Effects of genetic background and null mutation of 5-HT1A receptors on basal and stress-induced body temperature: modulation by serotonergic and GABAA-ergic drugs

Synthesis and Evaluation of the Antidepressant-like Properties of HBK-10, a Novel 2-Methoxyphenylpiperazine Derivative Targeting the 5-HT1A and D2 Receptors

The increasing number of patients reporting depressive symptoms requires the design of new antidepressants with higher efficacy and limited side effects. As our previous research showed, 2-methoxyphenylpiperazine derivatives are promising candidates to fulfill these criteria. In this study, we aimed to synthesize a novel 2-methoxyphenylpiperazine derivative, HBK-10, and investigate its in vitro and in vivo pharmacological profile. After assessing the affinity for serotonergic and dopaminergic receptors, and serotonin transporter, we determined intrinsic activity of the compound at the 5-HT_1A and D₂ receptors. Next, we performed behavioral experiments (forced swim test, tail suspension test) to evaluate the antidepressant-like activity of HBK-10 in naïve and corticosterone-treated mice. We also assessed the safety profile of the compound. We showed that HBK-10 bound strongly to 5-HT_1A and D₂ receptors and presented antagonistic properties at these receptors in the functional assays. HBK-10 displayed the antidepressant-like effect not only in naïve animals, but also in the corticosterone-induced mouse depression model, i.e., chronic administration of HBK-10 reversed corticosterone-induced changes in behavior. Moreover, the compound’s sedative effect was observed at around 26-fold higher doses than the antidepressant-like ones. Our study showed that HBK-10 displayed a favorable pharmacological profile and may represent an attractive putative treatment candidate for depression.

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.

No evidence of abnormal metabolic or inflammatory activity in the brains of patients with rheumatoid arthritis: results from a preliminary study using whole-brain magnetic resonance spectroscopic imaging (MRSI)

Introduction/objectives

Many individuals with rheumatoid arthritis (RA) report persistent fatigue even after management of peripheral disease activity. This study used whole-brain magnetic resonance spectroscopic imaging (MRSI) to investigate whether abnormal inflammatory activity in the central nervous system may be associated with such symptoms. We hypothesized that RA patients would show higher brain choline (CHO), myo-inositol (MI), and lactate (LAC), and higher brain temperature than healthy controls. We further hypothesized that the metabolite levels would be positively correlated with self-reported fatigue.

Method

Thirteen women with RA provided fatigue severity ratings and underwent whole-brain MRSI and a joint examination. Thirteen healthy controls (HC) provided comparison imaging and fatigue data. CHO, MI, LAC, and brain temperature in 47 brain regions were contrasted between groups using independent-samples t tests. Significant differences were determined using a false discovery rate (FDR)-adjusted p value threshold of ≤ 0.0023. Secondary analyses obtained correlations between imaging and clinical outcomes in the RA group.

Results

No brain metabolic differences were identified between the groups. In the RA group, fatigue severity was positively correlated with CHO in several brain regions—most strongly the right frontal lobe (r_s = 0.823, p < 0.001). MI was similarly correlated with fatigue, particularly in the right calcarine fissure (r_s = 0.829, p < 0.001). CHO in several regions was positively correlated with joint swelling and tenderness.

Conclusions

We conclude that abnormal brain metabolites are not a common feature of RA, but may been seen in patients with persistent fatigue or disease activity after conventional treatment.

Key Points • Whole-brain magnetic resonance spectroscopy revealed no metabolic abnormalities in the brain in patients with rheumatoid arthritis. • Brain choline levels were correlated with fatigue severity reported by RA patients and with peripheral joint swelling and tenderness. • Brain myo-inositol levels were similarly correlated with fatigue severity in RA patients.

Electronic supplementary material

The online version of this article (10.1007/s10067-019-04923-5) contains supplementary material, which is available to authorized users.

