On the elevated plus-maze the anxiolytic-like effects of the 5-HT(1A) agonist, 8-OH-DPAT, but not the anxiogenic-like effects of the 5-HT(1A) partial agonist, buspirone, are blocked by the 5-HT1A antagonist, WAY 100635

Effect of psilocybin on marble burying in ICR mice: role of 5-HT1A receptors and implications for the treatment of obsessive-compulsive disorder

Preliminary clinical findings, supported by preclinical studies employing behavioral paradigms such as marble burying, suggest that psilocybin may be effective in treating obsessive-compulsive disorder. However, the receptor mechanisms implicated in the putative anti-obsessional effect are not clear. On this background, we set out to explore (1) the role of serotonin 2A (5-HT2A) and serotonin 1A (5-HT1A) receptors in the effect of psilocybin on marble burying; (2) the effect of staggered versus bolus psilocybin administration and persistence of the effect; (3) the effect of the 5-HT1A partial agonist, buspirone, on marble-burying and the head twitch response (HTR) induced by psilocybin, a rodent correlate of psychedelic effects. Male ICR mice were administered psilocybin 4.4 mg/kg, escitalopram 5 mg/kg, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) 2 mg/kg, M100907 2 mg/kg, buspirone 5 mg/kg, WAY100635 2 mg/kg or combinations, intraperitoneally, and were tested on the marble burying test. HTR was examined in a magnetometer-based assay. The results show that (1) Psilocybin and escitalopram significantly reduced marble burying. The effect of psilocybin was not attenuated by the 5-HT2A antagonist, M100907. The 5-HT1A agonist, 8-OH-DPAT, reduced marble burying as did the 5-HT1A partial agonist, buspirone. The effect of 8-OH-DPAT was additive to that of psilocybin, but that of buspirone was not. The 5-HT1A antagonist, WAY100635, attenuated the effect of 8-OH-DPAT and buspirone but not the effect of psilocybin. (2) Psilocybin injections over 3.5 h had no effect on marble burying and the effect of bolus injection was not persistent. (3) Co-administration of buspirone with psilocybin blocked its effect on HTR. These data suggest that neither 5-HT2A nor 5-HT1A receptors are pivotally implicated in the effect of psilocybin on marble burying. Co-administration with buspirone may block the psychedelic effects of psilocybin without impeding its anti-obsessional effects.

Kamishoyosan Alleviates Anxiety-like Behavior in a Premenstrual Syndrome Rat Model

Kamishoyosan (KSS) is a traditional Japanese Kampo medicine that is prescribed for hormonal change-induced mood disorders including premenstrual syndrome (PMS). In clinical studies, KSS exhibited ameliorative effects on mood symptoms of PMS, such as anxiety and irritability. However, the mechanism underlying the beneficial effects of KSS is unclear. In the present study, we investigated the involvement of serotonergic machinery in the anxiolytic effects of KSS on hormonally-induced anxiety-like behavior in progesterone withdrawal (PWD) rats, which were used as a model of PMS. Female rats were injected with progesterone daily for 21 days. At 48 h after the final progesterone injection, anxiety-like behavior was evaluated using the elevated plus maze. KSS was administered orally to PWD rats 1 h prior to the test and significantly attenuated PWD-induced anxiety-like behavior. This ameliorative effect of KSS was reversed by WAY-100635, a serotonin (5-HT)_1A receptor antagonist. The effect of KSS on serotonergic transmission in the prefrontal cortex of PWD rats was also evaluated using an in vivo microdialysis procedure. KSS significantly increased the extracellular 5-HT level in the prefrontal cortex of PWD rats. In conclusion, our results suggest that KSS alleviates PWD-induced anxiety-like behavior at least partly by activating 5-HT_1A receptors and enhancing serotonergic transmission.

Animal Behavior in Psychedelic Research

Psychedelic-assisted psychotherapy holds great promise in the treatment of mental health disorders. Research into 5-hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelic compounds has increased dramatically over the past two decades. In humans, these compounds produce drastic effects on consciousness, and their therapeutic potential relates to changes in the processing of emotional, social, and self-referential information. The use of animal behavior to study psychedelics is under debate, and this review provides a critical perspective on the translational value of animal behavior studies in psychedelic research. Acute activation of 5-HT_2ARs produces head twitches and unique discriminative cues, disrupts sensorimotor gating, and stimulates motor activity while inhibiting exploration in rodents. The acute treatment with psychedelics shows discrepant results in conventional rodent tests of depression-like behaviors but generally induces anxiolytic-like effects and inhibits repetitive behavior in rodents. Psychedelics impair waiting impulsivity but show discrepant effects in other tests of cognitive function. Tests of social interaction also show conflicting results. Effects on measures of time perception depend on the experimental schedule. Lasting or delayed effects of psychedelics in rodent tests related to different behavioral domains appear to be rather sensitive to changes in experimental protocols. Studying the effects of psychedelics on animal behaviors of relevance to effects on psychiatric symptoms in humans, assessing lasting effects, publishing negative findings, and relating behaviors in rodents and humans to other more translatable readouts, such as neuroplastic changes, will improve the translational value of animal behavioral studies in psychedelic research. SIGNIFICANCE STATEMENT: Psychedelics like LSD and psilocybin have received immense interest as potential new treatments of psychiatric disorders. Psychedelics change high-order consciousness in humans, and there is debate about the use of animal behavior studies to investigate these compounds. This review provides an overview of the behavioral effects of 5-HT_2AR agonist psychedelics in laboratory animals and discusses the translatability of the effects in animals to effects in humans. Possible ways to improve the utility of animal behavior in psychedelic research are discussed.

Serotonin and Consciousness-A Reappraisal

The serotonergic system of the brain is a major modulator of behaviour. Here we describe a re-appraisal of its function for consciousness based on anatomical, functional and pharmacological data. For a better understanding, the current model of consciousness is expanded. Two parallel streams of conscious flow are distinguished. A flow of conscious content and an affective consciousness flow. While conscious content flow has its functional equivalent in the activity of higher cortico-cortical and cortico-thalamic networks, affective conscious flow originates in segregated deeper brain structures for single emotions. It is hypothesized that single emotional networks converge on serotonergic and other modulatory transmitter neurons in the brainstem where a bound percept of an affective conscious flow is formed. This is then dispersed to cortical and thalamic networks, where it is time locked with conscious content flow at the level of these networks. Serotonin acts in concert with other modulatory systems of the brain stem with some possible specialization on single emotions. Together, these systems signal a bound percept of affective conscious flow. Dysfunctions in the serotonergic system may not only give rise to behavioural and somatic symptoms, but also essentially affect the coupling of conscious affective flow with conscious content flow, leading to the affect-stained subjective side of mental disorders like anxiety, depression, or schizophrenia. The present model is an attempt to integrate the growing insights into serotonergic system function. However, it is acknowledged, that several key claims are still at a heuristic level that need further empirical support.

Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases?

Serotonin (5-HT) is one of the fundamental neurotransmitters that contribute to the information essential for an organism's normal, physiological function. Serotonin acts centrally and systemically. The 5-HT_1A receptor is the most widespread serotonin receptor, and participates in many brain-related disorders, including anxiety, depression, and cognitive impairments. The 5-HT_1A receptor can activate several different biochemical pathways and signals through both G protein-dependent and G protein-independent pathways. Preclinical experiments indicate that distinct signaling pathways in specific brain regions may be crucial for antidepressant-like, anxiolytic-like, and procognitive responses. Therefore, the development of new ligands that selectively target a particular signaling pathway(s) could open new possibilities for more effective and safer pharmacotherapy. This review discusses the current state of preclinical studies focusing on the concept of functional selectivity (biased agonism) regarding the 5-HT_1A receptor and its role in antidepressant-like, anxiolytic-like, and procognitive regulation. Such work highlights not only the differential effects of targeted autoreceptors, vs. heteroreceptors, but also the importance of targeting specific downstream intracellular signaling processes, thereby enhancing favorable over unfavorable signaling activation.

