Enhanced Cdk5 activity and p35 translocation in the ventral striatum of acute and chronic methamphetamine-treated rats

Epigenetic Regulatory Dynamics in Models of Methamphetamine-Use Disorder

Methamphetamine (METH)-use disorder (MUD) is a very serious, potentially lethal, biopsychosocial disease. Exposure to METH causes long-term changes to brain regions involved in reward processing and motivation, leading vulnerable individuals to engage in pathological drug-seeking and drug-taking behavior that can remain a lifelong struggle. It is crucial to elucidate underlying mechanisms by which exposure to METH leads to molecular neuroadaptive changes at transcriptional and translational levels. Changes in gene expression are controlled by post-translational modifications via chromatin remodeling. This review article focuses on the brain-region specific combinatorial or distinct epigenetic modifications that lead to METH-induced changes in gene expression.

LB100 attenuates methamphetamine-induced behavioral sensitization by inhibiting the Raf1-ERK 1/2 cascade in the caudate putamen

Methamphetamine (METH) abuse has become a serious social problem. Behavioral sensitization is a common behavioral paradigm used to study the neurobiological mechanism that underlies drug addiction. Our previous study demonstrated that the activity of protein phosphatase 2A (PP2A) and the level of phosphorylated extracellular signal-related kinase 1/2 (p-ERK 1/2) are increased in the caudate putamen (CPu) of METH-sensitive mice. However, the relationship between PP2A and ERK 1/2 in METH-induced behavioral sensitization remains unknown. Some studies have indicated that Raf1 may be involved in this process. In this study, LB100, a PP2A inhibitor for treating solid tumors, was first used to clarify the relationship between PP2A and ERK 1/2. In addition, Western blot was used to examine the levels of p-Raf1 (Ser 259) and p-ERK 1/2 (Thr 202/Tyr 204) in the CPu, hippocampus (Hip) and nucleus accumbens (NAc). Our results showed that 2 mg/kg LB100 significantly attenuated METH-induced behavioral sensitization. Furthermore, Western blot analysis revealed that pretreatment with 2 mg/kg LB100 remarkably reversed METH-induced reduction of p-Raf1, as well as upregulation of p-ERK 1/2 in the CPu. Taken together, these results indicate that PP2A plays an important role in METH-induced behavioral sensitization and phosphorylates ERK 1/2 by dephosphorylating p-Raf1 in the CPu to further regulate METH-induced behavioral sensitization.

Effects of nicotine on DARPP-32 and CaMKII signaling relevant to addiction

Paul Greengard brought to neuroscience the idea of, and evidence for, the role of second messenger systems in neuronal signaling. The fundamental nature of his contributions is evident in the far reach of his work, relevant to various subfields and topics in neuroscience. In this review, we discuss some of Greengard's work from the perspective of nicotinic acetylcholine receptors and their relevance to nicotine addiction. Specifically, we review the roles of dopamine- and cAMP-regulated phospho-protein of 32kDa (DARPP-32) and Ca2+/calmodulin-dependent kinase II (CaMKII) in nicotine-dependent behaviors. For each protein, we discuss the historical context of their discovery and initial characterization, focusing on the extensive biochemical and immunohistochemical work conducted by Greengard and colleagues. We then briefly summarize contemporary understanding of each protein in key intracellular signaling cascades and evidence for the role of each protein with respect to systems and behaviors relevant to nicotine addiction.

The multi-faceted impact of methamphetamine on Alzheimer's disease: From a triggering role to a possible therapeutic use

Although it has been initially synthesized for therapeutic purposes and currently FDA-approved and prescribed for obesity, attention-deficit/hyperactivity disorder, narcolepsy and depression, methamphetamine became a recreational drug that is nowadays massively manufactured illegally. Because it is a powerful and extremely addictive psychotropic agent, its abuse has turned out to become a major health problem worldwide. Importantly, the numerous effects triggered by this drug induce neurotoxicity in the brain ultimately leading to serious neurological impairments, tissue damage and neuropsychological disturbances that are reminiscent to most of the symptoms observed in Alzheimer's disease and other pathological manifestations in aging brain. In this context, there is a growing number of compelling evidence linking methamphetamine abuse with a higher probability of developing premature Alzheimer's disease and consequent neurodegeneration. This review proposes to establish a broad assessment of the effects that this drug can generate at the cellular and molecular levels in connection with the development of the age-related Alzheimer's disease. Altogether, the objective is to warn against the long-term effects that methamphetamine abuse may convey on young consumers and the increased risk of developing this devastating brain disorder at later stages of their lives, but also to discuss a more recently emerging concept suggesting a possible use of methamphetamine for treating this pathology under proper and strictly controlled conditions.

Systemic Administration of the Cyclin-Dependent Kinase Inhibitor (S)-CR8 Selectively Reduces Escalated Ethanol Intake in Dependent Rats

BACKGROUND

Chronic exposure to ethanol (EtOH) and other drugs of abuse can alter the expression and activity of cyclin-dependent kinase 5 (CDK5) and its cofactor p35, but the functional implication of CDK5 signaling in the regulation of EtOH-related behaviors remains unknown. In the present study, we sought to determine whether CDK5 activity plays a role in the escalation of EtOH self-administration triggered by dependence.

METHODS

We tested the effect of systemically administered (S)-CR8, a nonselective CDK inhibitor, on operant responding for EtOH or saccharin, a highly palatable reinforcer, in adult male Wistar rats. Half of the rats were made EtOH-dependent via chronic intermittent EtOH inhalation (CIE). We then sought to identify a possible neuroanatomical locus for the behavioral effect of (S)-CR8 by quantifying protein levels of CDK5 and p35 in subregions of the extended amygdala and prefrontal cortex from EtOH-naïve, nondependent, and dependent rats at the expected time of EtOH self-administration. We also analyzed the phosphorylation of 4 CDK5 substrates and of the CDK substrate consensus motif.

RESULTS

(S)-CR8 dose-dependently reduced EtOH self-administration in dependent rats. It had no effect on water or saccharin self-administration, nor in nondependent rats. The abundance of CDK5 or p35 was not altered in any of the brain regions analyzed. In the bed nucleus of the stria terminalis, CDK5 abundance was negatively correlated with intoxication levels during EtOH vapor exposure but there was no effect of dependence on the phosphorylation ratio of CDK5 substrates. In contrast, EtOH dependence increased the phosphorylation of low-molecular-weight CDK substrates in the basolateral amygdala (BLA).

CONCLUSIONS

The selective effect of (S)-CR8 on excessive EtOH intake has potential therapeutic value for the treatment of alcohol use disorders. Our data do not support the hypothesis that this effect would be mediated by the inhibition of up-regulated CDK5 activity in the extended amygdala nor prefrontal cortex. However, increased activity of CDKs other than CDK5 in the BLA may contribute to excessive EtOH consumption in alcohol dependence. Other (S)-CR8 targets may also be implicated.

