Methamphetamine-elicited alterations of dopamine- and serotonin-metabolite levels within μ-opioid receptor knockout mice: a microdialysis study

μ-Opioid receptors (μ-ORs) modulate methamphetamine (MA)-induced behavioral responses, increased locomotor activity and stereotyped behavior in the mouse model. We investigated the changes in dopamine (DA) and serotonin (5-HT) metabolism in the striatum following either acute or repeated MA treatment using in vivo microdialysis. We also studied the role of μ-ORs in the modulation of MA-induced DA and 5-HT metabolism within μ-OR knockout mice. Subsequent to either acute or repeated intraperitoneal administration of MA, wild-type mice revealed decreases in extracellular concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in a dose-dependent manner. Moreover, wild-type mice had reductions in basal concentrations of DOPAC and HVA following repeated MA treatment with a higher dose. The effects of acute, repeated or challenge MA administration upon extracellular levels of DOPAC and HVA within μ-OR knockout mice significantly differed from the wild-type controls. The duration of recovery to the basal levels of extracellular DA and 5-HT metabolites induced by MA were much longer in wild-type mice than for μ-OR knockout mice. These findings suggest that μ-ORs play a modulatory role in MA-induced DA and 5-HT metabolism in the mouse striatum. This possible mechanism of MA-induced behavioral change as modulated by μ-OR merits further study.     

Co-administration of dextromethorphan with methamphetamine attenuates methamphetamine-induced rewarding and behavioral sensitization

Summary Methamphetamine (MA) is well known as a potent CNS stimulant, which produces strong rewarding and behavioral sensitization after repeated administration. In the present study, we investigated whether co-administration of dextromethorphan (DM) with MA could suppress these effects induced by acute and chronic MA treatment. The conditioned place preference (CPP) test was used to examine the rewarding/drug seeking effects and locomotor and stereotypic activities were measured to investigate behavioral sensitization induced by chronic MA. Our results revealed that co-administration of DM (20 mg/kg, ip) with MA (2 mg/kg, ip) almost completely abolished the MA-induced CPP and behavioral sensitization. Furthermore, both of the acute and chronic MA could result in an increase of dopamine (DA) turnover rate in the NAc and mPFC. The acute effects of MA on DA turnover rate could be attenuated by the co-administration of DM in both regions. The chronic effect of MA on DA turnover rate in the mPFC was also attenuated by the co-administration of DM. These results suggest that the effect of DM on blocking MA-induced rewarding and behavioral sensitization may be related to its effect on inhibiting the activity of DA neurons projected to mPFC and/or NAc.     

PKCδ inhibition enhances tyrosine hydroxylase phosphorylation in mice after methamphetamine treatment

The present study was designed to evaluate the specific role of protein kinase C (PKC) δ in methamphetamine (MA)-induced dopaminergic toxicity. A multiple-dose administration regimen of MA significantly increases PKCδ expression, while rottlerin, a PKCδ inhibitor, significantly attenuates MA-induced hyperthermia and behavioral deficits. These behavioral effects were not significantly observed in PKCδ antisense oligonucleotide (ASO)-treated- or PKCδ knockout (−/−)-mice. There were no MA-induced significant decreases of dopamine (DA) content or tyrosine hydroxylase (TH) expression in the striatum in rottlerin-treated-, ASO-treated- or PKCδ (−/−)-mice. The administration of MA also results in a significant decrease of TH phosphorylation at ser 40, but not ser 31, while the inhibition of PKCδ consistently and significantly attenuates MA-induced reduction in the phosphorylation of TH at ser 40. Therefore, these results suggest that the MA-induced enhancement of PKCδ expression is a critical factor in the impairment of TH phosphorylation at ser 40 and that pharmacological or genetic inhibition of PKCδ may be protective against MA-induced dopaminergic neurotoxicity in vivo.     

