5-HT1A Receptor Partial Agonist Research Articles

Brexpiprazole for Agitation Associated With Dementia Due to Alzheimer's Disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disease characterized by progressive cognitive and functional decline. Nearly all patients with AD develop neuropsychiatric symptoms (NPSs). Agitation is one of the most distressing and challenging NPS. Brexpiprazole is an oral antipsychotic and is the first approved pharmacologic agent in the United States for the treatment of agitation associated with dementia due to AD. Its effect is thought to be from its partial serotonin 5-HT1A and dopamine D2 receptor agonist activity and serotonin 5-HT2A receptor antagonism. Brexpiprazole is a maintenance medication, and it should not be used “as needed” or as a “PRN” treatment for breakthrough agitation. Brexpiprazole is a major substrate of CYP2D6 and CYP3A4. Dose adjustments may be required for drug interactions or impaired renal or hepatic function. Clinical trials found brexpiprazole 2 to 3 mg/d demonstrated significant improvements in agitation, with brexpiprazole showing an approximate 5-point greater reduction on change in the Cohen-Mansfield Agitation Inventory total score at week 12 from baseline compared with placebo. Brexpiprazole is generally well tolerated and safe, and common adverse reactions when used for this indication include dizziness, headaches, insomnia, nasopharyngitis, somnolence, and urinary tract infections. Like other antipsychotics used for agitation in AD, brexpiprazole is associated with higher mortality rates compared with placebo. In a long-term care setting, there are several considerations for its use. Benefits include an oral agent that is well tolerated and clinical data showing statistically significant effects on agitation. However, brexpiprazole has not been studied in head-to-head clinical trials against other antipsychotics, and there are differing opinions if the agitation score reductions translate to a clinically meaningful difference. The approval of brexpiprazole signals favorably for upcoming agents for this indication, including escitalopram and dextromethorphan-bupropion. Both escitalopram and dextromethorphan-bupropion are currently undergoing clinical trials.

Aripiprazole and environmental enrichment independently improve functional outcome after cortical impact injury in adult male rats, but their combination does not yield additional benefits

Typical antipsychotic drugs (APDs) with D2antagonistic properties impede functional outcome after experimental traumatic brain injury (TBI) and reduce the effectiveness of environmental enrichment (EE). Here we test the hypothesis that aripiprazole (ARIP), an atypical APD with partial D2and 5-HT1Areceptor agonist activities will improve recovery after TBI and when combined with EE will further enhance the benefits. Anesthetized adult male rats received either a controlled cortical impact of moderate severity or sham injury and then were randomly assigned to EE or standard (STD) housing and once daily intraperitoneal injections of ARIP (0.1 mg/kg) or vehicle (VEH; 1.0 mL/kg) beginning 24 h after injury for 19 days. Motor (beam-walking time and beam-walk score) and cognitive (acquisition of spatial learning and memory) outcomes were assessed on post-operative days 1–5 and 14–19, respectively. Cortical lesion volume was quantified on day 21. There were no statistical differences among the sham groups, regardless of housing or treatment, so the data were pooled. The SHAM group performed better than all TBI groups on motor and spatial learning (p < 0.05) but did not differ from either EE group on memory retention. Regarding TBI, both EE groups improved motor and cognitive outcomes vs. the VEH-treated STD group (p < 0.05) but did not differ from one another (p > 0.05). The ARIP-treated STD group performed better than the VEH-treated STD group on beam-walk score and spatial learning (p < 0.05), but not beam-walking time or memory retention (p > 0.05). Cortical lesion volume was smaller in all treated groups compared to the TBI + STD + VEH group (p < 0.05). The data replicate previous work and extend the findings by demonstrating that 1) ARIP promotes recovery after TBI, but combining treatments does not yield additional benefits, which is contrary to the hypothesis, and 2) unlike APDs that exhibit D2 receptor antagonism, ARIP does not impede rehabilitation (i.e., EE).

