Inhibition of glycogen synthase kinase-3 by SB 216763 affects acquisition at lower doses than expression of amphetamine-conditioned place preference in rats

Glycogen Synthase Kinase-3 Inhibitors Block Morphine-Induced Locomotor Activation, Straub Tail, and Depression of Rearing in Mice Via a Possible Central Action

We investigated morphine-induced Straub's tail reaction (STR) in mice pretreated with or without glycogen synthase kinase-3 (GSK-3) inhibitors (SB216763 and AR-A014418) by using a newly modified, infrared beam sensor-based automated apparatus. Mice treated with a single injection of morphine (30 mg/kg, i.p.) showed a significant STR with a plateau level at a time point of 20 min after morphine challenge. Pretreatment of mice with SB216763 (5 mg/kg, s.c.) or AR-A014418 (3 mg/kg, i.p.) significantly inhibited morphine-induced STR and attenuated the duration of STR in a dose-dependent fashion. In the striatum and the nucleus accumbens, expression of pGSK-3β^Tyr216 but not GSK3β or pGSK-3β^Ser9 was largely but not significantly reduced after treatment with SB216763 (5 mg/kg, s.c.) in combination with/without morphine, indicating that the inhibitory effect of GSK-3 inhibitors on morphine-induced STR and hyperlocomotion might not depend on the direct blockade of GSK-3β function. In constipated mice after morphine challenge (30 mg/kg), the effect of GSK-3 inhibitors on gastrointestinal transit was examined to reveal whether the action of GSK-3 inhibitors on morphine effects was central and/or peripheral. Pretreatment with SB216763 (5 mg/kg) did not block constipation in morphine-injected mice. The mechanism of action seems to be central but not peripheral, although the underlying subcellular mechanism of GSK-3 inhibitors is not clear. Our measurement system is a useful tool for investigating the excitatory effects of morphine in experimental animals.

Anxiety and cognitive-related effects of Δ 9-tetrahydrocannabinol (THC) are differentially mediated through distinct GSK-3 vs. Akt-mTOR pathways in the nucleus accumbens of male rats

RATIONALE

Δ⁹-tetrahydrocannabinol (THC) is the primary psychoactive compound in cannabis and is responsible for cannabis-related neuropsychiatric side effects, including abnormal affective processing, cognitive and sensory filtering deficits and memory impairments. A critical neural region linked to the psychotropic effects of THC is the nucleus accumbens shell (NASh), an integrative mesocorticolimbic structure that sends and receives inputs from multiple brain areas known to be dysregulated in various disorders, including schizophrenia and anxiety-related disorders. Considerable evidence demonstrates functional differences between posterior vs. anterior NASh sub-regions in the processing of affective and cognitive behaviours influenced by THC. Nevertheless, the neuroanatomical regions and local molecular pathways responsible for these psychotropic effects are not currently understood.

OBJECTIVES

The objectives of this study were to characterize the effects of intra-accumbens THC in the anterior vs. posterior regions of the NASh during emotional memory formation, sensorimotor gating and anxiety-related behaviours.

METHODS

We performed an integrative series of translational behavioural pharmacological studies examining anxiety, sensorimotor gating and fear-related associative memory formation combined with regionally specific molecular signalling analyses in male Sprague Dawley rats.

RESULTS

We report that THC in the posterior NASh causes distortions in emotional salience attribution, impaired sensory filtering and memory retention and heightened anxiety, through a glycogen-synthase-kinase-3 (GSK-3)-β-catenin dependent signalling pathway. In contrast, THC in the anterior NASh produces anxiolytic effects via modulation of protein kinase B (Akt) phosphorylation states.

CONCLUSIONS

These findings reveal critical new insights into the neuroanatomical and molecular mechanisms associated with the differential neuropsychiatric side effects of THC in dissociable nucleus accumbens sub-regions.

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.

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.

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.

