The antipsychotic aripiprazole selectively prevents the stimulant and rewarding effects of morphine in mice

Pronociceptive role of spinal Cav2.3 (R-type) calcium channels in a mouse model of postoperative pain

BACKGROUND

More than 80% of patients may experience acute pain after a surgical procedure, and this is often refractory to pharmacological intervention. The identification of new targets to treat postoperative pain is necessary. There is an association of polymorphisms in the Cav2.3 gene with postoperative pain and opioid consumption. Our study aimed to identify Cav2.3 as a potential target to treat postoperative pain and to reduce opioid-related side effects.

EXPERIMENTAL APPROACH

A plantar incision model was established in adult male and female C57BL/6 mice. Cav2.3 expression was detected by qPCR and suppressed by siRNA treatment. The antinociceptive efficacy and safety of a Cav2.3 blocker-alone or together with morphine-was also assessed after surgery.

KEY RESULTS

Paw incision in female and male mice caused acute nociception and increased Cav2.3 mRNA expression in the spinal cord but not in the incised tissue. Intrathecal treatment with siRNA against Cav2.3, but not with a scrambled siRNA, prevented the development of surgery-induced nociception in both male and female mice, with female mice experiencing long-lasting effects. High doses of i.t. SNX-482, a Cav2.3 channel blocker, or morphine injected alone, reversed postoperative nociception but also induced side effects. A combination of lower doses of morphine and SNX-482 mediated a long-lasting reversal of postsurgical pain in female and male mice.

CONCLUSION

Our results demonstrate that Cav2.3 has a pronociceptive role in the induction of postoperative pain, indicating that it is a potential target for the development of therapeutic approaches for the treatment of postoperative pain.

No significant change of N6 -methyladenosine modification landscape in mouse brain after morphine exposure

OBJECTIVES

N6 -methyladenosine (m6 A) plays a crucial role in regulating neuroplasticity and different brain functions at the posttranscriptional level. However, it remains unknown whether m6 A modification is involved in acute and chronic morphine exposure.

MATERIALS AND METHODS

In this study, we conducted a direct comparison of m6 A levels and mRNA expression of m6 A-associated factors between morphine-treated and nontreated C57BL/6 wild-type mice. We established animal models of both acute and chronic morphine treatment and confirmed the rewarding effects of chronic morphine treatment using the conditioned place preference (CPP) assay. The activation status of different brain regions in response to morphine was assessed by c-fos staining. To assess overall m6 A modification levels, we employed the m6 A dot blot assay, while mRNA levels of m6 A-associated proteins were measured using a quantitative polymerase chain reaction (qPCR) assay. These analyses were performed to investigate whether and how m6 A modification and m6 A-associated protein expression will change following morphine exposure.

RESULTS

The overall m6 A methylation and mRNA levels of m6 A-associated proteins were not significantly altered in brain regions that were either activated or not activated during acute morphine stimulation. Similarly, the overall m6 A modification and mRNA levels of m6 A-associated proteins remained unaffected in several key brain regions associated with reward following chronic morphine exposure.

CONCLUSION

This study showed that the overall m6 A modification level and mRNA expression levels of m6 A-associated factors were not affected after acute and chronic morphine exposure in different brain regions, indicating m6 A modification may not be involved in brain response to morphine exposure.

Low Current Intensity Plus an Ineffective Dose of Morphine Affect Conditioning Place Preference Through Different Pathways in the Lateral Habenula

Background

The involvement of lateral habenula and the ineffective dose of morphine on reward-related learning and memory is less well-known. This study looked into the effects of electrical stimulation, GABAB receptor blockade, and a combination of both with morphine on conditioned place preference.

Materials and Methods

In this experiment, male rats were anesthetized with ketamine/xylazine (six rats in each group). A 5-day biased conditioned place preference paradigm was used for the behavioral test. The effects of electrical stimulation and phaclofen plus a low dose of morphine on the acquisition and expression phases were examined during conditioning sessions and before the test phase, respectively.

Results

The conditioning scores were reduced by antagonist injection during the acquisition phase. Interestingly, different intensities exhibited opposite effects on the acquisition phase. Conditioned place preference scores during the acquisition phase were significantly induced by 25 μA electrical stimulation, while conditioning scores were suppressed by electrical stimulation at 150 μA. Phaclofen (2 μg/rat) combined with high intensity induced aversion during the acquisition phase, while inhibiting expression. In contrast, high intensity with phaclofen (1 μg/rat) inhibited only the acquisition session. However, low intensity during the acquisition phase had an additive effect that was prevented by pretreatment with phaclofen (2 μg/rat), but this response was modified by the antagonist's low dose.

