Behavioral effects of the β3 adrenoceptor agonist SR58611A: Is it the putative prototype of a new class of antidepressant/anxiolytic drugs?

Potential of the Blue Calm® food supplement in the treatment of alcohol withdrawal-induced anxiety in adult zebrafish (Danio rerio)

Alcohol use disorder (AUD) is characterized by a set of behavioral, cognitive, nutritional, and physiological phenomena derived from the uncontrolled use of alcoholic beverages. There are cases in which AUD is associated with anxiety disorder, and when untreated, it requires careful pharmacotherapy. Blue Calm® (BC) is a food supplement indicated to aid restorative sleep, which has traces of medicinal plant extracts, as well as myo-inositol, magnesium bisglycinate, taurine, and L-tryptophan as its main chemical constituents. In this context, this study aimed to evaluate the potential of the BC in the treatment alcohol withdrawal-induced anxiety in adult zebrafish (aZF). Initially, BC was submitted to antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl radical. Subsequently, the aZF (n = 6/group) were treated with BC (0.1 or 1 or 10 mg/mL; 20 μL; p.o.), and the sedative effect and acute toxicity (96 h) were evaluated. Then, the anxiolytic-like effect and the possible GABAergic mechanism were analyzed through the Light & Dark Test. Finally, BC action was evaluated for treating alcohol withdrawal-induced anxiety in aZF. Molecular docking was performed to evaluate the interaction of the major chemical constituents of BC with the GABAA receptor. BC showed antioxidant potential, a sedative effect, was not toxic, and all doses of BC had an anxiolytic-like effect and showed potential for the treatment of alcohol withdrawal-induced anxiety in aZF. In addition to the anxiolytic action, the main chemical constituents of BC were confirmed in the molecular docking, thus suggesting that BC is an anxiolytic that modulates the GABAergic system and has pharmacological potential for the treatment of alcohol withdrawal-induced anxiety.

The Role of Beta-Adrenergic Receptors in Depression and Resilience

Norepinephrine is a catecholamine neurotransmitter that has been extensively implicated in the neurobiology of major depressive disorder (MDD). An accumulating body of evidence indicates that investigations into the action of norepinephrine at the synaptic/receptor level hold high potential for a better understanding of MDD neuropathology and introduce possibilities for developing novel treatments for depression. In this review article, we discuss recent advances in depression neuropathology and the effects of antidepressant medications based on preclinical and clinical studies related to beta-adrenergic receptor subtypes. We also highlight a beta-3 adrenergic receptor-involved mechanism that promotes stress resilience, through which antidepressant efficacy is achieved in both rodent models for depression and patients with major depression-an alternative therapeutic strategy that is conceptually different from the typical therapeutic approach in which treatment efficacy is achieved by reversing pathological alterations rather than by enhancing a good mechanism such as natural resilience. Altogether, in this review, we systematically describe the role of beta-adrenergic receptors in depression and stress resilience and provide a new avenue for developing a conceptually innovative treatment for depression.

Are Noradrenergic Transmission Reducing Drugs Antidepressants?

Major depressive disorder (MDD) remains a significant public health problem worldwide, and revised treatment strategies are therefore urgently needed, including the creation of novel antidepressant compounds or using existing molecular entities in new ways. Etiologic theories of MDD from decades ago have suggested that synaptic deficiencies of monoaminergic neurotransmitters play a causative role in this neuropsychiatric disorder, and that boosting monoamines with drugs such as SSRIs, SNRIs, TCAs, and MAOIs has antidepressant effects and in some individuals can even induce hypomania or mania. While other factors, such as various intracellular molecular pathways and hippocampal neurogenesis, undoubtedly also play a role in MDD, monoaminergic boosting drugs nonetheless have clearly demonstrated antidepressant properties. There is also, however, a body of studies in the preclinical literature suggesting that monoaminergic transmission reducing drugs, including noradrenergic ones, also have antidepressant-like behavioral properties in rodents. Given that there is increasing evidence that the monoamines have u-shaped or Janus-faced dose-response properties, in which a mid-range value is "optimal" in a variety of behavioral and physiological processes, it is plausible that either too much or too little synaptic norepinephrine in key circuits may exacerbate MDD in some individuals. Here we briefly review rodent depression-related behavioral data, focusing on the forced swim test, from three major classes of noradrenergic transmission reducing drugs (alpha2 agonists, beta blockers, alpha1 antagonists), and find much support for the hypothesis that they have antidepressant-like properties. Whether these drugs are antidepressants in human subjects remains to be determined.

Activation of β3-adrenoceptor increases the number of readily releasable glutamatergic vesicle via activating Ca2+/calmodulin/MLCK/myosin II pathway in the prefrontal cortex of juvenile rats

It is well known that β3-adrenoceptor (β3-AR) in many brain structures including prefrontal cortex (PFC) is involved in stress-related behavioral changes. SR58611A, a brain-penetrant β3-AR subtypes agonist, is revealed to exhibit anxiolytic- and antidepressant-like effects. Whereas activation of β3-AR exerts beneficial effects on cognitive function, the underlying cellular and molecular mechanisms have not been fully determined. In this study, whole cell patch-clamp recordings were employed to investigate the glutamatergic transmission of layer V/VI pyramidal cells in slices of the rat PFC. Our result demonstrated that SR58611A increased AMPA receptor-mediated excitatory postsynaptic currents (AMPAR-EPSCs) through activating pre-synaptic β3-AR. SR58611A enhanced the miniature EPSCs (mEPSCs) and reduced paired-pulse ratio (PPR) of AMPAR-EPSCs suggesting that SR58611A augments pre-synaptic glutamate release. SR58611A increased the number of readily releasable vesicle (N) and release probability (Pr) with no effects on the rate of recovery from vesicle depletion. Influx of Ca²⁺ through L-type Ca²⁺ channel contributed to SR58611A-mediated enhancement of glutamatergic transmission. We also found that calmodulin, myosin light chain kinase (MLCK) and myosin II were involved in SR58611A-mediated augmentation of glutamate release. Our current data suggest that SR58611A enhances glutamate release by the Ca²⁺/calmodulin/MLCK/myosin II pathway.