The serotonin 1A receptor modulates the social behaviour within groups of a cooperatively-breeding cichlid

The neurotransmitter serotonin (5-HT) reduces aggressive behaviour in a number of vertebrates, and the 5-HT_1A receptor is known to be involved in this regulation. However, the role of this receptor in the modulation of sociopositive behaviour remains largely unknown. Here we investigated the role of the 5-HT_1A receptor in the regulation of aggressive, submissive and affiliative behaviour in the cooperatively-breeding cichlid Neolamprologus pulcher. In two experiments, we performed intramuscular injections of a 5-HT_1A agonist (8-OH-DPAT) and antagonist (Way-100635) followed by recordings of social behaviour of injected fish within their social groups. We determined the concentrations and post-injection times when the drugs had the greatest effect on social behaviour. We recorded spontaneous social behaviour in both experiments. In the second experiment we also recorded behaviour after social groups received a territorial challenge by live presentations of either conspecifics or egg predators. The 5-HT_1A agonist caused an increase in aggression and a decrease in submission and affiliation, whereas the antagonist had the opposite effects. Thus, the 5-HT_1A receptor plays an important regulatory role not only for aggressive but also sociopositive behaviour.

Serotonin type-3 receptors differentially modulate anxiety and aggression during withdrawal from adolescent anabolic steroid exposure

Male Syrian hamsters (Mesocricetus auratus) administered anabolic/androgenic steroids during adolescent development display increased aggression and decreased anxious behavior during the adolescent exposure period. Upon withdrawal from anabolic/androgenic steroids, this neurobehavioral relationship shifts and hamsters exhibit decreased aggression and increased anxious behavior. This study investigated the hypothesis that alterations in anterior hypothalamic signaling through serotonin type-3 receptors modulate the behavioral shift between adolescent anabolic/androgenic steroid-induced aggressive and anxious behaviors during the withdrawal period. To test this, hamsters were administered anabolic/androgenic steroids during adolescence then withdrawn from drug exposure for 21 days and tested for aggressive and anxious behaviors following direct pharmacological manipulation of serotonin type-3 receptor signaling within the latero-anterior hypothalamus. Blockade of latero-anterior hypothalamic serotonin type-3 receptors both increased aggression and decreased anxious behavior in steroid-treated hamsters, effectively reversing the pattern of behavioral responding normally observed during anabolic/androgenic steroid withdrawal. These findings suggest that the state of serotonin neural signaling within the latero-anterior hypothalamus plays an important role in behavioral shifting between aggressive and anxious behaviors following adolescent exposure to anabolic/androgenic steroids.

Manipulation of dorsal raphe serotonergic neurons modulates active coping to inescapable stress and anxiety-related behaviors in mice and rats

Major depression and anxiety disorders are a social and economic burden worldwide. Serotonergic signaling has been implicated in the pathophysiology of these disorders and thus has been a crucial target for pharmacotherapy. However, the precise mechanisms underlying these disorders are still unclear. Here, we used species-optimized lentiviral vectors that were capable of efficient and specific transduction of serotonergic neurons in mice and rats for elucidation of serotonergic roles in anxiety-like behaviors and active coping behavior in both species. Immunohistochemical analyses revealed that lentiviral vectors with an upstream sequence of tryptophan hydroxylase 2 gene efficiently transduced serotonergic neurons with a specificity of approximately 95% in both mice and rats. Electrophysiological recordings showed that these lentiviral vectors induced sufficient expression of optogenetic tools for precise control of serotonergic neurons. Using these vectors, we demonstrate that acute activation of serotonergic neurons in the dorsal raphe nucleus increases active coping with inescapable stress in rats and mice in a time-locked manner, and that acute inhibition of these neurons increases anxiety-like behaviors specifically in rats. These findings further our understanding of the pathophysiological role of dorsal raphe serotonergic neurons in different species and the role of these neurons as therapeutic targets in major depression and anxiety disorders.

Δ-9-Tetrahydrocannabinol and Cannabidiol produce dissociable effects on prefrontal cortical executive function and regulation of affective behaviors

The use of cannabis for therapeutic and recreational purposes is growing exponentially. Nevertheless, substantial questions remain concerning the potential cognitive and affective side-effects associated with cannabis exposure. In particular, the effects of specific marijuana-derived phytocannabinoids on neural regions such as the prefrontal cortex (PFC) are of concern, given the role of the PFC in both executive cognitive function and affective processing. The main biologically active phytocannabinoids, ∆-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), interact with multiple neurotransmitter systems important for these processes directly within the PFC. Considerable evidence has demonstrated that acute or chronic THC exposure may induce psychotomimetic effects, whereas CBD has been shown to produce potentially therapeutic effects for both psychosis and/or anxiety-related symptoms. Using an integrative combination of cognitive and affective behavioral pharmacological assays in rats, we report that acute intra-PFC infusions of THC produce anxiogenic effects while producing no impairments in executive function. In contrast, acute infusions of intra-PFC CBD impaired attentional set-shifting and spatial working memory, without interfering with anxiety or sociability behaviors. In contrast, intra-PFC CBD reversed the cognitive impairments induced by acute glutamatergic antagonism within the PFC, and blocked the anxiogenic properties of THC, suggesting that the therapeutic properties of CBD within the PFC may be present only during pathologically aberrant states within the PFC. Interestingly, the effects of PFC THC vs. CBD were found to be mediated through dissociable CB1 vs. 5-HT_1A-dependent receptor signaling mechanisms, directly in the PFC.

The swimming plus-maze test: a novel high-throughput model for assessment of anxiety-related behaviour in larval and juvenile zebrafish (Danio rerio)

Larval zebrafish (Danio rerio) has the potential to supplement rodent models due to the availability of resource-efficient, high-throughput screening and high-resolution imaging techniques. Although behavioural models are available in larvae, only a few can be employed to assess anxiety. Here we present the swimming plus-maze (SPM) test paradigm, a tool to assess anxiety-related avoidance of shallow water bodies in early developmental stages. The “+” shaped apparatus consists of arms of different depth, representing different levels of aversiveness similarly to the rodent elevated plus-maze. The paradigm was validated (i) in larval and juvenile zebrafish, (ii) after administration of compounds affecting anxiety and (iii) in differentially aversive experimental conditions. Furthermore, we compared the SPM with conventional “anxiety tests” of zebrafish to identify their shared characteristics. We have clarified that the preference of deeper arms is ontogenetically conserved and can be abolished by anxiolytic or enhanced by anxiogenic agents, respectively. The behavioural readout is insensitive to environmental aversiveness and is unrelated to behaviours assessed by conventional tests involving young zebrafish. Taken together, we have developed a sensitive high-throughput test allowing the assessment of anxiety-related responses of zebrafish regardless of developmental stage, granting the opportunity to combine larva-based state-of-the-art methods with detailed behavioral analysis.

HBK-17, a 5-HT1A Receptor Ligand With Anxiolytic-Like Activity, Preferentially Activates ß-Arrestin Signaling

Numerous studies have proven that both stimulation and blockade of 5-HT_1A and the blockade of 5-HT₇ receptors might cause the anxiolytic-like effects. Biased agonists selectively activate specific signaling pathways. Therefore, they might offer novel treatment strategies. In this study, we investigated the anxiolytic-like activity, as well as the possible mechanism of action of 1-[(2,5-dimethylphenoxy)propyl]-4-(2-methoxyphenyl)piperazine hydrochloride (HBK-17). In our previous experiments, HBK-17 showed high affinity for 5-HT_1A and 5-HT₇ receptors and antidepressant-like properties. We performed the four plate test and the elevated plus maze test to determine anxiolytic-like activity. Toward a better understanding of the pharmacological properties of HBK-17 we used various functional assays to determine its intrinsic activity at 5-HT_1A, 5-HT_2A, 5-HT₇, and D₂ receptors and UHPLC-MS/MS method to evaluate its pharmacokinetic profile. We observed the anxiolytic-like activity of HBK-17 in both behavioral tests and the effect was reversed by the pretreatment with WAY-100635, which proves that 5-HT_1A receptor activation was essential for the anxiolytic-like effect. Moreover, the compound moderately antagonized D₂, weakly 5-HT₇ and very weakly 5-HT_2A receptors. We demonstrated that HBK-17 preferentially activated ß-arrestin signaling after binding to the 5-HT_1A receptor. HBK-17 was rapidly absorbed after intraperitoneal administration and had a half-life of about 150 min. HBK-17 slightly penetrated the peripheral compartment and showed bioavailability of approximately 45%. The unique pharmacological profile of HBK-17 encourages further experiments to understand its mechanism of action fully.

