Learning impairment in transgenic mice with central overexpression of corticotropin-releasing factor

Alterations in hippocampal cholinergic dynamics following CRF infusions into the medial septum of male and female rats

Corticoptropin releasing factor (CRF) is implicated in stress-related physiological and behavioral changes. The septohippocampal pathway regulates hippocampal-dependent mnemonic processes, which are affected in stress-related disorders, and given the abundance of CRF receptors in the medial septum (MS), this pathway is influenced by CRF. Moreover, there are sex differences in the MS sensitivity to CRF and its impact on hippocampal function. However, the mechanisms underlying these associations remain elusive. In the present study, we utilized an in vivo biosensor-based electrochemistry approach to examine the impact of MS CRF infusions on hippocampal cholinergic signaling dynamics in male and female rats. Our results show increased amplitudes of depolarization-evoked phasic cholinergic signals in the hippocampus following MS infusion of CRF at the 3 ng dose as compared to the infusion involving artificial cerebrospinal fluid (aCSF). Moreover, a trend for a sex × infusion interaction indicated larger cholinergic transients in females. On the contrary, intraseptal infusion of a physiologically high dose (100 ng) of CRF produced a subsequent reduction in phasic cholinergic transients in both males and females. The assessment of tonic cholinergic activity over 30 min post-infusion revealed no changes at the 3 ng CRF dose in either sex, but a significant infusion × sex interaction indicated a reduction in females at the 100 ng dose of CRF as compared to the aCSF. Taken together, our results show differential, dose-dependent modulatory effects of MS CRF on the dynamics of phasic and tonic modes of cholinergic signaling in the hippocampus of male and female rats. These cholinergic signaling modes are critical for memory encoding and maintaining arousal states, and may underlie sex differences in cognitive vulnerability to stress and stress-related psychiatric disorders.

Septohippocampal cholinergic system at the intersection of stress and cognition: Current trends and translational implications

Deficits in hippocampus-dependent memory processes are common across psychiatric and neurodegenerative disorders such as depression, anxiety and Alzheimer's disease. Moreover, stress is a major environmental risk factor for these pathologies and it exerts detrimental effects on hippocampal functioning via the activation of hypothalamic-pituitary-adrenal (HPA) axis. The medial septum cholinergic neurons extensively innervate the hippocampus. Although, the cholinergic septohippocampal pathway (SHP) has long been implicated in learning and memory, its involvement in mediating the adaptive and maladaptive impact of stress on mnemonic processes remains less clear. Here, we discuss current research highlighting the contributions of cholinergic SHP in modulating memory encoding, consolidation and retrieval. Then, we present evidence supporting the view that neurobiological interactions between HPA axis stress response and cholinergic signalling impact hippocampal computations. Finally, we critically discuss potential challenges and opportunities to target cholinergic SHP as a therapeutic strategy to improve cognitive impairments in stress-related disorders. We argue that such efforts should consider recent conceptualisations on the dynamic nature of cholinergic signalling in modulating distinct subcomponents of memory and its interactions with cellular substrates that regulate the adaptive stress response.

Neurocognitive effects of stress: a metaparadigm perspective

Stressful experiences, both physical and psychological, that are overwhelming (i.e., inescapable and unpredictable), can measurably affect subsequent neuronal properties and cognitive functioning of the hippocampus. At the cellular level, stress has been shown to alter hippocampal synaptic plasticity, spike and local field potential activity, dendritic morphology, neurogenesis, and neurodegeneration. At the behavioral level, stress has been found to impair learning and memory for declarative (or explicit) tasks that are based on cognition, such as verbal recall memory in humans and spatial memory in rodents, while facilitating those that are based on emotion, such as differential fear conditioning in humans and contextual fear conditioning in rodents. These vertically related alterations in the hippocampus, procedurally observed after subjects have undergone stress, are generally believed to be mediated by recurrently elevated circulating hypothalamic-pituitary-adrenal (HPA) axis effector hormones, glucocorticoids, directly acting on hippocampal neurons densely populated with corticosteroid receptors. The main purposes of this review are to (i) provide a synopsis of the neurocognitive effects of stress in a historical context that led to the contemporary HPA axis dogma of basic and translational stress research, (ii) critically reappraise the necessity and sufficiency of the glucocorticoid hypothesis of stress, and (iii) suggest an alternative metaparadigm approach to monitor and manipulate the progression of stress effects at the neural coding level. Real-time analyses can reveal neural activity markers of stress in the hippocampus that can be used to extrapolate neurocognitive effects across a range of stress paradigms (i.e., resolve scaling and dichotomous memory effects issues) and understand individual differences, thereby providing a novel neurophysiological scaffold for advancing future stress research.

Cognitive performance in patients with chronic tension-type headache and its relation to neuroendocrine hormones

Background

Tension-type headache is the most common headache to be seen in clinical practice. Depression is highly prevalent in chronic tension-type headache (CTTH) patients attending the clinical settings. Cognitive impairment and neuroendocrine dysregulation had been reported in patients with depression and patients with CTTH.

Objective

To assess the cognitive performance and investigate its possible relations to neuroendocrine levels in patients with CTTH.

Subjects and methods

Patients with CTTH, depression, and control subjects were recruited. CTTH was diagnosed according to the International Classification of Headache Disorders. Cognitive performance, depression severity, and pain intensity were assessed by the Montreal Cognitive Assessment Arabic version, Beck’s Depression Inventory, and McGill Pain Questionnaire respectively. Blood samples were collected in the morning within 60 min after waking up from 8:00 to 9:00 a.m. to measure serum levels of basal plasma CRH, ACTH, Cortisol, TSH, FT3, and FT4.

Results

Both patients with CTTH and depression had impaired cognitive performance. Patients with CTTH and patients with depression had altered the hypothalamus-pituitary-adrenal axis, and pituitary-thyroid axis. The hormonal levels significantly correlated with cognitive function in patient groups, especially patients with CTTH.

Conclusion

Patients with CTTH had cognitive dysfunction which could be related to neuroendocrine hormonal dysregulation.

