Implication of 5-HT2A subtype receptors in DOI activity in the four-plates test-retest paradigm in mice

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic- and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice 24 h post-treatment. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than anxiolytic effects.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT 2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic-and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice 24 h post-treatment. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than an anxiolytic effects.

Effects of a psychedelic 5-HT2A receptor agonist on anxiety-related behavior and fear processing in mice

Psychedelic-assisted psychotherapy gained considerable interest as a novel treatment strategy for fear-related mental disorders but the underlying mechanism remains poorly understood. The serotonin 2A (5-HT2A) receptor is a key target underlying the effects of psychedelics on emotional arousal but its role in fear processing remains controversial. Using the psychedelic 5-HT2A/5-HT2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) and 5-HT2A receptor knockout (KO) mice we investigated the effect of 5-HT2A receptor activation on emotional processing. We show that DOI administration did not impair performance in a spontaneous alternation task but reduced anxiety-like avoidance behavior in the elevated plus maze and elevated zero maze tasks. Moreover, we found that DOI did not block memory recall but diminished fear expression in a passive avoidance task. Likewise, DOI administration reduced fear expression in an auditory fear conditioning paradigm, while it did not affect retention of fear extinction when administered prior to extinction learning. The effect of DOI on fear expression was abolished in 5-HT2A receptor KO mice. Administration of DOI induced a significant increase of c-Fos expression in specific amygdalar nuclei. Moreover, local infusion of the 5-HT2A receptor antagonist M100907 into the amygdala reversed the effect of systemic administration of DOI on fear expression while local administration of DOI into the amygdala was sufficient to suppress fear expression. Our data demonstrate that activation of 5-HT2A receptors in the amygdala suppresses fear expression but provide no evidence for an effect on retention of fear extinction.

Psilocybin for End-of-Life Anxiety Symptoms: A Systematic Review and Meta-Analysis

OBJECTIVE

To systematically examine the effectiveness and tolerability of psilocybin for treating end-of-life anxiety symptoms.

METHODS

The Medline, Embase, CENTRAL, and PsycINFO databases were searched up to November 25, 2020. We enrolled clinical trials investigating psilocybin for treating end-of-life anxiety symptoms. Meta-analysis was conducted using random-effects model.

RESULTS

Overall, five studies were included, revealing that psilocybin was superior to the placebo in treating state anxiety at 1 day (Hedges' g, -0.70; 95% confidence interval, -1.01 to -0.39) and 2 weeks (-1.03; -1.47 to -0.60) after treatment. Psilocybin was more effective than placebo in treating trait anxiety at 1 day (-0.71; -1.15 to -0.26), 2 weeks (-1.08; -1.80 to -0.36), and 6 months (-0.84; -1.37 to -0.30) after treatment. Psilocybin was associated with transient elevation in systolic (19.00; 13.58-24.41 mm Hg) and diastolic (8.66; 5.18-12.15 mm Hg) blood pressure compared with placebo. The differences between psilocybin and placebo groups with regard to allcause discontinuation, serious adverse events, and heart rates were nonsignificant.

CONCLUSION

Psilocybin-assisted therapy could ameliorate end-of-life anxiety symptoms without serious adverse events. Because of the small sample sizes of the included studies and high heterogeneity on long-term outcomes, future randomized controlled trials with large sample sizes are needed.

The Chronic Treatment With 5-HT2A Receptor Agonists Affects the Behavior and the BDNF System in Mice