Activity of Serotonin 5-HT1A Receptor Biased Agonists in Rat: Anxiolytic and Antidepressant-like properties

Although serotonin 5-HT_1A receptors constitute attractive therapeutic targets, there is a lack of potential clinical candidates that have a high degree of selectivity and full agonist efficacy. Recently, novel 5-HT_1A receptor "biased agonists" F15599 (also known as NLX-101) and F13714 have been reported that exhibit distinctive properties for in vitro signaling, neurochemical, electrophysiological effects, and in brain imaging. The present study characterized their effects in rat models of anxiety (elevated plus-maze, EPM, and Vogel tests), in depressive-like behavior (forced swim test), and on the induction of the three serotonergic behaviors (forepaw treading, flat body posture, and lower lip retraction). The prototypical 5-HT_1A receptor ligands (±)8-OH-DPAT and buspirone were tested as comparators. In the elevated plus-maze, F15599, F13714, and (±)8-OH-DPAT dose-dependently increased the amount and percentage of time spent in the open arms with minimal effective doses (MED) of 5 mg/kg p.o., 2.5 mg/kg p.o. and 1.25 mg/kg s.c., respectively. The effects of the three agonists were abolished by pretreatment with the selective 5-HT_1A receptor antagonist, WAY100635 (0.63 mg/kg s.c.). Buspirone did not show significant activity in the EPM. In contrast, in the Vogel test only buspirone was active, significantly increasing the number of licks and shocks accepted (active dose: 1.25 mg/kg s.c.). However, WAY100635 failed to reverse the effects of buspirone in this test, suggesting that they were not 5-HT_1A receptor-mediated. In the forced swim test, F15599, F13714, and (±)8-OH-DPAT were potently active, abolishing immobility (MED: 0.63 mg/kg p.o., 0.63 mg/kg p.o. and 0.16 mg/kg s.c., respectively). Buspirone was not active. In measures of serotonergic behavior, F13714 and (±)8-OH-DPAT robustly elicited all three signs of serotonergic behaviors, whereas F15599 and buspirone elicited only lower-lip retraction. Taken together, these observations highlight the distinct profiles of activity of 5-HT_1A agonists and suggest that the novel biased agonist F15599 combines pronounced activity in a test of anxiety (elevated plus-maze) with potent antidepressant-like effects and low propensity to induce serotonergic behaviors. These data suggest that selective biased agonists could constitute promising pharmacotherapeutics for mood disorders.

A behavioral mechanistic investigation of the role of 5-HT1A receptors in the mediation of rat maternal behavior

Previous work suggests that 5-HT_1A receptors play a special role in rodent maternal aggression, but not in other aspects of maternal care (e.g. pup retrieval and nest building). The present study re-assessed the basic effects of 5-HT_1A activation or blockade on various maternal responses in postpartum female rats. We also examined the possible behavioral mechanisms underlying the maternal effects of 5-HT_1A. Sprague-Dawley mother rats were injected with a 5-HT_1A agonist 8-OH-DPAT (0.1, 0.5 or 1.0 mg/kg, sc), a 5-HT_1A antagonist WAY-101405 (0.1, 0.5 or 1.0 mg/kg, sc) or 0.9% saline solution on postpartum days 3, 5, and 7. Maternal behavior was tested 30 min before, 30 min, 120 min, and 240 min after the injection. Acute and repeated 8-OH-DPAT treatment significantly disrupted pup retrieval, pup licking, nursing, and nest building in a dose-dependent fashion, whereas WAY-101405 had no effect at the tested doses. The 5-HT_1A receptor specificity of 8-OH-DPAT's action was confirmed as its maternal disruption effect was reversed by pretreatment of WAY-100635 (a highly selective 5-HT_1A receptor antagonist). Subsequent pup preference test found that 8-OH-DPAT did not decrease the pup preference over a novel object, thus no inhibition on maternal motivation or maternal affect. The pup separation test and pup retrieval on an elevated plus maze test also failed to find any motivational and motor impairment effect with 8-OH-DPAT. However, 8-OH-DPAT at the maternal disruptive dose did disrupt the prepulse inhibition (a measure of attentional function) of acoustic startle response and enhanced the basal startle response. These findings suggest that stimulation of 5-HT_1A receptors by 8-OH-DPAT impairs maternal care by partially interfering with the attentional processing or basal anxiety. More work is needed to further delineate the psychological and neuronal mechanisms underlying the maternal disruptive effect of 5-HT_1A receptor activation.

5-HT1A receptor-dependent modulation of emotional and neurogenic deficits elicited by prolonged consumption of alcohol

Repeated episodes of binge-like alcohol consumption produce anxiety, depression and various deleterious effects including alterations in neurogenesis. While the involvement of the serotonin receptor 1 A (5-HT1A) in the regulation of anxiety-like behavior and neurogenesis is well documented, its contribution to alcohol withdrawal-induced anxiety and alcohol-induced deficits in neurogenesis is less documented. Using the Drinking-In-the-Dark (DID) paradigm to model chronic long-term (12 weeks) binge-like voluntary alcohol consumption in mice, we show that the selective partial activation of 5-HT1A receptors by tandospirone (3 mg/kg) prevents alcohol withdrawal-induced anxiety in a battery of behavioral tests (marble burying, elevated-plus-maze, open-field), which is accompanied by a robust decrease in binge-like ethanol intake (1 and 3 mg/kg). Furthermore, using triple immunolabelling of proliferation and neuronal differentiation markers, we show that long-term DID elicits profound deficits in neurogenesis and neuronal fate specification in the dorsal hippocampus that are entirely reversed by a 2-week chronic treatment with the 5-HT1A partial agonist tandospirone (3 mg/kg/day). Together, our results confirm previous observations that 5-HT1A receptors play a pivotal role in alcohol drinking behavior and the associated emotional and neurogenic impairments, and suggest that 5-HT1A partial agonists represent a promising treatment strategy for alcohol abuse.

Nucleus incertus contributes to an anxiogenic effect of buspirone in rats: Involvement of 5-HT1A receptors

The nucleus incertus (NI), a brainstem structure with diverse anatomical connections, is implicated in anxiety, arousal, hippocampal theta modulation, and stress responses. It expresses a variety of neurotransmitters, neuropeptides and receptors such as 5-HT1A, D2 and CRF1 receptors. We hypothesized that the NI may play a role in the neuropharmacology of buspirone, a clinical anxiolytic which is a 5-HT1A receptor partial agonist and a D2 receptor antagonist. Several preclinical studies have reported a biphasic anxiety-modulating effect of buspirone but the precise mechanism and structures underlying this effect are not well-understood. The present study implicates the NI in the anxiogenic effects of a high dose of buspirone. Systemic buspirone (3 mg/kg) induced anxiogenic effects in elevated plus maze, light-dark box and open field exploration paradigms in rats and strongly activated the NI, as reflected by c-Fos expression. This anxiogenic effect was reproduced by direct infusion of buspirone (5 μg) into the NI, but was abolished in NI-CRF-saporin-lesioned rats, indicating that the NI is present in neural circuits driving anxiogenic behaviour. Pharmacological studies with NAD 299, a selective 5-HT1A antagonist, or quinpirole, a D2/D3 agonist, were conducted to examine the receptor system in the NI involved in this anxiogenic effect. Opposing the 5-HT1A agonism but not the D2 antagonism of buspirone in the NI attenuated the anxiogenic effects of systemic buspirone. In conclusion, 5-HT1A receptors in the NI contribute to the anxiogenic effect of an acute high dose of buspirone in rats and may be functionally relevant to physiological anxiety.

Interactions of a standardized flavonoid fraction from Tilia americana with Serotoninergic drugs in elevated plus maze

ETHNOPHARMACOLOGICAL RELEVANCE

Tilia americana var. mexicana (Schltdl) Hardin (Tiliaceae) aerial parts (bracts and flowers) are used in the traditional Mexican medicine to treat nervous disorders, as sedative and to treat insomnia. A fraction of this species called FC1 (organic fraction from this plant) was proposed, described as anxiolytic and characterized by the presence of flavonoids. In the present work, this fraction was standardized, and its interaction with different serotonergic drugs was tested. We used the elevated plus maze model as anxiety test and the open field test so as to observe a possible effect on mice׳s motor behavior.

MATERIAL AND METHODOLOGY

HPLC technique was used to quantify the flavonoids contained in a fraction called F1C. Different doses of F1C were administered to ICR mice (12.5, 25, 37.5 and 50mg/kg, oral pathway) then they were exposed to elevated plus maze or open field test. After, each dose of F1C fraction was co-administered with different drugs, in order to evaluate the animal׳s behavior: DOI agonist (2.0mg/kg) and KET antagonist (0.03mg/kg) of 5-HT2A receptors; 8-OH-DPAT (0.1mg/kg) selective agonist and WAY100635 (0.5mg/kg) antagonist of 5HT1 receptors.