Mechanisms Regulating the Association of Protein Phosphatase 1 with Spinophilin and Neurabin

Protein phosphorylation is a key mediator of signal transduction, allowing for dynamic regulation of substrate activity. Whereas protein kinases obtain substrate specificity by targeting specific amino acid sequences, serine/threonine phosphatase catalytic subunits are much more promiscuous in their ability to dephosphorylate substrates. To obtain substrate specificity, serine/threonine phosphatases utilize targeting proteins to regulate phosphatase subcellular localization and catalytic activity. Spinophilin and its homologue neurabin are two of the most abundant dendritic spine-localized protein phosphatase 1 (PP1) targeting proteins. The association between spinophilin and PP1 is increased in the striatum of animal models of Parkinson's disease (PD). However, mechanisms that regulate the association of spinophilin and neurabin with PP1 are unclear. Here, we report that the association between spinophilin and PP1α or PP1γ1 was increased by CDK5 expression and activation in a heterologous cell system. This increased association is at least partially due to phosphorylation of PP1. Conversely, CDK5 expression and activation decreased the association of PP1 with neurabin. As with dopamine depletion, methamphetamine (METH) abuse causes persistent alterations in dopamine signaling which influence striatal medium spiny neuron function and biochemistry. Moreover, both METH toxicity and dopamine depletion are associated with deficits in motor control and motor learning. Pathologically, we observed a decreased association of spinophilin with PP1 in rat striatum evaluated one month following a binge METH paradigm. Behaviorally, we found that loss of spinophilin recapitulates rotarod pathology previously observed in dopamine-depleted and METH-treated animals. Together, these data have implications in multiple disease states associated with altered dopamine signaling such as PD and psychostimulant drug abuse and delineate a novel mechanism by which PP1 interactions with spinophilin and neurabin may be differentially regulated.

Epigenetic Effects Induced by Methamphetamine and Methamphetamine-Dependent Oxidative Stress

Methamphetamine is a widely abused drug, which possesses neurotoxic activity and powerful addictive effects. Understanding methamphetamine toxicity is key beyond the field of drug abuse since it allows getting an insight into the molecular mechanisms which operate in a variety of neuropsychiatric disorders. In fact, key alterations produced by methamphetamine involve dopamine neurotransmission in a way, which is reminiscent of spontaneous neurodegeneration and psychiatric schizophrenia. Thus, understanding the molecular mechanisms operated by methamphetamine represents a wide window to understand both the addicted brain and a variety of neuropsychiatric disorders. This overlapping, which is already present when looking at the molecular and cellular events promoted immediately after methamphetamine intake, becomes impressive when plastic changes induced in the brain of methamphetamine-addicted patients are considered. Thus, the present manuscript is an attempt to encompass all the molecular events starting at the presynaptic dopamine terminals to reach the nucleus of postsynaptic neurons to explain how specific neurotransmitters and signaling cascades produce persistent genetic modifications, which shift neuronal phenotype and induce behavioral alterations. A special emphasis is posed on disclosing those early and delayed molecular events, which translate an altered neurotransmitter function into epigenetic events, which are derived from the translation of postsynaptic noncanonical signaling into altered gene regulation. All epigenetic effects are considered in light of their persistent changes induced in the postsynaptic neurons including sensitization and desensitization, priming, and shift of neuronal phenotype.

Effect of methamphetamine exposure on the plasma levels of endothelial-derived microparticles

BACKGROUND

Methamphetamine (Meth), a neurotoxin, induces inflammation, oxidative stress, and triggers endothelial dysfunction and cardiovascular disease which is the second cause of death among individuals with Meth-use disorder. Oxidative stress and inflammation trigger the microparticle (MP) release. These are extracellular vesicles extracted from cell surface and identified in biological fluids. MP levels alter during pathological conditions, suggesting its potential biomarker role. In this respect, we designed the present experiment to investigate the effects of Meth on the plasma level of the endothelial-derived microparticle (EMP).

METHODS

Animals received Meth (4 mg/kg i.p.) for 1, 7 and 14 days and then, the plasma level of EMPs was evaluated, using cell surface markers, including AnnexinV, CD144, CD31, CD41a antigens with the flow cytometry method. The biochemical indices and locomotor activity were also assessed in a rat model.

RESULTS

Meth increased locomotor activity (Meth-1, 277.12 ± 20.17; Meth-7, 262.25 ± 11.95; Meth-14, 265.75 ± 14.75), inflammatory and oxidative indices as evidenced by rising of the C-reactive protein (Meth-7, 39.4 ± 1.24; Meth-14, 38.58 ± 2.19, vs 8.65 ± 0.45, mg/L) and malondialdehyde (Meth-7, 9.74 ± 1.38; Meth-14, 14.6 ± 1.45, vs 4.43 ± 0.32 nmol/L) plasma levels. We also found that Meth triggered endothelial injury, as demonstrated by elevated levels of EMP (Meth-7, 4.77 ± 0.22; Meth-14, 5.91 ± 0.34, % total events/mL) compared with control group.

CONCLUSION

Our data showed that Meth exposure stimulates inflammatory and oxidative pathways and facilitates the EMPs shedding. Measuring the level of EMPs might be applied as a potential diagnostic index to monitor the endothelial dysfunction in substance-use disorders.

Cdk5 Is Essential for Amphetamine to Increase Dendritic Spine Density in Hippocampal Pyramidal Neurons

Psychostimulant drugs of abuse increase dendritic spine density in reward centers of the brain. However, little is known about their effects in the hippocampus, where activity-dependent changes in the density of dendritic spine are associated with learning and memory. Recent reports suggest that Cdk5 plays an important role in drug addiction, but its role in psychostimulant's effects on dendritic spines in hippocampus remain unknown. We used in vivo and in vitro approaches to demonstrate that amphetamine increases dendritic spine density in pyramidal neurons of the hippocampus. Primary cultures and organotypic slice cultures were used for cellular, molecular, pharmacological and biochemical analyses of the role of Cdk5/p25 in amphetamine-induced dendritic spine formation. Amphetamine (two-injection protocol) increased dendritic spine density in hippocampal neurons of thy1-green fluorescent protein (GFP) mice, as well as in hippocampal cultured neurons and organotypic slice cultures. Either genetic or pharmacological inhibition of Cdk5 activity prevented the amphetamine-induced increase in dendritic spine density. Amphetamine also increased spine density in neurons overexpressing the strong Cdk5 activator p25. Finally, inhibition of calpain, the protease necessary for the conversion of p35 to p25, prevented amphetamine's effect on dendritic spine density. We demonstrate, for the first time, that amphetamine increases the density of dendritic spine in hippocampal pyramidal neurons in vivo and in vitro. Moreover, we show that the Cdk5/p25 signaling and calpain activity are both necessary for the effect of amphetamine on dendritic spine density. The identification of molecular mechanisms underlying psychostimulant effects provides novel and promising therapeutic approaches for the treatment of drug addiction.

Potential for targeting dopamine/DARPP-32 signaling in neuropsychiatric and neurodegenerative disorders

INTRODUCTION

Alterations in dopamine neurotransmission has been implicated in pathophysiology of neuropsychiatric and neurodegenerative disorders, and DARPP-32 plays a pivotal role in dopamine neurotransmission. DARPP-32 likely influences dopamine-mediated behaviors in animal models of neuropsychiatric and neurodegenerative disorders and therapeutic effects of pharmacological treatment. Areas covered: We will review animal studies on the biochemical and behavioral roles of DARPP-32 in drug addiction, schizophrenia and Parkinson's disease. In general, under physiological and pathophysiological conditions, DARPP-32 in D1 receptor expressing (D1R) -medium spiny neurons (MSNs) promotes dopamine/D1 receptor/PKA signaling, whereas DARPP-32 in D2 receptor expressing (D2R)-MSNs counteracts dopamine/D2 receptor signaling. However, the function of DARPP-32 is differentially regulated in acute and chronic phases of drug addiction; DARPP-32 enhances D1 receptor/PKA signaling in the acute phase, whereas DARPP-32 suppresses D1 receptor/PKA signaling in the chronic phase through homeostatic mechanisms. Therefore, DARPP-32 plays a bidirectional role in dopamine neurotransmission, depending on the cell type and experimental conditions, and is involved in dopamine-related behavioral abnormalities. Expert opinion: DARPP-32 differentially regulates dopamine signaling in D1R- and D2R-MSNs, and a shift of balance between D1R- and D2R-MSN function is associated with behavioral abnormalities. An adjustment of this imbalance is achieved by therapeutic approaches targeting DARPP-32-related signaling molecules.