Serotonin 5-HT2A receptors and the brain-derived neurotrophic factor (BDNF) are involved in the pathophysiology and treatment of many psychiatric diseases. However, the interaction between 5-HT2A and BDNF is still poorly understood. In the present paper, the effects of chronic treatment with mixed 5-HT2A/2C receptor agonist DOI, highly selective 5-HT2A agonists TCB-2 and 25CN-NBOH on behavior and the BDNF system have been investigated. Chronic treatment of males of C57Bl/6 mice with DOI, TCB-2 and 25CN-NBOH (1 mg/kg, i.p., 14 days) resulted in desensitization of 5-HT2A receptors. Treatment with 25CN-NBOH significantly increased startle amplitude. At the same time all used drugs failed to affect anxiety, exploratory and stereotyped behavior as well as spatial memory and learning. TCB-2 and 25CN-NBOH increased the BDNF mRNA level. All 5-HT2A agonists increased the proBDNF level but failed to alter the mature BDNF protein level. TrkB and p75NTR mRNA levels were affected by all utilized agonists. All drugs decreased the total level as well as membrane TrkB protein one indicating downregulation of TrkB receptors. All agonists decreased the membrane p75NTR protein level. Thus, we have shown for the first time that the chronic activation of the 5-HT2A receptor with agonists has affected the BDNF system almost on all levels-transcription, proBDNF production, TrkB and p75NTR receptors' level. The obtained data suggested possible suppression in BDNF-TrkB signaling under chronic treatment with 5-HT2A agonists.

The 5-hydroxytryptamine 2A receptor agonists DOI and 25CN-NBOH decrease marble burying and reverse 8-OH-DPAT-induced deficit in spontaneous alternation

5-Hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelics are increasingly recognized as potentially useful treatments of psychiatric disorders, such as obsessive-compulsive disorder, depression, anxiety, and drug dependence. There is limited understanding of the way they exert their therapeutic action, but inhibition of rigid behavior and cognition has been suggested as a key factor. To examine the role of 5-HT_2ARs in modulating repetitive behavior, we tested two 5-HT_2AR agonists, DOI, and the selective 25CN-NBOH, in two mouse tests of compulsive-like behavior. Using adult C57BL/6JOlaHsd male mice, we examined the effects of the two compounds on digging behavior in the marble burying test and on 8-OH-DPAT-disrupted spontaneous alternation behavior in the Y-maze. Both compounds dose-dependently decreased digging behavior in the marble burying test, indicating anti-compulsivity effects, which were not related to non-specific locomotor inhibition. Both 5-HT_2AR agonists also reversed 8-OH-DPAT-reduced alternation ratio in the spontaneous alternation behavior test, although the effects were less pronounced than in the marble burying test. This suggests that the 5-HT_2AR promotes exploratory behavior, but that the deficit produced by 8-OH-DPAT is too excessive to be fully reversed by 5-HT_2AR agonists. This study shows that agonism of 5-HT_2AR reduces repetitive behavioral patterns, supporting the theory that this is a potential new treatment approach to disorders of cognitive or behavioral inflexibility. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Behavioral Effects of Systemic, Infralimbic and Prelimbic Injections of a Serotonin 5-HT2A Antagonist in Carioca High- and Low-Conditioned Freezing Rats

The role of serotonin (5-hydroxytryptamine [5-HT]) and 5-HT2A receptors in anxiety has been extensively studied, mostly without considering individual differences in trait anxiety. Our laboratory developed two lines of animals that are bred for high and low freezing responses to contextual cues that are previously associated with footshock (Carioca High-conditioned Freezing [CHF] and Carioca Low-conditioned Freezing [CLF]). The present study investigated whether ketanserin, a preferential 5-HT2A receptor blocker, exerts distinct anxiety-like profiles in these two lines of animals. In the first experiment, the animals received a systemic injection of ketanserin and were exposed to the elevated plus maze (EPM). In the second experiment, these two lines of animals received microinjections of ketanserin in the infralimbic (IL) and prelimbic (PL) cortices and were exposed to either the EPM or a contextual fear conditioning paradigm. The two rat lines exhibited bidirectional effects on anxiety-like behavior in the EPM and opposite responses to ketanserin. Both systemic and intra-IL cortex injections of ketanserin exerted anxiolytic-like effects in CHF rats but anxiogenic-like effects in CLF rats. Microinjections of ketanserin in the PL cortex also exerted anxiolytic-like effects in CHF rats but had no effect in CLF rats. These results suggest that the behavioral effects of 5-HT2A receptor antagonism might depend on genetic variability associated with baseline reactions to threatening situations and 5-HT2A receptor expression in the IL and PL cortices. Highlights -CHF and CLF rats are two bidirectional lines that are based on contextual fear conditioning.-CHF rats have a more "anxious" phenotype than CLF rats in the EPM.-The 5-HT2A receptor antagonist ketanserin had opposite behavioral effects in CHF and CLF rats.-Systemic and IL injections either decreased (CHF) or increased (CLF) anxiety-like behavior.-PL injections either decreased (CHF) anxiety-like behavior or had no effect (CLF).

