Increases in cytoplasmic dopamine compromise the normal resistance of the nucleus accumbens to methamphetamine neurotoxicity

Methamphetamine (METH) is a neurotoxic drug of abuse that damages the dopamine (DA) neuronal system in a highly delimited manner. The brain structure most affected by METH is the caudate–putamen (CPu) where long-term DA depletion and microglial activation are most evident. Even damage within the CPu is remarkably heterogenous with lateral and ventral aspects showing the greatest deficits. The nucleus accumbens (NAc) is largely spared of the damage that accompanies binge METH intoxication. Increases in cytoplasmic DA produced by reserpine, l -DOPA or clorgyline prior to METH uncover damage in the NAc as evidenced by microglial activation and depletion of DA, tyrosine hydroxylase (TH), and the DA transporter. These effects do not occur in the NAc after treatment with METH alone. In contrast to the CPu where DA, TH, and DA transporter levels remain depleted chronically, DA nerve ending alterations in the NAc show a partial recovery over time. None of the treatments that enhance METH toxicity in the NAc and CPu lead to losses of TH protein or DA cell bodies in the substantia nigra or the ventral tegmentum. These data show that increases in cytoplasmic DA dramatically broaden the neurotoxic profile of METH to include brain structures not normally targeted for damage by METH alone. The resistance of the NAc to METH-induced neurotoxicity and its ability to recover reveal a fundamentally different neuroplasticity by comparison to the CPu. Recruitment of the NAc as a target of METH neurotoxicity by alterations in DA homeostasis is significant in light of the important roles played by this brain structure.     

Neurokinin-1 (NK-1) receptor antagonists abrogate methamphetamine-induced striatal dopaminergic neurotoxicity in the murine brain

Methamphetamine (METH) is an addictive substance that also causes extensive neural degeneration in the central nervous system. Because METH augments striatal substance P (SP) levels, we hypothesized that this neuropeptide plays a role in methamphetamine-induced toxicity and neural damage in the striatum. In this study we present evidence demonstrating that signaling through the neurokinin-1 (NK-1) receptor by SP plays an important role in methamphetamine-induced toxicity in the striatum. We tested the effects of the selective NK-1 receptor antagonists WIN-51,708 and L-733,060 on several markers of dopaminergic terminal toxicity in the mouse striatum. Administration of NK-1 receptor antagonist prevented the loss of dopamine transporters assessed by autoradiography and western blotting, the loss of tissue dopamine assessed by high-pressure liquid chromatography, and the loss of tyrosine hydroxylase, as well as the induction of glial fibrillary acidic protein determined by western blotting. Pre-treatment with NK-1 receptor antagonist had no effect on METH-induced hyperthermia. Pre-exposure of mice to either of the NK-1 receptor antagonists alone was without effect on all of these neurochemical markers. These results provide the first evidence that tachykinins, particularly SP, acting through NK-1 receptors, play a crucial role in the pathogenesis of nigrostriatal dopaminergic terminal degeneration induced by METH. This finding could lead to novel therapeutic strategies to offset drug addictions as well as in the treatment of a number of disorders including Parkinson's and Huntington's diseases.     

Signaling via dopamine D1 and D3 receptors oppositely regulates cocaine-induced structural remodeling of dendrites and spines

Repeated exposure to cocaine can induce persistent alterations in the brain. The structural remodeling of dendrites and dendritic spines is thought to play a critical role in cocaine addiction. We previously demonstrated that signaling via dopamine D1 and D3 receptors have opposite effects on cocaine-induced gene expression. Here, we show that cocaine-induced structural remodeling in the nucleus accumbens (NAc) and caudoputamen (CPu) is mediated by D1 receptors and inhibited by D3 receptors. In addition, chronic exposure to cocaine results in an altered number of asymmetric spine synapses via the actions of both D1 and D3 receptors. The contradictory effects of D1 and D3 receptor signaling on cocaine-induced structural remodeling is associated with NMDA-receptor R1 subunit (NR1) phosphorylation, and is dependent upon the activation of extracellular signal-regulated kinase (ERK). In addition, we found that D1 and D3 receptor signaling has contradictory effects upon the activation of the myocyte enhancer factor 2 (MEF2), which is involved in the dendritic remodeling after cocaine treatment. Together, these data suggest that dopamine D1 and D3 receptors differentially regulate the cocaine-induced structural remodeling of dendrites and spines via mechanisms involving the consecutive actions of NR1 phosphorylation, ERK activation, and MEF2 activity in the NAc and CPu.     