TFP5, a Peptide Inhibitor of Aberrant and Hyperactive Cdk5/p25, Attenuates Pathological Phenotypes and Restores Synaptic Function in CK-p25Tg Mice

It has been reported that cyclin-dependent kinase 5 (cdk5), a critical neuronal kinase, is hyperactivated in Alzheimer's disease (AD) and may be, in part, responsible for the hallmark pathology of amyloid plaques and neurofibrillary tangles (NFTs). It has been proposed by several laboratories that hyperactive cdk5 results from the overexpression of p25 (a truncated fragment of p35, the normal cdk5 regulator), which, when complexed to cdk5, induces hyperactivity, hyperphosphorylated tau/NFTs, amyloid-β plaques, and neuronal death. It has previously been shown that intraperitoneal (i.p.) injections of a modified truncated 24-aa peptide (TFP5), derived from the cdk5 activator p35, penetrated the blood-brain barrier and significantly rescued AD-like pathology in 5XFAD model mice. The principal pathology in the 5XFAD mutant, however, is extensive amyloid plaques; hence, as a proof of concept, we believe it is essential to demonstrate the peptide's efficacy in a mouse model expressing high levels of p25, such as the inducible CK-p25Tg model mouse that overexpresses p25 in CamKII positive neurons. Using a modified TFP5 treatment, here we show that peptide i.p. injections in these mice decrease cdk5 hyperactivity, tau, neurofilament-M/H hyperphosphorylation, and restore synaptic function and behavior (i.e., spatial working memory, motor deficit using Rota-rod). It is noteworthy that TFP5 does not inhibit endogenous cdk5/p35 activity, nor other cdks in vivo suggesting it might have no toxic side effects, and may serve as an excellent therapeutic candidate for neurodegenerative disorders expressing abnormally high brain levels of p25 and hyperactive cdk5.

Deficits in behavioral sensitization and dopaminergic responses to methamphetamine in adenylyl cyclase 1/8-deficient mice

The cAMP/protein kinase A pathway regulates methamphetamine (METH)-induced neuroplasticity underlying behavioral sensitization. We hypothesize that adenylyl cyclases (AC) 1/8 mediate these neuroplastic events and associated striatal dopamine regulation. Locomotor responses to METH (1 and 5 mg/kg) and striatal dopamine function were evaluated in mice lacking AC 1/8 (DKO) and wild-type (WT) mice. Only 5 mg/kg METH induced an acute locomotor response in DKO mice, which was significantly attenuated versus WT controls. DKO mice showed a marked attenuation in the development and expression of METH-induced behavioral sensitization across doses relative to WT controls. While basal and acute METH (5 mg/kg)-evoked accumbal dialysate dopamine levels were similar between genotypes, saline-treated DKO mice showed elevated tissue content of dopamine and homovanillic acid in the dorsal striatum (DS), reflecting dysregulated dopamine homeostasis and/or metabolism. Significant reductions in DS dopamine levels were observed in METH-sensitized DKO mice compared to saline-treated controls, an effect not observed in WT mice. Notably, saline-treated DKO mice had significantly increased phosphorylated Dopamine- and cAMP-regulated phosphoprotein levels, which were not further augmented following METH sensitization, as observed in WT mice. These data indicate that AC 1/8 are critical to mechanisms subserving drug-induced behavioral sensitization and mediate nigrostriatal pathway METH sensitivity. Calcium/calmodulin-stimulated adenylyl cyclase (AC) isoforms 1 and 8 were studied for their involvement in the adaptive neurobehavioral responses to methamphetamine. AC 1/8 double knockout (DKO) mice showed heightened basal locomotor activity and dorsal striatal dopamine responsivity. Conversely, methamphetamine-induced locomotor activity was attenuated in DKO mice, accompanied by reductions in dopamine and HVA content and impaired DARPP-32 activation. These findings indicate AC 1/8 signaling regulates the sensitivity of the nigrostriatal pathway subserving stimulant and neuroadaptive sensitizing effects of methamphetamine. 3-MT, 3-methoxytyramine; Ca(2+), calcium; CaM, calmodulin; cdk5; cyclin-dependent kinase 5; DA, dopamine; DARPP-32, dopamine- and cAMP-regulated phosphoprotein; D1R, dopamine D1 receptor; HVA, homovanillic acid; PKA, protein kinase A.

A new treatment for cognitive disorders related to in utero exposure to alcohol

Maternal alcohol consumption during pregnancy has detrimental effects on fetal central nervous system development. Maternal alcohol consumption prior to and during pregnancy significantly affects cognitive functions in offspring, which may be related to changes in cyclin-dependent kinase 5 because it is associated with modulation of synaptic plasticity and impaired learning and memory. In this study, we examined adult offspring in a maternal alcohol consumption model in rats. Y-maze test results showed that in utero exposure to alcohol impairs learning and memory capacities. Cyclin-dependent kinase 5 mRNA and protein expressions in the hippocampus of the offspring were significantly elevated, as assayed by quantitative real-time PCR and reverse transcription-PCR, immunofluorescence, and immuno-precipitation. Our experimental findings strongly suggest that altered cyclin-dependent kinase 5 may mediate impaired learning and memory in adult rats that were exposed to alcohol by maternal consumption while in utero.

Cyclin-dependent kinase 5 (Cdk5) regulates the function of CLOCK protein by direct phosphorylation

Circadian rhythm is a biological rhythm governing physiology and behavior with a period of ∼24 h. At the molecular level, circadian output is controlled by a molecular clock composed of positive and negative feedback loops in transcriptional and post-translational processes. CLOCK is a transcription factor known as a central component of the molecular clock feedback loops generating circadian oscillation. Although CLOCK is known to undergo multiple post-translational modifications, the knowledge of their entities remains limited. Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine-threonine kinase that is involved in various neuronal processes. Here, we report that Cdk5 is a novel regulator of CLOCK protein. Cdk5 phosphorylates CLOCK at the Thr-451 and Thr-461 residues in association with transcriptional activation of CLOCK. The Cdk5-dependent regulation of CLOCK function is mediated by alterations of its stability and subcellular distribution. These results suggest that Cdk5 is a novel regulatory component of the core molecular clock machinery.

Short and long access to cocaine self-administration activates tyrosine phosphatase STEP and attenuates GluN expression but differentially regulates GluA expression in the prefrontal cortex

RATIONALE

Dephosphorylation of extracellular signal-regulated kinase (ERK) and cyclic AMP response element binding protein (CREB) in the dorsomedial prefrontal cortex (dmPFC) at the end of short access (ShA) cocaine self-administration is implicated in cocaine seeking. However, what receptors and phosphatases mediate this effect and whether ERK/CREB and related phospho-proteins in the dmPFC react similarly during early withdrawal from long access (LgA) cocaine self-administration are unknown.

