicity, reduced energy production, and lowered antioxidant potential. These susceptibilities could be strengthened by the use of antioxidants to combat free radicals (e.g., vitamin E, lipoic acid); trying to improve energy generation by using mitochondriotropic/metabolic compounds (e.g., thiamine, coenzyme Q10, carnitine, riboflavin); by reducing excitotoxicity (e.g., glutamate antagonists) and other possible strategies, such as robust gene response, need to be investigated further. The drug-abuse-evoked encephalopathy still needs to be studied further to enable better preventative and protective strategies.

Neonatal Escherichia coli infection alters glial, cytokine, and neuronal gene expression in response to acute amphetamine in adolescent rats

Neonatal bacterial infection in rats alters the responses to a variety of subsequent challenges later in life. Here we explored the effects of neonatal bacterial infection on a subsequent drug challenge during adolescence, using administration of the psychostimulant amphetamine. Male rat pups were injected on postnatal day 4 (P4) with live Escherichia coli (E. coli) or PBS vehicle, and then received amphetamine (15mg/kg) or saline on P40. Quantitative RT-PCR was performed on micropunches taken from medial prefrontal cortex, nucleus accumbens, and the CA1 subfield of the hippocampus. mRNA for glial and neuronal activation markers as well as pro-inflammatory and anti-inflammatory cytokines were assessed. Amphetamine produced brain region specific increases in many of these genes in PBS controls, while these effects were blunted or absent in neonatal E. coli treated rats. In contrast to the potentiating effect of neonatal E. coli on glial and cytokine responses to an immune challenge previously observed, neonatal E. coli infection attenuates glial and cytokine responses to an amphetamine challenge.

FosB null mutant mice show enhanced methamphetamine neurotoxicity: potential involvement of FosB in intracellular feedback signaling and astroglial function

Previous studies show that (1) two members of fos family transcription factors, c-Fos and FosB, are induced in frontal brain regions by methamphetamine; (2) null mutation of c-Fos exacerbates methamphetamine-induced neurotoxicity; and (3) null mutation of FosB enhances behavioral responses to cocaine. Here we sought a role of FosB in responses to methamphetamine by studying FosB null mutant (-/-) mice. After a 10 mg/kg methamphetamine injection, FosB(-/-) mice were more prone to self-injury. Concomitantly, the intracellular feedback regulators of Sprouty and Rad-Gem-Kir (RGK) family transcripts had lower expression profiles in the frontoparietal cortex and striatum of the FosB(-/-) mice. Three days after administration of four 10 mg/kg methamphetamine injections, the frontoparietal cortex and striatum of FosB(-/-) mice contained more degenerated neurons as determined by Fluoro-Jade B staining. The abundance of the small neutral amino acids, serine, alanine, and glycine, was lower and/or was poorly induced after methamphetamine administration in the frontoparietal cortex and striatum of FosB(-/-) mice. In addition, methamphetamine-treated FosB(-/-) frontoparietal and piriform cortices showed more extravasation of immunoglobulin, which is indicative of blood-brain barrier dysfunction. Methamphetamine-induced hyperthermia, brain dopamine content, and loss of tyrosine hydroxylase immunoreactivity in the striatum, however, were not different between genotypes. These data indicate that FosB is involved in thermoregulation-independent protective functions against methamphetamine neurotoxicity in postsynaptic neurons. Our findings suggest two possible mechanisms of FosB-mediated neuroprotection: one is induction of negative feedback regulation within postsynaptic neurons through Sprouty and RGK. Another is supporting astroglial function such as maintenance of the blood-brain barrier, and metabolism of serine and glycine, which are important glial modulators of nerve cells.

Decreased reinforcing effects of cocaine following 2 weeks of continuous D-amphetamine treatment in rats

RATIONALE

Recent studies have investigated D-amphetamine as a potential agonist medication for cocaine dependence. In rats, a 14-day continuous infusion of D: -amphetamine via osmotic mini-pump has been shown to decrease cocaine-reinforced responding under a progressive ratio (PR) schedule of reinforcement.

OBJECTIVES

This study was designed to assess the influences of the D-amphetamine treatment dose and self-administered cocaine dose on the magnitude of this effect.

MATERIALS AND METHODS

Experiment 1: rats were trained to self-administer 1.5 mg/kg/inj cocaine under a PR schedule, then implanted with D-amphetamine mini-pumps for 14 days (days 1-7, 5 mg/kg/day; days 8-14, 7.5 mg/kg/day). Breakpoints were evaluated throughout the treatment period and 14 days post-treatment. Experiment 2: rats were trained to self-administer cocaine under a PR schedule and initial dose-response curves were determined before implantation of D-amphetamine mini-pumps. During the 14-day D-amphetamine (5 mg/kg/day) treatment period, rats self-administered one of four cocaine doses (0.19, 0.38, 0.75, or 1.5 mg/kg/inj). A post-treatment PR dose-response curve and responding under a fixed ratio 1 (FR1) schedule were evaluated after mini-pump removal.

