Risperidone: review of its therapeutic utility in depression

There is extensive evidence to implicate dysregulation of noradrenergic, serotonergic, and dopaminergic neurotransmission in the pathophysiology of mood disorders. The receptor profile for risperidone, an atypical antipsychotic with demonstrated efficacy in schizophrenia, is consistent with possible antidepressant activity. Specifically, risperidone is a potent antagonist of central 5-HT2A receptors, addressing symptoms such as insomnia, agitation, and weight loss and may indirectly enhance 5-HT1A-mediated neurotransmission. A search of the worldwide medical literature published through December 2000 revealed 24 publications pertinent to the clinical use of risperidone in the treatment of patients with depressive symptomatology. In schizophrenia, in which depression is a common comorbid condition, the results of eight randomized, blinded, and controlled trials consistently demonstrated that treatment with risperidone significantly reduced scores on various measures of depressive symptoms. Moreover, these effects were distinct from improvements in negative and positive symptoms. Antidepressant effects also were observed in two large meta-analyses of trials in patients with schizophrenia or schizoaffective disorder. Observations from uncontrolled studies and case reports of risperidone therapy of other psychiatric disorders were similarly suggestive of antidepressant activity. Collectively, the evidence we present in this review indicates that risperidone's therapeutic benefits in psychiatric medicine extend beyond potent and effective antipsychotic activity and may include effectiveness in treating depression and related affective disorders. Systematic studies are now needed to evaluate the utility of concomitant therapy with an atypical antipsychotic in psychotic, bipolar, and treatment-resistant depressive syndromes.     

Quetiapine: a review of its use in the management of bipolar depression

Quetiapine (Seroquel?) is an orally administered atypical antipsychotic that is indicated for the treatment of schizophrenia and bipolar disorder, including bipolar depression. An extended-release (XR) formulation of quetiapine is also available. This review summarizes the pharmacological properties, efficacy and tolerability of quetiapine and quetiapine XR in patients with bipolar depression. Quetiapine is an antagonist at both serotonin 5-HT2 and dopamine D2 receptors, and its antipsychotic effects are thought to stem from interactions at these receptors. The antidepressant effects of quetiapine are poorly understood, but may be related to antagonism of 5-HT2A receptors in cortical regions, partial agonism of 5-HT1A in the prefrontal cortex in association with increased extracellular dopamine release in the region, or to reduced synaptic reuptake of noradrenaline resulting from inhibition of the noradrenaline reuptake transporter by the quetiapine metabolite norquetiapine. The efficacy and tolerability of quetiapine was evaluated in five 8-week, randomized, double-blind, placebo-controlled, multicentre or multinational trials in patients with a major depressive episode (MDE) associated with bipolar disorder. Across trials, monotherapy with oral quetiapine 300 or 600?mg/day (or quetiapine XR 300?mg/day) produced significantly greater improvements than placebo in depressive symptoms (primary endpoint), according to the change in the Montgomery-Asberg Depression Rating Scale total score. In general, quetiapine and quetiapine XR were also associated with significantly higher MDE response and remission rates than placebo. Across trials, quetiapine and quetiapine XR produced significantly greater improvements in global severity of illness scores than placebo, according to changes in the Clinical Global Impressions scale score. There were no differences in treatment outcomes between quetiapine 300?mg/day and 600?mg/day dosage groups. Patients with bipolar depression who responded to quetiapine during two 8-week acute treatment trials also benefited from continuing quetiapine therapy for up to 52 weeks. Compared with quetiapine responders randomized to placebo, quetiapine responders who continued quetiapine 300 or 600?mg/day had a significantly reduced risk of recurrence of any mood events and of depression mood events, but not of hypomanic/manic events. In a randomized, double-blind, placebo-controlled trial, quetiapine maintenance therapy for up to 104 weeks was more efficacious than placebo or lithium in prolonging the time to recurrence of any mood event (primary endpoint). Patients in this trial had bipolar I disorder with mania, depression or a mixed episode as the index episode, and the trial included only patients who were responsive to acute phase quetiapine, which may have introduced a positive bias in favour of quetiapine over lithium during maintenance therapy. Quetiapine 300 or 600?mg/day and quetiapine XR 300?mg/day was generally well tolerated in patients with bipolar depression, with most treatment-emergent adverse events being of mild to moderate severity. The most frequent adverse events occurring during the acute treatment phase were dry mouth, sedation, somnolence, dizziness (quetiapine and quetiapine XR), constipation (quetiapine) and increased appetite (quetiapine XR). Extrapyramidal symptoms (EPS) occurred across quetiapine and placebo groups, but there were no significant differences between quetiapine and placebo recipients on objective measures of EPS and akathisia. In some trials, quetiapine recipients experienced significantly greater weight gain than placebo recipients. Across trials, some quetiapine recipients had clinically relevant increases in blood glucose or lipid parameters, although these also occurred in patients from other treatment groups. The clinical significance of these changes is uncertain. In conclusion, quetiapine and quetiapine XR are valuable additions to the first-line treatments for bipolar depression. Further head-to-head trials of quetiapine versus other drug regimens that are effective in bipolar depression would be of considerable interest.     