OBJECTIVES

The effects of ShA vs. LgA cocaine self-administration on the phosphorylation of protein phosphatase 2A (PP2A) and striatal-enriched protein tyrosine phosphatase (STEP), as well as GluN and GluA receptor subtype expression in the dmPFC during early withdrawal, were compared.

METHODS

Rats self-administered cocaine or received saline during 2- or 6-h daily sessions for 10-11 days. Two hours after the final session, the dmPFC was dissected out and processed for immunoblotting.

RESULTS

Similar to previous findings after ShA cocaine, phospho-ERK and phospho-CREB in the dmPFC were decreased after LgA cocaine. Cocaine elevated phospho-PP2A (deactivation) and decreased phospho-STEP (activation) in both ShA and LgA cocaine rats. GluN1, GluN2B, and phospho-GluN2B Tyr1472 in the dmPFC were decreased after ShA and LgA cocaine. Further, a significant reduction of GluA2, GluA1, and phospho-GluA1 Ser845 was found only in LgA rats.

CONCLUSIONS

Activation of phospho-STEP may underlie ERK and CREB dephosphorylation in the dmPFC as well as internalization and degradation of GluN complexes during early withdrawal from both ShA and LgA cocaine self-administration, whereas differential alteration of AMPA receptor subunits after ShA and LgA cocaine self-administration depends on cocaine intake.

Up-regulation of protein tyrosine nitration in methamphetamine-induced neurotoxicity through DDAH/ADMA/NOS pathway

Protein tyrosine nitration is an important post-translational modification mediated by nitric oxide (NO) associated oxidative stress, occurring in a variety of neurodegenerative diseases. In our previous study, an elevated level of dimethylarginine dimethylaminohydrolase 1 (DDAH1) protein was observed in different brain regions of acute methamphetamine (METH) treated rats, indicating the possibility of an enhanced expression of protein nitration that is mediated by excess NO through the DDAH1/ADMA (Asymmetric Dimethylated l-arginine)/NOS (Nitric Oxide Synthase) pathway. In the present study, proteomic methods, including stable isotope labeling with amino acids in cell culture (SILAC) and two dimensional electrophoresis, were used to determine the relationship between protein nitration and METH induced neurotoxicity in acute METH treated rats and PC12 cells. We found that acute METH administration evokes a positive activation of DDAH1/ADMA/NOS pathway and results in an over-production of NO in different brain regions of rat and PC12 cells, whereas the whole signaling could be repressed by DDAH1 inhibitor N(ω)-(2-methoxyethyl)-arginine (l-257). In addition, enhanced expressions of 3 nitroproteins were identified in rat striatum and increased levels of 27 nitroproteins were observed in PC12 cells. These nitrated proteins are key factors for Cdk5 activation, cytoskeletal structure, ribosomes function, etc. l-257 also displayed significant protective effects against METH-induced protein nitration, apoptosis and cell death. The overall results illustrate that protein nitration plays a significant role in the acute METH induced neurotoxicity via the activation of DDAH1/ADMA/NOS pathway.

Cdk5: An Emerging Kinase in Pain Signaling

Pain is an important survival mechanism for an organism. It can turn into severe mental and physical disorder however, if the molecular and/or cellular pathways involved in pain signaling are altered. Chronic pain is characterized by an altered pain perception that includes allodynia (a response to a normally non-noxious stimulus) and hyperalgesia (an exaggerated response to a normally noxious stimulus). Past few years of pain research has been mainly focused on precise understanding of the molecular and cellular nociceptive signatures altered during chronic pain, so that more effective pain relievers can be developed. The importance of protein kinases in normal cellular homeostasis and disease pathogenesis has evolved rapidly in the past few decades. The recent advancement defining the role of multiple protein kinases in regulating neuronal plasticity and pain sensitization has gained enough attention of pharmaceutical industry to develop specific and selective kinase inhibitors as analgesics. Cyclin-dependent kinase 5 (Cdk5) is one such emerging kinase in pain biology. We will discuss here the recent advancement and therapeutic potential of Cdk5 in pain signaling.

Dopamine D2 receptor-mediated Akt/PKB signalling: initiation by the D2S receptor and role in quinpirole-induced behavioural activation

The short and long isoforms of the dopamine D2 receptor (D2S and D2L respectively) are highly expressed in the striatum. Functional D2 receptors activate an intracellular signalling pathway that includes a cAMP-independent route involving Akt/GSK3 (glycogen synthase kinase 3). To investigate the Akt/GSK3 response to the seldom-studied D2S receptor, we established a rat D2S receptor-expressing cell line [HEK (human embryonic kidney)-293/rD2S]. We found that in HEK-293/rD2S cells, the D2/D3 agonists bromocriptine and quinpirole significantly induced Akt and GSK3 phosphorylation, as well as ERK1/2 (extracellular-signal-regulated kinase 1/2) activation. The D2S receptor-induced Akt signals were profoundly inhibited by the internalization blockers monodansyl cadaverine and concanavalin A. Activation of the D2S receptor in HEK-293/rD2S cells appeared to trigger Akt/phospho-Akt translocation to the cell membrane. In addition to our cell culture experiments, we studied D2 receptor-dependent Akt in vivo by systemic administration of the D2/D3 agonist quinpirole. The results show that quinpirole evoked Akt-Ser⁴⁷³ phosphorylation in the ventral striatum. Furthermore, intra-accumbens administration of wortmannin, a PI3K (phosphoinositide 3-kinase) inhibitor, significantly suppressed the quinpirole-evoked behavioural activation. Overall, we demonstrate that activation of the dopamine D2S receptor stimulates Akt/GSK3 signalling. In addition, in vivo Akt activity in the ventral striatum appears to play an important role in systemic D2/D3 agonist-induced behavioural activation.

Increased Cdk5/p35 activity in the dentate gyrus mediates depressive-like behaviour in rats

Depression is one of the most pervasive and debilitating psychiatric diseases, and the molecular mechanisms underlying the pathophysiology of depression have not been elucidated. Cyclin-dependent kinase 5 (Cdk5) has been implicated in synaptic plasticity underlying learning, memory, and neuropsychiatric disorders. However, whether Cdk5 participates in the development of depressive diseases has not been examined. Using the chronic mild stress (CMS) procedure, we examined the effects of Cdk5/p35 activity in the hippocampus on depressive-like behaviour in rats. We found that CMS increased Cdk5 activity in the hippocampus, accompanied by translocation of neuronal-specific activator p35 from the cytosol to the membrane in the dentate gyrus (DG) subregion. Inhibition of Cdk5 in DG but not in the cornu ammonis 1 (CA1) or CA3 hippocampal subregions inhibited the development of depressive-like symptoms. Overexpression of p35 in DG blocked the antidepressant-like effect of venlafaxine in the CMS model. Moreover, the antidepressants venlafaxine and mirtazapine, but not the antipsychotic aripiprazole, reduced Cdk5 activity through the redistribution of p35 from the membrane to the cytosol in DG. Our results showed that the development of depressive-like behaviour is associated with increased Cdk5 activity in the hippocampus and that the Cdk5/p35 complex plays a key role in the regulation of depressive-like behaviour and antidepressant actions.