Involvement of 5-HT2A receptor hyperfunction in the anxiety-like behavior induced by doxorubicin and cyclophosphamide combination treatment in rats

We examined whether combination treatment with doxorubicin and cyclophosphamide, a traditional chemotherapy for breast cancer, induced anxiety-like behavior in rats. Furthermore, we evaluated the role of the serotonin (5-HT)2A receptor subtype in the anxiety-like behavior induced by such chemotherapy. Rats were intraperitoneally injected with doxorubicin and cyclophosphamide once a week for 2 weeks. This caused the rats to display anxiety-like behavior during the light–dark test. In addition, we examined the rats' 5-HT2A receptor-mediated behavioral responses. Combination treatment with doxorubicin and cyclophosphamide significantly increased (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, (a 5-HT2A receptor agonist)-induced wet-dog shake activity. This anxiety-like behavior was significantly inhibited by mirtazapine, a 5-HT2A receptor antagonist/5-HT1A receptor agonist, and tandospirone, a partial 5-HT1A receptor agonist, but not by fluoxetine, a selective serotonin reuptake inhibitor. The anxiety-like behavior induced by doxorubicin and cyclophosphamide combination treatment is mediated by hyperfunctioning of the 5-HT2A receptor. Thus, 5-HT2A receptor antagonists or 5-HT1A receptor agonists might be useful for treating chemotherapy-induced anxiety disorders.

The role of new antidepressants in clinical practice in Canada: a brief review of vortioxetine, levomilnacipran ER, and vilazodone.

Although many branded and generic antidepressants are approved for the treatment of major depressive disorder (MDD) in Canada, efficacy and tolerability differ among patients, and new treatment options are needed. Symptom types (eg, fatigue, energy/motivation, cognition, and functioning), medication type, treatment duration, and the need for maintenance therapy are factors that may influence treatment effectiveness. Three antidepressants, vortioxetine, levomilnacipran extended-release (ER), and vilazodone have recently become available in Canada. The aim of this review is to contextualize differences in their mechanistic and clinical profiles, thereby providing practitioners with knowledge to support treatment decisions. In trials versus placebo, each drug improved depressive symptoms in adult patients with MDD. The antidepressant effect of vortioxetine may be related to enhanced serotonergic activity via reuptake inhibition and agonism and/or antagonism of various serotonin receptors. Vortioxetine may also improve cognitive functioning in MDD, and has proven efficacious in relapse prevention. Nausea was the most commonly reported adverse event (AE); rates of sexual dysfunction were low and abrupt discontinuation was well tolerated. Levomilnacipran ER, a serotonin norepinephrine reuptake inhibitor, demonstrated greater improvement versus placebo in functional impairment as well as depressive symptoms; in post hoc analyses, improvement in symptoms of motivation and energy were observed. Nausea was the most commonly reported AE; gradual discontinuation is recommended to avoid discontinuation syndrome. Vilazodone is a serotonin reuptake inhibitor and partial serotonergic 5-HT1A receptor agonist. In addition to improvement in depressive symptoms, evidence suggests that vilazodone may be particularly well suited for depressed patients with high anxiety levels. Diarrhea, nausea, and headache were the most common AEs; low rates of sexual dysfunction were reported. The 2016 Canadian Network for Mood and Anxiety Treatments guidelines for MDD includes vortioxetine as a first-line treatment; levomilnacipran ER and vilazodone are considered as second-line treatments due to lack of relapse prevention data at the time of approval.

Neurochemical and behavioural effects of hypidone hydrochloride (YL-0919): a novel combined selective 5-HT reuptake inhibitor and partial 5-HT1A agonist.

