Role of cortical and striatal 5-HT1A receptors in alleviating antipsychotic-induced extrapyramidal disorders

Efficacy and Safety of Lurasidone vs. Quetiapine XR in Acutely Psychotic Patients With Schizophrenia in Korea: A Randomized, Double-Blind, Active-Controlled Trial

OBJECTIVE

This study was performed to evaluate the efficacy and safety of lurasidone (160 mg/day) compared to quetiapine XR (QXR; 600 mg/day) in the treatment of acutely psychotic patients with schizophrenia.

METHODS

Patients were randomly assigned to 6 weeks of double-blind treatment with lurasidone 160 mg/day (n=105) or QXR 600 mg/day (n=105). Primary efficacy measure was the change from baseline to week 6 in Positive and Negative Syndrome Scale (PANSS) total score and Clinical Global Impressions severity (CGI-S) score. Adverse events, body measurements, and laboratory parameters were assessed.

RESULTS

Lurasidone demonstrated non-inferiority to QXR on the PANSS total score. Adjusted mean±standard error change at week 6 on the PANSS total score was -26.42±2.02 and -27.33±2.01 in the lurasidone and QXR group, respectively. The mean difference score was -0.91 (95% confidence interval -6.35-4.53). The lurasidone group showed a greater reduction in PANSS total and negative subscale on week 1 and a greater reduction in end-point CGI-S score compared to the QXR group. Body weight, body mass index, and waist circumference in the lurasidone group were reduced, with significantly lower mean change compared to QXR. Endpoint changes in glucose, cholesterol, triglycerides, and low-density lipoprotein levels were also significantly lower. The most common adverse drug reactions with lurasidone were akathisia and nausea.

CONCLUSION

Lurasidone 160 mg/day was found to be non-inferior to QXR 600 mg/day in the treatment of schizophrenia with comparable efficacy and tolerability. Adverse effects of lurasidone were generally tolerable, and beneficial effects on metabolic parameters can be expected.

Pathophysiological Mechanisms of Antipsychotic-Induced Parkinsonism

Among neurological adverse reactions in patients with schizophrenia treated with antipsychotics (APs), drug-induced parkinsonism (DIP) is the most common motility disorder caused by drugs affecting dopamine receptors. One of the causes of DIP is the disruption of neurotransmitter interactions that regulate the signaling pathways of the dopaminergic, cholinergic, GABAergic, adenosinergic, endocannabinoid, and other neurotransmitter systems. Presently, the development mechanisms remain poorly understood despite the presence of the considered theories of DIP pathogenesis.

TPN672: A Novel Serotonin-Dopamine Receptor Modulator for the Treatment of Schizophrenia

TPN672 [7-(2-(4-(benzothiophen-4-yl) piperazin-1-yl)ethyl)quinolin-2(1H)-one maleate] is a novel antipsychotic candidate with high affinity for serotonin and dopamine receptors that is currently in clinical trial for the treatment of psychiatric disorders. In vitro binding study showed that TPN672 exhibited extremely high affinity for serotonin 1A receptor (5-HT1AR) (K i = 0.23 nM) and 5-HT2AR (K i = 2.58 nM) as well as moderate affinity for D3R (K i = 11.55 nM) and D2R (K i = 17.91 nM). In vitro functional assays demonstrated that TPN672 acted as a potent 5-HT1AR agonist, D2R/D3R partial agonist, and 5-HT2AR antagonist. TPN672 displayed robust antipsychotic efficacy in rodent models (e.g., blocking phencyclidine-induced hyperactivity), significantly better than aripiprazole, and ameliorated negative symptoms and cognitive deficits in the sociability test, dark avoidance response, Morris water maze test, and novel object recognition test. The results of electrophysiological experiments showed that TPN672 might inhibit the excitability of the glutamate system through activating 5-HT1AR in medial prefrontal cortex, thereby improving cognitive and negative symptoms. Moreover, the safety margin (the ratio of minimum catalepsy-inducing dose to minimum effective dose) of TPN672 was about 10-fold, which was superior to aripiprazole. In conclusion, TPN672 is a promising new drug candidate for the treatment of schizophrenia and has been shown to be more effective in attenuating negative symptoms and cognitive deficits while having lower risk of extrapyramidal symptoms and hyperprolactinemia. SIGNIFICANCE STATEMENT: TPN672 is a promising new drug candidate for the treatment of schizophrenia and has been shown to be more effective in attenuating negative symptoms and cognitive deficits while having a lower risk of extrapyramidal symptoms and hyperprolactinemia. A phase I clinical trial is now under way to test its tolerance, pharmacokinetics, and pharmacodynamic effects in human volunteers. Accordingly, the present results will have significant impact on the development of new antischizophrenia drugs.

