Amphetamine increases the phosphorylation of neuromodulin and synapsin I in rat striatal synaptosomes

Amphetamine-induced neurite injury in PC12 cells through inhibiting GAP-43 pathway

Amphetamine (AMPH) causes the degeneration of dopamine terminals in the central nervous system. The mechanisms for this damage are unclear. We found AMPH reduced level of GAP-43 in the striatum of rats that receives rich dopaminergic terminals. Using PC12 cells as dopaminergic neuronal models, we further found that AMPH inhibited GAP-43 and GAP-43 phosphorylation in PC12 cells. The reduced GAP-43 was correlated with neurite injury of PC12 cells. The PKCβ1, an upstream molecule of GAP-43, was also inhibited by AMPH. Phorbol 12-myristate 13-acetate (PMA) as a specific activator of PKC increased levels of PKCβ1 and GAP-43, and efficiently prevented neurite degeneration of PC12 cells induced by AMPH. On the other side, enzastuarin, an inhibitor of PKC, decreased levels of PKCβ1 and GAP-43, and caused neurite injury of PC12 cells. Together, our results suggest that AMPH induces neurite injury in PC12 cells through inhibiting PKCβ1/GAP-43 pathway.

The protein kinase Cβ-selective inhibitor, enzastaurin, attenuates amphetamine-stimulated locomotor activity and self-administration behaviors in rats

RATIONALE

Pathological amphetamine (AMPH) use is a serious public health concern with no pharmacological treatment options. Protein kinase Cβ (PKCβ) has been implicated in the mechanism of action of AMPH, such that inhibition of PKCβ attenuates AMPH-stimulated dopamine efflux in vivo. With this in mind, inhibition of PKCβ may be a viable therapeutic target for AMPH use disorder.

OBJECTIVE

The purpose of this study is to demonstrate that selective pharmacological inhibition of PKCβ alters AMPH-stimulated behaviors in rats.

METHODS

Rats were administered intracerebroventricular (i.c.v.) injections of the PKCβ-selective inhibitor enzastaurin 0.5, 3, 6, or 18 h before evaluating AMPH-stimulated locomotion (0.32-3.2 mg/kg). Rats were trained to make responses for different doses of AMPH infusions or sucrose under a fixed ratio 5 schedule of reinforcement, and the effects of enzastaurin pretreatment 3 or 18 h prior to a self-administration session were determined. Also, the effect of enzastaurin on AMPH-stimulated PKC activity in the ventral striatum was evaluated.

RESULTS

A large dose of enzastaurin (1 nmol) decreased AMPH-stimulated locomotor activity 0.5 h following enzastaurin administration. Small doses of enzastaurin (10-30 pmol) attenuated AMPH-stimulated locomotor activity and shifted the AMPH dose-effect curve to the right following an 18-h pretreatment. Rats pretreated with enzastaurin 18 h, but not 3, prior to a self-administration session showed a decrease in the number of responses for AMPH, shifted the ascending limb of the amphetamine dose effect curve, and produced no change in responses for sucrose. AMPH-stimulated PKC activity was decreased following a 0.5- or 18-h pretreatment, but not a 3-h pretreatment of enzastaurin.

CONCLUSIONS

These results demonstrate that inhibition of PKCβ will decrease AMPH-stimulated behaviors and neurobiological changes and suggest that PKCβ is potentially a viable target for AMPH use disorder.

Ruboxistaurin Reduces Cocaine-Stimulated Increases in Extracellular Dopamine by Modifying Dopamine-Autoreceptor Activity

Cocaine is a highly abused drug, and cocaine addiction affects millions of individuals worldwide. Cocaine blocks normal uptake function at the dopamine transporter (DAT), thus increasing extracellular dopamine. Currently, no chemical therapies are available to treat cocaine abuse. Previous works showed that the selective inhibitors of protein kinase Cβ (PKCβ), enzastaurin and ruboxistaurin, attenuate dopamine overflow and locomotion stimulated by another psychostimulant drug, amphetamine. We now test if ruboxistaurin similarly affects cocaine action. Perfusion of 1 μM ruboxistaurin directly into the core of the nucleus accumbens via retrodialysis reduced cocaine-stimulated increases in dopamine overflow, measured using microdialysis sampling, with simultaneous reductions in locomotor behavior. Because cocaine activity is highly regulated by dopamine autoreceptors, we examined whether ruboxistaurin was acting at the level of the D2 autoreceptor. Perfusion of 5 μM raclopride, a selective D2-like receptor antagonist, before addition of ruboxistaurin, abrogated the effect of ruboxistaurin on cocaine-stimulated dopamine overflow and hyperlocomotion. Further, ruboxistaurin was inactive against cocaine-stimulated locomotor activity in mice with a genetic deletion in D2 receptors as compared to wild-type mice. In contrast, blockade or deletion of dopamine D2 receptors did not abolish the attenuating effect of ruboxistaurin on amphetamine-stimulated activities. Therefore, the inhibition of PKCβ reduces dopamine overflow and locomotor activity stimulated by both cocaine and amphetamine, but the mechanism of action differs for each stimulant. These data suggest that inhibition of PKCβ would serve as a target to reduce the abuse of either amphetamine or cocaine.

Molecular Mechanisms of Amphetamines

There is a plethora of amphetamine derivatives exerting stimulant, euphoric, anti-fatigue, and hallucinogenic effects; all structural properties allowing these effects are contained within the amphetamine structure. In the first part of this review, the interaction of amphetamine with the dopamine transporter (DAT), crucially involved in its behavioral effects, is covered, as well as the role of dopamine synthesis, the vesicular monoamine transporter VMAT2, and organic cation 3 transporter (OCT3). The second part deals with requirements in amphetamine's effect on the kinases PKC, CaMKII, and ERK, whereas the third part focuses on where we are in developing anti-amphetamine therapeutics. Thus, treatments are discussed that target DAT, VMAT2, PKC, CaMKII, and OCT3. As is generally true for the development of therapeutics for substance use disorder, there are multiple preclinically promising specific compounds against (meth)amphetamine, for which further development and clinical trials are badly needed.

A role for nucleus accumbens glutamate in the expression but not the induction of behavioural sensitization to ethanol

Mechanisms underlying differential sensitivity to behavioural sensitization to ethanol (EtOH) remain poorly understood, although accumulating evidence suggests a role for glutamatergic processes in the ventral striatum. Efforts to address this issue can benefit from the well-documented fact that in any given cohort, some of the mice (High sensitized; HS) show robust sensitization, while others (Low sensitized; LS) show little, if any, sensitization. Here, we examined whether this variability might be differentially associated with nucleus accumbens (NAc) glutamate processes. Male DBA mice received 5 EtOH (2.2g/kg) or saline injections twice a week and were challenged with EtOH (1.8g/kg) 2 weeks after injection 5. When an EtOH challenge was administered 2 weeks following the induction of sensitization, HS, but not LS, mice showed a robust increase in glutamate levels (67%, P<0.01) as measured by in vivo microdialysis. In a separate cohort, the mGlu2/3 agonist LY354740 (10mg/kg), given prior to the EtOH challenge, abolished the expression of sensitization. To ascertain whether enhanced release could also be observed during the induction of sensitization, glutamate levels were measured after the 1st and 5th EtOH injection and were found to be unchanged in HS mice, although briefly elevated in LS mice at injection 5. To further assess possible glutamate involvement during the induction of sensitization, sensitizing EtOH injections were co-administered with NMDAR antagonists. At the doses used, MK-801 (0.25mg/kg) and CGS 19755 (10mg/kg) blocked the expression of sensitization, but did not significantly interfere with the development of EtOH sensitization. Within the limitations of the present design, the results suggest an important role for EtOH-induced glutamate release in the NAc when sensitization is well established, but not necessarily during the development of sensitization.

Tamoxifen and amphetamine abuse: Are there therapeutic possibilities?

Although best known as a selective estrogen receptor modulator (SERM), tamoxifen is a drug with a wide range of activities. Tamoxifen has demonstrated some efficacy has a therapeutic for bipolar mania and is believed to exert these effects through inhibition of protein kinase C (PKC). As the symptoms of amphetamine treatment in rodents are believed to mimic the symptoms of a manic episode, many of the preclinical studies for this indication have demonstrated that tamoxifen inhibits amphetamine action. The amphetamine-induced increase in extracellular dopamine which gives rise to the 'manic' effects is due to interaction of amphetamine with the dopamine transporter. We and others have demonstrated that PKC reduces amphetamine-induced reverse transport through the dopamine transporter. In this review, we will outline the actions of tamoxifen as a SERM and further detail another known action of tamoxifen-inhibition of PKC. We will summarize the literature showing how tamoxifen affects amphetamine action. Finally, we will present our hypothesis that tamoxifen, or an analog, could be used therapeutically to reduce amphetamine abuse in addition to treating mania.