RESULTS

Experiment 1: breakpoints for 1.5 mg/kg/inj cocaine were unchanged by the increasing dose of D-amphetamine. Experiment 2: the PR dose-response curve was shifted downward after the treatment period in rats that had self-administered 0.19 and 0.38 mg/kg/inj cocaine. In contrast, rats in the 0.75 and 1.5 mg/kg/inj groups demonstrated increased rates of cocaine intake under an FR1 schedule after the treatment period.

CONCLUSIONS

These data suggest that continuous D-amphetamine treatment attenuates the reinforcing effects of cocaine.

Amphetamine causes dopamine depletion and cell death in the mouse olfactory bulb

Amphetamine is a neurotoxic psychostimulant that causes dopamine depletion and neuronal death in the rodent striatum. In the present study, we sought to determine if toxic doses of the drug can also induce pathological changes in the mouse olfactory bulb. We found that injections of amphetamine (10 mg/kg x 4, given 2 h apart) caused significant decreases in dopamine levels in that structure. This dose of the drug also induced substantial increases in the number of terminal deoxynucleotidyl transferase-mediated deoxyribonucleotide triphosphate (dNTP) nick end labeling (TUNEL)-positive cells in the olfactory bulb indicative of elevated DNA fragmentation. These results show that the toxic effects of amphetamine involve the olfactory bulb in addition to the striatum. These observations need to be taken into consideration when discussing the clinical course of amphetamine addiction.

Immunohistochemical increase in cyclooxygenase-2 without apoptosis in different brain areas of subchronic nicotine- and D-amphetamine-treated rats

Cyclooxygenase-2 (COX-2) upregulation has been related to both neurodegeneration and physiological processes. To clarify whether nicotine-induced upregulation of COX-2 occurs, and to analyse its significance, a comparative immunohistochemical and Western blot study was performed on the frontoparietal cortex, hippocampus and cerebellar cortex of rats treated (14 days) with nicotine, D(+)amphetamine (0.35 and 1.16 mg free base/kg/day, respectively), or both drugs simultaneously. None of these treatments promoted neuronal apoptosis. Lipid peroxidation increased in the hippocampus of the nicotine-treated rats and in all the brain regions examined in the D(+)amphetamine rats, but not in the double-treated animals. Both molecules increased the COX-2 content (as determined by the number of immunopositive neurons and the intensity of their immunodeposits) in an area-, layer- and neuron type-dependent manner, in all brain regions in which a large number of COX-2 immunopositive neurons were observed in controls (the somatosensory cortical areas, CA-1, CA-3, the gyrus dentatus, the ectorhinal/perirhinal areas, and the gyrus cingularis). No increase was seen in the motor cortical areas, while a reduction was recorded in the cerebellar cortex; these regions had only a few immunopositive neurons in controls. Western blot analysis revealed a 50-80% increase in COX-2 in the brain cortex and hippocampus of nicotine-treated rats, and similar increases (150-200%) in the cortex of the D(+)amphetamine- and nicotine + D(+)amphetamine-treated rats. Nicotine-induced upregulation of COX-2 seems to be related to neuronal plasticity rather than neurodegeneration. Nicotine agonists might be useful in the treatment of cognitive disorders.

Dopamine receptor activation reveals a novel, kynurenate-sensitive component of striatal N-methyl-D-aspartate neurotoxicity

The N-methyl-d-aspartate (NMDA) subtype of glutamate receptors plays an important role in brain physiology, but excessive receptor stimulation results in seizures and excitotoxic nerve cell death. NMDA receptor-mediated neuronal excitation and injury can be prevented by high, non-physiological concentrations of the neuroinhibitory tryptophan metabolite kynurenic acid (KYNA). Here we report that endogenous KYNA, which is formed in and released from astrocytes, controls NMDA receptors in vivo. This was revealed with the aid of the dopaminergic drugs d-amphetamine and apomorphine, which cause rapid, transient decreases in striatal KYNA levels in rats. Intrastriatal injections of the excitotoxins NMDA or quinolinate (but not the non-NMDA receptor agonist kainate) at the time of maximal KYNA reduction resulted in two- to threefold increases in excitotoxic lesion size. Pre-treatment with a kynurenine 3-hydroxylase inhibitor or with dopamine receptor antagonists, i.e., two classes of pharmacological agents that prevented the reduction in brain KYNA caused by dopaminergic stimulation, abolished the potentiation of neurotoxicity. Thus, the present study identifies a previously unappreciated role of KYNA as a functional link between dopamine receptor stimulation and NMDA neurotoxicity in the striatum.

Update on amphetamine neurotoxicity and its relevance to the treatment of ADHD

OBJECTIVE

A review of amphetamine treatment for attention-deficit/hyperactivity disorder (ADHD) was conducted, to obtain information on the long-term neurological consequences of this therapy.