Role of high-affinity dopamine uptake and impulse activity in the appearance of extracellular dopamine in striatum after administration of exogenous L-DOPA: studies in intact and 6-hydroxydopamine-treated rats

The differential behavioral and neurochemical effects of exogenous L-DOPA in animals with intact versus dopamine (DA)-denervated striata raise questions regarding the role of DA terminals in the regulation of dopaminergic neurotransmission after administration of exogenous L-DOPA. In vivo microdialysis was used to monitor the effect of exogenous L-DOPA on extracellular DA in intact and DA-denervated striata of awake rats. In intact striatum, a small increase in extracellular DA was observed after administration of L-DOPA (50 mg/kg i.p.) but in DA-denervated striatum a much larger increase in extracellular DA was elicited. Additional experiments assessed the role of high-affinity DA uptake and impulse-dependent neurotransmitter release in the effect of exogenous L-DOPA on extracellular DA in striatum. Pretreatment with GBR-12909 (20 mg/kg i.p.), a selective DA uptake inhibitor, enhanced the ability of L-DOPA to increase extracellular DA in intact striatum. However, in DA-denervated striatum, inhibition of DA uptake did not alter the extracellular DA response to L-DOPA. Impulse-dependent neurotransmitter release was blocked by the infusion of tetrodotoxin (TTX; 1 microM), an inhibitor of fast sodium channels, through the dialysis probe. Application of TTX significantly attenuated the L-DOPA-induced increase in extracellular DA observed in striatum of intact rats pretreated with GBR-12909. In a similar manner, TTX infusion significantly attenuated the increase in extracellular DA typically observed in striatum of 6-OHDA-lesioned rats after the administration of L-DOPA. The present results indicate that DA terminals, via high-affinity uptake, play a crucial role in the clearance of extracellular DA formed from exogenous L-DOPA in intact striatum. This regulatory mechanism is absent in the DA-denervated striatum. In addition, this study has shown that DA synthesized from exogenous L-DOPA primarily is released by an impulse-dependent mechanism in both intact and DA-denervated striatum. The latter result suggests an important role for a nondopaminergic neuronal element in striatum that serves as the primary source of extracellular DA formed from exogenous L-DOPA.     

d-Fenfluramine Increases Striatal Extracellular Dopamine In Vivo Independently of Serotonergic Terminals or Dopamine Uptake Sites

Abstract: The effect of various doses of the serotonin (5-HT) release-inducing agent d -fenfluramine ( d -fenf) on extracellular dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) was studied in vivo in the striatum of halothane-anesthetized rats, following systemic and local administration. At 5 and 10 but not 2.5 mg/kg, d -fenf administered intraperitoneally significantly increased DA extracellular concentration and reduced DOPAC outflow. A concentration-dependent enhancement of DA dialysate content was also found following intrastriatal application (5, 10, 25, and 50 µ M ). The bilateral administration of 5,7-dihydroxytryptamine into the dorsal raphe nucleus, which markedly depleted 5-HT in the striatum, did not modify the effect on extracellular DA concentration of 25 µ M d -fenf locally applied into the striatum. The enhancement of extracellular DA level induced by 25 µ M d -fenf was slightly but significantly reduced by the local application of 25 µ M citalopgram. The blockade of DA uptake sites by nomifensine (0.1, 0.3, and 1 µ M ) did not modify significantly the effect of d -fenf. The rise of DA outflow induced by 25 µ M d -fenf was strongly reduced in the presence of 1 µ M tetrodotoxin (TTX) or by the removal of Ca²⁺ from the perfusion medium. The results obtained show that d -fenf increases the striatal extracellular DA concentration by a Ca²⁺-dependent and TTX-sensitive mechanism that is independent of striatal 5-HT itself or DA uptake sites.     