RESULTS

The HPLC quantitative analysis revealed the F1C composition (mg/g of extract): tiliroside (28.56), glucoside of quercetin (16.25), quercitrin (7.96), rutin (3.93), Kaempferol (2.83). The Emax for F1C curve was 80.6% for time to open arms with an ED50 of 15.09 mg/kg. The combination of F1C with DOI gives a significant increase of the F1C anxiolytic effect (Emax=111% and ED50=13.51 mg/kg), while KET blocks it completely (Emax=12.25% and ED50=2.4 mg/kg). The administration of F1C with 8-OH-DPAT does not generate significant changes on the time to open arms, although it does induce a decrement in F1C potency (Emax=83.3% and ED50=33.3mg/kg). When F1C and WAY-100365 are combined, the anxiolytic activity of the fraction decreases (Emax=33.3% and ED50=102.10mg/kg).

CONCLUSIONS

The medicinal use attributed to Tilia americana for their effect on central nervous system, could be in part in the flavonoid fraction (F1C) with anxiolytic activity which is dose dependent, and has the ability to interact with the serotonergic system. It is necessary to advance in the study of the mechanism of action, using other techniques such in vitro analysis.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Anxiolytic-Like Effects of Chrysanthemum indicum Aqueous Extract in Mice: Possible Involvement of GABAA Receptors and 5-HT1A Receptors

Chrysanthemum indicum Linne is an ancient herbal medicine used to treat bone and muscle deterioration, ocular infl ammation, headache, and anxiety in Korea, China, and Japan. Furthermore, tea derived from Chrysanthemum indicum Linne has been used to treat anxiety by facilitating relaxation and curing insomnia. However, no reports exist on the anxiolytic-like effects of Chrysanthemum indicum Linne water extract (CWE) in mice. In the present study, we investigated the anxiolytic-like effects of CWE using the elevated plus-maze (EPM) test in mice. CWE, at a dose of 500 mg/kg (p.o.), signifi cantly increased the time spent in the open arms of the EPM compared to a vehicle-injected control group. Moreover, the effect of CWE (500 mg/kg) was blocked by bicuculline (a selective GABA_A receptor antagonist) and WAY 100635 (a selective 5-HT_1A receptor antagonist). Taken together, these fi ndings suggest that the anxiolytic-like effects of CWE might be mediated by the GABA_A receptor and the 5-HT_1A receptor.

Mechanisms of cannabidiol neuroprotection in hypoxic-ischemic newborn pigs: role of 5HT(1A) and CB2 receptors

The mechanisms underlying the neuroprotective effects of cannabidiol (CBD) were studied in vivo using a hypoxic-ischemic (HI) brain injury model in newborn pigs. One- to two-day-old piglets were exposed to HI for 30 min by interrupting carotid blood flow and reducing the fraction of inspired oxygen to 10%. Thirty minutes after HI, the piglets were treated with vehicle (HV) or 1 mg/kg CBD, alone (HC) or in combination with 1 mg/kg of a CB₂ receptor antagonist (AM630) or a serotonin 5HT(1A) receptor antagonist (WAY100635). HI decreased the number of viable neurons and affected the amplitude-integrated EEG background activity as well as different prognostic proton-magnetic-resonance-spectroscopy (H(±)-MRS)-detectable biomarkers (lactate/N-acetylaspartate and N-acetylaspartate/choline ratios). HI brain damage was also associated with increases in excitotoxicity (increased glutamate/N-acetylaspartate ratio), oxidative stress (decreased glutathione/creatine ratio and increased protein carbonylation) and inflammation (increased brain IL-1 levels). CBD administration after HI prevented all these alterations, although this CBD-mediated neuroprotection was reversed by co-administration of either WAY100635 or AM630, suggesting the involvement of CB₂ and 5HT(1A) receptors. The involvement of CB₂ receptors was not dependent on a CBD-mediated increase in endocannabinoids. Finally, bioluminescence resonance energy transfer studies indicated that CB₂ and 5HT(1A) receptors may form heteromers in living HEK-293T cells. In conclusion, our findings demonstrate that CBD exerts robust neuroprotective effects in vivo in HI piglets, modulating excitotoxicity, oxidative stress and inflammation, and that both CB₂ and 5HT(1A) receptors are implicated in these effects.

Serotonin modulates anxiety-like behaviors during withdrawal from adolescent anabolic-androgenic steroid exposure in Syrian hamsters

From the U.S. to Europe and Australia anabolic steroid abuse remains high in the adolescent population. This is concerning given that anabolic steroid use is associated with a higher incidence of pathological anxiety that often appears during withdrawal from use. This study uses pubertal Syrian hamsters (Mesocricetus auratus) to investigate the hypothesis that adolescent anabolic/androgenic steroid (AAS) exposure predisposes hamsters to heightened levels of anxiety during AAS withdrawal that is modulated by serotonin (5HT) neural signaling. In the first two sets of experiments, adolescent AAS-treated hamsters were tested for anxiety 21 days after the cessation of AAS administration (i.e., during AAS withdrawal) using the elevated plus maze (EPM), dark/light (DL), and seed finding (SF) tests and then examined for differences in 5HT afferent innervation to select areas of the brain important for anxiety. In the EPM and DL tests, adolescent AAS exposure leads to significant increases in anxiety-like response during AAS withdrawal. AAS-treated hamsters showed long-term reductions in 5HT innervation within several areas of the hamster brain implicated in anxiety, most notably the anterior hypothalamus and the central and medial amygdala. However, no differences in 5HT were found in other anxiety areas, e.g., frontal cortex and lateral septum. In the last experiment, adolescent AAS-treated hamsters were scored for anxiety on the 21st day of AAS withdrawal following the systemic administration of saline or one of three doses of fluoxetine, a selective serotonin reuptake inhibitor. Saline-treated hamsters showed high levels of AAS withdrawal-induced anxiety, while treatment with fluoxetine reduced AAS withdrawal-induced anxiety. These findings indicate that early AAS exposure has potent anxiogenic effects during AAS withdrawal that are modulated, in part, by 5HT signaling.

Cannabidiol blocks long-lasting behavioral consequences of predator threat stress: possible involvement of 5HT1A receptors

Posttraumatic stress disorder (PTSD) is an incapacitating syndrome that follows a traumatic experience. Predator exposure promotes long-lasting anxiogenic effect in rodents, an effect related to symptoms found in PTSD patients. Cannabidiol (CBD) is a non-psychotomimetic component of Cannabis sativa with anxiolytic effects. The present study investigated the anti-anxiety actions of CBD administration in a model of PTSD. Male Wistar rats exposed to a predator (cat) received, 1 h later, singled or repeated i.p. administration of vehicle or CBD. Seven days after the stress animals were submitted to the elevated plus maze. To investigate the involvement of 5HT1A receptors in CBD effects animals were pre-treated with WAY100635, a 5HT1A receptor antagonist. To explore possible neurobiological mechanisms involved in these effects, 5HT1A receptor mRNA and BDNF protein expression were measured in the hippocampus, frontal cortex, amygdaloid complex and dorsal periaqueductal gray. Repeated administration of CBD prevented long-lasting anxiogenic effects promoted by a single predator exposure. Pretreatment with WAY100635 attenuated CBD effects. Seven days after predator exposure 5HT1A mRNA expression was up regulated in the frontal cortex and hippocampus. CBD and paroxetine failed to prevent this effect. No change in BDNF expression was found. In conclusion, predator exposure promotes long-lasting up-regulation of 5HT1A receptor gene expression in the hippocampus and frontal cortex. Repeated CBD administration prevents the long-lasting anxiogenic effects observed after predator exposure probably by facilitating 5HT1A receptors neurotransmission. Our results suggest that CBD has beneficial potential for PTSD treatment and that 5HT1A receptors could be a therapeutic target in this disorder.

