Time course of brain temperature and caudate/putamen microdialysate levels of amphetamine and dopamine in rats after multiple doses of d-amphetamine

Acupuncture inhibition of methamphetamine-induced behaviors, dopamine release and hyperthermia in the nucleus accumbens: mediation of group II mGluR

Methamphetamine (METH) increases metabolic neuronal activity in the mesolimbic dopamine (DA) system and mediates the reinforcing effect. To explore the underlying mechanism of acupuncture intervention in reducing METH-induced behaviors, we investigated the effect of acupuncture on locomotor activity, ultrasonic vocalizations, extracellular DA release in the nucleus accumbens (NAcs) using fast-scan cyclic voltammetry and alterations of brain temperature (an indicator of local brain metabolic activity) produced by METH administration. When acupuncture was applied to HT7, but not TE4, both locomotor activity and 50-kHz ultrasonic vocalizations were suppressed in METH-treated rats. Acupuncture at HT7 attenuated the enhancement of electrically stimulated DA release in the NAc of METH-treated rats. Systemic injection of METH produced a sustained increase in NAc temperature, which was reversed by the DA D1 receptor antagonist SCH 23390 or acupuncture at HT7. Acupuncture inhibition of METH-induced NAc temperature was prevented by pre-treatment with a group II metabotropic glutamate receptors (mGluR2/3) antagonist EGLU into the NAc or mimicked by injection of an mGluR2/3 agonist DCG-IV into the NAc. These results suggest that acupuncture reduces extracellular DA release and metabolic neuronal activity in the NAc through activation of mGluR2/3 and suppresses METH-induced affective states and locomotor behavior.

The time course of blood brain barrier leakage and its implications on the progression of methamphetamine-induced seizures

The initial goals of these experiments were to determine: 1) if blood-brain barrier (BBB) breakdown was a cause or an effect of METH-induced seizures; 2) all the brain regions where BBB is disrupted as seizures progress; and 3) the correlations between body temperature and vascular leakage and neurodegeneration. A fourth objective was added after initial experimentation to determine if sub-strain differences existed in adult male C57 B6 J (Jackson laboratories, JAX) versus C57 B6N (Charles River, CR) mice involving their susceptibility to BBB breakdown and seizure severity. With the 1st "maximal" intensity myoclonic-tonic seizure (MCT) varying degrees of IgG infiltration across the BBB (≤1 mm²) were prominent in olfactory system (OS) associated regions and in thalamus, hypothalamus and neocortex. IgG infiltration areas in the OS-associated regions of the bed nucleus of the stria terminalis, septum and more medial amygdala nuclei, and the hypothalamus were increased significantly by the time continuous behavioral seizures (CBS) developed. Mice receiving METH that had body temperatures of ≥40 °C had IgG infiltration along with MCT or CBS but peak body temperatures above 40 °C did not significantly increase IgG infiltration. Neurodegeneration seen at ≥6 h was restricted to the OS in both JAX and CR mice and was most prominent in the posteromedial cortical amygdaloid nucleus. Neurodegeneration in the anterior septum (tenia tecta) was seen only in the JAX mice. We hypothesize that METH-induced hypertension and hyperthermia lead to BBB breakdown and other vascular dysfunctions in the OS brain regions resulting in OS hyperexcitation. Excitation of the OS neural network then leads to the development of seizures. These seizures in turn exacerbate the energy depletions and the reactive oxygen stress produced by hyperthermia further damaging the BBB and vascular function. These events form a recurrent cycle that results in ever increasing seizure activity and neurotoxicity.

Amphetamine- and methamphetamine-induced hyperthermia: Implications of the effects produced in brain vasculature and peripheral organs to forebrain neurotoxicity

