5-HT1A receptor knockout mice and mice overexpressing corticotropin-releasing hormone in models of anxiety

Animal Models of Depression: What Can They Teach Us about the Human Disease?

Depression is apparently the most common psychiatric disease among the mood disorders affecting about 10% of the adult population. The etiology and pathogenesis of depression are still poorly understood. Hence, as for most human diseases, animal models can help us understand the pathogenesis of depression and, more importantly, may facilitate the search for therapy. In this review we first describe the more common tests used for the evaluation of depressive-like symptoms in rodents. Then we describe different models of depression and discuss their strengths and weaknesses. These models can be divided into several categories: genetic models, models induced by mental acute and chronic stressful situations caused by environmental manipulations (i.e., learned helplessness in rats/mice), models induced by changes in brain neuro-transmitters or by specific brain injuries and models induced by pharmacological tools. In spite of the fact that none of the models completely resembles human depression, most animal models are relevant since they mimic many of the features observed in the human situation and may serve as a powerful tool for the study of the etiology, pathogenesis and treatment of depression, especially since only few patients respond to acute treatment. Relevance increases by the fact that human depression also has different facets and many possible etiologies and therapies.

DTI-identified microstructural changes in the gray matter of mice overexpressing CRF in the forebrain

Increased corticotroping releasing factor (CRF) contributes to brain circuit abnormalities associated with stress-related disorders including posttraumatic stress disorder. However, the causal relationship between CRF hypersignaling and circuit abnormalities associated with stress disorders is unclear. We hypothesized that increased CRF exposure induces changes in limbic circuit morphology and functions. An inducible, forebrain-specific overexpression of CRF (CRFOE) transgenic mouse line was used to longitudinally investigate its chronic effects on behaviors and microstructural integrity of several brain regions. Behavioral and diffusion tensor imaging studies were performed before treatment, after 3-4 wks of treatment, and again 3 mo after treatment ended to assess recovery. CRFOE was associated with increased perseverative movements only after 3 wks of treatment, as well as reduced fractional anisotropy at 3 wks in the medial prefrontal cortex and increased fractional anisotropy in the ventral hippocampus at 3 mo compared to the control group. In the dorsal hippocampus, mean diffusivity was lower in CRFOE mice both during and after treatment ended. Our data suggest differential response and recovery patterns of cortical and hippocampal subregions in response to CRFOE. Overall these findings support a causal relationship between CRF hypersignaling and microstructural changes in brain regions relevant to stress disorders.

Stimulation of 5-HT receptors in anterodorsal BNST guides fear to predictable and unpredictable threat

Through pharmacological manipulation of the serotonergic (5-Hydroxytryptamin, 5-HT) system, combined with behavioral analysis, we tested the hypothesis that fear responses to predictable and unpredictable threat are regulated through stimulation of 5-HT receptors (5-HT-R) in the anterodorsal section of the bed nucleus of the stria terminalis (adBNST). Local adBNST application of 5-HT1A-R antagonist WAY100635 and 5-HT1B-R antagonist NAS-181 before fear retrieval enhanced freezing, 24 h after predictable fear conditioning. In contrast, increased fear responses to unpredictable threat were blocked by 5-HT1A-R agonist Buspirone (given before conditioning or retrieval) and 5-HT1B-R agonist CP-94253 (applied before training). Prolonged fear responses were also blocked by local application of the 5-HT2A-R antagonist R-96544 before fear retrieval, and conversely, local application of the 5-HT2A-R agonist NBOH-2C-CN hydrochloride before fear retrieval enhanced freezing 24 h after predictable conditioning, indicating augmented fear responses. Activation of inhibitory 5-HT1A- or 5-HT1B-Rs and the blockade of the excitatory 5-HT2A-R before unpredictable fear conditioning significantly reduced freezing during retrieval. The results from this study suggest that modulation of inhibitory 5-HT1A/1B-R and/or excitatory 5-HT2A-R activity in the adBNST may represent potential targets for the development of new treatment strategies in anxiety disorders. In addition, this study supports the validity and reliability of the mouse model of modulated fear to predictable and unpredictable threats to study mechanisms of fear and anxiety in combination with pharmacological manipulations.

Sex-biased cellular signaling: molecular basis for sex differences in neuropsychiatric diseases

The recognition that there are fundamental biological sex differences that extend beyond those that define sexual behavior and reproductive function has inspired the drive toward inclusion of both sexes in research design. This is supported by an underlying clinical rationale that studying both sexes is necessary to elucidate pathophysiology and develop treatments for the entire population. However, at a more basic level, sex differences, like genetic differences, can be exploited to better understand biology. Here, we discuss how sex differences at the molecular level of cell signaling and protein trafficking are amplified to create a state of vulnerability that under the right conditions can result in symptoms of neuropsychiatry disease. Although this dialogue focuses on the specific example of corticotropin-releasing factor, the potential for analogous sex differences in signaling and/or trafficking of receptors for other neuromodulators has broad biological and therapeutic implications.

HPA Axis Interactions with Behavioral Systems

Perhaps the most salient behaviors that individuals engage in involve the avoidance of aversive experiences and the pursuit of pleasurable experiences. Engagement in these behaviors is regulated to a significant extent by an individual's hormonal milieu. For example, glucocorticoid hormones are produced by the hypothalamic-pituitary-adrenocortical (HPA) axis, and influence most aspects of behavior. In turn, many behaviors can influence HPA axis activity. These bidirectional interactions not only coordinate an individual's physiological and behavioral states to each other, but can also tune them to environmental conditions thereby optimizing survival. The present review details the influence of the HPA axis on many types of behavior, including appetitively-motivated behaviors (e.g., food intake and drug use), aversively-motivated behaviors (e.g., anxiety-related and depressive-like) and cognitive behaviors (e.g., learning and memory). Conversely, the manuscript also describes how engaging in various behaviors influences HPA axis activity. Our current understanding of the neuronal and/or hormonal mechanisms that underlie these interactions is also summarized. © 2016 American Physiological Society. Compr Physiol 6:1897-1934, 2016.

Alterations in the corticotropin-releasing hormone (CRH) neurocircuitry: Insights into post stroke functional impairments

Although it is well accepted that changes in the regulation of the hypothalamic-pituitary adrenal (HPA) axis may increase susceptibility to affective disorders in the general population, this link has been less examined in stroke patients. Yet, the bidirectional association between depression and cardiovascular disease is strong, and stress increases vulnerability to stroke. Corticotropin-releasing hormone (CRH) is the central stress hormone of the HPA axis pathway and acts by binding to CRH receptors (CRHR) 1 and 2, which are located in several stress-related brain regions. Evidence from clinical and animal studies suggests a role for CRH in the neurobiological basis of depression and ischemic brain injury. Given its importance in the regulation of the neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation to stress, CRH is likely associated in the pathophysiology of post stroke emotional impairments. The goals of this review article are to examine the clinical and experimental data describing (1) that CRH regulates the molecular signaling brain circuit underlying anxiety- and depression-like behaviors, (2) the influence of CRH and other stress markers in the pathophysiology of post stroke emotional and cognitive impairments, and (3) context and site specific interactions of CRH and BDNF as a basis for the development of novel therapeutic targets. This review addresses how the production and release of the neuropeptide CRH within the various regions of the mesocorticolimbic system influences emotional and cognitive behaviors with a look into its role in psychiatric disorders post stroke.