Region-specific enhancement of basal extracellular and cocaine-evoked dopamine levels following constitutive deletion of the Serotonin(1B) receptor

The behavioral effects of cocaine are enhanced following constitutive deletion of the serotonin(1B) receptor. The neural substrates mediating the enhanced response to cocaine are unknown. The present studies determined whether basal dopamine dynamics or cocaine-evoked dopamine levels are altered in projection areas of mesostriatal or mesoaccumbens dopamine neurons following serotonin(1B) receptor deletion. Male wild-type and serotonin(1B) knockout mice were implanted with microdialysis guide cannulas aimed at the dorsal striatum or nucleus accumbens. The zero net flux method of quantitative microdialysis was used to quantify basal extracellular dopamine concentrations (DA(ext)) and the extraction fraction of dopamine (E(d)), which provides an index of dopamine uptake. Conventional microdialysis techniques were used to quantify cocaine (0, 5.0, and 20.0 mg/kg)-evoked dopamine overflow. Basal DA(ext) and E(d) did not differ in striatum of wild-type and knockout mice. Similarly, cocaine-stimulated dopamine overflow did not differ between genotype. The basal E(d) did not differ in the nucleus accumbens of wild-type and knockout mice. However, DA(ext) was significantly elevated in the nucleus accumbens of knockout mice. Cocaine-evoked dopamine overflow (nM) was also enhanced in the nucleus accumbens of knockout mice. However, the cocaine-induced increase in dopamine levels, relative to basal values, did not differ between genotype. These data demonstrate that deletion of the serotonin(1B) receptor is associated with increases in basal DA(ext) in the nucleus accumbens. This increase is not associated with an alteration in E(d), suggesting increased basal dopamine release in these animals. It is hypothesized that these alterations in presynaptic neuronal activity are a compensatory response to constitutive deletion of the serotonin(1B) receptor and may contribute to the enhanced behavioral effects of psychostimulants observed in knockout mice.     

Methamphetamine-induced spectrin proteolysis in the rat striatum

Methamphetamine (METH) is a widely abused psychostimulant. Multiple high doses of METH cause long-term toxicity to dopamine (DA) and serotonin (5-HT) nerve terminals in the brain, as evidenced by decreases in DA and 5-HT content, decreases in tyrosine and tryptophan hydroxylase activities, decreases in DA and 5-HT re-uptake sites, and nerve terminal degeneration. Multiple high doses of METH are known to elicit a rapid increase in DA release and hyperthermia. Although METH also produces a delayed and sustained rise in glutamate, no studies have shown whether METH produces structural evidence of excitotoxicity in striatum, or identified the receptors that mediate this toxicity directly, independent of alterations in METH-induced hyperthermia. These experiments investigated whether METH can cause excitotoxicity as evidenced by cytoskeletal protein breakdown in a glutamate receptor-dependent manner. METH increased calpain-mediated spectrin proteolysis in the rat striatum 5 and 7 days after METH administration without affecting caspase 3-dependent spectrin breakdown. This effect was completely blocked with the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, GYKI 52466, but not the NMDA receptor antagonist, MK-801. However, AMPA or NMDA receptor antagonism did not attenuate the METH-induced depletions of the dopamine transporter (DAT). Independent mechanisms involved in mediating spectrin proteolysis and DAT protein loss are discussed.     

