Cocaine-induced hyperactivity and sensitization are dependent on GSK3

Cocaine and Its Abstinence Condition Modulate Striatal and Hippocampal Wnt Signaling in a Male Rat Model of Drug Self-Administration

Recent years have provided more and more evidence confirming the important role of Wnt/β-catenin signaling in the pathophysiology of mental illnesses, including cocaine use disorder. High relapse rates, which is a hallmark of drug addiction, prompt the study of changes in Wnt signaling elements (Wnt5a, Wnt7b, and Ctnnb1) in the motivational aspects of cocaine use and early drug-free period (3 days after the last exposure to cocaine). For this purpose, an animal model of intravenous cocaine self-administration and two types of drug-free period (extinction training and abstinence in the home cage) were used. The studies showed that chronic cocaine self-administration mainly disturbs the expression of Wnt5a and Ctnnb1 (the gene encoding β-catenin) in the examined brain structures (striatum and hippocampus), and the examined types of early abstinence are characterized by a different pattern of changes in the expression of these genes. At the same time, in cocaine self-administrated animals, there were no changes in the level of Wnt5a and β-catenin proteins at the tested time points. Moreover, exposure to cocaine induces a significant reduction in the striatal and hippocampal expression of miR-374 and miR-544, which can regulate Wnt5a levels post-transcriptionally. In summary, previous observations from experimenter-administered cocaine have not been fully validated in the cocaine self-administration model. Yoked cocaine administration appears to disrupt Wnt signaling more than cocaine self-administration. The condition of the cocaine-free period, the routes of drug administration, and the motivational aspect of drug administration play an important role in the type of drug-induced molecular changes observed. Furthermore, in-depth research involving additional brain regions is needed to determine the exact role of Wnt signaling in short-term and long-lasting plasticity as well as in the motivational aspects of cocaine use, and thus to assess its potential as a target for new drug therapy for cocaine use disorder.

Glycogen Synthase Kinase 3: Ion Channels, Plasticity, and Diseases

Glycogen synthase kinase 3β (GSK3) is a multifaceted serine/threonine (S/T) kinase expressed in all eukaryotic cells. GSK3β is highly enriched in neurons in the central nervous system where it acts as a central hub for intracellular signaling downstream of receptors critical for neuronal function. Unlike other kinases, GSK3β is constitutively active, and its modulation mainly involves inhibition via upstream regulatory pathways rather than increased activation. Through an intricate converging signaling system, a fine-tuned balance of active and inactive GSK3β acts as a central point for the phosphorylation of numerous primed and unprimed substrates. Although the full range of molecular targets is still unknown, recent results show that voltage-gated ion channels are among the downstream targets of GSK3β. Here, we discuss the direct and indirect mechanisms by which GSK3β phosphorylates voltage-gated Na⁺ channels (Na_v1.2 and Na_v1.6) and voltage-gated K⁺ channels (K_v4 and K_v7) and their physiological effects on intrinsic excitability, neuronal plasticity, and behavior. We also present evidence for how unbalanced GSK3β activity can lead to maladaptive plasticity that ultimately renders neuronal circuitry more vulnerable, increasing the risk for developing neuropsychiatric disorders. In conclusion, GSK3β-dependent modulation of voltage-gated ion channels may serve as an important pharmacological target for neurotherapeutic development.

Neuroadaptations and TGF-β signaling: emerging role in models of neuropsychiatric disorders

Neuropsychiatric diseases are manifested by maladaptive behavioral plasticity. Despite the greater understanding of the neuroplasticity underlying behavioral adaptations, pinpointing precise cellular mediators has remained elusive. This has stymied the development of pharmacological interventions to combat these disorders both at the level of progression and relapse. With increased knowledge on the putative role of the transforming growth factor (TGF- β) family of proteins in mediating diverse neuroadaptations, the influence of TGF-β signaling in regulating maladaptive cellular and behavioral plasticity underlying neuropsychiatric disorders is being increasingly elucidated. The current review is focused on what is currently known about the TGF-β signaling in the central nervous system in mediating cellular and behavioral plasticity related to neuropsychiatric manifestations.

Decrease of glycogen synthase kinase 3β phosphorylation in the rat nucleus accumbens shell is necessary for amphetamineinduced conditioned locomotor activity

Phosphorylation levels of glycogen synthase kinase 3β (GSK3β) negatively correlated with psychomotor stimulant-induced locomotor activity. Locomotor sensitization induced by psychomotor stimulants was previously shown to selectively accompany the decrease of GSK3β phosphorylation in the nucleus accumbens (NAcc) core, suggesting that intact GSK3β activity in this region is necessary for psychomotor stimulants to produce locomotor sensitization. Similarly, GSK3β in the NAcc was also implicated in mediating the conditioned effects formed by the associations of psychomotor stimulants. However, it remains undetermined whether GSK3β plays a differential role in the two sub-regions (core and shell) of the NAcc in the expression of drug-conditioned behaviors. In the present study, we found that GSK3β phosphorylation was significantly lower in the NAcc shell obtained from rats expressing amphetamine (AMPH)-induced conditioned locomotor activity. Further, we demonstrated that these effects were normalized by treatment with lithium chloride, a GSK3β inhibitor. These results suggest that the behavior produced by AMPH itself and a conditioned behavior formed by associations with AMPH are differentially mediated by the two sub-regions of the NAcc.

GSK3β Activity in Reward Circuit Functioning and Addiction

Glycogen synthase kinase-3β (GSK3β), primarily described as a regulator of glycogen metabolism, is a molecular hub linking numerous signaling pathways and regulates many cellular processes like cytoskeletal rearrangement, cell migration, apoptosis, and proliferation. In neurons, the kinase is engaged in molecular events related to the strengthening and weakening of synapses, which is a subcellular manifestation of neuroplasticity. Dysregulation of GSK3β activity has been reported in many neuropsychiatric conditions, like schizophrenia, major depressive disorder, bipolar disorder, and Alzheimer’s disease. In this review, we describe the kinase action in reward circuit-related structures in health and disease. The effect of pharmaceuticals used in the treatment of addiction in the context of GSK3β activity is also discussed.

Chronic phenmetrazine treatment promotes D2 dopaminergic and α2-adrenergic receptor desensitization and alters phosphorylation of signaling proteins and local cerebral glucose metabolism in the rat brain

Phenmetrazine (PHEN) is a putative treatment for cocaine and psychostimulant recidivism; however, neurochemical changes underlying its activity have not been fully elucidated. We sought to characterize brain homeostatic adaptations to chronic PHEN, specifically on functional brain activity (local cerebral glucose utilization), G-Protein Coupled Receptor-stimulated G-protein activation, and phosphorylation of ERK1/2Thr202/Tyr204, GSK3βTyr216, and DARPP-32Thr34. Male Sprague-Dawley rats were implanted with sub-cutaneous minipumps delivering either saline (vehicle), acute (2-day) or chronic (14-day) low dose (25 mg/kg/day) or high dose (50 mg/kg/day) PHEN. Acute administration of high dose PHEN increased local cerebral glucose utilization measured by 2-[14C]-deoxyglucose uptake in basal ganglia and motor-related regions of the rat brain. However, chronically treated animals developed tolerance to these effects. To identify the neurochemical changes associated with PHEN's activity, we performed [35S]GTPγS binding assays on unfixed and immunohistochemistry on fixed coronal brain sections. Chronic PHEN treatment dose-dependently attenuated D2 dopamine and α2-adrenergic, but not 5-HT1A, receptor-mediated G-protein activation. Two distinct patterns of effects on pERK1/2 and pDARPP-32 were observed: 1) chronic low dose PHEN decreased pERK1/2, and also significantly increased pDARPP-32 levels in some regions; 2) acute and chronic PHEN increased pERK1/2, but chronic high dose PHEN treatment tended to decrease pDARPP-32. Chronic low dose, but not high dose, PHEN significantly reduced pGSK3β levels in several regions. Our study provides definitive evidence that extended length PHEN dosage schedules elicit distinct modes of neuronal acclimatization in cellular signaling. These pharmacodynamic modifications should be considered in drug development for chronic use.

