Neurotoxic Effects Of Methamphetamine Research Articles

Neuroligin-1 plays an important role in methamphetamine-induced hippocampal synaptic plasticity

The neurotoxic effects of methamphetamine (METH) include not only neuronal apoptosis and autophagy, but also lead to substance use disorder and have become increasingly prominent. Studies suggest that synaptic plasticity may be the structural basis of METH-induced neurological impairment. Neuroligins are postsynaptic adhesion molecules involved in the regulation of synaptic organization and function. Animal studies have shown that neuroligin (NLG)− 1 is involved in memory formation; however, its role in METH-induced neurotoxicity is not clear. In the present study, we used 1 mM METH in vitro; mice in the acute and subacute exposure groups received intraperitoneal injections of 30 mg/kg METH (1 injection) or 15 mg/kg METH (8 separate injections at 12-h intervals). We found that the expression of NLG-1, Synapsin-1, and postsynaptic density-95 were increased after METH exposure. We further observed that METH-induced inhibition of long-term potentiation and spatial memory loss could be alleviated when mice were pretreated with NLG-1 small interfering RNA. Therefore, our study provides evidence that NLG-1 is involved in METH-induced hippocampal synaptic plasticity and may be a potential target for the treatment of METH-induced neurotoxicity.

A Zebrafish Model of Neurotoxicity by Binge-Like Methamphetamine Exposure.

Hyperthermia is a common confounding factor for assessing the neurotoxic effects of methamphetamine (METH) in mammalian models. The development of new models of methamphetamine neurotoxicity using vertebrate poikilothermic animals should allow to overcome this problem. The aim of the present study was to develop a zebrafish model of neurotoxicity by binge-like methamphetamine exposure. After an initial testing at 20 and 40 mg/L for 48 h, the later METH concentration was selected for developing the model and the effects on the brain monoaminergic profile, locomotor, anxiety-like and social behaviors as well as on the expression of key genes of the catecholaminergic system were determined. A concentration- and time-dependent decrease in the brain levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) was found in METH-exposed fish. A significant hyperactivity was found during the first hour of exposure, followed 3 h after by a positive geotaxis and negative scototaxis in the novel tank and in the light/dark paradigm, respectively. Moreover, the behavioral phenotype in the treated fish was consistent with social isolation. At transcriptional level, th1 and slc18a2 (vmat2) exhibited a significant increase after 3 h of exposure, whereas the expression of gfap, a marker of astroglial response to neuronal injury, was strongly increased after 48 h exposure. However, no evidences of oxidative stress were found in the brain of the treated fish. Altogether, this study demonstrates the suitability of the adult zebrafish as a model of METH-induced neurotoxicity and provides more information about the biochemical and behavioral consequences of METH abuse.

Inhibition of PLCβ1 signaling pathway regulates methamphetamine self-administration and neurotoxicity in rats

Studies have shown that the central renin–angiotensin system is involved in neurological disorders. Our previous studies have demonstrated that angiotensin II receptor type 1 (AT1R) in the brain could be a potential target against methamphetamine (METH) use disorder. The present study was designed to investigate the underlying mechanisms of the inhibitory effect of AT1R on various behavioural effects of METH. We first examined the effect of AT1R antagonist, candesartan cilexetil (CAN), on behavioural and neurotoxic effects of METH. Furthermore, we studied the role of phospholipase C beta 1 (PLCβ1) blockade behavioural and neurotoxic effects of METH. The results showed that CAN significantly attenuated METH-induced behavioral disorders and neurotoxicity associated with increased oxidative stress. AT1R and PLCβ1 were significantly upregulated in vivo and in vitro. Inhibition of PLCβ1 effectively alleviated METH-induced neurotoxicity and METH self-administration (SA) by central blockade of the PLCβ1 involved signalling pathway. PLCβ1 blockade significantly decreased the reinforcing and motivation effects of METH. PLCβ1 involved signalling pathway, as well as a more specific role of PLCβ1, involved the inhibitory effects of CAN on METH-induced behavioural dysfunction and neurotoxicity. Collectively, our findings reveal a novel role of PLCβ1 in METH-induced neurotoxicity and METH use disorder.