Combined Effects of Repetitive Mild Traumatic Brain Injury and Alcohol Drinking on the Neuroinflammatory Cytokine Response and Cognitive Behavioral Outcomes

The relationship between alcohol consumption and traumatic brain injury (TBI) often focuses on alcohol consumption increasing the likelihood of incurring a TBI, rather than alcohol use outcomes after TBI. However, patients without a history of an alcohol use disorder can also show increased problem drinking after single or multiple TBIs. Alcohol and mild TBI share diffuse deleterious neurological impacts and cognitive impairments; therefore, the purpose of these studies was to determine if an interaction on brain and behavior outcomes occurs when alcohol is consumed longitudinally after TBI. To examine the impact of mild repetitive TBI (rmTBI) on voluntary alcohol consumption, mice were subjected to four mild TBI or sham procedures over a 2 week period, then offered alcohol (20% v/v) for 2 weeks using the two-bottle choice, drinking in the dark protocol. Following the drinking period, mice were evaluated for neuroinflammatory cytokine response or tested for cognitive and behavioral deficits. Results indicate no difference in alcohol consumption or preference following rmTBI as compared to sham; however, increases in the neuroinflammatory cytokine response due to alcohol consumption and some mild cognitive behavioral deficits after rmTBI and alcohol consumption were observed. These data suggest that the cytokine response to alcohol drinking and rmTBI + alcohol drinking is not necessarily aggregate, but the combination does result in an exacerbation of cognitive behavioral outcomes.

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.

Amygdala, Medial Prefrontal Cortex and Glucocorticoid Interactions Produce Stress-Like Effects on Memory

Adverse stress effects on the hippocampal memory system are generally thought to be due to the high level of circulating glucocorticoids directly modifying the properties of hippocampal neurons and, accordingly, the results should be reproducible with exogenous administration of cortisol in humans and corticosterone in rodents. However, glucocorticoid levels increased to other events, such as exercise and environment enrichment, do not impair but instead enhance hippocampal memory, indicating that cortisol/corticosterone are not invariant causal factors of stress. To better model the complex psychophysiological attributes of stress (i.e., aversiveness, lack of controllability, and glucose metabolism), we examined the functions of the amygdala, medial prefrontal cortex (mPFC), and corticosterone on a hippocampal-based one-trial novel object recognition (OR) memory task in rats. Specifically, animals were subjected to amygdala stimulation, mPFC inactivation, and corticosterone treatments separately or in combination during behavioral testing. Collective amygdala, mPFC, and corticosterone manipulations significantly impaired OR memory comparable to behavioral stress. By contrast, single and dual treatments failed to reliably decrease memory functioning. These results suggest that negative mnemonic impacts of uncontrollable stress involve the amalgamation of heightened amygdala and diminished mPFC activities, and elevated circulating corticosterone level.

Sex differences in corticotropin releasing factor regulation of medial septum-mediated memory formation

Stress can disrupt memory and contribute to cognitive impairments in psychiatric disorders, including schizophrenia and attention deficit hyperactivity disorder. These diseases are more common in men than in women, with men showing greater cognitive impairments. Mnemonic deficits induced by stress are mediated, in part, by corticotropin releasing factor (CRF). However, where CRF is acting to regulate memory, and sex differences therein, is understudied. Here we assessed whether CRF in the medial septum (MS), which projects to the hippocampus, affected memory formation in male and female rats. CRF in the MS did not alter hippocampal-independent object recognition memory, but impaired hippocampal-dependent object location memory in both sexes. Interestingly, males were more sensitive than females to the disruptive effect of a low dose of CRF in the MS. Female resistance was not due to circulating ovarian hormones. However, compared to males, females had higher MS expression of CRF binding protein, which reduces CRF bioavailability and thus may mitigate the effect of the low dose of CRF in females. In contrast, there was no sex difference in CRF₁ expression in the MS. Consistent with this finding, CRF₁ antagonism blocked the memory impairment caused by the high dose of CRF in the MS in both sexes. Collectively, these results suggest that males are more vulnerable than females to the memory impairments caused by CRF in the MS. In both sexes, CRF₁ antagonists prevented MS-mediated memory deficits caused by high levels of CRF, and such levels can result from very stressful events. Thus, CRF₁ antagonists may be a viable option for treating cognitive deficits in stressed individuals with psychiatric disorders.

The CRF Family of Neuropeptides and their Receptors - Mediators of the Central Stress Response

Background:

Dysregulated stress neurocircuits, caused by genetic and/or environmental changes, underlie the development of many neuropsychiatric disorders. Corticotropin-releasing factor (CRF) is the major physiological activator of the hypothalamic-pituitary-adrenal (HPA) axis and conse-quently a primary regulator of the mammalian stress response. Together with its three family members, urocortins (UCNs) 1, 2, and 3, CRF integrates the neuroendocrine, autonomic, metabolic and behavioral responses to stress by activating its cognate receptors CRFR1 and CRFR2.

Objective:

Here we review the past and current state of the CRF/CRFR field, ranging from pharmacologi-cal studies to genetic mouse models and virus-mediated manipulations.

Results:

Although it is well established that CRF/CRFR1 signaling mediates aversive responses, includ-ing anxiety and depression-like behaviors, a number of recent studies have challenged this viewpoint by revealing anxiolytic and appetitive properties of specific CRF/CRFR1 circuits. In contrast, the UCN/CRFR2 system is less well understood and may possibly also exert divergent functions on physiol-ogy and behavior depending on the brain region, underlying circuit, and/or experienced stress conditions.

Conclusion:

A plethora of available genetic tools, including conventional and conditional mouse mutants targeting CRF system components, has greatly advanced our understanding about the endogenous mecha-nisms underlying HPA system regulation and CRF/UCN-related neuronal circuits involved in stress-related behaviors. Yet, the detailed pathways and molecular mechanisms by which the CRF/UCN-system translates negative or positive stimuli into the final, integrated biological response are not completely un-derstood. The utilization of future complementary methodologies, such as cell-type specific Cre-driver lines, viral and optogenetic tools will help to further dissect the function of genetically defined CRF/UCN neurocircuits in the context of adaptive and maladaptive stress responses.