The role of the mTOR pathway in models of drug-induced reward and the behavioural constituents of addiction

BACKGROUND

Exposure to drugs of abuse induces neuroadaptations in critical nodes of the so-called reward systems that are thought to mediate the transition from controlled drug use to the compulsive drug-seeking that characterizes addictive disorders. These neural adaptations are likely to require protein synthesis, which is regulated, among others, by the mechanistic target of the rapamycin kinase (mTOR) signalling cascade.

METHODS

We have performed a narrative review of the literature available in PubMed about the involvement of the mTOR pathway in drug-reward and addiction-related phenomena.

AIMS

The aim of this study was to review the underlying architecture of this complex intracellular network and to discuss the alterations of its components that are evident after exposure to drugs of abuse. The aim was also to delineate the effects that manipulations of the mTOR network have on models of drug reward and on paradigms that recapitulate some of the psychological components of addiction.

RESULTS

There is evidence for the involvement of the mTOR pathway in the acute and rewarding effects of drugs of abuse, especially psychostimulants. However, the data regarding opiates are scarce. There is a need to use sophisticated animal models of addiction to ascertain the real role of the mTOR pathway in this pathology and not just in drug-mediated reward. The involvement of this pathway in behavioural addictions and impulsivity should also be studied in detail in the future.

CONCLUSIONS

Although there is a plethora of data about the modulation of mTOR by drugs of abuse, the involvement of this signalling pathway in addictive disorders requires further research.

Arrestin recruitment to dopamine D2 receptor mediates locomotion but not incentive motivation

The dopamine (DA) D2 receptor (D2R) is an important target for the treatment of neuropsychiatric disorders such as schizophrenia and Parkinson's disease. However, the development of improved therapeutic strategies has been hampered by our incomplete understanding of this receptor's downstream signaling processes in vivo and how these relate to the desired and undesired effects of drugs. D2R is a G protein-coupled receptor (GPCR) that activates G protein-dependent as well as non-canonical arrestin-dependent signaling pathways. Whether these effector pathways act alone or in concert to facilitate specific D2R-dependent behaviors is unclear. Here, we report on the development of a D2R mutant that recruits arrestin but is devoid of G protein activity. When expressed virally in "indirect pathway" medium spiny neurons (iMSNs) in the ventral striatum of D2R knockout mice, this mutant restored basal locomotor activity and cocaine-induced locomotor activity in a manner indistinguishable from wild-type D2R, indicating that arrestin recruitment can drive locomotion in the absence of D2R-mediated G protein signaling. In contrast, incentive motivation was enhanced only by wild-type D2R, signifying a dissociation in the mechanisms that underlie distinct D2R-dependent behaviors, and opening the door to more targeted therapeutics.

GSK3β Modulates Timing-Dependent Long-Term Depression Through Direct Phosphorylation of Kv4.2 Channels

Spike timing-dependent plasticity (STDP) is a form of activity-dependent remodeling of synaptic strength that underlies memory formation. Despite its key role in dictating learning rules in the brain circuits, the molecular mechanisms mediating STDP are still poorly understood. Here, we show that spike timing-dependent long-term depression (tLTD) and A-type K+ currents are modulated by pharmacological agents affecting the levels of active glycogen-synthase kinase 3 (GSK3) and by GSK3β knockdown in layer 2/3 of the mouse somatosensory cortex. Moreover, the blockade of A-type K+ currents mimics the effects of GSK3 up-regulation on tLTD and occludes further changes in synaptic strength. Pharmacological, immunohistochemical and biochemical experiments revealed that GSK3β influence over tLTD induction is mediated by direct phosphorylation at Ser-616 of the Kv4.2 subunit, a molecular determinant of A-type K+ currents. Collectively, these results identify the functional interaction between GSK3β and Kv4.2 channel as a novel mechanism for tLTD modulation providing exciting insight into the understanding of GSK3β role in synaptic plasticity.

Glycogen synthase kinase-3 signaling in cellular and behavioral responses to psychostimulant drugs

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase implicated in numerous physiological processes and cellular functions through its ability to regulate the function of many proteins, including transcription factors and structural proteins. GSK-3β has been demonstrated to function as a regulator of multiple behavioral processes induced by drugs of abuse, particularly psychostimulant drugs. In this review, we provide an overview of the regulation of GSK-3β activity produced by psychostimulants, and the role of GSK-3β signaling in psychostimulant-induced behaviors including drug reward, associative learning and memory which play a role in the maintenance of drug-seeking. Evidence supports the conclusion that GSK-3β is an important component of the actions of psychostimulant drugs and that GSK-3β is a valid target for developing novel therapeutics. Additional studies are required to examine the role of GSK-3β in distinct cell types within the mesolimbic and memory circuits to further elucidate the mechanisms related to the acquisition, consolidation, and recall of drug-related memories, and potentially countering neuroadaptations that reinforce drug-seeking behaviors that maintain drug dependence.

Chronic mild stress alters synaptic plasticity in the nucleus accumbens through GSK3β-dependent modulation of Kv4.2 channels

Although major depressive disorder (MDD) is highly prevalent, its pathophysiology is poorly understood. Recent evidence suggests that glycogen-synthase kinase 3β (GSK3β) plays a key role in memory formation, yet its role in mood regulation remains controversial. Here, we investigated whether GSK3β activity in the nucleus accumbens (NAc) is associated with depression-like behaviors and synaptic plasticity. We performed whole-cell patch-clamp recordings of medium spiny neurons (MSNs) in the NAc and determined the role of GSK3β in spike timing-dependent long-term potentiation (tLTP) in the chronic unpredictable mild stress (CUMS) mouse model of depression. To assess the specific role of GSK3β in tLTP, we used in vivo genetic silencing by an adeno-associated viral vector (AAV2) short hairpin RNA against GSK3β. In addition, we examined the role of the voltage-gated potassium Kv4.2 subunit, a molecular determinant of A-type K⁺ currents, as a potential downstream target of GSK3β. We found increased levels of active GSK3β and augmented tLTP in CUMS mice, a phenotype that was prevented by selective GSK3β knockdown. Furthermore, knockdown of GSK3β in the NAc ameliorated depressive-like behavior in CUMS mice. Electrophysiological, immunohistochemical, biochemical, and pharmacological experiments revealed that inhibition of the Kv4.2 channel through direct phosphorylation at Ser-616 mediated the GSK3β-dependent tLTP changes in CUMS mice. Our results identify GSK3β regulation of Kv4.2 channels as a molecular mechanism of MSN maladaptive plasticity underlying depression-like behaviors and suggest that the GSK3β-Kv4.2 axis may be an attractive therapeutic target for MDD.

The selective GSK3 inhibitor, SAR502250, displays neuroprotective activity and attenuates behavioral impairments in models of neuropsychiatric symptoms of Alzheimer's disease in rodents

Glycogen synthase kinase 3 (GSK3) has been identified as a promising target for the treatment of Alzheimer’s disease (AD), where abnormal activation of this enzyme has been associated with hyperphosphorylation of tau proteins. This study describes the effects of the selective GSK3 inhibitor, SAR502250, in models of neuroprotection and neuropsychiatric symptoms (NPS) associated with AD. In P301L human tau transgenic mice, SAR502250 attenuated tau hyperphosphorylation in the cortex and spinal cord. SAR502250 prevented the increase in neuronal cell death in rat embryonic hippocampal neurons following application of the neurotoxic peptide, Aβ_25–35. In behavioral studies, SAR502250 improved the cognitive deficit in aged transgenic APP(SW)/Tau(VLW) mice or in adult mice after infusion of Aβ_25–35. It attenuated aggression in the mouse defense test battery and improved depressive-like state of mice in the chronic mild stress procedure after 4 weeks of treatment. Moreover, SAR502250 decreased hyperactivity produced by psychostimulants. In contrast, the drug failed to modify anxiety-related behaviors or sensorimotor gating deficit. This profile confirms the neuroprotective effects of GSK3 inhibitors and suggests an additional potential in the treatment of some NPS associated with AD.