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

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

The Combination of Scopolamine and Psychostimulants for the Prevention of Severe Motion Sickness

BACKGROUND AND AIMS

Severe motion sickness is a huge obstacle for people conducting precise aviation, marine or emergency service tasks. The combination of scopolamine and d-amphetamine is most effective in preventing severe motion sickness. However, this combination is not included in any present pharmacopoeia due to the abuse liability of d-amphetamine. We wanted to find a combination to replace it for the treatment of severe motion sickness.

METHODS AND RESULTS

We compared the efficacy of scopolamine, diphenhydramine, and granisetron (representing three classes of drugs) with different doses, and found that scopolamine was the most effective one. We also found scopolamine inhibited central nervous system at therapeutic doses and caused anxiety. Then, we combined it with different doses of psychostimulants (d-amphetamine, modafinil, caffeine) to find the best combination for motion sickness. The efficacy of scopolamine with modafinil (1 + 10 mg/kg) was equivalent to that of scopolamine with d-amphetamine (1 + 1 mg/kg); This combination also excited central nervous system and abolished the anxiety caused by scopolamine.

CONCLUSIONS

The optimal dose ratio of scopolamine and modafinil is 1:10. This combination is beneficial for motion sickness and can abolish the side effects of scopolamine. So, it might be a good replacement of scopolamine and d-amphetamine for severe motion sickness.

Cognitive disruptions in stress-related psychiatric disorders: A role for corticotropin releasing factor (CRF)

This article is part of a Special Issue "SBN 2014". Stress is a potential etiology contributor to both post-traumatic stress disorders (PTSD) and major depression. One stress-related neuropeptide that is hypersecreted in these disorders is corticotropin releasing factor (CRF). Dysregulation of CRF has long been linked to the emotion and mood symptoms that characterize PTSD and depression. However, the idea that CRF also mediates the cognitive disruptions observed in patients with these disorders has received less attention. Here we review literature indicating that CRF can alter cognitive functions. Detailed are anatomical studies revealing that CRF is poised to modulate regions required for learning and memory. We also describe preclinical behavioral studies that demonstrate CRF's ability to alter fear conditioning, impair memory consolidation, and alter a number of executive functions, including attention and cognitive flexibility. The implications of these findings for the etiology and treatment of the cognitive impairments observed in stress-related psychiatric disorders are described.

Herbal Medicine for Anxiety, Depression and Insomnia

The prevalence and comorbidity of psychiatric disorders such as depression, anxiety and insomnia are very common. These well-known forms of psychiatric disorders have been affecting many people from all around the world. Herb alone, as well as herbal formula, is commonly prescribed for the therapies of mental illnesses. Since various adverse events of western medication exist, the number of people who use herbs to benefit their health is increasing. Over the past decades, the exploration in the area of herbal psychopharmacology has received much attention. Literatures showed a variety of herbal mechanisms of action used for the therapy of depression, anxiety and insomnia, involving reuptake of monoamines, affecting neuroreceptor binding and channel transporter activity, modulating neuronal communication or hypothalamic-pituitary adrenal axis (HPA) etc. Nonetheless, a systematic review on herbal pharmacology in depression, anxiety and insomnia is still lacking. This review has been performed to further identify modes of action of different herbal medicine, and thus provides useful information for the application of herbal medicine.

Forebrain-specific CRF overproduction during development is sufficient to induce enduring anxiety and startle abnormalities in adult mice

Corticotropin releasing factor (CRF) regulates physiological and behavioral responses to stress. Trauma in early life or adulthood is associated with increased CRF in the cerebrospinal fluid and heightened anxiety. Genetic variance in CRF receptors is linked to altered risk for stress disorders. Thus, both heritable differences and environmentally induced changes in CRF neurotransmission across the lifespan may modulate anxiety traits. To test the hypothesis that CRF hypersignaling is sufficient to modify anxiety-related phenotypes (avoidance, startle, and conditioned fear), we induced transient forebrain-specific overexpression of CRF (CRFOE) in mice (1) during development to model early-life stress, (2) in adulthood to model adult-onset stress, or (3) across the entire postnatal lifespan to model heritable increases in CRF signaling. The consequences of these manipulations on CRF peptide levels and behavioral responses were examined in adulthood. We found that transient CRFOE during development decreased startle habituation and prepulse inhibition, and increased avoidance (particularly in females) recapitulating the behavioral effects of lifetime CRFOE despite lower CRF peptide levels at testing. In contrast, CRFOE limited to adulthood reduced contextual fear learning in females and increased startle reactivity in males but did not change avoidance or startle plasticity. These findings suggest that forebrain CRFOE limited to development is sufficient to induce enduring alterations in startle plasticity and anxiety, while forebrain CRFOE during adulthood results in a different phenotype profile. These findings suggest that startle circuits are particularly sensitive to forebrain CRFOE, and that the impact of CRFOE may be dependent on the time of exposure.

Depression and cardiovascular disease in women: is there a common immunological basis? A theoretical synthesis

Clinical studies have established an inherent comorbidity between depression and the development of cardiovascular disease (CVD). Furthermore, this comorbidity seems to be more amplified in women than in men. To further investigate this comorbidity, a thorough literature review was conducted on studies from 1992 to date. The PubMed database was accessed using the keywords: cardiovascular disease, inflammation, depression, and sex differences. Both human and animal studies were considered. This review takes the standpoint that depression and CVD are both inflammatory disorders, and that their co-occurrence may be related to how the hypothalamic–pituitary–adrenal axis, serotonergic transmission and circulation, and the renin–angiotensin–aldosterone system via angiotensin II are affected by the excess secretion of proinflammatory cytokines. More recently, preliminary research attributes this systemic inflammation to a global deficiency in CD4+CD25+FOXP3 regulatory T cells. 17-β estradiol and progesterone mediated modulation of cytokine secretion may partially explain the sex differences observed. These hormones and reproductive events associated with hormonal fluctuations are discussed in depth, including the analysis of perinatal models of depression and CVD, including preeclampsia. However, as evidenced by this review, there is a need for mechanistic research in humans to truly understand the nature and directionality of the relationship between depression and CVD.

