Risperidone, an atypical antipsychotic enhances the antidepressant-like effect of venlafaxine or fluoxetine: Possible involvement of alpha-2 adrenergic receptors

Three new oxygenated yohimbane-type alkaloids from Ophiorrhiza japonica

A series of oxygenated yohimbane alkaloids, including three new compounds, ophiorrhines H-J (1-3), and seven known compounds, were isolated from the aerial parts of Ophiorrhiza japonica. The structures with absolute configurations were elucidated by extensive MS and NMR spectroscopic methods, as well as the single crystal X-ray diffraction and ECD calculations. Ophiorrhines H (1) and I (2) represent key oxygenated intermediates in the formation of aromatic ring E in the demethoxycarbonyl-3,14-dihydrogambirtannine (10). Ophiorrhine J (3) is a highly oxidized yohimbane derivative with the planar superconjugated system. The cytotoxic activities of all alkaloids against five human cancer cell lines were evaluated.

Risperidone-associated enuresis—a case report

Background

Risperidone has been reported to be effective in treating both the positive and negative symptoms of schizophrenia, aggression, and behavioral disorders. While the metabolic side effect profile of this medication has been broadly studied, studies related to this medication’s bladder effects are relatively rare. We present a case of risperidone-induced enuresis in an adult male with schizophrenia that resolved upon discontinuation of the offending medication.

Case presentation

We describe a case of a 32-year-old man with a primary psychotic disorder who developed debilitating enuresis secondary to taking risperidone. Enuresis resolved upon switching to Seroquel.

Conclusion

Enuresis secondary to risperidone is not commonly discussed prior to initiation by the treating psychiatrist however can be debilitating. Discussing this potential side effect is critical to informed decision making on the patient’s part.

Effect of 5-HT6 Receptor Ligands Combined with Haloperidol or Risperidone on Antidepressant-/Anxiolytic-Like Behavior and BDNF Regulation in Hippocampus and Prefrontal Cortex of Rats

BACKGROUND

The presence of depressive and anxiety symptoms in patients with schizophrenia may have an important impact on treatment and compliance. Hence, interventions addressing such comorbidity in schizophrenia should be explored. One target may be a serotonergic 5-HT₆ receptor (5-HT₆R) since its ligands displayed antidepressant- and anxiolytic-like activities in preclinical experiments.

METHODS

Acute and chronic (21 days) administration of haloperidol or risperidone in combination with a selective 5-HT₆R agonist (WAY-181187) or antagonist (SB-742457) to rats was performed for detecting antidepressant- and anxiolytic-like behaviors. In addition, the level of brain-derived neurotrophic factor (BDNF) protein and its gene expression in hippocampus and prefrontal cortex were determined.

RESULTS

Both single and chronic administration of WAY-181187 with haloperidol produced antidepressant- and anxiolytic-like activities. SB-742457 did not provide full benefits in terms of improvement of haloperidol-induced adverse mood effects. However, the administration of SB-742457 with risperidone triggered its anxiolytic-like activity. Both 5-HT₆R ligands evoked no changes in haloperidol-induced effects on BDNF level. WAY-181187 induced repression of the BDNF gene while SB-742457 increased its expression in both structures. 5-HT₆R ligands, when combined with risperidone, did not change BDNF protein level and increased gene expression in the hippocampus, while they elevated BDNF level and potentiated gene expression in the prefrontal cortex.

CONCLUSION

The combined administration of WAY-181187 and haloperidol provided the greatest benefits, which were manifested by antidepressant-like effects and suppression of the anxiogenic-like properties. The combined administration of risperidone with both agonist and antagonist resulted only in an anxiolytic-like effect. It seems that the anxiolytic-like effects induced by haloperidol or risperidone with the addition of 5-HT₆R ligands are task-specific. The data on BDNF protein and gene expression did not fully correspond with the behavioral outcomes, and thus it appears that other factors/mechanisms are involved in the observed antidepressant- and/or anxiolytic-like effects.

Risperidone-induced Enuresis in a 12-year-old Child

Risperidone has been documented to be effective in the management of behavior problems, aggression, and conduct disorder in children. While metabolic side effects like weight gain and obesity have been attributed to Risperidone use in children, side effects of the drug related to the urinary bladder are rare. We present a case of Risperidone-induced enuresis in a 12-year-old boy with conduct disorder that resolved completely after stopping the medication.

