Suppression of oro-facial movements by rolipram, a cAMP phosphodiesterase inhibitor, in rats chronically treated with haloperidol

Identification of novel proteins associated with movement-related adverse antipsychotic effects by integrating GWAS data and human brain proteomes

Genome-wide association studies (GWAS) have identified some variants for movement-related adverse antipsychotic effects (MAAE), while how these variants confer MAAE remains unclear. We used the probabilistic Mendelian randomization (PMR) method to identify candidate proteins for MAAE by integrating MAAE GWASs and protein quantitative trait loci (pQTL) data. An independent pQTL data from the Banner project and brain-derived eQTL data were used to perform confirmatory PMR. A total of 56 proteins were identified as candidate targets for MAAE after false discovery rates (FDR) correction, such as GRIN2B, ADRA1A, and PED4B. 12 genes were replicated in the confirmatory PMR, and 18 genes had consistent evidence at the transcript level. Furthermore, we investigated the associations between candidate proteins and the motor symptoms of Parkinson's disease (PD). There were 24, 38, and 10 candidate proteins that were significantly associated with PD, PD motor subtypes, and PD motor progression, respectively. Enrichment analysis identified 34 GO terms and 17 pathways that may be involved in MAAE, such as glutamatergic synapse, glutamate receptor complex, and GABAergic synapse. Our study identified multiple candidate genes and pathways that were associated with MAAE, providing new insights into the biological mechanism of MAAE and targets for further mechanistic and therapeutic studies.

The Emerging Role of Phosphodiesterases in Movement Disorders

Cyclic nucleotide phosphodiesterase (PDE) enzymes catalyze the hydrolysis and inactivation of the cyclic nucleotides cyclic adenosine monophosphate and cyclic guanosine monophosphate, which act as intracellular second messengers for many signal transduction pathways in the central nervous system. Several classes of PDE enzymes with specific tissue distributions and cyclic nucleotide selectivity are highly expressed in brain regions involved in cognitive and motor functions, which are known to be implicated in neurodegenerative diseases, such as Parkinson's disease and Huntington's disease. The indication that PDEs are intimately involved in the pathophysiology of different movement disorders further stems from recent discoveries that mutations in genes encoding different PDEs, including PDE2A, PDE8B, and PDE10A, are responsible for rare forms of monogenic parkinsonism and chorea. We here aim to provide a translational overview of the preclinical and clinical data on PDEs, the role of which is emerging in the field of movement disorders, offering a novel venue for a better understanding of their pathophysiology. Modulating cyclic nucleotide signaling, by either acting on their synthesis or on their degradation, represents a promising area for development of novel therapeutic approaches. The study of PDE mutations linked to monogenic movement disorders offers the opportunity of better understanding the role of PDEs in disease pathogenesis, a necessary step to successfully benefit the treatment of both hyperkinetic and hypokinetic movement disorders. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Antipsychotic-Induced Dopamine Supersensitivity Psychosis: Pharmacology, Criteria, and Therapy

The first-line treatment for psychotic disorders remains antipsychotic drugs with receptor antagonist properties at D2-like dopamine receptors. However, long-term administration of antipsychotics can upregulate D2 receptors and produce receptor supersensitivity manifested by behavioral supersensitivity to dopamine stimulation in animals, and movement disorders and supersensitivity psychosis (SP) in patients. Antipsychotic-induced SP was first described as the emergence of psychotic symptoms with tardive dyskinesia (TD) and a fall in prolactin levels following drug discontinuation. In the era of first-generation antipsychotics, 4 clinical features characterized drug-induced SP: rapid relapse after drug discontinuation/dose reduction/switch of antipsychotics, tolerance to previously observed therapeutic effects, co-occurring TD, and psychotic exacerbation by life stressors. We review 3 recent studies on the prevalence rates of SP, and the link to treatment resistance and psychotic relapse in the era of second-generation antipsychotics (risperidone, paliperidone, perospirone, and long-acting injectable risperidone, olanzapine, quetiapine, and aripiprazole). These studies show that the prevalence rates of SP remain high in schizophrenia (30%) and higher (70%) in treatment-resistant schizophrenia. We then present neurobehavioral findings on antipsychotic-induced supersensitivity to dopamine from animal studies. Next, we propose criteria for SP, which describe psychotic symptoms and co-occurring movement disorders more precisely. Detection of mild/borderline drug-induced movement disorders permits early recognition of overblockade of D2 receptors, responsible for SP and TD. Finally, we describe 3 antipsychotic withdrawal syndromes, similar to those seen with other CNS drugs, and we propose approaches to treat, potentially prevent, or temporarily manage SP.