Dopaminergic Neuron-Specific Deletion of p53 Gene Attenuates Methamphetamine Neurotoxicity.

p53 plays an essential role in the regulation of cell death in dopaminergic (DA) neurons and its activation has been implicated in the neurotoxic effects of methamphetamine (MA). However, how p53 mediates MA neurotoxicity remains largely unknown. In this study, we examined the effect of DA-specific p53 gene deletion in DAT-p53KO mice. Whereas in vivo MA binge exposure reduced locomotor activity in wild-type (WT) mice, this was significantly attenuated in DAT-p53KO mice and associated with significant differences in the levels of the p53 target genes BAX and p21 between WT and DAT-p53KO. Notably, DA-specific deletion of p53 provided protection of substantia nigra pars reticulata (SNpr) tyrosine hydroxylase (TH) positive fibers following binge MA, with DAT-p53KO mice having less decline of TH protein levels in striatum versus WT mice. Whereas DAT-p53KO mice demonstrated a consistently higher density of TH fibers in striatum compared to WT mice at 10days after MA exposure, DA neuron counts within the substantia nigra pars compacta (SNpc) were similar. Finally, supportive of these results, administration of a p53-specific inhibitor (PFT-α) provided a similarly protective effect on MA binge-induced behavioral deficits. Neither DA specific p53 deletion nor p53 pharmacological inhibition affected hyperthermia induced by MA binge. These findings demonstrate a specific contribution of p53 activation in behavioral deficits and DA neuronal terminal loss by MA binge exposure.

Effects of adolescent methamphetamine and nicotine exposure on behavioral performance and MAP-2 immunoreactivity in the nucleus accumbens of adolescent mice

The neurotoxic effects of methamphetamine (MA) exposure in the developing and adult brain can lead to behavioral alterations and cognitive deficits in adults. Previous increases in the rates of adolescent MA use necessitate that we understand the behavioral and cognitive effects of MA exposure during adolescence on the adolescent brain. Adolescents using MA exhibit high rates of nicotine (NIC) use, but the effects of concurrent MA and NIC in the adolescent brain have not been examined, and it is unknown if NIC mediates any of the effects of MA in the adolescent. In this study, the long-term effects of a neurotoxic dose of MA with or without NIC exposure during early adolescence (postnatal day 30–31) were examined later in adolescence (postnatal day 41–50) in male C57BL/6J mice. Effects on behavioral performance in the open field, Porsolt forced swim test, and conditioned place preference test, and cognitive performance in the novel object recognition test and Morris water maze were assessed. Additionally, the effects of MA and/or NIC on levels of microtubule associated-2 (MAP-2) protein in the nucleus accumbens and plasma corticosterone were examined. MA and NIC exposure during early adolescence separately decreased anxiety-like behavior in the open field test, which was not seen following co-administration of MA/NIC. There was no significant effect of early adolescent MA and/or NIC exposure on the intensity of MAP-2 immunoreactivity in the nucleus accumbens or on plasma corticosterone levels. These results show that early adolescent MA and NIC exposure separately decrease anxiety-like behavior in the open field, and that concurrent MA and NIC exposure does not induce the same behavioral change as either drug alone.

The Persistent Neurotoxic Effects of Methamphetamine on Dopaminergic and Serotonergic Markers in Male and Female Rats.

Methamphetamine (METH) is a highly addictive substance abused world-wide in both males and females. Preclinical studies in male rodents suggest that large-dose exposure to METH can lead to persistent neurotoxic consequences to various brain regions. However, little research has focused on the potential role of sex in the neurotoxic consequences of METH exposure. The current study exposed male and female rats to large-doses of METH (4 injections of 7.5 mg/kg) or saline. Hyperthermia was promoted in the females exposed to METH such that similar hyperthermia occurred in males and females. Rats were sacrificed 8 d later and neurochemical changes were assessed in the striatum, hippocampus, frontal cortex and olfactory bulbs. Results revealed that male and female rats exposed to METH had similar decreases in dopamine (DA) transporter (DAT) immunoreactivity in the striatum, serotonin (5-HT) content and 5-HT transporter (SERT) function in the hippocampus, and 5-HT content in the frontal cortex. However, female rats exposed to METH had greater decreases in 5-HT content in the olfactory bulbs compared to sex-matched controls while male rats exposed to METH did not significantly differ from sex-matched controls. These findings suggest that when similar hyperthermia is maintained between male and female rats exposed to METH, the neurotoxic effects of METH were similar in some, but not all brain regions.

