Age- and stimulus-dependent changes in anxiety-related behaviour of transgenic mice with GR dysfunction

Annual Research Review: Transgenic mouse models of childhood-onset psychiatric disorders

Childhood-onset psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), mood disorders, obsessive compulsive spectrum disorders (OCSD), and schizophrenia (SZ), affect many school-age children, leading to a lower quality of life, including difficulties in school and personal relationships that persist into adulthood. Currently, the causes of these psychiatric disorders are poorly understood, resulting in difficulty diagnosing affected children, and insufficient treatment options. Family and twin studies implicate a genetic contribution for ADHD, ASD, mood disorders, OCSD, and SZ. Identification of candidate genes and chromosomal regions associated with a particular disorder provide targets for directed research, and understanding how these genes influence the disease state will provide valuable insights for improving the diagnosis and treatment of children with psychiatric disorders. Transgenic mouse models are one important approach in the study of human diseases, allowing for the use of a variety of experimental approaches to dissect the contribution of a specific chromosomal or genetic abnormality in human disorders. While it is impossible to model an entire psychiatric disorder in a single mouse model, these models can be extremely valuable in dissecting out the specific role of a gene, pathway, neuron subtype, or brain region in a particular abnormal behavior. In this review we discuss existing transgenic mouse models for childhood-onset psychiatric disorders. We compare the strength and weakness of various transgenic mouse models proposed for each of the common childhood-onset psychiatric disorders, and discuss future directions for the study of these disorders using cutting-edge genetic tools.

Gender-specific association of galanin polymorphisms with HPA-axis dysregulation, symptom severity, and antidepressant treatment response

Galanin (GAL) is an estrogen-inducible neuropeptide, highly expressed in brain regions reported to be involved in regulation of mood and anxiety. GAL possibly has a direct modulatory effect on hypothalamic-pituitary-adrenal (HPA)-axis regulation. Recent data from pharmacological and genetic studies indicate a significant function of GAL in stress-related disorders. By using a tag SNP approach covering the locus encoding preprogalanin (PPGAL), earlier findings of female-specific associations of polymorphisms in this locus with panic disorder were expanded to a larger sample of 268 outpatients with anxiety disorders (ADs). Within a larger sample of 541 inpatients with major depressive disorder (MDD), we then tested associations of one PPGAL tag SNP with specific depression symptom clusters and HPA-axis activity assessed by the combined dexamethasone-suppression/CRH-stimulation test both at inpatient admission and discharge (n=298). Gender specificity as well as dependence of the association on levels of circulating estrogens was analyzed. Genotyping revealed high linkage disequilibrium in the promoter area of the PPGAL gene, which includes several estrogen-response elements. Confirming earlier results, rs948854, tagging this promoter region, was associated with more severe anxiety pathology in female AD patients, but not in males. In premenopausal female MDD patients, the same allele of rs948854 was associated with more severe vegetative but not cognitive depressive symptoms at discharge and worse treatment response on antidepressant medication. Furthermore, this allele was associated with higher HPA-axis activity at admission. No significant case-control associations could be observed. However, because of power limitations of both patient samples, small effects cannot be excluded. The reported associations in independent samples of AD and MDD support an estrogen-dependent function of GAL in pathophysiology of anxiety and depression, affecting response to antidepressant treatment.

Neuropeptide Y modulates the antidepressant activity of imipramine in olfactory bulbectomized rats: involvement of NPY Y1 receptors

Since long-term treatment with imipramine increases the neuropeptide Y (NPY) levels in the frontal cortex and hypothalamus, the possibility exists that the antidepressant action of imipramine may be mediated via the NPY Y1 receptors. Bilateral olfactory bulbectomy (OBX) resulted in hyperactivity (increased number of ambulation, rearing and grooming episodes) in open field test (OFT) suggesting a depression-like condition. Chronic (14 days) administration of NPY, NPY Y1/Y5 receptor agonist [Leu(31), Pro(34)]-NPY (intracerebroventricular, i.c.v.) or tricyclic antidepressant imipramine (intraperitoneal) to OBX rats dose-dependently resulted in decreased hyperactivity in OFT, while selective NPY Y1 receptor antagonist BIBP3226 (i.c.v.) produced opposite effects. The antidepressant actions of imipramine were enhanced by co-administration of NPY or [Leu(31), Pro(34)]-NPY, and antagonized by BIBP3226 given at sub-effective doses. The data suggest that NPY, acting via NPY Y1 receptors, may be involved in antidepressant action of imipramine in OBX rats.