Elevated paternal glucocorticoid exposure modifies memory retention in female offspring

Recent studies have demonstrated that behavioral traits are subject to transgenerational modification by paternal environmental factors. We previously reported on the transgenerational influences of increased paternal stress hormone levels on offspring anxiety and depression-related behaviors. Here, we investigated whether offspring sociability and cognition are also influenced by paternal stress. Adult C57BL/6J male mice were treated with corticosterone (CORT; 25mg/L) for four weeks prior to paired-matings to generate F1 offspring. Paternal CORT treatment was associated with decreased body weights of female offspring and a marked reduction of the male offspring. There were no differences in social behavior of adult F1 offspring in the three-chamber social interaction test. Despite male offspring of CORT-treated fathers displaying hyperactivity in the Y-maze, there was no observable difference in short-term spatial working memory. Spatial learning and memory testing in the Morris water maze revealed that female, but not male, F1 offspring of CORT-treated fathers had impaired memory retention. We used our recently developed methodology to analyze the spatial search strategy of the mice during the learning trials and determined that the impairment could not be attributed to underlying differences in search strategy. These results provide evidence for the impact of paternal corticosterone administration on offspring cognition and complement the cumulative knowledge of transgenerational epigenetic inheritance of acquired traits in rodents and humans.

The water maze paradigm in experimental studies of chronic cognitive disorders: Theory, protocols, analysis, and inference

An instrumental step in assessing the validity of animal models of chronic cognitive disorders is to document disease-related deficits in learning/memory capacity. The water maze (WM) is a popular paradigm because of its low cost, relatively simple protocol and short procedure time. Despite being broadly accepted as a spatial learning task, inference of generalized, bona fide "cognitive" dysfunction can be challenging because task accomplishment is also reliant on non-cognitive processes. We review theoretical background, testing procedures, confounding factors, as well as approaches to data analysis and interpretation. We also describe an extended protocol that has proven useful in detecting early performance deficits in murine models of neuropsychiatric lupus and Alzheimer's disease. Lastly, we highlight the need for standardization of inferential criteria on "cognitive" dysfunction in experimental rodents and exclusion of preparations of a limited scientific merit. A deeper appreciation for the multifactorial nature of performance in WM may also help to reveal other deficits that herald the onset of neurodegenerative brain disorders.

Functional Impact of Corticotropin-Releasing Factor Exposure on Tau Phosphorylation and Axon Transport

Stress exposure or increased levels of corticotropin-releasing factor (CRF) induce hippocampal tau phosphorylation (tau-P) in rodent models, a process that is dependent on the type-1 CRF receptor (CRFR1). Although these preclinical studies on stress-induced tau-P provide mechanistic insight for epidemiological work that identifies stress as a risk factor for Alzheimer’s disease (AD), the actual impact of stress-induced tau-P on neuronal function remains unclear. To determine the functional consequences of stress-induced tau-P, we developed a novel mouse neuronal cell culture system to explore the impact of acute (0.5hr) and chronic (2hr) CRF treatment on tau-P and integral cell processes such as axon transport. Consistent with in vivo reports, we found that chronic CRF treatment increased tau-P levels and caused globular accumulations of phosphorylated tau in dendritic and axonal processes. Furthermore, while both acute and chronic CRF treatment led to significant reduction in CREB activation and axon transport of brain-derived neurotrophic factor (BDNF), this was not the case with mitochondrial transport. Acute CRF treatment caused increased mitochondrial velocity and distance traveled in neurons, while chronic CRF treatment modestly decreased mitochondrial velocity and greatly increased distance traveled. These results suggest that transport of cellular energetics may take priority over growth factors during stress. Tau-P was required for these changes, as co-treatment of CRF with a GSK kinase inhibitor prevented CRF-induced tau-P and all axon transport changes. Collectively, our results provide mechanistic insight into the consequences of stress peptide-induced tau-P and provide an explanation for how chronic stress via CRF may lead to neuronal vulnerability in AD.

Are Anxiety Disorders Associated with Accelerated Aging? A Focus on Neuroprogression

Anxiety disorders (AnxDs) are highly prevalent throughout the lifespan, with detrimental effects on daily-life functioning, somatic health, and quality of life. An emerging perspective suggested that AnxDs may be associated with accelerated aging. In this paper, we explored the association between AnxDs and hallmarks of accelerated aging, with a specific focus on neuroprogression. We reviewed animal and human findings that suggest an overlap between processes of impaired neurogenesis, neurodegeneration, structural, functional, molecular, and cellular modifications in AnxDs, and aging. Although this research is at an early stage, our review suggests a link between anxiety and accelerated aging across multiple processes involved in neuroprogression. Brain structural and functional changes that accompany normal aging were more pronounced in subjects with AnxDs than in coevals without AnxDs, including reduced grey matter density, white matter alterations, impaired functional connectivity of large-scale brain networks, and poorer cognitive performance. Similarly, molecular correlates of brain aging, including telomere shortening, Aβ accumulation, and immune-inflammatory and oxidative/nitrosative stress, were overrepresented in anxious subjects. No conclusions about causality or directionality between anxiety and accelerated aging can be drawn. Potential mechanisms of this association, limitations of the current research, and implications for treatments and future studies are discussed.

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.

Stress effects on the hippocampus: a critical review

Uncontrollable stress has been recognized to influence the hippocampus at various levels of analysis. Behaviorally, human and animal studies have found that stress generally impairs various hippocampal-dependent memory tasks. Neurally, animal studies have revealed that stress alters ensuing synaptic plasticity and firing properties of hippocampal neurons. Structurally, human and animal studies have shown that stress changes neuronal morphology, suppresses neuronal proliferation, and reduces hippocampal volume. Since the inception of stress research nearly 80 years ago, much focus has been on the varying levels of hypothalamic-pituitary-adrenal (HPA) axis neuroendocrine hormones, namely glucocorticoids, as mediators of the myriad stress effects on the hippocampus and as contributing factors to stress-associated psychopathologies such as post-traumatic stress disorder (PTSD). However, reports of glucocorticoid-produced alterations in hippocampal functioning vary widely across studies. This review provides a brief history of stress research, examines how the glucocorticoid hypothesis emerged and guides contemporary stress research, and considers alternative approaches to understanding the mechanisms underlying stress effects on hippocampal functioning.