Supraphysiologic-dose anabolic-androgenic steroid use: A risk factor for dementia?

Supraphysiologic-dose anabolic-androgenic steroid (AAS) use is associated with physiologic, cognitive, and brain abnormalities similar to those found in people at risk for developing Alzheimer's Disease and its related dementias (AD/ADRD), which are associated with high brain β-amyloid (Aβ) and hyperphosphorylated tau (tau-P) protein levels. Supraphysiologic-dose AAS induces androgen abnormalities and excess oxidative stress, which have been linked to increased and decreased expression or activity of proteins that synthesize and eliminate, respectively, Aβ and tau-P. Aβ and tau-P accumulation may begin soon after initiating supraphysiologic-dose AAS use, which typically occurs in the early 20s, and their accumulation may be accelerated by other psychoactive substance use, which is common among non-medical AAS users. Accordingly, the widespread use of supraphysiologic-dose AAS may increase the numbers of people who develop dementia. Early diagnosis and correction of sex-steroid level abnormalities and excess oxidative stress could attenuate risk for developing AD/ADRD in supraphysiologic-dose AAS users, in people with other substance use disorders, and in people with low sex-steroid levels or excess oxidative stress associated with aging.

Glycogen synthase kinase-3β genetic polymorphisms and insomnia in depressed patients: A prospective study

BACKGROUND

80-90% of patients with Major Depressive Episode (MDE) experience insomnia and up-to 50% severe insomnia. Glycogen Synthase Kinase-3β (GSK3B) is involved both in mood regulation and circadian rhythm. Since GSK3B polymorphisms could affect protein levels or functionality, we investigated the association of GSK3B polymorphisms with insomnia in a sample of depressed patients treated with antidepressants.

METHODS

In this 6-month prospective real-world treatment study in psychiatric settings (METADAP), 492 Caucasian patients requiring a new antidepressant treatment were included and genotyped for five GSK3B Single Nucleotide Polymorphisms (SNPs) (rs6808874, rs6782799, rs2319398, rs13321783, rs334558). Insomnia and MDE severity were rated using the Hamilton Depression Rating Scale (HDRS). Bi- and multivariate analyses were performed to assess the association between GSK3B SNPs and insomnia (main objective). We also assessed their association with MDE severity and HDRS response/remission after antidepressant treatment.

RESULTS

At baseline severe insomnia was associated with the GSK3B rs334558 minor allele (C+) [OR=1.81, CI95%(1.17-2.80), p=0.008]. GSK3B rs334558 C+ had greater insomnia improvement after 6 months of antidepressant treatment (p=0.007, β=0.17, t=2.736). No association was found between GSK3B SNPs and MDE baseline severity or 6-month response/remission.

CONCLUSION

GSK3B rs334558 was associated with insomnia but not with MDE severity in depressed patients. Targeting GSK3B in patients with MDE and a severe insomnia could be a way to improve their symptoms with greater efficiency. And it should be further studied whether the GSK3B-insomnia association may fit into the larger picture of mood disorders.

The β-adrenoceptor blocker propranolol ameliorates compulsive-like gambling behaviour in a rodent slot machine task: implications for iatrogenic gambling disorder

Previous work has shown that chronic administration of the dopamine D_2/3 receptor agonist ropinirole invigorates performance on a rodent slot machine task (rSMT). This behavioural change appears superficially similar to the iatrogenic gambling disorder (GD) observed in a sub-set of patients with Parkinson's disease (PD), and has been associated with increased activation of the intra-cellular signalling proteins GSK3β and CREB in the striatum. Here, we wanted to determine whether this response to ropinirole could be attenuated by targeting these signalling proteins, and if the loss of dopaminergic innervation characteristic of PD would alter ropinirole's effects on the rSMT. Male Long Evans rats were trained on the rSMT. Dopaminergic terminals innervating the dorsolateral striatum were then lesioned bilaterally using the neurotoxin 6-hydroxydopamine hydrochloride (6-OHDA). Subsequently animals were implanted with osmotic mini-pumps delivering ropinirole. Lastly, animals were given dietary lithium (Li⁺ ), to inhibit the activation of GSK3β, or injections of the ß-adrenoceptor antagonist propranolol, which potently inhibits CREB as a secondary mechanism of action, and any changes in ropinirole-induced increases in compulsive-like engagement in the rSMT evaluated. Chronic ropinirole increased the number of trials animals completed, reproducing our original finding. This increase in task engagement was not altered in animals with 6-OHDA lesions, a putative model of early PD. In addition, the effects of ropinirole were not attenuated by administration of Li⁺ , but were ameliorated by propranolol. These data suggest that propranolol may represent a potential pharmacotherapy for the treatment of iatrogenic gambling.

Effect of dietary palmitic and stearic acids on sucrose motivation and hypothalamic and striatal cell signals in the rat

We have reported that motivation for sucrose is increased in rats fed a moderate (31%) mixed-fat diet for 4-6 wk. In this study, rats were fed diets containing 32% stearic (STEAR) or palmitic (PALM) acid, and behavior, metabolic profile, and cell signals were compared with those of rats fed a matched low-fat diet (LF; 11% fat) diet. Rats fed STEAR or PALM increased sucrose motivation relative to LF rats (one-way ANOVA for lever presses; P = 0.03). Diet did not change fasting glucose, insulin, total cholesterol, triglycerides, intravenous glucose tolerance test glucose profile, percent body fat, or total kilocalories, although kilocalories as fat were increased (ANOVA, P < 0.05). Cell signals were assessed in rats ranked from high to low sucrose motivation. Diet did not alter Thr and Ser phosphorylation of Akt in the medial hypothalamus (HYP) and striatum (STR). However, Ser phosphorylation of GSK3Β was decreased in HYP and STR from both high- and low-performer tertiles of STEAR and PALM rats (ANOVA within each brain region, P < 0.05). Two histone 3 (H3) modifications were also assessed. Although there was no effect of diet on the transcription-repressive H3 modification, H3K27me3, the transcription-permissive H3 modification, H3K4me3, was significantly decreased in the HYP of high performers fed PALM or STEAR (ANOVA, P = 0.013). There was no effect of diet on H3K4me3 levels in HYP of low performers, or in STR. Our findings suggest signal-specific and brain region-specific effects of PALM or STEAR diets and may link downstream signaling effects of GSK3Β activity and H3 modifications with enhanced motivational behavior.

Wnt/β-catenin pathway in the prefrontal cortex is required for cocaine-induced neuroadaptations

Behavioral sensitization is a progressive and enduring enhancement of the motor stimulant effects elicited by repeated administration of drugs of abuse. It can be divided into two distinct temporal and anatomical domains, termed initiation and expression, which are characterized by specific molecular and neurochemical changes. This study examines the role of the Wnt canonical pathway mediating the induction of cocaine sensitization. We found that β-catenin levels in the prefrontal cortex (PFC), amygdala (Amyg) and dorsal striatum (CPu) are decreased in animals that show sensitization. Accordingly, GSK3β activity levels are increased in the same areas. Moreover, β-catenin levels in nuclear fraction, mRNA expression of Axin2 and Wnt7b are decreased in the PFC of sensitized animals. Then, in order to demonstrate that changes in the PFC are crucial for initiation of sensitization, we either rescue β-catenin levels with a systemic treatment of a GSK3β inhibitor (Lithium Chloride) or inhibit Wnt/β-catenin pathway with an intracerebral infusion of Sulindac before each cocaine injection. As expected, rescuing β-catenin levels in the PFC as well as CPu and Amyg blocks cocaine-induced sensitization, while decreasing β-catenin levels exclusively in the PFC exacerbates it. Therefore, our results demonstrate a new role for the Wnt/β-catenin pathway as a required neuroadaptation in inducing behavioral sensitization.