Nature vs. nurture: can enrichment rescue the behavioural phenotype of BDNF heterozygous mice?

In earlier experiments we have demonstrated that group-housing in a rather impoverished "standard" environment can be a crucial stress factor in male C57Bl/6 mice. The present study aimed at investigating the effect of combining a probable genetic vulnerability--postulated by the "Neurotrophin Hypothesis of Depression"--with the potentially modulating influence of a stressful environment such as "impoverished" standard housing conditions. For that purpose mice with a partial deletion of brain-derived neurotrophic factor (BDNF) were group-housed under standard and enriched housing conditions and analysed in a well-established test battery for emotional behaviours. Standard group-housing affected emotional behaviour in male and female BDNF heterozygous mice, causing an increase in anxiety, changes in exploration as well as nociception. Providing the animals' cages with supplementary enrichment, however, led to a rescue of emotional alterations, which emphasises the significance of external factors and their relevance for a valid investigation of genetic aspects in these mutants as well as others, which may be examined in terms of stress-responsiveness or emotionality.

Central CRH system in depression and anxiety--evidence from clinical studies with CRH1 receptor antagonists

Basic and clinical studies provide convincing evidence that altered stress hormone regulation frequently observed in depression and anxiety are caused by elevated secretion of the hypothalamic neuropeptides corticotrophin releasing hormone (CRH) and vasopressin. CRH predominantly acts through CRH(1) receptors to produce a number of anxiety- and depression-like symptoms, which resulted in extensive validation of CRH(1) receptors as potential drug target. A number of orally available nonpeptidergic small molecules capable to pass the blood-brain barrier have been discovered; only some of these compounds entered clinical development. Here, we summarize results from clinical studies of two CRH(1) receptor antagonists. In the first study originally designed as a safety and tolerability trial in major depression, it was observed that the CRH(1) receptor antagonist NBI-30775/R121919 has a clinical profile comparable to the antidepressant paroxetine. In a second study the effect of another CRH(1) receptor antagonist, NBI-34041, upon stress hormone secretion in response to a psychosocial stressor was investigated. Administration of this compound reduced the stress-elicited secretion of cortisol. Both compounds, however, did not impair the CRH-induced release of ACTH and cortisol rejecting the possibility that the peripheral stress hormone system is impaired by CRH(1) receptor antagonists. From these studies we conclude that both CRH(1) receptor antagonists have psychotropic effects unrelated to their neuroendocrine action, which is in line with behavioral data obtained from transgenic mice. The results of the clinical studies underscore that CRH(1) receptor antagonists represent promising novel therapeutics in the psychopharmacology of depression and anxiety.

High-affinity CRF1 receptor antagonist NBI-34041: preclinical and clinical data suggest safety and efficacy in attenuating elevated stress response

There is an extensive evidence that corticotropin releasing factor (CRF) is hypersecreted in depression and anxiety, and blockade of CRF could have therapeutic benefit. We report preclinical data and the results of a clinical Phase I study with the novel nonpeptide CRF(1) antagonist NBI-34041/SB723620. Preclinical data conducted with different cell lines expressing human CRF receptors and in Wistar and Sprague-Dawley rats indicate that NBI-34041 is effective in reducing endocrine responses to pharmacological and behavioral challenge mediated by CRF(1) receptors. These specific properties and its well-documented safety profile enabled a clinical Phase I study with 24 healthy male subjects receiving NBI-34041 (10, 50, or 100 mg) or placebo for 14 days. Regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis was evaluated by intravenous stimulation with 100 microg of human CRF. Psychosocial stress response was investigated with the Trier Social Stress Test (TSST). Treatment with NBI-34041 did not impair diurnal adrenocorticotropic hormone (ACTH) and cortisol secretion or CRF evoked ACTH and cortisol responses but attenuated the neuroendocrine response to psychosocial stress. These results suggest that NBI-34041 is safe and does not impair basal regulation of the HPA system but improves resistance against psychosocial stress. NBI-34041 demonstrates that inhibition of the CRF system is a promising target for drug development against depression and anxiety disorders.