3,4-Methylenedioxypyrovalerone prevents while methylone enhances methamphetamine-induced damage to dopamine nerve endings: β-ketoamphetamine modulation of neurotoxicityby the dopamine transporter.

Methylone, 3,4-methylenedioxypyrovalerone (MDPV), and mephedrone are psychoactive ingredients of 'bath salts' and their abuse represents a growing public health care concern. These drugs are cathinone derivatives and are classified chemically as β-ketoamphetamines. Because of their close structural similarity to the amphetamines, methylone, MDPV, and mephedrone share most of their pharmacological, neurochemical, and behavioral properties. One point of divergence in their actions is the ability to cause damage to the CNS. Unlike methamphetamine, the β-ketoamphetamines do not damage dopamine (DA) nerve endings. However, mephedrone has been shown to significantly accentuate methamphetamine neurotoxicity. Bath salt formulations contain numerous different psychoactive ingredients, and individuals who abuse bath salts also coabuse other illicit drugs. Therefore, we have evaluated the effects of methylone, MDPV, mephedrone, and methamphetamine on DA nerve endings. The β-ketoamphetamines alone or in all possible two-drug combinations do not result in damage to DA nerve endings but do cause hyperthermia. MDPV completely protects against the neurotoxic effects of methamphetamine while methylone accentuates it. Neither MDPV nor methylone attenuates the hyperthermic effects of methamphetamine. The potent neuroprotective effects of MDPV extend to amphetamine-, 3,4-methylenedioxymethamphetamine-, and MPTP-induced neurotoxicity. These results indicate that β-ketoamphetamine drugs that are non-substrate blockers of the DA transporter (i.e., MDPV) protect against methamphetamine neurotoxicity, whereas those that are substrates for uptake by the DA transporter and which cause DA release (i.e., methylone, mephedrone) accentuate neurotoxicity. METH (a) enters DA nerve endings via the DAT, causes leakage of DA into the cytoplasm and then into the synapse via DAT-mediated reverse transport. Methylone (METHY) and mephedrone (MEPH; b), like METH, are substrates for the DAT but release DA from cytoplasmic pools selectively. When METH is combined with METHY or MEPH (c), DA efflux and neurotoxicity are enhanced. MDPV (d), which is a non-substrate blocker of the DAT, prevents METH uptake and efflux of DA. Therefore, bath salts that are substrates for the DAT and release DA (METHY, MEPH) accentuate METH neurotoxicity, whereas those that are non-substrate blockers of the DAT (MDPV) are neuroprotective.

Long-Term Effects of Early Adolescent Methamphetamine Exposure on Depression-Like Behavior and the Hypothalamic Vasopressin System in Mice

Methamphetamine (MA) has neurotoxic effects on the adult human brain that can lead to deficits in behavior and cognition. However, relatively little research has examined the behavioral or neurotoxic effects of MA in adolescents. The rising rates of adolescent MA use make it imperative that we understand the long-term effects of MA exposure on the adolescent brain and how these effects may differ from those seen in adults. In this study, the long-term effects of MA exposure during early adolescence on behavior and the vasopressin system in the paraventricular nucleus of the hypothalamus in late adolescent and adult male and female C57BL/6J mice were examined. MA exposure increased depression-like behavior in the Porsolt forced swim test in both late adolescent and adult male and female mice. Late adolescent male mice exposed to MA also showed a decrease in the number of vasopressin-immunoreactive neurons in the paraventricular nucleus compared to sex-matched saline-treated controls. Thus, similar to humans exposed to MA during adolescence, mice exposed to MA during adolescence show increased depression-like behavior later in life. These changes in behavior may be related to MA-induced alterations in vasopressin and the hypothalamic-pituitary-adrenal axis, especially in males.