Antidepressant activity: contribution of brain microdialysis in knock-out mice to the understanding of BDNF/5-HT transporter/5-HT autoreceptor interactions

Why antidepressants vary in terms of efficacy is currently unclear. Despite the leadership of selective serotonin reuptake inhibitors (SSRIs) in the treatment of depression, the precise neurobiological mechanisms involved in their therapeutic action are poorly understood. A better knowledge of molecular interactions between monoaminergic system, pre- and post-synaptic partners, brain neuronal circuits and regions involved may help to overcome limitations of current treatments and identify new therapeutic targets. Intracerebral in vivo microdialysis (ICM) already provided important information about the brain mechanism of action of antidepressants first in anesthetized rats in the early 1990s, and since then in conscious wild-type or knock-out mice. The principle of ICM is based on the balance between release of neurotransmitters (e.g., monoamines) and reuptake by selective transporters [e.g., serotonin transporter for serotonin 5-hydroxytryptamine (5-HT)]. Complementary to electrophysiology, this technique reflects pre-synaptic monoamines release and intrasynaptic events corresponding to ≈80% of whole brain tissue content. The inhibitory role of serotonergic autoreceptors infers that they limit somatodendritic and nerve terminal 5-HT release. It has been proposed that activation of 5-HT_1A and 5-HT_1B receptor sub-types limits the antidepressant-like activity of SSRIs. This hypothesis is based partially on results obtained in ICM experiments performed in naïve, non-stressed rodents. The present review will first remind the principle and methodology of ICM performed in mice. The crucial need of developing animal models that display anxiety and depression-like behaviors, neurochemical and brain morphological phenotypes reminiscent of these mood disorders in humans, will be underlined. Recently developed genetic mouse models have been generated to independently manipulate 5-HT_1A auto and heteroreceptors and ICM helped to clarify the role of the pre-synaptic component, i.e., by measuring extracellular levels of neurotransmitters in serotonergic nerve terminal regions and raphe nuclei. Finally, we will summarize main advantages of using ICM in mice through recent examples obtained in knock-outs (drug infusion through the ICM probe allows the search of a correlation between changes in extracellular neurotransmitter levels and antidepressant-like activity) or alternatives (infusion of a small-interfering RNA suppressing receptor functions in the mouse brain). We will also focus this review on post-synaptic components such as brain-derived neurotrophic factor in adult hippocampus that plays a crucial role in the neurogenic and anxiolytic/antidepressant-like activity of chronic SSRI treatment. Limitations of ICM will also be considered.

Cognitive, emotional and neurochemical effects of repeated maternal separation in adolescent rats

As an adverse early life experience, maternal separation (MS) induces profound neurochemical, cognitive and emotional dysfunction. Previous studies have reported that MS affected prepulse inhibition (PPI), anxiety-related behaviors, dopaminergic and serotonergic activity in adult rats, and in the present study, we investigated the effects of repeated (4h/day) maternal separation during postnatal days 1-21 on PPI and anxiety-related behaviors in an elevated plus maze, as well as dopamine D2 receptor (DRD2) and 5-HT1A receptor expression in the medial prefrontal cortex (mPFC), nucleus accumbens (NAc) and hippocampus in adolescent rats. Our findings show that repeated MS results in reduced PPI, increased anxiety-related behaviors, decreased DRD2 protein expression in the NAc and hippocampus, and decreased 5-HT1A protein expression in the mPFC and hippocampus in adolescent rats. These data further demonstrate that MS can be used as an animal model of neuropsychiatric disease.

Sex-biased stress signaling: the corticotropin-releasing factor receptor as a model

Sex differences in the prevalence or severity of many diseases and in the response to pharmacological agents are well recognized. Elucidating the biologic bases of these differences can advance our understanding of the pathophysiology of disease and facilitate the development of treatments. Despite the importance to medicine, this has been an area of limited research. Here, we review physiologic, cellular, and molecular findings supporting the idea that there are sex differences in receptor signaling and trafficking that can be determinants of pathology. The focus is on the receptor for corticotropin-releasing factor (CRF), the orchestrator of the stress response, which has been implicated in diverse stress-related diseases that show a female prevalence. Data are reviewed that show sex differences in the association of the CRF receptor (CRF1) with the Gs protein and β-arrestin 2 that would render females more responsive to acute stress and less able to adapt to chronic stress as a result of compromised CRF1 internalization. Because β-arrestin 2 serves to link CRF1 to Gs-independent signaling pathways, this sex-biased signaling is proposed to result in distinct cellular responses to stress that are translated to different physiologic and behavioral coping mechanisms and that can have different pathologic consequences. Because stress has been implicated in diverse medical and psychiatric diseases, these sex differences in CRF1 signaling could explain sex differences in a multitude of disorders. The possibility that analogous sex differences may occur with other G-protein-coupled receptors underscores the impact of this effect and is discussed.

Increased vulnerability of the brain norepinephrine system of females to corticotropin-releasing factor overexpression

Stress-related psychiatric disorders are more prevalent in women than men. As hypersecretion of the stress neuromediator, corticotropin-releasing factor (CRF) has been implicated in these disorders, sex differences in CRF sensitivity could underlie this disparity. Hyperarousal is a core symptom that is shared by stress-related disorders and this has been attributed to CRF regulation of the locus ceruleus (LC)-norepinephrine arousal system. We recently identified sex differences in CRF(1) receptor (CRF(1)) signaling and trafficking that render LC neurons of female rats more sensitive to CRF and potentially less able to adapt to excess CRF compared with male rats. The present study used a genetic model of CRF overexpression to test the hypothesis that females would be more vulnerable to LC dysregulation by conditions of excess CRF. In both male and female CRF overexpressing (CRF-OE) mice, the LC was more densely innervated by CRF compared with wild-type controls. Despite the equally dense CRF innervation of the LC in male and female CRF-OE mice, LC discharge rates recorded in slices in vitro were selectively elevated in female CRF-OE mice. Immunoelectron microscopy revealed that this sex difference resulted from differential CRF(1) trafficking. In male CRF-OE mice, CRF(1) immunolabeling was prominent in the cytoplasm of LC neurons, indicative of internalization, a process that would protect cells from excessive CRF. However, in female CRF-OE mice, CRF(1) labeling was more prominent on the plasma membrane, suggesting that the compensatory response of internalization was compromised. Together, the findings suggest that the LC-norepinephrine system of females will be particularly affected by conditions resulting in elevated CRF because of differences in receptor trafficking. As excessive LC activation has been implicated in the arousal components of stress-related psychiatric disorders, this may be a cellular mechanism that contributes to the increased incidence of these disorders in females.