Conclusions

A behavioral technique called conditioned place preference is frequently used to evaluate learning that is related to rewards. Therefore, lateral habenula electrical stimulation and phaclofen plus morphine could affect place preference through the involvement of the reward system.

The role of NMDA glutamate receptors in the lateral habenula on morphine-induced conditioned place preference in rats

The lateral habenula (LHb) has received special attention due to its role in modulating motivated behavior, stress response, and rewarding and aversive stimuli through monoamine transmission. In the present study, the involvement of the N-methyl-d-aspartate (NMDA) receptors of the LHb in the expression and acquisition phases of morphine-induced conditioned place preference (CPP) was studied in male rats. Bilateral injections of agonist/antagonist (MK-801) of NMDA receptor were performed during the conditioning sessions of the acquisition phase. In other separate groups, drugs were also injected into the LHb before the test session during the expression phase of CPP. A 5-day CPP bias paradigm was used to study the effect of injections of NMDA and MK-801 into the LHb on morphine reward-related behavior. Different doses of NMDA plus morphine reduced the CPP score during the acquisition phase, whereas MK-801 significantly increased conditioning scores during the acquisition phase of CPP. The injection of agonists and antagonists of NMDA receptors in LHb had no significant effect on CPP scores and locomotion during the expression phase of CPP, whereas the motor activity in the acquisition phase was affected by the drugs. The reduction effect of NMDA on the CPP scores during the acquisition phase was blocked by pretreatment with MK-801. Our findings also suggest that NMDA receptors in the LHb may be involved in the acquisition phase of morphine-induced CPP.

Preclinical evidence for the use of the atypical antipsychotic, brexpiprazole, for opioid use disorder

Opioid addiction is characterized by adaptations in the mesolimbic dopamine system that occur during chronic opioid use. Alterations in dopaminergic transmission contribute to pathological drug-seeking behavior and other symptoms associated with opioid withdrawal following drug discontinuation, making drug abstinence challenging and contributing to high rates of relapse among those suffering from substance use disorder. Recently, the use of dopamine partial agonists has been proposed as a potential strategy to restore dopaminergic signalling during drug withdrawal, while avoiding the adverse side effects associated with stronger modulators of dopaminergic transmission. We investigated the effects of the atypical antipsychotic brexpiprazole, which is a partial agonist at dopamine D2 and D3 receptors, in a mouse model of opioid dependence. The development of opioid dependence in mice is characterized by locomotor sensitization, analgesic tolerance, opioid-induced hyperalgesia, and drug-seeking behavior. We set up four paradigms to model the effects of brexpiprazole on each of these adaptations that occur during chronic opioid use in male and female C57BL/6J mice. Concomitant treatment of brexpiprazole during chronic morphine administration attenuated the development of locomotor sensitization. Brexpiprazole treatment abolished morphine place preference and blocked reinstatement of this behavior following extinction. Brexpiprazole treatment did not alter morphine analgesia, nor did it impact the development of morphine tolerance. However, brexpiprazole treatment did prevent the expression of opioid-induced hyperalgesia in a tail-withdrawal assay, while failing to improve somatic withdrawal symptoms. Altogether, these results provide preclinical evidence for the efficacy of brexpiprazole as a modulator of dopamine-dependent behaviors during opioid use and withdrawal.

Insights into the mechanisms underlying opioid use disorder and potential treatment strategies

Opioid use disorder is a worldwide societal problem and public health burden. Strategies for treating opioid use disorder can be divided into those that target the opioid receptor system and those that target non-opioid receptor systems, including the dopamine and glutamate receptor systems. Currently, the clinical drugs used to treat opioid use disorder include the opioid receptor agonists methadone and buprenorphine, which are limited by their abuse liability, and the opioid receptor antagonist naltrexone, which is limited by poor compliance. Therefore, the development of effective medications with lower abuse liability and better potential for compliance is urgently needed. Based on recent advances in the understanding of the neurobiological mechanisms underlying opioid use disorder, potential treatment strategies and targets have emerged. This review focuses on the progress made in identifying potential targets and developing medications to treat opioid use disorder, including progress made by our laboratory, and provides insights for future medication development. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Inhibition of Geranylgeranylacetone on cholecystokinin-B receptor, BDNF and dopamine D1 receptor induced by morphine