Our previous studies revealed that hypidone hydrochloride (YL-0919), which acts as a selective 5-HT (serotonin) reuptake inhibitor (SSRI) and displays partial 5-HT1A receptor agonist properties, exerts a significant antidepressant effect in various animal models. The aim of present research was to further investigate the pharmacology of YL-0919. We first investigated the target profile of YL-0919 using [35 S]-GTPγS binding and microdialysis. To determine whether the 5-HT or noradrenergic systems are involved in the antidepressant-like effect of YL-0919, the 5-hydroxytryptophan (5-HTP)-induced head-twitch test and antagonism with a high dose of apomorphine were performed. Using the learned helplessness paradigm, the novelty suppressed feeding test, the Vogel-type conflict and elevated plus-maze test, we further verified the antidepressant-like and anxiolytic-like effects of YL-0919. The effects of YL-0919 on hippocampal long-term potentiation (LTP) and sexual behaviour were also evaluated. Data from the present study demonstrated that YL-0919 displays partial 5-HT1A receptor agonist properties, producing a greater impact on extracellular 5-HT levels than a conventional SSRI (fluoxetine), as well as significant antidepressant and anxiolytic effects. Furthermore, YL-0919 treatment rapidly influenced the synaptic plasticity (enhancing LTP) of rats. Finally, at doses close to those producing antidepressant-like effects, YL-0919 did not result in a marked inhibition of sexual function. These data suggest that YL-0919 is probably a fast-onset potent antidepressant with few side effects.

Involvement of presynaptic 5-HT1A receptors in the low propensity of brexpiprazole to induce extrapyramidal side effects in rats

Previous studies have shown that partial and full 5-HT1A receptor agonists reduce antipsychotic-induced catalepsy. Consequently, some antipsychotics combining balanced efficacy between dopamine (DA) D2 antagonism or partial agonism and 5-HT1A receptor agonism have a low propensity to induce extrapyramidal side effects (EPS), as reflected by low cataleptogenic activity in rodents. In the present experiments, we attempted to explore the importance of pre- and postsynaptic 5-HT1A agonistic properties of brexpiprazole and aripiprazole in the context of neurological side-effect liabilities. Additional measures of prefrontal cortical serotonin (5-HT) and DA levels using microdialysis were used to support that brexpiprazole has a preferential agonist effect on presynaptic 5-HT1A receptors.Brexpiprazole (3.0 and 10mg/kg, p.o.) as well as aripiprazole (8.0 and 30mg/kg, p.o.) failed to induce catalepsy in rats. Brexpiprazole (10mg/kg, p.o.) significantly reduced the cataleptic response induced by haloperidol (0.63mg/kg, s.c.), while aripiprazole (1.0–100mg/kg, p.o.) failed to reverse the effect of haloperidol and only showed a numeric decrease at 10mg/kg, (p.o.).When 5-HT1A receptors were blocked by the selective antagonist, WAY100635 (1.0mg/kg, s.c.), cataleptogenic properties of brexpiprazole (10mg/kg; p.o), but not aripiprazole (8.0 and 30mg/kg, p.o.) were unmasked.The (“biased”) 5-HT1A receptor agonists F15599 (postsynaptic preference) and F13714 (presynaptic preference) had differential effects on haloperidol-induced catalepsy: F13714 (0.16mg/kg, s.c.) counteracted catalepsy, whereas F15599 (0.040mg/kg, s.c.) had no significant effect at regionally-selective doses. These data support a role of presynaptic 5-HT1A receptors in the anticataleptic effect of brexpiprazole. The selective 5-HT2A antagonist M100907 (0.10mg/kg, s.c.) had no effect on haloperidol-induced catalepsy, arguing against a major role of 5-HT2A receptors in the cataleptogenic profile of brexpiprazole.The findings with brexpiprazole were supported using microdialysis studies: Brexpiprazole (3.0 and 10mg/kg, p.o.) decreased extracellular 5-HT levels in the medial prefrontal cortex (mPFC), while it failed to affect extracellular DA in the same samples, suggesting that the 5-HT1A agonist properties of brexpiprazole may be preferentially presynaptic.In conclusion, these results confirm that brexpiprazole and aripiprazole have low propensities to induce EPS. However, the low EPS risk of brexpiprazole is more likely dependent on its agonist properties on presynaptic 5-HT1A receptors, while that of aripiprazole is less sensitive to 5-HT1A receptor antagonism.