Assessing behavioural effects of chronic HPA axis activation using conditional CRH-overexpressing mice

The corticotropin-releasing hormone (CRH) and its cognate receptors have been implicated in the pathophysiology of stress-related disorders. Hypersecretion of central CRH and elevated glucocorticoid levels, as a consequence of impaired feedback control, have been shown to accompany mood and anxiety disorders. However, a clear discrimination of direct effects of centrally hypersecreted CRH from those resulting from HPA axis activation has been difficult. Applying a conditional strategy, we have generated two conditional CRH-overexpressing mouse lines: CRH-COE ( Del ) mice overexpress CRH throughout the body, while CRH-COE ( APit ) mice selectively overexpress CRH in the anterior and intermediate lobe of the pituitary. Both mouse lines show increased basal plasma corticosterone levels and consequently develop signs of Cushing's syndrome. However, while mice ubiquitously overexpressing CRH exhibited increased anxiety-related behaviour, overexpression of CRH in the pituitary did not produce alterations in emotional behaviour. These results suggest that chronic hypercorticosteroidism alone is not sufficient to alter anxiety-related behaviour but rather that central CRH hyperdrive on its own or in combination with elevated glucocorticoids is responsible for the increase in anxiety-related behaviour. In conclusion, the generated mouse lines represent valuable animal models to study the consequences of chronic CRH overproduction and HPA axis activation.

Effects of environmental manipulations in genetically targeted animal models of affective disorders

Mental illness is the leading cause of disability worldwide. We are only just beginning to reveal and comprehend the complex interaction that exists between the genetic makeup of an organism and the potential modifying effect of the environment in which it lives, and how this translates into mediating susceptibility to neurological and psychiatric conditions. The capacity to address this issue experimentally has been facilitated by the availability of rodent models which allow the precise manipulation of genetic and environmental factors. In this review, we discuss the valuable nature of animal models in furthering our understanding of the relationship between genetic and environmental factors in affective illnesses, such as anxiety and depressive disorders. We first highlight the behavioral impairments exhibited by genetically targeted animal models of affective disorders, and then provide a discussion of the underlying neurobiology, focusing on animal models that involve exposure to stress. This is followed by a review of recent studies that report of beneficial effects of environmental manipulations such as environmental enrichment and enhanced physical activity and discuss the likely mechanisms that mediate those benefits.

Lifelong CRF overproduction is associated with altered gene expression and sensitivity of discrete GABA(A) and mGlu receptor subtypes

RATIONALE

Repeated activation of corticotropin-releasing factor (CRF) receptors is associated with increased anxiety and enhanced stress responsivity, which may be mediated via limbic GABAergic and glutamatergic transmission.

OBJECTIVE

The present study investigated molecular and functional alterations in GABA(A) receptor (GABA(A)R) and metabotropic glutamate receptor (mGluR) responsivity in transgenic mice that chronically overexpress CRF.

METHODS

CRF(1) receptor, GABA(A)R, and mGluR sensitivity were determined in CRF-overexpressing mice using the stress-induced hyperthermia (SIH) test. In addition, we measured mRNA expression levels of GABA(A)R α subunits and mGluRs in the amygdala and hypothalamus.

RESULTS

CRF-overexpressing mice were less sensitive to the anxiolytic effects of the CRF(1) receptor antagonists CP154,526 and DMP695, the GABA(A)R α(3)-selective agonist TP003 (0-3 mg/kg) and the mGluR(2/3) agonist LY379268 (0-10 mg/kg) in the SIH test. The hypothermic effect of the non-selective GABA(A)R agonist diazepam (0-4 mg/kg) and the α(1)-subunit-selective GABA(A)R agonist zolpidem (0-10 mg/kg) was reduced in CRF-overexpressing mice. No genotype differences were found using the GABA(A)R α(5)-subunit preferential compound SH-053-2'F-R-CH(3) and mGluR(5) antagonists MPEP and MTEP. CRF-overexpressing mice showed decreased expression levels of GABA(A)R α(2) subunit and mGluR(3) mRNA levels in the amygdala, whereas these expression levels were increased in the hypothalamus. CRF-overexpressing mice also showed increased hypothalamic mRNA levels of α(1) and α(5) GABA(A)R subunits.

CONCLUSIONS

We found that lifelong CRF overproduction is associated with altered gene expression and reduced functional sensitivity of discrete GABA(A) and mGluR receptor subtypes. These findings suggest that sustained over-activation of cerebral CRF receptors may contribute to the development of altered stress-related behavior via modulation of GABAergic and glutamatergic transmission.

Serotonin1A receptor deletion does not interact with maternal separation-induced increases in startle reactivity and prepulse inhibition deficits

RATIONALE

Early life stress is a risk factor for the development of psychopathology in later life. Consequences of adverse life events, however, may depend on the genetic makeup of an individual. Reduced serotonin(1A) receptor function may predispose to the development of anxiety disorders.

OBJECTIVE

Determine susceptibility of serotonin(1A) receptor knockout (1AKO) mice on different background strains to the effects of maternal separation (MS) by assessing startle plasticity in adulthood.

METHODS

1AKO mice on a 129S6 and a Swiss Webster (SW) background were used. MS groups were separated daily from their mother for 180 min/day from postnatal days 2 to 14. Control groups underwent normal animal facility rearing. In adulthood, effects on acoustic startle response, habituation, prepulse inhibition (PPI), and foot shock sensitization were determined.

RESULTS

MS increased startle reactivity and reduced PPI in 129S6 mice. These effects of MS were independent of genotype. MS had no effect on the other readouts. In SW mice, MS had no consistent effect on startle reactivity and did not alter startle plasticity in wild type or in 1AKO mice. 1AKO mice did not differ from wild-type mice in startle plasticity.

CONCLUSION

Serotonin(1A) receptor deletion does not enhance vulnerability to the effects of MS on startle plasticity. The life-long increase in startle reactivity and PPI deficit induced by MS are strain-dependent. Further, the use of startle reactivity and plasticity may have added value in translational studies relating to early life stress.

Spatiotemporal properties of locomotor activity after administration of central nervous stimulants and sedatives in mice

In the present study, we investigated the spatiotemporal properties of locomotor activity after administration of CNS sedatives (pentobarbital and diazepam) and stimulants (theophylline and caffeine) in an open field test. The absolute and relative distances traveled in central or peripheral regions within 2 h were analyzed. We found that both pentobarbital and diazepam increased total travel distances, especially within the initial 30 min, when traveling was mainly in the peripheral region. Pentobarbital induced this hyperactivity at higher doses (maximum at 30 mg/kg); while diazepam at higher doses (4 and 8 mg/kg) mainly decreased the traveled distance during 0-1 h but increased that in the periphery during 1-2 h. On the other hand, both theophylline and caffeine generally increased the traveled distance in the central region; this effect lasted longer with increasing dose. Caffeine increased the traveled distance at lower doses (maximum at 10 mg/kg) but decreased it at higher doses (30 and 100 mg/kg) during the initial 1 h. Theophylline exhibited a similar but smaller decrease at higher doses. Thus, we revealed the spatiotemporal properties that sedatives decrease central locomotion but induce a dose-related peripheral hyperactivity while stimulants induce central hyperactivity with a bell-shaped dose-response relation.