Anxiolytic effect of chronic intake of supplemental magnesium chloride in rat

Evidence suggest that magnesium dietary supplementation has several health benefits including lowering blood pressure, reducing insulin resistance, and improving symptoms of depression, anxiety, and migraine. Here, we aimed to study the effect of chronic magnesium supplementation on anxiety-like behavior in rats by supplementing with magnesium their drinking water for 30 days. Anxiety-like behavior was induced by subcutaneous injection of veratrin 30 min before performing elevated plus maze and open field tests to measure anxiety levels and locomotion, respectively. We quantify the concentration of magnesium in plasma and cerebrospinal fluid. We used diazepam to compare the efficacy of magnesium supplementation as an anxiolytic agent. Our results show that rats supplemented with magnesium had a statistically significant decrease in anxiety levels with not effects on locomotion and a statistically significant increase in concentration of magnesium in plasma and cerebrospinal fluid. However, the anxiolytic effect of magnesium supplementation washes-out in 12 days. We discuss the advantages of using supplemental magnesium as anxiolytic.

Repurposing beta-3 adrenergic receptor agonists for Alzheimer's disease: beneficial effects in a mouse model

Background

Old age, the most important risk factor for Alzheimer’s disease (AD), is associated with thermoregulatory deficits. Brown adipose tissue (BAT) is the main thermogenic driver in mammals and its stimulation, through β3 adrenergic receptor (β3AR) agonists or cold acclimation, counteracts metabolic deficits in rodents and humans. Studies in animal models show that AD neuropathology leads to thermoregulatory deficits, and cold-induced tau hyperphosphorylation is prevented by BAT stimulation through cold acclimation. Since metabolic disorders and AD share strong pathogenic links, we hypothesized that BAT stimulation through a β3AR agonist could exert benefits in AD as well.

Methods

CL-316,243, a specific β3AR agonist, was administered to the triple transgenic mouse model of AD (3xTg-AD) and non-transgenic controls from 15 to 16 months of age at a dose of 1 mg/kg/day i.p.

Results

Here, we show that β3AR agonist administration decreased body weight and improved peripheral glucose metabolism and BAT thermogenesis in both non-transgenic and 3xTg-AD mice. One-month treatment with a β3AR agonist increased recognition index by 19% in 16-month-old 3xTg-AD mice compared to pre-treatment (14-month-old). Locomotion, anxiety, and tau pathology were not modified. Finally, insoluble Aβ42/Aβ40 ratio was decreased by 27% in the hippocampus of CL-316,243-injected 3xTg-AD mice.

Conclusions

Overall, our results indicate that β3AR stimulation reverses memory deficits and shifts downward the insoluble Aβ42/Aβ40 ratio in 16-month-old 3xTg-AD mice. As β3AR agonists are being clinically developed for metabolic disorders, repurposing them in AD could be a valuable therapeutic strategy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00842-3.

Antiarrhythmic mechanisms of beta blocker therapy

Sympathetic activity plays an important role in modulation of cardiac rhythm. Indeed, while exerting positive tropic effects in response to physiologic and pathologic stressors, β-adrenergic stimulation influences cardiac electrophysiology and can lead to disturbances of the heart rhythm and potentially lethal arrhythmias, particularly in pathological settings. For this reason, β-blockers are widely utilized clinically as antiarrhythmics. In this review, the molecular mechanisms of β-adrenergic action in the heart, the cellular and tissue level cardiac responses to β-adrenergic stimulation, and the clinical use of β-blockers as antiarrhythmic agents are reviewed. We emphasize the complex interaction between cardiomyocyte signaling, contraction, and electrophysiology occurring over multiple time- and spatial-scales during pathophysiological responses to β-adrenergic stimulation. An integrated understanding of this complex system is essential for optimizing therapies aimed at preventing arrhythmias.

Everything You Always Wanted to Know about β3-AR * (* But Were Afraid to Ask)

The beta-3 adrenergic receptor (β₃-AR) is by far the least studied isotype of the beta-adrenergic sub-family. Despite its study being long hampered by the lack of suitable animal and cellular models and inter-species differences, a substantial body of literature on the subject has built up in the last three decades and the physiology of β₃-AR is unraveling quickly. As will become evident in this work, β₃-AR is emerging as an appealing target for novel pharmacological approaches in several clinical areas involving metabolic, cardiovascular, urinary, and ocular disease. In this review, we will discuss the most recent advances regarding β₃-AR signaling and function and summarize how these findings translate, or may do so, into current clinical practice highlighting β₃-AR’s great potential as a novel therapeutic target in a wide range of human conditions.

β3-Adrenergic receptor-dependent modulation of the medium afterhyperpolarization in rat hippocampal CA1 pyramidal neurons

Action potential firing in hippocampal pyramidal neurons is regulated by generation of an afterhyperpolarization (AHP). Three phases of AHP are recognized, with the fast AHP regulating action potential firing at the onset of a burst and the medium and slow AHPs supressing action potential firing over hundreds of milliseconds and seconds, respectively. Activation of β-adrenergic receptors suppresses the slow AHP by a protein kinase A-dependent pathway. However, little is known regarding modulation of the medium AHP. Application of the selective β-adrenergic receptor agonist isoproterenol suppressed both the medium and slow AHPs evoked in rat CA1 hippocampal pyramidal neurons recorded from slices maintained in organotypic culture. Suppression of the slow AHP was mimicked by intracellular application of cAMP, with the suppression of the medium AHP by isoproterenol still being evident in cAMP-dialyzed cells. Suppression of both the medium and slow AHPs was antagonized by the β-adrenergic receptor antagonist propranolol. The effect of isoproterenol to suppress the medium AHP was mimicked by two β₃-adrenergic receptor agonists, BRL37344 and SR58611A. The medium AHP was mediated by activation of small-conductance calcium-activated K⁺ channels and deactivation of H channels at the resting membrane potential. Suppression of the medium AHP by isoproterenol was reduced by pretreating cells with the H-channel blocker ZD7288. These data suggest that activation of β₃-adrenergic receptors inhibits H channels, which suppresses the medium AHP in CA1 hippocampal neurons by utilizing a pathway that is independent of a rise in intracellular cAMP. This finding highlights a potential new target in modulating H-channel activity and thereby neuronal excitability. NEW & NOTEWORTHY The noradrenergic input into the hippocampus is involved in modulating long-term synaptic plasticity and is implicated in learning and memory. We demonstrate that activation of functional β₃-adrenergic receptors suppresses the medium afterhyperpolarization in hippocampal pyramidal neurons. This finding provides an additional mechanism to increase action potential firing frequency, where neuronal excitability is likely to be crucial in cognition and memory.