METHOD

Several databases were accessed for research articles on the effects of amphetamine in the brain of laboratory animals and ADHD diagnosed individuals.

RESULTS

In early studies, high doses of amphetamine, comparable to amounts used by addicts, were shown to damage dopaminergic pathways. More recent studies, using therapeutic regimens, appear contradictory. One paradigm shows significant decreases in striatal dopamine and transporter density after oral administration of "therapeutic" doses in primates. Another shows morphological evidence of "trophic" dendritic growth in the brains of adult and juvenile rats given systemic injections mimicking "therapeutic" treatment. Imaging studies of ADHD-diagnosed individuals show an increase in striatal dopamine transporter availability that may be reduced by methylphenidate treatment.

CONCLUSION

Clarification of the neurological consequences of chronic AMPH treatment for ADHD is needed.

Effects of short-term abstinence from escalating doses of D-amphetamine on drug and sucrose-evoked dopamine efflux in the rat nucleus accumbens

Abstinence from high doses of psychostimulant drugs, in both humans and rodents, is linked to adverse psychological effects including anhedonia, a core symptom of major depression, manifested behaviorally as decreased responding for rewarding stimuli. The present study used brain microdialysis in freely moving rats to examine the effect of D-amphetamine (D-amph) withdrawal on changes in extracellular dopamine (DA) levels in the nucleus accumbens (NAc) evoked by D-amph or behavior related to sucrose consumption. D-amph was administered intraperitoneally (i.p.) according to an escalating dose (ED) schedule (from 1 to 10 mg/kg, 3 doses/day). We first confirmed the development of tolerance by monitoring DA efflux in the NAc in response to 5 and 10 mg/kg doses of D-amph administered during the ED schedule of drug administration and again in response to the 5 mg/kg dose of D-amph 72 h following the last 10 mg/kg D-amph injection. In a separate study, DA efflux in the NAc was first shown to be increased significantly during both preparatory and consummatory phases of responding for a 4% sucrose solution. Withdrawal from the ED schedule of D-amph caused a selective attenuation of DA efflux only during the preparatory phase of the sucrose test. These results provided convincing evidence of neurochemical adaptation within the mesocorticolimbic DA pathway during and following the administration of an ED schedule of D-amph as well as suppressed neurochemical responses to a psychostimulant drug and cues associated with a natural reward after withdrawal from drug treatment. Accordingly, these findings support the hypothesis that downregulation of mesocorticolimbic DA function maintained during D-amph withdrawal may account for the selective disruption of motivated behavior reported in studies employing psychostimulant drug withdrawal as a model of depression in rodents.

Increased oxidative stress in submitochondrial particles after chronic amphetamine exposure

Previous studies have suggested that reactive oxygen species (ROS) production may play a role in the pathophysiology of many neuropsychiatric disorders, such as bipolar disorder (BD) and schizophrenia (SCZ). In addition, there is an emerging body of data indicating that BD and SCZ may be associated with mitochondrial dysfunction. We studied the effects of acute and chronic d-amphetamine on ROS production in submitochondrial particles of rat brain. Male Wistar rats were divided in two experimental groups: acute and chronic treatment. In the acute treatment, rats received one single IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline (control group). In the chronic treatment, rats received one daily IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline for 7 days. Locomotor activity was assessed with the open field task, and thiobarbituric acid reactive substances (TBARS) and superoxide production were measured in submitochondrial particles of the prefrontal cortex and hippocampus. Both acute and chronic amphetamine treatment increased locomotor behavior. Chronic amphetamine exposure induced a 3- to 6-fold increase of TBARS and a 1.5- to 2-fold increase of superoxide production in submitochondrial particles of prefrontal cortex and hippocampus (P < 0.05). No effects on superoxide or TBARS were observed with acute treatment. These findings suggest that amphetamine-induced mitochondrial ROS generation may be a useful model to investigate the hypothesis of altered brain energy metabolism associated with BD and SCZ. Further studies assessing the effects of mood stabilizers and antipsychotics in preventing mitochondrial oxidative stress are necessary.

Changes in Antioxidant Defense Enzymes after d-amphetamine Exposure: Implications as an Animal Model of Mania

Studies have demonstrated that oxidative stress is associated with amphetamine-induced neurotoxicity, but little is known about the adaptations of antioxidant enzymes in the brain after amphetamine exposure. We studied the effects of acute and chronic amphetamine administration on superoxide dismutase (SOD) and catalase (CAT) activity, in a rodent model of mania. Male Wistar rats received either a single IP injection of D-: amphetamine (1 mg/kg, 2 mg/kg, or 4 mg/kg) or vehicle (acute treatment). In the chronic treatment rats received a daily IP injection of either D-: amphetamine (1 mg/kg, 2 mg/kg, or 4 mg/kg) or vehicle for 7 days. Locomotor behavior was assessed using the open field test. SOD and CAT activities were measured in the prefrontal cortex, hippocampus, and striatum. Acute and to a greater extent chronic amphetamine treatment increased locomotor behavior and affected SOD and CAT activities in the prefrontal cortex, hippocampus and striatum. Our findings suggest that amphetamine exposure is associated with an imbalance between SOD and CAT activity in the prefrontal cortex, hippocampus and striatum.

