Repeated Methamphetamine Treatment Research Articles

Differentially Expressed Genes in Period 2-Overexpressing Mice Striatum May Underlie Their Lower Sensitivity to Methamphetamine Addiction-Like Behavior.

Previous reports have demonstrated that genetic mechanisms greatly mediate responses to drugs of abuse, including methamphetamine (METH). The circadian gene Period 2 (Per2) has been previously associated with differential responses towards METH in mice. While the behavioral consequences of eliminating Per2 have been illustrated previously, Per2 overexpression has not yet been comprehensively described; although, Per2-overexpressing (Per2 OE) mice previously showed reduced sensitivity towards METH-induced addiction-like behaviors. To further elucidate this distinct behavior of Per2 OE mice to METH, we identified possible candidate biomarkers by determining striatal differentially expressed genes (DEGs) in both drug-naïve and METH-treated Per2 OE mice relative to wild-type (WT), through RNA sequencing. Of the several DEGs in drug naïve Per2 OE mice, we identified six genes that were altered after repeated METH treatment in WT mice, but not in Per2 OE mice. These results, validated by quantitative real-time polymerase chain reaction, could suggest that the identified DEGs might underlie the previously reported weaker METH-induced responses of Per2 OE mice compared to WT. Gene network analysis also revealed that Asic3, Hba-a1, and Rnf17 are possibly associated with Per2 through physical interactions and predicted correlations, and might potentially participate in addiction. Inhibiting the functional protein of Asic3 prior to METH administration resulted in the partial reduction of METH-induced conditioned place preference in WT mice, supporting a possible involvement of Asic3 in METH-induced reward. Although encouraging further investigations, our findings suggest that these DEGs, including Asic3, may play significant roles in the lower sensitivity of Per2 OE mice to METH.

ERK-Directed Phosphorylation of mGlu5 Gates Methamphetamine Reward and Reinforcement in Mouse.

Methamphetamine (MA) is a highly addictive psychomotor stimulant drug. In recent years, MA use has increased exponentially on a global scale, with the number of MA-involved deaths reaching epidemic proportions. There is no approved pharmacotherapy for treating MA use disorder, and we know relatively little regarding the neurobiological determinants of vulnerability to this disease. Extracellular signal-regulated kinase (ERK) is an important signaling molecule implicated in the long-lasting neuroadaptations purported to underlie the development of substance use disorders, but the role for this kinase in the propensity to develop addiction, particularly MA use disorder, is uncharacterized. In a previous MA-induced place-conditioning study of C57BL/6J mice, we characterized mice as MA-preferring, -neutral, or -avoiding and collected tissue from the medial prefrontal cortex (mPFC). Using immunoblotting, we determined that elevated phosphorylated ERK expression within the medial prefrontal cortex (mPFC) is a biochemical correlate of the affective valence of MA in a population of C57BL/6J mice. We confirmed the functional relevance for mPFC ERK activation for MA-induced place-preference via site-directed infusion of the MEK inhibitor U0126. By contrast, ERK inhibition did not have any effect upon MA-induced locomotion or its sensitization upon repeated MA treatment. Through studies of transgenic mice with alanine point mutations on T1123/S1126 of mGlu5 that disrupt ERK-dependent phosphorylation of the receptor, we discovered that ERK-dependent mGlu5 phosphorylation normally suppresses MA-induced conditioned place-preference (MA-CPP), but is necessary for this drug’s reinforcing properties. If relevant to humans, the present results implicate individual differences in the capacity of MA-associated cues/contexts to hyper-activate ERK signaling within mPFC in MA Use Disorder vulnerability and pose mGlu5 as one ERK-directed target contributing to the propensity to seek out and take MA.