Molecular mechanism of noradrenaline during the stress-induced major depressive disorder

Chronic stress-induced depression is a common hallmark of many psychiatric disorders with high morbidity rate. Stress-induced dysregulation of noradrenergic system has been implicated in the pathogenesis of depression. Lack of monoamine in the brain has been believed to be the main causative factor behind pathophysiology of major depressive disorder (MDD) and several antidepressants functions by increasing the monoamine level at the synapses in the brain. However, it is undetermined whether the noradrenergic receptor stimulation is critical for the therapeutic effect of antidepressant. Contrary to noradrenergic receptor stimulation, it has been suggested that the desensitization of β-adrenoceptor is involved in the therapeutic effect of antidepressant. In addition, enhanced noradrenaline (NA) release is central response to stress and thought to be a risk factor for the development of MDD. Moreover, fast acting antidepressant suppresses the hyperactivation of noradrenergic neurons in locus coeruleus (LC). However, it is unclear how they alter the firing activity of LC neurons. These inconsistent reports about antidepressant effect of NA-reuptake inhibitors (NRIs) and enhanced release of NA as a stress response complicate our understanding about the pathophysiology of MDD. In this review, we will discuss the role of NA in pathophysiology of stress and the mechanism of therapeutic effect of NA in MDD. We will also discuss the possible contributions of each subtype of noradrenergic receptors on LC neurons, hypothalamic-pituitary-adrenal axis (HPA-axis) and brain derived neurotrophic factor-induced hippocampal neurogenesis during stress and therapeutic effect of NRIs in MDD.

Deletion of p22phox-dependent oxidative stress in the hypothalamus protects against obesity by modulating 3-adrenergic mechanisms

A role for oxidative stress in the brain has been suggested in the pathogenesis of diet-induced obesity (DIO), although the underlying neural regions and mechanisms remain incompletely defined. We tested the hypothesis that NADPH oxidase-dependent oxidative stress in the paraventricular nucleus (PVN), a hypothalamic energy homeostasis center, contributes to the development of DIO. Cre/LoxP technology was coupled with selective PVN adenoviral microinjection to ablate p22^phox , the obligatory subunit for NADPH oxidase activity, in mice harboring a conditional p22^phox allele. Selective deletion of p22^phox in the PVN protected mice from high-fat DIO independent of changes in food intake or locomotor activity. This was accompanied by β₃-adrenoceptor-dependent increases in energy expenditure, elevations in brown adipose tissue thermogenesis, and browning of white adipose tissue. These data reveal a potentially novel role for brain oxidative stress in the development of DIO by modulating β₃-adrenoceptor mechanisms and point to the PVN as an underlying neural site.

Concordance and incongruence in preclinical anxiety models: Systematic review and meta-analyses

Rodent defense behavior assays have been widely used as preclinical models of anxiety to study possibly therapeutic anxiety-reducing interventions. However, some proposed anxiety-modulating factors - genes, drugs and stressors - have had discordant effects across different studies. To reconcile the effect sizes of purported anxiety factors, we conducted systematic review and meta-analyses of the literature on ten anxiety-linked interventions, as examined in the elevated plus maze, open field and light-dark box assays. Diazepam, 5-HT1A receptor gene knockout and overexpression, SERT gene knockout and overexpression, pain, restraint, social isolation, corticotropin-releasing hormone and Crhr1 were selected for review. Eight interventions had statistically significant effects on rodent anxiety, while Htr1a overexpression and Crh knockout did not. Evidence for publication bias was found in the diazepam, Htt knockout, and social isolation literatures. The Htr1a and Crhr1 results indicate a disconnect between preclinical science and clinical research. Furthermore, the meta-analytic data confirmed that genetic SERT anxiety effects were paradoxical in the context of the clinical use of SERT inhibitors to reduce anxiety.

Evaluating the teratogenicity of the selective ß3-adrenoceptor agonist, CL 316.243 hydrate by employing FETAX (frog embryo teratogenesis assay)

In this study, the frog embryo teratogenesis assay (FETAX - Xenopus) technique was employed to evaluate the potential teratogenicity of the selective ß-adrenoceptor (AR) agonist, CL 316.243. In this context, CL 316.243 was applied to the South African clawed frog (Xenopus laevis) embryos. The media containing the CL 316.24-exposed embryos were monitored and changed/replaced once every 24 hours. Using FETAX, we determined the minimum concentrations to inhibit growth (MCIG) for CL 316.243. The 96-hour no observable adverse effect concentration (NOAEC), the 96-hour lowest observable adverse effect concentration (LOAEC), the 96-hour EC₅₀ (malformation) and the 96-hour LC₅₀ (lethal concentration) for mortality and malformation could not be determined because the used concentrations did not affect viability or the presence of abnormalities. On the other hand, the MCIG of CL 316.243 was determined as 1 mg/L. Our results demonstrated that CL 316.243 administration was associated with no of teratogenic and toxic effects. However, from first concentration we used (1 to 5 mg/L) length of embryos reduced significantly (p < 0.001) when compared to control of Xenopus embryos. Further studies should be conducted with different concentrations in order to investigate the optimal concentrations for treating preterm labor with these substances.

Elements toward novel therapeutic targeting of the adrenergic system

Adrenergic receptors belong to the family of the G protein coupled receptors that represent important targets in the modern pharmacotherapies. Studies on different physiological and pathophysiological properties of the adrenergic system have led to novel evidences and theories that suggest novel possible targeting of such system in a variety of pathologies and disorders, even beyond the classical known therapeutic possibilities. Herein, those advances have been illustrated with selected concepts and different examples. Furthermore, we illustrated the applications and the therapeutic implications that such findings and advances might have in the contexts of experimental pharmacology, therapeutics and clinic. We hope that the content of this work will guide researches devoted to the adrenergic aspects that combine neurosciences with pharmacology.