Dopamine transporter (DAT) knockdown in the nucleus accumbens improves anxiety- and depression-related behaviors in adult mice

Many epidemiological and clinical studies have demonstrated a strong comorbidity between anxiety and depression, and a number of experimental studies indicates that the dopamine transporter (DAT) is involved in the pathophysiology of anxiety and depression. However, studies using laboratory animals have yielded inconclusive results. The aim of the present study was to examine the effects of DAT manipulation on anxiety- and depression-like behaviors in mice. For this purpose, animals were stereotaxically injected with DAT siRNA-expressing lentiviral vectors (siDAT) in the caudate putamen (CPu) or in the nucleus accumbens (Nacc) and the behavioral outcomes were assessed using the open-field (OF), elevated-plus maze (EPM), light-dark box (LDB), sucrose preference (SPT), novelty suppressed feeding (NSF), and forced-swim (FST) tests. The results showed that in the Nacc, but not in the CPu, siDAT increased the time spent at the center of the arena and decreased the number of fecal boli in the OF test. In the EPM and LDB tests, Nacc siDAT injection increased the entries and time spent on open arms, and increased the time spent in the light side of the box, respectively, suggesting an anxiolytic-like activity. In addition, siDAT, in the Nacc, induced significant antidepressant-like effects, evidenced by increased sucrose preference, shorter latency to feed in the NSF test, and decreased immobility time in the FST. Most importantly, Pearson's test clearly showed significant correlations between DAT mRNA in the Nacc with anxiety and depression parameters. Overall, these results suggest that low DAT levels, in the Nacc, might act as protective factors against anxiety and depression. Therefore, targeting DAT activity might be a very attractive approach to tackle affective disorders.

Immediate and long-term antidepressive-like effects of pre-pubertal escitalopram and omega-3 supplementation combination in young adult stress-sensitive rats

Major depressive disorder (MDD) affects a significant number of children and adolescents, yet treatment options for this population remain very limited. Escitalopram (ESC) is one of only two antidepressants approved as treatment for juvenile depression. Still, delayed onset of action, and immediate plus the risk of lasting side effects contribute to low patient adherence, and places the medical prescriber in a difficult situation weighing the potential long-term effects of juvenile treatment against the known consequences of untreated MDD. Research into alternative or augmentation strategies and their long-term effects are needed to improve clinical outcome and better our understanding of the long-term consequences of early-life treatment. We investigated the early-life (postnatal day 35 (PND35)) and lasting (PND60) bio-behavioural effects of pre-pubertal (PND21 to PND34) escitalopram (ESC) administration and/or ω-3 supplementation (OM3) in stress sensitive Flinders Sensitive Line rats. Only ESC treatment showed a strong trend to decrease depressive-like behaviour via significantly increased climbing behaviour on PND35. However, OM3 treatment reduced locomotor activity and increased hippocampal neuroplasticity on PND35, suggesting improved coping behaviour and masking of possible antidepressant-like effects. Reduced locomotor activity lasted into early-adulthood on PND60, despite a treatment-free period from PND35 to PND60. Regardless, early-adulthood antidepressive-like behaviour was only observed in the combination treatment (ESC + OM3) group, despite a significant increase in serotonin turnover, suggesting strong neurodevelopmental process to be involved. Taken together, the combination of ESC and OM3 might induce lasting beneficial neurodevelopmental effects in a stress-sensitive population, suggesting a possible role in current treatment strategies.

The influence of aripiprazole and venlafaxine on the antidepressant-like effect observed in prenatally stressed rats (animal model of depression)

Depression is a nosological entity which may appear alone or concomitantly (e.g. in schizophrenia). Analysis of data from both clinical and experimental studies allows a conclusion that atypical antipsychotics, such as aripiprazole (ARI), may also be effective in treating depression in addition to antidepressants. The aim of the studies was to determine antidepressant efficacy of ARI, venlafaxine (VEN) and combined therapy using both drugs, in prenatally stressed rats (animal depression model) and control group. In addition, this article was aimed at determining the effect of these drugs on locomotor activity of these animals. The effect of chronic stress used in pregnant rats and the use of drugs such as ARI (1.5 mg/kg) and VEN (20 mg/kg) were studied in forced swimming test (FST; antidepressant effect) and locomotor activity test. Performed tests confirmed the antidepressant effect of ARI, VEN and efficacy of combined drugs in FST in both prenatally stressed rats (effect present upon single administration and after 7, 14 and 21 days of testing) and control group rats (effect present upon single administration and 7 days of testing). Moreover, upon single administration of the used drugs to prenatally stressed rats, it was found sedative effect - reduced animals' locomotor activity. Study results have proven antidepressant and sedative efficacy of ARI, VEN and combined administration of these drugs. Due to the small amount of data on the above preparations, in particular in the context of animal depression models, further studies in this respect are recommended.