Translational Studies in the Complex Role of Neurotransmitter Systems in Anxiety and Anxiety Disorders

Discovery of innovative anxiolytics is severely hampering. Existing anxiolytics are developed decades ago and are still the therapeutics of choice. Moreover, lack of new drug targets forecasts a severe jeopardy in the future treatment of the huge population of CNS-diseased patients. We simply lack the knowledge on what is wrong in brains of anxious people (normal and diseased). Translational research, based on interacting clinical and preclinical research, is extremely urgent. In this endeavor, genetic and genomic approaches are part of the spectrum of contributing factors. We focus on three druggable targets: serotonin transporter, 5-HT_1A, and GABA_A receptors. It is still uncertain whether and how these targets are involved in normal and diseased anxiety processes. For serotonergic anxiolytics, the slow onset of action points to indirect effects leading to plasticity changes in brain systems leading to reduced anxiety. For GABA_A benzodiazepine drugs, acute anxiolytic effects are found indicating primary mechanisms directly influencing anxiety processes. Close translational collaboration between fundamental academic and discovery research will lead to badly needed breakthroughs in the search for new anxiolytics.

Genetic structure of phenotypic robustness in the collaborative cross mouse diallel panel

Developmental stability and canalization describe the ability of developmental systems to minimize phenotypic variation in the face of stochastic micro-environmental effects, genetic variation and environmental influences. Canalization is the ability to minimize the effects of genetic or environmental effects, whereas developmental stability is the ability to minimize the effects of micro-environmental effects within individuals. Despite much attention, the mechanisms that underlie these two components of phenotypic robustness remain unknown. We investigated the genetic structure of phenotypic robustness in the collaborative cross (CC) mouse reference population. We analysed the magnitude of fluctuating asymmetry (FA) and among-individual variation of cranial shape in reciprocal crosses among the eight parental strains, using geometric morphometrics and a diallel analysis based on a Bayesian approach. Significant differences among genotypes were found for both measures, although they were poorly correlated at the level of individuals. An overall positive effect of inbreeding was found for both components of variation. The strain CAST/EiJ exerted a positive additive effect on FA and, to a lesser extent, among-individual variance. Sex- and other strain-specific effects were not significant. Neither FA nor among-individual variation was associated with phenotypic extremeness. Our results support the existence of genetic variation for both developmental stability and canalization. This finding is important because robustness is a key feature of developmental systems. Our finding that robustness is not related to phenotypic extremeness is consistent with theoretical work that suggests that its relationship to stabilizing selection is not straightforward.

Homer2 regulates alcohol and stress cross-sensitization

An interaction exists between stress and alcohol in the etiology and chronicity of alcohol use disorders, yet a knowledge gap exists regarding the neurobiological underpinnings of this interaction. In this regard, we employed an 11-day unpredictable, chronic, mild stress (UCMS) procedure to examine for stress-alcohol cross-sensitization of motor activity as well as alcohol consumption/preference and intoxication. We also employed immunoblotting to relate the expression of glutamate receptor-related proteins within subregions of the nucleus accumbens (NAC) to the manifestation of behavioral cross-sensitization. UCMS mice exhibited a greater locomotor response to an acute injection of 2 g/kg alcohol than unstressed controls and this cross-sensitization extended to alcohol intake (0-20 percent), as well as to the intoxicating and sedative properties of 3 and 5 g/kg alcohol, respectively. Regardless of prior alcohol injection (2 g/kg), UCMS mice exhibited elevated NAC shell levels of mGlu1α, GluN2b and Homer2, as well as lower phospholipase Cβ within this subregion. GluN2b levels were also lower within the NAC core of UCMS mice. The expression of stress-alcohol locomotor cross-sensitization was associated with lower mGlu1α within the NAC core and lower extracellular signal-regulated kinase activity within both NAC subregions. As Homer2 regulates alcohol sensitization, we assayed also for locomotor cross-sensitization in Homer2 wild-type (WT) and knock-out (KO) mice. WT mice exhibited a very robust cross-sensitization that was absent in KO animals. These results indicate that a history of mild stress renders an animal more sensitive to the psychomotor and rewarding properties of alcohol, which may depend on neuroplasticity within NAC glutamate transmission.