Glycogen synthase kinase 3 beta alters anxiety-, depression-, and addiction-related behaviors and neuronal activity in the nucleus accumbens shell

Psychiatric disorders such as anxiety, depression and addiction are often comorbid brain pathologies thought to share common mechanistic biology. As part of the cortico-limbic circuit, the nucleus accumbens shell (NAcSh) plays a fundamental role in integrating information in the circuit, such that modulation of NAcSh circuitry alters anxiety, depression, and addiction-related behaviors. Intracellular kinase cascades in the NAcSh have proven important mediators of behavior. To investigate glycogen-synthase kinase 3 (GSK3) beta signaling in the NAcSh in vivo we knocked down GSK3beta expression with a novel adeno-associated viral vector (AAV2) and assessed changes in anxiety- and depression-like behavior and cocaine self-administration in GSK3beta knockdown rats. GSK3beta knockdown reduced anxiety-like behavior while increasing depression-like behavior and cocaine self-administration. Correlative electrophysiological recordings in acute brain slices were used to assess the effect of AAV-shGSK3beta on spontaneous firing and intrinsic excitability of tonically active interneurons (TANs), cells required for input and output signal integration in the NAcSh and for processing reward-related behaviors. Loose-patch recordings showed that TANs transduced by AAV-shGSK3beta exhibited reduction in tonic firing and increased spike half width. When assessed by whole-cell patch clamp recordings these changes were mirrored by reduction in action potential firing and accompanied by decreased hyperpolarization-induced depolarizing sag potentials, increased action potential current threshold, and decreased maximum rise time. These results suggest that silencing of GSK3beta in the NAcSh increases depression- and addiction-related behavior, possibly by decreasing intrinsic excitability of TANs. However, this study does not rule out contributions from other neuronal sub-types.

Role of Wnt/β-catenin pathway in the nucleus accumbens in long-term cocaine-induced neuroplasticity: a possible novel target for addiction treatment

Cocaine addiction is a chronic relapsing disorder characterized by the loss of control over drug-seeking and taking, and continued drug use regardless of adverse consequences. Despite years of research, effective treatments for psycho-stimulant addiction have not been identified. Persistent vulnerability to relapse arises from a number of long-lasting adaptations in the reward circuitry that mediate the enduring response to the drug. Recently, we reported that the activity of the canonical or Wnt/β-catenin pathway in the prefrontal cortex (PFC) is very important in the early stages of cocaine-induced neuroadaptations. In the present work, our main goal was to elucidate the relevance of this pathway in cocaine-induced long-term neuroadaptations that may underlie relapse. We found that a cocaine challenge, after a period of abstinence, induced an increase in the activity of the pathway which is revealed as an increase in the total and nuclear levels of β-catenin (final effector of the pathway) in the nucleus accumbens (NAcc), together with a decrease in the activity of glycogen synthase kinase 3β (GSK3β). Moreover, we found that the pharmacological modulation of the activity of the pathway has long-term effects on the cocaine-induced neuroplasticity at behavioral and molecular levels. All the results imply that changes in the Wnt/β-catenin pathway effectors are long-term neuroadaptations necessary for the behavioral response to cocaine. Even though more research is needed, the present results introduce the Wnt canonical pathway as a possible target to manage cocaine long-term neuroadaptations.

GSK-3β inhibitors reverse cocaine-induced synaptic transmission dysfunction in the nucleus accumbens

Nucleus accumbens receives glutamatergic projection from the prefrontal cortex (PFC) and dopaminergic input from the Ventral tegmental area (VTA). Recent studies have suggested a critical role for serine/threonine kinase glycogen synthase kinase 3β (GSK3β) in cocaine-induced hyperactivity; however, the effect of GSK3β on the modulation of glutamatergic and dopaminergic afferents is unclear. In this study, we found that the GSK3 inhibitors, LiCl (100 mg/kg, i.p.) or SB216763 (2.5 mg/kg, i.p.), blocked the cocaine-induced hyperlocomotor activity in rats. By employing single-unit recordings in vivo, we found that pretreatment with either SB216763 or LiCl for 15 min reversed the cocaine-inhibited firing frequency of medium spiny neuron (MSN) in the nucleus accumbens (NAc). Preperfusion of SB216763 (5 μM) ameliorated the inhibitory effect of cocaine on both the α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (up to 99 ± 6.8% inhibition) and N-methyl-D-aspartic acid receptor (NMDAR)-mediate EPSC (up to 73 ± 9.7% inhibition) in the NAc in brain slices. The effect of cocaine on AMPA and NMDA receptor-mediate excitatory postsynaptic current (EPSC) were mimicked by the D1 -like receptor agonist SKF 38393 and blocked by the D1 -like receptor antagonist SCH 23390, whereas D2 -like receptor agonist or antagonist failed to mimic or to block the action of cocaine. Preperfusion of SB216763 for 5 min also ameliorated the inhibitory effect of SKF38393 on both AMPA and NMDA receptor-mediated components of EPSC, indicate the effect of SB216763 on cocaine was via the D1 -like receptor. Moreover, cocaine inhibited the presynaptic release of glutamate in the NAc, and SB216763 reversed this effect. In conclusion, D1 receptor-GSK3β pathway, which mediates glutamatergic transmission in the NAc core through a presynaptic mechanism, plays an important role in acute cocaine-induced hyperlocomotion.

Ceftriaxone attenuates acute cocaine-evoked dopaminergic neurotransmission in the nucleus accumbens of the rat

BACKGROUND AND PURPOSE

Ceftriaxone is a β-lactam antibiotic and glutamate transporter activator that reduces the reinforcing effects of psychostimulants. Ceftriaxone also reduces locomotor activation following acute psychostimulant exposure, suggesting that alterations in dopamine transmission in the nucleus accumbens contribute to its mechanism of action. In the present studies we tested the hypothesis that pretreatment with ceftriaxone disrupts acute cocaine-evoked dopaminergic neurotransmission in the nucleus accumbens.

EXPERIMENTAL APPROACH

Adult male Sprague-Dawley rats were pretreated with saline or ceftriaxone (200 mg kg(-1) , i.p. × 10 days) and then challenged with cocaine (15 mg kg(-1) , i.p.). Motor activity, dopamine efflux (via in vivo microdialysis) and protein levels of tyrosine hydroxylase (TH), the dopamine transporter and organic cation transporter as well as α-synuclein, Akt and GSK3β were analysed in the nucleus accumbens.

KEY RESULTS

Ceftriaxone-pretreated rats challenged with cocaine displayed reduced locomotor activity and accumbal dopamine efflux compared with saline-pretreated controls challenged with cocaine. The reduction in cocaine-evoked dopamine levels was not counteracted by excitatory amino acid transporter 2 blockade in the nucleus accumbens. Pretreatment with ceftriaxone increased Akt/GSK3β signalling in the nucleus accumbens and reduced levels of dopamine transporter, TH and phosphorylated α-synuclein, indicating that ceftriaxone affects numerous proteins involved in dopaminergic transmission.