The adverse effects of amphetamine- (AMPH) and methamphetamine- (METH) induced hyperthermia on vasculature, peripheral organs and peripheral immune system are discussed. Hyperthermia alone does not produce amphetamine-like neurotoxicity but AMPH and METH exposures that do not produce hyperthermia (≥40°C) are minimally neurotoxic. Hyperthermia likely enhances AMPH and METH neurotoxicity directly through disruption of protein function, ion channels and enhanced ROS production. Forebrain neurotoxicity can also be indirectly influenced through the effects of AMPH- and METH- induced hyperthermia on vasculature. The hyperthermia and the hypertension produced by high doses amphetamines are a primary cause of transient breakdowns in the blood-brain barrier (BBB) resulting in concomitant regional neurodegeneration and neuroinflammation in laboratory animals. This BBB breakdown can occur in the amygdala, thalamus, striatum, sensory and motor cortex and hippocampus. Under these conditions, repetitive seizures greatly enhance neurodegeneration in hippocampus, thalamus and amygdala. Even when the BBB is less disrupted, AMPH- or METH- induced hyperthermia effects on brain vasculature may play a role in neurotoxicity. In this case, striatal and cortical vascular function are adversely affected, and even greater ROS, immune and damage responses are seen in the meninges and cortical surface vasculature. Finally, muscle and liver damage and elevated cytokines in blood can result when amphetamines produce hyperthermia. Proteins, from damaged muscle may activate the peripheral immune system and exacerbate liver damage. Liver damage can further increase cytokine levels, immune system activation and increase ammonia levels. These effects could potentially enhance vascular damage and neurotoxicity.

Serum myoglobin, but not lipopolysaccharides, is predictive of AMPH-induced striatal neurotoxicity

Determinants of amphetamine (AMPH)-induced neurotoxicity are poorly understood. The role of lipopolysaccharides (LPS) and organ injury in AMPH-induced neurotoxicity was examined in adult male Sprague-Dawley rats that were give AMPH and became hyperthermic during the exposure. Environmentally-induced hyperthermia (EIH) in the rat was compared to AMPH to determine whether AMPH-induced increases in LPS and peripheral toxicities were solely attributable to hyperthermia. Muscle, liver, and kidney function were determined biochemically at 3h or 1 day after AMPH or EIH exposure and histopathology at 1 day after treatment. Circulating levels of LPS were monitored (via limulus amoebocyte coagulation assay) during AMPH or EIH exposure. Blood LPS levels were detected in 40-50% of the AMPH and EIH rats, but the presence of LPS in the serum had no effect on organ damage or striatal dopamine depletions (neurotoxicity). In both CR and NCTR rats, serum bound urea nitrogen and creatinine levels increased at 3h after EIH or AMPH (2- to 3-fold above control) but subsided by 1 day. Alanine transaminase was increased (indicating liver dysfunction) by both AMPH and EIH at 3 h (2- to 10-fold above control) in CR rats, but the levels were not significantly different between the control and AMPH groups in NCTR animals. Mild liver necrosis was detected in 1 of 7 rats examined in the AMPH group and in 1 of 5 rats examined in the EIH group (only NCTR rats were examined). Serum myoglobin increased (indicating muscle damage) in both CR and NCTR rats at 3h and was more pronounced with AMPH (≈5-fold above control) than EIH. Our results indicate that: (1) "free" blood borne LPS often increases with EIH and AMPH but may not be necessary for striatal neurotoxicity and CNS immune responses; (2) liver or kidney dysfunction may result from muscle damage; however, it is not sufficient nor necessary to produce, but may exacerbate, neurotoxicity; (3) AMPH-induced serum myoglobin release is a potential biomarker and possibly a factor in AMPH-induced toxicity processes.

Early ontogeny of D-amphetamine-induced one-trial behavioral sensitization

The early ontogeny of D-amphetamine-induced one-trial behavioral sensitization was characterized using male and female preweanling and preadolescent rats. In Experiment 1, rats were injected with saline or D-amphetamine (1, 4, or 8mg/kg) in activity chambers or the home cage on postnatal day (PD) 12, PD 16, PD 20, or PD 24. One day later, rats were challenged with either 0.5 or 2mg/kg D-amphetamine and distance traveled was measured in activity chambers for 120min. In Experiment 2, saline or D-amphetamine was administered in activity chambers on PD 24, while a challenge injection of D-amphetamine (0.25-4mg/kg) was given on PD 25. At younger ages (PD 13 and PD 17), a strong sensitized response was evident on the test day regardless of whether rats were pretreated with D-amphetamine (4 or 8mg/kg) before being placed in the activity chamber or 30min after being returned to the home cage. Rats did not display D-amphetamine-induced behavioral sensitization on PD 21, nor was context-dependent sensitization apparent on PD 25 even when a broad dose range of D-amphetamine was used. When low doses of D-amphetamine were administered on the pretreatment and test days (1 and 0.5mg/kg, respectively), sensitized responding was not evident at any age. In summary, D-amphetamine-induced one-trial behavioral sensitization was only apparent within a narrow developmental window during early ontogeny. This ontogenetic pattern of sensitized responding is similar to the one produced by methamphetamine and distinct from the pattern produced by cocaine. The unique sensitization profiles resulting from repeated D-amphetamine and cocaine treatment may be a consequence of their different mechanisms of action.