PKCβ Inhibitors Attenuate Amphetamine-Stimulated Dopamine Efflux

Amphetamine abuse afflicts over 13 million people, and there is currently no universally accepted treatment for amphetamine addiction. Amphetamine serves as a substrate for the dopamine transporter and reverses the transporter to cause an increase in extracellular dopamine. Activation of the beta subunit of protein kinase C (PKCβ) enhances extracellular dopamine in the presence of amphetamine by facilitating the reverse transport of dopamine and internalizing the D2 autoreceptor. We previously demonstrated that PKCβ inhibitors block amphetamine-stimulated dopamine efflux in synaptosomes from rat striatum in vitro. In this study, we utilized in vivo microdialysis in live, behaving rats to assess the effect of the PKCβ inhibitors, enzastaurin and ruboxistaurin, on amphetamine-stimulated locomotion and increases in monoamines and their metabolites. A 30 min perfusion of the nucleus accumbens core with 1 μM enzastaurin or 1 μM ruboxistaurin reduced efflux of dopamine and its metabolite 3-methoxytyramine induced by amphetamine by approximately 50%. The inhibitors also significantly reduced amphetamine-stimulated extracellular levels of norepinephrine. The stimulation of locomotor behavior by amphetamine, measured simultaneously with the analytes, was comparably reduced by the PKCβ inhibitors. Using a stable isotope label retrodialysis procedure, we determined that ruboxistaurin had no effect on basal levels of dopamine, norepinephrine, glutamate, or GABA. In addition, normal uptake function through the dopamine transporter was unaltered by the PKCβ inhibitors, as measured in rat synaptosomes. Our results support the utility of using PKCβ inhibitors to reduce the effects of amphetamine.

Beta2-containing nicotinic acetylcholine receptors mediate calcium/calmodulin-dependent protein kinase-II and synapsin I protein levels in the nucleus accumbens after nicotine withdrawal in mice

Nicotinic acetylcholine receptors are calcium-permeable and the initial targets for nicotine. Studies suggest that calcium-dependent mechanisms mediate some behavioral responses to nicotine; however, the post-receptor calcium-dependent mechanisms associated with chronic nicotine and nicotine withdrawal remain unclear. The proteins calcium/calmodulin-dependent protein kinase II (CaMKII) and synapsin I are essential for neurotransmitter release and were shown to be involved in drug dependence. In the current study, using pharmacological techniques, we sought to (a) complement previously published behavioral findings from our lab indicating a role for calcium-dependent signaling in nicotine dependence and (b) expand on previously published acute biochemical and pharmacological findings indicating the relevance of calcium-dependent mechanisms in acute nicotine responses by evaluating the function of CaMKII and synapsin I after chronic nicotine and withdrawal in the nucleus accumbens, a brain region implicated in drug dependence. Male mice were chronically infused with nicotine for 14 days, and treated with the β2-selective antagonist dihydro-β-erythroidine (DHβE), or the α7 antagonist, methyllycaconitine citrate (MLA) 20min prior to dissection of the nucleus accumbens. Results show that phosphorylated and total CaMKII and synapsin I protein levels were significantly increased in the nucleus accumbens after chronic nicotine infusion, and reduced after treatment with DHβE, but not MLA. A spontaneous nicotine withdrawal assessment also revealed significant reductions in phosphorylated CaMKII and synapsin I levels 24h after cessation of nicotine treatment. Our findings suggest that post-receptor calcium-dependent mechanisms associated with nicotine withdrawal are mediated through β2-containing nicotinic receptors.

Amphiphysin I but not dynamin I nor synaptojanin mRNA expression increased after repeated methamphetamine administration in the rat cerebrum and cerebellum

Dopamine increases/decreases synaptic vesicle recycling and in schizophrenia the proteins/mRNA is decreased. We isolated cDNA clone, similar to amphiphysin 1 (vesicle protein) mRNA from the neocortex of rats injected repeatedly with methamphetamine using polymerase chain reaction (PCR) differential display. This clone is highly homologous to the 3' region of the human amphiphysin gene. PCR extension study using a primer specific for the rat amphiphysin 1 gene and a primer located within the clone revealed that it is the 3' UTR region of the rat amphiphysin 1 gene. Furthermore, in situ hybridization revealed that amphiphysin 1 mRNA is expressed in the cerebrum, medial thalamus, hippocampus and cerebellum. In the cerebellum, amphiphysin mRNA expression was confined to upper granule cell layer. Repeated methamphetamine administration increased amphiphysin I mRNA expression in both anterior part of the cerebrum, and the cerebellum. However, the repeated administration did not alter mRNA expression of the other vesicle proteins, synaptotagmin I, synapsin I, synaptojanin and dynamin I, we conclude that the repeated administration selectively increased amphiphysin 1 mRNA expression. Thus, amphiphysin 1 does not work as synaptic recycling, but it is suggested, as a part of pathogenesis of brain tissue injury (under Ca²⁺ and Mg²⁺ devoid environment) in repeated methamphetamine-injected states, the gene regulate actin-asssembly, learning, cell stress signaling and cell polarity.

Successful combined therapy with tamoxifen and lithium in a paradoxical sleep deprivation-induced mania model

BACKGROUND

Previous studies have suggested that manic states and sleep deprivation could contribute to the pathophysiology of bipolar disorder (BD) through protein kinase C (PKC) signaling abnormalities. Moreover, adjunctive therapy has become a standard strategy in the management of BD patients who respond poorly to current pharmacological treatments.

AIM

Thus, the aim of this study was to investigate the possible involvement of PKC inhibition by tamoxifen both separately or in combination with lithium, in paradoxical sleep deprivation (PSD)-induced hyperactivity, one facet of mania-like behavior.

MATERIALS & METHODS

Adult male C57BL/6J mice were randomly distributed (n = 7/group) in 24-h PSD or control groups and injected intraperitoneally (i.p.) with vehicle, lithium (50, 100, or 150 mg/kg) or tamoxifen (0.5, 1.0, or 2.0 mg/kg - experiment 1). In a second experiment, mice were injected i.p. with vehicle or a combination of subeffective doses of lithium and tamoxifen. Animals were subjected to a protocol based on repetitive PSD conditions, followed by assessment of locomotion activity in the open-field task.

RESULTS

PSD significantly increased locomotor activity in both experiments. These behavioral changes were prevented by a treatment with lithium or tamoxifen, or a combined treatment with both lithium and tamoxifen.

DISCUSSION

Therefore, our findings suggest that lithium and tamoxifen exert reversal effects against PSD-induced hyperactivity in mice.

CONCLUSION

Furthermore, tamoxifen as an adjunct to lithium therapy provides support for an alternative treatment of individuals who either do not respond adequately or cannot tolerate the adverse effects associated with therapeutic doses of lithium.

Dopamine transporter trafficking: rapid response on demand

The dopamine transporter (DAT) is a primary determinant of the concentration of dopamine in the synapse and is involved in a number of psychiatric and neurological diseases. The transporter actively takes up its physiological substrate, dopamine, when it is on the surface of the plasmalemmal membrane, but the concentration of DAT in the membrane is highly regulated by substrate. Substrates initially, and very rapidly, recruit more DAT into the membrane for greater function, but continued presence of substrate downregulates the activity of DAT and even membrane DAT content. This biphasic regulation is orchestrated by numerous signal transduction mechanisms, including a palette of protein kinases. Understanding the mechanisms of rapid regulation of DAT could provide new therapeutic strategies to improve transporter function and modulate responses to its more notorious substrates, amphetamine and methamphetamine.