Serotonin/dopamine interaction: Electrophysiological and neurochemical evidence

The interaction between serotonin (5-HT) and dopamine (DA) in the central nervous system (CNS) plays an important role in the adaptive properties of living animals to their environment. These are two modulatory, divergent systems shaping and regulating in a widespread manner the activity of neurobiological networks and their interaction. The concept of one interaction linking these two systems is rather elusive when looking at the mechanisms triggered by these two systems across the CNS. The great variety of their interacting mechanisms is in part due to the diversity of their neuronal origin, the density of their fibers in a given CNS region, the distinct expression of their numerous receptors in the CNS, the heterogeneity of their intracellular signaling pathway that depend on the cellular type expressing their receptors, and the state of activity of neurobiological networks, conditioning the outcome of their mutual influences. Thus, originally conceptualized as inhibition of 5-HT on DA neuron activity and DA neurotransmission, this interaction is nowadays considered as a multifaceted, mutual influence of these two systems in the regulation of CNS functions. These new ways of understanding this interaction are of utmost importance to envision the consequences of their dysfunctions underlined in several CNS diseases. It is also essential to conceive the mechanism of action of psychotropic drugs directly acting on their function including antipsychotic, antidepressant, antiparkinsonian, and drug of abuse together with the development of therapeutic strategies of Alzheimer's diseases, epilepsy, obsessional compulsive disorders. The 5-HT/DA interaction has a long history from the serendipitous discovery of antidepressants and antipsychotics to the future, rationalized treatments of CNS disorders.

Discovery of Novel Indolealkylpiperazine Derivatives as Potent 5-HT1A Receptor Agonists for the Potential Future Treatment of Depression

Depression is a severe psychiatric disorder that affects over 100 million people worldwide. 5-HT_1A receptor agonists have been implicated in the treatment of a variety of central nervous system diseases, especially depression. In this study, based on FW01, a selective potent 5-HT_1AR agonist discovered via dynamic pharmacophore-based virtual screening, a series of indolealkylpiperazine derivatives with a benzamide moiety were designed and synthesized by the modification of the amide tail group as well as indole head group of FW01. Among all tested compounds, 13m displayed potent agonistic activity towards 5-HT_1AR with an EC₅₀ value of 1.01 nM. Molecular docking studies were performed to disclose the mechanism of its potent agonistic activity and high selectivity. Finally, the activation model of 5-HT_1AR induced by 13m was proposed.

Design, Synthesis, and Structure-Activity Relationship Studies of Novel Indolyalkylpiperazine Derivatives as Selective 5-HT1A Receptor Agonists

5-HT_1A receptor (5-HT_1AR) agonists have been implicated in the treatment of a variety of central nervous system (CNS) diseases such as depression and anxiety, et al. Based on our previously found compound FW01 (K_i = 51 ± 16 nM) obtained by virtual screening, a series of FW01 derivatives were designed and synthesized by the modification of the amide tail group as well as indole headgroup of FW01. SAR exploration found that amide tail group and indole headgroup play pivotal roles in determining the binding affinity and selectivity on dopamine and serotonin receptor subtypes. Among all tested compounds, 9_24 has a K_i value of 5 ± 0.6 nM with a good selectivity toward 5-HT_1AR. The [³⁵S] GTPγS assay showed that 9_24 is a full agonist toward 5-HT_1AR with an EC₅₀ value of 0.059 nM, which shows 266.2 and 146.4-fold selectivity to 5-HT_2A and D₃ respectively. Molecular dynamics simulations and molecular docking studies with 5-HT_1AR-9_24 were performed to disclose the mechanism of its high activity and selectivity. Finally, a detailed stepwise 9_24 induced signal transduction mechanism of 5-HT_1AR is proposed.