SN79, a sigma receptor ligand, blocks methamphetamine-induced microglial activation and cytokine upregulation

Methamphetamine (METH) abuse is associated with several negative side effects including neurotoxicity in specific brain regions such as the striatum. The precise molecular mechanisms by which METH usage results in neurotoxicity remain to be fully elucidated, with recent evidence implicating the importance of microglial activation and neuroinflammation in damaged brain regions. METH interacts with sigma receptors which are found in glial cells in addition to neurons. Moreover, sigma receptor antagonists have been shown to block METH-induced neurotoxicity in rodents although the cellular mechanisms underlying their neuroprotection remain unknown. The purpose of the current study was to determine if the prototypic sigma receptor antagonist, SN79, mitigates METH-induced microglial activation and associated increases in cytokine expression in a rodent model of METH-induced neurotoxicity. METH increased striatal mRNA and protein levels of cluster of differentiation 68 (CD68), indicative of microglial activation. METH also increased ionized calcium binding adapter molecule 1 (IBA-1) protein expression, further confirming the activation of microglia. Along with microglial activation, METH increased striatal mRNA expression levels of IL-6 family pro-inflammatory cytokines, leukemia inhibitory factor (lif), oncostatin m (osm), and interleukin-6 (il-6). Pretreatment with SN79 reduced METH-induced increases in CD68 and IBA-1 expression, demonstrating its ability to prevent microglial activation. SN79 also attenuated METH-induced mRNA increases in IL-6 pro-inflammatory cytokine family members. The ability of a sigma receptor antagonist to block METH-induced microglial activation and cytokine production provides a novel mechanism through which the neurotoxic effects of METH may be mitigated.

Peripheral Ammonia as a Mediator of Methamphetamine Neurotoxicity

Ammonia is metabolized by the liver and has established neurological effects. The current study examined the possibility that ammonia contributes to the neurotoxic effects of methamphetamine (METH). The results show that a binge dosing regimen of METH to the rat increased plasma and brain ammonia concentrations that were paralleled by evidence of hepatotoxicity. The role of peripheral ammonia in the neurotoxic effects of METH was further substantiated by the demonstration that the enhancement of peripheral ammonia excretion blocked the increases in brain and plasma ammonia and attenuated the long-term depletions of dopamine and serotonin typically produced by METH. Conversely, the localized perfusion of ammonia in combination with METH, but not METH alone or ammonia alone, into the striatum recapitulated the neuronal damage produced by the systemic administration of METH. Furthermore, this damage produced by the local administration of ammonia and METH was blocked by the GYKI 52466 [4-(8-methyl-9H-1,3-dioxolo[4,5-h][2,3]benzodiazepin-5-yl)-benzamine hydrochloride], an AMPA receptor antagonist. These findings highlight the importance of ammonia derived from the periphery as a small-molecule mediator of METH neurotoxicity and more broadly emphasize the importance of peripheral organ damage as a possible mechanism that mediates the neuropathology produced by drugs of abuse and other neuroactive molecules.

Serum brain‐derived neurotrophic factor levels were reduced during methamphetamine early withdrawal

Methamphetamine (METH) abuse is an increasing public health problem worldwide. Many of the METH-induced physical and mental problems are associated with the neurotoxic effects of METH. Animal studies have shown that brain-derived neurotrophic factor (BDNF) decreased after repeated amphetamine administration and increased at 30 and 90 days from psychostimulant withdrawal, suggesting that there might be a psychostimulant-induced neuroprotective dysfunction followed by a neuroadaptive process in the brain. However, current research on the role of BDNF in human METH addiction is limited, particularly during early withdrawal. The aim of this study was to assess the serum BDNF levels in METH abusers during the early withdrawal stage. Two groups of subjects were enrolled: (1) 59 DSM-IV METH abusers confirmed by board-certified psychiatrists during the first 3 weeks of withdrawal; (2) 59 age- and sex-matched healthy controls. We found that serum BDNF levels were significantly and constantly lower in the METH abusers during early withdrawal than those of the healthy controls. This indicates that METH abusers might have severe BDNF dysfunction and an impaired neuroprotective function after repetitive METH misuse.