The effects of methamphetamine on serotonin transporter activity: role of dopamine and hyperthermia

Multiple administrations of methamphetamine (METH) rapidly decreased serotonin (5HT) transporter (SERT) function in rat striatum and hippocampus. The purpose of this study was to identify the mechanisms/ factors contributing to this METH-induced decrease in SERT function. Multiple high-dose METH injections rapidly decreased 5HT uptake without altering binding of the 5HT transporter ligand paroxetine. Hyperthermia contributed to this deficit in transporter function in striatum and hippocampus, as prevention of METH-induced hyperthermia attenuated this decrease. A role for dopamine (DA) was suggested by findings that pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine, the D1 antagonist SCH-23390, or the D2 antagonist eticlopride attenuated the METH-induced decrease in striatal, but not hippocampal, SERT activity. These effects were independent of the ability of these DA-antagonizing drugs to prevent METH-induced hyperthermia. These results suggest that DA contributes to the decrease in SERT function caused by multiple METH injections in the striatum, but not hippocampus, and that hyperthermia facilitates these deficits in SERT function in both brain regions. In contrast, the response of SERT to a single administration of METH was DA and hyperthermia independent. These findings suggest that the mechanisms/ factors involved in decreasing SERT activity after a single administration of METH are distinct from that caused by multiple administrations.     

Stereoselective inhibition of dopaminergic activity by gamma vinyl-GABA following a nicotine or cocaine challenge: a PET/microdialysis study

Elevation of endogenous GABA by the racemic mixture of gamma vinyl-GABA (GVG, Vigabatrin) decreases extracellular nucleus accumbens (NAc) dopamine (DA) levels and diminishes the response to many drugs of abuse known to elevate DA in the mesocorticolimbic system. We investigated the effects of the individual enantiomers (S(+)-GVG, R(-)-GVG) on cocaine-induced NAc DA in rodents as well as the effects of nicotine-induced increases in primates. In a series of microdialysis experiments in freely moving animals, S(+)-GVG (150 mg/kg), R(-)-GVG (150 mg/kg) or racemic (R, S) GVG (300 mg/kg) was administered 2.5 hours prior to cocaine (20 mg/kg) administration. When compared with cocaine alone, the R(-) enantiomer did not significantly inhibit cocaine induced NAc DA release. S(+)-GVG, at half the dose of the racemic mixture (150 mg/kg), inhibited cocaine-induced DA elevation by 40%, while the racemic mixture (300 mg/kg) inhibited cocaine-induced DA release by 31%. In addition, our PET studies in primates demonstrated that S(+)-GVG completely inhibits nicotine-induced increases in the corpus striatum, again at half the dose of the racemic mixture. The R(-) enantiomer was ineffective. Although the S(+) enantiomer has been well established as the active compound in the treatment of epilepsy, the efficacy of this enantiomer with regard to mesolimbic DA inhibition generates a complex series of clinical and neurochemical issues. Further investigations will determine the locus of action and physiologic properties of each enantiomer.     

Adenylyl cyclase-5 activity in the nucleus accumbens regulates anxiety-related behavior

Type 5 adenylyl cyclase (AC5) is highly concentrated in the dorsal striatum and nucleus accumbens (NAc), two brain areas which have been implicated in motor function, reward, and emotion. Here we demonstrate that mice lacking AC5 (AC5-/-) display strong reductions in anxiety-like behavior in several paradigms. This anxiolytic behavior in AC5-/- mice was reduced by the D(1) receptor antagonist SCH23390 and enhanced by the D(1) dopamine receptor agonist, dihydrexidine (DHX). DHX-stimulated c-fos induction in AC5-/- mice was blunted in the dorso-lateral striatum, but it was overactivated in the dorso-medial striatum and NAc. The siRNA-mediated inhibition of AC5 levels within the NAc was sufficient to produce an anxiolytic-like response. Microarray and RT-PCR analyses revealed an up-regulation of prodynorphin and down-regulation of cholecystokinin (CCK) in the NAc of AC5-/- mice. Administration of nor-binaltorphimine (a kappa opioid receptor antagonist) or CCK-8s (a CCK receptor agonist) reversed the anxiolytic-like behavior exhibited by AC5-/- mutants. Taken together, these results suggest an essential role of AC5 in the NAc for maintaining normal levels of anxiety.     