Methamphetamine self-administration acutely decreases monoaminergic transporter function

Numerous preclinical studies have demonstrated that noncontingent methamphetamine (METH) administration rapidly decreases both dopamine (DA) transporter (DAT) and vesicular monoamine-2 transporter (VMAT-2) function. Because of the importance of transporter function to the abuse and neurotoxic liabilities of METH, and previous research indicating that the effects of noncontingent METH treatment do not necessarily predict effects of contingent exposure, the present study examined the acute impact of METH self-administration on these transporters. Results revealed that five days of METH self-administration (4 h/session; 0.06 mg/infusion) decreased DAT and VMAT-2 activity, as assessed in synaptosomes and vesicles, respectively, prepared from striatal tissue 1 h after the final self-administration session. METH self-administration increased core body temperatures as well. Brain METH and amphetamine (AMPH) levels, assessed 1 h after the final self-administration session, were approximately twice greater in high-pressing rats compared to low-pressing rats despite similar changes in DAT function. In conclusion, the present manuscript is the first to describe transporter function and METH/AMPH levels after self-administration in rodents. These data provide a foundation to investigate complex questions including how the response of dopaminergic systems to METH self-administration contributes to contingent-related processes such as dependence.

A guide to neurotoxic animal models of Parkinson's disease

Parkinson's disease (PD) is a neurological movement disorder primarily resulting from damage to the nigrostriatal dopaminergic pathway. To elucidate the pathogenesis, mechanisms of cell death, and to evaluate therapeutic strategies for PD, numerous animal models have been developed. Understanding the strengths and limitations of these models can significantly impact the choice of model, experimental design, and data interpretation. The primary objectives of this article are twofold: First, to assist new investigators who are contemplating embarking on PD research to navigate through the available animal models. Emphasis will be placed on common neurotoxic murine models in which toxic molecules are used to lesion the nigrostriatal dopaminergic system. And second, to provide an overview of basic technical requirements for assessing the pathology, structure, and function of the nigrostriatal pathway.

Amphetamine alters behavior and mesocorticolimbic dopamine receptor expression in the monogamous female prairie vole

We have recently established the socially monogamous prairie vole (Microtus ochrogaster) as an animal model with which to investigate the involvement of mesocorticolimbic dopamine (DA) in the amphetamine (AMPH)-induced impairment of social behavior. As the majority of our work, to date, has focused on males, and sex differences are commonly reported in the behavioral and neurobiological responses to AMPH, the current study was designed to examine the behavioral and neurobiological effects of AMPH treatment in female prairie voles. We used a conditioned place preference (CPP) paradigm to determine a dose-response curve for the behavioral effects of AMPH in female prairie voles, and found that conditioning with low to intermediate (0.2 and 1.0 mg/kg), but not very low (0.1 mg/kg), doses of AMPH induced a CPP. We also found that exposure to a behaviorally relevant dose of AMPH (1.0 mg/kg) induced an increase in DA concentration in the nucleus accumbens (NAcc) and caudate putamen but not the medial prefrontal cortex or ventral tegmental area (VTA). Finally, repeated AMPH exposure (1.0 mg/kg once per day for 3 consecutive days; an injection paradigm that has been recently shown to alter DA receptor expression and impair social bonding in male prairie voles) increased D1, but not D2, receptor mRNA in the NAcc, and decreased D2 receptor mRNA and D2-like receptor binding in the VTA. Together, these data indicate that AMPH alters mesocorticolimbic DA neurotransmission in a region- and receptor-specific manner, which, in turn, could have profound consequences on social behavior in female prairie voles.