Basolateral amygdala cdk5 activity mediates consolidation and reconsolidation of memories for cocaine cues

Cocaine use and relapse involves learned associations between cocaine-associated environmental contexts and discrete stimuli and cocaine effects. Initially, these contextual and discrete cues undergo memory consolidation after being paired with cocaine exposure. During abstinence, cocaine cue memories can undergo memory reconsolidation after cue exposure without the drug. We used a conditioned place preference (CPP) procedure in rats to study the role of neuronal protein kinase cyclin-dependent kinase 5 (Cdk5) in consolidation and reconsolidation of cocaine cue memories. We found that the expression of cocaine CPP in drug-free tests 1 d after CPP training (four pairings of 10 mg/kg cocaine with one context and four pairings of saline with a different context) increased Cdk5 activity, and levels of the Cdk5 activator p35 in basolateral but not central amygdala. We also found that basolateral (but not central) amygdala injections of the Cdk5 inhibitor beta-butyrolactone (100 ng/side) immediately (but not 6 h) after cocaine-context pairings during training prevented subsequent cocaine CPP expression. After training, acute basolateral (but not central) amygdala beta-butyrolactone injections immediately before testing prevented the expression of cocaine CPP; this effect was also observed on a second test performed 1 d later, suggesting an effect on reconsolidation of cocaine cue memories. In support, basolateral beta-butyrolactone injections, given immediately (but not 6 h) after a single exposure to the cocaine-paired context, prevented cocaine CPP expression 1 and 14 d after the injections. Results indicate that basolateral amygdala Cdk5 activity is critical for consolidation and reconsolidation of the memories of cocaine-associated environmental cues.

Methamphetamine acts on subpopulations of neurons regulating sexual behavior in male rats

Methamphetamine (Meth) is a highly addictive stimulant. Meth abuse is commonly associated with the practice of sexual risk behavior and increased prevalence of Human Immunodeficiency Virus and Meth users report heightened sexual desire, arousal, and sexual pleasure. The biological basis for this drug-sex nexus is unknown. The current study demonstrates that Meth administration in male rats activates neurons in brain regions of the mesolimbic system that are involved in the regulation of sexual behavior. Specifically, Meth and mating co-activate cells in the nucleus accumbens core and shell, basolateral amygdala, and anterior cingulate cortex. These findings illustrate that in contrast to current belief drugs of abuse can activate the same cells as a natural reinforcer, that is sexual behavior, and in turn may influence compulsive seeking of this natural reward.

The internal state of medium spiny neurons varies in response to different input signals

BACKGROUND

Parkinson's disease, schizophrenia, Huntington's chorea and drug addiction are manifestations of malfunctioning neurons within the striatum region at the base of the human forebrain. A key component of these neurons is the protein DARPP-32, which receives and processes various types of dopamine and glutamate inputs and translates them into specific biochemical, cellular, physiological, and behavioral responses. DARPP-32's unique capacity of faithfully converting distinct neurotransmitter signals into appropriate responses is achieved through a complex phosphorylation-dephosphorylation system that evades intuition and predictability.

RESULTS

To gain deeper insights into the functioning of the DARPP-32 signal transduction system, we developed a dynamic model that is robust and consistent with available clinical, pharmacological, and biological observations. Upon validation, the model was first used to explore how different input signal scenarios are processed by DARPP-32 and translated into distinct static and dynamic responses. Secondly, a comprehensive perturbation analysis identified the specific role of each component on the system's signal transduction ability.

CONCLUSIONS

Our study investigated the effects of various patterns of neurotransmission on signal integration and interpretation by DARPP-32 and showed that the DARPP-32 system has the capability of discerning surprisingly many neurotransmission scenarios. We also screened out potential mechanisms underlying this capability of the DARPP-32 system. This type of insight deepens our understanding of neuronal signal transduction in normal medium spiny neurons, sheds light on neurological disorders associated with the striatum, and might aid the search for intervention targets in neurological diseases and drug addiction.

The D(3) dopamine receptor inhibits dopamine release in PC-12/hD3 cells by autoreceptor signaling via PP-2B, CK1, and Cdk-5

The function of the D(3) dopamine (DA) receptor remains ambiguous largely because of the lack of selective D(3) receptor ligands. To investigate the function and intracellular signaling of D(3) receptors, we established a PC-12/hD3 clone, which expresses the human D(3) DA receptor in a DA producing cell line. In this model, we find that the D(3) receptor functions as an autoreceptor controlling neurotransmitter secretion. Pre-treatment with 3,6a,11, 14-tetrahydro-9-methoxy-2 methyl-(12H)-isoquino[1,2-b] pyrrolo[3,2-f][1,3] benzoxanzine-1-carboxylic acid, a D(3) receptor preferring agonist, dose-dependently suppressed K+-evoked [3H]DA release in PC-12/hD3 cells but not in the control cell line. This effect was prevented by D(3) receptor preferring antagonists GR103691 and SB277011-A. Furthermore, activation of D(3) receptors significantly inhibits forskolin-induced cAMP accumulation and leads to transient increases in phosphorylation of cyclin-dependent kinase 5 (Cdk5), dopamine and cAMP-regulated phosphoprotein of M(r) 32 000 and Akt. Because we observed differences in Cdk5 phosphorylation as well as Akt phosphorylation after DA stimulation, we probed the ability of Cdk5 and phosphatidylinositol-3 kinase (PI3K) to influence DA release. Cdk5 inhibitors, roscovitine, or olomoucine, but not the PI3K inhibitor wortmannin, blocked the D(3) receptor inhibition of DA release. In a complimentary experiment, over-expression of Cdk5 potentiated D(3) receptor suppression of DA release. Pertussis toxin, 3-[(2,4,6-trimethoxyphenyl)methylidenyl]-indolin-2-one and cyclosporine A also attenuated D(3) receptor-mediated inhibition of DA release indicating that this phenomenon acts through Gi/oalpha and casein kinase 1, and phosphatase protein phosphatase 2B (calcineurin), respectively. In support of previous data that D(3) DA receptors reduce transmitter release from nerve terminals, the current results demonstrate that D(3) DA receptors function as autoreceptors to inhibit DA release and that a signaling pathway involving Cdk5 is essential to this regulation.

Caffeine and a selective adenosine A2A receptor antagonist induce reward and sensitization behavior associated with increased phospho-Thr75-DARPP-32 in mice

RATIONALE

Caffeine, an antagonist of adenosine A(1) and A(2A) receptor, is the most widely used psychoactive substance in the world. Evidence indicates that caffeine interacts with the neuronal systems involved in drug reinforcing. Although adenosine A(1) and/or A(2A) receptor have been found to play important roles in the locomotor stimulation and probably reinforcing effect of caffeine, the relative contribution of the A(1) and/or A(2A) receptors to the acute and chronic motor activation and reinforcing effects of caffeine has not been completely investigated.

OBJECTIVE

The roles of adenosine A(1) and/or A(2A) receptor and the association of phospho-Thr75-dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) in the motor activation and reinforcing effects of caffeine, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective A(1) antagonist, and 5-amino-7-(beta-phenylethyl)-2-(8-furyl) pyrazolol [4,3-e]-1,2,4-triazolol [1,5-c] pyrimidine (SCH58261), a selective A(2A) receptor antagonist were examined.

METHODS

Locomotor stimulation and behavioral sensitization of caffeine, DPCPX, and SCH58261 were studied in C57BL/6 male mice following acute and chronic administration. Conditioned place preference (CPP) paradigm was used to evaluate the drug-seeking potential of these compounds. Furthermore, the expression of phospho-Thr75-DARPP-32 in striatal membrane from behaviorally sensitized mice was analyzed by Western blot.