Propriétés pharmacologiques de la vortioxetine et leurs conséquences pré-cliniques

Selective Serotonin Reuptake Inhibitors (SSRIs) are extensively used for the treatment of major depressive disorder (MDD). SSRIs are defined as indirect receptor agonists since the activation of postsynaptic receptors is a consequence of an increase in extracellular concentrations of serotonin (5-HT) mediated by the blockade of serotonin transporter. The activation of some serotoninergic receptors (5-HT1A, post-synaptic, 5-HT1B post-synaptic, 5-HT2B, and 5-HT4), but not all (5-HT1A, pre-synaptic, 5-HT1B pre-synaptic, 5-HT2A, 5-HT2C, 5-HT3, and probably 5-HT6), induces anxiolytic/antidepressive - like effects. Targetting specifically some of them could potentially improve the onset of action and/or efficacy and/or prevent MD relapse. Vortioxetine (Brintellix, 1- [2-(2,4-dimethylphenyl-sulfanyl)-phenyl]-piperazine) is a novel multi-target antidepressant drug approved by the Food and Drug Administration (FDA) and by European Medicines Agency. Its properties are markedly different from the extensively prescribed SSRIs. Compared to the SSRIs, vortioxetine is defined as a multimodal antidepressant drug since it is not only a serotonin reuptake inhibitor, but also a 5-HT1D, 5-HT3, 5-HT7 receptor antagonist, 5-HT1B receptor partial agonist and 5-HT1A receptor agonist. This specific pharmacological profile enables vortioxetine to affect not only the serotoninergic and noradrenergic systems, but also the histaminergic, cholinergic, gamma-butyric acid (GABA) ergic and glutamatergic ones. Thus, vortioxetine not only induces antidepressant-like or anxiolytic-like activity but also improves cognitive parameters in several animal models. Indeed, vortioxetine was shown to improve working memory, episodic memory, cognitive flexibility and spatial memory in young adult rodents and also in old animal models. These specific effects of the vortioxetine are of interest considering that cognitive dysfunction is a common comorbidity to MDD. Altogether, even though this molecule still needs to be investigated further, especially in the insufficient-response to antidepressant drugs, vortioxetine is already an innovative therapeutic option for the treatment of major depression.

Antidepressant-like activity of aroxyalkyl derivatives of 2-methoxyphenylpiperazine and evidence for the involvement of serotonin receptor subtypes in their mechanism of action

Since serotonin (5-HT) is strongly involved in the etiology and pathophysiology of depression, the development of new antidepressants is still based on the serotonergic system. The complexity of serotonergic system provides an opportunity for the development of compounds with multiple and complementary mechanism of action. This study describes serotonin receptor profile, functional characterization, and pharmacological in vivo evaluation of new aroxyalkyl derivatives of 2-methoxyphenylpiperazine. The obtained results allowed for the identification of compound 3, (1-[3-(2,6-dimethylphenoxy)propyl]-4-(2-methoxyphenyl)piperazine hydrochloride), a partial 5-HT1A receptor agonist, and 5-HT2A receptor antagonist, with high affinity toward 5-HT7 receptors, showing antidepressant- and anxiolytic-like properties. Moreover, 5-HT1A receptor activation is crucial for the antidepressant-like activity of compound 3. The rest of the compounds (except compounds 1 and 9) showed antidepressant but not anxiolytic-like properties, which did not result from 5-HT1A receptors activation. Furthermore, the compounds are 5-HT1A and weak 5-HT3 receptors antagonists, and some of them 5-HT2A antagonists. Moreover, none of the studied compounds impaired motor coordination at antidepressant-like doses. Since the studied compounds exhibited activity in behavioral assays and interacted with various receptors, the results of our experiments are very promising and require further studies.

The electrophysiological effects of the serotonin 1A receptor agonist buspirone in emotional face processing