Antipsychotic Treatment of Behavioral and Psychological Symptoms of Dementia (BPSD): Management of Extrapyramidal Side Effects

Antipsychotic drugs are often used for the treatment of behavioral and psychological symptoms of dementia (BPSD), especially psychosis and behavioral disturbances (e.g., aggression and agitation). They are prescribed alone or in conjunction with anti-dementia (e.g., anti-Alzheimer’s disease drugs) and other psychotropic drugs (e.g., antidepressants). However, antipsychotic drugs frequently produce serious extrapyramidal side effects (EPS) including Parkinsonian symptoms (e.g., bradykinesia, akinesia, tremor, and muscle rigidity). Therefore, appropriate drug choice and combination strategy are important in the treatment of BPSD. Among anti-Alzheimer’s disease drugs, cholinesterase inhibitors (ChEIs, e.g., donepezil and galantamine) have a propensity to potentiate EPS associated with antipsychotic treatment in a synergistic manner. In contrast, the NMDA receptor antagonist memantine reduces antipsychotic-induced EPS. Antidepressant drugs, which inhibit 5-HT reuptake into the nerve terminals, also synergistically augment antipsychotic-induced EPS, while mirtazapine (α₂, 5-HT₂ and 5-HT₃ antagonist) reduces the EPS induction. Importantly, previous studies showed that multiple 5-HT receptors play crucial roles in modulating EPS associated with antipsychotic treatment. Specifically, activation of 5-HT_1A receptors or blockade of 5-HT₂, 5-HT₃ and 5-HT₆ receptors can alleviate EPS induction both by antipsychotics alone and by combined antipsychotic treatments with ChEIs or 5-HT reuptake inhibitors. In this article, we review antipsychotic use in treating BPSD and discuss the favorable drug selection in terms of the management of antipsychotic-induced EPS.

Synthesis and Biological Evaluation of Fused Tricyclic Heterocycle Piperazine (Piperidine) Derivatives As Potential Multireceptor Atypical Antipsychotics

Herein, a novel series of multireceptor ligands was developed as polypharmacological antipsychotic agents using the designed multiple ligand approach between dopamine receptors and serotonin receptors. Among them, compound 47 possessed unique pharmacological features, exhibiting high affinities for D₂, D₃, 5-HT_1A, 5-HT_2A, and 5-HT₆ receptors and low efficacy at the off-target receptors (5-HT_2C, histamine H₁, and adrenergic α₁ receptor). Compound 47 showed dose-dependent inhibition of apomorphine- and MK-801-induced motor behavior, and the conditioned avoidance response with low cataleptic effect. Moreover, compound 47 resulted nonsignificantly serum prolactin levels and weight gain change compared with risperidone. Additionally, compound 47 possessed a favorable pharmacokinetic profile with oral bioavailability of 58.8% in rats. Furthermore, compound 47 displayed procognition properties in a novel object recognition task in rats. Taken together, compound 47 may constitute a novel class of atypical antipsychotic drugs for schizophrenia.

Synthesis and biological evaluation of a series of multi-target N-substituted cyclic imide derivatives with potential antipsychotic effect

In the present study, a series of multi-target N-substituted cyclic imide derivatives which possessed potent dopamine D₂, serotonin 5-HT_1A and 5-HT_2A receptors properties were synthesized and evaluated as potential antipsychotics. Among these compounds, (3aR,4R,7S,7aS)-2-(4-(4-(benzo[b]thiophen-4-yl)piperazin-1-yl)butyl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-dione hydrochloride (3d) held a promising pharmacological profile. 3d not only showed potent and balanced in vitro activities on D₂/5-HT_1A/5-HT_2A receptors, but also endowed with low to moderate activities on 5-HT_2C, H₁, α_1A, M₃ receptors and hERG channel, suggesting a low liability to induce side effects such as weight gain, orthostatic hypotension and QT prolongation. In animal behavioral studies, 3d reduced phencyclidine-induced hyperlocomotion with a high threshold for catalepsy induction. Compound 3d was selected as a potential antipsychotic candidate for further development.

Glycine-Binding Site Stimulants of NMDA Receptors Alleviate Extrapyramidal Motor Disorders by Activating the Nigrostriatal Dopaminergic Pathway