Pharmacological and methodological aspects of the separation-induced vocalization test in guinea pig pups; a systematic review and meta-analysis

The separation-induced vocalization test in guinea pig pups is one of many that has been used to screen for anxiolytic-like properties of drugs. The test is based on the cross-species phenomenon that infants emit distress calls when placed in social isolation. Here we report a systematic review and meta-analysis of pharmacological intervention in the separation-induced vocalization test in guinea pig pups. Electronic databases were searched for original research articles, yielding 32 studies that met inclusion criteria. We extracted data on pharmacological intervention, animal and methodological characteristics, and study quality indicators. Meta-analysis showed that the different drug classes in clinical use for the treatment of anxiety disorders, have comparable effects on vocalization behaviour, irrespective of their mechanism of action. Of the experimental drugs, nociception (NOP) receptor agonists proved very effective in this test. Analysis further indicated that the commonly used read-outs total number and total duration of vocalizations are equally valid. With regard to methodological characteristics, repeated testing of pups as well as selecting pups with moderate or high levels of vocalization were associated with larger treatment effects. Finally, reporting of study methodology, randomization and blinding was poor and Egger's test for small study effects showed that publication bias likely occurred. This review illustrates the value of systematic reviews and meta-analyses in improving translational value and methodological aspects of animal models. It further shows the urgent need to implement existing publication guidelines to maximize the output and impact of experimental animal studies.

Serotonin: a never-ending story

The neurotransmitter serotonin is an evolutionary ancient molecule that has remarkable modulatory effects in almost all central nervous system integrative functions, such as mood, anxiety, stress, aggression, feeding, cognition and sexual behavior. After giving a short outline of the serotonergic system (anatomy, receptors, transporter) the author's contributions over the last 40 years in the role of serotonin in depression, aggression, anxiety, stress and sexual behavior is outlined. Each area delineates the work performed on animal model development, drug discovery and development. Most of the research work described has started from an industrial perspective, aimed at developing animals models for psychiatric diseases and leading to putative new innovative psychotropic drugs, like in the cases of the SSRI fluvoxamine, the serenic eltoprazine and the anxiolytic flesinoxan. Later this research work mainly focused on developing translational animal models for psychiatric diseases and implicating them in the search for mechanisms involved in normal and diseased brains and finding new concepts for appropriate drugs.

The behavioral pharmacology of zolpidem: evidence for the functional significance of α1-containing GABA(A) receptors

RATIONALE

Zolpidem is a positive allosteric modulator of γ-aminobutyric acid (GABA) with preferential binding affinity and efficacy for α1-subunit containing GABA(A) receptors (α1-GABA(A)Rs). Over the last three decades, a variety of animal models and experimental procedures have been used in an attempt to relate the behavioral profile of zolpidem and classic benzodiazepines (BZs) to their interaction with α1-GABA(A)Rs.

OBJECTIVES

This paper reviews the results of rodent and non-human primate studies that have evaluated the effects of zolpidem on motor behaviors, anxiety, memory, food and fluid intake, and electroencephalogram (EEG) sleep patterns. Also included are studies that examined zolpidem's discriminative, reinforcing, and anticonvulsant effects as well as behavioral signs of tolerance and withdrawal.

RESULTS

The literature reviewed indicates that α1-GABA(A)Rs play a principle role in mediating the hypothermic, ataxic-like, locomotor- and memory-impairing effects of zolpidem and BZs. Evidence also suggests that α1-GABA(A)Rs play partial roles in the hypnotic, EEG sleep, anticonvulsant effects, and anxiolytic-like of zolpidem and diazepam. These studies also indicate that α1-GABA(A)Rs play a more prominent role in mediating the discriminative stimulus, reinforcing, hyperphagic, and withdrawal effects of zolpidem and BZs in primates than in rodents.