Glucocorticoid receptor transgenic mice as models for depression

In the era of mutant mice generated as molecular in vivo models for complex pathogenetic and therapeutic aspects of particular human diseases, glucocorticoid receptor transgenic mice represent an interesting and promising tool. Animals carrying mutations of this receptor show alterations in the hypothalamic-pituitary-adrenal (HPA)-system, which are comparable to those observed in depressed patients. Furthermore, similarities that may model the human disease have been described on the behavioral and pharmacological level, which increase the impact of such mutants. In this review we summarize different approaches used to alter or eliminate glucocorticoid receptor expression and function, and discuss their relevance as models for depression.

Mutant mouse models of depression: Candidate genes and current mouse lines

Depression is a multifactorial and multigenetic disease. At present, three main theories try to conceptualize its molecular and biochemical mechanisms, namely the monoamine-, the hypothalamus-pituitary-adrenal- (HPA-) system- and the neurotrophin-hypotheses. One way to explore, validate or falsify these hypotheses is to alter the expression of genes that are involved in these systems and study their respective role in animal behavior and neuroendocrinological parameters. Following an introduction in which we briefly describe each hypothesis, we review here the different mouse lines generated to study the respective molecular pathways. Among the many mutant lines generated, only a few can be regarded as genetic depression models or as models of predisposition for a depressive syndrome after stress exposure. However, this is likely to reflect the human situation where depressive syndromes are complex, can vary to a great extent with respect to their symptomatology, and may be influenced by a variety of environmental factors. Mice with mutations of candidate genes showing depression-like features on behavioral or neurochemical levels may help to define a complex molecular framework underlying depressive syndromes. Because it is conceivable that manipulation of one single genetic function may be necessary but not sufficient to cause complex behavioral alterations, strategies for improving genetic modeling of depression-like syndromes in animals possibly require a simultaneous targeted dysregulation of several genes involved in the pathogenesis of depression. This approach would correspond to the new concept of 'endophenotypes' in human depression research trying to identify behavioral traits which are thought to be encoded by a limited set of genes.

An integrative approach to the neurophysiological substrates of social withdrawal and aggression

An integrative model of the neurophysiology of aggression and social withdrawal is proposed. A detailed overview of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis is presented first, because we consider it to be a critical system that interacts with a variety of physiological processes to modulate affect-related behaviors. This detailed analysis of the LHPA axis is then used to clarify the research literature that links aggression and social withdrawal to LHPA functioning. We then review the role of amygdala and prefrontal cortex functioning in modulating aggression and social withdrawal. Particular attention is paid to how the amygdala and the prefrontal cortex interact with the LHPA system and the environment to produce specific behavioral tendencies throughout development. A brief overview of the implied methodological and theoretical model is provided. We explain how a detailed understanding of specific physiological processes is essential in order to develop appropriate research protocols. In addition, we suggest that future research should focus on the mapping of distinct integrative biosocial profiles that are related to specific behaviors during different developmental stages.

Effects of periadolescent versus adult cocaine exposure on cocaine conditioned place preference and motor sensitization in mice

RATIONALE

Age of initial exposure to addictive substances is inversely proportional to risk of developing drug dependence. There is debate, however, as to whether intake at a young age causes dependency or whether young people who experiment with addictive substances are predisposed to dependency by other factors. OBJECTIVES. We tested the relationship between cocaine exposure at two different ages in mice and the development of subsequent drug-seeking behavior to test for age-specific exposure effects.

METHODS

We performed dose-response analysis of cocaine conditioned place preference (CPP) and locomotor activity in periadolescent and adult C57Bl/6J mice. In addition, we pretreated periadolescent and adult C57Bl/6J mice with cocaine or saline in the home cage or a drug-associated context, and then examined their behavior in a biased CPP procedure in adulthood.

RESULTS

Dose-response relationships were similar between the two age groups. In the pretreatment experiments, we observed locomotor sensitization during the pretreatment in periadolescent but not adult mice. We also observed an enhanced aversion to the non-preferred side of the chamber in periadolescent mice compared to adult mice, which was alleviated by cocaine association with that side. Third, we observed that after further conditioning in adulthood, there were no pretreatment-specific effects.

CONCLUSIONS

Our results are consistent with a "vulnerable brain" hypothesis for responses to cocaine based on our findings that periadolescent mice exhibit greater locomotor sensitization to cocaine, and greater baseline anxiety responses that are alleviated by cocaine exposure compared to adult mice.

Genetically modified laboratory animals--what welfare problems do they face?