Increased tau phosphorylation and aggregation in the hippocampus of mice overexpressing corticotropin-releasing factor

Clinical and basic science research suggests that stress and/or changes in central stress signaling intermediates may be involved in Alzheimer's disease (AD) pathogenesis. Although the links between stress and AD remain unsettled, data from our group and others have established that stress exposure in rodents may confer susceptibility to AD pathology by inducing hippocampal tau phosphorylation (tau-P). Work in our laboratory has shown that stress-induced tau-P requires activation of the type-1 corticotropin-releasing factor receptor (CRFR1). CRF overexpressing (CRF-OE) mice are a model of chronic stress that display cognitive impairment at 9-10 month of age. In this study we used 6-7 month old CRF-OE mice to examine whether sustained exposure to CRF and stress steroids would impact hippocampal tau-P and kinase activity in the presence or absence of the CRFR1-specific antagonist, R121919, given daily for 30 days. CRF-OE mice had significantly elevated tau-P compared to wild type (WT) mice at the AT8 (S202/T204), PHF-1 (S396/404), S262, and S422 sites. Treating CRF-OE mice with R121919 blocked phosphorylation at the AT8 (S202/T204) and PHF-1 (S396/404) sites, but not at the S262 and S422 sites and reduced phosphorylation of c-Jun N Terminal Kinase (JNK). Examination of hippocampal extracts from CRF-OE mice at the ultrastructural level revealed negatively stained round/globular aggregates that were positively labeled by PHF-1. These data suggest critical roles for CRF and CRFR1 in tau-P and aggregation and may have implications for the development of AD cognitive decline.

CRF₂ receptor-deficiency reduces recognition memory deficits and vulnerability to stress induced by cocaine withdrawal

Psychostimulant drug abuse, dependence and withdrawal are associated with cognitive dysfunction and impact stress-sensitive systems. The corticotropin-releasing factor (CRF) system orchestrates stress responses via CRF1 and CRF2 receptors and is implicated in substance use disorders. However, CRF2 role in psychostimulant drug-induced cognitive dysfunction remains to be elucidated. In the present study, wild-type and CRF2-/- mice are injected with cocaine and memory assessed by the novel object recognition (NOR) task throughout relatively long periods of drug withdrawal. Following recovery from the drug-induced memory deficits, the mice are stressed prior to the NOR task and brain gene expression evaluated by in situ hybridization. Cocaine impairs NOR memory in wild-type and CRF2-/- mice. However, following cocaine withdrawal NOR memory deficits last less time in CRF2-/- than in wild-type mice. Furthermore, a relatively mild stressor induces the re-emergence of NOR deficits in long-term cocaine-withdrawn wild-type but not CRF2-/- mice. Cocaine-withdrawn mice show a genotype-independent higher c-fos expression in the NOR memory-relevant perirhinal cortex than drug-naïve mice. However neither genotype nor drug withdrawal affect the expression of tyrosine hydroxylase in the ventral tegmental area or the locus coeruleus and CRF in the central nucleus of the amygdala or the paraventricular nucleus of the hypothalamus, brain regions implicated in stress and drug responses. These data indicate a new role for the CRF2 receptor in cognitive deficits induced by cocaine withdrawal, both as regards to their duration and their re-induction by stress. Interestingly, prototypical brain stress systems other than CRF do not appear to be involved.

Effects of electroconvulsive seizures on depression-related behavior, memory and neurochemical changes in Wistar and Wistar-Kyoto rats

BACKGROUND

Investigations in healthy outbred rat strains have shown a potential role for brain-derived neurotrophic factor (BDNF) and the hypothalamic-pituitary-adrenal (HPA) axis in the antidepressant and memory side effects of electroconvulsive therapy (ECT, or ECS in animals). The Wistar-Kyoto (WKY) rat strain is used as a genetic model of depression yet no studies to date have directly compared the impact of ECS on the WKY strain to its healthy outbred control (Wistar).

OBJECTIVE

The objective of this study is to examine behavioral (antidepressant and retrograde memory) and neurochemical (BDNF and HPA axis) changes immediately (1day) and at a longer delay (7days) after repeated ECS (5 daily administrations) in WKY and Wistar rats.

METHODS

Male Wistar and WKY rats received 5days of repeated ECS or sham treatment and were assessed 1 and 7days later for 1) depression-like behavior and mobility; 2) retrograde memory; and 3) brain BDNF protein, brain corticotropin-releasing factor (CRF) and plasma corticosterone levels.

RESULTS

Both strains showed the expected antidepressant response and retrograde memory impairments at 1day following ECS, which were sustained at 7days. In addition, at 1day after ECS, Wistar and WKY rats showed similar elevations in brain BDNF and extra-hypothalamic CRF and no change in plasma corticosterone. At 7days after ECS, Wistar rats showed sustained elevations of brain BDNF and CRF, whereas WKY rats showed a normalization of brain BDNF, despite sustained elevations of brain CRF.

CONCLUSIONS

The model of 5 daily ECS was effective at eliciting behavioral and neurochemical changes in both strains. A temporal association was observed between brain CRF levels, but not BDNF, and measures of antidepressant effectiveness of ECS and retrograde memory impairments suggesting that extra-hypothalamic CRF may be a potential important contributor to these behavioral effects after repeated ECS/ECT.

CRF1 receptor-deficiency induces anxiety-like vulnerability to cocaine

RATIONALE

The intake of psychostimulant drugs may induce cognitive dysfunction and negative affective-like states, and is associated with increased activity of stress-responsive systems. The corticotropin-releasing factor (CRF) system mediates neuroendocrine, behavioural and autonomic responses to stressors, and might be implicated in substance-related disorders. CRF signalling is mediated by two receptor types, named CRF1 and CRF2.

OBJECTIVES

The present study aims to elucidate the role for the CRF1 receptor in cognitive dysfunction and anxiety-like states induced by cocaine.