Regulation of rat cortical 5-hydroxytryptamine2A receptor-mediated electrophysiological responses by repeated daily treatment with electroconvulsive shock or imipramine.

Down-regulation of 5-hydroxytryptamine(2A) (5-HT(2A)) receptors has been a consistent effect induced by most antidepressant drugs. In contrast, electroconvulsive shock (ECS) up-regulates the number of 5-HT(2A) receptor binding sites. However, the effects of antidepressants on 5-HT(2A) receptor-mediated responses on identified cells of the cerebral cortex have not been examined. The purpose of the present study was to compare the effects of the tricyclic antidepressant imipramine and ECS on 5-HT(2A) receptor-mediated electrophysiological responses involving glutamatergic and GABAergic neurotransmission in the rat medial prefrontal cortex (mPFC) and piriform cortex, respectively. The electrophysiological effects of activating 5-HT(2A) receptors were consistent with 5-HT(2A) receptor binding regulation for imipramine and ECS except for the mPFC where chronic ECS decreased the potency of 5-HT at a 5-HT(2A) receptor-mediated response. These findings are consistent with the general hypothesis that chronic antidepressant treatments shift the balance of serotonergic neurotransmission towards inhibitory effects in the cortex.     

Different actions for acute and chronic administration of mirtazapine on serotonergic transmission associated with raphe nuclei and their innervation cortical regions

The atypical antidepressant, mirtazapine enhances noradrenergic transmission, but its effects on serotonergic transmission remain to be clarified. The present study determined the effects of acute and chronic administration of mirtazapine on serotonergic transmissions in raphe nuclei and their innervation regions, frontal and entorhinal cortex, using multiple-probes microdialysis with real-time PCR and western blotting. Acute administration of mirtazapine did not affect extracellular serotonin level in raphe nuclei or cortex; however, chronic administration increased extracellular serotonin level in raphe nuclei without affecting that in cortex. Blockade of 5-HT1A receptor, but not that of the 5-HT2A/2C receptor, enhanced the effects of acute administration of mirtazapine on extracellular serotonin level in raphe nuclei. Chronic mirtazapine administration reduced the inhibitory function associated with somatodendritic 5-HT1A receptor in raphe nuclei, but enhanced postsynaptic 5-HT1A receptor in serotonergic innervated cortical regions. Chronic administration reduced the expression of mRNA and protein of serotonin transporter and 5-HT1A receptor in raphe nuclei, but not in the cortices. These results suggested that acute administration of mirtazapine probably activated serotonergic transmission, but its stimulatory action was abolished by activated inhibitory 5-HT1A receptor. Chronic administration of mirtazapine resulted in increased extracellular serotonin level via reduction of serotonin transporter with reduction of somatodendritic 5-HT1A autoreceptor function in raphe nuclei. These pharmacological actions of mirtazapine include its serotonergic profiles as noradrenergic and specific serotonergic antidepressant (NaSSA).     

Strategies for producing faster acting antidepressants

Existing antidepressant treatments exhibit limited efficacy and a slow onset of action. Several neurobiological adaptive mechanisms might delay the clinical effects of antidepressants, whose therapeutic action is primarily triggered by an increase of serotonergic and noradrenergic neurotransmission. Here, we review several potential mechanisms that could be useful to increase the speed of current antidepressant drugs, such as additional blockade of aminergic autoreceptors or antagonism of certain postsynaptic (5-HT2A, 5-HT2C) receptors. The potential use of strategies not based on monoaminergic transmission, such as CRF and NK1 receptor antagonists, or more novel strategies, based on glutamatergic or GABAergic transmission or on intracellular messengers, are also reviewed.     