Withdrawal from continuous amphetamine administration abolishes latent inhibition but leaves prepulse inhibition intact

RATIONALE

Schizophrenia has been associated with dysregulation of dopamine (DA) transmission and impairment in a number of experimental tasks, including sensorimotor gating assessed using prepulse inhibition (PPI) and selective attention assessed using latent inhibition (LI). We have demonstrated in previous studies that after withdrawal from escalating (ESC) dosages of amphetamine (AMPH), animals exhibited disruption of LI but no alteration of PPI. Moreover, these animals always showed behavioural sensitization to an AMPH challenge.

OBJECTIVE

In this study, we were interested in testing whether a different administration schedule would elicit disruption of both LI and PPI.

METHODS

Animals were treated with continuous AMPH release (via osmotic mini-pumps at a dosage of 10 mg kg(-1) day(-1) for 7 days) and tested for their performance in L and PPI during withdrawal in a drug free state. Rats received AMPH treatment during the induction phase in their home cages or in the activity chambers. Following withdrawal, the expression of behavioural sensitization to an AMPH challenge was tested in both cases in the activity chambers.

RESULTS

Animals pretreated with AMPH from both groups did not exhibit behavioural sensitization. Withdrawal from continuous administration induced LI attenuation with no effect on PPI.

CONCLUSIONS

These findings are similar to what was previously found with respect to an ESC AMPH regime. The only difference between the schedules was that the ESC AMPH schedule led to behavioural sensitization whereas the continuous AMPH did not. It is suggested that the expression of sensitization may not be a prerequisite for observed LI disruption.

Involvement of cytokines in human immunodeficiency virus-1 protein Tat and methamphetamine interactions in the striatum

Human immunodeficiency virus-1 (HIV-1) infection of the brain causes elevation in pro-inflammatory cytokines and inflammatory changes in the striatum. HIV-1-infected individuals who also abuse drugs including the psychostimulant methamphetamine (MA) develop more severe encephalitis and neuronal damage compared to HIV-1-infected patients who do not abuse drugs. In previous studies, we demonstrated that the HIV-1 protein Tat and MA interacted to cause enhanced loss of dopamine in the rat striatum via the destruction of dopaminergic terminals. Since both Tat and MA activate glia and induce cytokine production, we investigated the role of cytokines in the synergistic neurotoxicity induced by Tat and MA using cytokine arrays. Significant increases in monocyte chemotactic protein (MCP-1), interleukin-1 alpha (IL-1alpha) and tissue inhibitor of metalloproteinase-1 (TIMP-1) levels were noted 4 h following Tat + MA treatment compared to saline, Tat or MA. MCP-1 and TIMP-1 levels remained elevated 16 h after Tat + MA compared to saline or MA but were not different from the Tat-treated group at this time point. Weak, but significant elevations in cytokine-induced neutrophil chemoattractant-3 (CINC-3), ciliary neurotrophic factor (CNTF) and macrophage inflammatory protein-3 alpha (MIP-3alpha) were also noted with Tat + MA. The interaction of Tat and MA was prevented in mice genetically deficient in MCP-1 with a consequent attenuation of Tat + MA neurotoxicity. Our findings suggest that HIV-1 infection with concurrent drug abuse might profoundly increase chemokine levels in the striatum resulting in enhanced damage to the dopaminergic system.

Methamphetamine and human immunodeficiency virus protein Tat synergize to destroy dopaminergic terminals in the rat striatum

Dysfunction of the dopaminergic system accompanied by loss of dopamine in the striatum is a major feature of human immunodeficiency virus-1-associated dementia. Previous studies have shown that human immunodeficiency virus-1-associated dementia patients with a history of drug abuse have rapid neurological progression, prominent psychomotor slowing, more severe encephalitis and more severe dendritic and neuronal damage in the frontal cortex compared with human immunodeficiency virus-1-associated dementia patients without a history of drug abuse. In a previous study, we showed that methamphetamine and human immunodeficiency virus-1 protein Tat interact to produce a synergistic decline in dopamine levels in the rat striatum. The present study was carried out to understand the underlying cause for the loss of dopamine. Male Sprague-Dawley rats were administered saline, methamphetamine, Tat or Tat followed by methamphetamine 24 h later. Two and seven days later the animals were killed and tissue sections from striatum were processed for silver staining to examine terminal degeneration while sections from striatum and substantia nigra were processed for tyrosine hydroxylase immunoreactivity. Striatal tissue was also analyzed by Western blotting for tyrosine hydroxylase protein levels. Compared with controls, methamphetamine+Tat-treated animals showed extensive silver staining and loss of tyrosine hydroxylase immunoreactivity and protein levels in the ipsilateral striatum. There was no apparent loss of tyrosine hydroxylase in the substantia nigra. Markers for oxidative stress were significantly increased in striatal synaptosomes from Tat+methamphetamine group compared with controls. The results indicate that methamphetamine and Tat interact to produce an enhanced injury to dopaminergic nerve terminals in the striatum with sparing of the substantia nigra by a mechanism involving oxidative stress. These findings suggest a possible mode of interaction between methamphetamine and human immunodeficiency virus-1 infection to produce enhanced dopaminergic neurotoxicity in human immunodeficiency virus-1 infected/methamphetamine-abusing patients.