Morphine is the pain releasing and abusing drug. Morphine leads to addiction by activating dopaminergic rewarding system consisted of the ventral tegmental area (VTA) and nucleus accumbens (NAc). Cholecystokinin (CCK) is a gut-brain neuropeptide and involved in morphine dependence. Brain-derived neurotrophic factor (BDNF) is a neurotrophin and plays roles in regulating addiction. Geranylgeranylacetone (GGA) is a medicine of protecting gastric mucosal injury and protecting neurons. Our previous study showed that GGA blocked morphine-induced withdrawal and relapse through inducing thioredoxin 1(Trx1). In this study, we investigated that whether cholecystokinin-B receptor (CCKB receptor) and BDNF were related to GGA inhibition on morphine addiction. At first, we made conditioned place preference (CPP) model and confirmed again that GGA blocked the expression of morphine-CPP in present study. Then, our results showed that morphine increased the expressions of dopamine D1 receptor, tyrosine hydroxylase (TH), CCKB receptor and BDNF in the VTA and NAc in mice, which was inhibited by GGA. These results suggest that CCK and BDNF in dopaminergic systems are associated with the role of GGA blocking morphine-CPP.

Effects of the monoamine stabilizer, (-)-OSU6162, on cocaine-induced locomotion and conditioned place preference in mice

Cocaine addiction is a severe mental disorder for which few treatment options are available. The underlying mechanisms include facilitation of monoamine-neurotransmission, particularly dopamine. Here, we tested the hypothesis that the monoamine stabilizers, (-)-OSU6162 ((3S)-3-(3-methylsulfonylphenyl)-1-propylpiperidine) and aripiprazole (7-[4-[4-(2,3-dichlorophenyl)piperazin-1-yl]butoxy]-3,4-dihydro-1H-quinolin-2-one), prevent cocaine-induced behaviors. Male Swiss mice received injections of (-)-OSU6162 or aripiprazole and cocaine and were tested for cocaine-induced hyperlocomotion, locomotor sensitization, and acquisition and expression of conditioned place preference (CPP). The increase in the distance traveled induced by cocaine (20 mg/kg) was prevented by pretreatment with aripiprazole (1 and 10 mg/kg), whereas (-)-OSU6162 (3 mg/kg) exerted a minor effect. Aripiprazole, however, also impaired spontaneous locomotion. Neither (-)-OSU6162 nor aripiprazole interfered with the locomotor sensitization and expression of CPP induced by cocaine (15 mg/kg). (-)-OSU6162 (3 mg/kg), but not aripiprazole, prevented the acquisition of CPP induced by cocaine (15 mg/kg). (-)-OSU6162 exerts a minor effect in reducing cocaine-induced stimulatory activity and context-related memories, which are responsible for triggering drug seeking. Further studies are required to establish whether (-)-OSU6162 could be a candidate drug for the treatment of cocaine addiction.

Aripiprazole prevents from development of vincristine-induced neuropathic nociception by limiting neural NOS overexpression and NF-kB hyperactivation

PURPOSE

Increased nitric oxide (NO) synthesis and NF-kB activation have been shown as critical players in the pathophysiology of vincristine-induced peripheral neuropathy. Consistently, neural nitric oxide synthase (nNOS) inhibitors alleviated the neuropathic pain. Previous studies demonstrated that aripiprazole is capable of modulating NO synthesis and also has been reported its modulatory effect on NF-kB activity.

METHODS

Aripiprazole was administered daily to the male Wistar rats at the same time with establishing neuropathic model by I.P. injection of vincristine every 2 days, over 2 weeks. Efficacy of aripiprazole in suppressing the development of neuropathy was evaluated by assessing changes in body weight, mechanical threshold, withdrawal latency, sciatic nerve conduction velocity (SNCV), and compound motor action potential (CMAP) characteristics. Expression of nNOS and NF-kB activation were evaluated by western blotting RESULTS: Rats receiving aripiprazole during neuropathy establishment period demonstrated a normal weight gain pattern, a significantly higher mechanical withdrawal threshold, and SNCV compared to vincristine-treated group. Furthermore, the amplitude and area of CMAP were significantly higher in aripiprazole group. Western blotting demonstrated a significantly reduced expression of nNOS and NF-kB activation in dorsal root ganglia of aripiprazole co-treated rats.

CONCLUSION

In conclusion, aripiprazole effectively prevents from vincristine-induced neuropathy by limiting nNOS overexpression and NF-kB hyperactivation.

Opposing roles of CB1 and CB2 cannabinoid receptors in the stimulant and rewarding effects of cocaine

BACKGROUND AND PURPOSE

The endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) bind to CB₁ and CB₂ cannabinoid receptors in the brain and modulate the mesolimbic dopaminergic pathway. This neurocircuitry is engaged by psychostimulant drugs, including cocaine. Although CB₁ receptor antagonism and CB₂ receptor activation are known to inhibit certain effects of cocaine, they have been investigated separately. Here, we tested the hypothesis that there is a reciprocal interaction between CB₁ receptor blockade and CB₂ receptor activation in modulating behavioural responses to cocaine.