Dopamine D1 and D2 Receptors Differentially Regulate Rac1 and Cdc42 Signaling in the Nucleus Accumbens to Modulate Behavioral and Structural Plasticity After Repeated Methamphetamine Treatment

BackgroundMethamphetamine (METH) is a highly addictive psychostimulant that strongly activates dopamine receptor signaling in the nucleus accumbens (NAc). However, how dopamine D1 and D2 receptors (D1Rs and D2Rs, respectively) as well as downstream signaling pathways, such as those involving Rac1 and Cdc42, modulate METH-induced behavioral and structural plasticity is largely unknown. MethodsUsing NAc conditional D1R and D2R deletion mice, Rac1 and Cdc42 mutant viruses, and a series of behavioral and morphological methods, we assessed the effects of D1Rs and D2Rs on Rac1 and Cdc42 in modulating METH-induced behavioral and structural plasticity in the NAc. ResultsD1Rs and D2Rs in the NAc consistently regulated METH-induced conditioned place preference, locomotor activation, and dendritic and spine remodeling of medium spiny neurons but differentially regulated METH withdrawal–induced spatial learning and memory impairment and anxiety. Interestingly, Rac1 and Cdc42 signaling were oppositely modulated by METH, and suppression of Rac1 signaling and activation of Cdc42 signaling were crucial to METH-induced conditioned place preference and structural plasticity but not to locomotor activation. D1Rs activated Rac1 and Cdc42 signaling, while D2Rs inhibited Rac1 signaling but activated Cdc42 signaling to mediate METH-induced conditioned place preference and structural plasticity but not locomotor activation. In addition, NAc D1R deletion aggravated METH withdrawal–induced spatial learning and memory impairment by suppressing Rac1 signaling but not Cdc42 signaling, while NAc D2R deletion aggravated METH withdrawal–induced anxiety without affecting Rac1 or Cdc42 signaling. ConclusionsD1Rs and D2Rs differentially regulate Rac1 and Cdc42 signaling to modulate METH-induced behavioral plasticity and the structural remodeling of medium spiny neurons in the NAc.

Repeated methamphetamine treatment increases spine density in the nucleus accumbens of serotonin transporter knockout mice.

AimRepeated psychostimulant drug treatment, including methamphetamine, in rodents readily produces behavioral sensitization, which reflects altered brain function caused by repeated drug exposure. Dendritic remodeling of medium spiny neurons in the nucleus accumbens is thought to be an essential mechanism underlying behavioral sensitization. We recently showed that chronic methamphetamine treatment did not produce behavioral sensitization in serotonin transporter knockout mice.MethodsIn this study, we report the spine density of medium spiny neurons in the nucleus accumbens after repeated methamphetamine injection to examine morphological alterations in serotonin transporter knockout mice.ResultsGolgi‐COX staining clearly showed that the spine density of medium spiny neurons in the nucleus accumbens increased following repeated methamphetamine treatment in both wild‐type and serotonin transporter knockout mice.ConclusionsOur results suggested that augmented serotonergic neurotransmission produced by serotonin transporter deletion prevents the development of behavioral sensitization in a manner that is independent of dendritic remodeling in the nucleus accumbens.

Protein Kinase Cδ Gene Depletion Protects Against Methamphetamine-Induced Impairments in Recognition Memory and ERK1/2 Signaling via Upregulation of Glutathione Peroxidase-1 Gene.

Accumulating evidence has suggested that repeated treatment with methamphetamine (MA) resulted in cognitive impairments. Importantly, we show that selective upregulation of protein kinase Cδ (PKCδ) in the prefrontal cortex (PFC) of wild-type mice persisted for 28days post withdrawal of MA. On day 28, the MA-induced increase in phospho-PKCδ expression and decrease in phospho-ERK1/2 expression were significantly attenuated by both the Src inhibitor PP2 and the dopamine D1 receptor antagonist SCH 23390. However, neither protein kinase A inhibitor H89 nor calmodulin-dependent protein kinase II inhibitor KN93 attenuated MA-induced alterations in phospho-PKCδ expression and phospho-ERK1/2 expression. Since PKCδ knockout (KO) significantly increased the expression of glutathione peroxidase (GPx)-1, we also utilized GPx-1 KO and GPx-1-overexpressing transgenic (GPx-1 TG) mice. Repeated MA treatment induced cognitive impairment, as assessed by the novel object recognition test. Moreover, the extent of cognitive impairment correlated with the extent of increased phospho-PKCδ expression and decreased GPx1 expression. In the absence of MA, exposure to novel objects increased phospho-ERK1/2 and GPx-1 expression in the PFC; however, these expression levels were decreased in the presence of MA. PKCδ KO and GPx-1 TG mice each exhibited significantly attenuated MA-induced decreases in phospho-ERK1/2 and GPx-1 expression. Consistently, PKCδ inhibition induces GPx/GSH-dependent antioxidant systems. More importantly, the antipsychotic drug clozapine significantly protected against cognitive impairment and was associated with alterations in phospho-ERK1/2 and phospho-PKCδ expression. However, GPx-1 KO potentiated MA-induced cognitive deficits and alterations in phospho-ERK1/2 and phospho-PKCδ expression. These results suggest that MA induces cognitive impairment by inhibiting ERK1/2 signaling, activating PKCδ, and inactivating GPx-1 by upregulating Src kinase or the D1 receptor. They also suggest that clozapine requires activation of ERK1/2 signaling via positive modulation between the phospho-PKCδ and GPx-1 genes to restore cognitive function.

