Ontogeny of methamphetamine-induced neurotoxicity and associated hyperthermic response

The ubiquitin-proteasome system and learning-dependent synaptic plasticity - A 10 year update

Over 25 years ago, a seminal paper demonstrated that the ubiquitin-proteasome system (UPS) was involved in activity-dependent synaptic plasticity. Interest in this topic began to expand around 2008 following another seminal paper showing that UPS-mediated protein degradation controlled the "destabilization" of memories following retrieval, though we remained with only a basic understanding of how the UPS regulated activity- and learning-dependent synaptic plasticity. However, over the last 10 years there has been an explosion of papers on this topic that has significantly changed our understanding of how ubiquitin-proteasome signaling regulates synaptic plasticity and memory formation. Importantly, we now know that the UPS controls much more than protein degradation, is involved in plasticity underlying drugs of abuse and that there are significant sex differences in how ubiquitin-proteasome signaling is used for memory storage processes. Here, we aim to provide a critical 10-year update on the role of ubiquitin-proteasome signaling in synaptic plasticity and memory formation, including updated cellular models of how ubiquitin-proteasome activity could be regulating learning-dependent synaptic plasticity in the brain.

Peri-adolescent exposure to (meth)amphetamine in animal models

Experimentation with psychoactive drugs is often initiated in the peri-adolescent period, but knowledge of differences in the outcomes of peri-adolescent- vs adult-initiated exposure is incomplete. We consider the existing animal research in this area for (meth)amphetamines. Established for a number of phenotypes, is lower sensitivity of peri-adolescents than adults to acute effects of (meth)amphetamines, including neurotoxic effects of binge-level exposure. More variable are data for long-term consequences of peri-adolescent exposure on motivational and cognitive traits. Moreover, investigations often exclude an adult-initiated exposure group critical for answering questions about outcomes unique to peri-adolescent initiation. Despite this, it is clear from the animal research that (meth)amphetamine exposure during the peri-adolescent period, whether self- or other-administered, impacts brain motivational circuitry and cognitive function, and alters adult sensitivity to other drugs and natural rewards. Such consequences occurring in humans have the potential to predispose toward unfortunate and potentially disastrous family, social and livelihood outcomes.

AMPed-up adolescents: The role of age in the abuse of amphetamines and its consequences on cognition and prefrontal cortex development

Adolescent use of amphetamine and its closely related, methylated version methamphetamine, is alarmingly high in those who use drugs for nonmedical purposes. This raises serious concerns about the potential for this drug use to have a long-lasting, detrimental impact on the normal development of the brain and behavior that is ongoing during adolescence. In this review, we explore recent findings from both human and laboratory animal studies that investigate the consequences of amphetamine and methamphetamine exposure during this stage of life. We highlight studies that assess sex differences in adolescence, as well as those that are designed specifically to address the potential unique effects of adolescent exposure by including groups at other life stages (typically young adulthood). We consider epidemiological studies on age and sex as vulnerability factors for developing problems with the use of amphetamines, as well as human and animal laboratory studies that tap into age differences in use, its short-term effects on behavior, and the long-lasting consequences of this exposure on cognition. We also focus on studies of drug effects in the prefrontal cortex, which is known to be critically important for cognition and is among the later maturing brain regions. Finally, we discuss important issues that should be addressed in future studies so that the field can further our understanding of the mechanisms underlying adolescent use of amphetamines and its outcomes on the developing brain and behavior.

Postmortem Study of Molecular and Histological Changes in the CA1 Hippocampal Region of Chronic Methamphetamine User

Methamphetamine (Meth) is recognized as one of the most important new distributed abused drug that causes severe damage to the different parts of the brain, especially hippocampus. Previous studies have demonstrated that Meth can induce apoptosis and cell death in the brain. In this study, we evaluated the long-term effects of Meth abuse in the CA1 region of postmortem hippocampus. Postmortem molecular and histological analysis was performed for five non-addicted subjects and five Meth addicted ones. Iba-1 (microglia) and glial fibrillary acidic protein, GFAP (astrocytes) expression were assayed by western blotting and immunohistochemistry (IHC) methods. Histopathological assessment was done with stereological counts of hippocampal cells stained with hematoxylin and eosin (H and E). Tunel staining was used to detect DNA damage in human brains. In addition, protein-protein interaction analysis network was investigated. Western blotting and immunohistochemistry assay showed overexpression of GFAP and Iba-1 protein in the CA1 hippocampal region of Meth users’ brain. Stereological analysis in the CA1 region revealed increased neuron degeneration. Furthermore, significant apoptosis and cell death were confirmed by Tunel assay in the hippocampus. The prominent role of TLR4, IL1B, CASP1, and NLRP3 in the molecular mechanism of Meth was highlighted via PPI network analysis. Chronic Meth use can induce GFAP and Iba-1 upregulation and neuronal apoptosis in the CA1 region of the postmortem hippocampus.

Effects of intrastriatal dopamine D1 or D2 antagonists on methamphetamine-induced egocentric and allocentric learning and memory deficits in Sprague-Dawley rats

RATIONALE

Methamphetamine (MA) is an abused psychostimulant that causes cognitive deficits after chronic use. Neostriatal dopamine receptors play a role in MA monoamine neurotoxicity. Blocking dopamine receptors prior to MA exposure in adult rats attenuates monoamine reductions and reactive gliosis.

OBJECTIVES

We tested whether blocking dopamine receptors protects against cognitive deficits.

METHODS

First, we determined the effects of MA alone versus MA in combination with the dopamine receptor D1 antagonist SCH-23390 or the dopamine receptor D2 antagonist sulpiride on cFos expression and monoamines at the age when rats in the cognitive experiment were to begin testing and monoamines in rats after cognitive testing.

RESULTS

SCH-23390 infused into the neostriatum prior to systemic administration of MA attenuated MA-induced cFos activation while sulpiride induced cFos activation. Two weeks after MA, rats had dopamine and serotonin reductions that were attenuated by each antagonist. Other rats treated the same way, were tested for egocentric learning and memory in the Cincinnati water maze, for navigational strategy in a star water maze, and spatial learning and memory in a Morris water maze. Pre-treatment with SCH-23390 or sulpiride attenuated the effects of MA on egocentric and spatial learning and memory. MA-treated rats showed a shift from an egocentric to a disorganized strategy in the star maze that was less disorganized in groups receiving MA and an antagonist. Post-behavior monoamine reductions remained but were attenuated by the antagonists but not identically to what was seen in rats not behaviorally tested.

CONCLUSIONS

The results show for the first time that dopamine receptors are mediators of MA-induced cognitive deficits.

Developmental perspectives on methamphetamine abuse: Exploring adolescent vulnerabilities on brain and behavior

Most people that experience illicit drugs do so for the first time during adolescence, and methamphetamine (meth) is no exception. Therefore, research into the effects of meth should highlight the adolescent period. Despite this, the vast majority of current literature has mainly focused on meth exposure during adulthood. In this review, we first describe existing literature that compares the behavioral effects of meth where exposure occurs in adolescence compared to adulthood. Given that there are actually very few such studies, we also look at what is known about neural effects of meth in the adult brain, and relate these to normal neural development occurring during the adolescent period to establish how meth may target maturing regions and related neurochemistry. What emerges overall is that adolescents appear to be more vulnerable to the rewarding and reinforcing effects of meth, and that meth indeed has effects on areas that are in flux during adolescence. However, there is some evidence for a paradoxical resistance to the neurotoxic effects during this period. We highlight the need for further age-related research to better understand, treat, and prevent meth use disorders and addiction in general.