Phosphodiesterase inhibition and modulation of corticostriatal and hippocampal circuits: Clinical overview and translational considerations

The corticostriatal and hippocampal circuits contribute to the neurobiological underpinnings of several neuropsychiatric disorders, including Alzheimer's disease, Parkinson's disease and schizophrenia. Based on biological function, these circuits can be clustered into motor circuits, associative/cognitive circuits and limbic circuits. Together, dysfunctions in these circuits produce the wide range of symptoms observed in related neuropsychiatric disorders. Intracellular signaling in these circuits is largely mediated through the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway with an additional role for the cyclic guanosine monophosphate (cGMP)/ protein kinase G (PKG) pathway, both of which can be regulated by phosphodiesterase inhibitors (PDE inhibitors). Through their effects on cAMP response element-binding protein (CREB) and Dopamine- and cAMP-Regulated PhosphoProtein MR 32 kDa (DARPP-32), cyclic nucleotide pathways are involved in synaptic transmission, neuron excitability, neuroplasticity and neuroprotection. In this clinical review, we provide an overview of the current clinical status, discuss the general mechanism of action of PDE inhibitors in relation to the corticostriatal and hippocampal circuits and consider several translational challenges.

Phosphodiesterase Inhibitors as a Therapeutic Approach to Neuroprotection and Repair

A wide diversity of perturbations of the central nervous system (CNS) result in structural damage to the neuroarchitecture and cellular defects, which in turn are accompanied by neurological dysfunction and abortive endogenous neurorepair. Altering intracellular signaling pathways involved in inflammation and immune regulation, neural cell death, axon plasticity and remyelination has shown therapeutic benefit in experimental models of neurological disease and trauma. The second messengers, cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP), are two such intracellular signaling targets, the elevation of which has produced beneficial cellular effects within a range of CNS pathologies. The only known negative regulators of cyclic nucleotides are a family of enzymes called phosphodiesterases (PDEs) that hydrolyze cyclic nucleotides into adenosine monophosphate (AMP) or guanylate monophosphate (GMP). Herein, we discuss the structure and physiological function as well as the roles PDEs play in pathological processes of the diseased or injured CNS. Further we review the approaches that have been employed therapeutically in experimental paradigms to block PDE expression or activity and in turn elevate cyclic nucleotide levels to mediate neuroprotection or neurorepair as well as discuss both the translational pathway and current limitations in moving new PDE-targeted therapies to the clinic.

A prospective comparative study of risperidone long-acting injectable for treatment-resistant schizophrenia with dopamine supersensitivity psychosis

OBJECTIVE

Dopamine supersensitivity psychosis (DSP) is considered to be one cause of treatment-resistant schizophrenia (TRS). The authors investigated the efficacy of risperidone long-acting injections (RLAI) in patients with TRS and DSP.

METHOD

This is a multicenter, prospective, 12-month follow-up, observational study that included unstable and severe TRS patients with and without DSP. 115 patients with TRS were recruited and divided into two groups according to the presence or absence of DSP which was judged on the basis of the clinical courses and neurological examinations. RLAI was administered adjunctively once every 2weeks along with oral antipsychotics. We observed changes in scores for the Brief Psychiatric Rating Scales (BPRS), Clinical Global Impression-Severity of Illness (CGI-S), Global Assessment of Functioning Scale (GAF), and Extrapyramidal Symptom Rating Scale (ESRS) during the study. Of the assessed 94 patients, 61 and 33 were categorized into the DSP and NonDSP groups, respectively.

RESULTS

While baseline BPRS total scores, CGI-S scores and GAF scores did not differ, the ESRS score was significantly higher in the DSP group compared with the NonDSP group. Treatment significantly reduced BPRS total scores and CGI-S scores, and increased GAF scores in both groups, but the magnitudes of change were significantly greater in the DSP group relative to the NonDSP group. ESRS scores were also reduced in the DSP group. Responder rates (≥20% reduction in BPRS total score) were 62.3% in the DSP group and 21.2% in the NonDSP group.

CONCLUSIONS

It is suggested that DSP contributes to the etiology of TRS. Atypical antipsychotic drugs in long-acting forms, such as RLAI, can provide beneficial effects for patients with DSP.