Effects of VMAT2 inhibitors lobeline and GZ‐793A on methamphetamine‐induced changes in dopamine release,metabolism and synthesis in vivo

Vesicular monoamine transporter‐2 (VMAT2) inhibitors reduce methamphetamine (METH) reward in rats. The current study determined the effects of VMAT2 inhibitors lobeline (LOB; 1 or 3 mg/kg) and N‐(1,2R‐dihydroxylpropyl)‐2,6‐cis‐di(4‐methoxyphenethyl)piperidine hydrochloride (GZ‐793A; 15 or 30 mg/kg) on METH‐induced (0.5 mg/kg, SC) changes in extracellular dopamine (DA) and its metabolite dihydroxyphenylacetic acid (DOPAC) in the reward‐relevant nucleus accumbens (NAc) shell using in vivo microdialysis. The effect of GZ‐793A (15 mg/kg) on DA synthesis in tissue also was investigated in NAc, striatum, medial prefrontal cortex and orbitofrontal cortex. In NAc shell, METH produced a time‐dependent increase in extracellular DA and decrease in DOPAC. Neither LOB nor GZ‐793A alone altered extracellular DA; however, both drugs increased extracellular DOPAC. In combination with METH, LOB did not alter the effects of METH on DA; however, GZ‐793A, which has greater selectivity than LOB for inhibiting VMAT2, reduced the duration of the METH‐induced increase in extracellular DA. Both LOB and GZ‐793A enhanced the duration of the METH‐induced decrease in extracellular DOPAC. METH also increased tissue DA synthesis in NAc and striatum, whereas GZ‐793A decreased synthesis; no effect of METH or GZ‐793A on DA synthesis was found in medial prefrontal cortex or orbitofrontal cortex. These results suggest that selective inhibition of VMAT2 produces a time‐dependent decrease in DA release in NAc shell as a result of alterations in tyrosine hydroxylase activity, which may play a role in the ability of GZ‐793A to decrease METH reward.

     

Neurokinin-1 receptor (NK-1R) expression is induced in human colonic epithelial cells by proinflammatory cytokines and mediates proliferation in response to substance P

We have previously shown that the receptor for substance P (SP), neurokinin-1 receptor (NK-1R), is a marker of human mucosal but not peripheral mononuclear cells. In the present study, we investigate NK-1R expression in the human colonic mucosa in vivo, particularly in the epithelial cells. We investigate the influence of proinflammatory Th1 cytokines and SP on expression and function of NK-1R in colonic epithelial cells in vitro. Using in situ hybridization to detect NK-1R mRNA, and immunohistochemistry to detect NK-1R protein, colonic epithelial cells were found to express NK-1R in vivo. In contrast, colon epithelial cell lines (Caco-2, HT29, SW620, T84) were negative for NK-1R mRNA and protein. However, stimulation with a proinflammatory cytokine cocktail containing IFN-gamma, TNF-alpha, and IL-1beta, caused induction of NK-1R expression. Expression of NK-1R in human colonic epithelial cells in vivo may therefore reflect cytokine conditioning by the mucosal microenvironment. SP did not alter ion transport in monolayers of cytokine-treated T84 cells. While SP stimulated epithelial ion transport in colonic mucosae ex vivo, this was not a direct effect of SP on the epithelial cells, and appeared to be neurally mediated. However, SP (10(-10)-10(-8) M) elicited a dose-dependent proliferative effect on cytokine-stimulated, but not unstimulated, SW620 cells. Proliferation of the epithelial cells in response to SP was mediated specifically via cytokine-induced NK-1R, since an NK-1R-specific antagonist (Spantide 1) completely blocked SP-mediated proliferation in the cytokine-treated cells. Our results therefore demonstrate that proinflammatory cytokines induce expression of NK-1R in human colonic epithelial cell lines, and that SP induces proliferation of the epithelial cells via cytokine-induced NK-1R.     

Decreased level of Nurr1 in heterozygous young adult mice leads to exacerbated acute and long-term toxicity after repeated methamphetamine exposure