EXPERIMENTAL APPROACH

Male Swiss mice received i.p. injections of cannabinoid-related drugs followed by cocaine, and were then tested for cocaine-induced hyperlocomotion, c-Fos expression in the nucleus accumbens and conditioned place preference. Levels of endocannabinoids after cocaine injections were also analysed.

KEY RESULTS

The CB₁ receptor antagonist, rimonabant, and the CB₂ receptor agonist, JWH133, prevented cocaine-induced hyperlocomotion. The same results were obtained by combining sub-effective doses of both compounds. The CB₂ receptor antagonist, AM630, reversed the inhibitory effects of rimonabant in cocaine-induced hyperlocomotion and c-Fos expression in the nucleus accumbens. Selective inhibitors of anandamide and 2-AG hydrolysis (URB597 and JZL184, respectively) failed to modify this response. However, JZL184 prevented cocaine-induced hyperlocomotion when given after a sub-effective dose of rimonabant. Cocaine did not change brain endocannabinoid levels. Finally, CB₂ receptor blockade reversed the inhibitory effect of rimonabant in the acquisition of cocaine-induced conditioned place preference.

CONCLUSION AND IMPLICATIONS

The present data support the hypothesis that CB₁ and CB₂ receptors work in concert with opposing functions to modulate certain addiction-related effects of cocaine.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

A high-refined carbohydrate diet facilitates compulsive-like behavior in mice through the nitric oxide pathway

Obesity is characterized by abnormal adipose tissue expansion and is associated with chronic inflammation. Obesity itself may induce several comorbidities, including psychiatric disorders. It has been previously demonstrated that proinflammatory cytokines are able to up-regulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) release, which both have a role in compulsive related behaviors.

OBJECTIVE

To evaluate whether acute or chronic consumption of a high-refined carbohydrate-containing (HC) diet will modify burying-behavior in the Marble Burying Test (MBT) through augmentation of NO signaling in the striatum, a brain region related to the reward system. Further, we also verified the effects of chronic consumption of a HC diet on the reinforcing effects induced by cocaine in the Conditioned Place Preference (CPP) test.

METHODS

Male BALB/c mice received a standard diet (control diet) or a HC diet for 3 days or 12 weeks.

RESULTS

An increase in burying behavior occurred in the MBT after chronic consumption of a HC diet that was associated with an increase of nitrite levels in the striatum. The pre-treatment with Aminoguanidine (50 mg/kg), a preferential inhibitor of iNOS, prevented such alterations. Additionally, a chronic HC diet also induced a higher expression of iNOS in this region and higher glutamate release from striatal synaptosomes. Neither statistical differences were observed in the expression levels of the neuronal isoform of NOS nor in microglia number and activation. Finally, the reinforcing effects induced by cocaine (15 mg/kg, i.p.) during the expression of the conditioned response in the CPP test were not different between the chronically HC diet fed mice and the control group. However, HC diet-feeding mice presented impairment of cocaine-preference extinction.

CONCLUSION

Altogether, our results suggest that the chronic consumption of a HC diet induces compulsive-like behavior through a mechanism possibly associated with NO activation in the striatum.

Peripheral Antinociception Induced by Aripiprazole Is Mediated by the Opioid System

Background

Aripiprazole is an antipsychotic drug used to treat schizophrenia and related disorders. Our previous study showed that this compound also induces antinociceptive effects. The present study aimed to assess the participation of the opioid system in this effect.

Methods

Male Swiss mice were submitted to paw pressure test and hyperalgesia was induced by intraplantar injection of prostaglandin E₂ (PGE₂, 2 μg). Aripiprazole was injected 10 min before the measurement. Naloxone, clocinnamox, naltrindole, nor-binaltorphimine, and bestatin were given 30 min before aripiprazole. Nociceptive thresholds were measured in the 3rd hour after PGE₂ injection.

Results

Aripiprazole (100 μg/paw) injected locally into the right hind paw induced an antinociceptive effect that was blocked by naloxone (50 μg/paw), a nonselective opioid receptor antagonist. The role of μ-, δ-, and κ-opioid receptors was investigated using the selective antagonists, clocinnamox (40 μg/paw), naltrindole (15, 30, and 60 μg/paw), and nor-binaltorphimine (200 μg/paw), respectively. The data indicated that only the δ-opioid receptor antagonist inhibited the peripheral antinociception induced by aripiprazole. Bestatin (400 μg), an aminopeptidase-N inhibitor, significantly enhanced low-dose (25 μg/paw) aripiprazole-induced peripheral antinociception.