Electrical stimulation of rat medial prefrontal cortex enhances forebrain serotonin output: implications for electroconvulsive therapy and transcranial magnetic stimulation in depression.

Decreased activity of the prefrontal cortex (PFC), as well as reduced serotonergic neurotransmission, is considered as a characteristic feature of major depression. The mechanism by which electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS) achieve their antidepressant effects may involve changes in PFC activity. It is, however, still unclear whether these changes are accompanied by increased synaptic availability of serotonin (5-HT). In the present study, 5-HT efflux in the rat ventral hippocampus and amygdala was analyzed using in vivo microdialysis during low-current electrical stimulation of PFC and other cortical regions. Electrical stimulation of the medial PFC produced current-dependent increases in limbic 5-HT output in both urethane-anesthetized and behaving rats. No effects on 5-HT levels were seen after comparable stimulation of either the lateral parts of the PFC, the medial precentral area, the primary motor cortex or the parietal cortex. This pronounced regional specificity of the effect of medial PFC stimulation on limbic 5-HT output suggests that activation of this particular area might play a crucial role in such antidepressant treatments as ECT and TMS.     

The dual transporter inhibitor duloxetine: a review of its preclinical pharmacology, pharmacokinetic profile, and clinical results in depression

Major depressive disorder (MDD) poses a significant health problem and is estimated to be the third most costly and disabling disorder in the United States. Pharmacotherapy of depression has been successful, but improvements in response rates, remission rates, side effects, compliance and faster onset of therapeutic action have become prime objectives in drug development. There is considerable support for the hypothesis that dysfunctional serotonergic or noradrenergic neurotransmission may be etiological in depressed patients. Duloxetine is a balanced and potent reuptake inhibitor of serotonin (5-HT) and norepinephrine (NE) being studied as an antidepressant medication. In this review, we highlight the preclinical pharmacology, pharmacokinetic profile, and effects of duloxetine in the pharmacotherapy of depression. Evidence for 5-HT and NE reuptake inhibition by duloxetine comes from in vitro and in vivo transporter binding and functional uptake studies. Taken together with efficacy data from in vivo microdialysis, electrophysiological and behavioral studies, it is evident that duloxetine is balanced as a dual serotonin norepinephrine uptake inhibitor in vivo. The clinical efficacy and safety of duloxetine in the treatment of MDD has been studied in 6 multicenter, randomized, double-blind, placebo-controlled trials. In these studies, duloxetine was found to be effective in the treatment of emotional/psychological and painful physical symptoms associated with depression. More importantly, duloxetine appears to have better response rates and remission from depressive symptoms, perhaps due to its ability to treat a wider range of symptoms.     

A combination of mirtazapine and milnacipran augments the extracellular levels of monoamines in the rat brain

Mirtazapine, an antidepressant, antagonizes α(2)-adrenergic autoreceptors and heteroreceptors, which leads to enhanced noradrenergic and serotonergic transmission without inhibiting monoamine transporters. Using a microdialysis technique, we investigated whether co-administration of mirtazapine and a serotonin noradrenaline reuptake inhibitor (SNRI), milnacipran, augments the effects of each drug on the extracellular levels of monoamines by pharmacological synergy. Mirtazapine increased the extracellular levels of noradrenaline and serotonin in the dorsal hippocampus. In contrast, it increased the levels of noradrenaline and dopamine without changing serotonin levels in the prefrontal cortex. Milnacipran increased the levels of all monoamines evaluated in both areas, and the combined treatment with mirtazapine augmented these changes. The combined treatment with idazoxan, an α(2) adrenoceptor antagonist, and milnacipran also increased all monoamine levels in the prefrontal cortex. Ketanserin, a serotonin 5-HT(2A) receptor antagonist, showed no effect in combination with milnacipran, while SB242084, a 5-HT(2C) receptor antagonist, augmented the effects of milnacipran on the levels of serotonin and dopamine in the prefrontal cortex. These results suggest that combined treatment with mirtazapine and milnacipran augments the extracellular levels of noradrenaline, serotonin and dopamine through the blockade of α(2) adrenoceptors without regional specificity, whereas mirtazapine enhances serotonergic transmission in a region-specific manner. 5-HT(2C) receptor antagonism may also partly contribute to the amplification effects of mirtazapine on serotonin and dopamine levels. These neurochemical changes could play a role in reported advantageous clinical effects in patients treated with an SNRI and mirtazapine.     