Neurotoxicology of Synthetic Cathinone Analogs

The present review briefly explores the neurotoxic properties of methcathinone, mephedrone, methylone, and methylenedioxypyrovalerone (MDPV), four synthetic cathinones most commonly found in "bath salts." Cathinones are β-keto analogs of the commonly abused amphetamines and display pharmacological effects resembling cocaine and amphetamines, but despite their commonalities in chemical structures, synthetic cathinones possess distinct neuropharmacological profiles and produce unique effects. Among the similarities of synthetic cathinones with their non-keto analogs are their targeting of monoamine systems, the release of neurotransmitters, and their stimulant properties. Most of the literature on synthetic cathinones has focused on describing their properties as psychostimulants, their behavioral effects on locomotion, memory, and potential for abuse, whereas descriptions of their neurotoxic properties are not abundant. The biochemical gauges of neurotoxicity induced by non-keto analogs are well studied in humans and experimental animals and include their ability to induce neuroinflammation, oxidative stress, excitotoxicity, temperature alterations as well as dysregulation of neurotransmitter systems and induce changes in monoamine transporters and receptors. These neurotoxicity gauges will serve as parameters to discuss the effects of the four previously mentioned synthetic cathinones alone or in combination with either another cathinone or with some of their non-keto analogs. Bath salts are not a defined combination of drugs and may consist of one synthetic cathinone compound or combinations of more cathinones. Furthermore, this review also presents some of the mechanisms that are thought to underlie this toxicity. A better understanding of the cellular and molecular mechanisms involved in the synthetic cathinones-induced neurotoxicity should contribute to generate modern therapeutic approaches to prevent or attenuate the adverse consequences of use of these drugs in humans.

Effects of Neonatal Methamphetamine and Stress on Brain Monoamines and Corticosterone in Preweanling Rats

Neonatal exposure to methamphetamine (MA) and developmental chronic stress significantly alter neurodevelopmental profiles that show a variety of long-term physiological and behavioral effects. In the current experiment, Sprague-Dawley rats were exposed to one of two housing conditions along with MA. Rats were given 0 (saline), 5, or 7.5 mg/kg MA, four times per day from postnatal day (P)11 to 15 or P11 to 20. Half of the litters were reared in cages with standard bedding and half with no bedding. Separate litters were assessed at P15 or P20 for organ weights (adrenals, spleen, thymus); corticosterone; and monoamine assessments (dopamine, serotonin, norepinephrine) and their metabolites within the neostriatum, hippocampus, and prefrontal cortex. Findings show neonatal MA altered monoamines, corticosterone, and organ characteristics alone, and as a function of developmental age and stress compared with controls. These alterations may in part be responsible for MA and early life stress-induced long-term learning and memory deficits.

Consequences of adolescent use of alcohol and other drugs: Studies using rodent models

Studies using animal models of adolescent exposure to alcohol, nicotine, cannabinoids, and the stimulants cocaine, 3,4-methylenedioxymethampethamine and methamphetamine have revealed a variety of persisting neural and behavioral consequences. Affected brain regions often include mesolimbic and prefrontal regions undergoing notable ontogenetic change during adolescence, although it is unclear whether this represents areas of specific vulnerability or particular scrutiny to date. Persisting alterations in forebrain systems critical for modulating reward, socioemotional processing and cognition have emerged, including apparent induction of a hyper-dopaminergic state with some drugs and/or attenuations in neurons expressing cholinergic markers. Disruptions in cognitive functions such as working memory, alterations in affect including increases in social anxiety, and mixed evidence for increases in later drug self-administration has also been reported. When consequences of adolescent and adult exposure were compared, adolescents were generally found to be more vulnerable to alcohol, nicotine, and cannabinoids, but generally not to stimulants. More work is needed to determine how adolescent drug exposure influences sculpting of the adolescent brain, and provide approaches to prevent/reverse these effects.

Sex-Dependent Changes in Striatal Dopamine Transport in Preadolescent Rats Exposed Prenatally and/or Postnatally to Methamphetamine

Methamphetamine (MA) is the most commonly used psychostimulant drug, the chronic abuse of which leads to neurodegenerative changes in the brain. The global use of MA is increasing, including in pregnant women. Since MA can cross both placental and haematoencephalic barriers and is also present in maternal milk, children of chronically abused mothers are exposed prenatally as well as postnatally. Women seem to be more vulnerable to some aspects of MA abuse than men. MA is thought to exert its effects among others via direct interactions with dopamine transporters (DATs) in the brain tissue. Sexual dimorphism of the DAT system could be a base of sex-dependent actions of MA observed in behavioural and neurochemical studies. Possible sex differences in the DATs of preadolescent offspring exposed to MA prenatally and/or postnatally have not yet been evaluated. We examined the striatal synaptosomal DATs (the activity and density of surface expressed DATs and total DAT expression) in preadolescent male and female Wistar rats (31-35-day old animals) exposed prenatally and/or postnatally to MA (daily 5 mg/kg, s.c. to mothers during pregnancy and lactation). To distinguish between specific and nonspecific effects of MA on DATs, we also evaluated the in vitro effects of lipophilic MA on the fluidity of striatal membranes isolated from preadolescent and young adult rats of both sexes. We observed similar changes in the DATs of preadolescent rats exposed prenatally or postnatally (MA-mediated drop in the reserve pool but no alterations in surface-expressed DATs). However, prenatal exposure evoked significant changes in males and postnatal exposure in females. A significant decrease in the activity of surface-expressed DATs was found only in postnatally exposed females sensitized to MA via prenatal exposure. MA applied in vitro increased the fluidity of striatal membranes of preadolescent female but not male rats. In summary, DATs of preadolescent males are more sensitive to prenatal MA exposure via changes in the reserve pool and those of preadolescent females to postnatal MA exposure via the same mechanism. The combination of prenatal and postnatal MA exposure increases the risk of dopaminergic deficits via alterations in the activity of surface-expressed DATs especially in preadolescent females. MA-mediated changes in DATs of preadolescent females could be still enhanced via nonspecific disordering actions of MA on striatal membranes.

Neurobehavioral Effects from Developmental Methamphetamine Exposure

Intrauterine methamphetamine exposure adversely affects the neurofunctional profile of exposed children, leading to a variety of higher order cognitive deficits, such as decreased attention, reduced working-memory capability, behavioral dysregulation, and spatial memory impairments (Kiblawi et al. in J Dev Behav Pediatr 34:31-37, 2013; Piper et al. in Pharmacol Biochem Behav 98:432-439 2011; Roussotte et al. in Neuroimage 54:3067-3075, 2011; Twomey et al. in Am J Orthopsychiatry 83:64-72, 2013). In animal models of developmental methamphetamine, both neuroanatomical and behavioral outcomes critically depend on the timing of methamphetamine administration. Methamphetamine exposure during the third trimester human equivalent period of brain development results in well-defined and persistent wayfinding and spatial navigation deficits in rodents (Vorhees et al. in Neurotoxicol Teratol 27:117-134, 2005, Vorhees et al. in Int J Dev Neurosci 26:599-610, 2008; Vorhees et al. in Int J Dev Neurosci 27:289-298, 2009; Williams et al. in Psychopharmacology (Berl) 168:329-338, 2003b), whereas drug delivery during the first and second trimester equivalents produces no such effect (Acuff-Smith et al. in Neurotoxicol Teratol 18:199-215, 1996; Schutova et al. in Physiol Res 58:741-750, 2009a; Slamberova et al. in Naunyn Schmiedebergs Arch Pharmacol 380:109-114, 2009, Slamberova et al. in Physiol Res 63:S547-S558, 2014b). In this review, we examine the impact of developmental methamphetamine on emerging neural circuitry, neurotransmission, receptor changes, and behavioral outcomes in animal models. The review is organized by type of effects and timing of drug exposure (prenatal only, pre- and neonatal, and neonatal only). The findings elucidate functional patterns of interconnected brain structures (e.g., frontal cortex and striatum) and neurotransmitters (e.g., dopamine and serotonin) involved in methamphetamine-induced developmental neurotoxicity.