Fluoxetine treatment is effective in a rat model of childhood-induced post-traumatic stress disorder

Although selective serotonin reuptake inhibitors (SSRIs) are first-line treatment for post-traumatic stress disorder (PTSD) patients, their therapeutic efficacy is limited. Childhood adversities are considered a risk factor for developing PTSD in adulthood but may trigger PTSD without additional trauma in some individuals. Nevertheless, just as childhood is considered a vulnerable period it may also be an effective period for preventive treatment. Using a rat model of childhood-induced PTSD, pre-pubertal stress (juvenile stress, JVS), we compared the therapeutic effects of fluoxetine and examined the effectiveness of 1 month of fluoxetine treatment following JVS and into adulthood compared to treatment in adulthood. Since not all individuals develop PTSD following a trauma, comparing only group means is not the adequate type of analysis. We employed a behavioral profiling approach, which analyzes individual differences compared to the normal behavior of a control group. Animals exposed to JVS exhibited a higher proportion of affected animals as measured using the elevated plus maze 8 weeks after JVS. Fluoxetine treatment following the JVS significantly decreased the proportion of affected animals as measured in adulthood. Fluoxetine treatment in adulthood was not effective. The results support the notion that childhood is not only a vulnerable period but also an effective period for preventive treatment.

Exploring a post-traumatic stress disorder paradigm in Flinders sensitive line rats to model treatment-resistant depression II: response to antidepressant augmentation strategies

OBJECTIVE

Post-traumatic stress disorder (PTSD) displays high co-morbidity with major depression and treatment-resistant depression (TRD). Earlier work demonstrated exaggerated depressive-like symptoms in a gene×environment model of TRD and an abrogated response to imipramine. We extended the investigation by studying the behavioural and monoaminergic response to multiple antidepressants, viz. venlafaxine and ketamine with/without imipramine.

METHODS

Male Flinders sensitive line (FSL) rats, a genetic model of depression, were exposed to a time-dependent sensitisation (TDS) model of PTSD and compared with stress naive controls. 7 days after the TDS procedures, immobility and coping (swimming and climbing), behaviours in the forced swim test (FST) as well as hippocampal and cortical 5-hydroxyindoleacetic acid (5HIAA) and noradrenaline (NA) levels were analysed. Response to imipramine, venlafaxine and ketamine treatment (all 10 mg/kg×7 days) alone and in combination were subsequently studied.

RESULTS

TDS exacerbated depressive-like behaviour of FSL rats in the FST. Imipramine, venlafaxine and ketamine were ineffective as monotherapy in TDS-exposed FSL rats. However, combining imipramine with either venlafaxine or ketamine resulted in significant anti-immobility effects and enhanced coping behaviours. Only ketamine+imipramine (frontal-cortical 5HIAA and NA), ketamine alone (frontal-cortical and hippocampal NA) and venlafaxine+imipramine (frontal-cortical NA) altered monoamine responses versus untreated TDS-exposed FSL rats.

CONCLUSION

Exposure of FSL rats to TDS inhibits antidepressant response at behavioural and neurochemical levels. Congruent with TRD, imipramine plus venlafaxine or ketamine overcame treatment resistance in these animals. These data further support the hypothesis that exposure of FSL rats to a PTSD-like paradigm produces a valid animal model of TRD and warrants further investigation.