Phf8 loss confers resistance to depression-like and anxiety-like behaviors in mice

PHF8 is a histone demethylase with specificity for repressive modifications. While mutations of PHF8 have been associated with cognitive defects and cleft lip/palate, its role in mammalian development and physiology remains unexplored. Here, we have generated a Phf8 knockout allele in mice to examine the consequences of Phf8 loss for development and behaviour. Phf8 deficient mice neither display obvious developmental defects nor signs of cognitive impairment. However, we report a striking resiliency to stress-induced anxiety- and depression-like behaviour on loss of Phf8. We further observe misregulation of serotonin signalling within the prefrontal cortex of Phf8 deficient mice and identify the serotonin receptors Htr1a and Htr2a as direct targets of PHF8. Our results clarify the functional role of Phf8 in mammalian development and behaviour and establish a direct link between Phf8 expression and serotonin signalling, identifying this histone demethylase as a potential target for the treatment of anxiety and depression.

5-HT2A Agonists: A Novel Therapy for Functional Neurological Disorders?

Functional neurological disorders are frequently encountered in clinical practice. They have a poor prognosis and treatment options are limited. Their etiology is unknown, but leading theories propose a disturbance of somatic self-representation: the mind perceives dysfunction of a body region despite intact motor and sensory pathways. Central to this model is the concept of an abnormal top-down cognitive influence upon sensorimotor function. There is growing interest in the use of 5-HT2A agonists in the management of neuropsychiatric conditions. Recent studies have shown that these agents induce changes in neural activity that disrupt hierarchical brain dynamics and modulate networks subserving self-related processing. Converging evidence suggests they may hold unique therapeutic potential in functional neurological disorders. This is of importance given the considerable personal and societal burden of this condition and we argue a clinical trial to test this hypothesis is warranted.

Rapid and sustained symptom reduction following psilocybin treatment for anxiety and depression in patients with life-threatening cancer: a randomized controlled trial

BACKGROUND

Clinically significant anxiety and depression are common in patients with cancer, and are associated with poor psychiatric and medical outcomes. Historical and recent research suggests a role for psilocybin to treat cancer-related anxiety and depression.

METHODS

In this double-blind, placebo-controlled, crossover trial, 29 patients with cancer-related anxiety and depression were randomly assigned and received treatment with single-dose psilocybin (0.3 mg/kg) or niacin, both in conjunction with psychotherapy. The primary outcomes were anxiety and depression assessed between groups prior to the crossover at 7 weeks.

RESULTS

Prior to the crossover, psilocybin produced immediate, substantial, and sustained improvements in anxiety and depression and led to decreases in cancer-related demoralization and hopelessness, improved spiritual wellbeing, and increased quality of life. At the 6.5-month follow-up, psilocybin was associated with enduring anxiolytic and anti-depressant effects (approximately 60-80% of participants continued with clinically significant reductions in depression or anxiety), sustained benefits in existential distress and quality of life, as well as improved attitudes towards death. The psilocybin-induced mystical experience mediated the therapeutic effect of psilocybin on anxiety and depression.

CONCLUSIONS

In conjunction with psychotherapy, single moderate-dose psilocybin produced rapid, robust and enduring anxiolytic and anti-depressant effects in patients with cancer-related psychological distress.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00957359.