Methamphetamine blunts Ca(2+) currents and excitatory synaptic transmission through D1/5 receptor-mediated mechanisms in the mouse medial prefrontal cortex.

Psychostimulant addiction is associated with dysfunctions in frontal cortex. Previous data demonstrated that repeated exposure to methamphetamine (METH) can alter prefrontal cortex (PFC)-dependent functions. Here, we show that withdrawal from repetitive non-contingent METH administration (7 days, 1 mg/kg) depressed voltage-dependent calcium currents (ICa ) and increased hyperpolarization-activated cation current (IH ) amplitude and the paired-pulse ratio of evoked excitatory postsynaptic currents (EPSCs) in deep-layer pyramidal mPFC neurons. Most of these effects were blocked by systemic co-administration of the D1/D5 receptor antagonist SCH23390 (0.5 and 0.05 mg/kg). In vitro METH (i.e. bath-applied to slices from naïve-treated animals) was able to emulate its systemic effects on ICa and evoked EPSCs paired-pulse ratio. We also provide evidence of altered mRNA expression of (1) voltage-gated calcium channels P/Q-type Cacna1a (Cav 2.1), N-type Cacna1b (Cav 2.2), T-type Cav 3.1 Cacna1g, Cav 3.2 Cacna1h, Cav 3.3 Cacna1i and the auxiliary subunit Cacna2d1 (α2δ1); (2) hyperpolarization-activated cyclic nucleotide-gated channels Hcn1 and Hcn2; and (3) glutamate receptors subunits AMPA-type Gria1, NMDA-type Grin1 and metabotropic Grm1 in the mouse mPFC after repeated METH treatment. Moreover, we show that some of these changes in mRNA expression were sensitive D1/5 receptor blockade. Altogether, these altered mechanisms affecting synaptic physiology and transcriptional regulation may underlie PFC functional alterations that could lead to PFC impairments observed in METH-addicted individuals.

Adenosine 2A receptors modulate reward behaviours for methamphetamine.

Addiction to methamphetamine (METH) is a global health problem for which there are no approved pharmacotherapies. The adenosine 2A (A2 A ) receptor presents a potential therapeutic target for METH abuse due to its modulatory effects on striatal dopamine and glutamate transmission. Notably, A2 A receptor signalling has been implicated in the rewarding effects of alcohol, cocaine and opiates; yet, the role of this receptor in METH consumption and seeking is essentially unknown. Therefore, the current study used A2 A knockout (KO) mice to assess the role of A2 A in behaviours relevant to METH addiction. METH conditioned place preference was absent in A2 A KO mice compared with wild-type (WT) littermates. Repeated METH treatment produced locomotor sensitization in both genotypes; however, sensitization was attenuated in A2 A KO mice in a dose-related manner. METH intravenous self-administration was intact in A2 A KO mice over a range of doses and schedules of reinforcement. However, the motivation to self-administer was reduced in A2 A KO mice. Regression analysis further supported the observation that the motivation to self-administer METH was reduced in A2 A KO mice even when self-administration was similar to WT mice. Sucrose self-administration was also reduced in A2 A KO mice but only at higher schedules of reinforcement. Collectively, these data suggest that A2 A signalling is critically required to integrate rewarding and motivational properties of both METH and natural rewards.

Methamphetamine alters the normal progression by inducing cell cycle arrest in astrocytes.