Conclusion

The results suggest the participation of the opioid system via δ-opioid receptor in the peripheral antinociceptive effect induced by aripiprazole.

Inhibition of Reinforcing, Hyperalgesic, and Motor Effects of Morphine by Buspirone in Rats

Morphine and other opioids are among the most effective prescription medications for the treatment of pain. Addiction and hyperalgesia associated with their long-term use limits the clinical utility of these drugs. In view of a role of somatodendritic serotonin-1A receptors in addiction and analgesic effects of morphine, the present study concerns effects of co-use of buspirone, a partial agonist at the serotonin-1A receptor, on reinforcing, hyperalgesic, and motor effects of morphine in rats. A dose of morphine (7.5 mg/kg) producing moderate effects on motor activity and analgesia, and buspirone (doses of 0, 1.0, and 2.0 mg/kg) were injected intraperitoneally. Reinforcing effects were monitored in a conditioned place preference (CPP) paradigm and associated changes in motor activity were monitored during a drug conditioning phase. The hot plate test was used to monitor nociceptive response. Acute administration of morphine decreased motor activity and reduced pain perception. Repeated administration was reinforcing in the CPP paradigm and was associated with hyperalgesia and tolerance in motor depressant effects of morphine. These effects of repeated morphine administration were blocked in rats cotreated with buspirone. Pain perception was also slightly reduced in rats repeatedly treated with higher doses of buspirone. The findings are important for improving and extending therapeutic medications for pain.

PERSPECTIVE

The present study shows an important role of serotonin-1A receptors in morphine-induced hyperalgesia and addiction. It shows that buspirone, a prescription medicine for anxiety and depression can block addictive and hyperalgesic effects of morphine. Clinicians should consider buspirone as adjunctive therapy with morphine to improve therapeutic medications in pain.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Therapies in early development for the treatment of opiate addiction

INTRODUCTION

Opiate drugs are psychoactive substances used to manage severe pain. However, their chronic use is associated with the development of addiction. Opiate addiction represents a significant public health concern.

AREAS COVERED

This review focuses on the most recent advances in the pharmacological treatment of opiate addiction, from those being tested in clinical trials (Phase I and II), to preclinical studies that point to new targets. Readers will gain knowledge of the wide variety of treatments used to treat opiate addiction, including their strengths and weaknesses, and the promising pharmacological targets identified by preclinical research.

EXPERT OPINION

Among the currently available agonist therapies, new dosage forms of buprenorphine can increase patient acceptability and compliance. New extended-release forms of naltrexone are building hope of retaining opiate-dependent subjects in a drug-free state. Unfortunately, the review of the literature shows that successful preclinical studies are often followed by discouraging results in human clinical trials. Nevertheless, all targets of potential interest should be tested exhaustively. Indeed, a number of new targets and research lines (genetics and neuroinflammation approaches) may lead to breakthroughs in the future.

Effects of aripiprazole on caffeine-induced hyperlocomotion and neural activation in the striatum

Aripiprazole is an antipsychotic that acts as a partial agonist at dopamine D2 receptors. In addition to its antipsychotic activity, this compound blocks the effects of some psychostimulant drugs. It has not been verified, however, if aripiprazole interferes with the effects of caffeine. Hence, this study tested the hypothesis that aripiprazole prevents caffeine-induced hyperlocomotion and investigated the effects of these drugs on neural activity in the striatum. Male Swiss mice received injections of vehicle or antipsychotic drugs followed by vehicle or caffeine. Locomotion was analyzed in a circular arena and c-Fos protein expression was quantified in the dorsolateral, dorsomedial, and ventrolateral striatum, and in the core and shell regions of nucleus accumbens. Aripiprazole (0.1, 1, and 10 mg/kg) prevented caffeine (10 mg/kg)-induced hyperlocomotion at doses that do not change basal locomotion. Haloperidol (0.01, 0.03, and 0.1 mg/kg) also decreased caffeine-induced hyperlocomotion at all doses, although at the two higher doses, this compound reduced basal locomotion. Immunohistochemistry analysis showed that aripiprazole increases c-Fos protein expression in all regions studied, whereas caffeine did not alter c-Fos protein expression. Combined treatment of aripiprazole and caffeine resulted in a decrease in the number of c-Fos positive cells as compared to the group receiving aripiprazole alone. In conclusion, aripiprazole prevents caffeine-induced hyperlocomotion and increases neural activation in the striatum. This latter effect is reduced by subsequent administration of caffeine. These results advance our understanding on the pharmacological profile of aripiprazole.