In this article, we respond to public concern expressed about the welfare of genetically modified (GM) nonhuman animals. As a contribution to the debate on this subject, we attempt in this article to determine in what situations the practice of genetic modification in rodents may generate significant welfare problems. After a brief discussion of the principles of animal welfare, we focus on the problem of animal suffering and review some types of gene modifications likely to cause predictable welfare problems. In this article, we also consider suffering that may be involved in the process of generating GM animals. Finally, we discuss the role of GM animals in attempts to reduce, replace, and refine the use of animals in research.

Amygdala kindling increases fear responses and decreases glucocorticoid receptor mRNA expression in hippocampal regions

Amygdala kindling dramatically increases fearful behavior in rats. Because kindling-induced fear increases in magnitude as rats receive more stimulations, kindling provides an excellent model for studying the nature and neural mechanisms of fear sensitization. In the present experiment, we studied whether the development of kindling-induced fear is related to changes in glucocorticoid receptor (GR) mRNA expression in various brain regions. Rats received 20, 60 or 100 amygdala kindling stimulations or 100 sham stimulations. One day after the final stimulation, their fearful behavior was assessed in an unfamiliar open field. Then, the rats were sacrificed and their brains were processed for in situ hybridization of GR mRNA expression. We found that compared with the sham-stimulated rats, the rats that received 60 or 100 kindling stimulations were significantly more fearful in the open field and also had significantly less GR mRNA expression in the dentate gyrus and CA1 subfield of the hippocampus. Importantly, the changes in fearful behavior were significantly correlated with the changes in GR mRNA expression. These results suggest that alterations in GR mRNA expression in hippocampal regions may play a role in the development of kindling-induced fear.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Effects of cocaine on c-fos and NGFI-B mRNA expression in transgenic mice underexpressing glucocorticoid receptors

Numerous evidences suggest that stress and stress-related hormones can modulate the activity of the brain reward pathway and thus may account for individual vulnerability towards the reinforcing effects of drugs of abuse. Transgenic (TG) mice expressing an antisense mRNA against the glucocorticoid receptor (GR), which partially blocks GR expression, were used to assess the role of GR dysfunction on cocaine (COC)-induced c-fos and Nerve-Growth Factor Inducible-B (NGFI-B, or Nur77) gene expression. These two genes belong to different families of transcription factors and have been shown to be modulated by various dopaminergic drugs. TG and wild-type (WT) mice were both acutely and repeatedly treated with COC (20 mg/kg, i.p.). In the chronic experiment, mice received a 5-day treatment of COC and were challenged 5 days later with COC or vehicle. Locomotor activity was assessed during the entire chronic experiment in the mouse home cages. Animals were sacrificed 1 h after the last injection and NGFI-B and c-fos mRNA levels in the prefrontal cortex, the nucleus accumbens and the striatum were measured by in situ hybridization. Acute COC administration led to significantly smaller c-fos increases in TG mice compared to WT, whereas repeated COC treatment potentiated c-fos induction both in TG and WT mice to equivalent levels. TG mice displayed higher basal NGFI-B expression in the nucleus accumbens and the level of NGFI-B mRNA was differently modulated by COC in TG mice compared to WT mice. In accordance with data on c-fos expression, behavioral data indicate a blunted locomotor effect on the first COC injection in TG mice, a phenomenon corrected by the repeated COC treatment. These results suggest that an alteration of the hypothalamus-pituitary-adrenal axis can modify COC-induced regulation of the transcription factors c-fos and NGFI-B, and that these changes parallel those seen at the behavioral level. It also demonstrates that the differences at the behavioral and molecular levels noted between TG and WT mice after acute COC injection disappear following repeated COC administration, suggesting that repeated COC has a greater impact in TG mice underexpressing GRs.

Genetic basis of anxiety-like behaviour: a critical review

The way genetic and/or environmental factors influence psychiatric disorders is an enduring question in the field of human psychiatric diseases. Anxiety-related disorders provide a relevant example of how such an interaction is involved in the aetiology of a psychiatric disease. In this paper we review the literature on that subject, reporting data derived from human and rodent studies. We present in a critical way the animal models used in the studies aimed at investigating the genetic basis of anxiety, including inbred mice, selected lines, multiple marker strains, or knockout mice and review data reporting environmental components influencing anxiety-related behaviours. We conclude that anxiety is a complex behaviour, underlined not only by genetic or environmental factors but also by multiple interactions between these two factors.