Co-administration of betulinic acid and methamphetamine causes toxicity to dopaminergic and serotonergic nerve terminals in the striatum of late adolescent rats

Psychostimulant methamphetamine (METH) is toxic to striatal dopaminergic and serotonergic nerve terminals in adult, but not in the adolescent, brain. Betulinic acid (BA) and its derivatives are promising anti-HIV agents with some toxic properties. Many METH users, particularly young men, are HIV-positive; therefore, they might be treated with BA or its derivative for HIV infection. It is not known whether BA, or any of its derivatives, are neurotoxic in combination with METH in the adolescent brain. The present study investigated the effects of BA and binge METH in the striatum of late adolescent rats. BA or METH alone did not decrease the levels of dopaminergic or serotonergic markers in the striatum whereas BA and METH together decreased these markers in a BA dose-dependent manner. BA+METH also caused decreases in the levels of mitochondrial complex I in the same manner; BA alone only slightly decreased the levels of this enzyme in striatal synaptosomes. BA or METH alone increased cytochrome c. METH alone decreased parkin, increased complex II and striatal BA levels. These results suggest that METH in combination with BA can be neurotoxic to striatal dopaminergic and serotonergic nerve terminals in the late adolescent brain via mitochondrial dysfunction and parkin deficit. We report a synergistic neurotoxicity of betulinic acid (BA) and methamphetamine (METH) to monoaminergic terminals in the striatum of male late adolescent rats. BA contribution to the neurotoxicity is decreasing mitochondrial complex I whereas METH contribution is decreasing parkin and increasing brain concentration of BA. We propose that clinical use of BA in young male METH users can be neurotoxic.

Behavioral pharmacology of designer cathinones: a review of the preclinical literature

"Bath salts" is one street name for a family of synthetic cathinones that display pharmacological effects resembling cocaine and commonly abused amphetamines. Despite extensive legislation aimed at the criminalization of bath salts, several designer cathinones are gaining a foothold in the illicit drug scene; for example, in the United Kingdom, mephedrone (4-methylmethcathinone, MEPH) is highly popular among drug abusers whereas, in the United States, MDPV (methylenedioxypyrovalerone) and methylone are highly prevalent. To date, knowledge about the hazards of designer cathinones is based mostly on hospital reports and anecdotal evidence derived from online surveys. Despite the paucity of preclinical studies directed toward designer cathinones, a number of invaluable findings arising from those studies are enabling scientists to develop their neuropharmacological profiles. Despite their commonalities in chemical structures, synthetic cathinones possess distinct neuropharmacological profiles and produce different behavioral effects, including unique effects on locomotor activity, learning, anxiety, thermoregulation, and abuse liability. The present review will discuss the behavioral effects of MEPH, MDPV, and methylone and compare those effects to established psychostimulant drugs. The rise in the use of designer cathinones in the United States and abroad justifies further investigations into these compounds, both for a greater understanding of the danger that "bath salts" pose to the public, and to provide insight into replacement cathinones as they emerge onto the market.

Cognitive impairments from developmental exposure to serotonergic drugs: citalopram and MDMA

We previously showed that developmental 3,4-methylenedioxymethamphetamine (MDMA) treatment induces long-term spatial and egocentric learning and memory deficits and serotonin (5-HT) reductions. During brain development, 5-HT is a neurotrophic factor influencing neurogenesis, synaptogenesis, migration, and target field organization. MDMA (10 mg/kg × 4/d at 2 h intervals) given on post-natal day (PD) 11-20 in rats (a period of limbic system development that approximates human third trimester brain development) induces 50% reductions in 5-HT during treatment and 20% reductions when assessed as adults. To determine whether the 5-HT reduction is responsible for the cognitive deficits, we used citalopram (Cit) pretreatment to inhibit the effects of MDMA on 5-HT reuptake in a companion study. Cit attenuated MDMA-induced 5-HT reductions by 50% (Schaefer et al., 2012). Here we tested whether Cit (5 or 7.5 mg/kg × 2/d) pretreatment attenuates the cognitive effects of MDMA. Within each litter, different offspring were treated on PD11-20 with saline (Sal) + MDMA, Cit + MDMA, Cit + Sal or Sal + Sal. Neither spatial nor egocentric learning/memory was improved by Cit pretreatment. Unexpectedly, Cit + Sal (at both doses) produced spatial and egocentric learning deficits as severe as those caused by Sal + MDMA. These are the first data showing cognitive deficits resulting from developmental exposure to a selective serotonin reuptake inhibitor. These data indicate the need for further research on the long-term safety of antidepressants during pregnancy.

Glial reactivity in resistance to methamphetamine-induced neurotoxicity

Neurotoxic regimens of methamphetamine (METH) result in reactive microglia and astrocytes in striatum. Prior data indicate that rats with partial dopamine (DA) loss resulting from prior exposure to METH are resistant to further decreases in striatal DA when re-exposed to METH 30 days later. Such resistant animals also do not show an activated microglia phenotype, suggesting a relation between microglial activation and METH-induced neurotoxicity. To date, the astrocyte response in such resistance has not been examined. Thus, this study examined glial-fibrillary acidic protein (GFAP) and CD11b protein expression in striata of animals administered saline or a neurotoxic regimen of METH on post-natal days 60 and/or 90 (Saline:Saline, Saline:METH, METH:Saline, METH:METH). Consistent with previous work, animals experiencing acute toxicity (Saline:METH) showed both activated microglia and astocytes, whereas those resistant to the acute toxicity (METH:METH) did not show activated microglia. Interestingly, GFAP expression remained elevated in rats exposed to METH at PND60 (METH:Saline), and was not elevated further in resistant rats treated for the second time with METH (METH:METH). These data suggest that astrocytes remain reactive up to 30 days post-METH exposure. In addition, these data indicate that astrocyte reactivity does not reflect acute, METH-induced DA terminal toxicity, whereas microglial reactivity does.

[Dialysis for severe rhabdomyolysis 7 days after multiple trauma]

A case report of severe rhabdomyolysis in a 33-year-old motorcyclist after multiple trauma is described. The injuries included severe thoracic and abdominal trauma as well as injuries to the extremities and spinal column. During the first 3 days of treatment a forced volume therapy was performed because of increased levels of creatine kinase during which the patients condition stabilized both hemodynamically and respiratorily. On day 10 the patient developed a rise in temperature to 42°C with no evidence of a re-infection and the creatine kinase levels rose to 109,830 U/l. A continuous hemofiltration was started because of acute renal failure. The creatine kinase levels declined significantly and renal function also returned to normal with adequate diuresis up to day 20. After intensive questioning of the relatives a history of long-term use of anabolic steroids, clenbuterol as well as the intake of testosterone enanthate was conceded. Cocaine and amphetamines were also taken regularly by the patient.

Methamphetamine treatment during development attenuates the dopaminergic deficits caused by subsequent high-dose methamphetamine administration

Administration of high doses of methamphetamine (METH) causes persistent dopaminergic deficits in both nonhuman preclinical models and METH-dependent persons. Noteworthy, adolescent [i.e., postnatal day (PND) 40] rats are less susceptible to this damage than young adult (PND90) rats. In addition, biweekly treatment with METH, beginning at PND40 and continuing throughout development, prevents the persistent dopaminergic deficits caused by a "challenge" high-dose METH regimen when administered at PND90. Mechanisms underlying this "resistance" were thus investigated. Results revealed that biweekly METH treatment throughout development attenuated both the acute and persistent deficits in VMAT2 function, as well as the acute hyperthermia, caused by a challenge METH treatment. Pharmacokinetic alterations did not appear to contribute to the protection afforded by the biweekly treatment. Maintenance of METH-induced hyperthermia abolished the protection against both the acute and persistent VMAT2-associated deficits suggesting that alterations in thermoregulation were caused by exposure of rats to METH during development. These findings suggest METH during development prevents METH-induced hyperthermia and the consequent METH-related neurotoxicity.

Cockayne syndrome B protects against methamphetamine-enhanced oxidative DNA damage in murine fetal brain and postnatal neurodevelopmental deficits

Methamphetamine (METH) increases the oxidative DNA lesion 8-oxoguanine (8-oxoG) in fetal mouse brain, and causes postnatal motor coordination deficits after in utero exposure. Like oxoguanine glycosylase 1 (OGG1), the Cockayne syndrome B (CSB) protein is involved in the repair of oxidatively damaged DNA, although its function is unclear. Here we used CSB-deficient Csb(m/m) knockout mice to investigate the developmental role of DNA oxidation and CSB in METH-initiated neurodevelopmental deficits. METH (40 mg/kg intraperitoneally) administration to pregnant Csb females on gestational day 17 increased 8-oxoG levels in Csb(m/m) fetal brains (p < 0.05). CSB modulated 8-oxoG levels independent of OGG1 activity, as 8-oxoG incision activity in fetal nuclear extracts was identical in Csb(m/m) and Csb(+/+)mice. This CSB effect was evident despite 7.1-fold higher OGG1 activity in Csb(+/+) mice compared to outbred CD-1 mice. Female Csb(m/m) offspring exposed in utero to METH exhibited motor coordination deficits postnatally (p < 0.05). In utero METH exposure did not cause dopaminergic nerve terminal degeneration, in contrast to adult exposures. This is the first evidence that CSB protects the fetus from xenobiotic-enhanced DNA oxidation and postnatal functional deficits, suggesting that oxidatively damaged DNA is developmentally pathogenic, and that fetal CSB activity may modulate the risk of reactive oxygen species-mediated adverse developmental outcomes.

