Tandospirone potentiates the fluoxetine-induced increases in extracellular dopamine via 5-HT(1A) receptors in the rat medial frontal cortex

Direct serotonin release in humans shapes aversive learning and inhibition

The role of serotonin in human behaviour is informed by approaches which allow in vivo modification of synaptic serotonin. However, characterising the effects of increased serotonin signalling in human models of behaviour is challenging given the limitations of available experimental probes, notably selective serotonin reuptake inhibitors. Here we use a now-accessible approach to directly increase synaptic serotonin in humans (a selective serotonin releasing agent) and examine its influence on domains of behaviour historically considered core functions of serotonin. Computational techniques, including reinforcement learning and drift diffusion modelling, explain participant behaviour at baseline and after week-long intervention. Reinforcement learning models reveal that increasing synaptic serotonin reduces sensitivity for outcomes in aversive contexts. Furthermore, increasing synaptic serotonin enhances behavioural inhibition, and shifts bias towards impulse control during exposure to aversive emotional probes. These effects are seen in the context of overall improvements in memory for neutral verbal information. Our findings highlight the direct effects of increasing synaptic serotonin on human behaviour, underlining its role in guiding decision-making within aversive and more neutral contexts, and offering implications for longstanding theories of central serotonin function.

Augmentation therapy with tandospirone citrate in vascular depression patients with mild cognitive impairment: A prospective randomized clinical trial

Cognitive impairment is a prominent clinical manifestation of vascular depression (VaDep). The current study aimed to assess the efficacy of tandospirone citrate in VaDep cases with mild cognitive impairment (VaDep-MCI) as well as the role of plasma monoamine neurotransmitters during the treatment. In this single-blind, randomized controlled study, 116 participants were randomly assigned to the tandospirone (tandospirone citrate-escitalopram) and control (escitalopram) groups. The primary endpoints were changes in cognitive test scores from baseline to Week 8, including the Rey Auditory Verbal Learning Test (RAVLT), Semantic Verbal Fluency (SVF) test, Trail Making Test (TMT), Digital Span Test (DST) and Clock Drawing Test (CDT) scores. Generalized estimating equation models were used to examine repeated measures. The results showed that compared with the changes in the control group from baseline to Week 8, the tandospirone group showed more significant changes in SVF score at Weeks 4 (p < 0.05) and 8 (p < 0.001), and TMT (B-A) score at Week 8 (p < 0.05). RAVLT, DST and DCT scores were relatively stable in both groups during the study period. Moreover, mediation analysis showed that these results were not mediated by the alleviation of depression symptoms. Partial Spearman correlation analysis showed that only plasma 5-hydroxytryptamine (5-HT) was positively correlated with Hamilton Depression Rating Scale score after Bonferroni correction (r = 0.347, p < 0.001). Augmentation therapy with tandospirone citrate improved the executive and language functions of VaDep-MCI patients. Additionally, plasma 5-HT levels may serve as a potential biomarker of VaDep severity. These findings may provide clinical insights into the treatment of vascular depression.

Apocynin-Tandospirone Derivatives Suppress Methamphetamine-Induced Hyperlocomotion in Rats with Neonatal Exposure to Dizocilpine

Accumulating evidence implicates oxidative stress as a potential pathophysiological mechanism of schizophrenia. Accordingly, we synthesized new chemicals using apocynin and tandospirone as lead compounds (A-2, A-3 and A-4). These novel compounds decreased reactive oxygen species (ROS) concentrations in vitro and reversed decreases in glutathione levels in the medial prefrontal cortex of rats transiently exposed to MK-801, an N-methyl-d-aspartate receptor antagonist, in the neonatal period. To determine whether A-2, A-3 and A-4 show behavioral effects associated with antipsychotic properties, the effects of these compounds on methamphetamine (MAP)-induced locomotor and vertical activity were examined in the model rats. A-2 and A-3, administered for 14 days around the puberty period, ameliorated MAP-induced hyperlocomotion in MK-801-treated rats in the post-puberty period, while A-4 suppressed MAP-induced vertical activity. These findings indicate that apocynin-tandospirone derivatives present anti-dopaminergic effects and may alleviate psychotic symptoms of schizophrenia.