CRF receptor blockade prevents initiation and consolidation of stress effects on affect in the predator stress model of PTSD

Post traumatic stress disorder (PTSD) is a chronic anxiety disorder initiated by an intensely threatening, traumatic event. There is a great need for more efficacious pharmacotherapy and preventive treatments for PTSD. In animals, corticotropin-releasing factor (CRF) and the CRF1 receptor play a critical role in behavioural and neuroendocrine responses to stress. We tested the hypothesis that CRF1 activation is required for initiation and consolidation of long-term effects of trauma on anxiety-like behaviour in the predator exposure (predator stress) model of PTSD. Male C57BL6 mice were treated with the selective CRF1 antagonist CRA0450 (2, 20 mg/kg) 30 min before or just after predator stress. Long-term effects of stress on rodent anxiety were measured 7 d later using acoustic startle, elevated plus maze (EPM), light/dark box, and hole-board tests. Predator stress increased startle amplitude and delayed startle habituation, increased time in and decreased exits from the dark chamber in the light/dark box test, and decreased risk assessment in the EPM. CRF1 antagonism had limited effects on these behaviours in non-stressed controls, with the high dose decreasing risk assessment in the EPM. However, in stressed animals CRF1 antagonism blocked initiation and consolidation of stressor effects on startle, and returned risk assessment to baseline levels in predator-stressed mice. These findings implicate CRF1 activation in initiation and post-trauma consolidation of predator stress effects on anxiety-like behaviour, specifically on increased arousal as measured by exaggerated startle behaviours. These data support further research of CRF1 antagonists as potential prophylactic treatments for PTSD.

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.

CRH signaling. Molecular specificity for drug targeting in the CNS

There is an urgent need to generate new drugs or improve existing ones in the pharmacology of mood disorders. The corticotropin-releasing hormone (CRH) system is closely involved in the development and course of depression, and drugs targeting this system arguably offer hope to improve the current tools for drug treatment of depression. Recent clinical studies in depressed patients showed that CRHR1 antagonists improve clinical symptoms of anxiety and depression and reduce stress hormone release following psychosocial stress. These effects of CRHR1 antagonists were not associated with reduced secretory capacity of corticotrophic cells because of CRH receptor abundance at the pituitary level, which contrasts with CRH receptors in the brain. This is in accordance with previous studies showing that CRH injections into the mouse brain activate MAPK pathways in a brain region-specific manner pointing toward differences in signaling pathways beyond the receptor level. We will highlight this and discuss how these brain area-specific differences may offer opportunities for drug discovery. An additional puzzle in the search of new targets for depression is the lack of bona fide animal models helping to discover the antidepressants that are not monoamine based. We recently developed a conditional mouse model that overexpresses CRH in a spatio-temporal-regulated fashion and permits to dissect precisely the contribution of different brain areas to the CRH-dependent behaviors. Recent findings obtained with this mouse model and its usefulness in the context of the CRH-dependent, region-specific changes in depression will be discussed.

Noradrenergic and serotonergic mechanisms in the neurobiology of posttraumatic stress disorder and resilience

Posttraumatic stress disorder (PTSD) is characterized mainly by symptoms of re-experiencing, avoidance and hyperarousal as a consequence of catastrophic and traumatic events that are distinguished from ordinary stressful life events. Although extensive research has already been done, the etiology of PTSD remains unclear. Research on the impact of trauma on neurobiological systems can be expected to inform the development of treatments that are directed specifically to symptoms of PTSD. During the past 25 years there has been a dramatic increase in the knowledge about noradrenergic and serotonergic mechanisms in stress response, PTSD and more recently in resilience and this knowledge has justified the use of antidepressants with monoaminergic mechanisms of action for patients with PTSD. Nevertheless, available treatments of PTSD are only to some extent effective and enhanced understanding of the neurobiology of PTSD may lead to the development of improved treatments for these patients. In the present review, we aim to close existing gaps between basic research in psychopathology, neurobiology and treatment development with the ultimate goal to translate basic research into clinically relevant findings which may directly benefit patients with PTSD.

Effect of perphenazine enanthate on open-field test behaviour and stress-induced hyperthermia in domestic sheep

The open-field test (OFT) and stress-induced hyperthermia (SIH) have been used to measure individual differences in fear. The present study has been designed as a pharmacological validation of OFT and SIH as indicators of fear in sheep using perphenazine enanthate (PPZ), a long-acting neuroleptic. Twenty four ewes of two breeds, Lacaune and Ripollesa, were tested in an arena measuring 5mx2.5m. Treatment group received one dose of 1.5mg/kg of PPZ and control group received sterile sesame oil. All animals were tested for 10min and behaviours were recorded. Rectal temperature was measured at the beginning (T1) and at the end (T2) of the test. SIH was defined as the difference between T2 and T1. Sheep were tested on days 1, 2, 3, 4, 7 and 9 after PPZ injection. Variables were analysed using a mixed model. PPZ decreased bleats on days 2, 3, 4 and the SIH response on days 2 and 3. Breed differences were observed. Treated animals showed positive correlations between SIH and bleats; squares entered; attempts to escape and negative correlation between SIH and visits to the food bucket. Our results suggest that behaviour and SIH on the OFT are useful measures of fear in sheep.

A single episode of restraint stress regulates central corticotrophin- releasing hormone receptor expression and binding in specific areas of the mouse brain

The importance of restraining stress-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) system within tolerable limits requires efficient mechanisms for feedback inhibition. Recently, central corticotrophin-releasing hormone (CRH) receptor type 1 (CRHR1) has been shown to mediate HPA system feedback inhibition. To date, most of the data regarding stress-associated expression changes of CRHR1 and CRHR2 mRNA and their ligand CRH have been generated in rats. Taken considerable species differences into consideration, and with the growing importance of transgenic mice, a systematic analysis of the time course of expression changes of CRH and its two receptors in the mouse brain is needed to provide more insight into the regulation of the HPA system, both under physiological and pathophysiological conditions in this species. We analysed in detail the time course of expression changes of CRH, CRHR1 and CRHR2 mRNA after of restraint stress in mice in stress-relevant brain regions (paraventricular nucleus, hippocampus, neocortex). We could show a rapid, strong and long-lasting decrease in cortical and hippocampal CRHR1 mRNA expression after stress, whereas CRHR2 mRNA increased in the same neuroanatomical areas. In situ hybridisation analyses could be further confirmed at the protein level by CRH receptor autoradiography with changes in CRH binding that persisted even 7 days after a single episode of restraint stress. Our observation that stress has opposing effects on CRHR1 and CRHR2 neuronal systems supports the idea that regulation of the relative contribution of the two CRH receptors to brain CRH pathways may be essential in coordinating physiological responses to stress. We further hypothesise that the sustained alteration of CRH receptor expression and binding after a single episode of stress could mediate the long-term effects of stress on neuroendocrine function and emotional regulation.