RESULTS

Caffeine and SCH58261 but not DPCPX induced CPP and locomotor sensitization in C57BL/6 mice. The locomotor sensitization after chronic treatment was associated with increased DARPP-32 phosphorylation at Thr75 in the striatum.

CONCLUSION

Caffeine-induced reinforcing effect and behavioral sensitization are mediated by antagonism at adenosine A(2A) receptor. These effects are associated with phosphorylation of DARPP-32 at Thr75 in the striatum.

Intermittent Dopaminergic stimulation causes behavioral sensitization in the addicted brain and parkinsonism

The gold standard therapy for Parkinson's disease (PD) consists in chronic administration of pulses of the dopamine (DA) precursor l-dihydroxyphenylalanine (l-DOPA). Although the main brain area which is DA-deficient is the dorsal striatum (more the putamen than the caudate nucleus), other DA-innervated brain regions (i.e., the ventral striatum and other limbic areas) are affected by systemic administration of l-DOPA. While such a therapy produces an increase in synaptic and nonsynaptic DA, which replace the neurotransmitter deficiency, peaks of extracellular DA in the course of disease progression produce abnormal involuntary movements related to behavioral sensitization. Methamphetamine (METH), a widely abused drug, is known to produce behavioral sensitization, related to DA release (more in the ventral than dorsal striatum as well as other limbic regions). The present review discusses the overlapping between these treatments, based on pulses of DA stimulation with an emphasis on the class of DA receptors; signal transduction pathways; rearranged expression of neurotransmitters, cotransmitters, and their receptors coupled with ultrastructural changes. In fact, all these levels of synaptic plasticity show a surprising homology following these treatments, posing the mechanisms of behavioral sensitization during DA-replacement therapy in PD very close to the neurobiological mechanisms operating during METH abuse. In line with this view is the growing evidence of addictive behaviors in PD patients during the course of DA-replacement therapy.

Transient enhanced expression of Cdk5 activator p25 after acute and chronic d-amphetamine administration

The cellular and molecular mechanisms of sensitization in the addictive process are still unclear. Recently, chronic treatment with cocaine has been shown to upregulate the expression of cyclin-dependent kinase 5 (cdk5) and its specific activator, p35, in the striatum, as a downstream target gene of DeltaFosB, and has been implicated in compensatory adaptive changes associated with psychostimulants. Cdk5 is a serine/threonine kinase and its activation is achieved through association with a regulatory subunit, either p35 or p39. P35 is cleaved by the protease calpain, which results in the generation of a truncated product termed p25, which contains all elements necessary for cdk5 activation. The cdk5/p35 complex plays an essential role in neuronal development and survival. It has also been involved in neuronal trafficking and transport and in dopaminergic transmission, indicating its role either in presynaptic and postsynaptic signaling. In this study we report that the cdk5/p35 complex participates in acute and chronic d-amphetamine (AMPH)-evoked behavioral events, and we show a surprisingly transient enhanced expression of p25 and a lasting increased expression of p35 in dorsal striatal synaptosomes after acute and chronic AMPH administration. Pak1, a substrate for cdk5, is also enriched in the synaptosomal fraction of acute AMPH-treated rats. Our data suggest that the transient upregulation of p25 may regulate the activity of cdk5 in phosphorylating particular substrates, such as Pak1, implicated in the compensatory adaptive morphophysiologic changes associated with the process of behavioral sensitization to psychostimulants.

Quantitative trait locus analysis identifies rat genomic regions related to amphetamine-induced locomotion and Galpha(i3) levels in nucleus accumbens

Identification of the genetic factors that underlie stimulant responsiveness in animal models has significant implications for better understanding and treating stimulant addiction in humans. F(2) progeny derived from parental rat strains F344/NHsd and LEW/NHsd, which differ in responses to drugs of abuse, were used in quantitative trait locus (QTL) analyses to identify genomic regions associated with amphetamine-induced locomotion (AIL) and G-protein levels in the nucleus accumbens (NAc). The most robust QTLs were observed on chromosome 3 (maximal log ratio statistic score (LRS(max))=21.3) for AIL and on chromosome 2 (LRS(max)=22.0) for Galpha(i3). A 'suggestive' QTL (LRS(max)=12.5) was observed for AIL in a region of chromosome 2 that overlaps with the Galpha(i3) QTL. Novelty-induced locomotion (NIL) showed different QTL patterns from AIL, with the most robust QTL on chromosome 13 (LRS(max)=12.2). Specific unique and overlapping genomic regions influence AIL, NIL, and inhibitory G-protein levels in the NAc. These findings suggest that common genetic mechanisms influence certain biochemical and behavioral aspects of stimulant responsiveness.

Protein kinases and addiction

Although drugs of abuse have different chemical structures and interact with different protein targets, all appear to usurp common neuronal systems that regulate reward and motivation. Addiction is a complex disease that is thought to involve drug-induced changes in synaptic plasticity due to alterations in cell signaling, gene transcription, and protein synthesis. Recent evidence suggests that drugs of abuse interact with and change a common network of signaling pathways that include a subset of specific protein kinases. The best studied of these kinases are reviewed here and include extracellular signal-regulated kinase, cAMP-dependent protein kinase, cyclin-dependent protein kinase 5, protein kinase C, calcium/calmodulin-dependent protein kinase II, and Fyn tyrosine kinase. These kinases have been implicated in various aspects of drug addiction including acute drug effects, drug self-administration, withdrawal, reinforcement, sensitization, and tolerance. Identifying protein kinase substrates and signaling pathways that contribute to the addicted state may provide novel approaches for new pharmacotherapies to treat drug addiction.

Valproate and acetyl-L-carnitine prevent methamphetamine-induced behavioral sensitization in mice

This study deals with the possible inhibitory role played by acetyl-l-carnitine (ALC) against methamphetamine (METH)-induced behavioral sensitization. Because valproate (VAL) inhibits the behavioral sensitization exerted by different psychostimulants, we investigated ALC's potential to prevent the amplification of METH-mediated psychomotor effects. We therefore evaluated the locomotor effects of VAL or ALC alone or in combination with METH after acute (day 1) as well as repeated (day 7) drug challenge. Finally, to assess the induction of behavioral sensitization, we also recorded the METH-mediated locomotor response after 7 days of drug suspension (day 15). Results showed that both VAL and ALC prevented the METH-induced sensitization. Another interesting observation was the significantly higher METH-induced hyperactivity at day 15 (after a 7-day drug-free period), indicating that behavioral sensitization developed during the washout period. Results also showed that both the acute and repeated coadministration of METH with either VAL or ALC inhibited METH-induced hyperactivity. We present different hypotheses concerning similar but also peculiar mechanisms that might underlie the preventive action of VAL and ALC. These data add to a growing body of literature that illustrates the potential of ALC in protecting against the insult of dysfunctional mitochondrial metabolism and psychostimulant-mediated neurotoxicity. By demonstrating an in vivo action against one of the most abused drugs, these results raise the possibility of beneficial effects of ALC in abuse behavior.