Emotional face processing is critically modulated by the serotonergic system, and serotonin (5-HT) receptor agonists impair emotional face processing. However, the specific contribution of the 5-HT1A receptor remains poorly understood. Here we investigated the spatiotemporal brain mechanisms underpinning the modulation of emotional face processing induced by buspirone, a partial 5-HT1A receptor agonist. In a psychophysical discrimination of emotional faces task, we observed that the discrimination fearful versus neutral faces were reduced, but not happy versus neutral faces. Electrical neuroimaging analyses were applied to visual evoked potentials elicited by emotional face images, after placebo and buspirone administration. Buspirone modulated response strength (i.e., global field power) in the interval 230–248ms after stimulus onset. Distributed source estimation over this time interval revealed that buspirone decreased the neural activity in the right dorsolateral prefrontal cortex that was evoked by fearful faces. These results indicate temporal and valence-specific effects of buspirone on the neuronal correlates of emotional face processing. Furthermore, the reduced neural activity in the dorsolateral prefrontal cortex in response to fearful faces suggests a reduced attention to fearful faces. Collectively, these findings provide new insights into the role of 5-HT1A receptors in emotional face processing and have implications for affective disorders that are characterized by an increased attention to negative stimuli.

Dual Ligands Targeting Dopamine D2 and Serotonin 5-HT&lt;sub&gt;1A&lt;/sub&gt; Receptors as New Antipsychotical or Anti-Parkinsonian Agents

Psychiatric disorders like schizophrenia and neurodegenerative diseases like Parkinson's disease are associated with poly-factorial pathogenic mechanisms, with several neurotransmitter systems closely involved. In addition to the cerebral dopaminergic (DA) system, the serotoninergic (5-HT) system also plays a crucial role in regulating psychoemotional, cognitive and motor functions in the central nervous system (CNS). Among the large 5-HT receptor family, accumulating data have revealed new insights into the therapeutic benefit of the 5-HT1A receptor in treating various CNS disorders, especially schizophrenia and Parkinson's disease. The present review discusses the advance of dual agents with mixed actions at the dopamine D2 and serotonin 5-HT1A receptors in the treatment of these diseases. Aripiprazole was the only marketed drug with dual D2 and 5-HT1A profile. It is a partial D2 and 5-HT1A receptor agonist and has been prescribed as an atypical antipsychotical drug. Two other drugs Cariprazine and Pardoprunox are being investigated in clinic. Most of the other candidate compounds, including Bifeprunox, Sarizotan, Mazapertine succinate, PF-217830, and Adoprazine were discontinued due to either non-optimal pharmacokinetic properties or insufficient therapeutical efficacy. Although much effort has been done to highlight the advantages of the 5-HT1A and D2 dual approach, it has to be pointed out that many of these drugs showed poly-pharmacological profile by targeting many other receptors and/or transporters besides the D2 and 5-HT1A receptors. In this regard, 'pure' compounds exclusively acting on the D2 and 5-HT1A receptors are highly needed to further validate this approach. Meanwhile, safety concerns and in vivo pharmacokinetic alerts should also be implanted to the drug design art early.

Role of Hypothalamic-pituitary-adrenal-axis in Affective Disorders: Anti-depressant and Anxiolytic Activity of Partial 5-HT1A Agonist in Adrenalectomised Rats

Background:Depression is a neurological disorder characterized by sad mood, loss of pleasure, agitation and retardation. Though most relevant neuronal pathophysiology is characterized by decrease in monoamine namely; serotonin (5-HT), dopamine, noradrenaline level in central areas regulating mood and behavior, it inadequately explains the exact mechanism involved. Buspirone (BUS), a partial 5-HT1A receptor agonist has shown promising anti-depressant and anxiolytic properties in various pre-clinical and clinical studies, but the molecular and cellular mechanisms are still unclear.Objective:The aim of this study was to investigate, in vivo, the role of hypothalamic-pituitary-adrenal (HPA) axis dysregulation in pathophysiology of depression-related disorders and the anti-depressant like activity of BUS. To simulate HPA axis dysregulation, rats were subjected to bilateral adrenalectomy (ADX).Materials and Methods:We have analyzed effect of BUS (10 mg/kg, i.p.) in ADX and sham rats using open field, sucrose consumption, elevated plus maze and hyper-emotionality tests.Results:In all animal models tested, ADX rats exhibited significant depressive and anxiogenic states while BUS was effective in reversing the psychological diseased condition developed.Conclusion:Taken together, these data showed a prominent role of HPA axis in depression and neuronal mechanism of BUS as anti-depressant and anxiolytic agent. Moreover, our findings suggest that BUS can be a better candidate for stress related depression and anxiety.