Immunology, signal transduction, and behavior in hypothalamic-pituitary-adrenal axis-related genetic mouse models

A classical view of the neuroendocrine-immune network assumes bidirectional interactions where pro-inflammatory cytokines influence hypothalamic-pituitary-adrenal (HPA) axis-derived hormones that subsequently affect cytokines in a permanently servo-controlled circle. Nevertheless, this picture has been continuously evolving over the last years as a result of the discovery of redundant expression and extended functions of many of the molecules implicated. Thus, cytokines are not only expressed in cells of the immune system but also in the central nervous system, and many hormones present at hypothalamic-pituitary level are also functionally expressed in the brain as well as in other peripheral organs, including immune cells. Because of this intermingled network of molecules redundantly expressed, the elucidation of the unique roles of HPA axis-related molecules at every level of complexity is one of the major challenges in the field. Genetic engineering in the mouse offers the most convincing method for dissecting in vivo the specific roles of distinct molecules acting in complex networks. Thus, various immunological, behavioral, and signal transduction studies performed with different HPA axis-related mutant mouse lines to delineate the roles of beta-endorphin, the type 1 receptor of corticotropin-releasing hormone (CRHR1), and its ligand CRH will be discussed here.

Decline in serotonergic firing activity and desensitization of 5-HT1A autoreceptors after chronic unpredictable stress

Chronic stressful life events are risk factors for contracting depression, the pathophysiology of which is strongly associated with impairments in serotonergic (5-HT) neurotransmission. Indeed, in rodents, exposure to chronic unpredictable stress (CUS) produces depressive-like behaviours such as behavioural despair and anhedonia. To date, there have not been many studies that especially explore in vivo changes in 5-HT neurotransmission associated with CUS in the rat. Therefore, using in vivo electrophysiology, we evaluated whether CUS that induces anhedonia-like behaviours concurrently impairs midbrain raphe 5-HT neuronal activity. Unlike unstressed and acutely stressed rats, CUS produced progressive reductions in sucrose intake and preference (anhedonia-like). These were associated with a decrease in the spontaneous firing activity (35.4%) as well as in the number of spontaneously active 5-HT neurons, and a desensitization of somatodendritic 5-HT1A autoreceptors in the dorsal raphe. These results suggest that CUS dramatically decreases 5-HT neural activity and 5-HT1A autoreceptor sensitivity, and may represent endophenotypic features of depressive-like states.

5-HT1A gene variants and psychiatric disorders: a review of current literature and selection of SNPs for future studies

5-HT1A receptors are key components of the serotonin system, acting both pre- and post- synaptically in different brain areas. There is a growing amount of evidence showing the importance of 5-HT1A in different psychiatric disorders, from mood to anxiety disorders, moving through suicidal behaviour and psychotic disorders. Findings in the literature are not consistent with any definite 5-HT1A influence in psychiatric disorders. 5-HT1A gene variants have been reported to play some role in mood disorders, anxiety disorders and psychotic disorders. Again, the literature findings are not unequivocal. Concerning response to treatment, the C(-1019)G variant seems to be of primary interest in antidepressant response: C allele carriers generally show a better response to treatment, especially in Caucasian samples. Together with the C(-1019)G (rs6295) variant, the Ile28Val (rs1799921), Arg219Leu (rs1800044) and Gly22Ser (rs1799920) variants have been investigated in possible associations with psychiatric disorders, also with no definitive results. This lack of consistency can be also due to an incomplete gene investigation. To make progress on this point, a list of validated single nucleotide polymorphisms (SNPs) covering the whole gene is proposed for further investigations.

CRF1 not glucocorticoid receptors mediate prepulse inhibition deficits in mice overexpressing CRF

BACKGROUND

Both corticotropin-releasing factor (CRF) and glucocorticoid receptors (GR) are implicated in the psychotic symptoms of psychiatric disorders. Correspondingly, it is of interest to determine their respective involvement in the sensorimotor gating deficits displayed by transgenic mice overexpressing CRF. These mice reveal lifelong elevations of CRF and corticosterone levels.

METHODS

Effects of the GR antagonists ORG34517 (5-45 mg/kg by mouth [PO]) and mifepristone (5-45 mg/kg PO) and the CRF(1) receptor antagonists CP154,526 (20-80 mg/kg intraperitoneally [IP]) and DMP695 (2.5-40.0 mg/kg IP) on prepulse inhibition (PPI) of the acoustic startle response were studied in mice overexpressing CRF and in their wild-type littermates. In addition, PPI was measured in both genotypes 2 weeks after adrenalectomy with or without exogenous corticosterone administration via subcutaneous pellet implant (20 mg corticosterone).

RESULTS

ORG34517 and mifepristone did not influence perturbation of PPI in mice overexpressing CRF; reducing corticosterone levels by adrenalectomy likewise did not improve PPI. Further, elevation in corticosterone levels by pellet implantation did not disrupt PPI in wild-type mice. Conversely, both CRF(1) receptor antagonists, CP154,526 (40-80 mg/kg IP) and DMP695 (40 mg/kg IP), significantly restored PPI in CRF-overexpressing mice.

CONCLUSIONS

Sustained overactivation of CRF(1) receptors rather than excessive GR receptor stimulation underlies impaired sensorimotor gating in CRF-overexpressing mice. CRF(1) receptors thus may play a role in the expression of psychotic features in stress-related psychiatric disorders.

Altered behavioural adaptation in mice with neural corticotrophin-releasing factor overexpression

Overproduction of corticotrophin-releasing factor (CRF), the major mediator of the stress response, has been linked to anxiety, depression and addiction. CRF excess results in increased arousal, anxiety and altered cognition in rodents. The ability to adapt to a potentially threatening stimulus is crucial for survival, and impaired adaptation may underlie stress-related psychiatric disorders. Therefore, we examined the effects of chronic transgenic neural CRF overproduction on behavioural adaptation to repeated exposure to a non-home cage environment. We report that CRF transgenic mice show impaired adaptation in locomotor response to the novel open field. In contrast to wild-type (WT) mice, anxiety-related behaviour of CRF transgenic mice does not change during repeated exposure to the same environment over the period of 7 days or at retest 1 week later. We found that locomotor response to novelty correlates significantly with total locomotor activity and activity in the centre at the last day of testing and at retest in WT but not in CRF transgenic mice. Mice were divided into low responders and high responders on the basis of their initial locomotor response to novelty. We found that differences in habituation and re-exposure response are related to individual differences in locomotor response to novelty. In summary, these results show that CRF transgenic mice are fundamentally different from WT in their ability to adapt to an environmental stressor. This may be related to individual differences in stress reactivity. These findings have implications for our understanding of the role of CRF overproduction in behavioural maladaptation and stress-related psychiatric disorders.