A controlled study of the efficacy and safety of tandospirone citrate combined with escitalopram in the treatment of vascular depression: A pilot randomized controlled trial at a single-center in China

Vascular depression can respond poorly to antidepressants. This study aimed to explore the efficacy and safety of tandospirone plus escitalopram for treating vascular depression with anxiety. This pilot randomized controlled trial included consecutive inpatients/outpatients with vascular depression/anxiety at the Department of Neurology, Fujian Medical University Union Hospital, China (January 2014 to December 2016). Among 157 patients screened, 100 were randomly divided into the tandospirone + escitalopram (combination therapy) and escitalopram (monotherapy) groups equally, and then followed for 8 weeks. Efficacy was evaluated using the Hamilton Depression (HAMD), Hamilton Anxiety (HAMA), Clinical Global Impression (CGI) and Mini-Mental State examination (MMSE) scales. Adverse events (AEs) were assessed with the Treatment Emergent Symptom Scale (TESS). HAMD and HAMA scores decreased progressively, showing reductions versus baseline at 1, 2, 4 and 8 weeks in both groups (P < 0.001). HAMD and HAMA scores were lower in the tandospirone + escitalopram group than those in the escitalopram group at 1 and 2 weeks (P < 0.001), but not at 4 and 8 weeks. Improvements in CGI scores (severity, improvement and efficacy indexes) were greater in the tandospirone + escitalopram group than that in the escitalopram group at 1 and 2 weeks (P < 0.01), but not at 4 and 8 weeks. The tandospirone + escitalopram group had higher MMSE scores than that in the escitalopram group at 4 and 8 weeks (P < 0.01). All AEs were mild, and the rates were comparable between groups. Augmentation of escitalopram with tandospirone accelerates the onset of anti-depressive and anxiolytic effects and improves cognitive function in patients with vascular depression and anxiety.

Role of tandospirone, a 5-HT1A receptor partial agonist, in the treatment of central nervous system disorders and the underlying mechanisms

5-hydroxytryptamine (5-HT, serotonin) is an important neurotransmitter in the modulation of the cognitive, behavioral and psychological functions in animals and humans. Among the fourteen subtypes of 5-HT receptor, 5-HT1A receptor has been extensively studied. Tandospirone, an azapirone derivative with strong and selective agonist effect on 5-HT1A receptor, has been used for the treatment of anxiety disorders especially generalized anxiety disorder for decades. Recently, tandospirone showed the efficacy in relieving the syndromes of social anxiety disorder and post-traumatic stress disorder as well as in potentiating the effect of antidepressants in the treatment of depression in both preclinical and clinical studies. More impressively, the beneficial effect of tandospirone has been revealed on improvement of motor dysfunction of Parkinson's disease and cognitive deficits of schizophrenia either in monotherapy or in combination with other drugs. This review discusses the superiority of tandospirone in the treatment of the disorders and associated mechanisms in central nervous system from the literature.

Serotonergic modulation of the activity of mesencephalic dopaminergic systems: Therapeutic implications

Since their discovery in the mammalian brain, it has been apparent that serotonin (5-HT) and dopamine (DA) interactions play a key role in normal and abnormal behavior. Therefore, disclosure of this interaction could reveal important insights into the pathogenesis of various neuropsychiatric diseases including schizophrenia, depression and drug addiction or neurological conditions such as Parkinson's disease and Tourette's syndrome. Unfortunately, this interaction remains difficult to study for many reasons, including the rich and widespread innervations of 5-HT and DA in the brain, the plethora of 5-HT receptors and the release of co-transmitters by 5-HT and DA neurons. The purpose of this review is to present electrophysiological and biochemical data showing that endogenous 5-HT and pharmacological 5-HT ligands modify the mesencephalic DA systems' activity. 5-HT receptors may control DA neuron activity in a state-dependent and region-dependent manner. 5-HT controls the activity of DA neurons in a phasic and excitatory manner, except for the control exerted by 5-HT_2C receptors which appears to also be tonically and/or constitutively inhibitory. The functional interaction between the two monoamines will also be discussed in view of the mechanism of action of antidepressants, antipsychotics, anti-Parkinsonians and drugs of abuse.

Blonanserin reverses the phencyclidine (PCP)-induced impairment in novel object recognition (NOR) in rats: role of indirect 5-HT(1A) partial agonism

Blonanserin is an atypical antipsychotic drug (APD) which, compared to other atypical APDs, is a relatively selective serotonin (5-HT)2A and dopamine D2 antagonist. Comparing blonanserin with more broadly acting atypical APDs could be useful to test the contributions of actions at other monoamine receptors, e.g. 5-HT1A receptors, to the reversal of PCP-induced novel object recognition (NOR) deficit. In this study, we tested the effect of blonanserin alone, and in combination with 5-HT1A agents, on NOR deficit induced by subchronic treatment with the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP; 2 mg/kg), b.i.d., for 7 days. Blonanserin, 1mg/kg, but not 0.3mg/kg, improved the PCP-induced NOR deficit. However, at 1mg/kg, object exploration was diminished. Co-administration of sub-effective doses of blonanserin (0.3 mg/kg) and the 5-HT1A partial agonist, tandospirone (0.2 mg/kg), significantly reversed the NOR deficit without diminishing activity during the acquisition or retention periods. The combination of WAY100635 (0.6 mg/kg), a 5-HT1A antagonist, and blonanserin (1 mg/kg), also diminished object exploration which prevented assessment of the effect of this combination on NOR. WAY100635 (0.6 mg/kg) blocked the ameliorating effect of risperidone (0.1 mg/kg), another atypical APD with low affinity for 5-HT1A receptors, but did not impair exploration. These results suggest that blonansein and risperidone, atypical APDs which lack a direct action on 5-HT1A receptors require 5-HT1A receptor stimulation to reverse the subchronic PCP-induced NOR deficit and provide a support for clinical trial of blonanserin in combination with tandospirone to ameliorate cognitive impairment in schizophrenia and to have fewer side effects.