Long-lasting effects of fluoxetine and/or exercise augmentation on bio-behavioural markers of depression in pre-pubertal stress sensitive rats

Juvenile depression is of great concern with only limited treatment currently approved. Delayed onset of action, low remission and high relapse rates, and potential long-lasting consequences further complicates treatment and highlights the need for new treatment options. Studies reporting on long-lasting effects of early-life treatment have reported conflicting results, with the pre-adolescent period mostly overlooked. The anti-depressive effect of exercise, as a possible treatment option or augmentation strategy, is dependent on age and exercise intensity. We investigated the immediate (i.e. postnatal day 35 (PND35)) and lasting (PND60 to PND61) effects of pre-pubertal (PND21 to PND34) fluoxetine and/or exercise on bio-behavioural markers of depression and oxidative stress in stress sensitive Flinders Sensitive Line rats. Low, but not moderate, intensity exercise or 5, but not 10, mg/kg/day fluoxetine displayed anti-depressant-like properties at PND35. Pre-pubertal treatment with 5mg/kg/day fluoxetine or low intensity exercise exerted lasting anti-depressive-like effects into adulthood, whereas the combination of these two treatments did not. Furthermore, the combination of fluoxetine plus exercise reduced hippocampal BDNF levels as compared to exercise alone, which may explain the latter findings. In all treatment groups hippocampal SOD activity was significantly increased at PND61, suggesting an increased anti-oxidant capacity in adulthood. In conclusion, the data confirm the anti-depressant-like properties of both early-life fluoxetine and exercise in a genetic animal model of depression. However, optimal lasting effects of early-life interventions may require adjustment of antidepressant dose and/or exercise intensity to developmental age, and that a combination of antidepressant and exercise may not necessarily be augmentative.

Prazosin addition to fluvoxamine: A preclinical study and open clinical trial in OCD

The efficacy of selective serotonin reuptake inhibitors (SRIs) in psychiatric disorders may be "augmented" through the addition of atypical antipsychotic drugs. A synergistic increase in dopamine (DA) release in the prefrontal cortex has been suggested to underlie this augmentation effect, though the mechanism of action is not clear yet. We used in vivo microdialysis in rats to study DA release following the administration of combinations of fluvoxamine (10 mg/kg) and quetiapine (10 mg/kg) with various monoamine-related drugs. The results confirmed that the selective 5-HT1A antagonist WAY-100635 (0.05 mg/kg) partially blocked the fluvoxamine-quetiapine synergistic effect (maximum DA increase dropped from 325% to 214%). A novel finding is that the α1-adrenergic blocker prazosin (1 mg/kg), combined with fluvoxamine, partially mimicked the effect of augmentation (maximum DA increase 205%; area-under-the-curve 163%). As this suggested that prazosin augmentation might be tested in a clinical study, we performed an open clinical trial of prazosin 20 mg addition to SRI in therapy-resistant patients with obsessive-compulsive disorder applying for neurosurgery. A small, non-significant reduction in Yale Brown Obsessive Compulsive Scale (Y-BOCS) scores was observed in 10 patients and one patient was classified as a responder with a reduction in Y-BOCS scores of more than 25%. We suggest that future clinical studies augmenting SRIs with an α1-adrenergic blocker in less treatment resistant cases should be considered. The clinical trial "Prazosin in combination with a serotonin reuptake inhibitor for patients with Obsessive Compulsive disorder: an open label study" was registered at 24/05/2011 under trial number ISRCTN61562706: http://www.controlled-trials.com/ISRCTN61562706.

Thalidomide reduces mechanical hyperalgesia and depressive-like behavior induced by peripheral nerve crush in mice

BACKGROUND

It has been shown that chronic pain is able to induce depressive disorders in humans, in part, due to peripheral inflammation that reaches the central nervous system. However, the mechanisms involved remain to be established. The purpose of this study was to investigate whether sciatic nerve crush could produce depression-like behaviors, in addition to pain-related behaviors, in mice. Once confirmed, this model was used to investigate tumor necrosis factor-α (TNF-α) as a key mediator involved in the pathophysiology of both pain and depression.

EXPERIMENTAL APPROACH

Male Swiss mice were divided into three groups, naïve, sham and operated. In the operated group, the sciatic nerve was crushed. Following surgery, animals from the operated group were treated daily by oral gavage (p.o.) with saline (10 ml/kg), fluoxetine (20 mg/kg) or thalidomide (10 mg/kg) for 15 days. Mechanical hyperalgesia was evaluated every 3 days by von Frey filaments and depressive-like behavior was assessed at the end of day 15, using the tail suspension test (TST) and the forced swimming test (FST). Then, samples from the prefrontal cortex, hippocampus and sciatic nerve were processed to measure TNF-α levels by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Crush caused significant mechanical hyperalgesia and depressive-like behaviors and increased TNF-α levels in the sciatic nerve, prefrontal cortex and hippocampus of operated animals. Treatment with fluoxetine or thalidomide reversed crush-induced mechanical hyperalgesia, depressive-like behaviors and the increased TNF-α levels in the sciatic nerve, prefrontal cortex and hippocampus.