CONCLUSIONS

The psychopharmacological data from both rodents and non-human primates suggest that zolpidem has a unique pharmacological profile when compared with classic BZs. The literature reviewed here provides an important framework for studying the role of different GABA(A)R subtypes in the behavioral effects of BZ-type drugs and helps guide the development of new pharmaceutical agents for disorders currently treated with BZ-type drugs.

5-HT(1A) [corrected] receptors in mood and anxiety: recent insights into autoreceptor versus heteroreceptor function

RATIONALE

Serotonin (5-HT) neurotransmission is intimately linked to anxiety and depression and a diverse body of evidence supports the involvement of the main inhibitory serotonergic receptor, the serotonin-1A (5-HT(1A)) subtype, in both disorders.

OBJECTIVES

In this review, we examine the function of 5-HT(1A) receptor subpopulations and re-interpret our understanding of their role in mental illness in light of new data, separating both spatial (autoreceptor versus heteroreceptor) and the temporal (developmental versus adult) roles of the endogenous 5-HT(1A) receptors, emphasizing their distinct actions in mediating anxiety and depression-like behaviors.

RESULTS

It is difficult to unambiguously distinguish the effects of different populations of the 5-HT(1A) receptors with traditional genetic animal models and pharmacological approaches. However, with the advent of novel genetic systems and subpopulation-selective pharmacological agents, direct evidence for the distinct roles of these populations in governing emotion-related behavior is emerging.

CONCLUSIONS

There is strong and growing evidence for a functional dissociation between auto- and heteroreceptor populations in mediating anxiety and depressive-like behaviors, respectively. Furthermore, while it is well established that 5-HT(1A) receptors act developmentally to establish normal anxiety-like behaviors, the developmental role of 5-HT(1A) heteroreceptors is less clear, and the specific mechanisms underlying the developmental role of each subpopulation are likely to be key elements determining mood control in adult subjects.

The role of the serotonergic and GABA system in translational approaches in drug discovery for anxiety disorders

There is ample evidence that genetic factors play an important role in anxiety disorders. In support, human genome-wide association studies have implicated several novel candidate genes. However, illumination of such genetic factors involved in anxiety disorders has not resulted in novel drugs over the past decades. A complicating factor is the heterogeneous classification of anxiety disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and diverging operationalization of anxiety used in preclinical and clinical studies. Currently, there is an increasing focus on the gene × environment (G × E) interaction in anxiety as genes do not operate in isolation and environmental factors have been found to significantly contribute to the development of anxiety disorders in at-risk individuals. Nevertheless, extensive research on G × E mechanisms in anxiety has not resulted in major breakthroughs in drug discovery. Modification of individual genes in rodent models has enabled the specific study of anxiety in preclinical studies. In this context, two extensively studied neurotransmitters involved in anxiety are the gamma-aminobutyric acid (GABA) and 5-HT (5-hydroxytryptamine) system. In this review, we illustrate the complex interplay between genes and environment in anxiety processes by reviewing preclinical and clinical studies on the serotonin transporter (5-HTT), 5-HT1A receptor, 5-HT2 receptor, and GABAA receptor. Even though targets from the serotonin and GABA system have yielded drugs with known anxiolytic efficacy, the relation between the genetic background of these targets and anxiety symptoms and development of anxiety disorders is largely unknown. The aim of this review is to show the vast complexity of genetic and environmental factors in anxiety disorders. In light of the difficulty with which common genetic variants are identified in anxiety disorders, animal models with translational validity may aid in elucidating the neurobiological background of these genes and their possible role in anxiety. We argue that, in addition to human genetic studies, translational models are essential to map anxiety-related genes and to enhance our understanding of anxiety disorders in order to develop potentially novel treatment strategies.