Animal models for screening anxiolytic-like drugs: a perspective

Contemporary biological psychiatry uses experimental animal models to increase our understanding of affective disorder pathogenesis. Modern anxiolytic drug discovery mainly targets specific pathways and molecular determinants within a single phenotypic domain. However, greater understanding of the mechanisms of action is possible through animal models. Primarily developed with rats, animal models in anxiety have been adapted with mixed success for mice, easy-to-use mammals with better genetic possibilities than rats. In this review, we focus on the three most common animal models of anxiety in mice used in the screening of anxiolytics. Both conditioned and unconditioned models are described, in order to represent all types of animal models of anxiety. Behavioral studies require careful attention to variable parameters linked to environment, handling, or paradigms; this is also discussed. Finally, we focus on the consequences of re-exposure to the apparatus. Test-retest procedures can provide new answers, but should be intensively studied in order to revalidate the entire paradigm as an animal model of anxiety.

Psychedelics

Psychedelics (serotonergic hallucinogens) are powerful psychoactive substances that alter perception and mood and affect numerous cognitive processes. They are generally considered physiologically safe and do not lead to dependence or addiction. Their origin predates written history, and they were employed by early cultures in many sociocultural and ritual contexts. After the virtually contemporaneous discovery of (5R,8R)-(+)-lysergic acid-N,N-diethylamide (LSD)-25 and the identification of serotonin in the brain, early research focused intensively on the possibility that LSD and other psychedelics had a serotonergic basis for their action. Today there is a consensus that psychedelics are agonists or partial agonists at brain serotonin 5-hydroxytryptamine 2A receptors, with particular importance on those expressed on apical dendrites of neocortical pyramidal cells in layer V. Several useful rodent models have been developed over the years to help unravel the neurochemical correlates of serotonin 5-hydroxytryptamine 2A receptor activation in the brain, and a variety of imaging techniques have been employed to identify key brain areas that are directly affected by psychedelics. Recent and exciting developments in the field have occurred in clinical research, where several double-blind placebo-controlled phase 2 studies of psilocybin-assisted psychotherapy in patients with cancer-related psychosocial distress have demonstrated unprecedented positive relief of anxiety and depression. Two small pilot studies of psilocybin-assisted psychotherapy also have shown positive benefit in treating both alcohol and nicotine addiction. Recently, blood oxygen level-dependent functional magnetic resonance imaging and magnetoencephalography have been employed for in vivo brain imaging in humans after administration of a psychedelic, and results indicate that intravenously administered psilocybin and LSD produce decreases in oscillatory power in areas of the brain's default mode network.

5-HT2A Receptor Activation Normalizes Exaggerated Fear Behavior in p-Chlorophenylalanine (PCPA)-Treated Rats

Deficits in serotonin (5-hydroxytryptamine, 5-HT) neurotransmission are implicated in abnormal emotional behaviors such as aggression, anxiety, and depression. However, the specific 5-HT receptor mechanisms involved are not well understood. The role of 5-HT₂ receptors in fear potentiated startle, (FPS) was examined in rats chronically treated with p-chlorophenylalanine (PCPA) to reduce brain 5-HT. PCPA-treated rats show an enhanced magnitude of FPS. Systemic administration of the 5-HT₂ receptor agonist (±)-2,5-Dimethoxy-4-iodoamphetamine hydrochloride (DOI) reduced FPS in both PCPA-treated and saline (SAL)-treated control animals, normalizing the exaggerated fear response in PCPA-treated rats. In both SAL- and PCPA-treated animals, the DOI-induced reduction of learned fear was reversed by the 5-HT₂ antagonist ketanserin, but not by the 5-HT_2B/2C antagonist SB 206553. Together, these findings suggest 5-HT_2A receptors are critical regulators of learned fear, and that 5-HT_2A receptors may be an important pharmacological target to normalize exaggerated learned fear resulting from chronic 5-HT-ergic disruption.