Differential Roles of Accumbal GSK3β in Cocaine versus Morphine-Induced Place Preference, U50,488H-Induced Place Aversion, and Object Memory

Previous research has demonstrated that activity of glycogen synthase kinase-3 (GSK3) is necessary for the rewarding effects of cocaine. In the present study, a conditional GSK3β gene knockdown model was used to determine if GSK3β activity specifically in the nucleus accumbens is important for cocaine conditioned reward. The roles of accumbal GSK3β in morphine conditioned reward, trans-(±)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide methanesulfonate salt (U50,488H)-induced conditioned place aversion, and cognitive function were also studied. Adult male and female GSK3β-floxed or wild-type mice were injected with adeno-associated virus/Cre into the nucleus accumbens to reduce expression of GSK3β and underwent behavioral testing 4 weeks later. The development of cocaine-induced conditioned place preference was significantly attenuated in mice with reduced levels of GSK3β in the nucleus accumbens, whereas the development of morphine-induced place preference remained intact. Conditional knockdown of GSK3β in the accumbens prevented the development of conditioned aversion produced by U50,488H, a κ-opioid receptor agonist. Cognitive memory tests revealed deficits in object location memory, but not novel object recognition in mice with accumbal GSK3β knockdown. These data demonstrate that GSK3β in the nucleus accumbens is required for cocaine conditioned place preference and U50,488H conditioned place aversion, as well as spatial memory in object location task, indicating differential roles of GSK3β in the psychostimulant and opiate reward process, as well as in memory for spatial locations and object identity. SIGNIFICANCE STATEMENT: Knockdown of GSK3β in the nucleus accumbens attenuated the development of cocaine-induced place preference, as well as conditioned place aversion to U50,488H, a κ-opioid receptor agonist. In contrast, the development of morphine place preference was not altered by GSK3β knockdown. GSK3β knockdown in nucleus accumbens impaired performance in the object location task, but not the novel object recognition task. These results elucidate different physiological roles of accumbal GSKβ in conditioned reward, aversion, and memory.

Small-Molecule SB216763-Loaded Microspheres Repair Peripheral Nerve Injury in Small Gap Tubulization

Peripheral nerve injury has yet to be fully resolved because of its complicated pathological process. SB216763 is a small molecular compound that can enhance the remyelination of peripheral nerves by inhibiting glycogen synthase kinase-3β (GSK3β). GSK-3β inhibitor stimulates myelin gene expression and restores the myelin structure. Herein, we presented the effect of integrating small gap tubulization with SB216763-loaded microspheres by using a chitosan conduit. In vitro, SB216763 could promote neurite growth of dorsal root ganglia. In vivo studies showed that SB216763 increased the number of myelinated axons and the thickness of myelin sheaths. Electrophysiological examination and sciatic functional index results also indirectly indicated the role of SB216763 in repairing peripheral nerve injury. SB216763 promoted the recovery of muscle function. Therefore, combining SB216763-loaded PLGA microspheres with conduit small gap tubulization shows potential for applications in repairing peripheral nerve injury.

Disparate Effects of Lithium and a GSK-3 Inhibitor on Neuronal Oscillatory Activity in Prefrontal Cortex and Hippocampus

Glycogen synthase kinase-3 (GSK-3) plays a critical role in cognitive dysfunction associated with Alzheimer’s disease (AD), yet the mechanism by which GSK-3 alters cognitive processes in other disorders, such as schizophrenia, remains unknown. In the present study, we demonstrated a role for GSK-3 in the direct regulation of neuronal oscillations in hippocampus (HIP) and prelimbic cortex (PL). A comparison of the GSK-3 inhibitors SB 216763 and lithium demonstrated disparate effects of the drugs on spatial memory and neural oscillatory activity in HIP and PL. SB 216763 administration improved spatial memory whereas lithium treatment had no effect. Analysis of neuronal local field potentials in anesthetized animals revealed that whereas both repeated SB 216763 (2.5 mg/kg) and lithium (100 mg/kg) induced a theta frequency spike in HIP at approximately 10 Hz, only SB 216763 treatment induced an overall increase in theta power (4–12 Hz) compared to vehicle. Acute administration of either drug suppressed slow (32–59 Hz) and fast (61–100 Hz) gamma power. In PL, both drugs induced an increase in theta power. Repeated SB 216763 increased HIP–PL coherence across all frequencies except delta, whereas lithium selectively suppressed delta coherence. These findings demonstrate that GSK-3 plays a direct role in the regulation of theta oscillations in regions critically involved in cognition, and highlight a potential mechanism by which GSK-3 may contribute to cognitive decline in disorders of cognitive dysfunction.

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.