Determination of GABA(Aα1) and GABA (B1) receptor subunits expression in tissues of gilts during the late gestation

GABA(Aα1) and GABA(B1) receptor subunits are responsible for most behavioral, physiological and pharmacological effects of GABA receptors. We investigated the expression of GABA(Aα1) and GABA(B1) receptor subunits in different tissues of gilts during late pregnancy in hot summer. The mRNA abundance of GABA(Aα1) receptor subunit in different tissues of gilts at d 90 and d 110 of gestation was as follows: d 90: brain > lung > liver > ovary > spleen > kidney > heart; d 110: brain > lung > spleen > liver > ovary > kidney > heart. And, the mRNA abundance of GABA(B1) receptor subunit was as follows: d 90: spleen > lung > brain > kidney > ovary > liver > heart; d 110: spleen > lung > kidney > brain > ovary > liver > heart. The results in this trial indicated that the GABA(Aα1) receptor subunit was abundantly expressed in brain, while GABA(B1) receptor subunit was abundant in spleen and lung of gilts during late gestation. There were no gestation stage-dependent effects on GABA(Aα1) and GABA(B1) receptor subunits expression in all tissues.

Models of anxiety: stress-induced hyperthermia (SIH) in singly housed mice

Described in this unit is the stress-induced hyperthermia (SIH) test in mice in a single-housed format. This protocol has proven reliable in detecting the anxiolytic properties of test compounds. In this test, SIH is quantified in singly housed mice using a rectal temperature measurement as the stressor. Rectal temperature is measured twice at a 10-min interval. Due to the stress experienced during the first temperature measurement, the temperature of the second measurement (T(2)) is ∼0.8° to 1.5°C higher than that of the first (T(1)). This difference in temperature (ΔT = T(2) - T(1)) is defined as the SIH response. The SIH response is reduced by different classes of anxiolytics. The SIH test is simple and robust, it does not require training of animals, and test compound effects on motor behavior, feeding, and nociception do not affect test outcome. Furthermore, it is one of few anxiety tests that focuses on the physiological component of anxiety.

The age of anxiety: role of animal models of anxiolytic action in drug discovery

Anxiety disorders are common, serious and a growing health problem worldwide. However, the causative factors, aetiology and underlying mechanisms of anxiety disorders, as for most psychiatric disorders, remain relatively poorly understood. Animal models are an important aid in giving insight into the aetiology, neurobiology and, ultimately, the therapy of human anxiety disorders. The approach, however, is challenged with a number of complexities. In particular, the heterogeneous nature of anxiety disorders in humans coupled with the associated multifaceted and descriptive diagnostic criteria, creates challenges in both animal modelling and in clinical research. In this paper, we describe some of the more widely used approaches for assessing the anxiolytic activity of known and potential therapeutic agents. These include ethological, conflict-based, hyponeophagia, vocalization-based, physiological and cognitive-based paradigms. Developments in the characterization of translational models are also summarized, as are the challenges facing researchers in their drug discovery efforts in developing new anxiolytic drugs, not least the ever-shifting clinical conceptualization of anxiety disorders. In conclusion, to date, although animal models of anxiety have relatively good validity, anxiolytic drugs with novel mechanisms have been slow to emerge. It is clear that a better alignment of the interactions between basic and clinical scientists is needed if this is to change.

Cross-species behavioural genetics: A starting point for unravelling the neurobiology of human psychiatric disorders

Identifying the genetic and neurobiological mechanisms underlying certain behavioural traits is an important strategy to understand the aetiology of various psychiatric disorders and to find potential new treatment possibilities. It has proven a great challenge to develop paradigms that allow translational research for behavioural phenotypes that are relevant for disorders across the psychiatric spectrum. Recently, there has been increasing attention for studies that implement rodent behavioural paradigms in the home cage to assess the association between genetic backgrounds and behavioural traits. The application of interspecies genetics to unravel these traits has revealed novel insights in the genetic mechanisms that are encoding phenotypes relevant to biological processes underlying psychiatric disorders. By means of two examples, namely the stress-induced hyperthermia paradigm and the home cage environment, this review aims to show that by using individual genetic variations with phenotypes obtained from mice and across categories of neuropsychiatric disorders, novel insights in the neurobiological trajectory of psychiatric disorders can be obtained.