Buspirone blocks the enhancing effect of the anxiogenic drug RS 79948-197 on consolidation of habit memory

Previous findings indicate that post-training administration of the anxiogenic α(2)-adrenoceptor antagonist RS 79948-197 facilitates the consolidation of dorsal striatal-dependent habit memory. The present study examined the effect of concurrent administration of the anxiolytic serotonin 5-HT(1A) receptor partial agonist buspirone on anxiety-induced facilitation of habit memory. Male Long-Evans rats were trained in a response learning version of a water plus-maze task that requires animals to learn to make the same body turn response on each trial in order to reach a hidden escape platform. Immediately following training on days 1-3, rats received peripheral injections of either saline, buspirone (1.5 mg/kg, 2.0 mg/kg, or 5.0 mg/kg), RS 79948-197 (0.1 mg/kg), or RS 79948-197 and buspirone together. Post-training injections of RS 79948-197 alone significantly enhanced memory consolidation. The highest dose of buspirone (5.0 mg/kg) also enhanced response learning. However, concurrent administration of a dose of buspirone (1.5 mg/kg) that itself had no effect on acquisition blocked the memory enhancing effects of RS 79948-197. These findings suggest that the facilitation of habit memory observed following drug-induced anxiety can be prevented by co-administration of an anxiolytic agent.

Decision time and perseveration of adolescent rats in the T-maze are affected differentially by buspirone and independent of 5-HT-1A expression

Disruption of spontaneous alternation behavior (SAB) by the serotonin 1A (5-HT-1A) receptor agonist, 8-hydroxy-dipropylaminotetraline (8-OH-DPAT), results in repetitive behaviors that have been used to model the perseveration and indecisiveness of human obsessive-compulsive disorder (OCD). In the present study, we compared the effects of buspirone to those of 8-OH-DPAT in two strains of adolescent rats and analyzed repetitive choices of arms of the maze and prolonged apparent decision time due to induction of vicarious trial and error (VTE) behavior. In adolescent Sprague-Dawley (SD) rats, 8-OH-DPAT induced repetitive choices of arms of the maze (perseveration) and increased the apparent decision time. Buspirone induced VTE behavior and increased apparent decision time without perseveration. This distinct effect of buspirone was seen in SD adolescents but not in Long-Evans (LE) adolescents which appeared to be insensitive to buspirone. Lack of responsiveness to buspirone was dependent on the developmental stage because buspirone induced VTE behavior and prolonged decision time in LE adults. Western blotting of brain 5-HT-1A receptors showed expression of receptor protein in adolescent LE brain was comparable to that of adolescent SD and adult LE. The 5-HT-1A antagonist WAY 100365 blocked the effect 8-OH-DPAT on repetitive choice of arms but not the effect of buspirone on VTE behavior. We conclude that the adolescent LE rat has normal levels of 5-HT-1A receptor and that the effect of buspirone on VTE behavior is not mediated by the 5-HT-1A receptor. The LE strain may provide a useful system for further study of the adolescent brain and potential genetic differences in induction of repetitive behaviors.

The modified Geller-Seifter test in rats was insensitive to GABAB receptor positive modulation or blockade, or 5-HT1A receptor activation

RATIONALE

Both the GABA(B) receptor positive modulator GS39783 and the GABA(B) receptor antagonist CGP46381 exhibit anxiolytic-like properties in animal models. In the present studies, the effects of GS39783 and CGP46381 in the modified Geller-Seifter task were assessed. First, the predictive validity of the task was confirmed by assessing the effects of multiple anxiolytic and non-anxiolytic compounds on punished and unpunished responding.

METHODS

Rats were trained in the modified Geller-Seifter task. After successful acquisition of the task, chlordiazepoxide, diazepam, MPEP, haloperidol, GS39783, 8-OH-DPAT, alprazolam and CGP46381 were tested consecutively. For each test compound, doses were administered in a randomized, counter-balanced, within-subjects design. Drug tests were performed only when rats exhibited baseline performance (the punished and time-out response rates were less than 10% of the unpunished response rate).

RESULTS

Chlordiazepoxide, diazepam, alprazolam and MPEP released punished responding with variable effects on unpunished responding. Haloperidol had a small but significant effect on punished responding at an intermediate dose, and decreased unpunished responding at the highest dose tested. In contrast, administration of the GABA(B) receptor positive modulator GS398783 or the GABA(B) receptor antagonist CGP46381 at doses up to 30 mg/kg had no effects on either punished or unpunished responding. The 5-HT(1A) agonist 8-OH-DPAT did not release punished responding, but significantly decreased unpunished responding at the highest dose tested.

SUMMARY

The modified Geller-Seifter task generally exhibits good predictive validity for anxiolytic-like compounds. Neither GABA(B) receptor positive allosteric modulation nor blockade exhibited anxiolytic-like properties in the modified Geller-Seifter task. The 5-HT(1A) partial agonist buspirone was similarly ineffective.

The serotonin-1A receptor in anxiety disorders

The serotonin system plays an important role in the neural processing of anxiety. The involvement of the main inhibitory serotonergic receptor, the serotonin-1A (5-HT1A) subtype, in dysfunctional forms of anxiety has been supported by findings from a wide range of preclinical research and clinical trials, including treatment studies, genetic research, and neuroimaging data. The following article summarizes preclinical results with a focus on 5-HT1A receptor knockout and transgenic mice as genetic models of anxiety. Behavioral, autonomic, and endocrinological changes in these mice are reported. This article also presents genetic polymorphisms in humans associated with increased anxiety scores and pharmacological data focused on 5-HT1A receptor agonists and antagonists. Furthermore, molecular neuroimaging results are presented. Recent positron emission tomography (PET) studies have reported reduced 5-HT1A receptor binding in patients with panic disorder and social anxiety disorder, but not in posttraumatic stress disorder. In healthy subjects, increased anxiety scores might be associated with lower 5-HT1A receptor binding. This overview of preclinical and clinical data provides strong evidence for the key role of the 5-HT1A receptor in the serotonergic dysregulation of anxiety disorders.

Individual differences in the sensitivity to serotonergic drugs: a pharmacobehavioural approach using rats selected on the basis of their response to novelty

RATIONALE

The mechanisms underlying individual differences in the response to serotonergic drugs are poorly understood. Rat studies may contribute to our knowledge of the neuronal substrates that underlie these individual differences.

OBJECTIVES

A pharmacobehavioural study was performed to assess individual differences in the sensitivity to serotonergic drugs in rats that were selected based on their response to a novel environment.

METHODS

Low responders (LR) and high responders (HR) to novelty rats were tested on the elevated T-maze following systemic injections of increasing doses of various serotonergic agents. The duration of avoidance of the open arms was scored for five trials.

RESULTS

The duration of avoidance behaviour was larger in saline-treated LR rats compared to saline-treated HR rats. The 5-HT1A agonist 8-OH-DPAT and the 5-HT2 agonists mCPP and DOI decreased the duration of avoidance behaviour in LR rats, but increased it in HR rats. The 5-HT3 agonist SR57227A and the 5-HT releaser/reuptake inhibitor d-fenfluramine increased the duration of avoidance behaviour in both types of rat. However, higher doses of SR57227A were required to alter avoidance behaviour in HR than in LR rats. The onset of the effects of SR57227A, d-fenfluramine and WAY100635 was faster in LR than in HR rats. The described effects were receptor specific. A model explaining the data is presented.

CONCLUSIONS

These data demonstrate that LR and HR rats differ in their sensitivity to serotonergic drugs that act at 5-HT3, 5-HT2 and 5-HT1A receptors. The implications of these individual differences for individual-specific treatment of substance abuse are briefly discussed.

Animal models of anxiety and anxiolytic drug action

Animal models of anxiety attempt to represent some aspect of the etiology, symptomatology, or treatment of human anxiety disorders, in order to facilitate their scientific study. Within this context, animal models of anxiolytic drug action can be viewed as treatment models relevant to the pharmacological control of human anxiety. A major purpose of these models is to identify novel anxiolytic compounds and to study the mechanisms whereby these compounds produce their anxiolytic effects. After a critical analysis of "face," "construct," and "predictive" validity, the biological context in which animal models of anxiety are to be evaluated is specified. We then review the models in terms of their general pharmacological profiles, with particular attention to their sensitivity to 5-HTIA agonists and antidepressant compounds. Although there are important exceptions, most of these models are sensitive to one or perhaps two classes of anxiolytic compounds, limiting their pharmacological generality somewhat, but allowing in depth analysis of individual mechanisms of anxiolytic drug action (e.g., GABAA agonism). We end with a discussion of possible sources of variability between models in response to 5-HTIA agonists and antidepressant drugs.