(+)-Methamphetamine-induced monoamine reductions and impaired egocentric learning in adrenalectomized rats is independent of hyperthermia

Methamphetamine (MA) is widely abused and implicated in residual cognitive deficits. In rats, increases in plasma corticosterone and egocentric learning deficits are observed after a 1-day binge regimen of MA (10 mg/kg x 4 at 2-h intervals). The purpose of this experiment was to determine if adrenal inactivation during and following MA exposure would attenuate the egocentric learning deficits in the Cincinnati water maze (CWM). In the first experiment, the effects of adrenalectomy (ADX) or sham surgery (SHAM) on MA-induced neurotoxicity at 72 h were determined. SHAM-MA animals showed typical patterns of hyperthermia, whereas ADX-MA animals were normothermic. Both SHAM-MA- and ADX-MA-treated animals showed increased neostriatal glial fibrillary acidic protein and decreased monoamines in the neostriatum, hippocampus, and entorhinal cortex. In the second experiment, SHAM-MA- and ADX-MA-treated groups showed equivalently impaired CWM performance 2 weeks post-treatment (increased latencies, errors, and start returns) compared to SHAM-saline (SAL) and ADX-SAL groups with no effects on novel object recognition, elevated zero maze, or acoustic startle/prepulse inhibition. Post-testing, monoamine levels remained decreased in both MA-treated groups in all three brain regions, but were not as large as those observed at 72-h post-treatment. The data demonstrate that MA-induced learning deficits can be dissociated from drug-induced increases in plasma corticosterone or hyperthermia, but co-occur with dopamine and serotonin reductions.

Methamphetamine and lentivirus interactions: reciprocal enhancement of central nervous system disease

Use of methamphetamine is increasingly a significant factor for the spread of human immunodeficiency virus type 1, for in certain populations, there is a convergence of methamphetamine abuse with human immunodeficiency virus type 1 infection. Methamphetamine and human immunodeficiency virus type 1 are both individually neuropathogenic, and the neuropathology caused by these two agents occurs in overlapping brain regions. However, the biological interaction of methamphetamine with lentiviruses remains unknown. Here, we investigate the effects of simultaneous exposure of these two agents on disease progression using the feline immunodeficiency virus model. The study models the bingeing methamphetamine user with sequential and repeated episodes of use, which were interrupted by periods of abstinence. Methamphetamine exposure significantly accelerated and enhanced the severity of the feline immunodeficiency virus model-induced central nervous system functional pathology, as measured in delays in brainstem auditory evoked potentials. Reciprocally, feline immunodeficiency virus enhanced the severity of the methamphetamine-induced effects on brain monoamine neurotransmitter and dopamine transporter levels. The results of this study indicate that a dual potentiation occurred. That is, methamphetamine enhanced feline immunodeficiency virus model-induced central nervous system disease and feline immunodeficiency virus model enhanced the toxic effects of methamphetamine, heralding a significant concern for those individuals that are exposed to both agents.

Dopamine is not essential for the development of methamphetamine-induced neurotoxicity

It is widely believed that dopamine (DA) mediates methamphetamine (METH)-induced toxicity to brain dopaminergic neurons, because drugs that interfere with DA neurotransmission decrease toxicity, whereas drugs that increase DA neurotransmission enhance toxicity. However, temperature effects of drugs that have been used to manipulate brain DA neurotransmission confound interpretation of the data. Here we show that the recently reported ability of l-dihydroxyphenylalanine to reverse the protective effect of alpha-methyl-para-tyrosine on METH-induced DA neurotoxicity is also confounded by drug effects on body temperature. Further, we show that mice genetically engineered to be deficient in brain DA develop METH neurotoxicity, as long as the thermic effects of METH are preserved. In addition, we demonstrate that mice genetically engineered to have unilateral brain DA deficits develop METH-induced dopaminergic deficits that are of comparable magnitude on both sides of the brain. Taken together, these findings demonstrate that DA is not essential for the development of METH-induced dopaminergic neurotoxicity and suggest that mechanisms independent of DA warrant more intense investigation.

Relationships among gender, age, time, and temperature in methamphetamine-induced striatal dopaminergic neurotoxicity

A neurotoxic regimen of methamphetamine (MA-40 mg/kg ip) administered at 0 (control-MA vehicle), 0.5 and 72 h prior to determinations of striatal dopamine (DA) and DOPAC (3,4-dihydroxyphenylacetic acid)/DA ratios were compared among juvenile and adult female and male mice. Adult females and males showed similar depletions in striatal DA at 0.5 h post-MA, but males showed greater DA depletions and DOPAC/DA ratios at 72 h post-MA. Juvenile mice showed neither sex differences, nor any MA neurotoxicity upon striatal DA or DOPAC/DA ratios. Following MA, body temperatures increased in all mice, but increases in adult males were greater than adult females; juveniles showed no sex differences and body temperature increases were similar to that of adult males. MA-evoked DA output was greater in adult compared to juvenile males and a biologically effective regimen of testosterone to juvenile males neither increased MA-evoked DA output nor decreased MA-induced striatal DA like that observed in adult males. These results demonstrate: (1) Unlike adults, juvenile mice show neither a sex difference for MA-induced neurotoxicity or body temperature increases, nor MA neurotoxicity, (2) Initial effects of MA (0.5 h) in adult females and males are similar, but at 72 h post-MA females show no further striatal DA depletion, (3) Increased striatal DA depletion within adult versus juvenile males may be related to initially higher MA-evoked DA responses, and (4) Testosterone fails to convert juvenile males into adults with regard to MA effects.

Methamphetamine self-administration and the effect of contingency on monoamine and metabolite tissue levels in the rat

A number of studies have shown that exposure to high doses of methamphetamine (MA) is toxic to central dopamine (DA) and serotonin (5-HT) neurons. In most of those studies, however, high doses of MA were experimenter-administered during a short exposure time. Because contingency is a determinant for many effects of drug exposure, the present objective was to investigate the effects of self-administered MA on tissue monoamine levels following a short (24 hours) or longer (7 days) withdrawal period. As previously reported, a noncontingent "binge" high-dose treatment regimen (4 injections of 10 mg/kg MA administered every 2 hours) produced persistent depletion of cortical 5-HT and striatal DA. Effects of self-administered MA (0.1 mg/kg/infusion) were then determined following a 20-day duration where a yoked design was employed such that some rats received MA contingent on an operant lever press and others received either MA or saline dependent on the responses of the contingent rat. Self-administered MA produced a transient striatal DA depletion with a more persistent increase in DA turnover, indicating the presence of some lasting adaptations. Furthermore, the yoked design revealed that there was no effect of contingency on these parameters.

MDMA, methamphetamine and their combination: possible lessons for party drug users from recent preclinical research

The substituted amphetamines 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') and methamphetamine (METH, 'ice', 'speed') are increasingly popular drugs amongst party-drug users. Studies with humans have investigated the acute and possible long-term adverse effects of these drugs, yet outcomes of such studies are often ambiguous due to a variety of confounding factors. Studies employing animal models have value in determining the acute and long-term effects of MDMA and METH on brain and behaviour. Self-administration studies show that intravenous METH is a particularly potent reinforcer in rats and other species. In contrast, MDMA appears to have powerful effects in enhancing social behaviour in laboratory animals. Brief exposure to MDMA or METH may produce long-term reductions in dopamine, serotonin and noradrenaline in the brain and alterations in the density of various receptor and transporter proteins. However it is still unclear, particularly in the case of MDMA, whether this reflects a 'neurotoxic' effect of the drug. Lasting alterations in social behaviour, anxiety, depressive symptoms and memory have been demonstrated in laboratory rats given MDMA or METH and this matches long-term changes reported in some human studies. Recent laboratory studies suggest that MDMA/METH combinations may produce greater adverse neurochemical and behavioural effects than either drug alone. This is of some concern given recent evidence that party drug users may be frequently exposed to this combination of drugs.