D(1) receptor agonists reverse the subchronic phencyclidine (PCP)-induced novel object recognition (NOR) deficit in female rats

Development of dopamine (DA) D(1) receptor agonists is a priority to improve cognitive impairment in schizophrenia (CIS). This study examined the dose-response relationship of the selective D(1) agonist, SKF38393 (0.5-40 mg/kg), to reverse the deficit in novel object recognition (NOR), an analog of declarative memory in man, produced by subchronic phencyclidine (PCP), an N-methyl-D-aspartate (NMDA) receptor non-competitive antagonist, and the ability of the D(1) antagonists, SCH23390 (0.05 mg/kg) and SKF83566 (0.15 mg/kg), to impair NOR in normal Long-Evans female rats. We also examined the ability of tandospirone, a serotonin (5-HT)(1A) receptor partial agonist, and LY341495, a mGluR2/3 receptor antagonist, to potentiate or block the effects of SKF38393 on NOR, respectively. SKF38393 reversed the persistent NOR deficit produced by subchronic PCP; the dose-response curve for SKF38393 was an inverted U-shape, with the peak effect at 6 mg/kg. SKF83566 and SCH23390 impaired NOR in normal rats. Co-administration of sub-effective doses of SKF38393 (0.25 mg/kg) and tandospirone (0.2 mg/kg) improved the PCP-induced NOR deficit, while LY341495 (1 mg/kg) blocked the ameliorating effect of SKF38393 (6 mg/kg), respectively. These data provide the first evidence that the reversal of the PCP-induced NOR deficit by D(1) agonism has an inverted U-shaped dose-response curve and that 5-HT(1A) and mGluR2/3 receptor signalling facilitates the efficacy of D(1) agonism to improve these deficits. These data suggest that although D(1) agonists may be useful to improve CIS, these agents, particularly higher doses, may also worsen cognitive function in some patients, because of an inverted U-shaped dose response curve.

The role of 5-HT1A receptors in phencyclidine (PCP)-induced novel object recognition (NOR) deficit in rats

RATIONALE

Atypical antipsychotic drugs (APDs), many of which are direct or indirect serotonin (5-HT)(1A) agonists, and tandospirone, a 5-HT(1A) partial agonist, have been reported to improve cognition in schizophrenia.

OBJECTIVES AND METHODS

We tested the effect of 5-HT(1A) agonism, alone, and in combination with other psychotropic agents, including the atypical APD, lurasidone, in reversing the deficit in novel object recognition (NOR) induced by subchronic treatment with the non-competitive NMDA receptor antagonist, phencyclidine (PCP) (2 mg/kg, b.i.d., for 7 days).

RESULTS

Subchronic treatment with PCP induced a persistent NOR deficit. Lurasidone (0.1 mg/kg), a potent 5-HT(1A) partial agonist, 5-HT(2A) antagonist, and weaker D(2) antagonist, tandospirone (0.6 mg/kg), and the selective post-synaptic 5-HT(1A) agonist, F15599 (0.16 mg/kg), ameliorated the subchronic PCP-induced-NOR deficit. The 5-HT(1A) antagonist, WAY100635 (0.6 mg/kg), blocked the ameliorating effects of tandospirone and lurasidone. The combination of sub-effective doses of tandospirone (0.2 mg/kg) and lurasidone (0.03 mg/kg) also reversed the PCP-induced NOR-deficit. Buspirone, a less potent partial 5-HT(1A) agonist than tandospirone, was less effective. Co-administration of tandospirone (0.2 mg/kg) and pimavanserin (3 mg/kg), a relatively selective 5-HT(2A) receptor inverse agonist, did not reverse the effect of sub-chronic PCP on NOR. The D(2) antagonist, haloperidol, blocked the ameliorating effect of tandospirone on the PCP-induced deficit in NOR.