Disparity in the temporal appearance of methamphetamine-induced apoptosis and depletion of dopamine terminal markers in the striatum of mice

Methamphetamine (METH) causes damage in the striatum at pre- and post-synaptic sites. Exposure to METH induces long-term depletions of dopamine (DA) terminal markers such as tyrosine hydroxylase (TH) and DA transporters (DAT). METH also induces neuronal apoptosis in some striatal neurons. The purpose of this study is to demonstrate which occurs first, apoptosis of some striatal neurons or DA terminal toxicity in mice. This is important because the death of striatal neurons leaves the terminals in a state of deafferentation. A bolus injection (i.p.) of METH (30 mg/kg) induces apoptosis (TUNEL staining) in approximately 25% of neurons in the striatum at 24 h after METH. However, in contrast to apoptosis, depletion of TH (Western blotting) begins to appear at 24 h after METH in dorsal striatum while the ventral striatum is unaffected. The peak of TH depletion (approximately 80% decrease relative to control) occurs at 48 h after METH. Autoradiographic analysis of DAT sites showed that depletion begins to appear 24 h after METH and peaks at 2 days (approximately 60% depletion relative to control). Histological analysis of the induction of glial fibrillary acidic protein (GFAP) by METH in striatal astrocytes revealed an increase at 48 h after METH that peaked at 3 days. These data demonstrate that striatal apoptosis precedes the depletion (toxicity) of DA terminal markers in the striatum of mice, suggesting that the ensuing state of deafferentation of the DA terminals may contribute to their degeneration.

Methamphetamine-induced striatal apoptosis in the mouse brain: comparison of a binge to an acute bolus drug administration

Methamphetamine (METH) is a psychostimulant that induces neural damage in experimental animals and humans. A binge (usually in the 5-10 mg/kg dose range 4 x at 2 h intervals) and the acute bolus drug administration (20-40 mg/kg) of METH have been employed frequently to study neurotoxicity in the brain. In this study we have compared these drug delivery schedules to determine their efficacy to induce striatal apoptosis. Exposure of male mice to a binge of METH at 10mg/kg 4x at 2 h intervals (cumulative dose of 40 mg/kg) was approximately four times less effective in inducing apoptotic cell death (TUNEL staining) 24 h after METH treatment in the striatum than a single bolus administration of 30 mg/kg of METH. The residual TUNEL staining observed three days after METH treatment is proportionately equivalent between a binge and the acute bolus drug administration. Interestingly, a binge of METH induces a hyperthermic response of longer duration. This study demonstrates that an acute bolus drug administration of METH is more effective inducing striatal apoptosis in mice, and therefore, is more suitable for studies assessing the impact of METH on sites post-synaptic to the striatonigral dopamine terminals.

Chronic administration of quetiapine alleviates the anxiety-like behavioural changes induced by a neurotoxic regimen of dl-amphetamine in rats

We have demonstrated that the atypical antipsychotic drugs prevent cell death in PC12 cells induced by various cytotoxins and have protective effects on methamphetamine-induced neurotoxcity in rats. The present study was designed to examine the possible effects of chronic administration of quetiapine, an atypical antipsychotic drug, on the anxiety-like behavioural consequences of a neurotoxic regimen of dl-amphetamine. Rats were treated with quetiapine (10 mg/kg/day; i.p.) for 33 days. During days 15-19 of this period, the animals were given dl-amphetamine (20 mg/kg/day; s.c.) 1 h after the administration of quetiapine. The repeated administration of dl-amphetamine resulted in a decrease of tyrosine hydroxylase (TH) immunostaining in the caudate putamen, hyperthermia, and anxiety-like behavioural changes. The behavioural changes were indicated by a significant increase in the time spent in the light box in the light/dark box test, an increase in the ratios of ambulation distance inside the inner circle over the total ambulation distance and rearings inside the inner circle over the total rearings in the open field test, and an increase in the time spent in open arms in the elevated plus-maze test. Chronic administration of quetiapine significantly attenuated the dl-amphetamine-induced hyperthermia, and the anxiety-like behavioural changes in the light/dark box and in the open field tests. These results suggest that quetiapine can normalize the dl-amphetamine-induced anxiety-like behavioural changes, and might be helpful in the treatment for amphetamine-induced emotional changes.