Early-life blockade of 5-HT(1A) receptors alters adult anxiety behavior and benzodiazepine sensitivity

BACKGROUND

Early-life stress may affect 5-HT(1A) receptor circuitry, which could result in increased anxiety in later life. An increased anxiety phenotype in 5-HT(1A) receptor KO mice (1AKO) mice has been ascribed to 5-HT(1A) receptor absence during the early postnatal period. Thus, subtle and transient serotonergic changes during the early postnatal period may lead to an increased risk for developing stress-related disorders during adulthood.

METHODS

Wildtype and 1AKO mice on a Swiss-Webster (SW) background were treated during the early postnatal period with vehicle or the 5-HT(1A) receptor antagonist WAY-100,635.

RESULTS

Pharmacologic 5-HT(1A) receptor blockade during the early postnatal period induced long-lasting effects on anxiety and benzodiazepine sensitivity in adolescent and adult mice on a Swiss-Webster background and resembles the SW 1AKO phenotype. Furthermore, WAY-100,635-treated mice had increased cortical gamma-aminobutyric acid-A receptor (GABA(A)R) alpha(1) and alpha(3) subunit levels and increased hippocampal GABA(A)R alpha(2) subunit levels.

CONCLUSIONS

Absence of 5-HT(1A)R signaling during early stages of brain maturation predisposes an organism to affective dysfunction later in life. Because early-life treatment with WAY-100,635 in Swiss-Webster mice reduced diazepam sensitivity and increased GABA(A)R alpha subunit levels in the prefrontal cortex and hippocampus, our data suggest a putative link between early-life disruption of the serotonergic system and the emergence of increased anxiety and decreased benzodiazepine responsivity at adult age. Moreover, early-life 5-HT(1A) receptor functionality appears to be essential for the development of normal GABA(A)R functionality. This study may have clinical implications for psychoactive drug use during pregnancy and for the pharmacogenetic background of benzodiazepine sensitivity.

5-HT1A autoreceptor levels determine vulnerability to stress and response to antidepressants

Most depressed patients don't respond to their first drug treatment, and the reasons for this treatment resistance remain enigmatic. Human studies implicate a polymorphism in the promoter of the serotonin-1A (5-HT(1A)) receptor gene in increased susceptibility to depression and decreased treatment response. Here we develop a new strategy to manipulate 5-HT(1A) autoreceptors in raphe nuclei without affecting 5-HT(1A) heteroreceptors, generating mice with higher (1A-High) or lower (1A-Low) autoreceptor levels. We show that this robustly affects raphe firing rates, but has no effect on either basal forebrain serotonin levels or conflict-anxiety measures. However, compared to 1A-Low mice, 1A-High mice show a blunted physiological response to acute stress, increased behavioral despair, and no behavioral response to antidepressant, modeling patients with the 5-HT(1A) risk allele. Furthermore, reducing 5-HT(1A) autoreceptor levels prior to antidepressant treatment is sufficient to convert nonresponders into responders. These results establish a causal relationship between 5-HT(1A) autoreceptor levels, resilience under stress, and response to antidepressants.

Dissociating anxiolytic and sedative effects of GABAAergic drugs using temperature and locomotor responses to acute stress

RATIONALE

The stress-induced hyperthermia (SIH) model is an anxiety model that uses the transient rise in body temperature in response to acute stress. Benzodiazepines produce anxiolytic as well as sedative side effects through nonselective binding to GABA(A) receptor subunits. The GABA(A) receptor alpha(1) subunit is associated with sedation, whereas the GABA(A) receptor alpha(2) and alpha(3) subunits are involved in anxiolytic effects.