Neuroanatomical circuits in depression: implications for treatment mechanisms.

We previously investigated the functional neuroanatomy of familial pure depressive disease (FPDD) using positron emission tomography (PET) measurements of regional blood flow and obtained evidence that flow is increased in the left prefrontal cortex, amygdala, and medial thalamus and is decreased in the medial caudate. These data along with other evidence suggested that circuits involving the prefrontal cortex, amygdala, and related parts of the striatum, pallidum, and medial thalamus are involved in the pathophysiology of FPDD. One of these circuits, the limbic-thalamo-cortical circuit, which includes the amygdala, the medio-dorsal thalamus, and parts of the ventral and medial prefrontal cortex, may be engaged in abnormal reverberatory activity that maintains the cognitive and emotional set of depression. Using this hypothesis as a neural model to investigate antidepressant treatment mechanisms, we review evidence that the changes in dopaminergic, serotonergic, and noradrenergic function induced by somatic antidepressant therapies may yield modulatory effects on limbic-thalamo-cortical activity. We also discuss preliminary findings of treatment-associated changes in this circuit in studies comparing PET images acquired before and during antidepressant treatment.     

The 5-HT1A receptor in schizophrenia: a promising target for novel atypical neuroleptics?

Increasing attention is being directed towards the role of the serotonergic system in the neurochemistry of schizophrenia and antipsychotic drug treatment. This review considers the 5-HT1A receptor in this context. In patients with schizophrenia, the majority of post-mortem studies have reported increases in 5-HT1A receptor density in the prefrontal cortex in the approximate range 15-80%. Although the pathophysiological significance of this finding is unclear, given the location of a major proportion of these receptors on pyramidal cells, it may reflect an abnormal glutamatergic network. In terms of drug treatment, 5-HT1A agonists clearly display anticataleptic activity in rats. In addition, 5-HT1A agonists consistently increase dopamine release in the prefrontal cortex in rodents, which is an effect that might be predicted to improve negative symptoms. 5-HT1A agonists augment classical neuroleptics in some rat models of antipsychotic action and may be capable of modulating the glutamatergic network therapeutically. Despite the encouraging preclinical data, there is a paucity of clinical studies of 5-HT1A agonist augmentation of neuroleptics in the treatment of schizophrenia. However, the clinical relevance may be clarified by the atypical antipsychotic drugs clozapine, quetiapine and ziprasidone which combine D2 receptor antagonism and 5-HT1A agonism. In conclusion, given the increased prefrontal 5-HT1A receptor density in the illness, and the anticataleptic activity of 5-HT1A agonists combined with their ability to evoke prefrontal dopamine release, there is now a sufficient rationale to examine thoroughly the role of the 5-HT1A receptor in schizophrenia and antipsychotic drug treatment.     

Neuropsychiatric disorders and the multiple human brain serotonin receptor subtypes and subsystems

Most evaluations of the contributions of possible alterations in serotonergic neurotransmission to the etiology and treatment of neuropsychiatric disorders preceded the recent explosion of information regarding multiple serotonin (5-HT) receptors and brain 5-HT subsystems. This review provides an appraisal of some examples where drugs acting at different 5-HT receptor subtypes have provided new treatment or have contributed to the development of knowledge regarding various neuropsychiatric disorders, including anxiety, panic disorder, obsessive-compulsive disorder, depression, schizophrenia, alcoholism, migraine, sexual dysfunction, and Alzheimer's disease.     

Serotonin 1A receptors, serotonin transporter binding and serotonin transporter mRNA expression in the brainstem of depressed suicide victims.