Implications of chronic methamphetamine use: a literature review

Methamphetamine (MA) abuse is increasing to epidemic proportions, both nationally and globally. Chronic MA use has been linked to significant impairments in different arenas of neuropsychological function. To better understand this issue, a computerized literature search (PubMed, 1964-2004) was used to collect research studies examining the neurobiological and neuropsychiatric consequences of chronic MA use. Availability of MA has markedly increased in the United States due to recent technological improvements in both mass production and clandestine synthesis, leading to significant public health, legal, and environmental problems. MA intoxication has been associated with significant psychiatric and medical comorbidity. Research in animal models and human subjects reveals complicated mechanisms of neurotoxicity by which chronic MA use affects catecholamine neurotransmission. This pathology may underlie the characteristic cognitive deficits that plague chronic MA users, who experience impairments in memory and learning, psychomotor speed, and information processing. These impairments have the potential to compromise, in turn, the ability of MA abusers to engage in, and benefit from, psychosocially based chemical-dependency treatment. Development of pharmacological interventions to improve these cognitive impairments in this population may significantly improve the degree to which they may be able to participate in treatment. Atypical antipsychotics may have some promise in this regard.

Amphetamine induces apoptosis of medium spiny striatal projection neurons via the mitochondria‐dependent pathway

Amphetamine (AMPH) is a psychostimulant whose chronic abuse may cause impairments in attention and memory in humans. These cognitive deficits might be related to neurotoxic effects of the drug. One such toxic effect is the well-described destruction of striatal dopaminergic terminals in mammals. In the present study, we investigated the possibility that AMPH might also cause neuronal apoptosis in the rodent striatum. Administration of a dose of the drug (10 mg/kg, 4 times, every 2 h) that is toxic to dopaminergic terminals resulted in the appearance of striatal cells that were positive for cleaved caspase-3 and for terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL), observations that are indicative of an ongoing apoptotic process. Dual immunofluorescence staining revealed that cleaved caspase-3-positive cells express calbindin and DARPP-32, but not somatostatin, parvalbumin, or cholinergic markers. In addition, AMPH also caused increased expression of p53 and Bax at both transcript and protein levels; in contrast, Bcl-2 levels were decreased after the AMPH injections. Moreover, Bax knockout mice showed resistance to AMPH-induced apoptotic cell death but not to AMPH-induced destruction of dopaminergic terminals. When taken together, these observations indicate that injections of doses of AMPH that are known to destroy striatal dopamine terminals can also cause apoptotic death of postsynaptic medium spiny projection neurons via mitochondria-dependent mechanisms.

The distribution of cocaine in mice differs by age and strain

Few studies have examined the influence of the age and the strain of mouse on the pharmacokinetics of psychostimulants, or the role of pharmacokinetics in age-related differences in drug responses. The present study compared concentrations of cocaine, and its metabolite, benzoylecgonine (BZE), in the blood and brain of early (P35) and later (P42) periadolescent and adult (P63) CD-1 and C57BL/6 male mice 15 min after acute intraperitoneal injection of cocaine (20 mg/kg). Brain levels of cocaine and BZE after seven daily cocaine injections in CD-1 and C57BL/6 mice beginning on P35 and on P63 were also measured. P35 periadolescents of both strains had lower blood cocaine levels than did the adults, but only C57BL/6 periadolescents had lower brain cocaine levels than the adults. C57BL/6 mice of both ages had higher blood cocaine levels than did the corresponding CD-1 mice. Concomitant with lower cocaine levels, periadolescent CD-1 mice had higher blood BZE levels than the adults, suggesting that periadolescents may metabolize cocaine faster. Brain cocaine levels in P42 C57BL/6 mice were similar to those of adults. Cocaine-induced activity did not differ between periadolescent and adult CD-1 mice after a single injection of cocaine, whereas periadolescent C57BL/6 mice had lower activity levels than did the adults after a single cocaine injection. Periadolescent CD-1 mice exhibited higher levels of locomotor activity following cocaine injection than did periadolescent C57BL/6 mice. Following chronic cocaine administration, cocaine and BZE levels in the brains of periadolescent and adult mice did not differ from each other in either strain. However, brain cocaine levels at both ages were lower in CD-1 mice than in C57BL/6 mice. In conclusion, the age and the strain of mouse significantly affect the levels of cocaine obtained in brain and blood following acute administration. Our data are consistent with the notion that CD-1 and C57BL/6 mice metabolize cocaine faster during the early periadolescent period than as adults. Furthermore, potentially important strain differences between CD-1 and C57BL/6 mice were noted in cocaine levels following acute and chronic cocaine administration, and in locomotor activity following acute cocaine administration.