Adrenaline rush: the role of adrenergic receptors in stimulant-induced behaviors

Psychostimulants, such as cocaine and amphetamines, act primarily through the monoamine neurotransmitters dopamine (DA), norepinephrine, and serotonin. Although stimulant addiction research has largely focused on DA, medication development efforts targeting the dopaminergic system have thus far been unsuccessful, leading to alternative strategies aimed at abating stimulant abuse. Noradrenergic compounds have shown promise in altering the behavioral effects of stimulants in rodents, nonhuman primates, and humans. In this review, we discuss the contribution of each adrenergic receptor (AR) subtype (α1, α2, and β) to five stimulant-induced behaviors relevant to addiction: locomotor activity, conditioned place preference, anxiety, discrimination, and self-administration. AR manipulation has diverse effects on these behaviors; each subtype profoundly influences outcomes in some paradigms but is inconsequential in others. The functional neuroanatomy and intracellular signaling mechanisms underlying the impact of AR activation/blockade on these behaviors remain largely unknown, presenting a new frontier for research on psychostimulant-AR interactions.

Effect of β3 adrenoceptor activation in the basolateral amygdala on ethanol seeking behaviors

RATIONALE

The interaction between ethanol (EtOH) and anxiety plays an integral role in the development and maintenance of alcoholism. Many medications in pre-clinical or clinical trials for the treatment of alcoholism share anxiolytic properties. However, these drugs typically have untoward side effects, such as sedation or impairment of motor function that may limit their clinical use. We have recently demonstrated that BRL 37344 (BRL), a selective β3-adrenoceptor (AR) agonist, enhances a discrete population of GABAergic synapses in the basolateral amygdala (BLA) that mediates feed-forward inhibition from lateral paracapsular (LPC) GABAergic interneurons onto BLA pyramidal cells. Behavioral studies revealed that intra-BLA infusion of BRL significantly reduced measures of unconditioned anxiety-like behavior without locomotor depressant effects.

OBJECTIVES

The present studies tested the effect of BRL (0.1, 0.5, or 1.0 μg/side) on EtOH self-administration using an intermittent access home cage two-bottle choice procedure and limited access operant responding for EtOH or sucrose.

RESULTS

Intra-BLA infusion of BRL did not reduce home cage, intermittent EtOH self-administration. However, using an operant procedure that permits the discrete assessment of appetitive (seeking) and consummatory measures of EtOH self-administration, BRL reduced measures of EtOH and sucrose seeking, but selectively reduced operant responding for EtOH during extinction probe trials. BRL had no effect on consummatory behaviors for EtOH or sucrose.

CONCLUSIONS

Together, these data suggest that intra-BLA infusion of BRL significantly reduces motivation to seek EtOH and provide initial evidence that β3-ARs and LPC GABAergic synapses may represent promising targets for the development of novel pharmacotherapies for the treatment of alcoholism.

Neurotransmissions of antidepressant-like effects of neuromedin U-23 in mice

Neuromedin U (NmU) is a widely distributed and multifunctional peptide in the central nervous system and the peripheral tissues. Little is know about the mechanisms of NmU on brain functions. The rodent isoform of the NmU, NmU-23, has been shown to have anxiolytic effects involved in the β-adrenergic and cholinergic nervous systems in elevated plus maze test. NmU-23 was tested for antidepressant-like effects in modified forced swimming test (FST) in mice and furthermore, the involvement of the adrenergic, serotonergic, cholinergic, dopaminergic or gaba-ergic receptors in the antidepressant-like effect of NmU-23 was studied in modified mice FST. Mice were pretreated with a non-selective α-adrenergic receptor antagonist phenoxybenzamine, an α1/α2β-adrenergic receptor antagonist, prazosin, an α2-adrenergic receptor antagonist, yohimbine, a β-adrenergic receptor antagonist, propranolol, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, nonselective muscarinic acetylcholine receptor antagonist, atropine, D2,D3,D4 dopamine receptor antagonist, haloperidol or γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline. NmU-23 showed the antidepressant-like effects by decreasing the immobility time and increasing the climbing and swimming time. Prazosin, haloperidol, and bicuculline prevented the effects of NmU-23 on the climbing and swimming time. Methysergide and cyproheptadine prevented the effects of NmU-23 on the immobility, swimming and climbing time. Atropine prevented the effects of NmU-23 on the climbing time. Phenoxybenzamine, yohimbine and propranolol did not change the effects of NmU-23. The results demonstrated that the antidepressant-like effect of NmU-23 is mediated, at least in part, by an interaction of the α2-adrenergic, 5-HT1-2 serotonergic, D2,D3,D4 dopamine receptor, muscarinic acetylcholine receptors and γ-aminobutyric acid subunit A (GABAA) receptor in a modified mouse FST.

Antidepressants and mood stabilizers effects on histone deacetylase expression in C57BL/6 mice: Brain region specific changes

To determine whether treatment with various antidepressants or mood stabilizers leads to region-specific changes, we investigated the effects of their subchronic (14 days of intraperitoneal injection) administration on the tissue concentration of monoamines, dopamine, serotonin, and norepinephrine, and the protein expression of acetylated histone H3 (AcH3) and histone deacetylases (HDACs) in the mouse striatum (ST), nucleus accumbens (Acb), hippocampus (Hip), cingulate cortex (Cg), and amygdala (Amy). Subchronic administration with the antidepressants (S)-citalopram oxalate (ECM), duloxetine hydrochloride (DLX), and mirtazapine (MIR) commonly induced significant increases in dopamine and serotonin levels in the ST and Cg. By contrast, no common profiles for dopamine, serotonin, or norepinephrine were identified in the Acb, Hip, or Amy. Treatment with sodium valproate (VPA), lithium chloride (Li), lamotrigine (LTG), levetiracetam (LTM), olanzapine (OLZ), clozapine (CLZ), clomipramine (CLM), ECM, and DLX induced significant increases in AcH3 expression in the Acb, while treatment with CLM, ECM, DLX, MIR, carbamazepine (CBZ), LTG, LTM, OLZ, or CLZ induced significant increases in HDAC2 and HDAC3 in the ST. CLM, MIR, VPA, CBZ, LTG, LTM, OLZ, or CLZ induced significant increases in HDAC3 in the Cg, and ECM, DLX, MIR, VPA, CBZ, LTG, LTM, or OLZ resulted in significant increases in HDAC5 in the Amy. Collectively, the changes of monoamine content were restricted for mood stabilizer effects, but increased expression of HDAC2, HDAC3, or HDAC5 in the ST, Cg, or Amy was often found, supporting the possibility that antidepressant-like effects involve epigenetic modifications associated with changes in HDAC expression.