Local proteins associated with methamphetamine-induced nigrostriatal dopaminergic neurotoxicity

The present study aimed to examine the proteins involved in the methamphetamine (MA)-induced nigrostriatal dopaminergic toxicity. Infusion of anisomycin into striatum and substantia nigra both abolished the MA-induced striatal dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) depletions, indicating a critical role of local protein synthesis in determining such dopaminergic toxicity. Moreover, local protein synthesis blockade reversed this neurotoxicity via a temperature-independent mechanism. We then employed a proteomic approach, two-dimensional gel electrophoresis (2-DE) in conjunction with mass spectrometry analysis, to identify the protein candidates associated with the MA-induced neurotoxicity. In striatal samples, 2-DE analysis revealed that the intensities of nine protein spots were altered by MA treatment. Mass spectrometry analysis allowed us to identify five proteins, including an up-regulated protein, alpha-synuclein, and four down-regulated proteins, ATPase, F-actin capping protein beta subunit, ubiquitin carboxy-terminal hydrolase/PGP 9.5, and peroxidase. MA-altered expression levels of alpha-synuclein and ubiquitin carboxy-terminal hydrolase/PGP 9.5 in striata were confirmed by western blotting analysis. Taken together, these results suggest that local up-regulation of alpha-synuclein and down-regulation of ubiquitin carboxy-terminal hydrolase/PGP 9.5 could be linked to the MA-induced dopaminergic terminal toxicity.     

Exposure to Far Infrared Ray Protects Methamphetamine-Induced Behavioral Sensitization in Glutathione Peroxidase-1 Knockout Mice via Attenuating Mitochondrial Burdens and Dopamine D1 Receptor Activation

Evidence indicates that stress conditions might lead to drug dependence. Recently, we have demonstrated that exposure to far infrared ray (FIR) attenuates acute restraint stress via induction of glutathione peroxidase-1 (GPx-1) gene. We investigated whether FIR affects methamphetamine (MA)-induced behavioral sensitization and whether FIR-mediated pharmacological activity requires interaction between dopamine receptor and GPx-1 gene. We observed that MA treatment significantly increased GPx-1 expression in the striatum of wild-type (WT) mice. Interestingly, exposure to FIR potentiated MA-induced increase in GPx-1 expression. This phenomenon was also observed in animals receiving MA with dopamine D1 receptor antagonist SCH23390. However, dopamine D2 receptor antagonist sulpiride did not affect MA-induced GPx-1 expression. FIR exposure or SCH23390, but not sulpiride, significantly attenuated MA-induced behavioral sensitization. Exposure to FIR significantly attenuated MA-induced dopamine D1 receptor expression, c-Fos induction and oxidative burdens. FIR-mediated antioxidant effects were also more pronounced in mitochondrial- than cytosolic-fraction. In addition, FIR significantly attenuated against MA-induced changes in mitochondrial superoxide dismutase and mitochondrial GPx activities, mitochondrial transmembrane potential, intramitochondrial Ca²⁺ level, mitochondrial complex-I activity, and mitochondrial oxidative burdens. The attenuation by FIR was paralleled that by SCH23390. Effects of FIR or SCH23390 were more sensitive to GPx-1 KO than WT mice, while SCH23390 treatment did not exhibit any additive effects on the protective activity mediated by FIR, indicating that dopamine D1 receptor constitutes a molecular target of FIR. Our result suggests that exposure to FIR ameliorates MA-induced behavioral sensitization via possible interaction between dopamine D1 receptor and GPx-1 gene.     