Role of serotonin-1A receptors in the action of antipsychotic drugs: comparison of prepulse inhibition studies in mice and rats and relevance for human pharmacology

This study aimed to explore strain and species differences in the involvement of 5-HT1A receptors in the action of antipsychotic drugs, using prepulse inhibition (PPI), a model of sensory processing which is deficient in schizophrenia patients. We used automated startle boxes to compare the effect of the 5-HT1A receptor agonist, (+/-)-8-hydroxy-dipropyl-amino-tetralin (8-OH-DPAT), on PPI in three mouse strains. Balb/c mice were then pretreated with antipsychotics, treated with 8-OH-DPAT or saline, and tested for PPI. 8-OH-DPAT treatment dose dependently increased PPI in Balb/c mice, but had less effect in 129Sv and C57Bl/6 mice. In Balb/c mice, the effect of 8-OH-DPAT was blocked by the typical antipsychotic and dopamine D2 receptor antagonist, haloperidol and the third generation antipsychotic, aripiprazole, which has activity at both 5-HT1A and dopamine D2 receptors. The atypical antipsychotics, clozapine, olanzapine and risperidone, had lesser effects. Similar to our earlier studies in rats, the present PPI results suggest that 5-HT1A receptors are involved in the action of some antipsychotic drugs in mice. Despite strain and species differences in the magnitude and direction of the effect of 8-OH-DPAT, downstream dopamine D2 receptor activation seems to be an important mediator. These comparative results allow a theoretical framework of receptor interactions, which may guide further studies on the involvement of 5-HT1A receptors in schizophrenia.

Buspirone induced acute and chronic changes of neural activation in the periaqueductal gray of rats

5-HT(1A) modulation within the midbrain periaqueductal gray (PAG) is closely associated with anxiety- or panic-like behavior. Several findings have demonstrated that the properties of buspirone (a 5-HT(1A) partial agonist) would function as either anxiolytic or panicolytic in both clinical and laboratory animal research. In this study, we have investigated the neuronal activity occurring within the different regions of the PAG induced by buspirone treatment. Twenty-eight albino Wistar rats (350-400 g) were injected with either acute or chronic saline/buspirone (each, n=7), respectively. Our results show that buspirone treatment reduced locomotor activity, body weight and fecal boli, particularly in the chronic buspirone group. Two-way ANOVA revealed a significant decrease of c-Fos-immunoreactive (ir) cells expression in all regions of the rostral PAG after both acute and chronic buspirone (acute buspirone (AB) and chronic buspirone (CB), respectively) treatment. However, no effects on c-Fos-ir were detected in the caudal lateral periaqueductal gray (lPAG) and ventrolateral periaqueductal gray (vlPAG) in both the AB and CB groups, and in the dorsolateral periaqueductal gray (dlPAG) of the CB group. Interestingly, c-Fos-ir cells in the dorsomedial periaqueductal gray (dmPAG) column were reduced consistently in both the rostral and caudal PAG in both AB and CB groups. Besides, in all regions the number of c-Fos-ir cells was higher in the AB than in the CB group with exception of the rostral lPAG. In conclusion, the main anxiolytic effect of buspirone was specifically localized in all regions of the rostral PAG and in the caudal dmPAG. However, the caudal dlPAG, lPAG and vlPAG were found to be ineffective to buspirone treatment, probably due to their distinctive function in mediating higher level of anxiety in defensive behavior. This indicates that the longitudinal anatomical structure of the PAG possesses a different level of receptor sensitivity of 5-HT(1A) in the pathophysiology of anxiety and panic disorder.

Activation of septal 5-HT1A receptors alters spatial memory encoding, interferes with consolidation, but does not affect retrieval in rats subjected to a water-maze task

Using Long-Evans rats tested in a water maze, this study assessed the role of 5-HT1A/5-HT7 receptors of the medial septum in encoding, consolidation, and retrieval of spatial information. The testing protocol (acquisition: daily four-trial sessions over three consecutive days; retention: probe trial on day 4) was first validated by showing that intraseptal infusions of lidocaine (LIDO; 40 microg/0.5 microL) disrupted acquisition and retrieval of the task. 8-OH-DPAT (4 microg/0.5 microL) infused before each acquisition session prevented learning/retention of the platform location, an effect attenuated by pretreatment with the 5-HT1A receptor antagonist WAY 100635. With the 5-HT7 antagonist SB 269970, the 8-OH-DPAT-induced acquisition deficit seemed attenuated, but there was no subsequent retention. When infused immediately, 1, 4, or 6 h after each acquisition session, 8-OH-DPAT did not hinder consolidation. When the infusions were performed 2 h postacquisition, however, consolidation was disrupted. Finally, when infused before a probe trial after drug-free acquisition, 8-OH-DPAT had no effect, suggesting no interference with retrieval processes. We also established that 8-OH-DPAT had no effects when the platform was visible, and altered neither home-cage activity nor anxiety-related behavior (elevated plus-maze). Altogether, these results show that 5-HT1A receptors in the septal region contribute both to declarative-like information encoding and subsequently, within a given postacquisition time window, to its consolidation. They do not participate in the retrieval of recently learned declarative-like information. These observations suggest that 5-HT1A receptors of the medial septum contribute to a serotonin-mediated mechanism involved in the encoding and consolidation, not the retrieval of spatial hippocampal-dependent knowledge. These results might have some relevance to approaches aimed at modifying serotonergic functions in the brain for the treatment of disorders such as depression, anxiety, post-traumatic stress, and amnesia.

Involvement of 5-HT1A and GABAA receptors in the anxiolytic-like effects of Cinnamomum cassia in mice

An elevated plus maze (EPM) test was used to determine if the 5-HT1A, GABAA, and benzodiazepine receptors play a role in the anxiolytic-like effects of a 50% EtOH extract of Cinnamomum cassia (C. cassia) in mice. A single treatment with C. cassia (750 mg/kg, p.o.) significantly increased the number of entries into and the time spent in the open arms of the EPM compared with the controls. A repeated treatment with C. cassia (100 mg/kg, 5 days, p.o.) significantly increased the time spent in the open arms of the EPM. Moreover, WAY 100635, (+)-bicuculline, and flumazenil blocked the effect of C. cassia. However, there were no changes in the locomotor activity and horizontal wire test observed in any group compared with the controls. Taken together, these results show that C. cassia has no adverse effects, such as myorelaxant effects, and might be an effective anxiolytic agent by regulating the serotonergic and GABAergic system.

Elevated mazes as animal models of anxiety: effects of serotonergic agents

This article reviews reported results about the effects of drugs that act upon the serotonergic neurotransmission measured in three elevated mazes that are animal models of anxiety. A bibliographic search has been performed in MEDLINE using different combinations of the key words X-maze, plus-maze, T-maze, serotonin and 5-HT, present in the title and/or the abstract, with no time limit. From the obtained abstracts, several publications were excluded on the basis of the following criteria: review articles that did not report original results, species other than the rat, intracerebral drug administration alone, genetically manipulated rats, and animals having any kind of experimental pathology. The reported results indicate that the effect of drugs on the inhibitory avoidance task performed in the elevated T-maze and on the spatio temporal indexes of anxiety measured in the X and plus mazes correlate with their effect in patients diagnosed with generalized anxiety disorder. In contrast, the drug effects on the one-way escape task in the elevated T-maze predict the drug response of panic disorder patients. Overall, the drug effects assessed with the avoidance task in the T-maze are more consistent than those measured through the anxiety indexes of the X and plus mazes. Therefore, the elevated T-maze is a promising animal model of generalized anxiety and panic disorder.

Serotonin and psychostimulant addiction: Focus on 5-HT1A-receptors

Serotonin(1A)-receptors (5-HT(1A)-Rs) are important components of the 5-HT system in the brain. As somatodendritic autoreceptors they control the activity of 5-HT neurons, and, as postsynaptic receptors, the activity in terminal areas. Cocaine (COC), amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine ("Ecstasy", MDMA) are psychostimulant drugs that can lead to addiction-related behavior in humans and in animals. At the neurochemical level, these psychostimulant drugs interact with monoamine transporters and increase extracellular 5-HT, dopamine and noradrenalin activity in the brain. The increase in 5-HT, which, in addition to dopamine, is a core mechanism of action for drug addiction, hyperactivates 5-HT(1A)-Rs. Here, we first review the role of the various 5-HT(1A)-R populations in spontaneous behavior to provide a background to elucidate the contribution of the 5-HT(1A)-Rs to the organization of psychostimulant-induced addiction behavior. The progress achieved in this field shows the fundamental contribution of brain 5-HT(1A)-Rs to virtually all behaviors associated with psychostimulant addiction. Importantly, the contribution of pre- and postsynaptic 5-HT(1A)-Rs can be dissociated and frequently act in opposite directions. We conclude that 5-HT(1A)-autoreceptors mainly facilitate psychostimulant addiction-related behaviors by a limitation of the 5-HT response in terminal areas. Postsynaptic 5-HT(1A)-Rs, in contrast, predominantly inhibit the expression of various addiction-related behaviors directly. In addition, they may also influence the local 5-HT response by feedback mechanisms. The reviewed findings do not only show a crucial role of 5-HT(1A)-Rs in the control of brain 5-HT activity and spontaneous behavior, but also their complex role in the regulation of the psychostimulant-induced 5-HT response and subsequent addiction-related behaviors.