Behavioural and neurochemical changes induced by stress-related conditions are counteracted by the neurokinin-2 receptor antagonist saredutant

These experiments were undertaken to assess the mechanisms underlying the antidepressant-like effects of the neurokinin-2 (NK(2)) receptor antagonist saredutant (SR48968) in rats tested in the forced swim test (FST), by analysing hippocampal brain-derived neurotrophic factor (BDNF) and plasma corticosterone [as index of hypothalamic-pituitary-adrenal (HPA) axis activity]. Male Wistar rats received three intraperitoneal injections over 24 h of vehicle, saredutant (5 mg/kg), citalopram (15 mg/kg), clomipramine (50 mg/kg). Rats were subjected to restraint stress (4 h) 24 h prior to the FST procedure. This stress procedure increased immobility and decreased swimming behaviour in the FST; furthermore, it lowered hippocampal BDNF protein expression and increased plasma corticosterone levels. Saredutant and clomipramine or citalopram, used here as positive controls, reduced the immobility time in the FST both under basal conditions and after stress exposure. This effect was not attributable to changes in locomotion, because locomotor activity was unchanged when assessed in the open field test. Pretreatment with para-cholorophenylalanine (150 mg/kg, 72 h and 48 h prior to FST) abolished the effect of citalopram and saredutant on immobility time. At neurochemical level, saredutant attenuated activation of HPA axis in stressed animals more than clomipramine or citalopram. The behavioural effects of saredutant support the hypothesis that NK(2) receptor activity is involved in stress-related disorders. These effects of saredutant may be related to normalization of the HPA axis. Moreover, saredutant increases BDNF expression in the hippocampus, confirming the role of NK(2) receptor blockade in BDNF activation following stressor application.

Involvement of serotonin receptor subtypes in the antidepressant-like effect of beta receptor agonist Amibegron (SR 58611A): an experimental study

New therapeutic strategies against depression, with less side effects and thus greater efficacy in larger proportion of depressed patients, are needed. Amibegron (SR58611A) is the first selective β3 adrenergic agent that has been shown to possess a profile of antidepressant activity in rodents. To investigate the involvement of serotonin receptors in the effects of amibegron, we used the serotonin 5HT1A receptor antagonist WAY-100635 (WAY) or serotonin 5HT2A-2C receptor antagonist ketanserin or serotonin 5HT3 receptor antagonist ondansetron in mice forced swimming test (FST). The locomotor activity was evaluated by measuring the total distance moved in the apparatus and the speed of the animals in the open field test. Imipramine (30mg/kg) significantly reduced immobility time compared to vehicle-treated group while amibegron (5 and 10mg/kg) dose dependently reduced immobility time in the FST. WAY(0.1mg/kg), ondansetron (1mg/kg), ketanserin(5mg/kg) had no effect on immobility time in naive mice while all of the drugs partially and significantly reversed amibegron (10mg/kg) induced decreasement in the immobility time in FST. None of the drugs alter locomotor activity in the open field test. The antidepressant-like effect of amibegron in the FST seems to be mediated by an interaction with serotonin 5-HT1A, serotonin 5-HT2A-2C and serotonin 5-HT3 receptors.

Neurotransmissions of antidepressant-like effects of kisspeptin-13

Kisspeptins are G protein-coupled receptor ligands originally identified as human metastasis suppressor gene products that have the ability to suppress melanoma and breast cancer metastasis and which have recently been found to play an important role in initiating the secretion of gonadotropin-releasing hormone at puberty. In the brain, the gene is transcribed within the hippocampal dentate gyrus. Kisspeptin-13, one of the endogenous isoforms, consists of 13 amino acids. In this work, antidepressant-like effects of kisspeptin-13 were studied and the potential involvement of the adrenergic, serotonergic, cholinergic, dopaminergic and gabaergic receptors in its antidepressant-like effects was investigated in a modified forced swimming test (FST) in mice. The mice were pretreated with a nonselective α-adrenergic receptor antagonist, phenoxybenzamine, an α(1)/α(2β)-adrenergic receptor antagonist, prazosin, an α(2)-adrenergic receptor antagonist, yohimbine, a β-adrenergic receptor antagonist, propranolol, a mixed 5-HT(1)/5-HT(2) serotonergic receptor antagonist, methysergide, a nonselective 5-HT(2) serotonergic receptor antagonist, cyproheptadine, a nonselective muscarinic acetylcholine receptor antagonist, atropine, a D(2),D(3),D(4) dopamine receptor antagonist, haloperidol, or a γ-aminobutyric acid subunit A receptor antagonist, bicuculline. The FST revealed that kisspeptin-13 reversed the immobility, climbing and swimming times, suggesting antidepressant-like effects. Phenoxybenzamine, yohimbine and cyproheptadine prevented the effects of kisspeptin-13 on the immobility, climbing and swimming times, whereas prazosin, propranolol, methysergide, atropine, haloperidol and bicuculline did not modify the effects of kisspeptin-13. The results demonstrated that the antidepressant-like effects of kisspeptin-13 in a modified mouse FST are mediated, at least in part, by an interaction of the α(2)-adrenergic and 5-HT(2) serotonergic receptors.

Toxicological effects of a mixture used in weight loss products: p-synephrine associated with ephedrine, salicin, and caffeine

p-Synephrine is an adrenergic amine found in Citrus aurantium L. fruits and has been used for weight loss in dietary supplements. There are commercial products containing this substance associated to caffeine, salicin, and ephedrine. The aim of this study was to evaluate the acute toxicity of this mixture in mice of both sexes. The significative results observed after acute oral administration to male and female mice of 300, 350, and 400 mg/kg total of p-synephrine, ephedrine, salicin, plus caffeine in a 10:4:6:80 w/w ratio included a reduction in locomotor activity and ptosis in all treated groups for both sexes. Seizures were also observed in male (400 mg/kg) and female groups (350 and 400 mg/kg). Gasping and tearing were observed in males. Salivation (400 mg/kg), agitation (350 and 400 mg/kg), and piloerection (all treated groups) were significantly observed only in females. Deaths occurred in males at 350 and 400 mg/kg treated groups and the necropsy showed cardiopulmonary hemorrhage. A reduction in locomotor activity was confirmed through the spontaneous locomotor activity test, in which the number of crossings considerably decreased (P < .01) in all treated groups. The rotarod test showed a decrease in motor coordination at 400 mg/kg. Body temperature decreased significantly (P < .01) in all treated groups compared to controls. The results suggested clear signs of toxicity of p-synephrine, ephedrine, salicin, and caffeine association; this toxicity augments the attentiveness on commercial products containing this mixture, given the expressive number of adverse events related to its utilization.