Differential effects of methamphetamine and cocaine on conditioned place preference and locomotor activity in adult and adolescent male rats

Human and animal laboratory studies show that adolescents and adults respond differently to drugs and that drug administration during adolescence leads to different behavioral effects than during adulthood. Although there are a number of studies on the effects of cocaine, little is known about the effects of methamphetamine in adolescent vs adult rats. In the present study, sensitivity to the conditioned reward of multiple doses of methamphetamine or cocaine was evaluated in male adolescent (PND 34) and adult (PND 66) rats using a conditioned place preference (CPP) paradigm. In addition, the locomotor-activating effects of methamphetamine were determined across a 5-day period of administration. After 3 days of training with cocaine, both adolescent and adult male rats developed CPP to cocaine, however, the dose-effect curve for cocaine CPP was shifted to the left in adolescent compared to adult rats. In contrast to the development of CPP to cocaine in both groups after 3 days of conditioning, methamphetamine CPP occurred only in adolescent, and not in adult rats. After 5 days of training, however, both adolescent and adult rats exhibited identical responses to multiple doses of methamphetamine and a significant CPP was observed in both groups. Daily administration of methamphetamine increased locomotor activity in both adolescent and adult rats, with a greater effect seen in the adults. In neither group, was there evidence of a significant sensitization to the locomotor-activating effects of methamphetamine. These data show that adolescents are more sensitive to psychostimulant reward and thus to the conditioned rewarding properties of cocaine or methamphetamine than adults. A better understanding of this difference may lead to age-specific preventions and treatments for psychostimulant abuse.

Oxoguanine glycosylase 1 protects against methamphetamine-enhanced fetal brain oxidative DNA damage and neurodevelopmental deficits

In utero methamphetamine (METH) exposure enhances the oxidative DNA lesion 7,8-dihydro-8-oxoguanine (8-oxoG) in CD-1 fetal mouse brain, and causes long-term postnatal motor coordination deficits. Herein we used oxoguanine glycosylase 1 (ogg1) knock-out mice to determine the pathogenic roles of 8-oxoG and OGG1, which repairs 8-oxoG, in METH-initiated neurodevelopmental anomalies. Administration of METH (20 or 40 mg/kg) on gestational day 17 to pregnant +/- OGG1-deficient females caused a drug dose- and gene dose-dependent increase in 8-oxoG levels in OGG1-deficient fetal brains (p < 0.05). Female ogg1 knock-out offspring exposed in utero to high-dose METH exhibited gene dose-dependent enhanced motor coordination deficits for at least 12 weeks postnatally (p < 0.05). Contrary to METH-treated adult mice, METH-exposed CD-1 fetal brains did not exhibit altered apoptosis or DNA synthesis, and OGG1-deficient offspring exposed in utero to METH did not exhibit postnatal dopaminergic nerve terminal degeneration, suggesting different mechanisms. Enhanced 8-oxoG repair activity in fetal relative to adult organs suggests an important developmental protective role of OGG1 against in utero genotoxic stress. These observations provide the most direct evidence to date that 8-oxoG constitutes an embryopathic molecular lesion, and that functional fetal DNA repair protects against METH teratogenicity.

Effect of +-methamphetamine on path integration learning, novel object recognition, and neurotoxicity in rats

RATIONALE

Methamphetamine (MA) has been implicated in cognitive deficits in humans after chronic use. Animal models of neurotoxic MA exposure reveal persistent damage to monoaminergic systems but few associated cognitive effects.

OBJECTIVES

Since questions have been raised about the typical neurotoxic dosing regimen used in animals and whether it adequately models human cumulative drug exposure, these experiments examined two different dosing regimens.

MATERIALS AND METHODS

Rats were treated with one of the two regimens: one based on the typical neurotoxic regimen (4 x 10 mg/kg every 2 h) and one based on pharmacokinetic modeling (Cho AK, Melega WP, Kuczenski R, Segal DS Synapse 39:161-166, 2001) designed to better represent accumulating plasma concentrations of MA as seen in human users (24 x 1.67 mg/kg once every 15 min) matched for total daily dose. In two separate experiments, dosing regimens were compared for their effects on markers of neurotoxicity or on behavior.

RESULTS

On markers of neurotoxicity, MA showed decreased dopamine (DA) and 5-HT, increased glial fibrillary acidic protein, and increased corticosterone levels regardless of dosing regimen 3 days post-treatment. Behaviorally, MA-treated groups, regardless of dosing regimen, showed hypoactivity, increased initial hyperactivity to a subsequent MA challenge, impaired novel object recognition, impaired learning in a multiple T water maze test of path integration, and no differences on spatial navigation or reference memory in the Morris water maze. After behavioral testing, reductions of DA and 5-HT remained.

CONCLUSIONS

MA treatment induces an effect on path integration learning not previously reported. Dosing regimen had no differential effects on behavior or neurotoxicity.

Comparison of time-dependent effects of (+)-methamphetamine or forced swim on monoamines, corticosterone, glucose, creatine, and creatinine in rats

Background

Methamphetamine (MA) use is a worldwide problem. Abusers can have cognitive deficits, monoamine reductions, and altered magnetic resonance spectroscopy findings. Animal models have been used to investigate some of these effects, however many of these experiments have not examined the impact of MA on the stress response. For example, numerous studies have demonstrated (+)-MA-induced neurotoxicity and monoamine reductions, however the effects of MA on other markers that may play a role in neurotoxicity or cell energetics such as glucose, corticosterone, and/or creatine have received less attention. In this experiment, the effects of a neurotoxic regimen of (+)-MA (4 doses at 2 h intervals) on brain monoamines, neostriatal GFAP, plasma corticosterone, creatinine, and glucose, and brain and muscle creatine were evaluated 1, 7, 24, and 72 h after the first dose. In order to compare MA's effects with stress, animals were subjected to a forced swim test in a temporal pattern similar to MA administration [i.e., (30 min/session) 4 times at 2 h intervals].

Results

MA increased corticosterone from 1–72 h with a peak 1 h after the first treatment, whereas glucose was only increased 1 h post-treatment. Neostriatal and hippocampal monoamines were decreased at 7, 24, and 72 h, with a concurrent increase in GFAP at 72 h. There was no effect of MA on regional brain creatine, however plasma creatinine was increased during the first 24 h and decreased by 72 h. As with MA treatment, forced swim increased corticosterone more than MA initially. Unlike MA, forced swim reduced creatine in the cerebellum with no change in other brain regions while plasma creatinine was decreased at 1 and 7 h. Glucose in plasma was decreased at 7 h.

Conclusion

Both MA and forced swim increase demand on energy substrates but in different ways, and MA has persistent effects on corticosterone that are not attributable to stress alone.