RESULTS

The genetic inactivation of the CRF1 receptor (CRF1+/- and CRF1-/-) does not influence recognition memory in drug-naïve mice, as assessed by the novel object recognition (NOR) test. Moreover, the chronic administration of escalating doses of cocaine (5-20 mg/kg, i.p.) induces NOR deficits, which are unaffected by CRF1 receptor-deficiency. However, the same drug regimen reveals an anxiety-like vulnerability to cocaine in CRF1-/- but not in wild-type or CRF1+/- mice, as assessed by the elevated plus maze test.

CONCLUSIONS

The present findings indicate dissociation of cognitive dysfunction and anxiety-like states induced by cocaine. Moreover, they unravel a novel mechanism of vulnerability to psychostimulant drugs.

Stress and glucocorticoid receptor-dependent mechanisms in long-term memory: from adaptive responses to psychopathologies

A proper response against stressors is critical for survival. In mammals, the stress response is primarily mediated by secretion of glucocorticoids via the hypothalamic-pituitary-adrenocortical (HPA) axis and release of catecholamines through adrenergic neurotransmission. Activation of these pathways results in a quick physical response to the stress and, in adaptive conditions, mediates long-term changes in the brain that lead to the formation of long-term memories of the experience. These long-term memories are an essential adaptive mechanism that allows an animal to effectively face similar demands again. Indeed, a moderate stress level has a strong positive effect on memory and cognition, as a single arousing or moderately stressful event can be remembered for up to a lifetime. Conversely, exposure to extreme, traumatic, or chronic stress can have the opposite effect and cause memory loss, cognitive impairments, and stress-related psychopathologies such as anxiety disorders, depression and post-traumatic stress disorder (PTSD). While more effort has been devoted to the understanding of the negative effects of chronic stress, much less has been done thus far on the identification of the mechanisms engaged in the brain when stress promotes long-term memory formation. Understanding these mechanisms will provide critical information for use in ameliorating memory processes in both normal and pathological conditions. Here, we will review the role of glucocorticoids and glucocorticoid receptors (GRs) in memory formation and modulation. Furthermore, we will discuss recent findings on the molecular cascade of events underlying the effect of GR activation in adaptive levels of stress that leads to strong, long-lasting memories. Our recent data indicate that the positive effects of GR activation on memory consolidation critically engage the brain-derived neurotrophic factor (BDNF) pathway. We propose and will discuss the hypothesis that stress promotes the formation of strong long-term memories because the activation of hippocampal GRs after learning is coupled to the recruitment of the growth and pro-survival BDNF/cAMP response element-binding protein (CREB) pathway, which is well-know to be a general mechanism required for long-term memory formation. We will then speculate about how these results may explain the negative effects of traumatic or chronic stress on memory and cognitive functions.

A possible solution for hair loss by inhibiting corticotropin-releasing factor (CRF) receptor from traditional Chinese medicine

Corticotropin-releasing factor (CRF) and corticotropin-releasing factor receptor (CRFR) play important roles in stress response, including anxiety and depression syndrome. The CRF expression also relates to chronic stress-related hair loss. This study utilizes the world's largest traditional Chinese medicine (TCM) database and molecular dynamics (MD) simulations to investigate novel CRFR inhibitors for treatment of alopecia. The docking and screening from TCM database results indicate the vitamin B2, 3 beta-isodihydrocadambine, and caribine display higher binding affinity than maltose in maltose binding protein (MBP). However, the results of MD simulation shows the caribine-facilitated CRFR approach closer to MBP, the 3D structure conformation of MBP and CRFR complex forms compact structure. Interestingly, the distance between the two proteins is reducing significantly after caribine dock into MBP binding site. Beside, from Ligand channel analysis, the paths of caribine demonstrate that residence time is increased in binding pocket. Hence, our finding suggests that caribine might be a potential lead compound to stimulate MBP and CRFR interaction, and help for baldless therapy in further study.

Sex-specific cell signaling: the corticotropin-releasing factor receptor model

Elucidating the biological basis for sex differences in diseases can reveal their pathophysiology and guide the development of individualized treatments. Here, we review evidence for the novel concept that receptor signaling can be sex biased such that the specific pathways engaged by ligand binding are determined by sex. As an example, this review focuses on the receptor for corticotropin-releasing factor (CRF), a stress-related peptide implicated in diverse psychiatric and medical disorders that are more prevalent in females. There is evidence for sex biases in CRF receptor coupling to G proteins and β-arrestin that render females more sensitive to acute stress and less able to adapt to chronic stress. Taken with evidence for sex biased signaling in other receptor systems, the studies demonstrate the broad potential impact of this characteristic in determining sex differences in disease and therapeutic efficacy and underscore the importance of studying females in medical and pharmacological research.

Sculpting the hippocampus from within: stress, spines, and CRH

Learning and memory processes carried out within the hippocampus are influenced by stress in a complex manner, and the mechanisms by which stress modulates the physiology of the hippocampus are not fully understood. This review addresses how the production and release of the neuropeptide corticotropin-releasing hormone (CRH) within the hippocampus during stress influences neuronal structure and hippocampal function. CRH functions in the contexts of acute and chronic stresses taking place during development, adulthood and aging. Current challenges are to uncover how the dynamic actions of CRH integrate with the well-established roles of adrenal-derived steroid stress hormones to shape the cognitive functions of the hippocampus in response to stress.

NOGO-66 receptor deficient mice show slow acquisition of spatial memory task performance

The Nogo-66 receptor (NgR1) is part of a co-receptor complex on neurons that transmits a signal for inhibition of neurite outgrowth. In addition, NgR1 function has also been related to other disorders such as schizophrenia and Alzheimer's disease. Here, we studied the effect of life-long deletion of NgR1 (ngr(-/-)) in tests for cognition and positive symptoms of schizophrenia. In the water maze, ngr(-/-) mice learned to locate the hidden platform as well as wild type mice, although with slower acquisition. Deletion of NgR1 did not affect amphetamine- or phencyclidine (PCP)-induced hyperactivity, two models of positive symptoms of schizophrenia. Taken together, ngr(-/-) animals show slower acquisition of a spatial learning and memory task.