Neurotransmission of the antidepressant-like effects of the growth hormone-releasing hormone antagonist MZ-4-71

MZ-4-71 is an antagonist of growth hormone-releasing hormone (GH-RH) which suppresses the secretion of GH-RH. It has been shown that MZ-4-71 has antidepressive-like effects in a modified forced swimming test (FST) in mice, exerts anxiolytic effects in an elevated plus maze test, improves memory consolidation in passive avoidance learning, and corrects the impairment of memory consolidation caused by β-amyloid 25-35 in mice. However, little is known about the mechanisms of action of MZ-4-71 on brain functions. The involvement of the adrenergic, serotonergic, cholinergic, dopaminergic or GABA-ergic receptors in the antidepressant-like action of MZ-4-71 (1.0 μg/2 μl, intracerebroventricular (i.c.v.)) was studied in a modified mouse forced swimming test (FST). Mice were pretreated with a non-selective α-adrenergic receptor antagonist, phenoxybenzamine, an α1/α2β-adrenergic receptor antagonist prazosin, an α2-adrenergic receptor antagonist, yohimbine, a β-adrenergic receptor antagonist, propranolol, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist methysergide, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a non-selective muscarinic acetylcholine receptor antagonist, atropine, a D2, D3, D4 dopamine receptor antagonist, haloperidol or a γ-aminobutyric acid subunit A (GABA-A) receptor antagonist bicuculline. Phenoxybenzamine, prazosin, methysergide, cyproheptadine and atropine prevented the effects of MZ-4-71 on the immobility, the climbing and the swimming times. Yohimbine, propranolol, haloperidol and bicuculline did not change the effects of MZ-4-71. The results demonstrated that the antidepressant-like effects of MZ-4-71 in this modified mouse FST are mediated, at least in part, by the an interaction of the α1-adrenergic, 5-HT1/5-HT2 serotonergic, and muscarinic acetylcholine receptors.

SR59230A, a beta-3 adrenoceptor antagonist, inhibits ultradian brown adipose tissue thermogenesis and interrupts associated episodic brain and body heating

Brown adipose tissue (BAT) thermogenesis occurs episodically in an ultradian manner approximately every 80-100 min during the waking phase of the circadian cycle, together with highly correlated increases in brain and body temperatures, suggesting that BAT thermogenesis contributes to brain and body temperature increases. We investigated this in conscious Sprague-Dawley rats by determining whether inhibition of BAT thermogenesis via blockade of beta-3 adrenoceptors with SR59230A interrupts ultradian episodic increases in brain and body temperatures and whether SR59230A acts on BAT itself or via sympathetic neural control of BAT. Interscapular BAT (iBAT), brain, and body temperatures, tail artery blood flow, and heart rate were measured in unrestrained rats. SR59230A (1, 5, or 10 mg/kg ip), but not vehicle, decreased iBAT, body, and brain temperatures in a dose-dependent fashion (log-linear regression P < 0.01, R(2) = 0.3, 0.4, and 0.4, respectively, n = 10). Ultradian increases in BAT, brain, and body temperature were interrupted by administration of SR59230A (10 mg/kg ip) compared with vehicle, resuming after 162 ± 24 min (means ± SE, n = 10). SR59230A (10 mg/kg ip) caused a transient bradycardia without any increase in tail artery blood flow. In anesthetized rats, SR59230A reduced cooling-induced increases in iBAT temperature without affecting cooling-induced increases in iBAT sympathetic nerve discharge. Inhibition of BAT thermogenesis by SR59230A, thus, reflects direct blockade of beta-3 adrenoceptors in BAT. Interruption of episodic ultradian increases in body and brain temperature by SR59230A suggests that BAT thermogenesis makes a substantial contribution to these increases.

Co-administration of subeffective anxiolytic doses of diazepam and hydroxyzine in elevated zero-maze in mice

OBJECTIVE

Benzodiazepines are from the most common drugs which are used for treatment of anxiety disorders. There are other drugs with antianxiety properties including antihistamines such as hydroxyzine, too. Body of evidence show that co-administration of two drugs which act through different mechanisms, makes the dose of each drug to be reduced, while preserving the desired effect with less adverse drug reactions. The aim of this study was to see whether co-administration of subeffective antianxiety doses of diazepam and hydroxyzine has any antianxiety effect in elevated zero-maze (EZM) in mice.

METHODS

To find the highest subeffective dose of each drug, different doses of hydroxyzine from 1.5 to 24 mg/kg and diazepam in doses of 0.25, 0.5 and 1 mg/kg were injected to male mice. Thirty minutes later, the animals were placed on EZM and various parameters of anxiety were recorded by a camera to assess later. After determination of subeffective antianxiety dose of the drugs, co-administration of hydroxyzine and diazepam was done and the anxiety parameters were measured.

RESULTS

In co-administration of 0.25 mg/kg of diazepam and 12 mg/kg hydroxyzine, as subeffective antianxiety doses of either drug, there were not any significant differences in main anxiety parameters, i.e., time spent in open areas and open area entries compared to control group. Hence, no anxiolytic effect was seen.

CONCLUSION

It seems that subeffective doses of diazepam and hydroxyzine may not have any facilitating or synergistic effect on each other in antianxiety responses in mice.

The beta3 adrenoceptor agonist, amibegron (SR58611A) counteracts stress-induced behavioral and neurochemical changes

These experiments were made to study the mechanisms underlying the antidepressant-like effects of the beta(3) adrenoceptor agonist amibegron (SR58611A). To this purpose, the expression levels of the hippocampal cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl-2) and Bax proteins were assessed, by using western blot analysis, in rats tested in the forced swim test (FST). Under basal conditions (no previous exposure to stressors), different groups of male Wistar rats received acutely or repeatedly (once/day for 7days) intraperitoneal (i.p.) injections of amibegron (1, 5 and 10mg/kg), the tricyclic antidepressant (TCA) clomipramine (50mg/kg), the selective serotonin reuptake inhibitor (SSRI) citalopram (15mg/kg) or their vehicles. The influence of stress-related conditions was studied in rats subjected to acute (4h) or repeated (4h/day for 7days) restraint stress, applied prior to the FST procedure. Compared to the control groups, both stressor procedures increased the immobility time in the FST and reduced hippocampal BDNF and Bcl-2/Bax ratio proteins expression, which were counteracted by amibegron (5 and 10mg/kg) treatment. Opposite effects were found in the CREB expression, since it was lower after acute and higher after repeated stress procedure, respectively. Again, these effects were reversed by amibegron treatment. Different results were obtained in animals treated with clomipramine or citalopram. Hence, it is likely that the observed behavioral effects of amibegron could be due, at least in part, to its action on hippocampal expression of neurotrophic and/or anti-apoptotic factors, supporting the hypothesis that beta(3) adrenoceptors may be a therapeutic target for the treatment of stress-related disorders.