Beta 2 subunit-containing nicotinic receptors mediate acute nicotine-induced activation of calcium/calmodulin-dependent protein kinase II-dependent pathways in vivo

Nicotine is the addictive component of tobacco, and successful smoking cessation therapies must address the various processes that contribute to nicotine addiction. Thus, understanding the nicotinic acetylcholine receptor (nAChR) subtypes and subsequent molecular cascades activated after nicotine exposure is of the utmost importance in understanding the progression of nicotine dependence. One possible candidate is the calcium/calmodulin-dependent protein kinase II (CaMKII) pathway. Substrates of this kinase include the vesicle-associated protein synapsin I and the transcription factor cAMP response element-binding protein (CREB). The goal of these studies was to examine these postreceptor mechanisms after acute nicotine treatment in vivo. We first show that administration of nicotine increases CaMKII activity in the ventral tegmental area (VTA), nucleus accumbens (NAc), and amygdala. In beta2 nAChR knockout (KO) mice, nicotine does not induce an increase in kinase activity, phosphorylated (p)Synapsin I, or pCREB. In contrast, alpha7 nAChR KO mice show nicotine-induced increases in CaMKII activity and pCREB, similar to their wild-type littermates. Moreover, we show that when animals are pretreated with the CaMKII inhibitors 4-[(2S)-2-[(5-isoquinolinylsulfonyl) methylamino]-3-oxo-3-(4-phenyl-1-piperazinyl)propyl]phenyl isoquinolinesulfonic acid ester (KN-62) and N-[2-[[[3-(4-chlorophenyl)-2 propenyl]methylamino]methyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulphonamide (KN-93), nicotine-induced increase in the kinase activity and pCREB was attenuated in the VTA and NAc, whereas pretreatment with (2-[N-(4-methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine, phosphate) (KN-92), the inactive analog, did not alter the nicotine-induced increase in pCREB. Taken together, these data suggest that the nicotine-induced increase in CaMKII activity may correlate with the nicotine-induced increase in pSynapsin I and pCREB in the VTA and NAc via beta2 subunit-containing nAChRs.

The PKC inhibitor Ro31-8220 blocks acute amphetamine-induced dopamine overflow in the nucleus accumbens

Acute administration of the psychostimulant amphetamine increases extracellular levels of dopamine (DA) by reversing the DA transporter on ascending midbrain DA neurons. In vitro studies using striatal synaptosomal, slice and nucleus accumbens (NAcc) tissue preparations have implicated protein kinase C (PKC) in this effect. The present study further examined this effect in vivo by assessing the ability of the PKC inhibitor, Ro31-8220 (10 microM), to inhibit acute amphetamine-induced DA overflow when applied with this drug to the NAcc via reverse dialysis. Amphetamine was applied at a concentration of 30 microM, and the core and shell subregions of the NAcc were assayed separately in freely moving rats. These brain regions play a role in the acute locomotor-activating and motivational effects of amphetamine. Consistent with the findings of previous in vitro experiments, reverse dialysis of Ro31-8220 with amphetamine robustly attenuated the ability of this drug to increase extracellular levels of dopamine in both the core and shell subregions of the NAcc. These results confirm that amphetamine stimulates dopamine overflow via a PKC-dependent mechanism.

Protein kinase C inhibitors: rationale for use and potential in the treatment of bipolar disorder

Bipolar disorder is one of the most severely debilitating of all medical illnesses. For a large number of patients, outcomes are quite poor. The illness results in tremendous suffering for patients and their families and commonly impairs functioning and workplace productivity. Risks of increased morbidity and mortality, unfortunately, are frequent occurrences as well. Until recently, little has been known about the specific molecular and cellular underpinnings of bipolar disorder. Such knowledge is crucial for the prospect of developing specific targeted therapies that are more effective and that have a more rapid onset of action than currently available treatments. Exciting recent data suggest that regulation of certain signalling pathways may be involved in the aetiology of bipolar disorder and that these pathways may be profitably targeted to treat the disorder. In particular, mania is associated with overactive protein kinase C (PKC) intracellular signalling, and recent genome-wide association studies of bipolar disorder have implicated an enzyme that reduces the activation of PKC. Importantly, the current mainstays in the treatment of mania, lithium (a monovalent cation) and valproate (a small fatty acid) indirectly inhibit PKC. In addition, recent clinical studies with the relatively selective PKC inhibitor tamoxifen add support to the relevance of the PKC target in bipolar disorder. Overall, a growing body of work both on a preclinical and clinical level indicates that PKC signalling may play an important role in the pathophysiology and treatment of bipolar disorder. The development of CNS-penetrant PKC inhibitors may have considerable benefit for this devastating illness.

Verapamil augmentation of lithium treatment improves outcome in mania unresponsive to lithium alone: preliminary findings and a discussion of therapeutic mechanisms

OBJECTIVES

Attenuation of protein kinase C (PKC) is a mechanism common to both established (lithium, valproate) and some novel (tamoxifen) antimanic agents. Verapamil, although primarily known as a calcium channel blocker, also has PKC inhibitory activity. Verapamil has shown antimanic activity in some but not all studies. Therefore, we investigated verapamil, used alone or as an adjunctive treatment, in manic patients who did not respond to an initial adequate trial of lithium.

METHODS

Each study phase lasted three weeks. Subjects were treated openly with lithium in Phase 1 (n = 45). Those who failed to respond were randomly assigned to double-blind treatment in Phase 2 with either verapamil (n = 10) or continued-lithium (n = 8). Phase 2 nonresponders (n = 10) were assigned to combined verapamil/lithium in Phase 3.

RESULTS

Response in Phase 2 did not differ significantly between verapamil and continued-lithium. During Phase 3, response to combined treatment was significantly better than overall response to monotherapy in Phase 2 (Fisher's Exact test, p = 0.043). Mania ratings improved during combined treatment in Phase 3 by 88.2% (linear mixed model analysis, F = 4.34, p = 0.013), compared with 10.5% improvement during Phase 2.

CONCLUSIONS

In this preliminary investigation, verapamil monotherapy did not demonstrate antimanic efficacy. By contrast, the combination of verapamil plus lithium was highly efficacious. Our findings thus suggest that verapamil may have potential utility as an adjunct to lithium. This effect may be mediated by additive actions on PKC inhibition, which may be an important mechanism for antimanic agents in general.

Depolarization recruits DCC to the plasma membrane of embryonic cortical neurons and enhances axon extension in response to netrin-1

The netrin-1 receptor Deleted in Colorectal Cancer (DCC) is required for the formation of major axonal projections by embryonic cortical neurons, including the corpus callosum, hippocampal commissure, and cortico-thalamic tracts. The presentation of DCC by axonal growth cones is tightly regulated, but the mechanisms regulating DCC trafficking within neurons are not well understood. Here, we investigated the mechanisms regulating DCC recruitment to the plasma membrane of embryonic cortical neurons. In embryonic spinal commissural neurons, protein kinase A (PKA) activation recruits DCC to the plasma membrane and enhances axon chemoattraction to netrin-1. We demonstrate that PKA activation similarly recruits DCC and increases embryonic cortical neuron axon extension, which, like spinal commissural neurons, respond to netrin-1 as a chemoattractant. We then determined if depolarization might recruit DCC to the plasma membrane. Neither netrin-1 induced axon extension, nor levels of plasma membrane DCC, were altered by depolarizing embryonic spinal commissural neurons with elevated levels of KCl. In contrast, depolarizing embryonic cortical neurons increased the amount of plasma membrane DCC, including at the growth cone, and increased axon outgrowth evoked by netrin-1. Inhibition of PKA, phosphatidylinositol-3-kinase, protein kinase C, or exocytosis blocked the depolarization-induced recruitment of DCC and suppressed axon outgrowth. Inhibiting protein synthesis did not affect DCC recruitment, nor were the distributions of trkB or neural cell adhesion molecule (NCAM) influenced by depolarization, consistent with selective mobilization of DCC. These findings identify a role for membrane depolarization modulating the response of axons to netrin-1 by regulating DCC recruitment to the plasma membrane.

Glutamate receptors as targets of protein kinase C in the pathophysiology and treatment of animal models of mania

Considerable biochemical evidence suggests that the protein kinase C (PKC) signaling cascade may be a convergent point for the actions of anti-manic agents, and that excessive PKC activation can disrupt prefrontal cortical regulation of thinking and behavior. To date, however, brain protein targets of PKC's anti-manic effects have not been fully identified. Here we showed that PKC activity was enhanced in the prefrontal cortex of animals treated with the psychostimulant amphetamine. Phosphorylation of MARCKS, a marker of PKC activity, was increased in the prefrontal cortex of animals treated with the psychostimulant amphetamine, as well as in sleep-deprived animals (another animal model of mania), but decreased in lithium-treated animals. The antidepressant imipramine, which shows pro-manic properties in patients with bipolar disorder (BPD), also enhanced phospho-MARCKS in prefrontal cortex in vivo. We further explored the functional targets of PKC in mania-associated behaviors. Neurogranin is a brain-specific, postsynaptically located PKC substrate. PKC phosphorylation of neurogranin was robustly increased by pro-manic manipulations and decreased by anti-manic agents. PKC phosphorylation of the NMDA receptor site GluN1S896 and the AMPA receptor site GluA1T840 was also enhanced in the prefrontal cortex of animals treated with the antidepressant imipramine, as well as in behaviorally sleep-deprived animals, in striking contrast to the reduced activity seen in lithium-treated animals. These results suggest that PKC may play an important role in regulating NMDA and AMPA receptor functions. The biochemical profile of the PKC pathway thus encompasses both pro- and anti-manic effects on behavior. These results suggest that PKC modulators or their intracellular targets may ultimately represent novel avenues for the development of new therapeutics for mood disorders.