CLINICAL TRIALS REGISTRATION

UMIN (UMIN000008487).

Phosphodiesterases: Regulators of cyclic nucleotide signals and novel molecular target for movement disorders

Movement disorders rank among the most common neurological disorders. During the last two decades substantial progress has been made in understanding of the pathological basis of these disorders. Although, several mechanisms have been proposed, downregulation of cyclic nucleotide mediated signaling cascade has consistently been shown to contribute to the striatal dysfunctioning as seen in movement disorders. Thus, counteracting dysregulated cyclic nucleotide signaling has been considered to be beneficial in movement disorders. Cyclic nucleotide phosphodiesterases (PDEs) are the enzymes responsible for the breakdown of cyclic nucleotides and upregulation in PDE activity has been reported in various movement disorders. Thus, PDE inhibition is considered to be a novel strategy to restore cerebral cyclic nucleotide levels and their downstream signalling cascade. Indeed, various PDE inhibitors have been tested pre-clinically and were reported to be neuroprotective in various neurodegenerative disorders associated with movement disabilities. In this review, we have discussed a putative role of PDE inhibitors in movement disorders and associated abnormalities.

Optimal extent of dopamine D2 receptor occupancy by antipsychotics for treatment of dopamine supersensitivity psychosis and late-onset psychosis

Several studies have proposed an optimal dopamine D2 receptor occupancy by antipsychotics (OOc) to establish optimal pharmacological treatment of schizophrenia. However, there are limitations to the use of the OOc, especially in application to patients with treatment-resistant schizophrenia, including dopamine supersensitivity psychosis (DSP) or late-onset psychosis (LOP). It has been suggested that D2 receptor density is up-regulated by chronic treatment of antipsychotics in DSP, whereas it may be low in LOP owing to age-related reduction. In estimation of the proposed OOc, these alterations have not been taken into account, which may be one of the factors contributing to the limited application of this index. We here hypothesize that there is an optimal range in the number of D2 receptors available for dopamine binding to elicit adequate neurotransmission in the treatment of patients with schizophrenia. We then estimated the OOc under the assumption that the range is constant while D2 density is variable. The results showed that the OOc and plasma level of antipsychotics increase with an increase in the D2 density but decrease with a decrease in the D2 density. That is, if the range of OOc is 65% to 78% in a standard D2 density, it becomes 82% to 89% under 2-fold up-regulated density and 42% to 63% under a 40% reduced density. The results also indicated that the reduction of the plasma antipsychotic level is greater during a given time period in patients with higher D2 density, as they need a higher antipsychotic dose to achieve the raised OOc, which would account for the clinical features of DSP, for example, acute exacerbation after a discontinuation of antipsychotics. On the other hand, in patients with lower D2 density, only a lower antipsychotic dose will achieve the OOc, and a small increase in the dose will result in a greater increase in occupancy and induce extrapyramidal adverse effects more easily. Furthermore, the reduction of the plasma antipsychotic level during the time period is smaller, which prolongs extrapyramidal adverse effects after discontinuation of antipsychotics in LOP. We also attempted to develop a strategy for the prevention and treatment of patients with DSP or LOP by focusing on D2 density.

Caffeine provokes adverse interactions with 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') and related psychostimulants: mechanisms and mediators

Concomitant consumption of caffeine with recreational psychostimulant drugs of abuse can provoke severe acute adverse reactions in addition to longer term consequences. The mechanisms by which caffeine increases the toxicity of psychostimulants include changes in body temperature regulation, cardiotoxicity and lowering of the seizure threshold. Caffeine also influences the stimulatory, discriminative and reinforcing effects of psychostimulant drugs. In this review, we consider our current understanding of such caffeine-related drug interactions, placing a particular emphasis on an adverse interaction between caffeine and the substituted amphetamine, 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy'), which has been most recently described and characterized. Co-administration of caffeine profoundly enhances the acute toxicity of MDMA in rats, as manifested by high core body temperature, tachycardia and increased mortality. In addition, co-administration of caffeine enhances the long-term serotonergic neurotoxicity induced by MDMA. Observations to date support an interactive model of drug-induced toxicity comprising MDMA-related enhancement of dopamine release coupled to a caffeine-mediated antagonism of adenosine receptors in addition to inhibition of PDE. These experiments are reviewed together with reports of caffeine-related drug interactions with cocaine, d-amphetamine and ephedrine where similar mechanisms are implicated. Understanding the underlying mechanisms will guide appropriate intervention strategies for the management of severe reactions and potential for increased drug-related toxicity, resulting from concomitant caffeine consumption.