Potential role of cortical 5-HT(2A) receptors in the anxiolytic action of cyamemazine in benzodiazepine withdrawal

The antipsychotic cyamemazine is a potent serotonin 5-HT(2A) receptor (5-HT(2AR)) antagonist. A positron emission tomography (PET) study in human patients showed that therapeutic doses of cyamemazine produced near saturation of 5-HT(2AR) occupancy in the frontal cortex, whereas dopamine D(2) occupancy remained below the level for motor side effects observed with typical antipsychotics. Recently, numerous studies have revealed the involvement of 5-HT(2AR) in the pathophysiology of anxiety and a double-blind, randomized clinical trial showed similar efficacy of cyamemazine and bromazepam in reducing the anxiety associated with benzodiazepine withdrawal. Therefore, we reviewed the above articles about 5-HT(2AR) and anxiety in order to understand better the anxiolytic mechanisms of cyamemazine in benzodiazepine withdrawal. The 5-HT(2AR) is the most abundant serotonin receptor subtype in the cortex. Non-pharmacological studies with antisense oligodeoxynucleotides and genetically modified mice clearly showed that cortical 5-HT(2AR) signaling positively modulates anxiety-like behavior. With a few exceptions, most other studies reviewed here further support this view. Therefore, the anxiolytic efficacy of cyamemazine in benzodiazepine withdrawal can be due to a 5-HT(2AR) antagonistic activity at the cortical level.

Identification of antidepressant-like ingredients in ginseng root (Panax ginseng C.A. Meyer) using a menopausal depressive-like state in female mice: participation of 5-HT2A receptors

RATIONALE

After reports of adverse effects with hormone replacement therapy, such as reproductive and breast cancer and coronary heart disease, much attention has been given to the development of new remedies to alleviate menopausal depression in women, but methods for their preclinical evaluation have not been clarified. We previously developed a procedure to predict the drug effect on the menopausal depressive-like state in female mice.

OBJECTIVES

We attempted to identify psychoactive components from ginseng root, one of the earliest known materials for menopausal disorder, and to clarify the possible mechanism involved.

METHODS

As an index of a depressive-like state, we used the prolongation of immobility time induced by an ovariectomy during the forced swimming test. Chronic treatment with the candidate substance began the day after ovariectomy and continued for 14 days. To examine whether the 5-HT(2A) receptor antagonist ritanserin antagonized the antidepressant-like effect of ginsenoside Rb(1), ritanserin was given as pretreatment 15 min before the daily administration of ginsenoside Rb(1) and the antagonistic effect was compared with ginsenoside Rb(1) alone.

RESULTS

Ginsenoside Rb(1) and compound K were active ingredients that dose-dependently prevented the prolongation of immobility time induced by ovariectomy. Co-administration of ritanserin, a 5-HT(2A)-receptor antagonist, antagonized the effect of ginsenoside Rb(1).

CONCLUSIONS

We suggest that ginsenoside Rb(1) and its metabolite, compound K, are antidepressant-like components of the ginseng root, and that 5-HT(2A) receptors may play an important role in mediating the antidepressant-like effect of ginsenoside Rb(1).

The role of serotonin-2 (5-HT2) and dopamine receptors in the behavioral actions of the 5-HT2A/2C agonist, DOI, and putative 5-HT2C inverse agonist, SR46349B

RATIONALE

Atypical antipsychotic efficacy is often attributed to actions at serotonin-2 (5-HT(2)) and dopamine receptors, indicating a potential benefit of understanding the interplay between these systems. Currently, it is known that 5-HT(2) receptors modulate dopamine release, although the role of specific dopamine receptors in 5-HT(2)-mediated behavior is not well understood.

OBJECTIVES

We examined the role of 5-HT(2A), 5-HT(2C), and dopamine (D1 and D2) receptors in the behavioral response to a 5-HT(2A/2C) agonist (DOI) and 5-HT(2A/2C) antagonist (SR46349B).

MATERIALS AND METHODS

Effects were assessed by measuring rabbit head bobs (previously characterized as 5-HT(2A) receptor-mediated) and body shakes (5-HT(2C)-mediated).