Active Metabolites as Antidepressant Drugs: The Role of Norquetiapine in the Mechanism of Action of Quetiapine in the Treatment of Mood Disorders

Active metabolites of some antipsychotic drugs exhibit pharmacodynamic and pharmacokinetic properties that may be similar to or differ from the original compound and that can be translated by a different profile of responses and interactions to clinical level. Some of these antipsychotics’ active metabolites might participate in mechanisms of antidepressant activity, as m-chlorophenylpiperazine (aripiprazole), 9-OH-risperidone and norquetiapine. Norquetiapine exhibits distinct pharmacological activity from quetiapine and plays a fundamental role in its antidepressant efficacy. In this review, we analyze the differential pharmacological aspects between quetiapine and norquetiapine, both from the pharmacokinetic and pharmacodynamic perspectives (affinity for dopaminergic, noradrenegic, and/or serotonergic receptors, etc.), as well as differential neuroprotective role. The pharmacological differences between the two drugs could explain the differential clinical effect, as well as some differences in tolerability profile and drug interactions. The available data are sufficient to arrive at the conclusion that antidepressant activity of quetiapine is mediated, at least in part, by the active metabolite norquetiapine, which selectively inhibits noradrenaline reuptake, is a partial 5-HT1A receptor agonist, and acts as an antagonist at presynaptic α2, 5-HT2C, and 5-HT7 receptors.

Effects of Chronic Administration of Buspirone to Female Mice in Conditions of Prolonged Psychoemotional Stress

The effects of chronic administration (30 days) of the partial 5-HT1A receptor agonist buspirone (0.05, 1, and 10 mg/kg i.p.) on the behavior of female C57BL/6 J mice in conditions of prolonged psychoemotional stress were studied. Stress was produced by keeping females in a cage with an aggressive male on the other side of a perforated partition, along with the daily occurrence of 10-min intermale confrontations between the aggressor and another male placed with it. Chronic administration of buspirone at all the doses tested had no effect on the behavior of the females assessed in the partition and open field tests at the end of the treatment period. The elevated plus maze test showed that buspirone had anxiolytic effects, but only at a dose of 1 mg/kg. In the Porsolt test, buspirone (1 mg/kg) produced a minor increase in the duration of immobility, pointing to some antidepressant effect. Thus, chronic administration of buspirone to females in conditions of prolonged psychoemotional stress had different effects on their behavior depending on the dose and test conditions.

An in vivo pharmacological evaluation of pardoprunox (SLV308) — A novel combined dopamine D2/D3 receptor partial agonist and 5-HT1A receptor agonist with efficacy in experimental models of Parkinson's disease

Partial D(2/3) dopamine (DA) receptor agonists provide a novel approach to the treatment of the motor symptoms of Parkinson's disease (PD) that may avoid common dopaminergic side-effects, including dyskinesia and psychosis. The present study focussed on the in vivo pharmacological and therapeutic characterisation of the novel D(2/3) receptor partial agonist and full 5-HT(1A) receptor agonist pardoprunox (SLV308; 7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolone monochloride). Pardoprunox induced contralateral turning behaviour in rats with unilateral 6-hydroxydopamine-induced lesions of the substantia nigra pars compacta (SNpc) (MED=0.03mg/kg; po). In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, pardoprunox dose-dependently increased locomotor activity (MED=0.03mg/kg; po) and decreased motor disability (MED=0.03mg/kg; po). The effects of pardoprunox were reversed by the D(2) antagonist sulpiride. In contrast pardoprunox attenuated novelty-induced locomotor activity (MED=0.01mg/kg; po), (+)-amphetamine-induced hyperlocomotion (MED=0.3mg/kg; po) and apomorphine-induced climbing (MED=0.6mg/kg; po) in rodents. Pardoprunox also induced 5-HT(1A) receptor-mediated behaviours, including flat body posture and lower lip retraction (MED=0.3mg/kg; po) and these were reversed by the 5-HT(1A) receptor antagonist WAY100635. Collectively, these findings demonstrate that pardoprunox possesses dopamine D2/3 partial agonist effects, 5-HT1A agonist effects and reduces parkinsonism in animal models. functional DA D(2) receptor partial agonist activity and is effective in experimental models predictive of efficacy in PD. The presence of functional 5-HT(1A) agonist activity might confer anti-dyskinetic activity and have effects that control neuropsychiatric components of PD.