Methamphetamine (MA) is a potent psychostimulant with a high addictive capacity, which induces many deleterious effects on the brain. Chronic MA abuse leads to cognitive dysfunction and motor impairment. MA affects many cells in the brain, but the effects on astrocytes of repeated MA exposure is not well understood. In this report, we used Gene chip array to analyze the changes in the gene expression profile of primary human astrocytes treated with MA for 3 days. Range of genes were found to be differentially regulated, with a large number of genes significantly downregulated, including NEK2, TTK, TOP2A, and CCNE2. Gene ontology and pathway analysis showed a highly significant clustering of genes involved in cell cycle progression and DNA replication. Further pathway analysis showed that the genes downregulated by multiple MA treatment were critical for G2/M phase progression and G1/S transition. Cell cycle analysis of SVG astrocytes showed a significant reduction in the percentage of cell in the G2/M phase with a concomitant increase in G1 percentage. This was consistent with the gene array and validation data, which showed that repeated MA treatment downregulated the genes associated with cell cycle regulation. This is a novel finding, which explains the effect of MA treatment on astrocytes and has clear implication in neuroinflammation among the drug abusers.

Serotonergic Modulation of Neuronal Activity in the Nucleus Accumbens Following Repeated Methamphetamine Administration in Rats

Electrophysiological studies were performed to determine whether serotonergic modulation in the nucleus accumbens (NAcc) was affected after repeated methamphetamine (MAP) administration. NAcc slices (400 μm) from Wistar rats administered MAP (5 mg/kg) or saline once daily for 5 days were prepared 1, 5, or 10 days after the final injection. Population spikes (PS) induced by local stimulation of NAcc were recorded. PS inhibition by serotonin was significantly attenuated in the MAP group at 5 days but did not differ at 1 or 10 days. We next analyzed the effects of serotonin receptor subtype (5-HT1A,2,3,4,6,7)-selective agonists of PS. Differences between saline and MAP groups in 5-HT1A,2,3,4,6 receptor agonist–induced changes of PS were small or not significant. Interestingly, 5-HT7 receptor agonists significantly enhanced PS in the MAP group. Changes in the secondary messenger system related to 5-HT7 receptors were also investigated. Adenylate cyclase activator–induced PS enhancements were significantly larger in the MAP group. However, dibutyryl-cAMP–induced PS enhancement was not significantly different. In conclusion, 5-HT–induced inhibition of PS in NAcc was attenuated 5 days after repeated MAP treatment: the change in the effect of 5-HT was probably due to enhancement of the excitatory modulation via the 5-HT7 receptor with adenylate cyclase signal transduction systems. [Supplementary Figure: available only at http://dx.doi.org/10.1254/jphs.13100FP]

Tetrahydropalmatine protects against methamphetamine-induced spatial learning and memory impairment in mice

The purpose of this study was to investigate the effect of methamphetamine (MA) on spatial learning and memory and the role of tetrahydropalmatine (THP) in MA-induced changes in these phenomena in mice. Male C57BL/6 mice were randomly divided into eight groups, according to different doses of MA, different doses of THP, treatment with both MA and THP, and saline controls. Spatial learning and memory were assessed using the Morris water maze. Western blot was used to detect the expression of extracellular signal-regulated protein kinase (ERK) in the mouse prefrontal cortex (PFC) and hippocampus. Repeated MA treatment significantly increased the escape latency in the learning phase and decreased the number of platform site crossings in the memory-test phase. ERK1/2 expression was decreased in the PFC but not in the hippocampus of the MA-treated mice. Repeated THP treatment alone did not affect the escape latency, the number of platform site crossings or the total ERK1/2 expression in the brain. Statistically significantly shorter escape latencies and more platform site crossings occurred in MA+THP-treated mice than in MA-treated mice. Repeated MA administration impairs spatial learning and memory in mice, and its co-administration with THP prevents this impairment, which is probably attributable to changed ERK1/2 expression in the PFC. This study contributes to uncovering the mechanism underlying MA abuse, and to exploring potential therapies.

Distinct roles of dopamine D3 receptors in modulating methamphetamine‐induced behavioral sensitization and ultrastructural plasticity in the shell of the nucleus accumbens

Persistent changes in behavior and psychological function that occur as a consequence of exposure to drugs of abuse are thought to be mediated by the structural plasticity of specific neural circuits such as the brain's dopamine (DA) system. Changes in dendritic morphology in the nucleus accumbens (NAc) accompany drug-induced enduring behavioral and molecular changes, yet ultrastructural changes in synapses following repeated exposure to drugs have not been well studied. The current study examines the role of DA D3 receptors in modulating locomotor activity induced by both acute and repeated methamphetamine (METH) administration and accompanying ultrastructural plasticity in the shell of NAc in mice. We found that D3 receptor mutant (D3−/−) mice exhibited attenuated acute locomotor responses as well as the development of behavioral sensitization to METH compared with wild-type mice. In the absence of obvious neurotoxic effects, METH induced similar increases in synaptic density in the shell of NAc in both wild-type and D3−/− mice. These results suggest that D3 receptors modulate locomotor responses to both acute and repeated METH treatment. In contrast, the D3 receptor is not obviously involved in modulating baseline or METH-induced ultrastructural changes in the NAc shell.