CONCLUSIONS

These results indicate that 5-HT(1A) agonism is adequate to ameliorate the PCP-induced impairment in NOR and suggest further study of utilizing the combination of a 5-HT(1A) agonist and an atypical APD to ameliorate some types of cognitive impairment in schizophrenia.

Aripiprazole augmentation in 13 patients with refractory obsessive-compulsive disorder: a case series

OBJECTIVES

The primary treatment for obsessive-compulsive disorder (OCD) is selective serotonin reuptake inhibitors (SSRI). However, approximately a third of patients do not respond to SSRIs and remain chronically affected.

METHODS

Therefore, we added aripiprazole to SSRI therapy for 13 patients with treatment-refractory OCD (subjects who failed to respond to SSRI therapy for at least 2 months, and for an average of 508 days). Participants underwent at least 7 weeks of treatment with aripiprazole augmentation.

RESULTS

Patients were evaluated using the Y-BOCS and GAF scales. Aripiprazole (3-12 mg)/SSRI co-therapy significantly improved Y-BOCS and GAF scores. However, many patients needed to take antiparkinsonian drugs to control extrapyramidal symptoms.

CONCLUSIONS

These results suggest that aripiprazole augmentation of SSRI therapy may be effective for treatment-refractory OCD.

Role of serotonin in central dopamine dysfunction

The interaction between serotonin (5-HT) and dopamine (DA)-containing neurons in the brain is a research topic that has raised the interest of many scientists working in the field of neuroscience since the first demonstration of the presence of monoamine-containing neurons in the mid 1960. The bulk of neuroanatomical data available clearly indicate that DA-containing neurons in the brain receive a prominent innervation from serotonin (5-hydroxytryptamine, 5-HT) originating in the raphe nuclei of the brainstem. Compelling electrophysiological and neurochemical data show that 5-HT can exert complex effects on the activity of midbrain DA neurons mediated by its various receptor subtypes. The main control seems to be inhibitory, this effect being more marked in the mesocorticolimbic DA system as compared to the DA nigrostriatal system. In spite of a direct effect of 5-HT by its receptors located on DA cells, 5-HT can modulate their activity indirectly, modifying gamma-aminobutyric (GABA)-ergic and glutamatergic input to the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc). Although 5-HT/DA interaction in the brain has been extensively studied, much work remains to be done to clarify this issue. The recent development of subtype-selective ligands for 5-HT receptors will not only allow a detailed understanding of this interaction but also will lead to the development of new treatment strategies, appropriate for those neuropsychiatric disorders in which an alteration of the 5-HT/DA balance is supposed.

Preclinical characterization of WAY-211612: a dual 5-HT uptake inhibitor and 5-HT (1A) receptor antagonist and potential novel antidepressant

BACKGROUND AND PURPOSE

As a combination of 5-HT selective reuptake inhibitor (SSRI) with 5-HT(1A) receptor antagonism may yield a rapidly acting antidepressant, WAY-211612, a compound with both SSRI and 5-HT(1A) receptor antagonist activities, was evaluated in preclinical models.

EXPERIMENTAL APPROACH

Occupancy studies confirmed the mechanism of action of WAY-211612, while its in vivo profile was characterized in microdialysis and behavioural models.

KEY RESULTS

WAY-211612 inhibited 5-HT reuptake (K(i) = 1.5 nmol.L(-1); K(B) = 17.7 nmol.L(-1)) and exhibited full 5-HT(1A) receptor antagonist activity (K(i) = 1.2 nmol.L(-1); K(B) = 6.3 nmol.L(-1); I(max) 100% in adenyl cyclase assays; K(B) = 19.8 nmol.L(-1); I(max) 100% in GTPgammaS). WAY-211612 (3 and 30 mg.kg(-1), po) occupied 5-HT reuptake sites in rat prefrontal cortex (56.6% and 73.6% respectively) and hippocampus (52.2% and 78.5%), and 5-HT(1A) receptors in the prefrontal cortex (6.7% and 44.7%), hippocampus (8.3% and 48.6%) and dorsal raphe (15% and 83%). Acute or chronic treatment with WAY-211612 (3-30 mg.kg(-1), po) raised levels of cortical 5-HT approximately twofold, as also observed with a combination of an SSRI (fluoxetine; 30 mg.kg(-1), s.c.) and a 5-HT(1A) antagonist (WAY-100635; 0.3 mg.kg(-1), s.c). WAY-211612 (3.3-30 mg.kg(-1), s.c.) decreased aggressive behaviour in the resident-intruder model, while increasing the number of punished crossings (3-30 mg.kg(-1), i.p. and 10-56 mg.kg(-1), po) in the mouse four-plate model and decreased adjunctive drinking behaviour (56 mg.kg(-1), i.p.) in the rat scheduled-induced polydipsia model.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that WAY-211612 may represent a novel antidepressant.