Chronic treatment with aripiprazole prevents development of dopamine supersensitivity and potentially supersensitivity psychosis

BACKGROUND

Long-term treatment of schizophrenia with antipsychotics is crucial for relapse prevention, but a prolonged blockade of D(2) dopamine receptors may lead to the development of supersensitivity psychosis. We investigated the chronic effects of aripiprazole (ARI) on dopamine sensitivity.

METHODS

We administered ARI (1.5 mg/kg/d), haloperidol (HAL; 0.75 mg/kg/d), or vehicle (VEH) via minipump for 14 days to drug-naive rats or to rats pretreated with HAL (0.75 mg/kg/d) or VEH via minipump for 14 days. On the seventh day following treatment cessation, we examined the effects of the treatment conditions on the locomotor response to methamphetamine and on striatal D(2) receptor density (N = 4-10/condition/experiment).

RESULTS

Chronic treatment with HAL led to significant increases in locomotor response and D(2) receptor density, compared with the effects of chronic treatment with either VEH or ARI; there were no significant differences in either locomotor response or D(2) density between the VEH- and ARI-treated groups. We also investigated the effects of chronic treatment with HAL, ARI, or VEH preceded by HAL or VEH treatment on locomotor response and D(2) density. ANOVA analysis indicated that the rank ordering of groups for both locomotor response and D(2) density was HAL-HAL > HAL-VEH > HAL-ARI > VEH-VEH.

CONCLUSIONS

Chronic treatment with ARI prevents development of dopamine supersensitivity and potentially supersensitivity psychosis, suggesting that by reducing excessive sensitivity to dopamine and by stabilizing sensitivity for an extended period of time, ARI may be helpful for some patients with treatment-resistant schizophrenia.

Brain region-specific decrease in the activity and expression of protein kinase A in the frontal cortex of regressive autism

Autism is a severe neurodevelopmental disorder that is characterized by impaired language, communication, and social skills. In regressive autism, affected children first show signs of normal social and language development but eventually lose these skills and develop autistic behavior. Protein kinases are essential in G-protein-coupled, receptor-mediated signal transduction and are involved in neuronal functions, gene expression, memory, and cell differentiation. We studied the activity and expression of protein kinase A (PKA), a cyclic AMP–dependent protein kinase, in postmortem brain tissue samples from the frontal, temporal, parietal, and occipital cortices, and the cerebellum of individuals with regressive autism; autistic subjects without a clinical history of regression; and age-matched developmentally normal control subjects. The activity of PKA and the expression of PKA (C-α), a catalytic subunit of PKA, were significantly decreased in the frontal cortex of individuals with regressive autism compared to control subjects and individuals with non-regressive autism. Such changes were not observed in the cerebellum, or the cortices from the temporal, parietal, and occipital regions of the brain in subjects with regressive autism. In addition, there was no significant difference in PKA activity or expression of PKA (C-α) between non-regressive autism and control groups. These results suggest that regression in autism may be associated, in part, with decreased PKA-mediated phosphorylation of proteins and abnormalities in cellular signaling.

Phosphodiesterase 4B genetic variants are not associated with antipsychotic-induced tardive dyskinesia

Phosphodiesterase 4B (PDE4B) has been evaluated as a genetic risk factor for schizophrenia. Selective PDE4 inhibitor drugs have antipsychotic-like effects and reduce tardive dyskinesia-like movements in animal models. We investigated whether PDE4B genetic variants are associated with antipsychotic-induced tardive dyskinesia incidence and severity in schizophrenia patients. Our sample consisted of 169 Caucasian patients taking typical antipsychotic medication for at least 1 year. We found two PDE4B gene variants to be nominally associated with tardive dyskinesia (rs1338719 and rs7528545) in the overall population and two other variants nominally associated with the presence of tardive dyskinesia and severity in female patients (rs1890196 and rs783036). None of these results survived correction for multiple testing. Overall, our results do not support a genetic association between tardive dyskinesia and PDE4B.