Individual and combined effects of methamphetamine and ketamine on conditioned place preference and NR1 receptor phosphorylation in rats

Methamphetamine (MA), a commonly abused psychostimulant, induces the drug dependence by enhancing the dopamine-mediated neurotransmission. Ketamine (KET) is a non-competitive N-methyl-D-aspartate receptor antagonist, which can be actually mixed with MA for polydrug abuse. In the present study, the individual and combined effects of KET (10 mg/kg, i.p.) and MA (1 mg/kg, i.p.) on conditioned place preference in rats were investigated. The alterations of serine 897 phosphorylations of NR1 receptors in the striatum and ventral tegmental area of after-conditioning rats were measured immunochemically. The results showed repeated administrations of MA, KET and their combination, at the doses studied, all could induce psychological dependences evaluated by conditioned place preference. KET was not able to suppress the MA-induced place preference. The modulations of NR1 phosphorylations in basal ganglia were partly responsible to place preference. Although the alterations induced by KET were not significant in most areas we studied, MA showed a significant increase in the ventral tegmental area but a marked decrease in caudate putamen and nucleus accumbens. Such alterations were much more significant when KET and MA were combined. These results have important implications for public awareness of harm with combined drug abuse. Further investigations toward the specific interaction of the two drugs are necessary.     

Selective stimulation of serotonin2c receptors blocks the enhancement of striatal and accumbal dopamine release induced by nicotine administration

The effects of acute and repeated nicotine administration on the extracellular levels of dopamine (DA) in the corpus striatum and the nucleus accumbens were studied in conscious, freely moving rats by in vivo microdialysis. Acute intraperitoneal (i.p.) injection of nicotine (1 mg/kg) increased DA outflow both in the corpus striatum and the nucleus accumbens. Repeated daily injection of nicotine (1 mg/kg, i.p.) for 10 consecutive days caused a significant increase in basal DA outflow both in the corpus striatum and the nucleus accumbens. Acute challenge with nicotine (1 mg/kg, i.p.) in animals treated repeatedly with this drug enhanced DA extracellular levels in both brain areas. However, the effect of nicotine was potentiated in the nucleus accumbens, but not in the corpus striatum. To test the hypothesis that stimulation of 5-HT (5-hydroxytryptamine, serotonin)(2C) receptors could affect nicotine-induced DA release, the selective 5-HT(2C) receptor agonist RO 60-0175 was used. Pretreatment with RO 60-0175 (1 and 3 mg/kg, i.p.) dose-dependently prevented the enhancement in DA release elicited by acute nicotine in the corpus striatum, but was devoid of any significant effect in the nucleus accumbens. RO 60-0175 (1 and 3 mg/kg, i.p.) dose-dependently reduced the stimulatory effect on striatal and accumbal DA release induced by an acute challenge with nicotine (1 mg/kg, i.p.) in rats treated repeatedly with this alkaloid. However, only the effect of 3 mg/kg RO 60-0175 reached statistical significance. The inhibitory effect of RO 60-0175 on DA release induced by nicotine in the corpus striatum and the nucleus accumbens was completely prevented by SB 242084 (0.5 mg/kg, i.p.) and SB 243213 (0.5 mg/kg, i.p.), two selective antagonists of 5-HT(2C) receptors. It is concluded that selective activation of 5-HT(2C) receptors can block the stimulatory action of nicotine on central DA function, an effect that might be relevant for the reported antiaddictive properties of RO 60-0175.     

Alpha-1B adrenergic receptor knockout mice are protected against methamphetamine toxicity

The psychostimulant methamphetamine (MA) is toxic to nigro-striatal dopaminergic terminals in both experimental animals and humans. In mice, three consecutive injections of MA (5 mg/kg, i.p. with 2 h of interval) induced a massive degeneration of the nigro-striatal pathway, as reflected by a 50% reduction in the striatal levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC), by a substantial reduction in striatal tyrosine hydroxylase and high-affinity DA transporter immunostaining, and by the development of reactive gliosis. MA-induced nigro-striatal degeneration was largely attenuated in mice lacking alpha1b-adrenergic receptors (ARs). MA-stimulated striatal DA release (measured by microdialysis in freely moving animals) and locomotor activity were also reduced in alpha1b-AR knockout mice. Pharmacological blockade of alpha-adrenergic receptors with prazosin also protected wild-type mice against MA toxicity. These results suggests that alpha1b-ARs may play a role in the toxicity of MA on nigro-striatal DA neurons.     