Expression profiling identifies the CRH/CRH-R1 system as a modulator of neurovascular gene activity

Corticotropin-releasing hormone receptor type 1 (CRH-R1)-deficient mice display reduced anxiety-like behavior, a chronic corticosterone deficit, and an impaired neuroendocrine stress response caused by disruption of the hypothalamic-pituitary-adrenocortical (HPA) axis. The molecular substrates and pathways of CRH/CRH-R1-dependent signaling mechanisms underlying the behavioral phenotype as well as the consequences of lifelong glucocorticoid deficit remain largely obscure. To dissect involved neuronal circuitries, we performed comparative expression profiling of brains of CRH-R1 mutant and wild-type mice using our custom made MPIP (Max Planck Institute of Psychiatry) 17k cDNA microarray. Microarray analysis yielded 107 genes showing altered expression levels when comparing CRH-R1 knockout mice with wild-type littermates. A significant proportion of differentially expressed genes was related to control of HPA and hypothalamic-pituitary-thyroid (HPT) axes reflecting not only the disturbance of the HPA axis in CRH-R1 mutant mice but also the interplay of both neuroendocrine systems. The spatial analysis of regulated genes revealed a prevalence for genes expressed in the cerebral microvasculature. This phenotype was confirmed by the successful cross-validation of regulated genes in CRH overexpressing mice. Analysis of the cerebral vasculature of CRH-R1 mutant and CRH overexpressing mice revealed alterations of functional rather than structural properties. A direct role of the CRH/CRH-R1 system was supported by demonstrating Crhr1 expression in the adult murine cerebral vasculature. In conclusion, these data suggest a novel, previously unknown role of the CRH/CRH-R1 system in modulating neurovascular gene expression and function.

Suppression of conditioning to ambiguous cues by pharmacogenetic inhibition of the dentate gyrus

Serotonin receptor 1A knockout (Htr1a(KO)) mice show increased anxiety-related behavior in tests measuring innate avoidance. Here we demonstrate that Htr1a(KO) mice show enhanced fear conditioning to ambiguous conditioned stimuli, a hallmark of human anxiety. To examine the involvement of specific forebrain circuits in this phenotype, we developed a pharmacogenetic technique for the rapid tissue- and cell type-specific silencing of neural activity in vivo. Inhibition of neurons in the central nucleus of the amygdala suppressed conditioned responses to both ambiguous and nonambiguous cues. In contrast, inhibition of hippocampal dentate gyrus granule cells selectively suppressed conditioned responses to ambiguous cues and reversed the knockout phenotype. These data demonstrate that Htr1a(KO) mice have a bias in the processing of threatening cues that is moderated by hippocampal mossy-fiber circuits, and suggest that the hippocampus is important in the response to ambiguous aversive stimuli.

The stress-induced hyperthermia paradigm as a physiological animal model for anxiety: A review of pharmacological and genetic studies in the mouse

This paper reviews the function, brain mechanisms and pharmacology of stress-induced hyperthermia (SIH) in a broad context. Hyperthermia itself is induced by all stressful stimuli and can be found across numerous species, including humans. As a model for anxiety, the process of insertion of a rectal probe increases temperature ranging from about 0.5-1.5 degrees C in 10-15min is called SIH. This temperature increase can be blocked by anxiolytic drugs. The methodological as well as pharmacological aspects of the group- (G-SIH) and singly housed (SIH) version of the paradigm are described in detail. Also, an overview is presented about studies using the SIH procedure in genetically modified mice together with the potential interference with immunological induction of a febrile response. The paper also presents data that highlight some of the limitations of the SIH procedure for use of drugs like nicotine, which contain particular characteristics such as short in vivo half-life, and/or disturbance of thermoregulation. The advantages and disadvantages of the SIH procedure as a physiological model of anxiety are discussed.

Cellular and molecular alterations in mice with deficient and reduced serotonin transporters

The function of serotonin transporters (SERTs) is related to mood regulation. Mice with deficient or reduced SERT function (SERT knockout mice) show several behavioral changes, including increased anxiety-like behavior, increased sensitivity to stress, and decreases in aggressive behavior. Some of these behavioral alterations are similar to phenotypes found in humans with short alleles of polymorphism in the 5-hydroxytryptamine (5-HT) transporter-linked promoter region (5-HTTLPR). Therefore, SERT knockout mice can be used as a tool to study 5-HTTLPR-related variations in personality and may be the etiology of affective disorders. This article focuses on the cellular and molecular alterations in SERT knockout mice, including changes in 5-HT concentrations and its metabolism, alterations in 5-HT receptors, impaired hypothalamic-pituitary-adrenal gland axis, developmental changes in the neurons and brain, and influence on other neurotransmitter transporters and receptors. It also discusses the possible relationships between these alterations and the behavioral changes in these mice. The knowledge provides the foundation for understanding the cellular and molecular mechanisms that mediate the SERT-related mood regulation, which may have significant impact on understanding the etiology of affective disorders and developing better therapeutic approaches for affective disorders.

Mice with mutations in the HPA-system as models for symptoms of depression

Genetically engineered mice hold promise to help us understand the effects of enhanced or reduced gene activity upon behavior and metabolism. Because many basic and clinical studies suggest that alterations of the hypothalamic pituitary adrenocortical (HPA) system are involved in the development and course of depression, mouse mutants with genetic modifications of genes regulating the HPA system were generated. This review summarizes these effects and concludes that advanced technologies allowing for regional overexpression or inactivation of genes or introduction of polymorphisms into the mouse genome are well suited to explain individual symptoms or symptom patterns prevalent among depressives. However, as depression is a complex disorder in which minor changes of many genes as well as environmental factors (including epigenetic programming) play a causal role and determine the phenotype, the use of mice with single gene mutations needs to be critically discussed when attempting to create a genetic animal model of depression.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Focal cerebral ischemia alters the spatio-temporal properties, but not the amount of activity in mice

Cerebral ischemia induces sensorimotor and cognitive dysfunctions in rodents; however, little is known about the changes in the spatio-temporal organization of locomotor activity after ischemia. In this study, we continuously assessed the spatio-temporal properties of locomotor activity in an enclosure (40 cm x 40 cm x 65 cm, arbitrarily divided into 16 zones) with feeding and drinking supplies, and observed the spatio-temporal changes in mice with focal cerebral ischemia. Locomotor tracks were recorded from 3rd to 24th h (total 22 h) after middle cerebral artery occlusion (MCAO) or sham operation. The absolute and relative distance traveled or time spent in different regions was analyzed. We found that there was no significant difference in total traveled distances over 22 h between the two groups. Control mice moved and stayed primarily in feeding and drinking zones, frequently in peripheral but rarely in central zones. However, ischemic mice lost such a property, almost evenly moved and stayed in 16 zones. Mice in both groups were more active (traveled more distances) shortly after they entered the enclosure, while ischemic mice returned to stable levels slower. The traveled distance had a remarkable circadian variation with more locomotion in the night in control mice, but not in ischemic mice. Most of the spatial parameters (ratios) of locomotor activity were closely correlated with the ischemic infarction, neuron densities (in cortex, hippocampal CA1 region and striatum), and typical behavioral assessments (neurological scores and inclined board test). Thus, these findings indicate that focal cerebral ischemia does not alter the amount of locomotor activity in mice, but impairs the spatio-temporal properties-prolonging the initial hyperactivity and losing regionally special distribution of the activity.