Forebrain CRF₁ modulates early-life stress-programmed cognitive deficits

Childhood traumatic events hamper the development of the hippocampus and impair declarative memory in susceptible individuals. Persistent elevations of hippocampal corticotropin-releasing factor (CRF), acting through CRF receptor 1 (CRF₁), in experimental models of early-life stress have suggested a role for this endogenous stress hormone in the resulting structural modifications and cognitive dysfunction. However, direct testing of this possibility has been difficult. In the current study, we subjected conditional forebrain CRF₁ knock-out (CRF₁-CKO) mice to an impoverished postnatal environment and examined the role of forebrain CRF₁ in the long-lasting effects of early-life stress on learning and memory. Early-life stress impaired spatial learning and memory in wild-type mice, and postnatal forebrain CRF overexpression reproduced these deleterious effects. Cognitive deficits in stressed wild-type mice were associated with disrupted long-term potentiation (LTP) and a reduced number of dendritic spines in area CA3 but not in CA1. Forebrain CRF₁ deficiency restored cognitive function, LTP and spine density in area CA3, and augmented CA1 LTP and spine density in stressed mice. In addition, early-life stress differentially regulated the amount of hippocampal excitatory and inhibitory synapses in wild-type and CRF₁-CKO mice, accompanied by alterations in the neurexin-neuroligin complex. These data suggest that the functional, structural and molecular changes evoked by early-life stress are at least partly dependent on persistent forebrain CRF₁ signaling, providing a molecular target for the prevention of cognitive deficits in adults with a history of early-life adversity.

The clinical implications of mouse models of enhanced anxiety

Mice are increasingly overtaking the rat model organism in important aspects of anxiety research, including drug development. However, translating the results obtained in mouse studies into information that can be applied in clinics remains challenging. One reason may be that most of the studies so far have used animals displaying 'normal' anxiety rather than 'psychopathological' animal models with abnormal (elevated) anxiety, which more closely reflect core features and sensitivities to therapeutic interventions of human anxiety disorders, and which would, thus, narrow the translational gap. Here, we discuss manipulations aimed at persistently enhancing anxiety-related behavior in the laboratory mouse using phenotypic selection, genetic techniques and/or environmental manipulations. It is hoped that such models with enhanced construct validity will provide improved ways of studying the neurobiology and treatment of pathological anxiety. Examples of findings from mouse models of enhanced anxiety-related behavior will be discussed, as well as their relation to findings in anxiety disorder patients regarding neuroanatomy, neurobiology, genetic involvement and epigenetic modifications. Finally, we highlight novel targets for potential anxiolytic pharmacotherapeutics that have been established with the help of research involving mice. Since the use of psychopathological mouse models is only just beginning to increase, it is still unclear as to the extent to which such approaches will enhance the success rate of drug development in translating identified therapeutic targets into clinical trials and, thus, helping to introduce the next anxiolytic class of drugs.

Mouse models of genetic effects on cognition: relevance to schizophrenia

Cognitive dysfunction is a core feature of schizophrenia. Growing evidence indicates that a wide variety of genetic mutations and polymorphisms impact cognition and may thus be implicated in various aspects of this mental disorder. Despite differences between human and rodent brain structure and function, genetic mouse models have contributed critical information about brain mechanisms involved in cognitive processes. Here, we summarize discoveries of genetic modifications in mice that impact cognition. Based on functional hypotheses, gene modifications within five model systems are described: 1) dopamine (D1, D2, D3, D4, D5, DAT, COMT, MAO); 2) glutamate (GluR-A, NR1, NR2A, NR2B, GRM2, GRM3, GLAST); 3) GABA (α(5), γ(2), α(4), δGABA(A), GABA(B(1)), GAT1); 4) acetylcholine (nAChRβ2, α7, CHRM1); and 5) calcium (CaMKII-α, neurogranin, CaMKKβ, CaMKIV). We also consider other risk-associated genes for schizophrenia such as dysbindin (DTNBP1), neuregulin (NRG1), disrupted-in-schizophrenia1 (DISC1), reelin and proline dehydrogenase (PRODH). Because of the presumed importance of environmental factors, we further consider genetic modifications within the stress-sensitive systems of corticotropin-releasing factor (CRF), brain-derived neurotrophic factor (BDNF) and the endocannabinoid systems. We highlight the missing information and limitations of cognitive assays in genetically modified mice models relevant to schizophrenia pathology.

Forebrain CRHR1 deficiency attenuates chronic stress-induced cognitive deficits and dendritic remodeling

Chronic stress evokes profound structural and molecular changes in the hippocampus, which may underlie spatial memory deficits. Corticotropin-releasing hormone (CRH) and CRH receptor 1 (CRHR1) mediate some of the rapid effects of stress on dendritic spine morphology and modulate learning and memory, thus providing a potential molecular basis for impaired synaptic plasticity and spatial memory by repeated stress exposure. Using adult male mice with CRHR1 conditionally inactivated in the forebrain regions, we investigated the role of CRH-CRHR1 signaling in the effects of chronic social defeat stress on spatial memory, the dendritic morphology of hippocampal CA3 pyramidal neurons, and the hippocampal expression of nectin-3, a synaptic cell adhesion molecule important in synaptic remodeling. In chronically stressed wild-type mice, spatial memory was disrupted, and the complexity of apical dendrites of CA3 neurons reduced. In contrast, stressed mice with forebrain CRHR1 deficiency exhibited normal dendritic morphology of CA3 neurons and mild impairments in spatial memory. Additionally, we showed that the expression of nectin-3 in the CA3 area was regulated by chronic stress in a CRHR1-dependent fashion and associated with spatial memory and dendritic complexity. Moreover, forebrain CRHR1 deficiency prevented the down-regulation of hippocampal glucocorticoid receptor expression by chronic stress but induced increased body weight gain during persistent stress exposure. These findings underscore the important role of forebrain CRH-CRHR1 signaling in modulating chronic stress-induced cognitive, structural and molecular adaptations, with implications for stress-related psychiatric disorders.