Lateral paracapsular GABAergic synapses in the basolateral amygdala contribute to the anxiolytic effects of beta 3 adrenoceptor activation

Norepinephrine (NE) is known to play an integral role in the neurobiological response to stress. Exposure to stressful stimuli increases NE levels in brain regions that regulate stress and anxiety, like the basolateral amygdala (BLA). NE is thought to increase excitability in these areas through alpha- and beta-adrenoceptors (ARs), leading to increased anxiety. Surprisingly, recent studies have shown that systemic beta 3-AR agonist administration decreases anxiety-like behaviors, suggesting that beta 3-ARs may inhibit excitability in anxiety-related brain regions. Therefore, in this study we integrated electrophysiological and behavioral approaches to test the hypothesis that the anxiolytic effects of beta 3-AR agonists may be mediated by an increase in BLA GABAergic inhibition. We examined the effect of a selective beta 3-AR agonist, BRL37344 (BRL), on GABAergic synapses arising from local circuit interneurons and inhibitory synapses originating from a recently described population of cells called lateral paracapsular (LPCS) interneurons. Surprisingly, BRL selectively enhanced LPCS-evoked inhibitory postsynaptic currents (eIPSCs) with no effect on local GABAergic inhibition. BRL also had no effect on glutamatergic synaptic excitation within the BLA. BRL potentiation of LPCS eIPSCs was blocked by the selective beta 3-AR antagonist, SR59230A, or by intracellular dialysis of Rp-CAMPS (cAMP-dependent protein kinase inhibitor), and this enhancement was not associated with any changes in spontaneous IPSCs or LPCS paired-pulse ratio. BRL also increased the amplitude of unitary LPCS IPSCs (uIPSCs) with no effect on uIPSC failure rate. Finally, bilateral BLA microinjection of BRL reduced anxiety-like behaviors in an open-field assay and the elevated plus-maze. Collectively, these data suggest that beta 3-AR activation selectively enhances LPCS, but not local, BLA GABAergic synapses, and that increases in LPCS-mediated inhibition may contribute to the anxiolytic profile of beta 3-AR agonists.

Norepinephrine directly activates adult hippocampal precursors via beta3-adrenergic receptors

Adult hippocampal neurogenesis is a critical form of cellular plasticity that is greatly influenced by neural activity. Among the neurotransmitters that are widely implicated in regulating this process are serotonin and norepinephrine, levels of which are modulated by stress, depression and clinical antidepressants. However, studies to date have failed to address a direct role for either neurotransmitter in regulating hippocampal precursor activity. Here we show that norepinephrine but not serotonin directly activates self-renewing and multipotent neural precursors, including stem cells, from the hippocampus of adult mice. Mechanistically, we provide evidence that beta(3)-adrenergic receptors, which are preferentially expressed on a Hes5-expressing precursor population in the subgranular zone (SGZ), mediate this norepinephrine-dependent activation. Moreover, intrahippocampal injection of a selective beta(3)-adrenergic receptor agonist in vivo increases the number of proliferating cells in the SGZ. Similarly, systemic injection of the beta-adrenergic receptor agonist isoproterenol not only results in enhancement of proliferation in the SGZ but also leads to an increase in the percentage of nestin/glial fibrillary acidic protein double-positive neural precursors in vivo. Finally, using a novel ex vivo "slice-sphere" assay that maintains an intact neurogenic niche, we demonstrate that antidepressants that selectively block the reuptake of norepinephrine, but not serotonin, robustly increase hippocampal precursor activity via beta-adrenergic receptors. These findings suggest that the activation of neurogenic precursors and stem cells via beta(3)-adrenergic receptors could be a potent mechanism to increase neuronal production, providing a putative target for the development of novel antidepressants.

Beta 3-adrenoreceptor regulation of nitric oxide in the cardiovascular system

The presence of a third beta-adrenergic receptor (beta 3-AR) in the cardiovascular system has challenged the classical paradigm of sympathetic regulation by beta1- and beta2-adrenergic receptors. While beta 3-AR's role in the cardiovascular system remains controversial, increasing evidence suggests that it serves as a "brake" in sympathetic overstimulation - it is activated at high catecholamine concentrations, producing a negative inotropic effect that antagonizes beta1- and beta2-AR activity. The anti-adrenergic effects induced by beta 3-AR were initially linked to nitric oxide (NO) release via endothelial NO synthase (eNOS), although more recently it has been shown under some conditions to increase NO production in the cardiovascular system via the other two NOS isoforms, namely inducible NOS (iNOS) and neuronal NOS (nNOS). We summarize recent findings regarding beta 3-AR effects on the cardiovascular system and explore its prospective as a therapeutic target, particularly focusing on its emerging role as an important mediator of NO signaling in the pathogenesis of cardiovascular disorders.