Effect of buspirone on thermal sensory and pain thresholds in human volunteers

BackgroundBuspirone is a partial 5-HT1A receptor agonist. Animal studies have shown that modulation of serotoninergic transmission at the 5-HT1A receptor can induce analgesia in acute pain models. However, no studies have been published so far on the effects of serotonin receptor agonists on pain perception in humans.MethodsThe effects of buspirone (30 mg p.o.) on thermal sensory and pain thresholds were investigated in twelve female volunteers (26 ± 2 yrs) in a prospective, randomized, double-blind, double-dummy, placebo-controlled study with morphine (10 mg i.v.) as positive control.ResultsMorphine significantly increased the heat pain detection threshold (ΔT: placebo 1.0°C and 1.3°C, p < 0.05) at 60 minutes. Buspirone caused mild sedation in six participants at 60 minutes, but was without effect on any of the measured parameters.ConclusionBuspirone in the maximal recommended dose was without significant effect on thermal pain. However, as it is only a partial agonist at the 5-HT1A receptor and also acts on other receptor types, the negative results of the present study do not rule out a possible analgesic effect of more specific 5-HT1A receptor agonists.

The partial 5-HT1A receptor agonist buspirone enhances neurogenesis in the opossum ( Monodelphis domestica)

We demonstrate for the first time that neurogenesis in the adult Monodelphis opossum has a typical mammalian pattern and occurs only in the dentate gyrus (DG) and subventricular zone (SVZ) of the lateral ventricles. In these two brain regions neurogenesis is present throughout the lifespan, although its rate is reduced by half in the old age. Treatment with buspirone, a partial 5-HT1A receptor agonist which is used in human clinic as an anxiolytic agent, boosts proliferation in the SVZ and DG in both adult and aged opossums. The neuronal phenotype dominates among newly generated cells in both non-treated and buspirone-treated opossums. We suggest that if functional importance of adult neurogenesis is in improving olfactory discrimination and generation of hippocampus-dependent memory, both spatial and emotional, then administration of drugs increasing the rate of neurogenesis via activation of 5-HT1A receptors may be a valuable aid in combating problems of the advanced age.

Augmentation of antidepressants with perospirone for treatment-resistant major depressive disorder

We examined the efficacy and tolerability of perospirone, a dopamine D2 and 5-HT2A receptor antagonist and a partial 5-HT1A receptor agonist, in the augmentation of antidepressant treatment of partially responding and nonresponding patients with major depressive disorder. Twelve patients with major depressive disorder and an incomplete or no response to different kinds of antidepressants (selective serotonin reuptake inhibitor, milnacipran, or sulpride) monotherapy or polytherapy for 8 weeks or more were treated with perospirone augmentation in an eight-week, open-label study. Data were gathered from July 2006 to March 2008. The mean duration of antidepressant pharmacotherapy at baseline was 28 weeks. At baseline, the mean (± SD) of the MADRS scores was 35.8 ± 10.1. The mean (± SD) initial dose of perospirone was 7.0 ± 2.9 mg/day and the final dose was 11.7 ± 6.6 mg/day. Significant reductions in MADRS scores were observed at weeks 2, 4, 6 and 8. Although two of the twelve subjects who completed the protocol achieved remission by the study endpoint, five of the twelve patients were responders (i.e., > 50% improvement in the MADRS score). Sleepiness and tremor were observed in six patients and one patient, respectively, resulting in a reduction of perospirone dose due to these side effects. The discontinuation rate after 8 weeks of treatment was zero. These findings suggest that perospirone may be an effective augmentation strategy for improving therapeutic response in patients with treatment-resistant major depressive disorder when administered in combination with standard antidepressant therapy. Based on this clinical evidence, a double-blind, placebo-controlled trial is warranted.