The abuse of psychostimulants, such as methamphetamine (METH), is prevalent in young adults and could lead to long-term adaptations in the midbrain dopamine system in abstinent human METH abusers. Nurr1 is a gene that is critical for the survival and maintenance of dopaminergic neurons and has been implicated in dopaminergic neuron related disorders. In this study, we examined the synergistic effects of repeated early exposure to methamphetamine in adolescence and reduction in Nurr1 gene levels. METH binge exposure in adolescence led to greater damage in the nigrostrial dopaminergic system when mice were exposed to METH binge later in life, suggesting a long-term adverse effect on the dopaminergic system. Compared to naïve mice that received METH binge treatment for the first time, mice pretreated with METH in adolescence showed a greater loss of tyrosine hydroxylase (TH) immunoreactivity in striatum, loss of THir fibers in the substantia nigra reticulata (SNr) as well as decreased dopamine transporter (DAT) level and compromised DA clearance in striatum. These effects were further exacerbated in Nurr1 heterozygous mice. Our data suggest that a prolonged adverse effect exists following adolescent METH binge exposure which may lead to greater damage to the dopaminergic system when exposed to repeated METH later in life. Furthermore, our data support that Nurr1 mutations or deficiency could be a potential genetic predisposition which may lead to higher vulnerability in some individuals.     

Cocaine withdrawal and neuro-adaptations in ion channel function

Chronic exposure to psychostimulants induces neuro-adaptations in ion channel function of dopamine (DA)-innervated cells localized within the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc). Although neuroplasticity in ion channel function is initially found in drug-sensitized animals, it has recently been believed to underlie the withdrawal effects of cocaine, including craving that leads to relapse in human addicts. Recent studies have also revealed remarkable differences in altered ion channel activities between mPFC pyramidal neurons and medium spiny NAc neurons in cocaine-withdrawn animals. In response to psychostimulant or certain “excitatory” stimuli, increased intrinsic excitability is found in mPFC pyramidal neurons, whereas decreased excitability is observed in medium spiny NAc cells in drug-withdrawn animals compared to drug-free control animals. These changes in ion channel function are modulated by interrupted DA/Ca²⁺ signaling with decreased DA D2 receptor function but increased D1 receptor signaling. More importantly, they are correlated to behavioral changes in cocaine-withdrawn human addicts and sensitized animals. Based on growing evidence, researchers have proposed that cocaine-induced neuro-adaptations in ion channel activity and DA/Ca²⁺ signaling in mPFC pyramidal neurons and medium spiny NAc cells may be the fundamental cellular mechanism underlying the cocaine withdrawal effects observed in human addicts.     

Effects of Glutamate Antagonists on Methamphetamine and 3,4-Methylenedioxymethamphetamine-Induced Striatal Dopamine Release In Vivo

Abstract: Several amphetamine analogues are reported to increase striatal glutamate efflux in vivo, whereas other data indicate that glutamate is capable of stimulating the efflux of dopamine (DA) in the striatum via a glutamate receptor-dependent mechanism. Based on these findings, it has been proposed that the ability of glutamate receptor-blocking drugs to antagonize the effects of amphetamine may be explained by their capacity to inhibit DA release induced by glutamate. To examine this possibility further, we investigated in vivo the ability of glutamate antagonists to inhibit DA release induced by either methamphetamine (METH) or 3,4-methylenedioxymethamphetamine (MDMA). Both METH and MDMA increased DA efflux in the rat striatum and, in animals killed 1 week later, induced persistent depletions of DA and serotonin in tissue. Pretreatment with MK-801 or CGS 19755 blocked the neurotoxic effects of METH and MDMA but, did not significantly alter striatal DA efflux induced by either stimulant. Infusion of 6-cyano-7-nitroquinoxaline-2,3-dione into the striatum likewise did not alter METH-induced DA overflow, and none of the glutamatergic antagonists affected the basal release of DA when given alone. The findings suggest that the neuroprotective effects of NMDA antagonists do not involve an inhibition of DA release, nor do the data support the proposal that glutamate tonically stimulates striatal DA efflux in vivo. Whether phasic increases in glutamate content might stimulate DA release, however, remains to be determined.     

Prophylactic and therapeutic targeting of the neurokinin-1 receptor limits neuroinflammation in a murine model of pneumococcal meningitis