CONCLUSIONS AND IMPLICATIONS

These results are the first evidence that ceftriaxone affects cocaine-evoked dopaminergic transmission, in addition to its well-described effects on glutamate, and suggest that its ability to attenuate cocaine-induced behaviours, such as psychomotor activity, is due in part to reduced dopaminergic neurotransmission in the nucleus accumbens.

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

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

Identifying a kinase network regulating FGF14:Nav1.6 complex assembly using split-luciferase complementation

Kinases play fundamental roles in the brain. Through complex signaling pathways, kinases regulate the strength of protein:protein interactions (PPI) influencing cell cycle, signal transduction, and electrical activity of neurons. Changes induced by kinases on neuronal excitability, synaptic plasticity and brain connectivity are linked to complex brain disorders, but the molecular mechanisms underlying these cellular events remain for the most part elusive. To further our understanding of brain disease, new methods for rapidly surveying kinase pathways in the cellular context are needed. The bioluminescence-based luciferase complementation assay (LCA) is a powerful, versatile toolkit for the exploration of PPI. LCA relies on the complementation of two firefly luciferase protein fragments that are functionally reconstituted into the full luciferase enzyme by two interacting binding partners. Here, we applied LCA in live cells to assay 12 kinase pathways as regulators of the PPI complex formed by the voltage-gated sodium channel, Nav1.6, a transmembrane ion channel that elicits the action potential in neurons and mediates synaptic transmission, and its multivalent accessory protein, the fibroblast growth factor 14 (FGF14). Through extensive dose-dependent validations of structurally-diverse kinase inhibitors and hierarchical clustering, we identified the PI3K/Akt pathway, the cell-cycle regulator Wee1 kinase, and protein kinase C (PKC) as prospective regulatory nodes of neuronal excitability through modulation of the FGF14:Nav1.6 complex. Ingenuity Pathway Analysis shows convergence of these pathways on glycogen synthase kinase 3 (GSK3) and functional assays demonstrate that inhibition of GSK3 impairs excitability of hippocampal neurons. This combined approach provides a versatile toolkit for rapidly surveying PPI signaling, allowing the discovery of new modular pathways centered on GSK3 that might be the basis for functional alterations between the normal and diseased brain.

Long-term parental methamphetamine exposure of mice influences behavior and hippocampal DNA methylation of the offspring

The high rate of methamphetamine (METH) abuse among young adults and women of childbearing age makes it imperative to determine the long-term effects of METH exposure on the offspring. We hypothesized that parental METH exposure modulates offspring behavior by disrupting epigenetic programming of gene expression in the brain. To simulate the human pattern of drug use, male and female C57Bl/6J mice were exposed to escalating doses of METH or saline from adolescence through adulthood; following mating, females continue to receive drug or saline through gestational day 17. F1 METH male offspring showed enhanced response to cocaine-conditioned reward and hyperlocomotion. Both F1 METH male and female offspring had reduced response to conditioned fear. Cross-fostering experiments have shown that certain behavioral phenotypes were modulated by maternal care of either METH or saline dams. Analysis of offspring hippocampal DNA methylation showed differentially methylated regions as a result of both METH in utero exposure and maternal care. Our results suggest that behavioral phenotypes and epigenotypes of offspring that were exposed to METH in utero are vulnerable to (a) METH exposure during embryonic development, a period when wide epigenetic reprogramming occurs, and (b) postnatal maternal care.

The effects of GSK-3β blockade on ketamine self-administration and relapse to drug-seeking behavior in rats

RATIONALE

The role of glycogen synthase kinase-3 (GSK-3) has recently been implicated in the neurochemical mechanism underlying ketamine-induced neuronal toxicity and behavioral disturbance.

OBJECTIVES

The primary goal of the present study was to determine the role of GSK-3β in ketamine self-administration (SA) and relapse to drug-seeking behavior after abstinence.

METHODS

In Experiment 1, the level of phosphorylated GSK-3β (p-GSK-3β) and total GSK-3β (t-GSK-3β) was determined in various brain areas following 14 days of ketamine SA. In Experiments 2 and 3, the effects of a GSK-3β inhibitor, SB216763 (2 and 4 mg/kg) and a GSK-3 inhibitor, lithium (LiCl, 100mg/kg) on the responding maintained by 0.5mg/kg/infusion ketamine SA were evaluated. In Experiments 4 and 5, rats underwent ketamine SA for 14 days followed by a 10-day abstinence period. The animals were treated with 2 or 4 mg/kg GSK-3β inhibitor, or 100mg/kg LiCl during the cue-induced relapse test. Seven days later, animals received the same drug treatment and underwent the drug-induced relapse test. Finally, the effect of saline and DMSO on locomotor activity was evaluated in Experiment 6.

RESULTS

Ketamine SA significantly decreased the ratio p-GSK-3β and t-GSK-3β (p-GSK-3β:t-GSK-3β) in the caudate putamen, nucleus accumbens, and ventral tegmental area. Both SB216763 and LiCl decreased responding on a progressive ratio schedule, but not on a fixed ratio schedule. Cue-induced relapse was suppressed only by 4mg/kg SB216763, whereas drug-induced relapse was inhibited by 2, 4 mg/kg SB216763 and LiCl. However, inactive responses were also suppressed by LiCl during progressive ratio and drug-induced relapse testing.

CONCLUSIONS

SB216763 was effective at decreasing ketamine SA under the PR schedule and reducing drug-seeking behavior after abstinence.

Glycine transporters GlyT1 and GlyT2 are differentially modulated by glycogen synthase kinase 3β

Inhibitory glycinergic neurotransmission is terminated by the specific glycine transporters GlyT1 and GlyT2 which actively reuptake glycine from the synaptic cleft. GlyT1 is associated with both glycinergic and glutamatergic pathways, and is the main regulator of the glycine levels in the synapses. GlyT2 is the main supplier of glycine for vesicle refilling, a process that is vital to preserve the quantal glycine content in synaptic vesicles. Therefore, to control glycinergic neurotransmission efficiently, GlyT1 and GlyT2 activity must be regulated by diverse neuronal and glial signaling pathways. In this work, we have investigated the possible functional modulation of GlyT1 and GlyT2 by glycogen synthase kinase 3 (GSK3β). This kinase is involved in mood stabilization, neurodegeneration and plasticity at excitatory and inhibitory synapses. The co-expression of GSK3β with GlyT1 or GlyT2 in COS-7 cells and Xenopus laevis oocytes, leads to inhibition and stimulation of GlyT1 and GlyT2 activities, respectively, with a decrease of GlyT1, and an increase in GlyT2 levels at the plasma membrane. The specificity of these changes is supported by the antagonism exerted by a catalytically inactive form of the kinase and through inhibitors of GSK3β such as lithium chloride and TDZD-8. GSK3β also increases the incorporation of 32Pi into GlyT1 and decreases that of GlyT2. The pharmacological inhibition of the endogenous GSK3β in neuron cultures of brainstem and spinal cord leads to an opposite modulation of GlyT1 and GlyT2.Our results suggest that GSK3β is important for stabilizing and/or controlling the expression of functional GlyTs on the neural cell surface.

Synthesis and evaluation of [(11)C]PyrATP-1, a novel radiotracer for PET imaging of glycogen synthase kinase-3β (GSK-3β)

INTRODUCTION

The dysfunction of glycogen synthase kinase-3β (GSK-3β) has been implicated in a number of diseases, including Alzheimer's disease. The ability to non-invasively quantify GSK-3β activity in vivo is therefore of critical importance, and this work is focused upon development of inhibitors of GSK-3β radiolabeled with carbon-11 to examine quantification of the enzyme using positron emission tomography (PET) imaging.

METHODS

(11)C PyrATP-1 was prepared from the corresponding desmethyl-piperazine precursor in an automated synthesis module. In vivo rodent and primate imaging studies were conducted on a Concorde MicroPET P4 scanner to evaluate imaging properties and in vitro autoradiography studies with rat brain samples were carried out to examine specific binding.