Subchronic steroid administration induces long lasting changes in neurochemical and behavioral response to cocaine in rats

The abuse of anabolic androgenic steroids (AASs), such as nandrolone, is not only a problem in the world of sports but is associated with the polydrug use of non-athletes. Among other adverse effects, AAS abuse has been associated with long term or even persistent psychiatric problems. We have previously found that nandrolone decanoate treatment could produce prolonged changes in rats’ brain reward circuits associated to drug dependence. The aim in this study was to evaluate whether AAS-induced neurochemical and behavioral changes are reversible.The increases in extracellular dopamine (DA) and serotonin (5-HT) concentration, as well as stereotyped behavior and locomotor activity (LMA) evoked by cocaine were attenuated by pretreatment with nandrolone. The recovery period, which was needed for the DA system to return back to the basic level, was fairly long compared to the dosing period of the steroid. In the 5-HT system, the time that system needed to return back to the basal level, was even longer than in the DA system. The attenuation was still seen though there were no detectable traces of nandrolone in the blood samples.Given that accumbal outflow of DA and 5-HT, as well as LMA and stereotyped behavior are all related to reward of stimulant drugs, this study suggests that nandrolone decanoate has significant, long-lasting but reversible effects on the rewarding properties of cocaine.     

B-HT 920 stimulates postsynaptic D2 dopamine receptors in the normal rat: electrophysiological and behavioral evidence

The putative autoreceptor-selective dopamine (DA) agonist B-HT 920 was tested using electrophysiological and behavioral models thought to reflect actions at postsynaptic D2 DA receptors. Direct iontophoretic application of B-HT 920 onto nucleus accumbens neurons caused a current-dependent inhibition of firing which could be attenuated by pretreatment with alpha-methyl-p-tyrosine (to deplete DA) and reinstated (enabled) by concurrent administration of the selective D1 DA receptor agonist SKF 38393. These findings suggest that, like other selective D2 DA receptor agonists, the postsynaptic effects of B-HT 920 require concurrent stimulation of D1 DA receptors. Behavioral indices of postsynaptic D2 DA receptor stimulation (stereotyped sniffing and rearing) were also evident following combined treatment with B-HT 920 and SKF 38393. Moreover, similar "low-level" stereotyped behaviors were also observed when B-HT 920 was administered alone following pretreatment with the alpha-2 adrenoceptor antagonists idazoxane and piperoxane, suggesting that alpha-2 agonist actions of B-HT 920, in some way, mask the expression of D2 receptor-mediated stereotyped responses. When B-HT 920 was combined with SKF 38393 following pretreatment with idazoxane, both the intensity and form (continual licking and gnawing) of stereotyped behavior was enhanced. Taken together, these electrophysiological and behavioral findings indicate that B-HT 920 possesses the properties of a selective D2 DA receptor agonist and cannot be considered as a DA autoreceptor-selective compound.     

A comparative study of the neurochemical profiles of remoxipride, raclopride and metoclopramide activity]

Effects of intraperitoneal administration of remoxipride (2.4 mg/kg), raclopride (1.2 mg/kg) and metoclopramide (5 mg/kg) on the concentration of monoamines and metabolites in various brain regions, on the DA and serotonin biosynthesis in the striatum and nucleus accumbens, on the K(+)-stimulated DA release from the isolated striatum, on the extracellular levels of DA and metabolites in the striatum of freely moving rats were studied. Remoxipride and raclopride increase DA turnover, biosynthesis and DA release, studied both in vitro and in vivo. Metoclopramide was shown to be more effective in increasing DA turnover and biosynthesis, while exerted less activity in regard to increasing DA release in vivo and failed to affect release in vitro. Possible neurochemical mechanisms underlying pharmacological effects of these drugs are discussed.     