The organic cation transporter-3 is a pivotal modulator of neurodegeneration in the nigrostriatal dopaminergic pathway

Toxic organic cations can damage nigrostriatal dopaminergic pathways as seen in most parkinsonian syndromes and in some cases of illicit drug exposure. Here, we show that the organic cation transporter 3 (Oct3) is expressed in nondopaminergic cells adjacent to both the soma and terminals of midbrain dopaminergic neurons. We hypothesized that Oct3 contributes to the dopaminergic damage by bidirectionally regulating the local bioavailability of toxic species. Consistent with this view, Oct3 deletion and pharmacological inhibition hampers the release of the toxic organic cation 1-methyl-4-phenylpyridinium from astrocytes and protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurodegeneration in mice. Furthermore, Oct3 deletion impairs the removal of the excess extracellular dopamine induced by methamphetamine and enhances striatal dopaminergic terminal damage caused by this psychostimulant. These results may have far-reaching implications for our understanding of the mechanism of cell death in a wide range of neurodegenerative diseases and may open new avenues for neuroprotective intervention.

Neurotoxicity of substituted amphetamines: Molecular and cellular mechanisms

The amphetamines, including amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA), are among abused drugs in the US and throughout the world. Their abuse is associated with severe neurologic and psychiatric adverse events including the development of psychotic states. These neuropsychiatric complications might, in part, be related to drug-induced neurotoxic effects, which include damage to dopaminergic and serotonergic terminals, neuronal apoptosis, as well as activated astroglial and microglial cells in the brain. The purpose of the present review is to summarize the toxic effects of AMPH, METH and MDMA. The paper also presents some of the factors that are thought to underlie this toxicity. These include oxidative stress, hyperthermia, excitotoxicity and various apoptotic pathways. Better understanding of the cellular and molecular mechanisms involved in their toxicity should help to generate modern therapeutic approaches to prevent or attenuate the long-term consequences of amphetamine use disorders in humans.

Escalating dose methamphetamine pretreatment alters the behavioral and neurochemical profiles associated with exposure to a high-dose methamphetamine binge

The neurotoxic effects of methamphetamine (METH) have been characterized primarily from the study of high-dose binge regimens in rodents. However, this drug administration paradigm does not include a potentially important feature of stimulant abuse in humans, that is, the gradual escalation of stimulant doses that frequently occurs prior to high-dose exposure. We have argued that pretreatment with escalating doses (EDs) might significantly alter the neurotoxic profile produced by a single high-dose binge. In the present study, we tested this hypothesis by pretreating rats with saline or gradually increasing doses of METH (0.1-4.0 mg/kg over 14 days), prior to an acute METH binge (4 x 6 mg/kg at 2 h intervals). These animals, whose behavior was continuously monitored throughout drug treatment, were then killed 3 days later for determination of caudate-putamen dopamine (DA) content, levels of [(3)H]WIN 35,428 binding to the DA transporter, and levels of [(3)H]dihydrotetrabenazine ([(3)H]DTBZ) binding to the vesicular monoamine transporter. ED pretreatment markedly attenuated the stereotypy response, as well as the hyperthermia and indices of sympathetic activation associated with the acute binge. In addition, ED pretreatment prevented the decline in [(3)H]WIN 35,428 binding, and significantly diminished the decrease in DA levels, but did not affect the decrease in [(3)H]DTBZ binding associated with the acute binge. We suggest that further study of the effects produced by a regimen which includes a gradual escalation of doses prior to high-dose METH binge exposure could more accurately identify the neurochemical and behavioral changes relevant to those that occur as a consequence of high-dose METH abuse in humans.

Brain hyperthermia is induced by methamphetamine and exacerbated by social interaction