Histamine-dependent behavioral response to methamphetamine in 12-month-old male mice

Methamphetamine (MA) use is a large problem across the United States. Effects of MA include hyperactivity and increased anxiety. Using a mouse model system, we examined behavioral performance in the open field and elevated zero maze and shock-startle response of 12-month-old wild-type mice injected with MA once (1mg/kg) 30min prior to behavioral testing. MA treatment resulted in behavioral sensitization in the open field, consistent with studies in younger mice. There was an increased activity in the elevated zero maze and an increased shock-startle response 30 and 60min post-injection. Since histamine mediates some effects of MA in the brain, we assessed whether 12-month-old mice lacking histidine decarboxylase (Hdc−/−), the enzyme required to synthesize histamine, respond differently to MA than wild-type (Hdc+/+) mice. Compared to saline treatment, acute and repeated MA administration increased activity in the open field and measures of anxiety, though more so in Hdc−/− than Hdc+/+ mice. In the elevated zero maze, opposite effects of MA on activity and measures of anxiety were seen in Hdc+/+ mice. In contrast, MA similarly increased the shock-startle response in Hdc−/− and Hdc+/+ mice, compared to saline-treated genotype-matched mice. These results are similar to those in younger mice, suggesting that the effects are not age-dependent. Overall, single or repeated MA treatment causes histamine-dependent changes in 12-month-old mice in the open field and elevated zero maze, but not in the shock-startle response.

Repeated methamphetamine treatment increases expression of TRPV1 mRNA in the frontal cortex but not in the striatum or hippocampus of mice

The transient receptor potential vanilloid type 1 (TRPV1) is a non-selective ligand-gated cationic channel. The distribution of TRPV1 mRNA in various regions of the brain has been successfully established. Methamphetamine (MAP) is a psychostimulant and a major drug of abuse in many parts of the world. The powerful rewarding properties of MAP are attributed to multiple pharmacological actions, but the mechanistic association between TRPV1 expression and MAP-induced drug addiction has not established. In the present study, we conducted a time-course analysis of TRPV1 mRNA levels in the frontal cortex, striatum, and hippocampus of mouse brain following repeated MAP (2 mg/kg, i.p.) treatment. Our results demonstrate that expression of TRPV1 mRNA is significantly increased 1, 2, 6, 24, 48 h, and 1 week after the last MAP treatment in the frontal cortex but not in the striatum or hippocampus. These data support a potential role for TRPV1 in the treatment of MAP-induced drug addiction.

Dysfunction of dopamine release in the prefrontal cortex of dysbindin deficient sandy mice: An in vivo microdialysis study

Dystrobrevin binding protein-1 gene ( DTNBP1), which encodes dysbindin protein, has been identified as a schizophrenia susceptibility gene. Dysbindin has been shown to contribute to the regulation of exocytosis and formation of synaptic vesicles. Although hypofrontality in schizophrenia underlies its pathophysiology, the molecular function of dysbindin in synaptic neurotransmission remains unclear. In the present study, we investigated depolarization-evoked dopamine (DA) and serotonin (5-HT) release in the prefrontal cortex (PFC) of sandy (sdy) mice, which have a deletion mutation in the gene encoding DTNBP1. In vivo microdialysis analysis revealed that extracellular DA levels in the PFC of wild-type mice were increased by 60 mM KCl stimulation, and the KCl-evoked DA release was significantly decreased in sdy mice compared with wild-type mice. Extracellular 5-HT levels in the PFC of wild-type mice were also increased by 60 mM KCl stimulation. The KCl-evoked 5-HT release did not differ between wild-type and sdy mice. There was no difference in basal levels of DA and 5-HT before the stimulation between two groups. Behavioral sensitization after repeated methamphetamine (METH) treatment was significantly reduced in sdy mice compared with wild-type mice whereas no difference was observed in METH-induced hyperlocomotion between two groups. These results suggest that dysbindin may have a role in the regulation of depolarization-evoked DA release in the PFC and in the development of behavioral sensitization induced by repeated METH treatment.