Protein kinase C inhibition by tamoxifen antagonizes manic-like behavior in rats: implications for the development of novel therapeutics for bipolar disorder

RATIONALE

In the context of bipolar disorder (BPD) research it was demonstrated that administration of the structurally dissimilar mood stabilizers lithium and valproate produced a striking reduction in protein kinase C (PKC) in rat brain. In a small clinical study, tamoxifen (a PKC inhibitor) had antimanic efficacy. However, both lithium and valproate exert many biochemical changes and attribution of therapeutic relevance to any molecular findings needs to be based on linking them to behavioral effects.

OBJECTIVES

The present study was designed to explore such relationship by studying the effects of PKC inhibition in amphetamine-induced behavioral animal models of mania and changes in GAP-43.

METHODS

The effects of two daily tamoxifen (1 mg/kg) i.p. injections on acute or chronic (7 injections) amphetamine (0.5 mg/kg) -induced behaviors and GAP-43 phosphorylation were tested.

RESULTS

The study demonstrates that tamoxifen significantly reduced amphetamine-induced hyperactivity in a large open field without affecting spontaneous activity levels and normalized amphetamine-induced increase in visits to the center of an open field (representing risk-taking behavior). Tamoxifen also attenuated amphetamine-induced phosphorylation of GAP-43, a result that is consistent with the behavioral findings.

CONCLUSIONS

These results support the possibility that PKC signaling may play an important role in the pathophysiology and treatment of BPD. These findings may have direct clinical implications as they offer a new avenue for attempts to develop more specific drugs for the disorder.

Roles of hippocampal N-methyl-D-aspartate receptors and calcium/calmodulin-dependent protein kinase II in amphetamine-produced conditioned place preference in rats

This study investigates the roles of hippocampal N-methyl-D-aspartate (NMDA) glutamate receptors and CaMKII (calcium/calmodulin-dependent protein kinase II) in amphetamine-produced conditioned place preference (AMPH-CPP) in rats. An earlier report showed that AMPH-CPP resulted in the enhancement of hippocampal CaMKII activity. In this study, AMPH-CPP significantly increased hippocampal GluR1 receptors, though AMPH-CPP was impaired by either blockade of NMDA receptors (AP5) or inhibition of CaMKII (KN-93) during conditioning. These treatments also impaired CPP if administered before testing, but CPP recovered during the next testing session. Therefore, these treatments had no effect on the extinction of CPP. If the conditioned rats were, however, reexposed to AMPH-CPP after a hippocampal-infusion of AP5 or KN-93, the extinction of the original CPP was greater than that seen in the controls. The hippocampal-infusion of D-cycloserine before CPP testing enhanced the extinction of CPP. These results, taken together, indicate that NMDA receptor activation and CaMKII activity are essential for the AMPH-CPP. AMPH-CPP reexposure is similar to the memory reconsolidation process, being disrupted by either a blockade of the NMDA receptor or an inhibition of CaMKII. Furthermore, the extinction of CPP resembles new learning, which is an active process and is facilitated by a partial NMDA agonist.

Mood stabilizers target cellular plasticity and resilience cascades: implications for the development of novel therapeutics

Bipolar disorder is a devastating disease with a lifetime incidence of about 1% in the general population. Suicide is the cause of death in 10 to 15% of patients and in addition to suicide, mood disorders are associated with many other harmful health effects. Mood stabilizers are medications used to treat bipolar disorder. In addition to their therapeutic effects for the treatment of acute manic episodes, mood stabilizers are useful as prophylaxis against future episodes and as adjunctive antidepressant medications. The most established and investigated mood-stabilizing drugs are lithium and valproate but other anticonvulsants (such as carbamazepine and lamotrigine) and antipsychotics are also considered as mood stabilizers. Despite the efficacy of these diverse medications, their mechanisms of action remain, to a great extent, unknown. Lithium's inhibition of some enzymes, such as inositol monophosphatase and glycogen synthase kinase-3, probably results in its mood-stabilizing effects. Valproate may share its anticonvulsant target with its mood-stabilizing target or may act through other mechanisms. It has been shown that lithium, valproate, and/or carbamazepine regulate numerous factors involved in cell survival pathways, including cyclic adenine monophospate response element-binding protein, brain-derived neurotrophic factor, bcl-2, and mitogen-activated protein kinases. These drugs have been suggested to have neurotrophic and neuroprotective properties that ameliorate impairments of cellular plasticity and resilience underlying the pathophysiology of mood disorders. This article also discusses approaches to develop novel treatments specifically for bipolar disorder.

Dopamine transporter activity mediates amphetamine-induced inhibition of Akt through a Ca2+/calmodulin-dependent kinase II-dependent mechanism

The primary mechanism for clearance of extracellular dopamine (DA) is uptake mediated by the dopamine transporter (DAT), which is governed, in part, by the number of functional DATs on the cell surface. Previous studies have shown that amphetamine (AMPH) decreases DAT cell surface expression, whereas insulin reverses this effect through the action of phosphatidylinositol 3-kinase (PI3K). Therefore, it is possible that AMPH causes DAT cell surface redistribution by inhibiting basal insulin signaling. Here, we show in a heterologous expression system and in murine striatal synaptosomes that AMPH causes a time-dependent decrease in the activity of Akt, a protein kinase immediately downstream of PI3K. This effect was blocked by the DAT inhibitor cocaine, suggesting that AMPH must interact with DAT to inhibit Akt. We also showed that AMPH is able to stimulate Ca2+/calmodulin-dependent kinase II (CaMKII) activity, both in the heterologous expression system as well as in murine striatal synaptosomes. The ability of AMPH to decrease Akt activity was blocked by the CaMKII inhibitor 2-[N-(2-hydroxyethyl)]-N-(4-methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine (KN93), but not by its inactive analog 2-[N-(4-methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine (KN92). Furthermore, preincubation with KN93 prevented the AMPH-induced decrease in DAT cell surface expression. Thus, AMPH, but not cocaine, decreases Akt activity through a CaMKII-dependent pathway, thereby providing a novel mechanism by which AMPH regulates insulin signaling and DAT trafficking.

Cellular plasticity cascades: genes-to-behavior pathways in animal models of bipolar disorder

BACKGROUND

Despite extensive research, the molecular/cellular underpinnings of bipolar disorder (BD) remain to be fully elucidated. Recent data has demonstrated that mood stabilizers exert major effects on signaling that regulate cellular plasticity; however, a direct extrapolation to mechanisms of disease demands proof that manipulation of candidate genes, proteins, or pathways result in relevant behavioral changes.

METHODS

We critique and evaluate the behavioral changes induced by manipulation of cellular plasticity cascades implicated in BD.

RESULTS

Not surprisingly, the behavioral data suggest that several important signaling molecules might play important roles in mediating facets of the complex symptomatology of BD. Notably, the protein kinase C and extracellular signal-regulated kinase cascades might play important roles in the antimanic effects of mood stabilizers, whereas glycogen synthase kinase (GSK)-3 might mediate facets of lithium's antimanic/antidepressant actions. Glucocorticoid receptor (GR) modulation also seems to be capable to inducing affective-like changes observed in mood disorders. And Bcl-2, amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors, and inositol homeostasis represent important pharmacological targets for mood stabilizers, but additional behavioral research is needed to more fully delineate their behavioral effects.

CONCLUSIONS

Behavioral data support the notion that regulation of cellular plasticity is involved in affective-like behavioral changes observed in BD. These findings are leading to the development of novel therapeutics for this devastating illness.

Biogenic Amine Neurotransmitter Transporters: Just When You Thought You Knew Them

Plasma membrane transporters have long been known to support the reuptake of biogenic amine neurotransmitters following release in the central and peripheral nervous systems. Using high-resolution imaging, patch-clamp and amperometric approaches, as well as molecular manipulations of transporter-regulatory pathways, surprising new details have been uncovered as to how transporters work and are influenced by signaling pathways and psychostimulants.