Aripiprazole in the treatment of depressive and anxiety disorders: a review of current evidence

Despite the availability of different classes of drugs for the treatment of depressive and anxiety disorders, there are a number of clinically significant unmet needs, such as a high prevalence of treatment resistance, partial response, subsyndromal symptomatology, recurrence and relapse. With the approval of atypical antipsychotics, which are associated with a lower adverse effect burden than typical antipsychotics, consideration of their off-label use for the treatment of affective disorders and various other psychiatric disorders has become a viable option. However, consideration should be given to the US FDA black box warning indicating that atypical antipsychotics may increase mortality risk, particularly in the elderly population with dementia-related psychosis. There has been much conjecture about the utility of these atypical drugs to facilitate traditional antidepressant therapy, either in combination (from the initiation of therapy) or as adjunctive therapy (in the case of partial/incomplete response). Nevertheless, at present, available evidence from randomized, placebo-controlled trials is sparse, and a formal risk/benefit assessment of the use of these agents in a nonpsychotic patient population is not yet possible. As a representative agent from the atypical antipsychotic class with a novel mechanism of action and a relatively low adverse effect burden, aripiprazole represents an interesting potential treatment for depressive and anxiety disorders. In this review, we focus on the rationale for the use of aripiprazole in these disorders. Preclinical data suggests that aripiprazole has a number of possible mechanisms of action that may be important in the treatment of depressive and anxiety disorders. Such mechanisms include aripiprazole action at serotonin (5-HT) receptors as a 5-HT1A partial receptor agonist, a 5-HT2C partial receptor agonist and a 5-HT2A receptor antagonist. Aripiprazole also acts as a dopamine D2 partial receptor agonist, and has a possible action at adrenergic receptors. Furthermore, aripiprazole may have possible neuroprotective effects. Clinical studies demonstrate that aripiprazole may be useful in the treatment of bipolar depression, major depressive disorder, treatment-resistant depression and possibly anxiety disorders. Clinical data also suggest that aripiprazole may have a lower adverse effect burden than the other atypical drugs. Future research may confirm the potential utility of aripiprazole in the treatment of depressive and anxiety disorders.

Oseltamivir (Tamiflu) increases dopamine levels in the rat medial prefrontal cortex

Oseltamivir (Tamiflu), a neuraminidase inhibitor, is effective for treating both seasonal flu and H5N1 influenza A virus infection. Oseltamivir is generally well tolerated, and its most common adverse effects are nausea and vomiting. However, neuropsychiatric behaviors including jumping and falling from balconies by young patients being treated by oseltamivir have been reported from Japan; this has led to warnings against its prescribing by many authorities. The pharmacological mechanism of the neuropsychiatric effects of oseltamivir remains unclear. Many studies reported that changes in neurotransmission and abnormal behaviors are closely related. We investigated the changes in dopamine and serotonin metabolism after systemic administration of oseltamivir in the medial prefrontal cortex (mPFC) of rats by using microdialysis. After systemic administration of oseltamivir (25mg/kg or 100mg/kg; intraperitoneally (i.p.)), extracellular dopamine in the mPFC was significantly increased as compared to the control values; 3,4-dihydroxyphenylacetic acid and homovanillic acid, the metabolites of dopamine, had also increased significantly. Serotonin was unchanged after the administration of oseltamivir. These findings suggest that oseltamivir increased dopamine release in the mPFC; further, they suggest that the increase in dopamine during oseltamivir treatment may have caused abnormal behaviors in young patients. In cases where oseltamivir is prescribed to children, close observation is required.

Differential behavioral syndrome evoked in the rats after multiple doses of SSRI fluoxetine with selective MAO inhibitors rasagiline or selegiline

This study investigated whether rasagiline and selegiline (MAO-B inhibitors) induce serotonin syndrome in fluoxetine-treated rats. Rats received rasagiline (0.1, 0.5, 2.0 mg/kg), or selegiline (0.8, 4.0, 16.0 mg/kg) (doses reflecting the clinical ratio of 1:8 base) in drinking water for 28 days. During the last 21 days, they received injections of fluoxetine 10 mg/kg (controls received water only, then saline injections; a fluoxetine only group received water only then fluoxetine). Serotonin syndrome was assessed using neurological severity score (NSS), food intake and weight gain. Mean NSS significantly increased, and weight and food consumption significantly decreased in rats receiving fluoxetine alone compared with controls. Selegiline 16 mg/kg but not rasagiline (regardless of dose) exacerbated these effects. We concluded that selegiline's amphetamine-like metabolites may increase synaptic cathecholamines and possibly serotonin, aggravating fluoxetine's effect. Rasagiline is devoid of this effect and may therefore be safer for use with serotonergic drugs in parkinsonian patients.