RESULTS

2035±518MBq (55±14mCi) of [(11)C]PyrATP-1 was obtained (1%-2% non-corrected radiochemical yield at end-of-synthesis based upon [(11)C]CO2) with high chemical (>95%) and radiochemical (>99%) purities, and good specific activities (143±52GBq/μmol (3874±1424Ci/mmol)), n=5. In vivo microPET imaging studies revealed poor brain uptake in rodents and non-human primates. Pretreatment of rodents with cyclosporin A resulted in moderately increased brain uptake suggesting Pgp transporter involvement. Autoradiography demonstrated high levels of specific binding in areas of the rodent brain known to be rich in GSK-3β.

CONCLUSION

(11)C PyrATP-1 is readily synthesized using standard carbon-11 radiochemistry. However the poor brain uptake in rodents and non-human primates indicates that the radiotracer is not suitable for the purposes of quantifying GSK-3β in neurological and psychiatric disorders.

White matter alterations in bipolar disorder: potential for drug discovery and development

OBJECTIVES

Brain white matter (WM) alterations have recently emerged as potentially relevant in bipolar disorder. New techniques such as diffusion tensor imaging allow precise exploration of these WM microstructural alterations in bipolar disorder. Our objective was to critically review WM alterations in bipolar disorder, using neuroimaging and neuropathological studies, in the context of neural models and the potential for drug discovery and development.

METHODS

We conducted a systematic PubMed and Google Scholar search of the WM and bipolar disorder literature up to and including January 2013.

RESULTS

Findings relating to WM alterations are consistent in neuroimaging and neuropathology studies of bipolar disorder, especially in regions involved in emotional processing such as the anterior frontal lobe, corpus callosum, cingulate cortex, and in fronto-limbic connections. Some of the structural alterations are related to genetic risk factors for bipolar disorder and may underlie the dysfunctional emotional processing described in recent neurobiological models of bipolar disorder. Medication effects in bipolar disorder, from lithium and other mood stabilizers, might impact myelinating processes, particularly by inhibition of glycogen synthase kinase-3 beta.

CONCLUSIONS

Pathways leading to WM alterations in bipolar disorder represent potential targets for the development and discovery of new drugs. Myelin damage in bipolar disorder suggests that the effects of existing pro-myelinating drugs should also be evaluated to improve our understanding and treatment of this disease.

Neuroprotective and anti-apoptotic effects of valproic acid on adult rat cerebral cortex through ERK and Akt signaling pathway at acute phase of traumatic brain injury

Mood stabilizer valproic acid (VPA), a widely used antiepileptic drug that has been demonstrated neuroprotective effect against various insults through multiple signaling pathways. The role of VPA in traumatic brain injury (TBI) remains unclear. In the present study, we investigated the neuroprotective potency of VPA for protection against TBI in adult rats, focusing on studying signaling mediators of two well characterized pro-survival molecules, extracellular signal-regulated protein kinase (ERK) and Akt. We found that treatment of VPA after TBI significantly attenuated brain edema, reduced contusion volume and the rate of neuronal apoptosis. The treatment also partly blocked an increase in capase-3 activity. VPA markedly up-regulated the activity of ERK and Akt expression. Moreover, treatment with either PD98059, an ERK inhibitor and/or LY294002, an Akt inhibitor, attenuated the neuroprotection of VPA against TBI to varying degrees. Taken together, these results demonstrated that treatment with VPA after TBI could be neuroprotective via activation of ERK and Akt signaling pathways.

The GSK3 signaling pathway is activated by cocaine and is critical for cocaine conditioned reward in mice

The Akt - GSK3 signaling pathway has been recently implicated in psychostimulant-induced behavioral and cellular effects. Here, the ability of cocaine to regulate the activity of Akt and GSK3 was investigated by measuring the phosphorylation states of the two kinases. The anatomical specificity of the response was determined, as was the contributions of dopamine and NMDA receptors to the actions of cocaine. As GSK3 activity was found to be increased by cocaine, subsequent experiments investigated the importance of GSK3 activation in cocaine conditioned reward. Adult male CD-1 mice were injected with cocaine or saline, and levels of phosphorylated Akt and GSK3α/β were measured 30 minutes later. Acute administration of cocaine significantly decreased the phosphorylation of Akt-Thr308 (pAkt-Thr308) and GSK3β in the caudate putamen and nucleus accumbens core, without altering pAkt-Ser473 and pGSK3α. To investigate the role of dopamine and NMDA receptors in the regulation of Akt and GSK3 by cocaine, specific receptor antagonists were administered prior to cocaine. Blockade of dopamine D2 receptors with eticlopride prevented the reduction of pAkt-Thr308 produced by cocaine, whereas antagonists at dopamine D1, dopamine D2 or glutamatergic NMDA receptors each blocked cocaine-induced reductions in pGSK3β. The potential importance of GSK3 activity in the rewarding actions of cocaine was determined using a cocaine conditioned place preference procedure. Administration of the selective GSK3 inhibitor, SB 216763, prior to cocaine conditioning sessions blocked the development of cocaine place preference. In contrast, SB 216763 did not alter the acquisition of a contextual fear conditioning response, demonstrating that SB 216763 did not globally inhibit contextual learning processes. The results of this study indicate that phosphorylation of GSK3β is reduced, hence GSK3β activity is increased following acute cocaine, an effect that is contingent upon both dopaminergic and glutamatergic receptors. Further, GSK3 activity is required for the development of cocaine conditioned reward.

Reactivation of cocaine reward memory engages the Akt/GSK3/mTOR signaling pathway and can be disrupted by GSK3 inhibition

RATIONAL

Memories return to a labile state following their retrieval and must undergo a process of reconsolidation to be maintained. Thus, disruption of cocaine reward memories by interference with reconsolidation may be therapeutically beneficial in the treatment of cocaine addiction.

OBJECTIVE

The objectives were to elucidate the signaling pathway involved in reconsolidation of cocaine reward memory and to test whether targeting this pathway could disrupt cocaine-associated contextual memory.

METHODS

Using a mouse model of conditioned place preference, regulation of the activity of glycogen synthase kinase-3 (GSK3), mammalian target of Rapamycin complex 1 (mTORC1), P70S6K, β-catenin, and the upstream signaling molecule Akt, was studied in cortico-limbic-striatal circuitry after re-exposure to an environment previously paired with cocaine.

RESULT

Levels of phosporylated Akt-Thr308, GSK3α-Ser21, GSK3β-Ser9, mTORC1, and P70S6K were reduced in the nucleus accumbens and hippocampus 10 min after the reactivation of cocaine cue memories. Levels of pAkt and pGSK3 were also reduced in the prefrontal cortex. Since reduced phosphorylation of GSK3 indicates heightened enzyme activity, the effect of a selective GSK3 inhibitor, SB216763, on reconsolidation was tested. Administration of SB216763 immediately after exposure to an environment previously paired with cocaine abrogated a previously established place preference, suggesting that GSK3 inhibition interfered with reconsolidation of cocaine-associated reward memories.

CONCLUSIONS

These findings suggest that the Akt/GSK3/mTORC1 signaling pathway in the nucleus accumbens, hippocampus, and/or prefrontal cortex is critically involved in the reconsolidation of cocaine contextual reward memory. Inhibition of GSK3 activity during memory retrieval can erase an established cocaine place preference.

L-isocorypalmine reduces behavioral sensitization and rewarding effects of cocaine in mice by acting on dopamine receptors

BACKGROUND

We previously reported isolation of l-isocorypalmine (l-ICP), a mono-demethylated analog of l-tetrahydropalmatine (l-THP), from the plant Corydalis yanhusuo. Here we characterized its in vitro pharmacological properties and examined its effects on cocaine-induced behaviors in mice.