Mice overexpressing corticotropin-releasing factor show brain atrophy and motor dysfunctions

Chronic stress and persistently high glucocorticoid levels can induce brain atrophy. Corticotropin-releasing factor (CRF)-overexpressing (OE) mice are a genetic model of chronic stress with elevated brain CRF and plasma corticosterone levels and Cushing's syndrome. The brain structural alterations in the CRF-OE mice, however, are not well known. We found that adult male and female CRF-OE mice had significantly lower whole brain and cerebellum weights than their wild type (WT) littermates (347.7+/-3.6mg vs. 460.1+/-4.3mg and 36.3+/-0.8mg vs. 50.0+/-1.3mg, respectively) without sex-related difference. The epididymal/parametrial fat mass was significantly higher in CRF-OE mice. The brain weight was inversely correlated to epididymal/parametrial fat weight, but not to body weight. Computerized image analysis system in Nissl-stained brain sections of female mice showed that the anterior cingulate and sensorimotor cortexes of CRF-OE mice were significantly thinner, and the volumes of the hippocampus, hypothalamic paraventricular nucleus and amygdala were significantly reduced compared to WT, while the locus coeruleus showed a non-significant increase. Motor functions determined by beam crossing and gait analysis showed that CRF-OE mice took longer time and more steps to traverse a beam with more errors, and displayed reduced stride length compared to their WT littermates. These data show that CRF-OE mice display brain size reduction associated with alterations of motor coordination and an increase in visceral fat mass providing a novel animal model to study mechanisms involved in brain atrophy under conditions of sustained elevation of brain CRF and circulating glucocorticoid levels.

Transient forebrain over-expression of CRF induces plasma corticosterone and mild behavioural changes in adult conditional CRF transgenic mice

BACKGROUND

Converging findings support a role for extra-hypothalamic CRF in the mediation of the stress response. The influence of CRF in the amygdala is well established, while less is known of its role in other areas of the forebrain where CRF and CRF(1) receptors are also expressed. In the present study CRF was genetically induced to allow forebrain-restricted expression in a temporally-defined manner at any time during the mouse lifespan. This mouse model may offer the possibility to establish a model of the pathogenesis of recurrent episodes of depression.

METHODS

Mice were engineered to carry both the rtTA transcription factor driven by the CamKII alpha promoter and the doxycycline-regulated operator (tetO) upstream of the CRF coding sequence. Molecular, biochemical and behavioural characterisation of this mouse is described.

RESULTS

Following a three-week period of transcriptional induction, double transgenic mice showed approximately 2-fold increased expression of CRF mRNA in the hippocampus and cortex, but not hypothalamus. These changes were associated with 2-fold increase in morning corticosterone levels, although responses to the dexamethasone suppression test or acute stress were unaffected. In contrast, induced mice displayed modestly altered behaviour in the Light and Dark test and Forced Swim test.

CONCLUSIONS

Transient induction of CRF expression in mouse forebrain was associated with endocrine and mild anxiety-like behavioural changes consistent with enhanced central CRF neurotransmission. This mouse allows the implementation of regimens with longer or repeated periods of induction which may model the initial stages of the pathology underlying recurrent depressive 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.

Corticotropin-releasing factor (CRF) receptor type 1-dependent modulation of synaptic plasticity

CRF receptor type (CRHR) 1 exerts neuroregulatory control on associative learning processes such as fear and anxiety like behaviour. Using hippocampal slices, we investigated the neuronal excitability in mice lacking CRHR1 (Crhr1(-/-)). Compared to wild-type mice, long-term potentiation (LTP) elicited by 100 pulses at 100Hz was not different. Unexpectedly, at lower frequencies (1, 5 or 10Hz), the resulting synaptic changes in CA1 neurons of Crhr1(-/-) were systematically shifted towards long-term depression (LTD). Furthermore, testing paired-pulse paradigm revealed a GABA receptor-dependent decrease of paired-pulse ratio in Crhr1(-/-). It might be assumed that a lack of CRHR1 induce developmental changes which resulted in altered GABAergic activity, producing attenuated synaptic potentiation after repetitive stimulation and thus favouring LTD in principal neurons. Since CRHR1 are located in GABAergic somata, axons and boutons the activity of these receptor types rather might contribute to the development of the neuronal ability for plasticity like processes on the level of NMDAR subunit composition and GABAergic activity.

Induction of autoimmune depression in mice by anti–ribosomal P antibodies via the limbic system

OBJECTIVE

Autoantibodies against ribosomal P proteins are linked to the neuropsychiatric manifestations of systemic lupus erythematosus (SLE). The present study was undertaken to assess how the specific brain-binding autoantibody anti-ribosomal P can induce a depression-type psychiatric disorder in mice.

METHODS

Mice were injected intracerebroventricularly with affinity-purified human anti-ribosomal P antibodies or IgG as control. Pharmacologic and immunologic treatments included the antidepressant drug fluoxetine, the antipsychotic drug haloperidol, and antiidiotypic antibodies. Behavior was assessed by the forced swimming test, motor deficits by rotarod, grip strength, and staircase tests, and cognitive deficits by T-maze alternation and passive avoidance tests.

RESULTS

Anti-ribosomal P antibodies induced depression-like behavior in the mice (mean +/- SEM 147.3 +/- 19.2 seconds of immobility versus 75.2 +/- 12.1 seconds of immobility in IgG-injected control mice; P < 0.005). The anti-ribosomal P antibody-induced depression-like behavior was partially blocked by a specific antiidiotypic antibody and significantly blocked by long-term treatment with fluoxetine, but not by short- or long-term treatment with haloperidol. The depressive behavior was not associated with any motor or cognitive deficits. Anti-ribosomal P antibodies specifically stained neurons in the hippocampus, cingulate cortex, and the primary olfactory piriform cortex, compatible with the previously described binding to the membrane-bound P0 ribosomal protein.

CONCLUSION

This is the first report of an experimental depression induced by a specific autoantibody. The results implicate olfactory and limbic areas in the pathogenesis of depression in general, and in central nervous system dysfunction in SLE in particular.