Regulation of amphetamine-stimulated dopamine efflux by protein kinase C beta

Evidence suggests that protein kinase C (PKC) and intracellular calcium are important for amphetamine-stimulated outward transport of dopamine in rat striatum. In this study, we examined the effect of select PKC isoforms on amphetamine-stimulated dopamine efflux, focusing on Ca(2+)-dependent forms of PKC. Efflux of endogenous dopamine was measured in superfused rat striatal slices; dopamine was measured by high performance liquid chromatography. The non-selective classical PKC inhibitor Gö6976 inhibited amphetamine-stimulated dopamine efflux, whereas rottlerin, a specific inhibitor of PKC delta, had no effect. A highly specific PKC beta inhibitor, LY379196, blocked dopamine efflux that was stimulated by either amphetamine or the PKC activator, 12-O-tetradecanoylphorbol-13-acetate. None of the PKC inhibitors significantly altered [3H]dopamine uptake. PKC beta(I) and PKC beta(II), but not PKC alpha or PKC gamma, were co-immunoprecipitated from rat striatal membranes with the dopamine transporter (DAT). Conversely, antisera to PKC beta(I) and PKC beta(II) but not PKC alpha or PKCg amma were able to co-immunoprecipitate DAT. Amphetamine-stimulated dopamine efflux was significantly enhanced in hDAT-HEK 293 cells transfected with PKC beta(II) as compared with hDAT-HEK 293 cells alone, or hDAT-HEK 293 cells transfected with PKCa lpha or PKC beta(I). These results suggest that classical PKC beta(II) is physically associated with DAT and is important in maintaining the amphetamine-stimulated outward transport of dopamine in rat striatum.

Repeated Amphetamine Couples Norepinephrine Transporter and Calcium Channel Activities in PC12 Cells

Repeated intermittent amphetamine enhances efflux of dopamine through the dopamine transporter in rat basal ganglia and through the norepinephrine transporter in rat pheochromocytoma PC12 cells. Extracellular Ca2+ is required for the detection of this enhancement in the rat. In this study, we examined the role of Ca2+ and Ca2+ channels in the enhanced amphetamine-induced dopamine efflux that develops in PC12 cells following repeated intermittent amphetamine. Repeated pretreatment of PC12 cells with 1 microM amphetamine followed by a drug-free period increased amphetamine-induced efflux of dopamine compared with controls. The enhancement in amphetamine-induced dopamine efflux depended upon the presence of extracellular Ca2+ and was inhibited by the blockade of N-type and L-type Ca2+ channels. The enhanced dopamine efflux was not altered by tetanus toxin or reserpine, treatments that abrogate synaptic vesicle-mediated, exocytotic dopamine efflux. Measurement of intracellular Ca2+ concentrations using fura-2/acetoxymethyl ester revealed that amphetamine increased intracellular Ca2+ by a transporter-dependent mechanism. In amphetamine-pretreated cells, amphetamine elicited a greater increase in intracellular Ca2+; this increase depended upon the presence of extracellular Ca2+ and N- and L-type Ca2+ channel activity. The enhanced amphetamine-induced dopamine efflux requires Ca2+/calmodulin kinase activity. In vehicle-treated cells, 1 microM amphetamine inhibited the calmodulin kinase activity although it did not in amphetamine-pretreated cells. This study suggests that repeated intermittent amphetamine couples norepinephrine transporter activity and Ca2+ signaling.

Emerging experimental therapeutics for bipolar disorder: insights from the molecular and cellular actions of current mood stabilizers

Bipolar disorder afflicts approximately 1-3% of both men and women, and is coincident with major economic, societal, medical, and interpersonal consequences. Current mediations used for its treatment are associated with variable rates of efficacy and often intolerable side effects. While preclinical and clinical knowledge in the neurosciences has expanded at a tremendous rate, recent years have seen no major breakthroughs in the development of novel types of treatment for bipolar disorder. We review here approaches to develop novel treatments specifically for bipolar disorder. Deliberate (ie not by serendipity) treatments may come from one of two general mechanisms: (1) Understanding the mechanism of action of current medications and thereafter designing novel drugs that mimics these mechanism(s); (2) Basing medication development upon the hypothetical or proven underlying pathophysiology of bipolar disorder. In this review, we focus upon the first approach. Molecular and cellular targets of current mood stabilizers include lithium inhibitable enzymes where lithium competes for a magnesium binding site (inositol monophosphatase, inositol polyphosphate 1-phosphatase, glycogen synthase kinase-3 (GSK-3), fructose 1,6-bisphosphatase, bisphosphate nucleotidase, phosphoglucomutase), valproate inhibitable enzymes (succinate semialdehyde dehydrogenase, succinate semialdehyde reductase, histone deacetylase), targets of carbamazepine (sodium channels, adenosine receptors, adenylate cyclase), and signaling pathways regulated by multiple drugs of different classes (phosphoinositol/protein kinase C, cyclic AMP, arachidonic acid, neurotrophic pathways). While the task of developing novel medications for bipolar disorder is truly daunting, we are hopeful that understanding the mechanism of action of current mood stabilizers will ultimately lead clinical trials with more specific medications and thus better treatments those who suffer from this devastating illness.

Intracellular Ca2+ regulates amphetamine-induced dopamine efflux and currents mediated by the human dopamine transporter

Although it is clear that amphetamine-induced dopamine (DA) release mediated by the dopamine transporter (DAT) is integral to the behavioral actions of this psychostimulant, the mechanism of this release is not clear. In this study, we explored the requirement for intracellular Ca(2+) in amphetamine-induced DA efflux and currents mediated by the human DAT. The patch-clamp technique in the whole-cell configuration was used on Na(+) and DA-preloaded human embryonic kidney 293 cells stably transfected with the human DAT (hDAT cells). Chelation of intracellular Ca(2+) by inclusion of 50 microM BAPTA in the whole-cell pipette reduced the voltage-dependent amphetamine-induced hDAT current, with the greatest effect seen at positive voltages. Likewise, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) reduced amphetamine-induced DA efflux as measured by amperometry. Furthermore, preincubation of the cells with 50 microM BAPTA acetoxy methyl ester (AM) or thapsigargin also blocked amphetamine-induced release of preloaded N-methyl-4-[(3)H]phenylpyridinium from superfused hDAT cells. BAPTA-AM also reduced DA release from striatal synaptosomes. Amphetamine also led to an increase in intracellular Ca(2+) that was blocked by prior treatment with 5 microM thapsigargin or 10 microM cocaine. These studies demonstrate that amphetamine-induced DAT-mediated currents and substrate efflux require internal Ca(2+) and that amphetamine can stimulate dopamine efflux by regulating cytoplasmic Ca(2+) levels through its interaction with DAT.

Effects of fenfluramine and antidepressants on protein kinase C activity in rat cortical synaptoneurosomes

Fenfluramine releases serotonin (5-HT) via the 5-HT transporter (SERT). Previous work has shown that amphetamine increases particulate protein kinase C (PKC) activity in striatal synaptoneurosomes. The increased PKC activity is linked to the outward transport of dopamine, and when release is diminished, the inward transport of amphetamine inhibits PKC instead. Since there is homology among monoamine transporters, this study was undertaken to determine if D-fenfluramine has similar effects on PKC. The role of 5-HT receptors and endogenous 5-HT were also examined. Naive rats and rats pretreated with p-chlorophenylalanine (PCPA), a 5-HT synthesis inhibitor, were sacrificed. Cortical synaptoneurosomes were prepared and incubated with fenfluramine. PKC activity was determined by thiophosphorylation of endogenous substrates. It was found that 5-HT, D/L-fenfluramine, and D-fenfluramine increased PKC activity in a time- and dose-dependent manner. The 5-HT-mediated increase in PKC activity was attenuated by pretreatment with the 5-HT(2) antagonist ketanserin, but not with the SERT inhibitor fluoxetine. The D-fenfluramine-induced increase in PKC activity was completely prevented, however, by pretreatment with SERT inhibitors and partially with ketanserin. It was also attenuated by pretreatment with PCPA, resulting in a dose-dependent inhibition of PKC instead. Thus, when 5-HT release was diminished the uptake of D-fenfluramine inhibited PKC. Similar effects have been observed with amphetamine. Unlike D-fenfluramine, the D/L-fenfluramine-induced increase in PKC activity was partially resistant to PCPA pretreatment but was attenuated with bupropion, a dopamine transporter (DAT) inhibitor. SERT inhibitors (sertraline, paroxetine, citalopram, and fluoxetine) also increased PKC activity. Nefazodone and bupropion increased PKC activity, but mirtazapine was relatively inactive. The SERT inhibitor-induced increase in PKC was unaffected by pretreatment with PCPA but was inhibited by calcium. Similar effects on PKC activity have been observed with DAT inhibitors. These results, showing that D-fenfluramine altered PKC activity similar to D-amphetamine, suggest that the topographic homology between DAT and SERT may extend to their effects on PKC activity.