Deprenyl treatment attenuates long-term pre- and post-synaptic changes evoked by chronic methamphetamine

Deprenyl, used clinically in Parkinson's disease, has multiple pharmacological effects which make it a good candidate to treat neurotoxicity. Thus, we investigated deprenyl's ability to attenuate methamphetamine-induced dopamine neurotoxicity. We also examined deprenyl's effect in changing markers associated with psychostimulant sensitization. A potential therapeutic effect on either pathological domain would be a boon in developing novel treatments for methamphetamine abuse. Adult male Sprague-Dawley rats were split into 6 groups. Three groups received a 7-day saline minipump with saline, 0.05 or 0.25 mg/kg SC deprenyl injections given for 10 days before, during and 5 days after the 7-day saline minipump implant. Similarly, 3 groups received methamphetamine pumps (25 mg/kg/day) with escalating daily injections of methamphetamine (0-6 mg/kg) in addition to the minipump treatment. These rats also received saline, 0.05 or 0.25 mg/kg deprenyl injections given before, during and the 7-day minipump treatment. Rats were killed on day 28 of withdrawal and brain samples taken. HPLC analysis for dopamine and 3,4-Dihydroxy-Phenylacetic Acid (DOPAC) revealed a loss of dopamine in the caudate and accumbens which was partially reversed by high dose deprenyl. Tyrosine hydroxylase immunostaining in the midbrain was unaffected by methamphetamine, suggesting that dopamine neurotoxicity was localized to the caudate. Western blot analysis of the caudate after methamphetamine revealed little change in Alpha-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionic Acid (AMPA) GluR1 or N-Methyl-d-Aspartate (NMDA) NR2B subunits, or their phosphorylation state. However, methamphetamine increased levels of GluR1 and its phosphorylation state in the prefrontal cortex (PFC), and these increases were attenuated by deprenyl. Methamphetamine also increased levels of PFC NR2B subunit, but these increases were not attenuated by deprenyl. We suggest that deprenyl may be effective in reducing the neurotoxic effects of methamphetamine and may also attenuate changes in prefrontal AMPA receptor function, presumably more associated with addiction rather than neurotoxicity.

Alterations in body temperature, corticosterone, and behavior following the administration of 5-methoxy-diisopropyltryptamine ('foxy') to adult rats: a new drug of abuse

Many drugs are used or abused in social contexts without understanding the ramifications of their use. In this study, we examined the effects of a newly popular drug, 5-methoxy-diisopropyltryptamine (5-MEO-DIPT; 'foxy' or 'foxy-methoxy'). Two experiments were performed. In the first, 5-MEO-DIPT (0, 10, or 20 mg/kg) was administered to rats four times on a single day and animals were examined 3 days later. The animals that received 5-MEO-DIPT demonstrated hypothermia during the period of drug administration and delayed mild hyperthermic rebound for at least 48 h. Corticosterone levels in plasma were elevated in a dose-dependent manner compared to saline-treated animals with minor changes in 5-HT turnover and no changes in monoamine levels. In experiment 2, rats were examined in behavioral tasks following either 0 or 20 mg/kg of 5-MEO-DIPT. The animals treated with 5-MEO-DIPT showed hypoactivity and an attenuated response to (+)-methamphetamine-induced stimulation (1 mg/kg). In a test of path integration (Cincinnati water maze), 5-MEO-DIPT-treated animals displayed deficits in performance compared to the saline-treated animals. No differences were noted in the ability of the animals to perform in the Morris water maze or on tests of novel object or place recognition. The data demonstrate that 5-MEO-DIPT alters the ability of an animal to perform certain cognitive tasks, while leaving others intact and disrupts the endocrine system. 5-MEO-DIPT may have the potential to induce untoward effects in humans.

Differential effects of psychoactive drugs in adolescents and adults

It is well known that most people who use psychoactive drugs started as teenagers. In spite of this, there has been little preclinical research on the effects of psychostimulants during adolescence. Recently, however, a number of laboratories have begun to focus on drug effects in adolescents as compared with adults. The data show that there are unique responses to drugs during this period of development. This review will focus on our current understanding of neurochemical and behavioral drug effects during adolescence.

Sex- and histamine-dependent long-term cognitive effects of methamphetamine exposure

As prenatal methamphetamine (MA) exposure results in long-term hippocampus-dependent cognitive deficits, the increased MA use in women of childbearing age is of great concern. As mice are most commonly used in genetic models, we started to study the potential effects of neonatal MA exposure in female and male mice on brain function 3 months later. As histamine (HA) might mediate some effects of MA in adulthood, we also tested whether in neonates HA might mediate the long-term effects of MA using HA H(3) receptor agonists and antagonists. Stimulation of HA H(3) receptors by H(3) agonists inhibits HA synthesis and release, whereas inhibition of H(3) receptors by H(3) receptor antagonists increases HA release. MA (5 mg/kg), the H(3) receptor antagonist thioperamide (5 mg/kg), and the H(3) receptor agonist immepip (5 mg/kg) alone or in the presence of MA (5 mg/kg) were administered once daily from postnatal days 11 to 20 and the mice were tested at 3 months of age. Here we show that in mice exposure to MA early in life causes sex-dependent impairments in object recognition, spatial learning, and memory in the water maze, and pre-pulse inhibition in adulthood. HA mediates these impairments. Increasing HA release mimicked, whereas inhibiting HA release blocked the long-term detrimental MA effects. This model could be used to determine the role of genetic and environmental factors in MA-dependent cognitive impairments and to develop therapeutic strategies to inhibit them.

Effects of postnatal exposure to methamphetamine on the development of the rat retina

Since the development of different cell types in the retina occurs at different rates, it is possible that exposure to an exogenous substance may produce effects during one time period, but not during another. This study aims to analyze the effects of methamphetamine (METH) in the growth pattern of an experimental model as well as neurochemical and immunohistochemical parameters of the dopaminergic system of the rat retina. The three development stages chosen in this study are key markers in rat eye development. Rats were given 15 mg/kg body weight per day of METH as subcutaneous injections in 0.9% saline (3 mL/kg weight/day) from the day after birth PND 1 to PND 6, PND 13, and PND 29. Each daily dose was split into two. The control group was injected subcutaneously with saline. Both the schedule and volume for injecting saline in the control group were the same as for the METH-treated group. There were no significant differences in the total number of offspring per litter among treatment groups. All offspring had similar body weight at birth. Analysis of body weight on PND 1, showed that animals treated with METH had similar body weights to control-treated animals and females had smaller weights than males. For growth evolution, only litters with a sex ratio of four males and four females were used. Animals treated with METH had smaller body weights than the control-treated animals for all ages studied (PND 7, 14, and 30). Within the control group at PND 30, a significant difference was found in the body weight of females, which was lower when compared with males. For the postnatal model, 7 deaths occurred for the METH-exposed group. No deaths occurred in the control group in a total of 16 saline-injected litters comprising 186 pups. Although the levels of dopamine (DA) was within normal values for the postnatally exposed METH group when compared with its respective control group at PND 7 and 30, at PND 14 this was not the case: in this experimental group, the level of DA was lower than in the control group for both females and males. Support for this result was not evident from the TH immunoreactivity studies, probably because the methodology lacks the sensitivity to distinguish any mild effects, such as that observed in the postnatal model at PND 14. The level of the DA metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) remained unaffected at all ages studied, for both females and males. The results obtained in this study support the view that, during the critical periods in which the catecholamines can influence the development of neurones, METH transiently affects the pattern of the dopaminergic system in the developing retina.

Comparison of monoamine and corticosterone levels 24 h following (+)methamphetamine, (+/-)3,4-methylenedioxymethamphetamine, cocaine, (+)fenfluramine or (+/-)methylphenidate administration in the neonatal rat

We have previously shown that neonatal administration of (+/-)3,4-methylenedioxymethamphetamine and (+)fenfluramine produce deficits in spatial and path integration learning, whereas (+)methamphetamine causes deficits in spatial learning. Conversely, cocaine and (+/-)methylphenidate have no effect on either form of learning following neonatal administration. The purpose of the present study was to determine whether corticosterone and/or monoamine levels were changed following subcutaneous administration of 10 mg/kg (+)methamphetamine, (+/-)3,4-methylenedioxymethamphetamine, (+)fenfluramine, (+/-)methylphenidate or cocaine every 2 h (total of four injections) on postnatal day 11. Twenty-four hours after the first dose, plasma, striatum and hippocampus were collected. Corticosterone levels were increased in methamphetamine-, fenfluramine-, methylenedioxymethamphetamine- and methylphenidate-treated rats relative to levels in saline-treated rats, whereas cocaine-treated rats were unaffected. In the striatum and hippocampus, serotonin and 5-hydroxyindolacetic acid were reduced in animals treated with methylenedioxymethamphetamine or fenfluramine, compared with levels in saline controls. Dopamine levels were not changed by any of the drugs, although 3,4-dihydroxyphenylacetic acid was decreased following methylenedioxymethamphetamine or methamphetamine. Minimal effects were seen in neurotransmitter levels following injection of cocaine or methylphenidate. These data suggest that drugs that affect corticosterone and hippocampal serotonin are associated with both spatial learning and path integration deficits, and those that affect corticosterone and 3,4-dihydroxyphenylacetic acid are associated with spatial learning deficits only.