5-HT1A receptors are involved in the anxiolytic effect of Delta9-tetrahydrocannabinol and AM 404, the anandamide transport inhibitor, in Sprague-Dawley rats

The mechanism mediating the effects of cannabinoids on anxiety-related responses appear to involve cannabinoid CB1 and non-CB1 receptors. However, other neurotransmitters may play a role in such effect. This study shows evidence of an interaction between endocannabinoid system and serotonin (5-HT), 1A receptor subtype on anxiety-like behavior in Sprague-Dawley rats. The exogenous cannabinoid agonist, Delta9-tetrahydrocannabinol (THC), and N-(4-hydroxyphenyl)-arachidonylamide, the anandamide transporter inhibitor (AM 404) were evaluated in the elevated plus maze test. THC (0.075-0.75 mg/kg i.p.), given 30 min and AM 404 (0.75-1.25 mg/kg i. p.), given 60 min before the test, exhibited a dose-response anxiolytic effect evaluated in terms of increase in the percentage of total entries and time spent in the open and decrease of total entries and time spent in the closed arms. The anxiolytic effect obtained with the maximal active dose of both THC (0.75 mg/kg) and AM 404 (1.25 mg/kg) was blocked by the 5-HT1A receptor antagonist, N-[2-[4-(2-methoxyphenyl) piperazin-1-yl]ethyl]-N-pyridin-2-yl-cyclohexanecarboxamide dihydro chloride (WAY-100635 (300 microg/kg, s.c.), given 30 min before THC or 15 min before AM 404. The combination of an ineffective dose of THC (0.015 mg/kg) or AM 404 (0.015 mg/kg) on anxiety-related responses with an ineffective dose of the 5HT(1A) receptor agonist, 8-Hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT) (7.5 microg/kg, i.p.), led to a synergistic effect. No interference with spontaneous motor activity, evaluated in an activity cage for 5 min, in rats given the drugs alone or in combination, was found. These data suggest that the anxiolytic effect produced by endo- and eso-cannabinoids is modulated by 5-HT1A receptors.

Effects of Milnacipran in Animal Models of Anxiety and Memory

Serotonin (5-HT) and noradrenaline (NA) are involved in both pathogenesis and recovery from depression and anxiety. We examined the effects of acute and chronic treatment with milnacipran, a serotonin/noradrenaline reuptake inhibitors (SNRIs) antidepressant, on anxiety and memory retention in rats. Male Wistar rats received acute or chronic administration of milnacipran (12.5, 25 or 50 mg/kg) or saline (control group). The animals were separately submitted to elevated plus-maze, inhibitory avoidance and open-field tasks 1 h after injection, in the acute group, or 23 h after last injection, in the chronic group. Our results showed an anxiolytic-like effect after chronic administration of milnacipran at doses of 25 and 50 mg/kg. The treatment does not interfere in memory retention and habituation to a novel environment at any doses studied. These findings support that milnacipran, an established SNRIs antidepressant, can also be useful in the treatment of anxiety disorders.

Effects of chronic treatment with fluvoxamine and paroxetine during adolescence on serotonin-related behavior in adult male rats

Selective Serotonin Reuptake Inhibitors (SSRIs) are designed to treat adults, but are increasingly prescribed for adolescents. SSRIs might cause permanent changes in serotonin-related behavior in adolescents, since their serotonergic system is still developing. Male Wistar rats were treated with paroxetine (15 mg/kg p.o.) or fluvoxamine (30 mg/kg p.o.) throughout adolescence. After a washout period their behavior in the elevated plus-maze, prepulse inhibition test, Forced swimming test and elevated T-maze were studied. In addition, the effects of the 5-HT(1A) receptor agonist 8-OH-DPAT on sexual behavior and lower lip retraction were measured. Paroxetine mildly inhibited weight gain during treatment. Both SSRIs caused a reduction in ejaculation frequency and in time spent on the open arm of the elevated plus-maze in adult rats. Fluvoxamine slightly increased avoidance latency in the elevated T-maze compared to paroxetine. No differences between the groups were found in the other tests. Apparently, chronic treatment with SSRIs during adolescence may cause mild changes in adult behavior.

Postsynaptic 5-HT1B receptors modulate electroshock-induced generalised seizures in rats

1. Although an important regulatory role for serotonin (5-HT) in seizure activation and propagation is well established, relatively little is known of the function of specific 5-HT receptor subtypes on seizure modulation. 2. The aim of the present study was to investigate the role of 5-HT(1A, 1B and 1D) receptors in modulating generalised seizures in the rat maximal electroshock seizure threshold (MEST) test. 3. The mixed 5-HT receptor agonists SKF 99101 (5-20 mg kg(-1) i.p.) and RU 24969 (1-5 mg kg(-1) i.p.), 0.5 h pretest, both produced marked dose-related increases in seizure threshold. These agents share high affinity for 5-HT(1A, 1B and 1D) receptors. 4. Antiseizure effects induced by submaximal doses of these agonists were maintained following p-chlorophenylalanine (150 mg kg(-1) i.p. x 3 days)-induced 5-HT depletion. 5. The anticonvulsant action of both SKF 99101 (15 mg kg(-1) i.p.) and RU 24969 (2.5 mg kg(-1) i.p.) was dose-dependently abolished by the selective 5-HT1B receptor antagonist SB-224289 (0.1-3 mg kg(-1) p.o., 3 h pretest) but was unaffected by the selective 5-HT1A receptor antagonist WAY 100635 (0.01-0.3 mg kg(-1) s.c., 1 h pretest). This indicates that 5-HT1B receptors are primarily involved in mediating the anticonvulsant properties of these agents. 6. In addition, the ability of the 5-HT(1B/1D) receptor antagonist GR 127935 (0.3-3 mg kg(-1) s.c., 60 min pretest) to dose-dependently inhibit SKF 99101-induced elevation of seizure threshold also suggests possible downstream involvement of 5-HT1D receptors in the action of this agonist, although confirmation awaits the identification of a selective 5-HT1D receptor antagonist. 7. Overall, these data demonstrate that stimulation of postsynaptic 5-HT1B receptors inhibits electroshock-induced seizure spread in rats.

Serotonin (1A) receptor involvement in acute 3,4-methylenedioxymethamphetamine (MDMA) facilitation of social interaction in the rat

The current study assessed whether various co-administered serotonin (5-HT) receptor antagonists could prevent some of the acute behavioral effects of 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") in rats. In the social interaction test, MDMA (5 mg/kg) significantly increased the duration of total social interaction between two conspecifics meeting for the first time. Microanalysis showed that MDMA increased adjacent lying and approach behaviours while reducing anogenital sniffing. MDMA (5 mg/kg) also caused elements of the serotonin syndrome including low body posture and piloerection. In the emergence test, MDMA significantly increased hide time and emergence latency indicating increased anxiety-like behavior. Pretreatment with the 5HT 1A receptor antagonist, WAY 100635 (1 mg/kg), prevented MDMA-induced increases in social interaction and markers of the serotonin syndrome while the 5-HT 1B receptor antagonist GR 55562 (1 mg/kg) and 5-HT 2A receptor antagonist ketanserin (1 mg/kg) were ineffective. The 5-HT 2B/2C receptor antagonist, SB 206553 (2 mg/kg), prevented MDMA-induced prosocial effects but caused pronounced thigmotaxis (hyperactivity at the periphery of the testing chamber). The anxiogenic effect of MDMA on the emergence test was not prevented by pretreatment with any of the 5-HT receptor antagonists tested. These results indicate that prosocial effect of MDMA may involve 5-HT 1A and possibly 5-HT 2B/2C receptors. In contrast, MDMA-induced generalised anxiety, as measured by the emergence test, seems unlikely to involve the 5-HT 1A, 5-HT 1B or 5-HT 2A, 5-HT 2B or 5-HT 2C receptors.