GABAA receptors mediate the attenuating effects of a 5‐HT3 receptor antagonist on methamphetamine‐induced behavioral sensitization in mice

We previously showed that 5-HT(3) receptors are involved in the development and expression of methamphetamine (MAP)-induced locomotor sensitization in mice. Here, we examined whether the dopaminergic or the GABAergic systems are involved in the attenuating effects of the 5-HT(3) receptor antagonist MDL72222 on MAP-induced locomotor sensitization. Quantitative autoradiography of D1 ([(3)H]SCH23390), D2 ([(3)H]raclopride) receptor, and GABA(A) receptor benzodiazepine ([(3)H]flunitrazepam) binding was carried out in the brains of mice treated with chronic MAP and pretreatment with MDL72222. No significant differences were found in D(1) and D(2) binding between the two groups, suggesting that the attenuating effects of MDL72222 on MAP-induced locomotor sensitization is not medicated by D1 and D2 receptors. Postsynaptic dopamine (DA) receptor supersensitivity was measured by challenge with apomorphine, a dopamine D(1) and D(2) receptor agonist, after repeated MAP treatment or pretreatment with MDL72222 before MAP. Apomorphine induced an enhanced locomotor activity in both chronic MAP-treated mice and mice pretreated with MDL 72222, with no significant differences between the two groups. The binding of [(3)H]flunitrazepam was significantly decreased in the motor and cingulate cortex, caudate putamen, and nucleus accumbens of mice in the repeated MAP treatment group compared with the control group, and this effect was reversed by pretreatment with MDL72222. This suggested that GABA(A) benzodiazepine binding sites are involved in the attenuating effects of a 5-HT(3) receptor antagonist on MAP-induced locomotor sensitization.

Microglia Activated with the Toll-Like Receptor 9 Ligand CpG Attenuate Oligomeric Amyloid β Neurotoxicity in in Vitro and in Vivo Models of Alzheimer’s Disease

Soluble oligomeric amyloid beta (oAbeta) 1-42 causes synaptic dysfunction and neuronal injury in Alzheimer's disease (AD). Although accumulation of microglia around senile plaques is a hallmark of AD pathology, the role of microglia in oAbeta1-42 neurotoxicity is not fully understood. Here, we showed that oAbeta but not fibrillar Abeta was neurotoxic, and microglia activated with unmethylated DNA CpG motif (CpG), a ligand for Toll-like receptor 9, attenuated oAbeta1-42 neurotoxicity in primary neuron-microglia co-cultures. CpG enhanced microglial clearance of oAbeta1-42 and induced higher levels of the antioxidant enzyme heme oxygenase-1 in microglia without producing neurotoxic molecules such as nitric oxide and glutamate. Among subclasses of CpGs, class B and class C activated microglia to promote neuroprotection. Moreover, intracerebroventricular administration of CpG ameliorated both the cognitive impairments induced by oAbeta1-42 and the impairment of associative learning in Tg2576 mouse model of AD. We propose that CpG may be an effective therapeutic strategy for limiting oAbeta1-42 neurotoxicity in AD.

Silibinin attenuates cognitive deficits and decreases of dopamine and serotonin induced by repeated methamphetamine treatment

Cognitive deficits are a core feature of patients with methamphetamine (METH) abuse. It has been reported that repeated METH treatment impairs long-term recognition memory in the novel object recognition test (NORT) in mice. Recent studies indicate that silibinin, a flavonoid derived from the herb milk thistle, has potent neuroprotective effects in cell cultures and several animal models of neurological diseases. However, its effect on the cognitive deficit induced by METH remains unclear. In the present study, we attempt to clarify the effect of silibinin on impairments of recognition memory caused by METH in mice. Mice were co-administered silibinin with METH for 7 days and then cognitive function was assessed by NORT after 7-day withdrawal. Tissue levels of dopamine and serotonin as well as their metabolites in the prefrontal cortex and hippocampus were measured 1 day after NORT. Silibinin dose-dependently ameliorated the impairment of recognition memory caused by METH treatment in mice. Silibinin significantly attenuated the decreases in the dopamine content of the prefrontal cortex and serotonin content of the hippocampus caused by METH treatment. We also found a correlation between the recognition values and dopamine and serotonin contents of the prefrontal cortex and hippocampus. The effect of silibinin on cognitive impairment may be associated with an amelioration of decreases in dopamine and serotonin levels in the prefrontal cortex and hippocampus, respectively. These results suggest that silibinin may be useful as a pharmacological tool to investigate the mechanisms of METH-induced cognitive impairments.