Hyperthermia is a symptom of methamphetamine (METH) intoxication and a factor implicated in neurotoxicity during chronic METH use. To characterize the thermic response to METH, it was injected once daily into rats at increasing doses (0, 1, 3, and 9 mg/kg, s.c.) while brain [nucleus accumbens (NAcc), hippocampus] and body (deep temporal muscle) temperatures were continuously monitored. METH produced dose-dependent hyperthermia, with brain structures (especially the NAcc) showing a more rapid and pronounced temperature increase than the muscle. At the highest dose, brain and body temperatures increased 3.5-4.0 degrees C above basal levels and remained elevated for 3-5 hr. Stressful and other high-activity situations such as interaction with a conspecific female are also known to induce a significant hyperthermic response in the rat. A combination of social interaction and METH administration was tested for additive effects. Male rats were exposed daily to a conspecific female for a total of 120 min, and METH was injected at the same doses 30 min after the initial contact with the female. An initial hyperthermic response ( approximately 1.5 degrees C) to social interaction was followed by a large and prolonged hyperthermic response (3.5-5.0 degrees C, 5-7 hr at 9 mg/kg) to METH, which was again stronger in brain structures (especially in the NAcc) than in the muscle. Although the combined effect of the hyperthermic events was not additive, METH administration during social interaction produced stronger and longer-lasting increases in brain and body temperature than that induced by drug alone, heating the brain in some animals near its biological limit (>41 degrees C).

Chronic access to a sucrose solution enhances the development of conditioned place preferences for fentanyl and amphetamine in male Long-Evans rats

Consumption of palatable food and fluids alters the behavioral consequences of psychoactive drugs. To further investigate the effects of intake of palatable nutrients on the rewarding properties of these drugs, the effects of chronic intake of a sweet sucrose solution on the development of conditioned place preferences (CPP) to a mu-opioid agonist, fentanyl, and to a stimulant drug, amphetamine, were examined. Male Long-Evans rats consumed laboratory chow and water or chow, water, and a 32% sucrose solution. CPP testing was conducted in a three-chamber apparatus. In Experiment 1 (over four conditioning days), rats received saline, 0.004, or 0.016 mg/kg sc fentanyl citrate before being placed on the nonpreferred side of the apparatus and saline (subcutaneously) before being placed on the preferred side during a separate session on the same day. When given access to all three chambers, rats injected with 0.016 mg/kg fentanyl spent significantly more time on the drug-paired side than rats injected with saline. Furthermore, sucrose-fed rats displayed a significantly greater CPP than chow-fed rats. After conditioning, rats were tested for fentanyl-induced antinociception using the tail-flick test. Using a cumulative dose procedure, fentanyl (0.003, 0.010, 0.030, and 0.100 mg/kg sc) led to dose-dependent increases in tail-flick latencies. Rats fed with sucrose displayed significantly greater responses to fentanyl than those in the chow group. In Experiment 2, rats spent significantly more time on the drug-paired side of the CPP apparatus following injections of 0.33 or 1.0 mg/kg amphetamine than after saline injections. Additionally, following injection of 0.33 mg/kg amphetamine, sucrose-fed rats spent significantly more time on the drug-paired side of the chamber than chow-fed rats.

Increased anxiety and impaired memory in rats 3 months after administration of 3,4-methylenedioxymethamphetamine ("ecstasy")

Male Wistar rats were administered either (a) a high dose regime of 3,4-methylenedioxymethamphetamine (MDMA) (4 x 5 mg/kg, i.p. over 4 h on each of 2 consecutive days), (b) a moderate dose regime of MDMA (1 x 5 mg/kg on each of 2 consecutive days), (c) D-amphetamine (4 x 1 mg/kg over 4 h on each of 2 days), or (d) vehicle injections. The high MDMA dose regime and the amphetamine treatment both produced acute hyperactivity and hyperthermia. Twelve weeks later, all rats were tested in the drug-free state on a battery of anxiety tests (elevated plus maze, emergence and social interaction tests). A further 2 weeks later they were tested on a novel object recognition memory task. Rats previously given the neurotoxic dose of MDMA showed greater anxiety-like behaviour on all three anxiety tests relative to both controls and D-amphetamine-treated rats. Rats given the moderate MDMA dose regime also showed increased anxiety-like behaviour on all three tests, although to a lesser extent than rats in the high dose group. In the object recognition task, rats given the high MDMA dose regime showed impaired memory relative to all other groups when tested at a 15-min delay but not at a 60-min delay. Rats previously exposed to amphetamine did not differ from saline controls in the anxiety or memory tests. These data suggest that moderate to heavy MDMA exposure over 48 h may lead to increased anxiety and memory impairment 3 months later, possibly through a neurotoxic effect on brain serotonin systems.