Effect of the postsynaptic 5-HT1A receptor antagonist MM-77 on stressed mice treated with 5-HT1A receptor agents

The pharmacological effect of the 5-HT1A receptor ligands, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), indorenate, and buspirone, alone or in combination with the antagonist MM-77, was studied in mice subjected to forced swimming. It was confirmed that this stressful factor produces an anxiolytic-like effect, which is reversed by the mentioned 5-HT1A receptor agonists. Only the 8-OH-DPAT-induced decrease of such an effect could be blocked by the postsynaptic antagonist of the 5-HT1A receptor 1-(2-methoxyphenyl)-4-[(4-succinimido)butyl]-piperazine (MM-77). Stressing by forced swimming seems to induce plastic changes in 5-HT1A receptors, which in turn modify the behavioural actions of 5-HT1A receptor agents.

Anxiolytic effect of berberine on exploratory activity of the mouse in two experimental anxiety models: interaction with drugs acting at 5-HT receptors

The aim of this study was to assess the anxiolytic effect of berberine (abbrev. BER) using two experimental anxiety models in the mouse. In the black and white test of anxiety, berberine (100, 500 mg/kg) produced an increase in the first time entry, time spent in the white section, and total changes between two compartments. On the other hand, in the elevated plus-maze test, berberine (100, 500 mg/kg) produced an increase in the time spent and arm entries in the open arms, and a decrease in the time spent and arm entries in the closed arms. Berberine (500 mg/kg) decreased locomotor activity in mice. Furthermore, BER at 100, 500 mg/kg decreased concentrations of NE, DA and 5-HT, and increased the concentrations of VMA, HVA and 5-HIAA in the brain stem. BER also attenuated the anxiogenic effect of WAY-100635, 8-OH DPAT and DOI and enhanced the anxiolytic effect of BUS, p-MPPI and RIT in the elevated plus-maze. These results suggested that berberine at 100 mg/kg had a significant anxiolytic-like effect, which was similar to that observed with 1 mg/kg diazepam and 2 mg/kg buspirone. The anxiolytic mechanism of BER might be related to the increase in turnover rates of monoamines in the brain stem and decreased serotonergic system activity. Moreover, BER decreased serotonergic system activity via activation of somatodendritic 5-HT1A autoreceptors and inhibition of postsynaptic 5-HT1A and 5-HT2 receptors.

Tricyclic pyridones as functionally selective human GABAAα2/3 receptor-ion channel ligands

A series of tricyclic pyridones has been evaluated as benzodiazepine site ligands with functional selectivity for the alpha(3) over the alpha(1) containing subtype of the human GABA(A) receptor ion channel. This investigation led to the identification of a high affinity, functionally selective, orally bioavailable benzodiazepine site ligand that demonstrated activity in rodent anxiolysis models and reduced sedation relative to diazepam.

Involvement of 5-HT1A receptors in behavioural effects of the cannabinoid receptor agonist CP 55,940 in male rats

We have studied the possible interaction between the cannabinoid receptor agonist CP 55,940 (1 and 50 microg/kg) and the 5-HT1A receptor antagonist WAY 100635 (1 mg/kg) in the modulation of plus-maze and holeboard activity in Wistar adult male rats. In the plus-maze, the higher dose of CP 55,940 induced an anxiogenic-like effect, whereas the lower dose induced anxiolytic-like responses. The 5-HT1A antagonist, which was silent in this test, attenuated the anxiogenic, but not the anxiolytic, effect of CP 55,940. In the holeboard, the higher dose of CP 55,940 significantly decreased head-dipping duration, and WAY 100635, which did not affect exploratory head-dipping when administered alone, antagonized this effect. The administration of WAY 100635 significantly increased grooming behaviour, and this effect was inhibited by the two doses of CP 55,940, which did not exert any effect, per se, on this parameter. We provide the first evidence implicating 5-HT1A receptors in anxiety-related behavioural responses to a cannabinoid agonist.

The effect of social factors on the anxiolytic efficacy of buspirone in male rats, male mice, and men

Earlier findings suggest that housing conditions in laboratory animals and life events in humans influence the efficacy of anxiolytic drugs. Here we report on the impact of social isolation on buspirone efficacy in male mice and rats as assessed by the elevated plus-maze. In addition, the impact of social support on buspirone efficacy was assessed in male patients. When administered 30 min before testing and irrespective of housing conditions, buspirone significantly suppressed locomotor activity both in mice (6 mg/kg) and rats (10 mg/kg) and, as such, other behavioral changes observed at this time point must be seen as behaviorally nonselective. However, these locomotor disruptive effects of buspirone were not evident in either species at longer injection-test intervals (2 and 4 h). When given 2 h prior to testing, a low (3 mg/kg) but not high (10 mg/kg) dose of buspirone increased the frequency of open arm exploration in rats (but not mice) irrespective of housing conditions. At the longest injection-test interval used (4 h), buspirone increased the duration of open arm exploration in individually housed, but not group-housed, rats. Similar, though somewhat less robust, effects were observed in male mice at this time. In a double-blind placebo-controlled study with male patients, chronic buspirone treatment (3 x 10 mg daily for 6 weeks) produced a highly significant reduction in scores on the Hamilton Rating Scale for Anxiety (HAM-A). Multiple regression analysis of social support received by patients indicated that the support of nonrelatives (but not of family or other relatives) was a strong positive predictor of buspirone efficacy. Taken together, our data support the hypothesis that social conditions affect the anxiolytic efficacy of buspirone. Results are discussed in relation to differences in the social organization of the three species investigated.

Mice lacking the serotonin transporter exhibit 5-HT(1A) receptor-mediated abnormalities in tests for anxiety-like behavior

The serotonin transporter (5-HTT) regulates serotonergic neurotransmission via clearance of extracellular serotonin. Abnormalities in 5-HTT expression or function are found in mood and anxiety disorders, and the 5-HTT is a major target for antidepressants and anxiolytics. The 5-HTT is further implicated in the pathophysiology of these disorders by evidence that genetic variation in the promoter region of the HTT (SLC6A4) is associated with individual differences in anxiety and neural responses to fear. To further evaluate the role of the 5-HTT in anxiety, we employed a mouse model in which the 5-HTT gene (htt) was constitutively inactivated. 5-HTT -/- mice were characterized for anxiety-related behaviors using a battery of tests (elevated plus maze, light<-->dark exploration test, emergence test, and open field test). Male and female 5-HTT -/- mice showed robust phenotypic abnormalities as compared to +/+ littermates, suggestive of increased anxiety-like behavior and inhibited exploratory locomotion. The selective 5-HT(1A) receptor antagonist, WAY 100635 (0.05-0.3 mg/kg), produced a significant anxiolytic-like effect in the elevated plus maze in 5-HTT -/- mice, but not +/+ controls. The present findings demonstrate abnormal behavioral phenotypes in 5-HTT null mutant mice in tests for anxiety-like and exploratory behavior, and suggest a role for the 5-HT(1A) receptor in mediating these abnormalities. 5-HTT null mutant mice provide a model to investigate the role of the 5-HTT in mood and anxiety disorders.

Hippocampal serotonergic system is involved in anxiety-like behavior induced by corticotropin-releasing factor

To clarify the interaction between anxiety-like behavior produced by corticotropin-releasing factor (CRF) and the 5-HT system, we investigated the effects of intracerebroventricular (i.c.v.) administration of CRF on an elevated plus-maze performance as indices of anxiety, measuring extracellular levels of 5-HT in the ventral hippocampus using an in vivo brain dialysis method in rats. The time spent in the open arms of the maze and the number of open arm entries were decreased in a dose-dependent manner by the administration of CRF (0.3-1.0 microg/rat). These effects of CRF were prevented by pretreatment with a 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, s.c.). In biochemical studies, CRF increased 5-HT release about 150-250% above baseline in the ventral hippocampus and this elevation was significantly inhibited by a CRF receptor antagonist, alpha-Helical CRF(9-41) (50 mug/rat), and 5-HT(1A) receptor agonist, 8-OH-DPAT (0.5 mg/kg, s.c.). These results suggested that the anxiety-like effect produced by CRF may have involved increased 5-HT transmission in the ventral hippocampus. Taken with the evidence for hypersecretion of CRF in patients with depression and anxiety-related disorders, our findings lead to the intriguing hypothesis that interaction between CRF and 5-HT, especially in the ventral hippocampus, plays a role in the etiology of affective and anxiety disorders.