Chronic haloperidol and clozapine produce different patterns of effects on phosphodiesterase-1B, -4B, and -10A expression in rat striatum

Phosphodiesterase-10A (PDE10A), -1B (PDE1B), -4B (PDE4B), and -4A (PDE4A) are important regulators of signal transduction in striatum due to their catalysis of cyclic AMP and cyclic GMP. The typical antipsychotic drug haloperidol and the atypical antipsychotic drug clozapine are thought to regulate cyclic nucleotide signaling in striatum. Since this brain region is essential in mediation of both therapeutic and extrapyramidal side effects, it was of interest to determine whether chronic treatment for 21 days with haloperidol (1 mg/kg) or clozapine (20 mg/kg) affected PDE expression in rat striatum. This was accomplished using SDS-PAGE/immunoblotting and real-time RT-PCR. Both antipsychotic drugs increased PDE10A and did not change PDE4A. By contrast, PDE1B was increased by haloperidol treatment, but not clozapine treatment, while PDE4B was increased by clozapine, but not haloperidol. In all cases, changes in protein expression were accompanied by corresponding changes in mRNA, and only were observed with chronic treatment. Up-regulation of PDEs may represent compensatory responses to haloperidol and clozapine treatments, due to altered cyclic nucleotide signaling, and that different patterns of effects produced by these drugs may be associated with their mechanisms of action.

Rolipram: a specific phosphodiesterase 4 inhibitor with potential antipsychotic activity

Currently available antipsychotic medications work primarily by antagonizing D2 dopamine receptors, thus raising intracellular cAMP levels. We hypothesized that intracellular stimulation of cAMP levels in the CNS would have similar effects to treatment with antipsychotic medication. To test this hypothesis, we studied the effect of an acute treatment of rolipram, an inhibitor of type 4 phosphodiesterases that degrade cAMP, on acoustic startle and prepulse inhibition (PPI) of the acoustic startle response in C57BL/6J mice known to exhibit poor PPI. PPI is disrupted in schizophrenia patients, and the ability of a drug to increase PPI in mice is predictive of antipsychotic efficacy. We show here that acute treatment with rolipram significantly increases PPI at doses that do not alter the acoustic startle response (lowest effective dose 0.66 mg/kg). In addition, rolipram (0.66 mg/kg) blocks the disruptive effects of amphetamine (10 mg/kg) on PPI. At a slightly higher dose (1.0 mg/kg), rolipram also induces catalepsy. Thus, phosphodiesterase-4 (PDE4) inhibition has many of the same behavioral effects as traditional antipsychotic medications. In contrast to traditional antipsychotics, these effects are achieved through alteration of an intracellular second messenger system rather than antagonism of neurotransmitter receptors. Given previous reports showing rolipram improves cognition, we conclude that PDE4 represents an important novel target for further antipsychotic drug development.

Phosphodiesterase inhibitors: a novel mechanism for receptor-independent antipsychotic medications

OVERVIEW

All current antipsychotic medications work by binding to Gi-coupled dopamine (DA) D2 receptors. Such medications are thought to affect cellular function primarily by decreasing DA-mediated regulation of intracellular cyclic adenosine monophosphate (cAMP).However, several studies indicate that cAMP signal transduction abnormalities in schizophrenia may not be limited to D2-containing cells. The current study examines the potential of using non-receptor-based agents that modify intracellular signal transduction as potential antipsychotic medications.

METHODS

The indirect DA agonist amphetamine has been used to model the auditory sensory processing deficits in schizophrenia. Such pharmacologically induced abnormalities are reversed by current antipsychotic treatments. This study examines the ability of the phosphodiesterase-4 inhibitor, rolipram, to reverse amphetamine-induced abnormalities in auditory-evoked potentials that are characteristic of schizophrenia.

RESULTS

Rolipram reverses amphetamine-induced reductions in auditory-evoked potentials.

CONCLUSION

This finding could lead to novel approaches to receptor-independent treatments for schizophrenia.