A murine dopamine neuron-specific cDNA library and microarray: increased COX1 expression during methamphetamine neurotoxicity

Due to brain tissue heterogeneity, the molecular genetic profile of any neurotransmitter-specific neuronal subtype is unknown. The purpose of this study was to purify a population of dopamine neurons, construct a cDNA library, and generate an initial gene expression profile and a microarray representative of dopamine neuron transcripts. Ventral mesencephalic dopamine neurons were purified by fluorescent-activated cell sorting from embryonic day 13.5 transgenic mice harboring a 4.5-kb rat tyrosine hydroxylase promoter-lacZ fusion. Nine-hundred sixty dopamine neuron cDNA clones were sequenced and arrayed for use in studies of gene expression changes during methamphetamine neurotoxicity. A neurotoxic dose of methamphetamine produced a greater than twofold up-regulation of the mitochondrial cytochrome c oxidase polypeptide I transcript from adult mouse substantia nigra at 12 h posttreatment. This is the first work to describe a gene expression profile for a neuronal subtype and to identify gene expression changes during methamphetamine neurotoxicity.

Methamphetamine neurotoxicity: necrotic and apoptotic mechanisms and relevance to human abuse and treatment

Research into methamphetamine-induced neurotoxicity has experienced a resurgence in recent years. This is due to (1) greater understanding of the mechanisms underlying methamphetamine neurotoxicity, (2) its usefulness as a model for Parkinson's disease and (3) an increased abuse of the substance, especially in the American Mid-West and Japan. It is suggested that the commonly used experimental one-day methamphetamine dosing regimen better models the acute overdose pathologies seen in humans, whereas chronic models are needed to accurately model human long-term abuse. Further, we suggest that these two dosing regimens will result in quite different neurochemical, neuropathological and behavioral outcomes. The relative importance of the dopamine transporter and vesicular monoamine transporter knockout is discussed and insights into oxidative mechanisms are described from observations of nNOS knockout and SOD overexpression. This review not only describes the neuropathologies associated with methamphetamine in rodents, non-human primates and human abusers, but also focuses on the more recent literature associated with reactive oxygen and nitrogen species and their contribution to neuronal death via necrosis and/or apoptosis. The effect of methamphetamine on the mitochondrial membrane potential and electron transport chain and subsequent apoptotic cascades are also emphasized. Finally, we describe potential treatments for methamphetamine abusers with reference to the time after withdrawal. We suggest that potential treatments can be divided into three categories; (1) the prevention of neurotoxicity if recidivism occurs, (2) amelioration of apoptotic cascades that may occur even in the withdrawal period and (3) treatment of the atypical depression associated with withdrawal.

Effect of temperature on dopamine transporter function and intracellular accumulation of methamphetamine: implications for methamphetamine-induced dopaminergic neurotoxicity

Hyperthermia exacerbates and hypothermia attenuates methamphetamine (METH)-induced dopamine (DA) neurotoxicity. The mechanisms underlying these temperature effects are unknown. Given the essential role of the DA transporter (DAT) in the expression of METH-induced DA neurotoxicity, we hypothesized that the effect of temperature on METH-induced DA neurotoxicity is mediated, at least in part, at the level of the DAT. To test this hypothesis, the effects of small, physiologically relevant temperature changes on DAT function were evaluated in two types of cultured neuronal cells: (1) a neuroblastoma cell line stably transfected with human DAT cDNA and (2) rat embryonic mesencephalic primary cells that naturally express the DAT. Temperatures for studies of DAT function were selected based on core temperature measurements in animals exposed to METH under usual ambient (22 degrees C) and hypothermic (6 degrees C) temperature conditions, where METH neurotoxicity was fully expressed and blocked, respectively. DAT function, determined by measuring accumulation of radiolabeled DA and 1-methyl-4-phenylpyridinium (MPP(+)), was found to directly correlate with temperature, with higher levels of substrate uptake at 40 degrees C, intermediate levels at 37 degrees C, and lower levels at 34 degrees C. DAT-mediated accumulation of METH also directly correlated with temperature, with greater accumulation at higher temperatures. These findings indicate that relatively small, physiologically relevant changes in temperature significantly alter DAT function and intracellular METH accumulation, and suggest that the effect of temperature on METH-induced DA neurotoxicity is mediated, at least in part, at the level of the DAT.