Effect of buspirone, a serotonin1A partial agonist, on cognitive function in schizophrenia: a randomized, double-blind, placebo-controlled study

In previous studies, we demonstrated that tandospirone, a serotonin-5-HT1A partial agonist, added to ongoing treatment with small to moderate doses of typical antipsychotic drugs, improved executive function and verbal learning and memory. However, tandospirone is not available in most countries, and atypical antipsychotic drugs (AAPDs) have largely replaced typical antipsychotic drugs as the primary treatment for schizophrenia. Therefore, the goal of this randomly assigned placebo-controlled double-blind study was to determine if the addition of buspirone, a widely available 5-HT1A partial agonist, would enhance cognitive function, in subjects with schizophrenia treated with AAPDs. Seventy-three patients with schizophrenia, who had been treated with an AAPD for at least three months, were randomly assigned to receive either buspirone, 30 mg/day, or matching placebo. All other medications remained unchanged. Attention, verbal fluency, verbal learning and memory, verbal working memory, and executive function, as well as psychopathology, were assessed at baseline, and 6 weeks, and 3 and 6 months after baseline. A significant Time x Group interaction effect was noted on the Digit Symbol Substitution Test, a measure of attention/speeded motor performance, due to better performance of the buspirone group compared to the placebo group at 3 months. No significant interaction effects were noted for other domains of cognition. Scores on the Brief Psychiatric Rating Scale (Total, Positive) were improved during treatment with buspirone but not placebo, but the effects did not reach statistical significance. The results of this study showed a possible benefit of buspirone augmentation of AAPDs to enhance attention. However, we did not replicate the results of the previous study with tandospirone, which may be due to the differences between tandospirone and buspirone, between typical antipsychotics and AAPDs, or a combination of the above. Further study to determine the usefulness of 5-HT1A agonist treatment in schizophrenia is indicated.

Tandospirone, a 5-HT1A agonist, ameliorates movement disorder via non-dopaminergic systems in rats with unilateral 6-hydroxydopamine-generated lesions

Serotonin 1A (5-HT1A) receptors are distributed throughout the brain with their highest concentrations in the frontal cortex, subthalamic nucleus and entopeduncular nucleus as well as the dorsal and median raphe nucleus. There is growing evidence that 5-HT1A receptor agonists have an antidepressant effect in individuals with major depressive disorders. Recent clinical studies suggest that tandospirone, a highly potent and selective 5-HT1A receptor agonist used clinically as an antidepressant in Japan and China, may act as an antiparkinsonian drug. In the present study, we investigated the effect of tandospirone on contralateral rotational behavior in a unilateral hemiparkinsonian rat model produced with 6-hydroxydopamine (6-OHDA). Tandospirone, as well as 8-hydroxy-2-(di-n-propylamino) tetralin (8-OHDPAT), significantly increased contralateral turnings in a dose-dependent manner (0.5-10 mg/kg). Tandospirone also remarkably potentiated the contralateral turning induced by 0.025 mg/kg of apomorphine. Pretreatment with WAY-100635, a 5-HT1A receptor antagonist, almost completely blocked the contralateral turning behavior evoked by tandospirone and 8-OHDPAT, but not that by apomorphine. SCH-23390, a selective dopamine D1 receptor antagonist, did not affect on the tandospirone-induced rotational behavior. These results suggested that tandospirone could act on postsynaptic 5-HT1A receptors and modulate excitatory amino acid pathways in the basal ganglia. Thus, tandospirone could have therapeutic potential for the treatment of Parkinson's disease by modulating neuronal activities of non-dopaminergic pathways.

Effects of divalproex and atypical antipsychotic drugs on dopamine and acetylcholine efflux in rat hippocampus and prefrontal cortex