Dysfunction of the N-methyl-d-aspartate (NMDA) receptor has been implicated in the pathogenesis of schizophrenia. Although agonists for the glycine-binding sites of NMDA receptors have potential as new medication for schizophrenia, their modulation of antipsychotic-induced extrapyramidal side effects (EPS) has not yet been clarified. We herein evaluated the effects of glycine-binding site stimulants of NMDA receptors on antipsychotic-induced EPS in mice and rats. d-cycloserine (DCS) and d-serine significantly improved haloperidol (HAL)-induced bradykinesia in mice, whereas glycine showed no effects. Sodium benzoate, a d-amino acid oxidase inhibitor, also attenuated HAL-induced bradykinesia. Improvements in HAL-induced bradykinesia by DCS were antagonized by the NMDA antagonist dizocilpine or nitric oxide synthase inhibitor L-N^G-Nitro-l-arginine methyl ester. In addition, DCS significantly reduced HAL-induced Fos expression in the dorsolateral striatum without affecting that in the nucleus accumbens. Furthermore, a microinjection of DCS into the substantia nigra pars compacta significantly inhibited HAL-induced EPS concomitant with elevations in dopamine release in the striatum. The present results demonstrated for the first time that stimulating the glycine-binding sites of NMDA receptors alleviates antipsychotic-induced EPS by activating the nigrostriatal dopaminergic pathway, suggesting that glycine-binding site stimulants are beneficial not only for efficacy, but also for side-effect management.

Nicotine Elicits Convulsive Seizures by Activating Amygdalar Neurons

Nicotinic acetylcholine (nACh) receptors are implicated in the pathogenesis of epileptic disorders; however, the mechanisms of nACh receptors in seizure generation remain unknown. Here, we performed behavioral and immunohistochemical studies in mice and rats to clarify the mechanisms underlying nicotine-induced seizures. Treatment of animals with nicotine (1–4 mg/kg, i.p.) produced motor excitement in a dose-dependent manner and elicited convulsive seizures at 3 and 4 mg/kg. The nicotine-induced seizures were abolished by a subtype non-selective nACh antagonist, mecamylamine (MEC). An α7 nACh antagonist, methyllycaconitine, also significantly inhibited nicotine-induced seizures whereas an α4β2 nACh antagonist, dihydro-β-erythroidine, affected only weakly. Topographical analysis of Fos protein expression, a biological marker of neural excitation, revealed that a convulsive dose (4 mg/kg) of nicotine region-specifically activated neurons in the piriform cortex, amygdala, medial habenula, paratenial thalamus, anterior hypothalamus and solitary nucleus among 48 brain regions examined, and this was also suppressed by MEC. In addition, electric lesioning of the amygdala, but not the piriform cortex, medial habenula and thalamus, specifically inhibited nicotine-induced seizures. Furthermore, microinjection of nicotine (100 and 300 μg/side) into the amygdala elicited convulsive seizures in a dose-related manner. The present results suggest that nicotine elicits convulsive seizures by activating amygdalar neurons mainly via α7 nACh receptors.

LASSBio-1422: a new molecular scaffold with efficacy in animal models of schizophrenia and disorders of attention and cognition

Aiming to identify new antipsychotic lead-compounds, our group has been working on the design and synthesis of new N-phenylpiperazine derivatives. Here, we characterized LASSBio-1422 as a pharmacological prototype of this chemical series. Adult male Wistar rats and CF1 mice were used for in-vitro and in-vivo assays, respectively. LASSBio-1422 [1 and 5 mg/kg, postoperatively (p.o.)] inhibited apomorphine-induced climbing as well as ketamine-induced hyperlocomotion (1 and 5 mg/kg, p.o.), animal models predictive of efficacy on positive symptoms. Furthermore, LASSBio-1422 (5 mg/kg, p.o.) prevented the prepulse impairment induced by apomorphine, (±)-2,5-dimethoxy-4-iodoamphetamine, and ketamine, as well as the memory impairment induced by ketamine in the novel object-recognition task at the acquisition, consolidation, and retrieval phases of memory formation. Potential extrapyramidal side-effects and sedation were assessed by catatonia, rota-rod, locomotion, and barbiturate sleeping time, and LASSBio-1422 (15 mg/kg, p.o.) did not affect any of the parameters observed. Binding assays showed that LASSBio-1422 has a binding profile different from the known atypical antipsychotic drugs: it does not bind to AMPA, kainate, N-methyl-D-aspartate, glicine, and mGluR2 receptors and has low or negligible affinity for D1, D2, and 5-HT2A/C receptors, but high affinity for D4 receptors (Ki=0.076 µmol/l) and, to a lesser extent, for 5-HT1A receptors (Ki=0.493 µmol/l). The antagonist action of LASSBio-1422 at D4 receptors was assessed through the classical GTP-shift assay. In conclusion, LASSBio-1422 is effective in rodent models of positive and cognitive symptoms of schizophrenia and its ability to bind to D4 and 5-HT1A receptors may at least in part explain its effects in these animal models.