Suicide and depression are associated with reduced serotonergic neurotransmission. In suicides, there is a reduction in serotonin transporter (SERT) sites and an increase in postsynaptic 5-HT(1A) receptors in localized regions of the prefrontal cortex. In depression, there is a diffuse decrease in SERT binding throughout the dorsoventral extent of the prefrontal cortex. Serotonergic innervation of the prefrontal cortex arises predominantly from neurons in the brainstem dorsal raphe nucleus (DRN). We, therefore, examined postmortem SERT binding and mRNA expression, as well as 5-HT(1A) autoreceptor binding in the DRN of 10 matched pairs of controls and depressed suicide victims. The concentration of SERT sites, SERT mRNA, and 5-HT(1A) binding was not different between controls and suicides (p >.05). In the DRN of suicides, the volume of tissue defined by 5-HT(1A) binding was 40% smaller than controls. An index of the total number of 5-HT(1A) receptors (receptor binding x volume of receptor distribution) was 43.3% lower in the DRN of suicides, compared with controls. The suicide group had 54% fewer DRN neurons expressing SERT mRNA compared with controls. In the serotonin neurons that expressed the SERT gene, expression per neuron was greater in suicides. Less total 5-HT(1A) and SERT binding is consistent with results of in vivo studies in depression. Less feedback inhibition of serotonin DRN firing via 5-HT(1A) autoreceptors and enhancement of serotonin action due to less uptake of serotonin, is consistent with compensatory changes in response to hypofunction in depressed suicides.     

Sustained antidepressant effect of sleep deprivation combined with pindolol in bipolar depression. A placebo-controlled trial.

Total sleep deprivation (TSD) shows powerful but transient clinical effects in patients affected by bipolar depression. Pindolol blocks the serotonergic 5-HT1A autoreceptor, thus improving the antidepressant effect of selective serotonin reuptake inhibitors. We evaluated the interaction of TSD and pindolol in the treatment of acute episodes of bipolar depression. Forty bipolar depressed inpatients were randomized to receive pindolol 7.5 mg/day or placebo for nine days in combination with three consecutive TSD cycles. Pindolol significantly improved the antidepressant effect of TSD, and prevented the short-term relapse after treatment. The response rate (HDRS scores < 8) at the end of treatment was 15/20 for pindolol, and 3/20 for placebo. Coadministration of pindolol and TSD resulted in a complete response, which could be sustained for six months with lithium salts alone, in 65% of cases. This results suggest a major role for serotonergic transmission in the mechanism of action of TSD, and makes TSD treatment more effective in the treatment of bipolar depression.     

Antidepressant properties of substance P antagonists: relationship to monoaminergic mechanisms?

Substance P (SP) is a neuropeptide with a known involvement in anxiety and nociception processes, which acts through the activation of neurokinin-1 (NK(1)) receptors. Recently, a NK(1) receptor antagonist has been shown to display antidepressant activity comparable to that of the selective serotonin reuptake inhibitor paroxetine, but with a better side effect profile. Given their lack of affinity for monoamine transmitters, the antidepressant role of NK(1) receptor antagonists has been attributed to a unique mechanism. However, monoaminergic neurons receive an important SP innervation and also posses NK(1) receptors (noradrenergic neurons of the locus coeruleus) or are in close apposition to NK(1)-containing cells (serotonergic neurons of the dorsal raphe nucleus). In addition, NK(1) receptors are expressed in brain regions involved in the regulation of affective behaviours and the neurochemical response to stress. For these reasons, it has also been postulated that the purported antidepressant action of NK(1) receptor antagonists may result from the modulation of such brain monoaminergic systems. Indeed, systemic administration of NK(1) receptor antagonists enhances the firing rate of dopaminergic, noradrenergic and serotonergic neurons. This effect on serotonergic cells is seen consistently only after long-term treatment and has been associated with a functional desensitisation of somatodendritic 5-HT(1A) autoreceptors. Mice lacking NK(1) receptors also show an increased basal firing rate of 5-HT cells in vivo. These observations are suggestive of a predominating inhibitory role of SP upon monoaminergic neurons under physiological conditions and would provide support for the antidepressant activity of NK(1) receptor antagonists, although this may be achieved through an indirect action on other transmitter systems. The possibility that this class of drugs can modulate the function of only certain serotonergic pathways could be the basis of their better side effect profile. However, although preliminary studies showed some therapeutic efficacy for NK(1) receptor antagonists, the first compound developed (MK-869) has been discontinued from Phase III trials because it was not more effective than placebo in the treatment of depression. Further research is needed to ascertain whether the mechanism of action of NK(1) receptor antagonists may be relevant to the antidepressant treatment.     