Dopamine D 1 receptor deletion strongly reduces neurotoxic effects of methamphetamine

Methamphetamine (METH) is a potent, highly addictive psychostimulant consumed worldwide. In humans and experimental animals, repeated exposure to this drug induces persistent neurodegenerative changes. Damage occurs primarily to dopaminergic neurons, accompanied by gliosis. The toxic effects of METH involve excessive dopamine (DA) release, thus DA receptors are highly likely to play a role in this process. To define the role of D 1 receptors in the neurotoxic effects of METH we used D 1 receptor knock-out mice (D 1R −/−) and their WT littermates. Inactivation of D 1R prevented METH-induced dopamine fibre loss and hyperthermia, and increases in gliosis and pro-inflammatory molecules such as iNOS in the striatum. In addition, D 1R inactivation prevented METH-induced loss of dopaminergic neurons in the substantia nigra. To explore the relationship between hyperthermia and neurotoxicity, METH was given at high ambient temperature (29 °C). In this condition, D 1R −/− mice developed hyperthermia following drug delivery and the neuroprotection provided by D 1R inactivation at 23 °C was no longer observed. However, reserpine, which empties vesicular dopamine stores, blocked hyperthermia and strongly potentiated dopamine toxicity in D 1R −/− mice, suggesting that the protection afforded by D 1R inactivation is due to both hypothermia and higher stored vesicular dopamine. Moreover, electrical stimulation evoked higher DA overflow in D 1R −/− mice as demonstrated by fast scan cyclic voltammetry despite their lower basal DA content, suggesting higher vesicular DA content in D 1R −/− than in WT mice. Altogether, these results indicate that the D 1R plays a significant role in METH-induced neurotoxicity by mediating drug-induced hyperthermia and increasing the releasable cytosolic DA pool.

Caffeine potentiates methamphetamine-induced toxicity both in vitro and in vivo

Ya-Ba, a combination of the two potent psychostimulants methamphetamine (METH) and caffeine (CAF), is commonly used by drug abusers in Thailand and neighboring countries. While the neurotoxic effects of METH are well documented, the toxicity of this combination is mostly unknown. This study aimed to elucidate the effects of this particular drug combination using both in vitro and in vivo models. We found that combined treatment of METH and CAF at individually non-toxic concentrations significantly decreased viability of human neuroblastoma SK-N-SH cells. The reduction in cell survival was accompanied by an increase in reactive oxygen species (ROS) formation and the Bax/Bcl-2 ratio. In vivo data showed that combined administration of METH and CAF increased the mortality rate of rats, with an increase in the level of thiobarbituric acid reactive substances (TBARS), the indicator of oxidative stress, in striatal tissues. The results indicate that caffeine potentiates the toxic effects of methamphetamine, possibly via a mechanism involving an increase in dopamine release and excess ROS generation.

CM156, a high affinity sigma ligand, attenuates the stimulant and neurotoxic effects of methamphetamine in mice

Methamphetamine (METH) is a highly addictive psychostimulant drug of abuse. Low and high dose administration of METH leads to locomotor stimulation, and dopaminergic and serotonergic neurotoxicity, respectively. The behavioral stimulant and neurotoxic effects of METH can contribute to addiction and other neuropsychiatric disorders, thus necessitating the identification of potential pharmacotherapeutics against these effects produced by METH. METH binds to σ receptors at physiologically relevant concentrations. Also, σ receptors are present on and can modulate dopaminergic and serotonergic neurons. Therefore, σ receptors provide a viable target for the development of pharmacotherapeutics against the adverse effects of METH. In the present study, CM156, a σ receptor ligand with high affinity and selectivity for σ receptors over 80 other non-σ binding sites, was evaluated against METH-induced stimulant, hyperthermic, and neurotoxic effects. Pretreatment of male, Swiss Webster mice with CM156 dose dependently attenuated the locomotor stimulation, hyperthermia, striatal dopamine and serotonin depletions, and striatal dopamine and serotonin transporter reductions produced by METH, without significant effects of CM156 on its own. These results demonstrate the ability of a highly selective σ ligand to mitigate the effects of METH.