METHODS

Receptor binding, cAMP and [(35)S]GTPγS assays were used to examine pharmacological actions of l-ICP in vitro. Effects of l-ICP on cocaine-induced locomotor hyperactivity and sensitization and conditioned place preference (CPP) in mice were investigated. HPLC was employed to analyze metabolites of l-ICP in mouse serum.

RESULTS

Among more than 40 targets screened, l-ICP and l-THP bound only to dopamine (DA) receptors. l-ICP was a high-affinity partial agonist of D1 and D5 receptors and a moderate-affinity antagonist of D2, D3 and D4 receptors, whereas l-THP bound to only D1 and D5 receptors, with lower affinities than l-ICP. At 10mg/kg (i.p.), l-ICP inhibited spontaneous locomotor activity for a shorter time than l-THP. Pretreatment with l-ICP reduced cocaine-induced locomotor hyperactivities. Administration of l-ICP before cocaine once a day for 5 days reduced cocaine-induced locomotor sensitization on days 5 and 13 after 7 days of withdrawal. Pretreatment with l-ICP before cocaine daily for 6 days blocked cocaine-induced CPP, while l-ICP itself did not cause preference or aversion. HPLC analysis showed that l-ICP was the main compound in mouse serum following i.p. injection of l-ICP.

CONCLUSIONS

l-ICP likely acts as a D1 partial agonist and a D2 antagonist to produce its in vivo effects and may be a promising agent for treatment of cocaine addiction.

Hyperactivity: glycogen synthase kinase-3 as a therapeutic target

The diagnosis of hyperactivity-associated disorders has increased within the past few years. The prevalence of hyperactivity-associated disorders is indicative of the need to more fully understand the underlying causes and to develop improved therapeutic interventions. There is increasing evidence that glycogen synthase kinase-3 (GSK3) mediates locomotor hyperactivity in a number of animal models, and therefore may be a potential target for therapeutic intervention in hyperactivity-associated behaviors. In this review, we discuss 1) the effect of manipulations of GSK3 in the absence of drugs and disorders on locomotor activity, 2) the role of GSK3 in drug-induced hyperactivity in rodents, and 3) regulation of locomotor activity by GSK3 in transgenic mouse models related to specific disorders. These studies link GSK3 regulation and activity to hyperactivity-associated behaviors and disease pathologies.

Long-lasting antidepressant action of ketamine, but not glycogen synthase kinase-3 inhibitor SB216763, in the chronic mild stress model of mice

Background

Clinical studies demonstrate that the N-methyl-D-aspartate (NMDA) receptor antagonist, ketamine, induces rapid antidepressant effects in patients with refractive major depressive disorder and bipolar depression. This rapid onset of action makes ketamine a highly attractive drug for patients, particularly those who do not typically respond to therapy. A recent study suggested that glycogen synthase kinase (GSK)-3 may underlie the rapid antidepressant action of ketamine, although the precise mechanisms are unclear. In this study, we examined the effects of ketamine and GSK-3 inhibitor SB216763 in the unpredictable, chronic mild stress (CMS) mouse model of mice.

Methodology/Principal Findings

Adult C57/B6 male mice were divided into 2 groups, a non-stressed control group and the unpredictable CMS (35 days) group. Then, either vehicle, ketamine (10 mg/kg), or the established GSK-3 inhibitor, SB216763 (10 mg/kg), were administered into mice in the CMS group, while vehicle was administered to controls. In the open field test, there was no difference between the four groups (control+vehicle, CMS+vehicle, CMS+ketamine, CMS+SB216763). In the sucrose intake test, a 1% sucrose intake drop, seen in CMS mice, was significantly attenuated after a single dose of ketamine, but not SB216763. In the tail suspension test (TST) and forced swimming test (FST), the increased immobility time seen in CMS mice was significantly attenuated by a single dose of ketamine, but not SB216763. Interestingly, the ketamine-induced increase in the sucrose intake test persisted for 8 days after a single dose of ketamine. Furthermore, a single administration of ketamine, but not SB216763, significantly attenuated the immobility time of the TST and FST in the control (non-stressed) mice.

Conclusions/Significance

These findings suggest that a single administration of ketamine, but not GSK-3 inhibitor SB216763, produces a long-lasting antidepressant action in CMS model mice.

Examination of methylphenidate-mediated behavior regulation by glycogen synthase kinase-3 in mice

Abnormalities in dopaminergic activity have been implicated in psychiatric diseases, such as attention deficit hyperactivity disorder (ADHD), and are treated with therapeutic stimulants, commonly methylphenidate or amphetamine. Amphetamine administration increases glycogen synthase kinase-3 (GSK3) activation, which is necessary for certain acute behavioral responses to amphetamine, including increased locomotor activity and impaired sensorimotor gating. Here, we tested if modulating GSK3 by administration of the GSK3 inhibitor lithium or expression of constitutively active GSK3 altered behavioral responses to methylphenidate administered to mice acutely or daily for 8 days. Methylphenidate or amphetamine was administered to mice intraperitoneally for 1 or 8 days. Open-field activity and pre-pulse inhibition (PPI) were measured. In contrast to lithium's blockade of acute amphetamine-induced locomotor hyperactivity, lithium treatment did not significantly reduce methylphenidate-induced locomotor hyperactivity in wild-type mice after acute or 8 days of repeated methylphenidate administration. Lithium treatment significantly increased the impairment in PPI caused by methylphenidate, but significantly reduced the amphetamine-induced PPI deficit. In GSK3 knockin mice, expression of constitutively active GSK3β, but not GSK3α, significantly increased locomotor hyperactivity after acute methylphenidate treatment, and significantly impaired PPI, preventing further methylphenidate-induced impairment of PPI that was evident in wild-type mice and GSK3α knockin mice. Lithium does not counteract locomotor activity and PPI responses to methylphenidate as it does these responses to amphetamine, indicating that different mechanisms mediate these behavioral responses to methylphenidate and amphetamine. Only active GSK3β, not GSK3α, modulates behavioral responses to MPH, indicating selectivity in the actions of GSK3 isoforms.

Control of neuronal ion channel function by glycogen synthase kinase-3: new prospective for an old kinase

Glycogen synthase kinase 3 (GSK-3) is an evolutionarily conserved multifaceted ubiquitous enzyme. In the central nervous system (CNS), GSK-3 acts through an intricate network of intracellular signaling pathways culminating in a highly divergent cascade of phosphorylations that control neuronal function during development and adulthood. Accumulated evidence indicates that altered levels of GSK-3 correlate with maladaptive plasticity of neuronal circuitries in psychiatric disorders, addictive behaviors, and neurodegenerative diseases, and pharmacological interventions known to limit GSK-3 can counteract some of these deficits. Thus, targeting the GSK-3 cascade for therapeutic interventions against this broad spectrum of brain diseases has raised a tremendous interest. Yet, the multitude of GSK-3 downstream effectors poses a substantial challenge in the development of selective and potent medications that could efficiently block or modulate the activity of this enzyme. Although the full range of GSK-3 molecular targets are far from resolved, exciting new evidence indicates that ion channels regulating excitability, neurotransmitter release, and synaptic transmission, which ultimately contribute to the mechanisms underling brain plasticity and higher level cognitive and emotional processing, are new promising targets of this enzyme. Here, we will revise this new emerging role of GSK-3 in controling the activity of voltage-gated Na(+), K(+), Ca(2+) channels and ligand-gated glutamate receptors with the goal of highlighting new relevant endpoints of the neuronal GSK-3 cascade that could provide a platform for a better understanding of the mechanisms underlying the dysfunction of this kinase in the CNS and serve as a guidance for medication development against the broad range of GSK-3-linked human diseases.