Microglial activation precedes dopamine terminal pathology in methamphetamine-induced neurotoxicity

Previous studies have demonstrated methamphetamine (METH)-induced toxicity to dopaminergic and serotonergic axons in rat striatum. Although several studies have identified the nature of reactive astrogliosis in this lesion model, the response of microglia has not been examined in detail. In this investigation, we characterized the temporal relationship of reactive microgliosis to neuropathological alterations of dopaminergic axons in striatum following exposure to methamphetamine. Adult male Sprague-Dawley rats were administered a neurotoxic regimen of methamphetamine and survived 12 h, or 1, 2, 4, and 6 days after treatment. Immunohistochemical methods were used to evaluate reactive changes in microglia throughout the brain of methamphetamine-treated rats, with a particular focus upon striatum. Pronounced morphological changes, indicative of reactive microgliosis, were evident in the brains of all methamphetamine-treated animals and were absent in saline-treated control animals. These included hyperplastic changes in cell morphology that substantially increased the size and staining intensity of reactive microglia. Quantitative analysis of reactive microglial changes in striatum demonstrated that these changes were most robust within the ventrolateral region and were maximal 2 days after methamphetamine administration. Analysis of tissue also revealed that microglial activation preceded the appearance of pathological changes in striatal dopamine fibers. Reactive microgliosis was also observed in extra-striatal regions (somatosensory and piriform cortices, and periaqueductal gray). These data demonstrate a consistent, robust, and selective activation of microglia in response to methamphetamine administration that, at least in striatum, precedes the appearance of morphological indicators of axon pathology. These observations raise the possibility that activated microglia may contribute to methamphetamine-induced neurotoxicity.

Amphetamine neurotoxicity: accomplishments and remaining challenges

In addition to the social, cultural and indirect medical complications of amphetamine analog abuse, this class of drugs is also known to have the potential to damage brain monoaminergic cells directly. Using methamphetamine as a prototype, this article provides a brief review of the history of amphetamine neurotoxicity research and the progress that has been made toward defining its characteristics. Remaining challenges for this line of investigation are outlined, and suggested avenues for addressing these challenges are provided.

Activation of metabotropic glutamate receptor 5 is associated with effect of amphetamine on brain neurons

The role of metabotropic glutamate receptor 5 (mGluR5) was explored in mechanisms underlying the action of amphetamine (AMPH). The activity of mGluR5 was monitored by measuring the level of [3H]inositol monophosphates in brain neurons, in response to stimulation of 2-choloro-5-hydroxyphenylglycine (CHPG), a selective agonist of mGluR5. Treatment with 1 microM of AMPH for 1 h or 7 days increased the CHPG (1 mM, 30 min)-evoked phosphoinositide turnover by 46% or 92% and 26% or 84% in cultured cortical and hippocampal neurons, respectively, from that of CHPG-only treated cells. When AMPH was present during CHPG application post-1 h or 7 day AMPH incubation, the rate of phosphoinositide hydrolysis in cortical neurons became 121% or 142% higher than that treated with CHPG only. The postnatal day (P) 21 (juvenile) and P60 (adult) rats received three intraperitoneal injections of 5 mg/kg of AMPH or saline daily for 6 days. They were challenged on the eighth day with one dosage and sacrificed 3 h later. Reversible 3H-glutamate binding detected increases of 22-89% in the binding levels of cortex and hippocampus of both ages following the AMPH injections. Increases of 13-18% in the levels of mGluR5 mRNA were seen in the juvenile pyramidal neurons of hippocampal CA1-4, granular cells of dentate gyrus, and ventral thalamic nuclei, as shown by in situ hybridization. The AMPH-induced altered activity of mGluR5 is probably associated with changes in the expression of the glutamate receptors, including mGluR5. AMPH may modify the sensitivity of mGluR5 or interact with the receptor itself.

Substance P and cholecystokinin regulate neurochemical responses to cocaine and methamphetamine in the striatum