Study on the suitability of a rat model for tardive dyskinesia and the preventive effects of various drugs

1. Male Sprague-Dawley rats (weighing 260-300 g) were administered 1.5 mg/kg of haloperidol (HPD) intraperitoneally once daily for 28 days to produce an animal model for tardive dyskinesia (TD). The daily administration of HPD significantly increased the frequency of involuntary orofacial movements (chewing movements, tongue protrusions and buccal tremors). 2. Its suitability as a model for TD was assessed in terms of the therapeutic effects of 6 drugs [trihexyphenodyl hydrochloride(THP), clonazepam(CZP), sodium valproate(VPA), alpha-tocopherol(Vit E), ritanserin(RS) and propranolol hydrochloride(PPL)]. These drugs were also used concomitantly with HPD to study their preventive effect. 3. As for the therapeutic effects of the drugs, both the single and the 14-day daily administrations of CZP as well as of VPA significantly suppressed the chewing movements. The results were mostly consistent with the effect of each drug on human TD, indicating this would be an excellent model for TD in terms of the drug responsiveness. 4. The concomitant administration of RS from the start of HPD administration significantly suppressed the appearance of chewing movements. The concomitant administration of Vit E for 42 days also suppressed chewing movements and buccal tremors. On the other hand, the concomitant administration of THP tended to aggravate these involuntary movements. 5. The fact that the therapeutic and preventive effects of the drugs on this model differed suggested that the development and recovery of the movements might also differ, at least in part.

Rolipram, a selective phosphodiesterase type-IV inhibitor, prevents induction of heat shock protein HSP-70 and hsp-70 mRNA in rat retrosplenial cortex by the NMDA receptor antagonist dizocilpine

The non-competitive NMDA receptor antagonists, such as (+)-MK-801 (dizocilpine), cause the expression of heat shock protein HSP-70 and pathomorphological damage in the retrosplenial cortex of the rat brain. However, the precise mechanism(s) underlying the neurotoxicity of NMDA receptor antagonists is unknown. The present study was undertaken to examine the role of phosphodiesterase type IV in the expression of heat shock genes induced by dizocilpine. Heat shock protein HSP-70, which is known as a sensitive marker of neuron injury, was induced in the retrosplenial cortex of the rat brain 24 h after a single administration of dizocilpine (1 mg/kg). Pretreatment with the specific phosphodiesterase type IV inhibitor rolipram (2.5, 5 or 10 mg/kg, 15 min before dizocilpine) attenuated the expression of HSP-70 and hsp-70 mRNA induced by dizocilpine (1 mg/kg) in a dose-dependent manner. Furthermore, another phosphodiesterase type IV inhibitor, Ro 20-1724 (5 or 10 mg/kg, 15 min before dizocilpine), and a non-selective phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) (5 or 10 mg/kg, 15 min before dizocilpine), significantly attenuated the expression of HSP-70 protein and hsp-70 mRNA induced in the retrosplenial cortex by dizocilpine. However, the induction of the immediate early gene c-fos and microglial activation in the retrosplenial cortex after administration of dizocilpine was not attenuated by pretreatment with rolipram (5 or 10 mg/kg, 15 min before dizocilpine). Moreover, histopathological study indicated that pretreatment with rolipram (5 or 10 mg/kg, 15 min before dizocilpine) did not prevent the formation of vacuoles caused by treatment with dizocilpine. The present findings suggest that phosphodiesterase type IV may play a significant role in the expression of HSP-70 protein and hsp-70 mRNA in the rat retrosplenial cortex after administration of dizocilpine, and that phosphodiesterase type IV may not play a role in the neurotoxicity of NMDA receptor antagonists such as dizocilpine.

Prevention of methamphetamine-induced behavioral sensitization in rats by a cyclic AMP phosphodiesterase inhibitor, rolipram

Effects of an interaction between rolipram, a cyclic adenosine 3', 5'-monophosphate (cyclic AMP) phosphodiesterase inhibitor, and methamphetamine on the development of behavioral sensitization were observed in rats. In vivo microdialysis showed that a single dose of 4 mg/kg methamphetamine (i.p.) significantly increased striatal dopamine levels while coadministration with 4 mg/kg rolipram (i.p.) did not affect these levels. Also, methamphetamine alone did not alter striatal cyclic AMP levels but coadministration with rolipram and rolipram alone significantly increased these levels. The administration of 4 mg/kg methamphetamine (i.p.) once a day for 5 days significantly enhanced hyperlocomotion and rearing induced by a 2-mg/kg methamphetamine challenge (i.p.) after a 1-week withdrawal period, compared with controls or coadministration with 4 mg/kg rolipram (i.p.). Striatal dopamine levels, detected by in vivo microdialysis, were increased following the challenge but were comparable between the groups. These findings suggest that rolipram prevents methamphetamine-induced behavioral sensitization by increasing cyclic AMP levels while not affecting dopamine-releasing processes.