Mood stabilizers (e.g., valproic acid) and antipsychotic drugs (APDs) are commonly co-administered in the treatment of bipolar disorder and schizophrenia. The basis for any synergism between these classes of drugs in either group of disorders has been little studied. Previous studies have shown that atypical APDs (e.g., clozapine) preferentially increases dopamine (DA) and acetylcholine (ACh) efflux in rat medial prefrontal cortex (mPFC) and hippocampus (HIP), both of which have been suggested to contribute to their ability to improve cognition in patients with schizophrenia. We have recently reported that the anticonvulsant mood stabilizers (AMS), valproic acid, carbamazepine, and zonisamide, but not lithium, also preferentially increase DA efflux in the rat mPFC, and that, at subthreshold doses, the AMS also augment the ability of the atypical APDs clozapine and risperidone to increase DA but not ACh efflux in the mPFC. The present study examined the ability of divalproex (DVX), which is chemically related to valproic acid, to enhance DA and ACh efflux in the HIP and to augment the effect of atypical APDs on ACh efflux in the HIP and mPFC. DVX, 500 mg/kg, significantly increased DA and ACh efflux in the HIP, and DA, but not ACh, efflux in the mPFC, whereas a lower dose of DVX, 50 mg/kg, had no effect on DA or ACh in either region. However, DVX, 50 mg/kg, combined with the atypical APDs olanzapine (1.0 mg/kg) or aripiprazole (0.3 mg/kg) significantly potentiated the effect of both APDs on DA, but not ACh efflux in the HIP and mPFC. Pretreatment of olanzapine or aripiprazole with the selective serotonin 5-HT(1A) antagonist, WAY100635 (1.0 mg/kg) partially but significantly blocked the effect of the combination of DVX, 50 mg/kg, and olanzapine or aripiprazole, on DA efflux in both the HIP and mPFC. WAY100635 did not affect the ability of the combination of olanzapine or aripiprazole and DVX to enhance ACh efflux in the HIP or mPFC. Subchronic administration of the combination of DVX, 50 mg/kg, and risperidone, produced significantly greater increases in DA and ACh efflux in the mPFC, but these increases were not significantly different from those following the acute administration of the combination of risperidone and DVX. These results provide further evidence that the AMS, DVX, augments the ability of atypical APDs to increase DA or ACh efflux in either the HIP or mPFC or both. The clinical significance of this potentiation for the beneficial clinical effects of this combination of agents and the differences between AMS in this regard warrants further study.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Neurochemical evaluation of the novel 5-HT1A receptor partial agonist/serotonin reuptake inhibitor, vilazodone

Vilazodone has been reported to be an inhibitor of 5-hydoxytryptamine (5-HT) reuptake and a partial agonist at 5-HT1A receptors. Using [35S]GTPgammaS binding in rat hippocampal tissue, vilazodone was demonstrated to have an intrinsic activity comparable to the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Vilazodone (1-10 mg/kg p.o.) dose-dependently displaced in vivo [3H]DASB (N,N-dimethyl-2-(2-amino-4-cyanophenylthio)benzylamine) binding from rat cortex and hippocampus, indicating that vilazodone occupies 5-HT transporters in vivo. Using in vivo microdialysis, vilazodone (10 mg/kg p.o.) was demonstrated to cause a 2-fold increase in extracellular 5-HT but no change in noradrenaline or dopamine levels in frontal cortex of freely moving rats. In contrast, administration of 8-OH-DPAT (0.3 mg/kg s.c.), either alone or in combination with a serotonin specific reuptake inhibitor (SSRI; paroxetine, 3 mg/kg p.o.), produced no increase in cortical 5-HT whilst increasing noradrenaline and dopamine 2 and 4 fold, respectively. A 2-fold increase in extracellular 5-HT levels (but no change in noradrenaline or dopamine levels) was observed after combination of the 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(pyridinyl)cyclohexanecarboxamide) (WAY-100635; 0.3 mg/kg s.c.) and paroxetine (3 mg/kg p.o.). In summary, vilazodone behaved as a high efficacy partial agonist at the rat hippocampal 5-HT1A receptors in vitro and occupied 5-HT transporters in vivo. In vivo vilazodone induced a selective increase in extracellular levels of 5-HT in the rat frontal cortex. This profile was similar to that seen with a 5-HT1A receptor antagonist plus an SSRI but in contrast to 8-OH-DPAT either alone or in combination with paroxetine.

On the trail of a cognitive enhancer for the treatment of schizophrenia

The aim of this critical review is to address that the study of cognition and antipsychotics is not always driven by logic and that research into real pro-cognitive drug treatments must be guided by a better understanding of the biochemical mechanisms underlying cognitive processes and deficits. Many studies have established that typical neuroleptic drugs do not improve cognitive impairment. Atypical antipsychotics improve cognition, but the pattern of improvement differs from drug to drug. Diminished cholinergic activity has been associated with memory impairments. Why atypical drugs improve aspects of cognition might lie in their ability to increase dopamine and acetylcholine in the prefrontal cortex. An optimum amount of dopamine activity in the prefrontal cortex is critical for cognitive functioning. Another mechanism is related to procedural learning, and would explain the quality of the practice during repeated evaluations with atypical antipsychotics due to a more balanced blockage of D2 receptors. Laboratory studies have shown that clozapine, ziprasidone, olanzapine, and risperidone all selectively increase acetylcholine release in the prefrontal cortex, whereas this is not true for haloperidol and thioridazine. A few studies have suggested that cholinomimetics or AChE inhibitors can improve memory functions not only in Alzheimer's disease but also in other pathologies. Some studies support the role of decreased cholinergic activity in the cognitive deficits while others demonstrate that decreased choline acetyltransferase activity is related to deterioration in cognitive performance in schizophrenia. Overall, results suggest the hypothesis that the cholinergic system is involved in the cognitive dysfunctions observed in schizophrenia and that increased cholinergic activity may improve these impairments. Furthermore, a dysfunction of glutamatergic neurotransmission could play a key role in cognitive deficits associated with schizophrenia. Further meta-analysis of various clinical trials in this field is required to account for matters on the grounds of evidence-based medicine.