Repeated amphetamine treatment induces neurite outgrowth and enhanced amphetamine-stimulated dopamine release in rat pheochromocytoma cells (PC12 cells) via a protein kinase C- and mitogen activated protein kinase-dependent mechanism

Repeated intermittent treatment with amphetamine (AMPH) induces both neurite outgrowth and enhanced AMPH-stimulated dopamine (DA) release in PC12 cells. We investigated the role of protein kinases in the induction of these AMPH-mediated events by using inhibitors of protein kinase C (PKC), mitogen activated protein kinase (MAP kinase) or protein kinase A (PKA). PKC inhibitors chelerythrine (100 nm and 300 nm), Ro31-8220 (300 nm) and the MAP kinase kinase inhibitor, PD98059 (30 micro m) inhibited the ability of AMPH to elicit both neurite outgrowth and the enhanced AMPH-stimulated DA release. The direct-acting PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA, 250 nm) mimicked the ability of AMPH to elicit neurite outgrowth and enhanced DA release. On the contrary, a selective PKA inhibitor, 100 micro m Rp-8-Br-cAMPS, blocked only the development of AMPH-stimulated DA release but not the neurite outgrowth. Treatment of the cells with acute AMPH elicited an increase in the activity of PKC and MAP kinase but not PKA. These results demonstrated that AMPH-induced increases in MAP kinase and PKC are important for induction of both the enhancement in transporter-mediated DA release and neurite outgrowth but PKA was only required for the enhancement in AMPH-stimulated DA release. Therefore the mechanisms by which AMPH induces neurite outgrowth and the enhancement in AMPH-stimulated DA release can be differentiated.

The effect of phosphorylation on amphetamine-mediated outward transport

Amphetamine elicits its locomotor-activating and drug-reinforcing effects by releasing the catecholamines dopamine and norepinephrine into the synapse. Amphetamine is a substrate of the plasmalemmal transporters for both dopamine and norepinephrine. As such, it binds to the transporters in conjunction with Na+ and Cl-, facilitating a conformational change leading the transporter to face inward. The subsequent binding of intracellular catecholamine results in an outward transport and release of the catecholamine into the synapse. Both inward and outward transport through the catecholamine transporters are regulated by protein kinases, particularly protein kinase C, but the effect of the enzyme on the two processes appears to be asymmetric. The purpose of this review is to discuss the evidence showing that protein kinase C activation facilitates outward transport through the catecholamine plasmalemmal transporters which may mediate amphetamine action in intact tissue.

Differential effects of amphetamine transport vs. dopamine reverse transport on particulate PKC activity in striatal synaptoneurosomes

Amphetamine has been shown to increase striatal particulate protein kinase C (PKC) activity [Giambalvo (1992b) Neuropharmacology 31:1211-1222]. The present study examined possible mechanisms involved. Specifically, the effects of calcium, endogenous DA, and DA receptors on the amphetamine-induced increase in PKC activity in striatal synaptoneurosomes were examined. Naïve rats and rats pretreated with N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinolone (EEDQ, i.p.), a nonselective irreversible receptor antagonist, or with alpha-methyl-p-tyrosine (AMPT, i.p.), a DA synthesis inhibitor, were sacrificed and striatal synaptoneurosomes were prepared. The tissue was incubated with amphetamine, with and without calcium, and PKC activity was then determined by the endogenous phosphorylation of endogenous substrate proteins, as described previously [Giambalvo (1988a) Biochem Pharmacol 37:4001-4007]. It was found that calcium enhanced the effect of amphetamine on PKC activity, even in rats pretreated with EEDQ. Intracellular calcium was required since pretreatment with 1,2-bis (2-aminophenoxy) ethane-N, N, N, N-tetracetic acid acetoxymethyl ester (BAPTA-AM) in vitro attenuated the amphetamine-induced increase in PKC activity, resulting in an inhibition of PKC activity instead. Likewise, endogenous DA was essential since pretreatment with AMPT resulted in a similar amphetamine-induced inhibition of PKC activity. Pretreatment with AMPT did not alter the inhibitory effect of the D2 DA agonist, LY 171555, on PKC activity. It did, however, abolish the calcium-dependent stimulatory effect of the D1 agonist SKF 38393 on PKC activity, rendering it inhibitory regardless of calcium. Considering that both BAPTA-AM and AMPT pretreatments, which diminished DA release without affecting uptake via different mechanisms, produced similar inhibitory effects on PKC activity by amphetamine, these results suggest that the inward transport of amphetamine had an inhibitory effect on PKC activity. In contrast, the outward transport of DA seemed to have a stimulatory effect on PKC activity since incubation with low sodium or with ouabain, conditions that promote DA reverse-transport, increased PKC activity. These results showed that PKC activity was altered differently during inward vs. outward transport. The amphetamine-induced increase in PKC activity was attenuated by pretreatment with DA uptake blockers (nomifensine, GBR 12935, and bupropion), even though these drugs by themselves also increased PKC activity. This effect was diminished by calcium and persisted in rats pretreated with EEDQ. Thus, calcium had a differential effect on the PKC activity induced by a transported substrate (amphetamine) vs. nontransported inhibitors (DA uptake blockers).

Effect of amphetamine and phencyclidine on DNA-binding activities of serum response and dyad symmetry elements

Acute administration of D-amphetamine sulphate (AMPH) and (1-[1-phenylcyclohexyl]piperidine hydrochloride) (phencyclidine; PCP) produces a characteristic spatio-temporal distribution of c-Fos protein in the brain. As transcriptional mechanisms underlying the induction of c-fos gene expression may be regulated in a stimulus-specific manner, we have analyzed the binding activities of serum response element (SRE), dyad symmetry element (DSE) and calcium response element (CRE), the major regulatory sites of the c-fos promoter. Electrophoretic mobility shift showed that SRE binding activity was increased for 50-60%, 2-6h after AMPH, while treatment with PCP resulted in light decrease of SRE binding activity throughout the same time period. Co-administration of AMPH and PCP induced gradual increase of SRE binding activity, reaching maximum (86%) at 6h. Binding of nuclear proteins to DSE sequence was increased 1-2h after administration of AMPH (72-87%) and remained elevated till the end of the time window observed. PCP and AMPH/PCP caused different temporal profile of DSE binding with peak (40-54%) 4-6h after administration. In contrast, DNA-binding activity of the CRE sequences remained unchanged throughout the time period of 6h under all conditions. Finally, supershift analysis clearly demonstrated presence of SRF and c-Fos protein in the transcriptional complexes bound to SRE and DSE sequences irrespective to AMPH, PCP or combined treatment. These findings also showed that the presence of c-Fos protein in SRE and DSE nucleocomplex support the hypothesis concerning autoregulation of c-fos gene expression during psychostimulant action in vivo.

Mechanisms underlying the effects of amphetamine on particulate PKC activity

Amphetamine stimulates particulate protein kinase C (PKC) activity that is associated with the outward-transport of dopamine (DA) (Giambalvo [2003] Synapse 49:125-133). This stimulatory effect requires intracellular calcium ([Ca](i)) and endogenous DA and when DA release is diminished, the inward-transport of amphetamine inhibits PKC activity. This study examines the mechanisms involved. It was found that synaptoneurosomes incubated with amphetamine showed a dose-dependent increase in phospholipase C and A(2) activities. Furthermore, pretreatments with the phospholipase C inhibitor D609 or the phospholipase A(2) inhibitors quinacrine or p-bromophenacylbromide attenuated the amphetamine-induced increase in PKC activity. This suggests that both phospholipases were essential for the amphetamine-induced increase in PKC activity. The Na/Ca antiporter was also involved, since pretreatment with amiloride or benzamil attenuated the amphetamine-induced increase in PKC activity. Since these drugs by themselves increased PKC activity, the return to basal activity after addition of amphetamine suggests that, in the absence of Na/Ca exchange, amphetamine had an inhibitory effect on PKC activity. This inhibitory effect might be due to the activation of phospholipase A(2) through an increase in intracellular pH induced by amphetamine. This was supported by the finding that pretreatment with dimethylamiloride, an inhibitor of the Na/H antiporter that increases intracellular [H(+)], attenuated the effects of amphetamine on PKC activity. Other drugs that decrease intracellular [H(+)] (ammonia, monensin) also inhibited PKC activity without Ca. In contrast to amphetamine, monensin had no effect on PKC activity with Ca. This could be related to its large differential effects on phospholipase A(2) vs. phospholipase C activity. Thus, the monensin-mediated decrease in PKC activity seen without Ca was partially attenuated by pretreatment with quinacrine. Furthermore, when Na/Ca antiporter was inhibited with benzamil, monensin inhibited PKC activity. These results suggest that amphetamine, as well as monensin, may have dual effects on PKC activity, a Ca-dependent stimulatory effect via phospholipase C, and an inhibitory effect via phospholipase A(2).