Role of Sigma Receptors in Methamphetamine-Induced Neurotoxicity

Methamphetamine (METH) is a widely abused substance world over. Currently, there is no effective pharmacotherapy to treat its effects. This necessitates identification of potential novel therapeutic targets. METH interacts with sigma (σ) receptors at physiologically relevant micromolar concentrations. In addition, σ receptors are present in organs like the brain, heart, and lungs at which METH acts. Additionally, σ receptors have been implicated in various acute and subchronic effects like locomotor stimulation, development of sensitization and neurotoxicity, where σ receptor antagonists attenuate these effects. σ Receptors may also have a role in METH-induced psychiatric complications such as depression, psychosis, cognitive and motor deficits. The neurotoxic effects of METH, which are cause for concern, can be prevented by σ receptor antagonists in mice. Mechanistically, METH-induced neurotoxicity involves factors like dopamine release, oxidative stress, endoplasmic reticulum stress, activation of mitochondrial death cascades, glutamate release, apoptosis, microglial activation, and hyperthermia. This review compiles studies from the literature that suggests an important role for σ receptors in many of the mechanisms of METH-induced neurotoxicity.

Environmental Enrichment does not Reduce the Rewarding and Neurotoxic Effects of Methamphetamine

Abuse of amphetamine analogues, such as methamphetamine (METH), represents an important health problem because of their powerful addictive and neurotoxic effects. Abuse of METH induces dopamine neuron terminals loss and cell death in the striatum similar to what is found in other neurodegenerative processes. Exposing mice and rats to enriched environments (EE) has been shown to produce significant protective effects against drug-induced reward as well as against neurodegenerative processes. Here, we investigated whether exposure to EE could reduce the METH-induced reward and neurotoxicity. For this, we reared mice for 2 months during early stages of life in standard environments or EE and then, at adulthood, we tested the ability of METH to induce conditioned place preference and neurotoxicity. We found that, contrary to what we found with other drugs such as cocaine and heroin, EE was unable to reduce the rewarding effects of METH. In addition, contrary to what we found with other toxins such as MPTP, EE did not diminish the striatal neurotoxicity induced by METH (4 x 10 mg/kg) as measured by dopamine content, tyrosine hydroxylase protein levels and apoptosis. Our results demonstrate that the rewarding and neurotoxic effects of METH are not reduced by EE and highlight the great risks associated with the increased popularity of this drug amongst the young population.

Neurotoxic Effects of Methamphetamine

In Parkinson's disease, depletion of dopamine in the striatum leads to various symptoms such as tremor, rigidity and akinesia. Methamphetamine use has significantly increased in USA and around the world and there are several reports showing that its long-term use increases the risk for dopamine depletion. However, the toxic mechanisms of methamphetamine are not well understood. This study was undertaken to gain greater mechanistic understanding of the toxicity induced by methamphetamine. We evaluated the effect of methamphetamine on the generation of reactive oxygen species, mitochondrial monoamine oxidase, complex I & IV activities. Behavioral analysis evaluated the effect on catalepsy, akinesia and swim score. Neurotransmitter levels were evaluated using high pressure liquid chromatography (HPLC) electrochemical detection (ECD). Results showed that methamphetamine caused significant generation of reactive oxygen species and decreased complex I activity in the mitochondria leading to dopamine depletion in the striatum.

Neuropharmacological Mechanisms Underlying the Neuroprotective Effects of Methylphenidate

Methylphenidate is a psychostimulant that inhibits the neuronal dopamine transporter. In addition, methylphenidate has the intriguing ability to provide neuroprotection from the neurotoxic effects of methamphetamine and perhaps also Parkinson’s disease; both of which may likely involve the abnormal accumulation of cytoplasmic dopamine inside dopaminergic neurons and the resulting formation of dopamine-associated reactive oxygen species. As delineated in this review, the neuroprotective effects of methylphenidate are due, at least in part, to its ability to attenuate or prevent this abnormal cytoplasmic dopamine accumulation through several possible neuropharmacological mechanisms. These may include 1) direct interactions between methylphenidate and the neuronal dopamine transporter which may attenuate or prevent the entry of methamphetamine into dopaminergic neurons and may also decrease the synthesis of cytoplasmic dopamine through a D2 receptor-mediated signal cascade process, and 2) indirect effects upon the functioning of the vesicular monoamine transporter-2 which may increase vesicular dopamine sequestration through both vesicle trafficking and the kinetic upregulation of the vesicular monoamine transporter-2 protein. Understanding these neuropharmacological mechanisms of methylphenidate neuroprotection may provide important insights into the physiologic regulation of dopaminergic systems as well as the pathophysiology of a variety of disorders involving abnormal dopamine disposition ranging from substance abuse to neurodegenerative diseases such as Parkinson’s disease.