Effects of lactational exposure to benzo[alpha]pyrene (B[alpha]P) on postnatal neurodevelopment, neuronal receptor gene expression and behaviour in mice

The harmful effects of exposure to benzo[alpha]pyrene (B[alpha]P), which is a neurotoxic pollutant, on mammalian neurodevelopment and/or behaviour as yet remain widely unclear. In the present investigation, we evaluated the impact of the lactational exposure to B[alpha]P on postnatal development of pups and behaviour of young mice. The neurobiological effects of B[alpha]P during lactation were also evaluated on pups' brain. Here, we found that lactational exposure to B[alpha]P at 2 and 20mg/kg affects the neuromaturation of pups by significantly decreasing their reflex as highlighted in surface righting reflex and negative geotaxis tests. However, we noted a significant increase in muscular strength of lactationally B[alpha]P mg/kg-exposed pups, which was probably due to the impact of the exposure to this toxic compound on body weight gain. At the pup stage, lactational exposure to B[alpha]P also provoked a neurobiological change, which was assessed by determination of neuronal receptor gene expression. Indeed, a significant reduction in gene expression of 5HT(1A) receptors in pups exposed to B[alpha]P through lactation was found in comparison to controls. Additionally, attenuation in the expression of MOR(1) mRNA was observed, but statistically significant only in animals receiving the higher dose. Neither the expression levels of ADRA(1D) nor GABA(A) mRNA were altered. Interestingly, the harmful effects of lactational exposure to B[alpha]P on behaviour and cognitive function were still found despite a long post-weaning period. Young mice whose mothers were exposed to B[alpha]P displayed a disinhibition behaviour towards the aversive spaces of the elevated plus maze. Furthermore, a significant increase of spontaneous alternation in the Y-maze was observed, but only in young mice whose mothers were orally exposed to the lower dose of B[alpha]P. Our results suggest a close link between the neurobiological change highlighted in pups' brain and the different behavioural disturbances observed during postnatal development period until young adult stage.

Anxiolytic effects in mice of a dual blocker of fatty acid amide hydrolase and transient receptor potential vanilloid type-1 channels

The endocannabinoid-inactivating enzyme, fatty acid amide hydrolase (FAAH), and the transient receptor potential vanilloid type-1 (TRPV1) channel are new targets for the development of anxiolytic drugs. We studied the effect on anxiety-like behavior in the elevated plus maze of a dual FAAH/TRPV1 blocker, N-arachidonoyl-serotonin (AA-5-HT). In male C57BL/6J mice, acute intraperitoneal administration of AA-5-HT (0.1-2.5 mg/kg) increased both the time spent and the number of entries in the open arm, while being inactive at the highest dose tested (5 mg/kg). AA-5-HT was more potent than selective blockers of FAAH or TRPV1 (URB597 and SB366791, respectively). In male Swiss mice, AA-5-HT had to be administered chronically to observe an anxiolytic effect at an intermediate dose (2.5 mg/kg), the highest dose (5 mg/kg) being anxiogenic, and 1 mg/kg being ineffective. In both strains, the anxiolytic effects of AA-5-HT were paralleled by elevation of brain endocannabinoid levels and were reversed by per se inactive doses of the cannabinoid receptors of type-1 (CB(1)) receptor antagonist AM251, or the TRPV1 agonist, olvanil. Immunohistochemical localization of CB(1) and TRPV1 receptors was observed in mouse prefrontal cortex, nucleus accumbens, amygdala, and hippocampus. Simultaneous 'indirect' activation of CB(1) receptors following FAAH inhibition, and antagonism at TRPV1 receptors might represent a new therapeutic strategy against anxiety.

Evaluation of anxiolytic-like effects of some short-acting benzodiazepine hypnotics in mice

Anxiolytic-like effects of some short-acting benzodiazepine hypnotics were examined with experimental paradigms of anxiety using an elevated plus-maze in male ICR mice. Diazepam was used as a positive control. The drug at a dose of 1 mg/kg significantly increased the percentage of time spent in the open arms and percentage of the number of open arm entries in the elevated plus-maze. Triazolam, brotizolam, rilmazafone, and lormetazepam also showed an anxiolytic-like effect as indicated by the significant increase in the percentage of time spent in the open arms and percentage of the number of open arm entries. Effects of short-acting benzodiazepine hypnotics used in the study were more potent than those of diazepam. In addition, the doses affecting the elevated plus-maze by benzodiazepine hypnotics were much smaller than those that showed muscle-relaxant activity measured by the rotarod test, indicating that anxiolytic-like effects of benzodiazepine hypnotics had high specificity and selectivity.

Concentrations of p-synephrine in fruits and leaves of Citrus species (Rutaceae) and the acute toxicity testing of Citrus aurantium extract and p-synephrine

Dietary supplements containing bitter orange unripe fruit extract/p-synephrine are consumed worldwide for lose weight. This study were conducted to determine the concentration of p-synephrine in unripe fruits and leaves from Citrus aurantium Lin, C. sinensis Osbeck, C. deliciosa Ten, C. limon Burm and C. limonia Osbeck, collected in Southern Brazil, and to evaluate the acute toxicity of C. aurantium extract and p-synephrine. A high performance liquid chromatographic method with diode array detector (HPLC-DAD) was optimized and validated for determination of p-synephrine. The results indicate that all of analyzed samples present p-synephrine in amounts that range from 0.012% to 0.099% in the unripe fruits and 0.029 to 0.438% in the leaves. Acute oral administration of C. aurantium extracts (2.5% p-synephrine, 300-5,000 mg/kg) in mice produced reduction of locomotor activity, p-synephrine (150-2,000 mg/kg) produced piloerection, gasping, salivation, exophtalmia and reduction in locomotor activity, which was confirmed in spontaneous locomotor activity test. All the effects were reversible and persisted for 3-4h. The toxic effects observed seem to be related with adrenergic stimulation and should alert for possible side effects of p-synephrine and C. aurantium.

Confirmation of antidepressant potential of the selective beta3 adrenoceptor agonist amibegron in an animal model of depression

The involvement of the noradrenergic system, particularly the beta1 and beta2 receptors, in depressive disorders has been frequently shown. Recently, however, it has been shown that the beta3 receptor may also contribute since amibegron (SR58611A), a selective beta3 receptor agonist, has antidepressant-like effects. The present experiment sought to confirm the antidepressant potential of amibegron by studying its effects in an animal model of depression, the Flinders Sensitive Line (FSL) rat. The FSL rat is innately highly immobile in the forced swim test and exhibits a decrease in immobility after chronic, not acute antidepressant treatment. FSL rats were treated for 14 consecutive days with amibegron (0.3, 1.0, or 3.0 mg/kg), fluoxetine (5 mg/kg) or desipramine (5 mg/kg) as positive controls, and vehicle, while the control strain, the Flinders Resistant Line (FRL) rats, was given either vehicle or 1.0 mg/kg amibegron. About 23-25 h after the last injection the rats were tested in the forced swim test. All doses of amibegron and the two active controls, fluoxetine and desipramine, significantly reduced immobility in the FSL rats. Thus, amibegron had a selective antidepressant-like effect in this study, confirming its antidepressant potential.