Cdk5 modulates cocaine reward, motivation, and striatal neuron excitability

Cyclin-dependent kinase 5 (Cdk5) regulates dopamine neurotransmission and has been suggested to serve as a homeostatic target of chronic psychostimulant exposure. To study the role of Cdk5 in the modulation of the cellular and behavioral effects of psychoactive drugs of abuse, we developed Cre/loxP conditional knock-out systems that allow temporal and spatial control of Cdk5 expression in the adult brain. Here, we report the generation of Cdk5 conditional knock-out (cKO) mice using the alphaCaMKII promoter-driven Cre transgenic line (CaMKII-Cre). In this model system, loss of Cdk5 in the adult forebrain increased the psychomotor-activating effects of cocaine. Additionally, these CaMKII-Cre Cdk5 cKO mice show enhanced incentive motivation for food as assessed by instrumental responding on a progressive ratio schedule of reinforcement. Behavioral changes were accompanied by increased excitability of medium spiny neurons in the nucleus accumbens (NAc) in Cdk5 cKO mice. To study NAc-specific effects of Cdk5, another model system was used in which recombinant adeno-associated viruses expressing Cre recombinase caused restricted loss of Cdk5 in NAc neurons. Targeted knock-out of Cdk5 in the NAc facilitated cocaine-induced locomotor sensitization and conditioned place preference for cocaine. These results suggest that Cdk5 acts as a negative regulator of neuronal excitability in the NAc and that Cdk5 may govern the behavioral effects of cocaine and motivation for reinforcement.

Morphine-induced analgesic tolerance, locomotor sensitization and physical dependence do not require modification of mu opioid receptor, cdk5 and adenylate cyclase activity

Acute morphine administration produces analgesia and reward, but prolonged use may lead to analgesic tolerance in patients chronically treated for pain and to compulsive intake in opioid addicts. Moreover, long-term exposure may induce physical dependence, manifested as somatic withdrawal symptoms in the absence of the drug. We set up three behavioral paradigms to model these adaptations in mice, using distinct regimens of repeated morphine injections to induce either analgesic tolerance, locomotor sensitization or physical dependence. Interestingly, mice tolerant to analgesia were not sensitized to hyperlocomotion, whereas sensitized mice displayed some analgesic tolerance. We then examined candidate molecular modifications that could underlie the development of each behavioral adaptation. First, analgesic tolerance was not accompanied by mu opioid receptor desensitization in the periaqueductal gray. Second, cdk5 and p35 protein levels were unchanged in caudate-putamen, nucleus accumbens and prefrontal cortex of mice displaying locomotor sensitization. Finally, naloxone-precipitated morphine withdrawal did not enhance basal or forskolin-stimulated adenylate cyclase activity in nucleus accumbens, prefrontal cortex, amygdala, bed nucleus of stria terminalis or periaqueductal gray. Therefore, the expression of behavioral adaptations to chronic morphine treatment was not associated with the regulation of micro opioid receptor, cdk5 or adenylate cyclase activity in relevant brain areas. Although we cannot exclude that these modifications were not detected under our experimental conditions, another hypothesis is that alternative molecular mechanisms, yet to be discovered, underlie analgesic tolerance, locomotor sensitization and physical dependence induced by chronic morphine administration.

The role of the cannabinoid type 1 receptor and down-stream cAMP/DARPP-32 signal in the nucleus accumbens of methamphetamine-sensitized rats

Blockade of the cannabinoid type 1 (CB(1)) receptor could suppress methamphetamine self-administration; however, the cellular mechanism remains unclear. In this study, we intended to investigate the significance of brain CB(1) receptors on the development of behavioral sensitization to methamphetamine. Male Sprague-Dawley rats treated with chronic methamphetamine (4 mg/kg, i.p.) for either 7 or 14 days developed behavioral sensitization to methamphetamine (1 mg/kg) at withdrawal day 7. A progressive decrease in numbers of CB(1) receptor (both Bmax and mRNA) but increase in binding affinity (Kd) was noticed during withdrawal days 3 to 7. Microinjection of CB(1) antagonist [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide] into the nucleus accumbens (NAc) at withdrawal day 7, significantly suppressed the behavioral sensitization to methamphetamine. In NAc brain slices preparation, acute incubation with CB(1) agonist (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP 55940) dose-dependently enhanced cAMP accumulation in sensitized rats; no change was noticed in control groups. Consequently, treatment of CP 55940 induced a dose-dependent (10 nmol/L-10 micromol/L) phosphorylation on down-stream dopamine and cAMP-regulated phosphoprotein of Mr 32 000 (DARPP-32)/Thr34 in sensitized rats, while only 10 micromol/L CP 55940 was able to enhance the phosphoDARPP-32/T34 in control groups. Alternatively, both basal activity of calcineurin (PP-2B) and CP 55940-induced changes in the amount of PP-2B in the NAc were both decreased in sensitized rats, but not in controls. Overall, we demonstrated that brain CB(1) receptor and its down-stream cAMP/DARPP-32/T34/PP-2B signaling are profoundly altered in methamphetamine-sensitized animals.

Activation of the cAMP/PKA/DARPP-32 signaling pathway is required for morphine psychomotor stimulation but not for morphine reward

Activation of the cAMP/PKA pathway in the dopaminoceptive neurons of the striatum has been proposed to mediate the actions of various classes of drugs of abuse. Here, we show that, in the mouse nucleus accumbens and dorsal striatum, acute administration of morphine resulted in an increase in the state of phosphorylation of the dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) at Thr34, without affecting phosphorylation at Thr75. The ability of morphine to stimulate Thr34 phosphorylation was prevented by blockade of dopamine D1 receptors. DARPP-32 knockout mice and T34A DARPP-32 mutant mice displayed a lower hyperlocomotor response to a single injection of morphine than wild-type controls. In contrast, in T75A DARPP-32 mutant mice, morphine-induced psychomotor activation was indistinguishable from that of wild-type littermates. In spite of their reduced response to the acute hyperlocomotor effect of morphine, DARPP-32 knockout mice and T34A DARPP-32 mutant mice were able to develop behavioral sensitization to morphine comparable to that of wild-type controls and to display morphine conditioned place preference. These results demonstrate that dopamine D1 receptor-mediated activation of the cAMP/DARPP-32 cascade in striatal medium spiny neurons is involved in the psychomotor action, but not in the rewarding properties, of morphine.

Structure-activity relationships of 3,4-dihydro-1H-quinazolin-2-one derivatives as potential CDK5 inhibitors

Cyclin-dependent kinase 5 (CDK5) is a serine/threonine kinase that plays a critical role in the early development of the nervous system. Deregulation of CDK5 is believed to contribute to the abnormal phosphorylation of various cellular substrates associated with neurodegenerative disorders such as Alzheimer's disease, amyotrophic lateral sclerosis, and ischemic stroke. Acyclic urea 3 was identified as a potent CDK5 inhibitor and co-crystallographic data of urea 3/CDK2 enzyme were used to design a novel series of 3,4-dihydroquinazolin-2(1H)-ones as CDK5 inhibitors. In this investigation we present our synthetic studies toward this series of compounds and discuss their biological relevance as CDK5 inhibitors.