Valproate Inhibits Methamphetamine Induced Hyperactivity via Glycogen Synthase Kinase 3β Signaling in the Nucleus Accumbens Core

Valproate (VPA) has recently been shown to influence the behavioral effects of psycho-stimulants. Although glycogen synthase kinase 3β (GSK3β) signaling in the nucleus accumbens (NAc) plays a key role in mediating dopamine (DA)-dependent behaviors, there is less direct evidence that how VPA acts on the GSK3β signaling in the functionally distinct sub-regions of the NAc, the NAc core (NAcC) and the NAc shell (NAcSh), during psycho-stimulant-induced hyperactivity. In the present study, we applied locomotion test after acute methamphetamine (MA) (2 mg/kg) injection to identify the locomotor activity of rats received repeated VPA (300 mg/kg) pretreatment. We next measured phosphor-GSK3β at serine 9 and total GSK3β levels in NAcC and NAcSh respectively to determine the relationship between the effect of VPA on MA-induced hyperlocomotor and changes in GSK3β activity. We further investigated whether microinjection of VPA (300 μg/0.5 μl/side, once daily for 7 consecutive days) into NAcC or NAcSh could affect hyperactivity induced by MA. Our data indicated that repeated VPA treatment attenuated MA-induced hyperlocomotor, and the effect was associated with decreased levels of phosphorylated GSK3β at Ser 9 in the NAcC. Moreover, repeated bilateral intra-NAcC, but not intra-NAcSh VPA treatment, significantly attenuated MA-induced hyperactivity. Our results suggested that GSK3β activity in NAcC contributes to the inhibitory effects of VPA on MA-induced hyperactivity.     

Differential neurochemical consequences of an escalating dose-binge regimen followed by single-day multiple-dose methamphetamine challenges

Chronic intake of methamphetamine (METH) causes tolerance to its behavioral and subjective effects. To better mimic human patterns of drug abuse, the present study used a rodent model that took into account various facets of human drug administration and measured METH-induced effects on brain monoamine levels. Adult male Sprague–Dawley rats were injected with METH or saline according to an escalating dose schedule for 2 weeks. This was followed by a challenge regimen of either saline or one of two doses of METH (3 × 10 mg/kg every 2 h or 6 × 5 mg/kg given every hour, both given within a single day). Both challenge doses of METH caused significant degrees of depletion of dopamine in the striatum and norepinephrine and serotonin in the striatum, cortex, and hippocampus. Animals pre-treated with METH showed significant attenuation of METH-induced striatal dopamine depletion but not consistent attenuation of norepinephrine and serotonin depletion. Unexpectedly, METH pre-treated animals that received the 3 × 10 mg/kg challenge showed less increases in tympanic temperatures than saline pre-treated rats whereas METH pre-treated animals that received the 6 × 5 mg/kg METH challenge showed comparable increases in temperatures to saline pre-treated rats. Therefore, pre-treatment-induced partial protection against monoamine depletion is probably not because of attenuated METH-induced hyperthermia in those rats.     

Human immunodeficiency virus-1 Tat protein and methamphetamine interact synergistically to impair striatal dopaminergic function

The human immunodeficiency virus (HIV)-1 transactivating protein Tat may be pathogenically relevant in HIV-1-induced neuronal injury. The abuse of methamphetamine (MA), which is associated with behaviors that may transmit HIV-1, may damage dopaminergic afferents to the striatum. Since Tat and MA share common mechanisms of injury, we examined whether co-exposure to these toxins would lead to enhanced dopaminergic toxicity. Animals were treated with either saline, a threshold dose of MA, a threshold concentration of Tat injected directly into the striatum, or striatal injections of Tat followed by exposure to MA. Threshold was defined as the highest concentration of toxin that would not result in a significant loss of striatal dopamine levels. One week later, MA-treated animals demonstrated a 7% decline in striatal dopamine levels while Tat-treated animals showed an 8% reduction. Exposure to both MA + Tat caused an almost 65% reduction in striatal dopamine. This same treatment caused a 56% reduction in the binding capacity to the dopamine transporter. Using human fetal neurons, enhanced toxicity was also observed when cells were exposed to both Tat and MA. Mitochondrial membrane potential was disrupted and could be prevented by treatment with antioxidants. This study demonstrates that the HIV-1 'virotoxin' Tat enhances MA-induced striatal damage and suggests that HIV-1-infected individuals who abuse MA may be at increased risk of basal ganglia dysfunction.     