OBJECTIVES

We therefore examined the effects of (non)subunit-selective GABA(A) receptor agonists on temperature and locomotor responses to novel cage stress.

RESULTS

Using telemetric monitoring of temperature and locomotor activity, we found that nonsubunit-selective GABA(A) receptor agonist diazepam as well as the alpha(3) subunit-selective receptor agonist TP003 dose-dependently attenuated SIH and locomotor responses. Administration of GABA(A) receptor alpha(1)-selective agonist zolpidem resulted in profound hypothermia and locomotor sedation. The GABA(A) receptor alpha(1)-selective antagonist betaCCt antagonized the hypothermia, but did not reverse the SIH response attenuation caused by diazepam and zolpidem. These results suggest an important regulating role for the alpha(1) subunit in thermoregulation and sedation. Ligands of extrasynaptic GABA(A) receptors such as alcohol and nonbenzodiazepine THIP attenuated the SIH response only at high doses.

CONCLUSIONS

The present study confirms a putative role for the GABA(A) receptor alpha(1) subunit in hypothermia and sedation and supports a role for alpha(2/3) subunit GABA(A) receptor agonists in anxiety processes. In conclusion, we show that home cage temperature and locomotor responses to novel home cage stress provide an excellent tool to assess both anxiolytic and sedative effects of various (subunit-selective) GABA(A)ergic compounds.

Maternal profiling of corticotropin-releasing factor receptor 2 deficient mice in association with restraint stress

Mice deficient in corticotropin-releasing factor receptor 2 (CRF2) (C57BL/6J:129Sv background) exhibit impaired maternal defense (protection of offspring) and are more reactive to stressors than wild-type mice. To further understand CRF2's role in maternal behavior, we crossed the knockout mice with a line bred for high maternal defense that also has elevated maternal care relative to inbred lines. Maternal care was normal in knockout mice (relative to wild-type). Maternal defense was impaired as previously observed. Exposure to a mild stressor (15 min restraint) did not trigger deficits in maternal defense in either genotype as determined by a two-way repeated measures ANOVA analysis. However, when examining difference scores between unrestrained and restrained conditions, knockout mice exhibited significant decreases in maternal defense with stress, suggesting knockouts are more susceptible to a mild stressor's effects. To gain possible insights into brain activity differences between WT and KO mice, we examined c-Fos expression in association with stress. Unrestrained KO mice exhibited significantly lower c-Fos levels relative to unrestrained WT mice in 9 regions, including lateral septum and periaqueductal gray. For WT mice, restraint stress triggered c-Fos activity increases in 3 regions while for KO mice, restraint stress triggered c-Fos increases in 16 regions. Taken together, our results suggest both altered behavioral and c-Fos responses to stress in lactating CRF2 KO mice.

NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile], a unique subtype-selective GABAA receptor positive allosteric modulator: in vitro actions, pharmacokinetic properties and in vivo anxiolytic efficacy