Peroxisome proliferator-activated receptor gamma activation relieves expression of behavioral sensitization to methamphetamine in mice

Peroxisome proliferator-activated receptor (PPAR) is a ligand-activated transcriptional factor that regulates lipid metabolism and inflammation. Behavioral sensitization is an experimental model of psychostimulant psychosis; it is elicited by repeated administration of psychostimulants and has recently been implicated in brain inflammation. We examined the involvement of PPARgamma, one of the isotypes of PPAR, in development of behavioral sensitization to the stimulant effect of methamphetamine (METH) (1 mg/kg, subcutaneously) in mice. Repeated administration of METH (once daily for 5 days) enhanced the locomotor-activating effect of METH, which was reproduced by METH challenge on withdrawal day 7 (test day 12). The protein level and the activity of PPARgamma were significantly increased in the nuclear fraction of whole brain after 5 days of METH administration (test day 5) and on withdrawal day 7 (test day 12). Both pioglitazone and ciglitazone (PPARgamma agonists; 0.5-5.0 microg, intracerebroventricularly (i.c.v.), once daily) prevented the expression of behavioral sensitization to METH challenge on withdrawal day 7, but not the sensitization that occurred during repeated administration of METH. In addition, the magnitude of expression of behavioral sensitization was augmented by treatments with GW9662 (a PPARgamma antagonist; 0.5-5.0 microg i.c.v., once daily) during the withdrawal period. The pioglitazone-induced alleviation of behavioral sensitization was synergistically facilitated by simultaneous i.c.v. injection of 9-cis-retinoic acid (1.0 microg), an agonist for the retinoid X receptor which is a ligand-activated nuclear receptor that forms heterodimers with PPAR. These results suggest that PPARgamma has a significant role in the expression of behavioral sensitization to METH in mice.

Cyclin-dependent kinase 5 in synaptic plasticity, learning and memory

Cyclin-dependent kinase 5 (Cdk5) is a serine/threonine kinase with a multitude of functions. Although Cdk5 is widely expressed, it has been studied most extensively in neurons. Since its initial characterization, the fundamental contribution of Cdk5 to an impressive range of neuronal processes has become clear. These phenomena include neural development, dopaminergic function and neurodegeneration. Data from different fields have recently converged to provide evidence for the participation of Cdk5 in synaptic plasticity, learning and memory. In this review, we consider recent data implicating Cdk5 in molecular and cellular mechanisms underlying synaptic plasticity. We relate these findings to its emerging role in learning and memory. Particular attention is paid to the activation of Cdk5 by p25, which enhances hippocampal synaptic plasticity and memory, and suggests formation of p25 as a physiological process regulating synaptic plasticity and memory.

Methamphetamine-induced sensitization differentially alters pCREB and DeltaFosB throughout the limbic circuit of the mammalian brain

Enhancements in behavior that accompany repeated, intermittent administration of abused drugs (sensitization) endure long after drug administration has ceased. Such persistence reflects changes in intracellular signaling cascades and associated gene transcription factors in brain regions that are engaged by abused drugs. This process is not characterized for the most potent psychomotor stimulant, methamphetamine. Using motor behavior as an index of brain state in rats, we verified that five once-daily injections of 2.5 mg/kg methamphetamine induced behavioral sensitization that was demonstrated (expressed) 3 and 14 days later. Using immunoblot procedures, limbic brain regions implicated in behavioral sensitization were assayed for extracellular signal-regulated kinase and its phosphorylated form (pERK/ERK, a signal transduction kinase), cAMP response element binding protein and its phosphorylated form (pCREB/CREB, a constitutively expressed transcriptional regulator), and DeltaFosB (a long-lasting transcription factor). pERK, ERK, and CREB levels were not changed for any region assayed. In the ventral tegmental area, pCREB and DeltaFosB also were not changed. pCREB (activated CREB) was elevated in the frontal cortex at 3 days withdrawal, but not at 14 days. pCREB levels were decreased at 14 days withdrawal in the nucleus accumbens and ventral pallidum. Accumbal and pallidal levels of DeltaFosB were increased at 3 days withdrawal, and this increase persisted to 14 days in the pallidum. Thus, only the ventral pallidum showed changes in molecular processes that consistently correlated with motor sensitization, revealing that this region may be associated with this enduring behavioral phenotype initiated by methamphetamine. The present findings expand our understanding of the neuroanatomical and molecular substrates that may play a role in the persistence of druginduced sensitization.

Prenatal cocaine and morphine alter brain cyclin-dependent kinase 5 (Cdk5) activity in rat pups

Pregnant rats received daily injections of saline, cocaine (20 mg/kg), morphine (2 mg/kg), or the combination of both drugs, on days 13-20 of gestation. Cyclin-dependent kinase 5 (Cdk5) activity was then measured in the resulting pups on postnatal days 1, 7, 14 and 28. Cocaine resulted in a time dependent increase in brain Cdk5 activity which peaked on day 14. Morphine, in contrast, induced a decrease in Cdk5 activity which was also maximal on day 14. Combined administration of the two drugs led to smaller increases than those seen after cocaine alone. These findings demonstrate that prenatal drug exposure can modify postnatal activity of Cdk5 in the brain and raise the possibility that alterations in Cdk5 may play a role in some of the neural and behavioral effects produced by these treatments.

Psychoactive drugs and regulation of the cAMP/PKA/DARPP-32 cascade in striatal medium spiny neurons

Changes in activity of the medium spiny neurons (MSNs) of dorsal and ventral striatum result in alterations of motor performance, ranging from rapid increases or decreases in locomotor activity, to long-term modifications of motor behaviours. In the dorsal striatum, MSNs can be distinguished based on the organization of their connectivity to substantia nigra pars reticulata (SNpr) and internal segment of the globus pallidus (GPi), which, in turn, control thalamocortical neurons. Approximately half of the MSNs project directly to SNpr and GPi, their activation leading to disinhibition of thalamocortical neurons and increased motor activity. The other subpopulation of MSNs connects to SNpr and GPi indirectly and when activated promotes inhibition of thalamocortical neurons, thereby reducing motor activity. The dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) is a modulator of the cAMP signalling pathway, highly expressed in MSNs. This review discusses the regulation of DARPP-32 exerted by psychoactive substances in specific populations of striatal projection neurons and its involvement in short- and long-term motor responses.

Protein expression profile in the striatum of acute methamphetamine-treated rats

PURPOSE

Methamphetamine (MAP) is an addictive drug with psychostimulant effects. It is known that MAP induces behavioral changes, including hyperlocomotion and stereotypical movements in rodents. These behavioral changes induced by MAP have been compared with behavioral changes in patients with MAP addiction and MAP psychosis. However, little is known about the underlying mechanisms of MAPs effects on global protein expression. 2-DE proteomics allows us to examine global changes in protein expression in complex biological systems and to propose possible hypotheses of the underlying mechanisms in various pathological conditions. In the present study, we aim to identify protein expression profiles in the striatum (ST) of acute low dose MAP (1 mg/kg)-treated rats using 2-DE proteomics.

MATERIALS AND METHODS

Rats were given an intraperitoneal injection of MAP (1 mg/kg) or saline. Locomotor activity was monitored. Proteins were extracted from the ST of MAP-treated and saline-treated control rats then separated and analyzed using 2-DE. RESULTS. Low dose MAP administration significantly increased locomotor activity. 2-DE analysis revealed 36 protein spots differentially regulated in the ST of acute MAP-treated rats compared to a vehicle-treated control. 26 protein spots have been identified using MALDI-TOF, including phosphoglycerate kinase 1, Dihydrolipoamide dehydrogenase, Voltage-dependent anion-selective channel protein 1, Rho GDP dissociation inhibitor alpha, peroxiredoxin 2, ubiquitin carboxy-terminal hydrolase L1, and actin beta, N-tropomodulin.

DISCUSSION

These proteins could be related to underlying mechanisms of acute low dose MAP effects, indicating mitochondrial dysfunction, oxidative damages, lysosomal degradation, degenerative processes, and neuronal modification.