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.

Mirtazapine has a therapeutic potency in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice model of Parkinson's disease

Background

Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA), shows multiple pharmacological actions such as inhibiting presynaptic α₂ noradrenaline receptor (NAR) and selectively activating 5-hydroxytriptamine (5-HT) 1A receptor (5-HT_1AR). Mirtazapine was also reported to increase dopamine release in the cortical neurons with 5-HT dependent manner. To examine whether mirtazapine has a therapeutic potency in Parkinson’s disease (PD), we examined this compound in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice model of PD.

Results

Male C57BL/6 mice were subjected to MPTP treatment to establish a PD model. Mirtazapine was administered once a day for 3 days after MPTP treatment. MPTP-induced motor dysfunction, assessed by beam-walking and rota-rod tests, was significantly improved by administration of mirtazapine. Biochemical examinations by high performance liquid chromatography and western blot analysis suggested mirtazapine facilitated utilization of dopamine by increasing turnover and protein expression of transporters, without affecting on neurodegenerative process by MPTP. These therapeutic effects of mirtazapine were reduced by administration of WAY100635, an inhibitor for 5HT_1AR, or of clonidine, a selective agonist for α₂-NAR, or of prazosin, an inhibitor for α₁-NAR, respectively.

Conclusion

Our results showed mirtazapine had a therapeutic potency against PD in a mouse model. Because PD patients sometimes show depression together, it will be a useful drug for a future PD treatment.

Role of cerebellar dopamine D(3) receptors in modulating exploratory locomotion and cataleptogenicity in rats

Dopamine D(3) receptors are highly expressed in the cerebellum; however, their pathophysiological functions are not fully understood. Here, we conducted microinjection studies to clarify the role of cerebellar D(3) receptors in modulating locomotion and cataleptogenicity in rats. Microinjection of the preferential D(3) agonist 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT) into lobe 9 of the cerebellum significantly reduced spontaneous locomotor activity with a U-shaped dose-response curve. The intracerebellar microinjection of 7-OH-DPAT did not elicit catalepsy by itself, but markedly potentiated catalepsy induction with a low dose (0.3mg/kg) of haloperidol. The catalepsy enhancement by 7-OH-DPAT occurred in a dose-dependent manner and was not associated with the locomotor inhibition. U-99194A (a selective D(3) antagonist) or AD-6048 (a preferential D(3) vs. D(2) antagonist) antagonized both the catalepsy enhancement and the locomotor inhibition with 7-OH-DPAT. In addition, U-99194A and AD-6048 per se significantly alleviated catalepsy induced by a high dose (0.5mg/kg) of haloperidol. Furthermore, microinjection of 7-OH-DPAT into the nucleus accumbens or the dorsolateral striatum neither affected spontaneous locomotor activity nor haloperidol (0.3mg/kg)-induced catalepsy. The present results illustrate for the first time the role of cerebellar D(3) receptors in modulating cataleptogenicity of antipsychotic agents, implying that blockade of cerebellar D(3) receptors contributes to the reduction of extrapyramidal side effects.

5-HT(1A) receptor: an old target as a new attractive tool in drug discovery from central nervous system to cancer

The serotonin receptor subtype 5-HT(1A) was one of the first serotonin receptor subtypes pharmacologically characterized. This receptor subtype has long been object of intense research and is implicated in the pathogenesis and treatment of anxiety and depressive disorders. In recent years, new chemical entities targeting the 5-HT(1A) receptor (alone or in combination with other molecular targets) have been proposed for novel therapeutic uses in neuroprotection, cognitive impairment, Parkinson's disease, pain treatment, malignant carcinoid syndrome, and prostate cancer. This Perspective compares existing data on expression and signaling activity of the 5-HT(1A) receptor to a ligand with an intrinsic agonist or antagonist profile. Our purpose is also to make a complete overview, useful for underlining the features needed to select a specific pharmacological profile rather than another one. This aspect could be really interesting to consider and justify the 5-HT(1A) receptor as a new attractive target for drug discovery.