Neuroglialpharmacology: myelination as a shared mechanism of action of psychotropic treatments

Current psychiatric diagnostic schema segregate symptom clusters into discrete entities, however, large proportions of patients suffer from comorbid conditions that fit neither diagnostic nor therapeutic schema. Similarly, psychotropic treatments ranging from lithium and antipsychotics to serotonin reuptake inhibitors (SSRIs) and acetylcholinesterase inhibitors have been shown to be efficacious in a wide spectrum of psychiatric disorders ranging from autism, schizophrenia (SZ), depression, and bipolar disorder (BD) to Alzheimer's disease (AD). This apparent lack of specificity suggests that psychiatric symptoms as well as treatments may share aspects of pathophysiology and mechanisms of action that defy current symptom-based diagnostic and neuron-based therapeutic schema. A myelin-centered model of human brain function can help integrate these incongruities and provide novel insights into disease etiologies and treatment mechanisms. Available data are integrated herein to suggest that widely used psychotropic treatments ranging from antipsychotics and antidepressants to lithium and electroconvulsive therapy share complex signaling pathways such as Akt and glycogen synthase kinase-3 (GSK3) that affect myelination, its plasticity, and repair. These signaling pathways respond to neurotransmitters, neurotrophins, hormones, and nutrition, underlie intricate neuroglial communications, and may substantially contribute to the mechanisms of action and wide spectra of efficacy of current therapeutics by promoting myelination. Imaging and genetic technologies make it possible to safely and non-invasively test these hypotheses directly in humans and can help guide clinical trial efforts designed to correct myelination abnormalities. Such efforts may provide insights into novel avenues for treatment and prevention of some of the most prevalent and devastating human diseases.

Inhibition of GSK3 attenuates amphetamine-induced hyperactivity and sensitization in the mouse

Glycogen synthase kinase 3 (GSK3) is implicated in mediating dopamine-dependent behaviors. Previous studies have demonstrated the ability of amphetamine, which increases extracellular dopamine levels and influences behavior, to regulate the activity of GSK3. This study used valproic acid and the selective GSK3 inhibitor, SB 216763, to examine the role of GSK3 in amphetamine-induced hyperactivity and the development of sensitized stereotypic behavior. Pretreatment with valproic acid (50-300 mg/kg, i.p.) or SB 216763 (2.5-5 mg/kg, i.p.) prior to amphetamine (2 mg/kg, i.p.) significantly reduced amphetamineinduced ambulation and stereotypy. To assess the development of sensitization to the stereotypic effects of amphetamine, mice were pretreated daily with valproic acid (300 mg/kg) or SB 216763 (5 mg/kg) prior to amphetamine (2 mg/kg) for 5 days. Upon amphetamine challenge (1 mg/kg) 7 days later, mice pretreated with valproate or SB 216763 showed a significant attenuation of amphetamine-induced sensitization of stereotypy. To determine whether regulation of GSK3 activity was associated with attenuation of acute amphetamine-induced hyperactivity by valproic acid, valproate (300 mg/kg) or vehicle was injected prior to amphetamine (2 mg/kg) or saline and brain tissue obtained. Analysis of the levels of phospho-GSK3α and β by immunoblot indicated that valproate increased phosphorylation of ser²¹-GSK3α in the frontal cortex, as well as ser⁹-GSK3β in the frontal cortex and caudate putamen of amphetamine-injected mice. These data support a role for GSK3 in acute amphetamine-induced hyperactivity and the development of sensitization to amphetamine-induced stereotypy.

Brain region differences in regulation of Akt and GSK3 by chronic stimulant administration in mice

Acute amphetamine administration activates glycogen synthase kinase-3 (GSK3) by reducing its inhibitory serine-phosphorylation in mouse striatum and cerebral cortex. This results from Akt inactivation and is required for certain behavioral effects of amphetamine, such as increased locomotor activity. Here we tested if regulation of Akt and GSK3 was similarly affected by longer-term administration of amphetamine, as well as of methylphenidate, since each of these is administered chronically in patients with attention deficit hyperactivity disorder (ADHD). Akt is activated by post-translational phosphorylation on Thr308, and modulated by Ser473 phosphorylation, whereas phosphorylation on Ser21/9 inhibits the two GSK3 isoforms, GSK3α and GSK3β. After eight days of amphetamine or methylphenidate treatment, striatal Akt and GSK3 were dephosphorylated similar to reported changes after acute amphetamine treatment. Oppositely, in the cerebral cortex and hippocampus Akt and GSK3 phosphorylation increased after eight days of amphetamine or methylphenidate treatment. These opposite brain region changes in Akt and GSK3 phosphorylation matched opposite changes in the association of Akt with β-arrestin and GSK3, which after eight days of amphetamine treatment were increased in the striatum and decreased in the cerebral cortex. Thus, whereas the acute dephosphorylating effect of stimulants on Akt and GSK3 in the striatum was maintained, the response switched in the cerebral cortex after eight days of amphetamine or methylphenidate treatment to cause increased phosphorylation of Akt and GSK3. These results demonstrate that prolonged administration of stimulants causes brain region-selective differences in the regulation of Akt and GSK3.

Cav 1.3 L-type Ca ( 2+) channels mediate long-term adaptation in dopamine D2L-mediated GluA1 trafficking in the dorsal striatum following cocaine exposure

AMPA receptor (AMPAR) plasticity at glutamatergic synapses in the mesostriatal dopaminergic pathway has been implicated in persistent cocaine-induced behavioral responses; however, the precise mechanism underlying these changes remains unknown. Utilizing cocaine psychomotor sensitization in mice we find that repeated cocaine results in a basal reduction of Ser 845 GluA1 and cell surface GluA1 levels in the dorsal striatum (dStr) following a protracted withdrawal period, an adaptation that is dependent on Cav 1.3 channels but not those expressed in the VTA. We find that the basally-induced decrease in this phosphoprotein is the result of recruitment of the striatal dopamine D2 pathway, as evidenced by enhanced levels of D2 receptor (D2R) mRNA expression and D2R function as examined using the D2R antagonist, eticlopride, as well as alterations in the phosphorylation status of several downstream molecular targets of D2R's, including CREB, DARPP-32, Akt and GSK3β. Taken together with our recently published findings examining similar phenomena in the nucleus accumbens (NAc), these results underscore the utilization of divergent molecular mechanisms in the dStr, in mediating cocaine-induced persistent behavioral changes.

Cocaine induces the expression of MEF2C transcription factor in rat striatum through activation of SIK1 and phosphorylation of the histone deacetylase HDAC5

Distinct forms of MEF2 transcription factor act as positive or negative regulators of dendritic spine formation, with MEF2C playing a key regulator role in synapse plasticity. We report here that acute cocaine treatment of rats induced the expression of MEF2C in the striatum through a recently discovered transduction pathway. Repeated injections were found to induce MEF2C to a lesser extent. The mechanism by which MEF2C was induced involves the subsequent activation of the salt-inducible kinase SIK1 and the phosphorylation of HDAC5, a member of the class IIa of HDACs. Cocaine activated SIK1 by phosphorylation on Thr-182 residue, which was accompanied by the nuclear import of the kinase. In the nuclear compartment, SIK1 then phosphorylated HDAC5 causing the shuttling of its phospho-form from the nucleus to the cytoplasm of striatal cells. Activation of SIK1 by cocaine was further validated by the phosphorylation of TORC1/3, which was followed by the shuttling of TORC proteins from the nucleus to the cytoplasm. Activation of MEF2C was assessed by measuring the expression of the MEF2C gene itself, since the gene is known to be under the control of its own product. Since MEF2C plays a key role in memory/learning processes, activation of this pathway by cocaine is probably involved in plasticity mechanisms whereby the drug establishes its long-term effects such as drug dependence.