There is increasing evidence that the tachykinin substance P (SP) can augment inflammatory immune responses within the CNS. We have recently demonstrated that resident CNS cells express high-affinity receptors for this neuropeptide (neurokinin-1 receptors [NK-1R]), and we have shown that SP can significantly augment glial inflammatory responses to clinically relevant Gram-negative bacteria. Furthermore, we provided evidence that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation following in vivo exposure to these pathogens. In this study, we demonstrate that SP similarly enhances inflammatory glial responses to the major Gram-positive causative agent of bacterial meningitis, Streptococcus pneumoniae, and show that endogenous SP/NK-1R interactions play a critical role in the development of CNS inflammation in an in vivo model of pneumococcal meningitis. Importantly, we provide the first demonstration, to our knowledge, that pharmacological targeting of the NK-1R not only prevents the development of damaging inflammation when administered prophylactically, but can also limit or reverse neuroinflammation associated with an established streptococcal CNS infection when delivered therapeutically. We show that an NK-1R antagonist attenuates increases in CNS inflammatory cytokine levels and decreases in immunosuppressive cytokine production associated with an ongoing S. pneumoniae infection. Furthermore, we demonstrate that such a therapeutic intervention reverses infection-associated gliosis and demyelination in the absence of changes in CNS bacterial burden. Together, these results suggest that targeting SP/NK-1R interactions is a strategy worthy of further study for the treatment of microbially induced neuroinflammation.     

Substance P Inhibits Hyperosmotic Stress-Induced Apoptosis in Corneal Epithelial Cells through the Mechanism of Akt Activation and Reactive Oxygen Species Scavenging via the Neurokinin-1 Receptor

Hyperosmolarity has been recognized as an important pathological factor in dry eye leading to ocular discomfort and damage. As one of the major neuropeptides of corneal innervation, substance P (SP) has been shown to possess anti-apoptotic effects in various cells. The aim of this study was to determine the capacity and mechanism of SP against hyperosmotic stress-induced apoptosis in cultured corneal epithelial cells. The cells were exposed to hyperosmotic stress by the addition of high glucose in the presence or absence of SP. The results showed that SP inhibited hyperosmotic stress-induced apoptosis of mouse corneal epithelial cells. Moreover, SP promoted the recovery of phosphorylated Akt level, mitochondrial membrane potential, Ca²⁺ contents, intracellular reactive oxygen species (ROS) and glutathione levels that impaired by hyperosmotic stress. However, the antiapoptotic capacity of SP was partially suppressed by Akt inhibitor or glutathione depleting agent, while the neurokinin-1 (NK-1) receptor antagonist impaired Akt activation and ROS scavenging that promoted by SP addition. In conclusion, SP protects corneal epithelial cells from hyperosmotic stress-induced apoptosis through the mechanism of Akt activation and ROS scavenging via the NK-1 receptor.     

Role of Corticotropin-Releasing Factor (CRF) Receptor-1 on the Catecholaminergic Response to Morphine Withdrawal in the Nucleus Accumbens (NAc)

Stress induces the release of the peptide corticotropin-releasing factor (CRF) into the ventral tegmental area (VTA), and also increases dopamine (DA) levels in brain regions receiving dense VTA input. Since the role of stress in drug addiction is well established, the present study examined the possible involvement of CRF1 receptor in the interaction between morphine withdrawal and catecholaminergic pathways in the reward system. The effects of naloxone-precipitated morphine withdrawal on signs of withdrawal, hypothalamo-pituitary-adrenocortical (HPA) axis activity, dopamine (DA) and noradrenaline (NA) turnover in the nucleus accumbens (NAc) and activation of VTA dopaminergic neurons, were investigated in rats pretreated with vehicle or CP-154,526 (selective CRF1R antagonist). CP-154,526 attenuated the increases in body weight loss and suppressed some of withdrawal signs. Pretreatment with CRF1 receptor antagonist resulted in no significant modification of the increased NA turnover at NAc or plasma corticosterone levels that were seen during morphine withdrawal. However, blockade of CRF1 receptor significantly reduced morphine withdrawal-induced increases in plasma adrenocorticotropin (ACTH) levels, DA turnover and TH phosphorylation at Ser40 in the NAc. In addition, CP-154,526 reduced the number of TH containing neurons expressing c-Fos in the VTA after naloxone-precipitated morphine withdrawal. Altogether, these results support the idea that VTA dopaminergic neurons are activated in response to naloxone-precipitated morphine withdrawal and suggest that CRF1 receptors are involved in the activation of dopaminergic pathways which project to NAc.     