Ontogeny of the adrenal response to (+)-methamphetamine in neonatal rats: the effect of prior drug exposure

We examined the ontogeny of the corticosterone response to (+)-methamphetamine in neonatal rats. In experiment-1, animals were injected with 10 mg/kg of (+)-methamphetamine or saline and plasma corticosterone levels were examined in separate groups 30 or 105 min later on postnatal day (P) 1, 3, 5, 7, 9, 11, 13, 15, 17, or 19. The adrenal response to methamphetamine was best described by a U-shaped function with the nadir of corticosterone release occurring between P7 and P13. Experiment-2 was similar except that the effect of four consecutive days of exposure to (+)-methamphetamine (four times daily at 2 h intervals with 10 mg/kg) was assessed with a single final dose early on the fifth day (i.e. P1-5, 3-7, 5-9, 7-11, 9-13, 11-15, 13-17, 15-19). The 30 min corticosterone response after multiple methamphetamine doses was augmented compared to single exposures, with the exception of the two earliest dosing intervals ending on P5 and P7, where the responses were lower. In addition, at 105 min, the levels of corticosterone were attenuated relative to a single drug administration. With the exception of animals receiving methamphetamine from P15 to P19, thymus weights were unaffected. The data demonstrate that (+)-methamphetamine is a robust activator of corticosterone release in developing animals and this release is extensively modified by age and previous drug exposure.

Long-term effects of a single adult methamphetamine challenge: minor impact on dopamine fibre density in limbic brain areas of gerbils

BACKGROUND

The aim of the study was to test long-term effects of (+)-methamphetamine (MA) on the dopamine (DA) innervation in limbo-cortical regions of adult gerbils, in order to understand better the repair and neuroplasticity in disturbed limbic networks.

METHODS

Male gerbils received a single high dose of either MA (25 mg/kg i.p.) or saline on postnatal day 180. On postnatal day 340 the density of immunoreactive DA fibres and calbindin and parvalbumin cells was quantified in the right hemisphere.

RESULTS

No effects were found in the prefrontal cortex, olfactory tubercle and amygdala, whereas the pharmacological impact induced a slight but significant DA hyperinnervation in the nucleus accumbens. The cell densities of calbindin (CB) and parvalbumin (PV) positive neurons were additionally tested in the nucleus accumbens, but no significant effects were found. The present results contrast with the previously published long-term effects of early postnatal MA treatment that lead to a restraint of the maturation of DA fibres in the nucleus accumbens and prefrontal cortex and a concomitant overshoot innervation in the amygdala.

CONCLUSION

We conclude that the morphogenetic properties of MA change during maturation and aging of gerbils, which may be due to physiological alterations of maturing vs. mature DA neurons innervating subcortical and cortical limbic areas. Our findings, together with results from other long-term studies, suggest that immature limbic structures are more vulnerable to persistent effects of a single MA intoxication; this might be relevant for the assessment of drug experience in adults vs. adolescents, and drug prevention programs.

Age-dependent (+)MDMA-mediated Neurotoxicity in Mice

In the present study the effects of a neurotoxic regimen of (+)-MDMA (20 mg/kgx4, s.c.) in 4- and 10-week-old C57Bl/6J mice during treatment and 7 days post-treatment were examined. Rectal temperatures monitored between (+)-MDMA injections (30 min post-injection/2 h intervals) revealed hyperthermic responses in both age groups, with the magnitude of the response significantly greater in older mice. Seven days post-treatment, immunoblot analyses of the vesicular monoamine transporter 2 (VMAT2), and tyrosine hydroxylase (TH) revealed significant reductions (-37 and -58%, respectively) in the older animals, but not in the younger group, compared to age-matched controls. Dopamine transporter (DAT) expression was significantly reduced in both 4- and 10-week-old animals (26 and 69.7%, respectively). (+)-MDMA-treated animals also exhibited significantly lower levels of striatal dopamine, and 3,4-dihydroxyphenylacetic acid than controls, again the effect being more pronounced in the older animals. Although both age groups showed evidence of (+)-MDMA-induced toxicity, our data revealed that older animals exhibited a greater hyperthermic response to (+)-MDMA and were also are more susceptible to subsequent dopaminergic damage than the younger animals.

Do preclinical findings of methamphetamine-induced motor abnormalities translate to an observable clinical phenotype?

This review summarizes the preclinical literature of the effects of methamphetamine (MA) on subcortical dopaminergic and GABAergic mechanisms underlying motor behavior with the goal of elucidating the clinical presentation of human MA-induced movement disorders. Acute and chronic MA exposure in laboratory animal can lead to a variety of motor dysfunctions including increased locomotor activity, stereotypies, diminished or enhanced response times, and parkinsonian-like features. With the exception of psychomotor impairment and hyperkinesia, MA-induced movement disorders are not well documented in humans. This review attempts to draw parallels between the animal and human changes in basal ganglia neurochemistry associated with MA exposure and offers explanations for why a parkinsonian phenotype is not apparent among individuals who use and abuse MA. Significant differences in the expression of neurotoxicity and presence of multiple environmental and pharmacologic confounds may account for the lack of a parkinsonian phenotype in humans despite evidence of altered dopamine function.

Amphetamine treatment similar to that used in the treatment of adult attention-deficit/hyperactivity disorder damages dopaminergic nerve endings in the striatum of adult nonhuman primates

Pharmacotherapy with amphetamine is effective in the management of attention-deficit/hyperactivity disorder (ADHD), now recognized in adults as well as in children and adolescents. Here we demonstrate that amphetamine treatment, similar to that used clinically for adult ADHD, damages dopaminergic nerve endings in the striatum of adult nonhuman primates. Furthermore, plasma concentrations of amphetamine associated with dopaminergic neurotoxicity in nonhuman primates are on the order of those reported in young patients receiving amphetamine for the management of ADHD. These findings may have implications for the pathophysiology and treatment of ADHD. Further preclinical and clinical studies are needed to evaluate the dopaminergic neurotoxic potential of therapeutic doses of amphetamine in children as well as adults.

Age-dependent methamphetamine-induced alterations in vesicular monoamine transporter-2 function: implications for neurotoxicity

Tens of thousands of adolescents and young adults have used illicit methamphetamine. This is of concern since its high-dose administration causes persistent dopaminergic deficits in adult animal models. The effects in adolescents are less studied. In adult rodents, toxic effects of methamphetamine may result partly from aberrant cytosolic dopamine accumulation and subsequent reactive oxygen species formation. The vesicular monoamine transporter-2 (VMAT-2) sequesters cytoplasmic dopamine into synaptic vesicles for storage and perhaps protection against dopamine-associated oxidative consequences. Accordingly, aberrant VMAT-2 function may contribute to the methamphetamine-induced persistent dopaminergic deficits. Hence, this study examined effects of methamphetamine on VMAT-2 in adolescent (postnatal day 40) and young adult (postnatal day 90) rats. Results revealed that high-dose methamphetamine treatment caused greater acute (within 1 h) decreases in vesicular dopamine uptake in postnatal day 90 versus 40 rats, as determined in a nonmembrane-associated subcellular fraction. Greater basal levels of VMAT-2 at postnatal day 90 versus 40 in this purified fraction seemed to contribute to the larger effect. Basal tissue dopamine content was also greater in postnatal day 90 versus 40 rats. In addition, postnatal day 90 rats were more susceptible to methamphetamine-induced persistent dopaminergic deficits as assessed by measuring VMAT-2 activity and dopamine content 7 days after treatment, even if drug doses were adjusted for age-related pharmacokinetic differences. Together, these data demonstrate dynamic changes in VMAT-2 susceptibility to methamphetamine as a function of development. Implications with regard to methamphetamine-induced dopaminergic deficits, as well as dopamine-associated neurodegenerative disorders such as Parkinson's disease, are discussed.