Ethanol triggers sphingosine 1-phosphate elevation along with neuroapoptosis in the developing mouse brain

Recent studies suggest that l-3,4 dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID), a severe complication of conventional L-DOPA therapy of Parkinson's disease, may be caused by dopamine (DA) release originating in serotonergic neurons. To evaluate the in vivo effect of a 5-HT(1A) agonist [(±)-8-hydroxy-2-(dipropylamino) tetralin hydrobromide, 8-OHDPAT] on the L-DOPA-induced increase in extracellular DA and decrease in [(11) C]raclopride binding in an animal model of advanced Parkinson's disease and LID, we measured extracellular DA in response to L-DOPA or a combination of L-DOPA and the 5-HT(1A) agonist, 8-OHDPAT, with microdialysis, and determined [(11) C]raclopride binding to DA receptors, with micro-positron emission tomography, as the surrogate marker of DA release. Rats with unilateral 6-hydroxydopamine lesions had micro-positron emission tomography scans with [(11) C]raclopride at baseline and after two pharmacological challenges with L-DOPA?+?benserazide with or without 8-OHDPAT co-treatment. Identical challenge regimens were used with the subsequent microdialysis concomitant with ratings of LID severity. The baseline increase of [(11) C]raclopride-binding potential (BP(ND) ) in lesioned striatum was eliminated by the L-DOPA challenge, while the concurrent administration of 8-OHDPAT prevented this L-DOPA-induced displacement of [(11) C]raclopride significantly in lesioned ventral striatum and near significantly in the dorsal striatum. With microdialysis, the L-DOPA challenge raised the extracellular DA in parallel with the emergence of strong LID. Co-treatment with 8-OHDPAT significantly attenuated the release of extracellular DA and LID. The 8-OHDPAT co-treatment reversed the L-DOPA-induced decrease of [(11) C]raclopride binding and increase of extracellular DA and reduced the severity of LID. The reversal of the effect of L-DOPA on [(11) C]raclopride binding, extracellular DA and LID by 5-HT agonist administration is consistent with the notion that part of the DA increase associated with LID originates in serotonergic neurons.     

Ketanserin pretreatment attenuates MDMA-induced dopamine release in the striatum as measured by in vivo microdialysis

Systemic administration of the amphetamine analogue, 3,4-methylenedioxymethamphetamine (MDMA) produced a dose-dependent increase in the extracellular concentration of dopamine (DA) in the striatum as measured by in vivo microdialysis in awake, freely-moving rats. The extracellular concentration of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), was significantly decreased in dialysate samples following the administration of MDMA (10 and 20 mg/kg, i.p.). The serotonin-2 (5-HT2) antagonist ketanserin (3 mg/kg, i.p.) had no effect on the extracellular concentration of DA or DOPAC in the striatum of vehicle- treated rats. The administration of ketanserin (3 mg/kg) 1 hr prior to MDMA (20 mg/kg) significantly attenuated the MDMA- induced increase in the extracellular concentration of DA without affecting the decrease in DOPAC concentrations. These data are suggestive that MDMA administration increases DA release in the striatum of awake, freely-moving rats. In addition, MDMA-induced increase in the extracellular concentration of DA in the striatum is mediated, in part, via 5-HT2 receptor mechanisms.     