RESULTS

As expected, DOI produced head bobs and body shakes, and these DOI-elicited behaviors were attenuated by the SR46349B pretreatment. Unexpectedly, SR46349B also induced head bobs when administered alone. However, SR46349B-elicited head bobs are distinguishable from those produced by DOI since the 5-HT(2A) antagonist, ketanserin, only attenuated DOI-elicited head bobs. Conversely, 5-HT(2C) ligands (SB242084 and SB206553) inhibited SR46349B but not DOI-induced head bobs. Furthermore, when administered alone, SB206553 (a 5-HT(2C) inverse agonist) produced head bobs, indicating the behavior can be either 5-HT(2A) or 5-HT(2C) mediated. Next, it was revealed that D1 and D2 receptors play a role in DOI-elicited head bobs, but only D1 receptors are required for SR46349B-elicited head bobs.

CONCLUSIONS

5-HT(2A) receptor agonism and 5-HT(2C) inverse agonism produce the same behavior, likely due to similar downstream actions at D1 receptors. Consequently, 5-HT(2C) agonism or D1 agonism may be effective therapies for disorders, such as schizophrenia, currently being treated with 5-HT(2A) antagonists.

Implication of the 5-HT2A and 5-HT2C (but not 5HT1A) receptors located within the periaqueductal gray in the elevated plus-maze test-retest paradigm in mice

A single exposure to the elevated plus-maze test (EPM) increases open arms avoidance and reduces or abolishes the anxiolytic-like effect of benzodiazepines assessed during a second trial, a phenomenon defined as "one-trial tolerance" (OTT). It has been emphasized that the dorsal portion of the midbrain periaqueductal gray (dPAG) plays a role on this enhanced aversion phenomenon in maze-experienced rodents. Given that intra-dPAG injections of a wide range of serotonergic 5-HT(1A), 5-HT(2A) and 5-HT(2C) receptor agonists produce anxiolytic-like effects in maze-naïve rodents, the present study examined the effects of the 5-HT(1A) receptor agonist 8-OH-DPAT (5.6 and 10.0nmol in 0.15microl) the preferential 5-HT(2A) receptor agonist DOI (2.0 and 8.0nmol in 0.1microl) and the preferential 5-HT(2C) receptor agonist MK-212 (21.2 and 63.6nmol in 0.1microl) microinjected into the dPAG prior to Trial 1 and Trial 2 on the behaviour of mice in the EPM. Test sessions were recorded and subsequently scored for anxiety-like behaviour (percentage of open arms entries and time) as well as general locomotor activity (closed arm entries). The results showed a lack of 8-OH-DPAT (5.6 and 10.0nmol) effect on the behaviour of maze-naïve and maze-experienced mice, while intra-dPAG microinfusions of DOI (8nmol) reduced anxiety-like behaviour only in maze-experienced mice that had received a similar treatment prior to Trial 1. Furthermore, intra-dPAG MK-212 (63.6nmol) showed an anxiolytic-like effect on both Trial 1 and Trial 2. Importantly, these effects were observed in the absence of any significant change in closed arm entries, the parameter considered to be a valid index of locomotor activity in the plus-maze. These results support the dPAG as a crucial structure involved in the neurobiology of the OTT phenomenon as well as accounting the role of the 5-HT(2A) and 5-HT(2C) receptors located within this midbrain structure on the emotional state induced by EPM test and retest paradigm mice.

The role of 5-HT2A and 5-HT2C receptors in the signal attenuation rat model of obsessive-compulsive disorder

Serotonin 5-HT2A and 5-HT2C receptors have been implicated in the pathophysiology of obsessive-compulsive disorder (OCD) and in the mechanism mediating the anti-compulsive effects of serotonin reuptake inhibitors. Yet it is currently unclear whether activation or blockade of these receptors would have an anti-compulsive effect. The present study tested the effects of 5-HT2A and 5-HT2C activation and blockade in the signal attenuation rat model of OCD. In this model, 'compulsive' behaviour is induced by attenuating a signal indicating that a lever-press response was effective in producing food. Experiments1-4 revealed that systemic administration of the 5-HT2C antagonist RS 102221 (2 mg/kg) selectively decreases compulsive lever-pressing, whereas systemic administration of the 5-HT2A antagonist MDL11,939(0.2-5 mg/kg) or of the 5-HT2A/2C agonist DOI (0.05-5 mg/kg) did not have a selective effect on this behaviour. Experiments 5 and 6 found that systemic co-administration of DOI (0.5 mg/kg) withMDL11,939 (1 mg/kg) or with RS 102221 (2 mg/kg) had a non-selective effect on lever-press responding,with the former manipulation increasing and the latter manipulation decreasing lever-pressing. Finally,experiment 7 demonstrated that administration of RS 102221 directly into the orbitofrontal cortex also exerts an anti-compulsive effect. The results of these experiments suggest that blockade of 5-HT2Creceptors may have an anti-compulsive effect in OCD patients, and that this effect may be mediated by5-HT2C receptors within the orbitofrontal cortex.