Methamphetamine-induced neurotoxicity and microglial activation are not mediated by fractalkine receptor signaling

Methamphetamine (METH) damages dopamine (DA) nerve endings by a process that has been linked to microglial activation but the signaling pathways that mediate this response have not yet been delineated. Cardona et al. [Nat. Neurosci. 9 (2006), 917] recently identified the microglial-specific fractalkine receptor (CX3CR1) as an important mediator of MPTP-induced neurodegeneration of DA neurons. Because the CNS damage caused by METH and MPTP is highly selective for the DA neuronal system in mouse models of neurotoxicity, we hypothesized that the CX3CR1 plays a role in METH-induced neurotoxicity and microglial activation. Mice in which the CX3CR1 gene has been deleted and replaced with a cDNA encoding enhanced green fluorescent protein (eGFP) were treated with METH and examined for striatal neurotoxicity. METH depleted DA, caused microglial activation, and increased body temperature in CX3CR1 knockout mice to the same extent and over the same time course seen in wild-type controls. The effects of METH in CX3CR1 knockout mice were not gender-dependent and did not extend beyond the striatum. Striatal microglia expressing eGFP constitutively show morphological changes after METH that are characteristic of activation. This response was restricted to the striatum and contrasted sharply with unresponsive eGFP-microglia in surrounding brain areas that are not damaged by METH. We conclude from these studies that CX3CR1 signaling does not modulate METH neurotoxicity or microglial activation. Furthermore, it appears that striatal-resident microglia respond to METH with an activation cascade and then return to a surveying state without undergoing apoptosis or migration.     

Two kinds of mitogen-activated protein kinase phosphatases, MKP-1 and MKP-3, are differentially activated by acute and chronic methamphetamine treatment in the rat brain

Two functionally different MAP kinase phosphatases (MKPs) were investigated to clarify their roles in behavioral sensitization to methamphetamine (METH). MKP-1 mRNA levels increased substantially by about 60-300% in a range of brain regions, including several cortices, the striatum and thalamus 0.5-1 h after acute METH administration. After chronic METH administration its increase was less pronounced, but a more than 50% increase was still seen in the frontal cortex. MKP-1 protein levels also increased 3 h after acute or chronic METH administration. MKP-3 mRNA levels increased by about 30-50% in several cortices, the striatum and hippocampus 1 h after acute METH administration, but only in the hippocampus CA1 after chronic METH administration. Pre-treatment with the D(1) dopamine receptor antagonist, SCH23390, attenuated the METH-induced increase of MKP-1 and MKP-3 mRNA in every brain region, while pre-treatment with the NMDA receptor antagonist, MK-801, attenuated it in some regions. These findings suggest that in METH-induced sensitization, MKP-1 and MKP-3 play important roles in the neural plastic modification in widespread brain regions in the earlier induction process, but in the later maintenance process, they do so only in restricted brain regions such as MKP-1 in the frontal cortices and MKP-3 in the hippocampus.     

The substance P/neurokinin-1 receptor system in lung cancer: Focus on the antitumor action of neurokinin-1 receptor antagonists

The last decades have seen no significant progress in extending the survival of lung cancer patients and there is an urgent need to improve current therapies. The substance P (SP)/neurokinin-1 receptor (NK-1R) system plays an important role in the development of cancer: SP and NK-1R antagonists respectively induce cell proliferation and inhibition in human cancer cell lines. No study of the involvement of this system in non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cells has been carried out in depth. Here, we demonstrate the involvement of the SP/NK-1R system in human H-69 (SCLC) and COR-L23 (NSCLC) cell lines: (1) they express isoforms of the NK-1R and mRNA for the NK-1R; (2) they overexpress the tachykinin 1 gene; (3) the NK-1R is involved in their viability; (4) SP induces their proliferation; (5) NK-1R antagonists (Aprepitant (Emend), L-733,060, L-732,138) inhibit the growth of both cell lines in a concentration-dependent manner; (6) the specific antitumor action of these antagonists against such cells occurs through the NK-1R; and (7) lung cancer cell death is due to apoptosis. We also demonstrate the presence of NK-1Rs and SP in all the human SCLC and NSCLC samples studied. Our findings indicate that the NK-1R may be a promising new target in the treatment of lung cancer and that NK-1R antagonists could be new candidate antitumor drugs in the treatment of SCLC and NSCLC.