Molecular modeling of the 3D structure of 5-HT(1A)R: discovery of novel 5-HT(1A)R agonists via dynamic pharmacophore-based virtual screening

The serotonin receptor subtype 1A (5-HT(1A)R) has been implicated in several neurological conditions, and potent 5-HT(1A)R agonists have therapeutic potential for the treatment of depression, anxiety, schizophrenia, and Parkinson's disease. In the present study, a homology model of 5-HT(1A)R was built based on the latest released high-resolution crystal structure of the β₂AR in its active state (PDB: 3SN6). A dynamic pharmacophore model, which takes the receptor flexibility into account, was constructed, validated, and applied to our dynamic pharmacophore-based virtual screening approach with the aim to identify potential 5-5-HT(1A)R agonists. The obtained hits were subjected to 55-HT(1A)R binding and functional assays, and 10 compounds with medium or high K(i) and EC₅₀ values were identified. Among them, FW01 (K(i) = 51.9 nM, EC₅₀ = 7 nM) was evaluated as the strongest agonist for 5-HT(1A)R. The active 5-HT(1A)R model and dynamic pharmacophore model obtained from this study can be used for future discovery and design of novel 5-HT(1A)R agonists. Also, by integrating all computational and available experimental data, a stepwise 5-HT(1A)R signal transduction model induced by agonist FW01 was proposed.

5-HT1A agonist alleviates serotonergic potentiation of extrapyramidal disorders via postsynaptic mechanisms

We previously demonstrated that 5-HT stimulants, including selective serotonin reuptake inhibitors (SSRIs), potentiated antipsychotic-induced extrapyramidal symptoms (EPS) by stimulating 5-HT2A/2C, 5-HT3 and 5-HT6 receptors. Here, we studied the effects of the 5-HT1A agonist (±)-8-hydroxy-2-(di-n-propylamino) tetralin ((±)-8-OH-DPAT) on the fluoxetine enhancement of EPS (i.e., bradykinesia and catalepsy) to determine if the 5-HT1A agonist can counteract the serotonergic potentiation of EPS. Fluoxetine did not induce EPS signs by itself, but significantly potentiated haloperidol-induced bradykinesia in mice. (±)-8-OH-DPAT (0.1-1mg/kg, i.p.) significantly attenuated the fluoxetine enhancement of haloperidol-induced bradykinesia in a dose-dependent manner. A selective 5-HT1A antagonist (s)-WAY-100135 completely reversed the anti-EPS action of (±)-8-OH-DPAT. Microinjection studies using rats revealed that local application of (±)-8-OH-DPAT into the dorsolateral striatum or the motor cortex significantly diminished fluoxetine-enhanced catalepsy. In contrast, (±)-8-OH-DPAT injected into the medial raphe nucleus failed to affect EPS induction. The present results illustrate that 5-HT1A agonist can alleviate the SSRI enhancement of EPS by activating postsynaptic 5-HT1A receptors in the striatum and cerebral cortex.

Withdrawal symptoms and rebound syndromes associated with switching and discontinuing atypical antipsychotics: theoretical background and practical recommendations

With the widespread use of atypical or second-generation antipsychotics, switching treatment has become current practice and more complicated, as the pharmacological profiles of these agents differ substantially despite their similarity in being 'atypical'. All share the ability to block dopamine D₂ receptors, and most of them also block serotonin 5-HT2A receptors. Apart from these common features, some atypical antipsychotics are also able to block or stimulate other dopamine or serotonin receptors, as well as histaminergic, muscarinergic or adrenergic receptors. As a result of the varying receptor affinities, in switching or discontinuing compounds several possible pitfalls have to be considered, including the occurrence of withdrawal and rebound syndromes. This article reviews the pharmacological background of functional blockade or stimulation of receptors of interest in regard to atypical antipsychotics and the implicated potential withdrawal and rebound phenomena. A MEDLINE search was carried out to identify information on withdrawal or rebound syndromes occurring after discontinuation of atypical antipsychotics. Using the resulting literature, we first discuss the theoretical background to the functional consequences of atypical antipsychotic-induced blockade or stimulation of neurotransmitter receptors and, secondly, we highlight the clinical consequences of this. We then review the available clinical literature on switching between atypical antipsychotics, with respect to the occurrence of withdrawal or rebound symptoms. Finally, we offer practical recommendations based on the reviewed findings. The systematic evaluation of withdrawal or rebound phenomena using randomized controlled trials is still understudied. Knowledge of pharmacological receptor-binding profiles may help clinicians in choosing adequate switching or discontinuation strategies for each agent. Results from large switching trials indicate that switching atypical antipsychotics can be performed in a safe manner. Treatment-emergent adverse events during or after switching are not always considered to be, at least in part, associated with the pre-switch antipsychotic. Further studies are needed to substantiate the evidence gained so far on different switching strategies. The use of concomitant medication, e.g., benzodiazepines or anticholinergic drugs, may help to minimize symptoms arising from the discontinuation or switching of antipsychotic treatment.