Genetic variation in cortico-amygdala serotonin function and risk for stress-related disease

The serotonin system is strongly implicated in the pathophysiology and therapeutic alleviation of stress-related disorders such as anxiety and depression. Serotonergic modulation of the acute response to stress and the adaptation to chronic stress is mediated by a myriad of molecules controlling serotonin neuron development (Pet-1), synthesis (tryptophan hydroxylase 1 and 2 isozymes), packaging (vesicular monoamine transporter 2), actions at presynaptic and postsynaptic receptors (5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C, 5-HT3A, 5-HT4, 5-HT5A, 5-HT6, 5-HT7), reuptake (serotonin transporter), and degradation (monoamine oxidase A). A growing body of evidence from preclinical rodents models, and especially genetically modified mice and inbred mouse strains, has provided significant insight into how genetic variation in these molecules can affect the development and function of a key neural circuit between the dorsal raphe nucleus, medial prefrontal cortex and amygdala. By extension, such variation is hypothesized to have a major influence on individual differences in the stress response and risk for stress-related disease in humans. The current article provides an update on this rapidly evolving field of research.

Animal models of anxiety in mice

Among the multiple possibilities to study human pathologies, animal models remain one of the most used pathways. They allow to access to unavailable answers in human patients and to learn about mechanisms of action of drugs. Primarily developed with rats, animal models in anxiety have been adapted with a mixed success for mice, an easy-to-use mammal with better genetic possibilities than rats. In this review, we have focused on the most used animal models in anxiety in mice. Both conditioned and unconditioned models are described, to represent all types of animal models of anxiety. Behavioural studies require strong care for variable parameters, linked to environment, handling or paradigm; we have discussed about this topic. Finally, we focused on the consequences of re-exposure to the apparatus. Test-retest procedures can bring in new answers, but should be deeply studied, to revalidate the whole paradigm as an animal model of anxiety.

Gamma-aminobutyric acid (GABA) receptor mediates suanzaorentang, a traditional Chinese herb remedy, -induced sleep alteration

The sedative-hypnotic medications, including benzodiazepines and non-benzodiazepines, are the most common treatments for insomnia. However, concerns regarding patterns of inappropriate use, dependence and adverse effects have led to caution in prescribing those sedative-hypnotic medications. On the other hand, a traditional Chinese herb remedy, suanzaorentang, has been efficiently and widely used in clinic for insomnia relief without severe side effects in Asia. Although suanzaorentang has been reported to improve sleep disruption in insomniac patients, its mechanism is still unclear. The present study was designed to elucidate the effects of oral administration of suanzaorentang on physiological sleep-wake architectures and its underlying mechanism in rats. We found that oral administration of suanzaorentang at the beginning of the dark onset dose-dependently increased non-rapid eye movement sleep (NREMS) during the dark period, but had no significant effect on rapid eye movement sleep (REMS). Our results also indicated that intracerebroventricular (ICV) administration of gamma-aminobutyric acid (GABA) receptor type A antagonist, bicuculline, significantly blocked suanzaorentang-induced enhancement in NREMS during the dark period, but GABA(B) receptor antagonist, 2-hydroxysaclofen had no effect. These results implicated that this traditional Chinese herb remedy, suanzaorentang increases spontaneous sleep activity and its effects may be mediated through the GABA(A) receptors, but not GABA(B) receptors.