Effects of neonatal RU486 on adult sexual, parental, and fearful behaviors in rats

Exposure to gonadal hormones during perinatal life influences later behavior. The finding that sex differences exist in progestin receptor expression in the perinatal rat brain suggests differential sensitivity of male and female brains to progesterone (C. K. Wagner, A. N. Nakayama, & G. J. De Vries, 1998). Because these sex differences are in neural sites that influence sexually differentiated sexual, parental, and fearful behaviors in adults, this study examined the effects of administering the progestin receptor antagonist RU486 for the first 10 days after birth on these behaviors in adulthood. Neonatal RU486 significantly reduced sexual behavior in males but did not impair reproduction in females. Neonatal RU486 did not affect parental responses of virgin rats exposed to pups (sensitization) but reduced fear in the elevated plus-maze in both sexes. Treatment of pups with RU486 affected neither mother-litter interactions nor plasma testosterone levels in males during or after treatment. These results suggest that neonatal exposure to progesterone, in addition to androgens and estrogens, influences behavioral development in rats.

Neurobiological correlates of individual differences in novelty-seeking behavior in the rat: differential expression of stress-related molecules

It is well established that individual rats exhibit marked differences in behavioral responses to a novel environment. Rats that exhibit high rates of locomotor activity and sustained exploration in such an environment also exhibit high concentrations of stress-induced plasma corticosterone, linking this behavior to the stress system. Furthermore, these high-responding (HR) rats, in contrast to their low-responding (LR) counterparts, have a greater propensity to self-administer drugs. Thus, HR rats have been described as "novelty" seeking in that they are more active and explore novel stimuli more vigorously, despite the fact that this elicits in them high stress responses. In this study, we have further characterized the behavior of HR and LR rats in tests of anxiety and characterized their stress responses to either experimenter- or self-imposed stressors. We then investigated the physiological basis of these individual differences, focusing on stress-related molecules, including the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR), corticotropin-releasing hormone (CRH) and pro-opiomelanocortin (POMC) in the context of the limbic-hypothalamo-pituitary adrenal axis. We have found that HR rats did not differ from LR in their basal expression of POMC in the pituitary. However, HR rats exhibited higher levels of CRH mRNA in the hypothalamic paraventricular nucleus but lower basal levels in the central nucleus of the amygdala. The basal expression of hippocampal MR is not different between HR and LR rats. Interestingly, the basal expression of hippocampal GR mRNA is significantly lower in HR than in LR rats. This low level of hippocampal GR expression in HR rats appears to be responsible, at least in part, for their decreased anxiety in exploring novelty. Indeed, the anxiety level of LR rats becomes similar to HR rats after the administration into the hippocampus of a GR antagonist, RU38486. These data indicate that basal differences in gene expression of key stress-related molecules may play an important role in determining individual differences in responsiveness to stress and novelty. They point to a new role of hippocampal GR, strongly implicating this receptor in determining individual differences in anxiety and novelty-seeking behavior.

Hypothalamic-pituitary-adrenal dysfunction in Apoe(-/-) mice: possible role in behavioral and metabolic alterations

Several neurological diseases are frequently accompanied by dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis regulates the secretion of glucocorticoids (GCs), which play important roles in diverse brain functions, including cognition, emotion, and feeding. Under physiological conditions, GCs are adaptive and beneficial; however, prolonged elevations in GC levels may contribute to neurodegeneration and brain dysfunction. In the current study, we demonstrate that apolipoprotein E (apoE) deficiency results in age-dependent dysregulation of the HPA axis through a mechanism affecting primarily the adrenal gland. Apoe(-/-) mice, which develop neurodegenerative alterations as they age, had an age-dependent increase in basal adrenal corticosterone content and abnormally increased plasma corticosterone levels after restraint stress, whereas their plasma and pituitary adrenocorticotropin levels were either unchanged or lower than those in controls. HPA axis dysregulation was associated with behavioral and metabolic alterations. When anxiety levels were assessed in the elevated plus maze, Apoe(-/-) mice showed more anxiety than wild-type controls. Apoe(-/-) mice also showed reduced activity in the open field. Finally, Apoe(-/-) mice showed age-dependent increases in food and water intake, stomach and body weights, and decreases in brown and white adipose tissues. These results support a key role for apoE in the tonic inhibition of steroidogenesis and HPA axis activity and have important implications for the behavioral analysis of Apoe(-/-) mice.