The novel positive allosteric modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile] possesses a functional selectivity profile at GABA(A) receptors of alpha(5) > alpha(3) > alpha(2) > alpha(1) based on oocyte electrophysiology with human GABA(A) receptors. Compared with other subtype-selective ligands, NS11394 is unique in having superior efficacy at GABA(A)-alpha(3) receptors while maintaining low efficacy at GABA(A)-alpha(1) receptors. NS11394 has an excellent pharmacokinetic profile, which correlates with pharmacodynamic endpoints (CNS receptor occupancy), yielding a high level of confidence in deriving in vivo conclusions anchored to an in vitro selectivity profile and allowing for translation to higher species. Specifically, we show that NS11394 is potent and highly effective in rodent anxiety models. The anxiolytic efficacy of NS11394 is most probably mediated through its high efficacy at GABA(A)-alpha(3) receptors, although a contributory role of GABA(A)-alpha(2) receptors cannot be excluded. Compared with benzodiazepines, NS11394 has a significantly reduced side effect profile in rat (sedation, ataxia, and ethanol interaction) and mouse (sedation), even at full CNS receptor occupancy. We attribute this benign side effect profile to very low efficacy of NS11394 at GABA(A)-alpha(1) receptors and an overall partial agonist profile across receptor subtypes. However, NS11394 impairs memory in both rats and mice, which is possibly attributable to its efficacy at GABA(A)-alpha(5) receptors, albeit activity at this receptor might be relevant to its antinociceptive effects (J Pharmacol Exp Ther 327:doi;10.1124/jpet.108.144, 2008). In conclusion, NS11394 has a unique subtype-selective GABA(A) receptor profile and represents an excellent pharmacological tool to further our understanding on the relative contributions of GABA(A) receptor subtypes in various therapeutic areas.

Stress-induced hyperthermia and basal body temperature are mediated by different 5-HT(1A) receptor populations: a study in SERT knockout rats

Disturbances in the serotonergic system are implicated in many central nervous system disorders. The serotonin transporter (SERT) regulates the serotonin homeostasis in the synapse. We recently developed a rat which lacks the serotonin transporter (SERT(-/-)). It is likely that adaptive changes take place at the level of pre- and postsynaptic 5-HT receptors. Because autonomic responses are often used to measure 5-HT(1A) receptor function, we analysed these responses by examining the effects of a 5-HT(1A) receptor agonist and antagonist under in vivo conditions in the SERT(-/-) rat. Moreover, we studied the effect of a mild stressor on the body temperature (stress-induced hyperthermia) because of the known involvement of 5-HT(1A) receptors in this phenomenon. Results show that core body temperature did not differ between genotypes under basal, non-stressed conditions. Compared to SERT(+/+) rats, stress-induced hyperthermia was reduced in SERT(-/-) rats. The 5-HT(1A) receptor agonist [R(+)-N-(2[4-(2,3-dihydro-2-2-hydroxy-methyl-1,4-benzodioxin-5-yl)-1-piperazininyl]ethyl)-4-fluorobenzoamide HCl (flesinoxan) reduced stress-induced hyperthermia in both genotypes. The flesinoxan-induced hypothermia in SERT(+/+) rats was blocked by the 5-HT(1A) receptor antagonist [N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl) cyclohexane carboxamide 3HCl (WAY100635). Moreover, WAY100635-induced hyperthermia in SERT(-/-), but not in SERT(+/+) rats. In SERT(-/-) rats, WAY100635 completely blocked the flesinoxan-induced reduction of stress-induced hyperthermia. Interestingly, flesinoxan-induced hypothermia was absent in SERT(-/-) rats. It is concluded that the SERT knockout rat reveals that 5-HT(1A) receptors modulating stress-induced hyperthermia belong to a population of receptors that differs from that involved in hypothermia.

Translational aspects of pharmacological research into anxiety disorders: the stress-induced hyperthermia (SIH) paradigm

In anxiety research, the search for models with sufficient clinical predictive validity to support the translation of animal studies on anxiolytic drugs to clinical research is often challenging. This review describes the stress-induced hyperthermia (SIH) paradigm, a model that studies the activation of the autonomic nervous system in response to stress by measuring body temperature. The reproducible and robust SIH response, combined with ease of testing, make the SIH paradigm very suitable for drug screening. We will review the current knowledge on the neurobiology of the SIH response, discuss the role of GABA(A) and serotonin (5-HT) pharmacology, as well as how the SIH response relates to infectious fever. Furthermore, we will present novel data on the SIH response variance across different mice and their sensitivity to anxiolytic drugs. The SIH response is an autonomic stress response that can be successfully studied at the level of its physiology, pharmacology, neurobiology and genetics and possesses excellent animal-to-human translational properties.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.