Blockade of M1 muscarinic acetylcholine receptors modulates the methamphetamine-induced psychomotor stimulant effect

Muscarinic acetylcholine receptors (M1–M5) regulate many key functions of the CNS and peripheral nervous system. In the present study, the role of M1 muscarinic receptors (M1R) in the psychomotor stimulant and sensitizing properties of methamphetamine (METH) is investigated using molecular, neurochemical, and behavioral approaches. Acute and repeated treatment with METH increased M1R mRNA expression in the frontal cortex and the CA2 region of the hippocampus. Repeated treatment with METH also increased M1R mRNA expression in the dentate gyrus. Dicyclomine, an M1R antagonist, did not affect the psychomotor effect of METH, but it attenuated METH-induced increases in the dopamine (DA) efflux in the nucleus accumbens (NAc). Dicyclomine enhanced the psychomotor effect of METH after repeated treatment with METH and 8.0 mg/kg of dicyclomine, and also augmented the increase in the NAc DA overflow evoked by repeated METH treatment. These results suggest that M1R plays a role in the METH-induced psychomotor stimulant effect by changing the release of DA in the NAc of mice.

Impact of Cannabinoid Receptor Ligands on Sensitisation to Methamphetamine Effects on Rat Locomotor Behaviour

The repeated administration of various drugs of abuse may lead to a gradually increased behavioural response to these substances, particularly an increase in locomotion and stereotypies may occur. This phenomenon is well known and described as behavioural sensitisation. An increased response to the drug tested, elicited by previous repeated administration of another drug is recognised as cross-sensitisation. Based on our earlier experiences with studies on mice, which confirmed sensitisation to methamphetamine and described cross-sensitisation to methamphetamine after pre-treatment with cannabinoid CB1 receptor agonist, we focused the present study on the use of another typical laboratory animal - the rat. A biological validity of the sensitisation phenomenon was expected to be enhanced if the results of both mouse and rat studies were conformable. Similar investigation in rats brought very similar results to those described earlier in mice. However, at least some interspecies differences were noted in the rat susceptibility to the development of sensitisation to methamphetamine effects. Comparing to mice, it was more demanding to titrate a dose of methamphetamine producing behavioural sensitisation. Furthermore, we were not able to provoke cross-sensitisation by repeated administration of cannabinoid CB1 receptor agonist methanandamide and similarly, we did not demonstrate the suppression of cross-sensitisation in rats that were repeatedly given combined pre-treatment with cannabinoid CB1 receptor antagonist AM 251 and methamphetamine. Finally, unlike mice, an alternative behavioural change was registered after repeated methamphetamine treatment instead: the occurrence of stereotypic behaviour (nose rubbing).

Neuropsychotoxicity of Abused Drugs: Involvement of Matrix Metalloproteinase-2 and -9 and Tissue Inhibitor of Matrix Metalloproteinase-2 in Methamphetamine-Induced Behavioral Sensitization and Reward in Rodents

Matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) function to remodel the pericellular environment. We have investigated the role of the MMP/ TIMP system in methamphetamine (METH) dependence in rodents, in which the remodeling of neural circuits may be crucial. Repeated METH treatment induced behavioral sensitization, which was accompanied by an increase in MMP-2/-9/ TIMP-2 activity in the brain. An antisense TIMP-2 oligonucleotide enhanced the sensitization, which was associated with a potentiation of the METH-induced release of dopamine in the nucleus accumbens (NAc). MMP-2/-9 inhibitors blocked the METH-induced behavioral sensitization and conditioned place preference (CPP), a measure of the rewarding effect of a drug, and reduced the METH-increased dopamine release in the NAc. In MMP-2– and MMP-9–deficient mice, METH-induced behavioral sensitization and CPP as well as dopamine release were attenuated. The MMP/ TIMP system may be involved in METH-induced sensitization and reward by regulating extracellular dopamine levels.