Possible involvement of histone acetylation in the development of emotional resistance to stress stimuli in mice

Recent reports have implied that aberrant biochemical processes in the brain frequently accompany subtle shifts in the cellular epigenetic profile that might underlie the pathogenic progression of psychiatric disorders. Furthermore, certain antidepressants or mood stabilizers have been reported to have the ability to modulate epigenetic parameters. We previously reported that pretreatment of mice with 5-HT(1A) receptor agonists 24 h before testing suppressed the decrease in emotional behaviors induced by exposure to acute restraint stress. Based on this finding, the aim of the present study was to examine the association between the development of emotional resistance to stress stimuli and the modulation of an epigenetic parameter, particularly histone acetylation. We found that acetylated histone H3 was increased in the hippocampus of mice that had developed resistance to emotional stress by pretreatment with flesinoxan (1 mg/kg, i.p.) 24 h before testing. On the other hand, pretreatment with benzodiazepine anxiolytic diazepam (1 mg/kg, i.p.) did not have similar effects. Interestingly, similar to flesinoxan, the histone deacetylase inhibitor trichostatin A also protected against the emotional changes induced by acute restraint stress, as well as histone H3 acetylation. The present findings suggest that the epigenetic mechanisms of gene regulation may play an important role in the development of emotional resistance to stress stimuli.

Modulation of antipsychotic-induced extrapyramidal side effects by medications for mood disorders

Antipsychotic drugs are widely used not only for schizophrenia, but also for mood disorders such as bipolar disorder and depression. To evaluate the interactions between antipsychotics and drugs for mood disorders in modulating extrapyramidal side effects (EPS), we examined the effects of antidepressants and mood-stabilizing drugs on haloperidol (HAL)-induced bradykinesia and catalepsy in mice and rats. The selective serotonin reuptake inhibitors (SSRIs), fluoxetine and paroxetine, and the tricyclic antidepressant (TCA) clomipramine, which showed no EPS by themselves, significantly potentiated HAL-induced bradykinesia and catalepsy in a dose-dependent manner. In contrast, the noradrenergic and specific serotonergic antidepressant (NaSSA) mirtazapine failed to augment, but rather attenuated HAL-induced bradykinesia and catalepsy. Mianserin also tended to reduce the EPS induction. In addition, neither treatment with lithium, sodium valproate nor carbamazepine potentiated HAL-induced EPS. Furthermore, treatment of animals with ritanserin (5-HT2A/2C antagonist), ondansetron (5-HT3 antagonist), and SB-258585 (5-HT6 antagonist) significantly antagonized the EPS augmentation by fluoxetine. Intrastriatal injection of ritanserin or SB-258585, but not ondansetron, also attenuated the EPS induction. The present study suggests that NaSSAs are superior to SSRIs or TCAs in combined therapy for mood disorders with antipsychotics in terms of EPS induction. In addition, 5-HT2A/2C, 5-HT3 and 5-HT6 receptors seem to be responsible for the augmentation of antipsychotic-induced EPS by serotonin reuptake inhibitors.

Therapeutic role of 5-HT1A receptors in the treatment of schizophrenia and Parkinson's disease

5-HT(1A) receptors have long been implicated in the pathogenesis and treatment of anxiety and depressive disorders. Recently, several lines of studies have revealed new insights into the therapeutic role of 5-HT(1A) receptors in treating schizophrenia and Parkinson's disease. Specifically, 5-HT(1A) receptors seem to be a promising target for alleviating antipsychotic-induced extrapyramidal side effects (EPS) and cognitive/affective disorders in schizophrenia. In the treatment of patients with Parkinson's disease, 5-HT(1A) agonists are expected to improve not only affective symptoms (e.g., anxiety and depression), but also the core parkinsonian symptoms as well as antiparkinsonian agents-induced side effects (e.g., L-DOPA-induced dyskinesia). Here, the therapeutic mechanisms mediated by 5-HT(1A) receptors in schizophrenia and Parkinson's disease are reviewed. This evidence should encourage discovery of new 5-HT(1A) ligands, which can resolve the unmet clinical needs in the current therapy.