Lu-AA21004, a multimodal serotonergic agent, for the potential treatment of depression and anxiety

Lu-AA21004, an oral, multimodal serotonergic agent, is currently under development by H Lundbeck and Takeda Pharmaceutical, for the potential treatment of depression and anxiety. Lu-AA21004 belongs to a novel chemical class of antidepressant agents, the bisarylsulfanyl amines, and possesses a novel pharmacological profile, with activity at serotonergic receptors 5-HT3, 5-HT7 and 5-HT1A, and also at the 5-HT transporter. Acute administration of Lu-AA21004 in rats inhibited the firing activity of serotonergic neurons of the dorsal raphe nucleus through 5-HT3 receptor blockade, with rapid recovery of firing activity upon cessation of treatment compared with an antidepressant of the SSRI class. Results from phase II clinical trials have reported improvement in depression and anxiety symptoms after 6 weeks of treatment. Lu-AA21004 was generally well tolerated, with adverse events related to sexual dysfunction occurring in a lower number of patients receiving Lu-AA21004 compared with venlafaxine. Phase III clinical trials with Lu-AA21004 in patients with major depressive disorder are underway and phase III trials in patients with generalized anxiety disorder have been completed. If initial outcomes from these clinical trials prove positive, Lu-AA21004 may pave the way for new multimodal therapies for the treatment of depression and anxiety.     

A model to explain the therapeutic effects of serotonin reuptake inhibitors: the role of 5-HT2 receptors

In this article, it is posited that major depression involves an underfunctioning dopamine system resulting from hypersensitive inhibitory 5-HT2 receptors located on dopaminergic neurons. After a few weeks, treatment with most antidepressant drugs leads to a downregulation of the 5-HT2 receptors that allows for increased dopaminergic firing, which is proposed to be decisive for the antidepressant effect. However, serotonin reuptake inhibitors (SRIs) therapeutic mechanisms probably differ between different therapeutic outcomes. It is hypothesized, that in women, the use of female sex steroids leads to a downregulation of 5-HT2C receptors that contributes to atypical depressive symptoms and premenstrual dysphoria. Consequently, these conditions can be assumed to benefit from the acute increase of serotonergic neurotransmission following ingestion of an SRI rather than the secondary receptor changes, which would explain why there is a therapeutic lag time when SRIs are used to treat depression but not premenstrual dysphoric disorder. The clinical predictions derived from this hypothesis are that 5-HT2 antagonists would be an effective treatment in melancholic depression, have a fast onset of action, speed the onset of SRIs, and can be an effective augmentation for SRI-refractory patients. In contrast, in atypical depression and premenstrual dysphoria a 5-HT2 antagonist would counteract the therapeutic effect of an SRI, while 5-HT2 agonists have a therapeutic potential. It is suggested that therapeutic response to 5-HT2 antagonists/agonists may be used as a diagnostic tool to dissect subgroups of depression.     

The effect of antidepressants on glucose homeostasis and insulin sensitivity: synthesis and mechanisms

Objective: To synthesise results from investigations reporting on the effect of antidepressants on glucose–insulin homeostasis. Method: The authors conducted a MedLine search of all English language articles from 1966 to October 2005 using the keywords: bipolar disorder, major depressive disorder, diabetes mellitus, glucose homeostasis, and the name of each antidepressant that has been indicated for major depression in Canada and the US up to October 2005. The search was supplemented with a manual review of relevant references. Both preclinical and clinical investigations were reviewed. Results: Some serotonergic antidepressants (e.g., fluoxetine) reduce hyperglycaemia, normalise glucose homeostasis and increase insulin sensitivity, whereas some noradrenergic antidepressants (e.g., desipramine) exert opposite effects. Dual-mechanism antidepressants (e.g., duloxetine and venlafaxine) do not appear to disrupt glucose homeostatic dynamics, whereas nonselective hydrazine monoamine oxidase inhibitors (e.g., phenelzine) are associated with hypoglycaemia and an increased glucose disposal rate. Conclusion: Some antidepressants exert a clinically significant effect on metabolism relevant to both therapeutic outcome and adverse events.     