Distribution and expression of CRF receptor 1 and 2 mRNAs in the CRF over-expressing mouse brain

Corticotropin-releasing factor (CRF) acts through CRF 1 and CRF 2 receptors (CRF1, CRF2). To test the hypothesis that CRF controls the expression of these receptors in a brain site- and receptor-type specific manner, we studied CRF1 mRNA and CRF2 mRNA expressions in mice with central CRF over-expression (CRF-OE) and using in situ hybridization. CRF1 and CRF2 mRNAs appear to be differentially distributed across the brain. The brain structures expressing the receptors are the same in wild-type (WT) and in CRF-OE mice. We therefore conclude that chronically elevated CRF does not induce or inhibit expression of these receptors in structures that normally do not or do, respectively, show these receptors. However, from counting cell body profiles positive for CRF1 and CRF2 mRNAs, clear differences appear in receptor expression between CRF-OE and WT mice, in a brain-structure-specific fashion. Whereas some structures do not differ, CRF-OE mice exhibit remarkably lower numbers of CRF1 mRNA-positive profiles in the subthalamic nucleus (-38.6%), globus pallidus (-31.5%), dorsal part of the lateral septum (-23.5%), substantia nigra (-22,8%), primary somatosensory cortex (-18.9%) and principal sensory nucleus V (-18.4%). Furthermore, a higher number of CRF2 mRNA-positive profiles are observed in the dorsal raphe nucleus (+32.2%). These data strongly indicate that central CRF over-expression in the mouse brain is associated with down-regulation of CRF1 mRNA and up-regulation of CRF2 mRNA in a brain-structure-specific way. On the basis of these results and the fact that CRF-OE mice reveal a number of physiological and autonomic symptoms that may be related to chronic stress, we suggest that CRF1 in the basal nuclei may be involved in disturbed information processing and that CRF2 in the dorsal raphe nucleus may play a role in mediating stress-induced release of serotonin by CRF.

Increased fear response to contextual cues in mice lacking the 5-HT1A receptor

Serotonin 1A receptor knockout (5-HT1AR KO) mice exhibit increased behavioral inhibition in conflict tests. To gain further insight into their anxiety-related phenotype, we subjected these mice to additional behavioral tests. First, we considered whether behavioral inhibition in these knockout mice is a consequence of reduced exploratory motivation. The knockout mice engage in normal exploration during a light-dark test and normal exploration of a novel object in a familiar environment, suggesting that the anxiety-related phenotype is not due to reduced exploratory drive. Second, we tested whether these mice exhibit increased behavioral inhibition in response to any aversive cues, or whether this response depends on cue modality. Knockout mice respond normally to discrete aversive cues in the Vogel lick-suppression test, arguing that their phenotype is restricted to conflict tests based on complex or spatial aversive cues. Third, to probe the processing of spatial aversive cues, we assessed fear conditioning to contextual cues. After contextual fear conditioning, knockout and wild-type (WT) mice express freezing responses when exposed to the training environment. However, when placed in an ambiguous environment containing both conditioned and novel cues, the freezing response of knockout mice does not significantly decrease as it does in WT mice, suggesting that the knockout fear response is biased toward threatening cues. We hypothesize that this inappropriate generalization of fearful behavior to a context containing both fearful and neutral stimuli, a phenomenon that occurs in a subset of human anxiety disorders such as panic disorder and post-traumatic stress disorder, underlies the anxiety phenotype of 5-HT1AR KO mice.

Medial hypothalamic 5-hydroxytryptamine (5-HT)1A receptors regulate neuroendocrine responses to stress and exploratory locomotor activity: application of recombinant adenovirus containing 5-HT1A sequences

Our previous studies found that serotonin transporter (SERT) knock-out mice showed increased sensitivity to minor stress and increased anxiety-like behavior but reduced locomotor activity. These mice also showed decreased density of 5-hydroxytryptamine (5-HT1A) receptors in the hypothalamus, amygdala, and dorsal raphe. To evaluate the contribution of hypothalamic 5-HT1A receptors to these phenotypes of SERT knock-out mice, two studies were conducted. Recombinant adenoviruses containing 5-HT1A sense and antisense sequences (Ad-1AP-sense and Ad-1AP-antisense) were used to manipulate 5-HT1A receptors in the hypothalamus. The expression of the 5-HT1A genes is controlled by the 5-HT1A promoter, so that they are only expressed in 5-HT1A receptor-containing cells. (1) Injection of Ad-1AP-sense into the hypothalamus of SERT knock-out mice restored 5-HT1A receptors in the medial hypothalamus; this effect was accompanied by elimination of the exaggerated adrenocorticotropin responses to a saline injection (minor stress) and reduced locomotor activity but not by a change in increased exploratory anxiety-like behavior. (2) To further confirm the observation in SERT-/- mice, Ad-1AP-antisense was injected into the hypothalamus of normal mice. The density and the function of 5-HT1A receptors in the medial hypothalamus were significantly reduced in Ad-1AP-antisense-treated mice. Compared with the control group (injected with Ad-track), Ad-1A-antisense-treated mice showed a significant reduction in locomotor activity, but again no changes in exploratory anxiety-like behaviors, tested by elevated plus-maze and open-field tests. Thus, the present results demonstrate that medial hypothalamic 5-HT1A receptors regulate stress responses and locomotor activity but may not regulate exploratory anxiety-like behaviors.

The corticotropin-releasing hormone gene and behavioral inhibition in children at risk for panic disorder

BACKGROUND

Behavioral inhibition to the unfamiliar (BI) is a heritable temperamental phenotype involving the tendency to display fearful, avoidant, or shy behavior in novel situations. BI is a familial and developmental risk factor for panic and phobic anxiety disorders. We previously observed an association between BI and a microsatellite marker linked to the corticotropin releasing hormone (CRH) gene in children at risk for panic disorder. To evaluate this further, we genotyped additional families for this marker and a panel of markers encompassing the CRH locus.

METHODS

Sixty-two families that included parents with panic disorder and children who underwent laboratory-based behavioral observations were studied. Family-based association tests and haplotype analysis were used to evaluate the association between BI and polymorphisms spanning the CRH locus.

RESULTS

We examined a set of markers which we found to reside in a block of strong linkage disequilibrium encompassing the CRH locus. The BI phenotype was associated with the microsatellite marker (p=.0016) and three single nucleotide polymorphisms (SNPs), including a SNP in the coding sequence of the gene (p=.023). Haplotype-specific tests revealed association with a haplotype comprising all of the markers (p=.015).

CONCLUSIONS

These results suggest that the CRH gene influences inhibited temperament, a risk factor for panic and phobic anxiety disorders. Genetic studies of anxiety-related temperament represent an important strategy for identifying the genetic basis of anxiety disorders.