Glial Cell Line-derived Neurotrophic Factor Reverses Ethanol-mediated Increases in Tyrosine Hydroxylase Immunoreactivity via Altering the Activity of Heat Shock Protein 90

We previously found that glial cell line-derived neurotrophic factor (GDNF) in the midbrain ventral tegmental area (VTA) negatively regulates alcohol drinking (He, D. Y., McGough, N. N., Ravindranathan, A., Jeanblanc, J., Logrip, M. L., Phamluong, K., Janak, P. H., and Ron, D. (2005) J. Neurosci. 25, 619-628). Several studies suggest a role for GDNF in the regulation of tyrosine hydroxylase (TH) levels in the midbrain (Georgievska, B., Kirik, D., and Bjorklund, A. (2004) J. Neurosci. 24, 6437-6445). Up-regulation of TH levels has been reported as a hallmark of biochemical adaptations to in vivo chronic exposure to drugs of abuse, including ethanol (Ortiz, J., Fitzgerald, L. W., Charlton, M., Lane, S., Trevisan, L., Guitart, X., Shoemaker, W., Duman, R. S., and Nestler, E. J. (1995) Synapse 21, 289-298). We hypothesized that GDNF plays an important role in regulating prolonged ethanol-mediated increases in TH protein levels. Using the SH-SY5Y dopaminergic-like cell line, we found that the increase in TH levels in the presence of ethanol required the activation of the cAMP/PKA pathway and was reversed by GDNF. Ethanol treatment did not alter the mRNA level or protein translation of TH, but enhanced the stability of the protein that was decreased by GDNF. Interestingly, we observed that ethanol treatment resulted in an increase in TH association with the chaperone heat shock protein (HSP90) that was mediated by the cAMP/PKA pathway and inhibited by GDNF. Taken together, these data suggest that prolonged ethanol exposure leads to increased association of TH and HSP90 via the cAMP/PKA pathway, resulting in the stabilization and subsequent accumulation of TH. GDNF reverses this ethanol-mediated adaptation by inhibiting the interaction of TH with HSP90.

Genetic or pharmacological blockade of noradrenaline synthesis enhances the neurochemical, behavioral, and neurotoxic effects of methamphetamine

N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) lesions of the locus coeruleus, the major brain noradrenergic nucleus, exacerbate the damage to nigrostriatal dopamine (DA) terminals caused by the psychostimulant methamphetamine (METH). However, because noradrenergic terminals contain other neuromodulators and the noradrenaline (NA) transporter, which may act as a neuroprotective buffer, it was unclear whether this enhancement of METH neurotoxicity was caused by the loss of noradrenergic innervation or the loss of NA itself. We addressed the specific role of NA by comparing the effects of METH in mice with noradrenergic lesions (DSP-4) and those with intact noradrenergic terminals but specifically lacking NA (genetic or acute pharmacological blockade of the NA biosynthetic enzyme dopamine beta-hydroxylase; DBH). We found that genetic deletion of DBH (DBH-/- mice) and acute treatment of wild-type mice with a DBH inhibitor (fusaric acid) recapitulated the effects of DSP-4 lesions on METH responses. All three methods of NA depletion enhanced striatal DA release, extracellular oxidative stress (as measured by in vivo microdialysis of DA and 2,3-dihydroxybenzoic acid), and behavioral stereotypies following repeated METH administration. These effects accompanied a worsening of the striatal DA neuron terminal damage and ultrastructural changes to medium spiny neurons. We conclude that NA itself is neuroprotective and plays a fundamental role in the sensitivity of striatal DA terminals to the neurochemical, behavioral, and neurotoxic effects of METH.