Effects of bifeprunox and aripiprazole on rat serotonin and dopamine neuronal activity and anxiolytic behaviour

The atypical antipsychotic bifeprunox is a partial dopamine D(2) and 5-HT(1A) receptor agonist. Using in-vivo electrophysiological and behavioural paradigms in the rat, the effects of bifeprunox and aripiprazole were assessed on ventral tegmental area (VTA) dopamine and dorsal raphe serotonin (5-HT) cell activity and on foot shock-induced ultrasonic vocalisation (USV). In VTA, bifeprunox and aripiprazole decreased (by 20-50%) firing of dopamine neurons. Interestingly, bursting activity was markedly reduced (by 70-100%), bursting being associated with a larger synaptic dopamine release than single spike firing. Both ligands reduced inhibition of firing rate induced by the full dopamine receptor agonist apomorphine, whereas the D(2) receptor antagonist haloperidol prevented these inhibitory effects, confirming partial D(2)-like agonistic properties. On 5-HT neurons, bifeprunox was more potent than aripiprazole to suppress firing activity. The 5-HT(1A) receptor antagonist WAY-100,635 prevented their effects. In the USV test of anxiolytic-like activity, bifeprunox had higher potency than aripiprazole to reduce vocalisations. Both WAY-100,635 and haloperidol reversed the effects of both agonists. The present in-vivo study shows that bifeprunox is a potent partial D(2)-like and 5-HT(1A) receptor agonist reducing preferentially the phasic activity of dopamine neurons. Thus, bifeprunox would be expected to be an effective compound against positive and negative symptoms of schizophrenia.

Aripiprazole augmentation in treatment-refractory obsessive–compulsive disorder

Obsessive–compulsive disorder (OCD) responds preferentially to cognitive behavioural therapy (CBT) and to pharmacological treatment such as antidepressant drugs like serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants with a predominantly serotonergic mechanism (Math and Janardhan Reddy 2007). Approximately half of OCD patients treated with an adequate trial of SSRIs fail to fully respond and continue to exhibit significant symptoms (Bloch et al 2006). Aripiprazole is a quinolinone derivative with a high affinity for dopamine D2 and D3 receptors as well as serotonin 5HT1A, 5-HT2A and 5-HT2B receptors. Aripiprazole is an atypical antipsychotic medication that works via partial dopaminergic, 5-HT1A, 5-HT2A and 5-HT2B receptor agonist activity (Rugino and Janvier 2005). We report a case of an OCD patient in whom a treatment regimen with escitalopram was successfully augmented with aripiprazole.

A Mathematical Model for Paroxetine Antidepressant Effect Time Course and Its Interaction with Pindolol

Although selective 5-HT reuptake inhibitors (SSRIs) block monoamine uptake within hours of administration to patients, their full clinical effect does not appear until 2-4 weeks after treatment onset. Pindolol, a betablocker with weak partial 5-HT1A receptor agonist activity has been shown to produce a more rapid onset of antidepressant action of SSRIs. However, the optimal dosing schedule of pindolol remains controversial. Building on a set-point model described previously for the hypothermic effect of 5-HT agonists, we have developed a model based on the concept of homeostatic control mechanisms, in which SSRIs exert their antidepressant effect by increasing the transduction set-point of the postsynaptic 5-HT1A receptor, and pindolol exerts its effect by increasing the rate of feedback mechanisms. The predictive distribution of the proportion of responders at each day of measurement (based on population simulation from the model) was not significantly different from the proportions observed in two published clinical trials, one with fluoxetine, the other with paroxetine alone or combined with pindolol. The model was applied to the simulation of paroxetine response (clinical score) time course with or without pindolol, after administration of different doses of each drug. The simulated total scores on the MADR scale obtained after treatment with paroxetine alone (20 mg/day) or paroxetine (20 mg/day) with different doses of pindolol (1.5, 7.5 and 37.5 mg/day) support that the reason for inconstant pindolol efficacy is that the 7.5 mg dose is too low. The model might be useful as a basis for clinical trial simulation.