Behavioral sensitization to delta 9-tetrahydrocannabinol and cross-sensitization with morphine: differential changes in accumbal shell and core dopamine transmission

Although cannabinoid-induced behavioral sensitization and cross-sensitization with opiates has been recently demonstrated, no information is available on the associated state and responsiveness of dopamine (DA) transmission in the nucleus accumbens (NAc) shell and core. In this study we investigate by means of dual probe microdialysis, the effect of exposure to a sensitizing regimen of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and morphine on the extracellular concentrations of DA under basal conditions and after challenge with Delta(9)-THC and morphine in the NAc shell and core. Different groups of male Sprague-Dawley rats were administered twice daily for 3 days with increasing doses of Delta(9)-THC (2, 4, and 8 mg/kg i.p.), morphine (10, 20, and 40 mg/kg s.c.), and vehicle. After 14-20 days from the last injection, the animals were implanted with two microdialysis probes, one aimed at the NAc shell and the other at the core. The following day animals pre-treated with Delta(9)-THC and vehicle controls were challenged with 150 microg/kg i.v. of Delta(9)-THC or 0.5 mg/kg i.v. of morphine. Animals pre-treated with morphine and their vehicle controls were administered with 150 microg/kg i.v. of Delta(9)-THC. Rats pre-exposed to Delta(9)-THC showed behavioral sensitization associated with a reduced stimulation of DA transmission in the NAc shell and an increased stimulation in the NAc core in response to Delta(9)-THC challenge. Pre-exposure to Delta(9)-THC induced behavioral sensitization to morphine also, but only a reduced stimulation of DA transmission in the NAc shell was observed. Animals pre-treated with morphine showed behavioral sensitization and differential changes of DA in the NAc shell and core in response to Delta(9)-THC challenge with a decreased response in the shell and an increased response in the core. The results show that Delta(9)-THC-induced behavioral sensitization is associated with changes in the responsiveness of DA transmission in the NAc subdivisions that are similar to those observed in the sensitization induced by other drugs of abuse.     

Role of serine racemase in behavioral sensitization in mice after repeated administration of methamphetamine

Background

The N-methyl-D-aspartate (NMDA) receptors play a role in behavioral abnormalities observed after administration of the psychostimulant, methamphetamine (METH). Serine racemase (SRR) is an enzyme which synthesizes D-serine, an endogenous co-agonist of NMDA receptors. Using Srr knock-out (KO) mice, we investigated the role of SRR on METH-induced behavioral abnormalities in mice.

Methodology/Principal Findings

Evaluations of behavior in acute hyperlocomotion, behavioral sensitization, and conditioned place preference (CPP) were performed. The role of SRR on the release of dopamine (DA) in the nucleus accumbens after administration of METH was examined using in vivo microdialysis technique. Additionally, phosphorylation levels of ERK1/2 proteins in the striatum, frontal cortex and hippocampus were examined using Western blot analysis. Acute hyperlocomotion after a single administration of METH (3 mg/kg) was comparable between wild-type (WT) and Srr-KO mice. However, repeated administration of METH (3 mg/kg/day, once daily for 5 days) resulted in behavioral sensitization in WT, but not Srr-KO mice. Pretreatment with D-serine (900 mg/kg, 30 min prior to each METH treatment) did not affect the development of behavioral sensitization after repeated METH administration. In the CPP paradigm, METH-induced rewarding effects were demonstrable in both WT and Srr-KO mice. In vivo microdialysis study showed that METH (1 mg/kg)-induced DA release in the nucleus accumbens of Srr-KO mice previously treated with METH was significantly lower than that of the WT mice previously treated with METH. Interestingly, a single administration of METH (3 mg/kg) significantly increased the phosphorylation status of ERK1/2 in the striatum of WT, but not Srr-KO mice.

Conclusions/Significance

These findings suggest first, that SRR plays a role in the development of behavioral sensitization in mice after repeated administration of METH, and second that phosphorylation of ERK1/2 by METH may contribute to the development of this sensitization as seen in WT but not Srr-KO mice.