The interaction between the internal clock and antidepressant efficacy

Sleep disturbances are often associated with depression and mood disorders, and certain manipulations of the sleep-wake cycle are effective as therapeutic interventions in the treatment of depression. Dysregulated circadian rhythms are thereby considered as causal. Circadian rhythms in mammals are mainly regulated by a core biological clock, located in the hypothalamic suprachiasmatic nucleus; its pacemaker activity is regulated by light and nonphotic modulatory pathways, and the driving mechanisms are serotonergic input from the raphe and the hormone melatonin originating from the pineal gland. In line, the concentration of brain serotonin and the levels of 5-HT2C receptors are high and highly expressed there. Agomelatine, a novel antidepressant drug with proven clinical efficacy in major depressive disorder, has a unique mechanism of action; it acts as an agonist at melatonergic MT1 and MT2 receptors and as an antagonist at 5-HT2C receptors. In animals, agomelatine was shown to increase noradrenaline and dopamine (but not serotonin) in the frontal cortex, to resynchronize the sleep-wake cycle in models with disrupted circadian rhythms, and to exhibit a clear antidepressant effect in various animal models of depression. On the basis of the functional relationship between melatonergic and serotonergic signaling in the suprachiasmatic nucleus, and given agomelatine's affinity at melatonergic and 5-HT2C receptors, the therapeutic efficacy of the drug may be due to the potential synergy of its action at these different receptors.     

Occurrence of mirtazapine-induced delirium in organic brain disorder

Mirtazapine is the first of a new class of antidepressants, the noradrenergic and specific serotonergic antidepressants. Its antidepressant effect appears to be related to its dual enhancement of both noradrenergic neurotransmission and serotonin 5-HT1 receptor-mediated serotonergic neurotransmission. Mirtazapine has demonstrated superior tolerability to the tricyclic antidepressants, primarily on account of its relative absence of anticholinergic, adrenergic and serotonin-related adverse effects. We observed mirtazapine-induced delirium in one organically depressed and two major depressed patients with subclinical brain disease. The appearance of hallucinations, psychomotoric agitation and cognitive changes after initiation of mirtazapine, and their prompt improvement after drug discontinuation, led to the impression that these were drug-induced phenomena. One possible hypothesis for the observed deliria is a central increase of norepinephrine after acute administration of mirtazapine. Subclinical brain disease might have favoured the occurrence of delirium in the three cases.     

Prefrontal cortical anandamide signaling coordinates coping responses to stress through a serotonergic pathway

The endocannabinoid system has recently emerged as a vital component of the stress response and is an appealing target for the treatment of mood and anxiety disorders. Additionally, corticolimbic endocannabinoid signaling is important for stress-induced regulation of emotional behavior. However, the mechanism by which this occurs remains elusive. Combining biochemical and behavioral analyses within the forced swim test, we examined whether stress-induced regulation of endocannabinoid signaling in the medial prefrontal cortex contributes to behavioral responses to stress, and whether these responses are dependent on serotonergic neurotransmission. Forced swim stress produced a rapid and pronounced reduction in medial prefrontal anandamide content, but had no effect on 2-arachidonoylglycerol content within this region. Local administration of the anandamide hydrolysis inhibitor URB597 (0.01μg) into the ventromedial region of the prefrontal cortex decreased passive coping responses and increased active behavioral strategies, a phenomenon which was blocked by local antagonism of the CB(1) receptor. Furthermore, local inhibition of anandamide hydrolysis within the medial PFC increased the firing rate of serotonergic neurons within the dorsal raphe, suggesting that prefrontal cortical endocannabinoid signaling may modulate stress coping behaviors through a regulation of serotonergic neurotransmission. Accordingly, serotonin depletion prevented the ability of inhibition of anandamide hydrolysis within the medial PFC to promote active stress coping responses. Collectively, these data argue that stress-induced changes in endocannabinoid signaling within the medial PFC modulate stress-coping behaviors through a regulation of serotonergic neurotransmission and provide a neuroanatomical framework by which we may understand the mechanisms subserving the antidepressant potential of the endocannabinoid system.