CONCLUSIONS

The sciatic nerve crush model represents a good model to study to mechanisms underlying both pain and depressive-like behaviors. Furthermore, inhibitors of TNF-α synthesis, like thalidomide, have a potential to treat depressive disorders associated with neuropathic pain.

Effect of risperidone on the fluoxetine-induced changes in extracellular dopamine, serotonin and noradrenaline in the rat frontal cortex

BACKGROUND

Several clinical reports have documented a beneficial effect of the addition of a low dose of risperidone to the ongoing treatment with antidepressants, in particular selective serotonin reuptake inhibitors, in the treatment of drug resistant depression. The aim of our study was to understand the mechanism of the clinical efficacy of a combination of fluoxetine (FLU) and risperidone (RIS) in drug-resistant depression. We studied the effect of FLU and RIS, given separately or jointly on the extracellular levels of dopamine (DA), serotonin (5-HT) and noradrenaline (NA) in the rat frontal cortex.

METHODS

Animals were given single intraperitoneal injections of RIS at a doses of 0.1 or 1 mg/kg and FLU at a dose of 10 mg/kg. The release of DA, 5-HT and NA in the rat frontal cortex was investigated using microdialysis in freely moving animals. The extracellular level of DA, 5-HT and NA was assayed by HPLC with coulochemical detection.

RESULTS

RIS (0.1 and 1 mg/kg) and FLU (10 mg/kg) increased the extracellular level of cortical DA, 5-HT and NA. Co-treatment of both drugs was more effective in increasing DA release than administration of each of the drugs alone at doses of RIS 1 mg/kg and FLU 10 mg/kg. Co-treatment of FLU and RIS 0.1 mg/kg was more potent than FLU alone, while the effect of joint injection of FLU and RIS 1 mg/kg was stronger than RIS 1 mg/kg alone on 5-HT release. The combination of FLU with both doses of RIS was not effective in increasing NA release as compared to drugs given alone.

CONCLUSIONS

Our data indicate that the effect of the combined administration of RIS and FLU on DA and 5-HT release in the rat frontal cortex may be of crucial importance to the pharmacotherapy of drug resistant depression.

Use of antipsychotics in the treatment of depressive disorders

Summary

There is a long history of using antipsychotic medications in the treatment of depressive disorders. Atypical antipsychotics, which have fewer side effects than traditional antipsychotics, have been used as monotherapy or adjunctively with antidepressants to treat depressive disorders with or without psychotic symptoms. The antidepressant effect of atypical antipsychotics involves regulation of monoamine, glutamate, gamma-aminobutyric acid (GABA), cortisol, and neurotrophic factors. To date, the United States Food and Drug Administration (USFDA) has approved aripiprazole and quetiapine slow-release tablets as adjunctive treatment for depressive disorders, and the combination of olanzapine and fluoxetine for the treatment of treatment-resistant depression. When using atypical antipsychotics in the treatment of depressed patients, clinicians need to monitor patients for the emergence of adverse effects including extrapyramidal symptoms (EPS), weight gain, and hyperglycemia.

Augmentation with atypical antipsychotics for depression: a review of evidence-based support from the medical literature