Mood stabilizer psychopharmacology

Mood stabilizers represent a class of drugs that are efficacious in the treatment of bipolar disorder. The most established medications in this class are lithium, valproic acid, and carbamazepine. In addition to their therapeutic effects for treatment of acute manic episodes, these medications often are useful as prophylaxis against future episodes and as adjunctive antidepressant medications. While important extracellular effects have not been excluded, most available evidence suggests that the therapeutically relevant targets of this class of medications are in the interior of cells. Herein we give a prospective of a rapidly evolving field, discussing common effects of mood stabilizers as well as effects that are unique to individual medications. Mood stabilizers have been shown to modulate the activity of enzymes, ion channels, arachidonic acid turnover, G protein coupled receptors and intracellular pathways involved in synaptic plasticity and neuroprotection. Understanding the therapeutic targets of mood stabilizers will undoubtedly lead to a better understanding of the pathophysiology of bipolar disorder and to the development of improved therapeutics for the treatment of this disease. Furthermore, the involvement of mood stabilizers in pathways operative in neuroprotection suggests that they may have utility in the treatment of classical neurodegenerative disorders.

Repeated, intermittent treatment with amphetamine induces neurite outgrowth in rat pheochromocytoma cells (PC12 cells)

Repeated, intermittent treatment with amphetamine (AMPH) leads to long-term neurobiological adaptations in rat brain including an increased number and branching of dendritic spines. This effect depends upon several different cell types in the intact brain. Here we demonstrate that repeated, intermittent AMPH treatment induces neurite outgrowth in cultured PC12 cells without the requirement for integrated synaptic pathways. PC12 cells were treated with 1 micro M AMPH for 5 min a day, for 5 days. After 10 days of withdrawal, there was an increase in the percentage of cells with neurites ( approximately 30%) and the length of neurites as well as an increase in the level of GAP-43 and neurofilament-M. Neurite outgrowth was enhanced as withdrawal time was increased. Neurite outgrowth was much greater following repeated, intermittent treatment with AMPH compared to continuous or single treatment with AMPH. Pretreatment with cocaine, a monoamine transporter blocker, inhibited the AMPH-mediated increase in neurite outgrowth. Neither NGF antibody nor DA receptor antagonists blocked AMPH-induced neurite outgrowth, demonstrating that AMPH-induced neurite outgrowth is not dependent on endogenous NGF release or DA receptors. Thus we have demonstrated that repeated, intermittent treatment with AMPH has a neurotrophic effect in PC12 cells. The effect requires the action of AMPH on the norepinephrine transporter, and shares characteristics in its development with other forms of sensitization but does not require an intact neuroanatomy.

Enhanced amphetamine-mediated dopamine release develops in PC12 cells after repeated amphetamine treatment

We previously demonstrated that rats treated with repeated, intermittent amphetamine displayed enhanced amphetamine-mediated dopamine release in the striatum. In this study, we examined whether amphetamine pretreatment would elicit enhanced amphetamine-mediated dopamine release in a cultured cell line in the absence of intact synaptic connections. PC12 cells pretreated with 1 microM amphetamine produced over twofold increase in amphetamine-mediated dopamine release upon challenge with 1 microM amphetamine as compared with vehicle-treated cells. No change in norepinephrine transporter density or [3H]dopamine uptake was detected. A withdrawal time of 6 days was required to observe the enhanced amphetamine-mediated dopamine release. Differentiation of the cells with nerve growth factor did not alter the amphetamine-mediated dopamine release in control cells or the development of enhanced release in amphetamine-treated cells. Our results demonstrate that repeated, intermittent amphetamine leads to a neuroadaptation resulting in enhanced amphetamine-induced dopamine release in catecholaminergic cells without the need of an intact neuroanatomy.

Differential trafficking of the vesicular monoamine transporter-2 by methamphetamine and cocaine

High-dose administration of cocaine or methamphetamine to rats acutely (< or = 24 h) alters vesicular dopamine transport. This study elucidates the nature of these changes. Results reveal a differential redistribution of the vesicular monoamine transporter-2 (VMAT-2) within striatal synaptic terminals after drug treatment. In particular, cocaine shifts VMAT-2 protein from a synaptosomal membrane fraction to a vesicle-enriched fraction, as assessed ex vivo in fractions prepared from treated rats. In contrast, methamphetamine treatment redistributes VMAT-2 from a vesicle-enriched fraction to a location that is not retained in a synaptosomal preparation. These data suggest that psychostimulants acutely and differentially affect VMAT-2 subcellular localization.

Impairing the amphetamine conditioning in rats through the inhibition of hippocampal calcium/calmodulin-dependent protein kinase II activity

Amphetamine is an addictive drug, possessing reinforcing properties that are believed to be associated with an environmental cue, which resembles a behavioral learning process. This study investigates the role of calcium/calmodulin-dependent protein kinase II (CaM-kinase II) in the acquisition of the amphetamine-produced conditioned place preference (CPP). In Experiment I, rats were trained in an amphetamine-produced (2 mg/kg, i.p.) CPP task. The amphetamine-saline pairing rats spent significantly more time in the box that was associated with the amphetamine injection. Moreover, these rats' hippocampal CaM-kinase II showed significantly higher Ca(2+)-independent activity than that of the controls. In experiment II, the rats received an intra-hippocampal or intra-accumbens injection of specific CaM-kinase II inhibitor (KN-93) or a controlled agent (KN-92) before training in the amphetamine-produced CPP task. The rats receiving the preconditioning intra-hippocampal KN-93 injection showed no amphetamine-produced CPP effect. These results, taken together, indicate that the biological basis of amphetamine-produced place preference behavior might be regulated by the hippocampal CaM-kinase II activity.

Differential changes in synaptic terminal protein expression between nucleus accumbens core and shell in the amphetamine-sensitized rat

Repeated, intermittent administration of psychostimulant drugs such as D-amphetamine (AMPH) produces a state of behavioral sensitization to the drug that can last up to weeks to months. The molecular basis of this enhanced sensitivity to AMPH is poorly understood; however, adaptive changes in the mesocorticolimbic dopamine system has been postulated to be of primary importance. In the present investigation we used Western blotting to examine the expression of candidate presynaptic proteins involved in regulating neurotransmitter release and synaptic plasticity. Specifically, syntaxin 1, synaptophysin and synapsin I protein levels were examined in the nucleus accumbens (Nacc) and ventral tegmental area (VTA) of Sprague-Dawley rats following AMPH-sensitization. Animals received five repeated administrations of AMPH (1.5 mg/kg, i.p. on alternate days) followed by 14 days of withdrawal. Levels of syntaxin 1 and synaptophysin were found to be significantly reduced in the Nacc core of sensitized animals compared to saline-treated and untreated controls. However, syntaxin 1 expression was significantly increased in the Nacc shell subregion of sensitized animals. No significant difference in the level of synapsin I was noted in any of the brain regions. Further, expression of none of the synaptic proteins was significantly altered in the VTA of sensitized animals. Given the importance of syntaxin and synaptophysin in learning and memory processes and in the regulation of neurotransmitter release, changes in these proteins suggest their involvement in the associative learning aspects of sensitization and differential neurotransmitter release in the Nacc subregions.

Tetanic stimulation and metabotropic glutamate receptor agonists modify synaptic responses and protein kinase activity in rat auditory cortex

We investigated whether tetanic-stimulation and activation of metabotropic glutamate receptors (mGluRs) can modify field-synaptic-potentials and protein kinase activity in rat auditory cortex, specifically protein kinase A (PKA) and protein kinase C (PKC). Tetanic stimulation (50 Hz, 1 s) increases PKA and PKC activity only if the CNQX-sensitive field-EPSP (f-EPSP) is also potentiated. If the f-EPSP is unchanged, then PKA and PKC activity remains unchanged. Tetanic stimulation decreases a bicuculline-sensitive field-IPSP (f-IPSP), and this occurs whether the f-EPSP is potentiated or not. Potentiation of the f-EPSP is blocked by antagonists of mGluRs (MCPG) and PKC (calphostin-C, tamoxifen), suggesting that the potentiation of the f-EPSP is dependent on mGluRs and PKC. PKC antagonists block the rise in PKC and PKA activity, which suggests that these may be coupled. In contrast, ACPD (agonist at mGluRs) decreases both the f-EPSP and the f-IPSP, but increases PKC and PKA activity. Quisqualate (group I mGluR agonist), decreases the f-IPSP, and increases PKA activity, suggesting that the increase in PKA activity is a result of activation of group I mGluRs. Additionally, the increase in PKC and PKA activity appears to be independent of the decrease of the f-EPSP and f-IPSP, because PKC antagonists block the increase in PKC and PKA activity levels but do not block ACPD's effect on the f-EPSP or f-IPSP. These data suggest that group I mGluRs are involved in potentiating the f-EPSP by a PKC and possibly PKA dependent mechanism which is separate from the mechanism that decreases the f-EPSP and f-IPSP.