Periadolescent rats (P41-50) exhibit increased susceptibility to D-methamphetamine-induced long-term spatial and sequential learning deficits compared to juvenile (P21-30 or P31-40) or adult rats (P51-60)

We have previously shown that P11-20 treatment with d-methamphetamine (MA) induces impaired spatial navigation in the Morris water maze (MWM), whereas P1-10 treatment does not. Little is known about the long-term behavioral consequences of MA during juvenile, adolescent, and early adult brain development. In dose-response experiments, we tested successive 10-day intervals of exposure to MA in rats (P21-30, P31-40, P41-50, and P51-60; four doses per day). MA dosing prior to P21 produces little or no toxicity; however, we observed an increased toxicity with advancing age. Across-age comparisons revealed no MWM acquisition or Cincinnati water maze (CWM) effects after MA treatment on P21-30 (2.5-10 mg/kg/dose), P31-40 (1.25-7.5 mg/kg/dose), or P51-60 (1.25-5.0 mg/kg/dose); however, significantly impaired MWM acquisition was observed after P41-50 MA treatment at the highest dose (6.25 mg/kg/dose). Learning in the CWM was also impaired in this group. No effects were seen at 1.25, 2.5, or 5 mg/kg/dose following P41-50 MA treatment. MWM reversal learning trials after P41-50 treatment showed a trend towards longer latency in all MA dose groups, but no effect on double-reversal trials. Reversal and double-reversal also showed no effects at the other exposure ages. No differences in straight channel swimming or cued learning in the MWM were seen after MA treatment at any exposure age. P41-50 is the periadolescent stage of brain development in rodents. The effects observed at this age may suggest a previously unrecognized period of susceptibility for MA-induced cognitive deficits.

Effects of neonatal exposure to methamphetamine: catecholamine levels in brain areas of the developing rat

Neonatal exposure to moderate doses of methamphetamine during the first month of life in the rat affects tyrosine hydroxylase gene expression in the substantia nigra and nigrostriatal tyrosine hydroxylase activity. The main goal of this work was to evaluate the ontogeny of the neurochemical effects of repeated exposure to moderate doses of methamphetamine during the first month of life in the rat. Norepinephrine, dopamine, and dihydroxyphenylacetic acid levels were measured in target areas of methamphetamine: the substantia nigra, ventral tegmental area, caudate-putamen, nucleus accumbens, and medial prefrontal cortex. On postnatal day 1 (PND1), Wistar rat litters, culled to eight pups, sex balanced, were randomly attributed to either methamphetamine or control groups. Methamphetamine groups were administered 10 mg of (+/-)-methamphetamine/kg body weight/day, subcutaneously, from PND1 until the day prior to sacrifice; control groups received isovolumetric saline. Groups were sacrificed on PND7, PND14, and PND30. Neonatal methamphetamine exposure increased norepinephrine levels in the substantia nigra of PND30 rats; on PND14, this variation was evident only in male pups. In the substantia nigra, the dihydroxyphenylacetic/dopamine ratio was also affected in PND30 males. In the ventral tegmental area, catecholamine levels were not affected by methamphetamine. Norepinephrine levels were also increased in the caudate-putamen of PND7 male and PND14 female methamphetamine-exposed pups and in the nucleus accumbens of PND14 female and PND30 male and female pups. Catecholamine levels in the medial prefrontal cortex were not affected by neonatal methamphetamine administration.

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.

Acute and chronic continuous methamphetamine have different long-term behavioral and neurochemical consequences

We compared two different methamphetamine dosing regimens and found distinct long-term behavioral and neurochemical changes. Adult rats were treated with 1-day methamphetamine injection (3x5 mg/kg s.c., 3 h apart) or 7-day methamphetamine minipump (20 mg/kg/day s.c.). The minipump regimen models the sustained methamphetamine plasma levels in some human bingers whereas the 1-day regimen models a naive user overdose. On withdrawal days 7 and 28, rats were acutely challenged with cocaine to test for behavioral sensitization and subsequently sacrificed for caudate and accumbens dopamine tissue content. Other rats were analyzed on withdrawal days 3, 7 or 28 using voltammetry in caudate slices. On withdrawal days 7 and 28, the methamphetamine injection but not the minipump rats showed behavioral cross-sensitization to cocaine. There was no change in baseline dopamine release, reuptake or sensitivity to quinpirole in any treatment group on either withdrawal day. However, consistent with the behavioral sensitization, cocaine had a greater effect in potentiating dopamine release and in blocking dopamine reuptake in methamphetamine injection versus saline irrespective of withdrawal day. The minipump group showed tolerance to the dopamine releasing effect of cocaine on withdrawal day 28 and had lower dopamine tissue content in the caudate versus the methamphetamine injection group. Dopamine turnover as measured by the DOPAC/dopamine ratio tended to be higher in the minipump-treated rats. These data suggest that the behavioral cross-sensitization seen in the methamphetamine injection rats could be in part due to the increased potency of cocaine in blocking dopamine reuptake and in increasing dopamine release. The decreased potency of cocaine in the caudate slices from the minipump-treated group may be related to decreased dopamine tissue content.

Methamphetamine exacerbates the toxic effect of kainic acid in the adult rat retina

The recreational use of the psychoactive drug, methamphetamine has increased markedly over the last three decades. It has long been known that this drug has detrimental effects upon the mammalian brain monoaminergic system, but the long- or short-term effects on the retina, a neurological extension of the central nervous system, have received little attention. The aim of this study was, therefore, to determine whether intraocular injection of methamphetamine (MA) is toxic to the healthy adult rat retina and to analyse its effects on the compromised retina after an injection of the ionotropic glutamate receptor agonist, kainate, which is known to cause retinal neuropathology. The equivalent of 1 mM (in the vitreous humour) MA and/or kainate (40 microM) were injected intravitreally. Flash electroretinograms (ERGs) were recorded before and 2 and 4 days after treatment. Five days after treatment, animals were killed and the retinas analysed either for the immunohistochemical localisation of various antigens or for electrophoresis/Western blotting. Some animals were kept for 19 days after treatment and the retinas analysed for tyrosine hydroxylase immunoreactivity. No differences could be found between vehicle- and MA-treated retinas with respect to the nature or localisation of either tyrosine hydroxylase immunoreactivity after 5 or 19 days or other antigens after 5 days. Moreover, the normal ERG and GFAP and calretinin protein antigens were unaffected by MA. Kainate treatment, however, caused a change in the ERGs after 2 and 4 days, an alteration in every antigen localised by immunohistochemistry and an increase in the retinal levels of calretinin and GFAP proteins. Significantly, the changes seen in the b-wave amplitude and implicit time of the ERG after 4 days and the increased level of GFAP protein after 5 days following kainate treatment were enhanced when MA was co-injected. Intravitreal injection of methamphetamine had no detectable detrimental effect on the normal adult rat retina but exacerbated the damaging effects of kainic acid. Such data suggest that a neurotoxic effect of MA may be more obviously illustrated when the tissue is already compromised as occurs in, for example, ischemia.

Neonatal methamphetamine administration induces region-specific long-term neuronal morphological changes in the rat hippocampus, nucleus accumbens and parietal cortex

Previous studies have demonstrated that rats exposed to methamphetamine (MA) during the neonatal period display deficits in spatial learning and memory. The underlying correlates are unknown; therefore, this study was devised to determine whether neuronal changes occur in the dentate gyrus (DG), nucleus accumbens (NAcc) and cortex of adult rats exposed to 10 mg/kg MA administered four times daily from P11-20 using Golgi-Cox staining [Gibb, R. & Kolb, B. (1998) J. Neurosci. Meth., 79, 1-4]. The DG and NAcc demonstrated a decrease in the number of spines per neuron and the NAcc showed an associated decrease in dendritic length. Selective changes in cortex were observed because increased dendritic length in the parietal cortex occurred with no change in the number of spines, and no differences were noted for either dendritic length or spines in the medial frontal cortex. The data suggest a potential cause for the learning and memory deficits induced by neonatal MA exposure; however, the underlying mechanism that produces these neuronal changes is unknown.

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.