Major depressive disorder (MDD) is a chronic mental illness that affects an estimated 5-26% of adults at some time in their lives. Treatment is often started as pharmacotherapy using a single drug such as a selective serotonin reuptake inhibitor. If a patient fails to respond adequately to the initial antidepressant, typically three pharmacotherapy options are available to the practitioner. The dose of the current therapy can be maximized, a change can be made to a different drug, or the current regimen can be augmented with another drug. Atypical antipsychotics have recently become a major focus for augmentation of traditional antidepressant therapy. This review summarizes the evidence for efficacy and safety of augmenting treatment-refractory or treatment-resistant depression with atypical antipsychotics. The National Library of Medicine's MEDLINE database was searched for all English-language articles published from January 1966-December 2011 describing the use of atypical antipsychotics in treatment-resistant depression. The literature retrieved was limited to case series, open-label trials, and randomized controlled trials (RCT). Studies of bipolar depression, psychotic depression, or studies conducted in children and adolescents were excluded. Thirty-five studies using atypical antipsychotics for augmentation treatment of depression were included in this analysis. Trials were identified for aripiprazole (six open-label; three RCT), clozapine (one case series), olanzapine (three open-label, including two case series; four RCT), quetiapine (four open-label; five RCT), risperidone (two open-label; five RCT), and ziprasidone (two open-label). The atypical antipsychotics may be effective as adjunctive therapy in MDD; however, their adverse effect profile may be unfavorable to some patients. Trying at least one alternative treatment strategy after an initial antidepressant is indicated before augmentation is implemented with these agents. If atypical antipsychotics are used, safety and efficacy should be frequently reassessed and dosage should be individualized.

Effect of chronic fluoxetine treatment on male and female rat erythrocyte and prefrontal cortex fatty acid composition

Omega-3 (n-3) polyunsaturated fatty acids (PUFA) and fluoxetine (FLX) have additive effects in the treatment of major depressive disorder, and FLX up-regulates genes that regulate fatty acid biosynthesis in vitro. Although these data suggest that FLX may augment n-3 fatty acid biosynthesis, the in vivo effects of FLX treatment on PUFA biosynthesis and peripheral and central membrane compositions are not known. In the present study, male and female rats were treated with FLX (10 mg/kg/day) through their drinking water for 30 days (P60-P90). Plasma FLX and norfluoxetine (NFLX) concentrations were determined by liquid chromatography tandem mass spectrometry, and erythrocyte and prefrontal cortex (PFC) fatty acid composition determined by gas chromatography. To confirm central effects of FLX, serotonin turnover in the PFC was determined by high performance liquid chromatography. Chronic FLX treatment resulted in clinically-relevant plasma FLX concentrations in male and female rats, and significantly decreased serotonin turnover in the PFC. After correcting for multiple comparisons, chronic FLX treatment did not significantly alter erythrocyte fatty acid composition in male or female rats. Chronic FLX treatment significantly and selectively increased docosapentaenoic acid (22:5n-6) in the PFC of female rats, but not in male rats. These preclinical findings do not support the hypothesis that chronic FLX treatment increases n-3 fatty acid biosynthesis or membrane composition.

Augmentation effect of combination therapy of aripiprazole and antidepressants on forced swimming test in mice

RATIONALE

A deficiency in brain monoamine systems (serotonin, dopamine, and/or norepinephrine) have long been hypothesized for the pathogenesis of depression. Drugs enhancing neurotransmission of those monoamines have been proven to have antidepressant effects. We hypothesized that aripiprazole, a partial D(2) agonist, could increase the activity of various antidepressants in the mice forced swimming test (FST), an animal model of depression.

OBJECTIVES

The scope of this study was to investigate the antidepressant-like effect of aripiprazole, when combined with conventional antidepressants drugs.

MATERIALS AND METHODS

This study assessed the effects of co-administration of aripiprazole with selective serotonin reuptake inhibitors (SSRIs; sertraline, paroxetine, and citalopram), selective serotonin-norepinephrine reuptake inhibitors (SNRIs; venlafaxine and minalcipran), selective norepinephrine reuptake inhibitor (NRI; desipramine), and the dual dopamine and norepinephrine reuptake inhibitor (bupropion), using the FST in mice. Subactive doses of aripiprazole and antidepressants sertraline, paroxetine, citalopram, venlafaxine, minalcipran, bupropion (4 and 8 mg/kg), and desipramine (2 and 4 mg/kg) were given i.p. 30 and 45 min, respectively, before the test.

RESULTS

Aripiprazole (0.03 and 0.06 mg/kg) combined with inactive doses of antidepressants, increased the activity of all antidepressants with the exception of bupropion and desipramine.

CONCLUSION

The augmentation effects of aripiprazole, in the present study, are in agreement with clinical evidence suggesting that aripiprazole may enhance the efficacy of therapeutic effect of SSRIs and SNRIs but not of NRI. These results suggest that augmentation effect of aripiprazole only appears when 5-HT system is activated and might implicate complex regulation between dopamine and 5-HT(1A) and 5-HT(2A) receptors.