Effect of acute and chronic administration of methamphetamine on calcium-calmodulin dependent protein kinase II activity in the rat brain

Several lines of evidence have implicated Ca2+/calmodulin (CaM)-dependent protein kinase II (CaM-kinase II), a multifunctional protein kinase, in the regulation of signal transduction after chronic administration of psychostimulants. CaM-Kinase II activities were decreased in discrete brain regions after a single methamphetamine (METH) injection to rats. Pretreatment with either SCH 23390 (a dopamine D1 receptor antagonist) or NMK-801 (an N-methyl-D-aspartate receptor antagonist) prevented the acute METH-induced decrease in CaM-kinase II activity in the parietal cortex, nucleus accumbens, and substantia nigra/ventral tegmental area (SN/VTA). Striatal CaM-kinase II activity was significantly lower than that of the chronic saline-treated controls after a one-week, but not a four-week, abstinence from chronic administration of METH. A METH challenge after a four-week abstinence period decreased CaM-kinase II activity in rats chronically injected with METH to a greater extent than in rats chronically injected with saline. Western blot analysis revealed that protein amount of CaM-kinase II was not altered after a single METH injection or after chronic METH injections, as compared with saline-treated controls. However, amounts of phosphorylated (Thr286) CaM-kinase II in the parietal cortex, striatum, and SN/VTA were significantly decreased at 3 h after an acute METH injection compared with saline-treated controls. It is suggested that dephosphorylation of CaM-kinase II may contribute to the decreased enzyme activities induced by acute METH administration, and that chronic treatment with METH leads to an enhanced capacity of METH to decrease CaM-kinase II activity after an extended withdrawal period.

Lithium regulates PKC-mediated intracellular cross-talk and gene expression in the CNS in vivo

It has become increasingly appreciated that the long-term treatment of complex neuropsychiatric disorders like bipolar disorder (BD) involves the strategic regulation of signaling pathways and gene expression in critical neuronal circuits. Accumulating evidence from our laboratories and others has identified the family of protein kinase C (PKC) isozymes as a shared target in the brain for the long-term action of both lithium and valproate (VPA) in the treatment of BD. In rats chronically treated with lithium at therapeutic levels, there is a reduction in the levels of frontal cortical and hippocampal membrane-associated PKC alpha and PKC epsilon. Using in vivO microdialysis, we have investigated the effects of chronic lithium on the intracellular cross-talk between PKC and the cyclic AMP (cAMP) generating system in vivo. We have found that activation of PKC produces an increase in dialysate cAMP levels in both prefrontal cortex and hippocampus, effects which are attenuated by chronic lithium administration. Lithium also regulates the activity of another major signaling pathway the c-Jun N-terminal kinase pathway--in a PKC-dependent manner. Both Li and VPA, at therapeutically relevant concentrations, increase the DNA binding of activator protein 1 (AP-1) family of transcription factors in cultured cells in vitro, and in rat brain ex vivo. Furthermore, both agents increase the expression of an AP-1 driven reporter gene, as well as the expression of several endogenous genes known to be regulated by AP-1. Together, these results suggest that the PKC signaling pathway and PKC-mediated gene expression may be important mediators of lithium's long-term therapeutic effects in a disorder as complex as BD.

Methamphetamine decreases calcium-calmodulin dependent protein kinase II activity in discrete rat brain regions

A Ca(2+)/calmodulin-dependent signaling cascade has been implicated in the regulation of dopaminergic neurotransmission after chronic administration of amphetamine and methamphetamine (METH). We found a decrease in Ca(2+)/calmodulin-dependent protein kinase II (CaM-kinase II) activity in five regions of the rat brain (parietal cortex; frontal cortex; hippocampus; striatum; and nucleus accumbens) after a single injection of METH. Pretreatment with the selective dopamine D1 receptor antagonist SCH 23390 prevented the acute METH-induced decrease in CaM-kinase II activity in the parietal cortex, striatum, nucleus accumbens, and substantia nigra/ventral tegmental area (SN/VTA). Pretreatment with the N-methyl-D-aspartate receptor antagonist MK-801 significantly restored the acute METH-induced decrease in CaM-kinase II activity in the parietal cortex, nucleus accumbens, and SN/VTA. Striatal CaM-kinase II activity was still significantly lower than that of the chronic saline-treated controls after a 1-week, but not a 4-week, abstinence from chronic administration of METH. A METH challenge after a 4-week abstinence period induced a more pronounced decrease in CaM-kinase II activity in rats chronically injected with METH than in rats chronically injected with saline. Western blot analysis revealed that the amount of CaM-kinase II protein was not altered after a single METH injection or after chronic METH injections, compared with saline-treated controls. However, amounts of phosphorylated (Thr(286)) CaM-kinase II in the parietal cortex, striatum and SN/VTA were significantly decreased at 3 h after an acute METH injection compared with saline-treated controls. These results suggest that dephosphorylation of CaM-kinase II may contribute to the decreased enzyme activities induced by acute METH administration, and that chronic treatment with METH leads to an enhanced capacity of METH to decrease CaM-kinase II activity after an extended withdrawal period.

Dopamine transporter antagonists block phorbol ester-induced dopamine release and dopamine transporter phosphorylation in striatal synaptosomes

We have reported that inhibition of protein kinase C blocks the Ca(2+)-independent reverse transport of dopamine mediated by amphetamine. In this study we investigated whether activation of protein kinase C by 12-O-tetradecanoyl phorbol-13-acetate (TPA) would mediate dopamine release through the plasmalemmal dopamine transporter. TPA, at 250 nM, increased the release of dopamine from rat striatal slices and synaptosomes while the inactive phorbol ester, 4alpha-phorbol, was ineffective. The TPA-mediated dopamine release was independent of extracellular calcium and was blocked by a selective protein kinase C inhibitor, Ro31-8220. The dopamine transporter antagonists, cocaine and GBR 12935 blocked the TPA-mediated dopamine release. In addition, cocaine blocked TPA-mediated phosphorylation of the plasmalemmal dopamine transporter. These results suggest that activation of protein kinase C results in reverse transport of dopamine through the plasmalemmal dopamine transporter and the phosphorylated substrate could be the dopamine transporter.

Ziskind-Somerfeld Research Award. Protein kinase C signaling in the brain: molecular transduction of mood stabilization in the treatment of manic-depressive illness

Understanding the biology of the pharmacological stabilization of mood will undoubtedly serve to provide significant insight into the pathophysiology of manic-depressive illness (MDI). Accumulating evidence from our laboratories and those of other researchers has identified the family of protein kinase C isozymes as a shared target in the brain for the long-term action of both lithium and valproate. In rats chronically treated with lithium, there is a reduction in the hippocampus of the expression of two protein kinase isozymes, alpha and epsilon, as well as a reduction in the expression of a major PKC substrate, MARCKS, which has been implicated in long-term neuroplastic events in the developing and adult brain. In addition, we have been investigating the down-stream impact of these mood stabilizers on another kinase system, GSK-3 beta and on the AP-1 family of transcription factors. Further studies have generated promising preliminary data in support of the antimanic action of tamoxifen, and antiestrogen that is also a PKC inhibitor. Future studies must address the therapeutic relevance of these protein targets in the brain using innovative strategies in both animal and clinical investigations to ultimately create opportunities for the discovery of the next generations of mood stabilizers for the treatment of MDI.

Molecular mechanisms of opiate and cocaine addiction

Chronic administration of opiates or cocaine has been shown to alter the activity or expression of diverse types of cellular proteins in specific target neurons within the central nervous system. Prominent examples include signaling proteins, such as receptors, G proteins, second-messenger synthetic enzymes, and protein kinases. It is now increasingly possible to relate particular molecular adaptations to specific behavioral actions of drugs of abuse in animal models of addiction. In addition, recent work has focused on a role for transcription factors, and the associated alterations in gene expression, in mediating part of this long-lasting, drug-induced molecular and behavioral plasticity.