Tandospirone activates neuroendocrine and ERK (MAP kinase) signaling pathways specifically through 5-HT1A receptor mechanisms in vivo

Tandospirone, an azapirone, is a selective serotonin(1A) (5-HT(1A)) receptor agonist. The effects of tandospirone on plasma hormones and on mitogen-activated protein (MAP) kinase activity in the brain of male rats were studied. Tandospirone produced a time- and dose-dependent increase in plasma levels of oxytocin, adrenocorticotropin (ACTH), corticosterone, and prolactin. The minimal dose of tandospirone that led to a significant elevation of plasma oxytocin, ACTH, and prolactin levels was 1.0 mg/kg (s.c.), while the minimal dose for corticosterone release was 3.0 mg/kg (s.c.). The ED(50) of tandospirone was 1.3 mg/kg for oxytocin, 1.2 mg/kg for ACTH, 3.0 mg/kg for corticosterone, and 0.24 mg/kg for prolactin. Pretreatment with the specific 5-HT(1A) receptor antagonist WAY 100,635 (0.3 mg/kg, s.c.) completely blocked the effects of tandospirone on plasma levels of oxytocin, ACTH, and corticosterone but shifted the dose-response curve for prolactin to the right. Tandospirone injection (10 mg/kg, s.c.) stimulated the MAP kinase signaling cascade, specifically the phosphorylation of p42/44 extracellular signal-regulated kinase (ERK). Western blot analysis revealed a significant increase in phosphorylated ERK (p-ERK) levels in the hypothalamic paraventricular nucleus (PVN) as well as the dorsal raphe nucleus 5 min following tandospirone injection. These increases were blocked by pretreatment with WAY 100,635 (0.3 mg/kg). The results are the first evidence that systemic 5-HT(1A) receptor agonist administration produces a rapid increase in p-ERK levels in vivo, providing further insight into the signaling mechanisms of the 5-HT(1A) receptor.

Perospirone, a novel atypical antipsychotic drug, potentiates fluoxetine-induced increases in dopamine levels via multireceptor actions in the rat medial prefrontal cortex

Perospirone is a novel atypical antipsychotic with a unique combination of 5-HT1A receptor agonism as well as 5-HT2A and D2 receptor antagonism. We investigated the effect of perospirone in combination with fluoxetine on dopamine release in the rat medial prefrontal cortex using microdialysis. Perospirone and fluoxetine increased dopamine release to 270 and 210% of the baseline value, respectively. A combination of perospirone and fluoxetine markedly increased dopamine release to 800% of the baseline value. Pretreatment with a selective 5-HT1A receptor antagonist, WAY 100635, suppressed the increase in dopamine levels induced by the administration of perospirone and fluoxetine to 330% of the baseline value. These findings suggest that perospirone potentiates fluoxetine-induced dopamine increases in part via the action of the 5-HT1A receptor and may augment the effect of fluoxetine in treatment-resistant depression.

Imaging brain phospholipase A2-mediated signal transduction in response to acute fluoxetine administration in unanesthetized rats

Fluoxetine, a selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor, is used widely to treat depression and related disorders. By inhibiting presynaptic 5-HT reuptake, fluoxetine is thought to act by increasing 5-HT in the synaptic cleft, thus 5-HT binding to postsynaptic 5-HT(2A/2C) receptors. These receptors can be coupled via a G-protein to phospholipase A(2) (PLA(2)), which when activated releases the second messenger arachidonic acid from synaptic membrane phospholipids. To image this activation, fluoxetine (10 mg/kg) or saline vehicle was administered i.p. to unanesthetized rats, and regional brain incorporation coefficients k(*) of intravenously injected radiolabeled arachidonic acid were measured after 30 min. Compared with vehicle, fluoxetine significantly increased k(*) in prefrontal, motor, somatosensory, and olfactory cortex, as well as in the basal ganglia, hippocampus, and thalamus. Many of these regions demonstrate high densities of the serotonin reuptake transporter and of 5-HT(2A/2C) receptors. Brain stem, spinal cord, and cerebellum, which showed no significant response to fluoxetine, have low densities of the transporters and receptors. The results show that it is possible to image quantitatively PLA(2)-mediated signal transduction in vivo in response to fluoxetine.