The mechanism of action of drugs of abuse like cocaine and amphetamines has been studied extensively in the dopamine terminal field areas of the caudate-putamen (CPu) and the nucleus accumbens (NAc) of the rodent brain. These brain regions contain several neuropeptides that must play important roles in the normal physiological functions of these brain regions. The study of neuropeptide physiology in the context of the neurobiological responses to drugs of abuse may shed some light on the intrinsic mechanism of action of neuropeptides of the CPu and the NAc. The neuropeptides substance P (SP) and cholecystokinin (CCK) are present in the striatum where they could play an important role regulating the effects of psychostimulants like cocaine and amphetamines (methamphetamine [METH] is a long acting derivative of d-amphetamine). These highly addictive agents induce the release of dopamine (DA) (and other catecholamines) from dopaminergic terminals of the striatum. The excessive release of DA in the striatum and the NAc has been implicated in the habit-forming properties of these drugs. In order to study the contribution of SP and CCK in the striatum during psychostimulant treatment, we employed selective non-peptide neurokinin-1 (NK-1) and cholecystokinin-2 (CCK-2) receptor antagonists that readily cross the blood brain barrier. We infused the neurokinin-1 receptor (NK-1R) antagonist, L-733,060, into the striatum of freely moving rats via a microdialysis probe in order to assess the effects of SP on cocaine-induced DA overflow in the striatum. Infusion of the NK-1R antagonist prior to a systemic injection of cocaine (10 mg/kg i.p.) significantly attenuated DA overflow in the striatum. Conversely, infusion of a CCK-2 receptor (CCK-2R) antagonist, L-369,293, through the microdialysis probe evoked DA overflow in the striatum in the absence of cocaine and potentiated DA overflow after a single injection of cocaine (10 mg/kg i.p.). Exposure to METH (10 mg/kg 4x at two-hour intervals) produced deficits of dopamine transporters (DAT) in mice striatum that are detectable three days after the treatment and are long lasting. Pre-treatment (i.p. injections) with the NK-1R antagonist, WIN-51,708 30 minutes before the 1st and 4th injections of METH prevented the loss of DAT in the striatum. Moreover, pre-treatment with the NK-1R antagonist prevents METH-induced cell death. Taken together, these results demonstrate that the NK-1R and the CCK-2R are important modulators of the actions of the psychostimulants cocaine and METH. Neuropeptide receptors represent an important control point mediating the effects of the neurotransmitter DA in the striatum of the rodent brain.

Methamphetamine-induced deficits of brain monoaminergic neuronal markers: distal axotomy or neuronal plasticity

We examined the effects of methamphetamine (METH) on monoaminergic (i.e. dopamine and serotonin) axonal markers and glial cell activation in the rat brain. Our findings indicate that the loss of dopamine transporters (DAT), serotonin transporters (5-HTT), vesicular monoamine transporter type-2 (VMAT-2) and glial cell activation induced by METH in the striatum and in the central gray are consistent with a degenerative process. Our novel finding of METH effects on monoaminergic neurons in the central gray may have important implications on METH-induced hyperthermia. In other brain regions examined, DAT and 5-HTT deficits after METH administration were present in the absence of lasting changes in VMAT-2 levels or glial cell activation. Brain regions exhibiting protracted deficits in DAT and/or 5-HTT and VMAT-2 levels also expressed increased levels of [(3)H]-R-PK11195 binding to peripheral benzodiazepine receptors, a quantitative marker of glial cell activation. Immunohistochemical assessment of microglia and astrocytes confirmed the PBR results. Microglia activation was more pronounced than astrocytosis in affected regions in most METH-exposed brains with the exception of a small number of rats that were most severely affected by METH based on loss of body weight. In these rats, both microglia and astrocytes were highly activated and expressed a distinct regional pattern suggestive of widespread brain injury. The reason for the pattern of glial cell activation in this group of rats is not currently known but it may be associated with METH-induced hyperthermia. In summary, our findings suggest two neurotoxic endpoints in the brain of METH-exposed animals. Brain regions exhibiting DAT and 5-HTT deficits that co-localize with decreased VMAT-2 levels and glial cell activation may represent monoaminergic terminal degeneration. However, the DAT and 5-HTT deficits in brain regions lacking a deficit in VMAT-2 and glial cell activation may reflect drug-induced modulation of these plasma membrane proteins.

Designer drugs: how dangerous are they?

Of the designer drugs, the amphetamine analogues are the most popular and extensively studied, ecstasy (3,4-methylenedioxymethamphetamine; MDMA) in particular. They are used recreationally with increasing popularity despite animal studies showing neurotoxic effects to serotonin (5-HT) and/or dopamine (DA) neurones. However, few detailed assessments of risks of these drugs exist in humans. Previously, there were no methods available for directly evaluating the neurotoxic effects of amphetamine analogues in the living human brain. However, development of in vivo neuroimaging tools have begun to provide insights into the effects of MDMA in human brain. In this review, contributions of brain imaging studies on the potential 5-HT and/or DA neurotoxic effects of amphetamine analogues will be highlighted in order to delineate the risks these drugs engender in humans, focusing on MDMA. An overview will be given of PET, SPECT and MR Spectroscopy studies employed in human users of these drugs. Most of these studies provide suggestive evidence that MDMA is neurotoxic to 5-HT neurones, and (meth)amphetamine to DA neurones in humans. These effects seem to be dose-related, leading to functional impairments such as memory loss, and are reversible in several brain regions. However most studies have had a retrospective design, in which evidence is indirect and differs in the degree to which any causative links can be implied between drug use and neurotoxicity. Therefore, at this moment, it cannot be ascertained that humans are susceptible to MDMA-induced 5-HT injury or (meth)amphetamine-induced DA injury. Finally, although little is known about other amphetamine analogues there are important questions as to the safety of these designer drugs as well, in view of the fact that they are chemically closely related to MDMA and some have been shown to be 5-HT neurotoxins in animals.

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.