Enhanced pelvic responses to stressors in female CRF-overexpressing mice

Acute stress affects gut functions through the activation of corticotropin-releasing factor (CRF) receptors. The impact of acute stress on pelvic viscera in the context of chronic stress is not well characterized. We investigated the colonic, urinary, and locomotor responses monitored as fecal pellet output (FPO), urine voiding, and ambulatory activity, respectively, in female and male CRF-overexpressing (CRF-OE) mice, a chronic stress model, and their wild-type littermates (WTL). Female CRF-OE mice, compared with WTL, had enhanced FPO to 2-min handling (150%) and 60-min novel environment (155%) but displayed a similar response to a 60-min partial restraint stress. Female CRF-OE mice, compared with WTL, also had a significantly increased number of urine spots (7.3 +/- 1.4 vs. 1.3 +/- 0.8 spots/h) and lower locomotor activity (246.8 +/- 47.8 vs. 388.2 +/- 31.9 entries/h) to a novel environment. Male CRF-OE mice and WTL both responded to a novel environment but failed to show differences between them in colonic and locomotor responses. Male WTL, compared with female WTL, had higher FPO (113%). In female CRF-OE mice, the CRF(1)/CRF(2) receptor antagonist astressin B and the selective CRF(2) receptor agonist mouse urocortin 2 (injected peripherally) prevented the enhanced defecation without affecting urine or locomotor responses to novel environment. RT-PCR showed that CRF(1) and CRF(2) receptors are expressed in the mouse colonic tissues. The data show that chronic stress, due to continuous central CRF overdrive, renders female CRF-OE mice to have enhanced pelvic and altered behavioral responses to superimposed mild stressors and that CRF(1)-initiated colonic response is counteracted by selective activation of CRF(2) receptor.

Hippocampal neuroplasticity induced by early-life stress: functional and molecular aspects

Whereas genetic factors contribute crucially to brain function, early-life events, including stress, exert long-lasting influence on neuronal function. Here, we focus on the hippocampus as the target of these early-life events because of its crucial role in learning and memory. Using a novel immature-rodent model, we describe the deleterious consequences of chronic early-life 'psychological' stress on hippocampus-dependent cognitive tasks. We review the cellular mechanisms involved and discuss the roles of stress-mediating molecules, including corticotropin releasing hormone, in the process by which stress impacts the structure and function of hippocampal neurons.

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.

Mild traumatic brain injury induces persistent cognitive deficits and behavioral disturbances in mice

Victims of mild traumatic brain injury (mTBI) do not show clear morphological brain defects, but frequently suffer from long-lasting cognitive deficits, emotional difficulties and behavioral disturbances. In the present study, we investigated the effects of experimental mTBI in mice on cognition, spatial and non-spatial tasks, and depressive-like behavior in mice. Experimental brain injury was induced using a concussive head trauma, which creates the TBI by a weight-drop device. Different groups of mice were tested at 7, 30, 60, and 90 days post-injury for cognitive function (the swim T-maze and the passive avoidance test) and for depression-like behavior (the forced swimming test). These tests have been used infrequently in the past in mTBI research. Significant differences were observed between the injured mice compared to the controls in both the swim T-maze (day 30: p < 0.001) and passive avoidance (day 30: p < 0.05) tests. In addition, a significant difference was detected in the forced swimming test between the injured mice and the controls (day 7: p < 0.05; day 90: p < 0.01), which showed a depressive- like state in the injured animals beginning 7 days post-injury. These results demonstrate that persistent deficits in these tests of cognitive learning abilities and emergence of depressive-like behavior in injured mice are similar to those reported in human post-concussion syndrome.

Dissecting the genetic effect of the CRH system on anxiety and stress-related behaviour

Corticotropin-releasing hormone (CRH) plays a central role in the adaptation of the body to stress. CRH integrates the endocrine, autonomic and behavioural responses to stress acting as a secretagogue within the line of the hypothalamic pituitary adrenocortical (HPA) system and as a neurotransmitter modulating synaptic transmission in the central nervous system. Accumulating evidence suggests that the neuroendocrine and behavioural symptoms observed in patients suffering from major depression are at least in part linked to a hyperactivity of the CRH system. Genetic modifications of the CRH system by conventional and conditional gene targeting strategies in the mouse allowed us to study the endogenous mechanisms underlying HPA system regulation and CRH-related neuronal circuitries involved in pathways mediating anxiety and stress-related behaviour.

Effects of CRF1 receptor antagonists and benzodiazepines in the Morris water maze and delayed non-matching to position tests

RATIONALE

Benzodiazepines continue to be widely used for the treatment of anxiety, but it is well known that benzodiazepines have undesirable side effects, including sedation, ataxia, cognitive deficits and the risk of addiction and abuse. CRF(1) receptor antagonists are being developed as potential novel anxiolytics, but while CRF(1) receptor antagonists seem to have a better side-effect profile than benzodiazepines with respect to sedation and ataxia, the effects of CRF(1) receptor antagonists on cognitive function have not been well characterized. It is somewhat surprising that the potential cognitive effects of CRF(1) receptor antagonists have not been more fully characterized since there is some evidence to suggest that these compounds may impair cognitive function.

OBJECTIVE

The Morris water maze and the delayed non-matching to position test are sensitive tests of a range of cognitive functions, including spatial learning, attention and short-term memory, so the objective of the present experiments was to assess the effects of benzodiazepines and CRF(1) receptor antagonists in these tests.

RESULTS

The benzodiazepines chlordiazepoxide and alprazolam disrupted performance in the Morris water maze and delayed non-matching to position at doses close to their therapeutic, anxiolytic doses. In contrast, the CRF(1) receptor antagonists DMP-904 and DMP-696 produced little or no impairment in the Morris water maze or delayed non-matching to position test even at doses 10-fold higher than were necessary to produce anxiolytic effects.

CONCLUSIONS

The results of the present experiments suggest that, with respect to their effects on cognitive functions, CRF(1) receptor antagonists seem to have a wider therapeutic index than benzodiazepines.

Heart rate dynamics and behavioral responses during acute emotional challenge in corticotropin-releasing factor receptor 1-deficient and corticotropin-releasing factor-overexpressing mice

The role of corticotropin-releasing factor in autonomic regulation of heart rate, heart rate variability and behavior responses was investigated in two genetic mouse models: corticotropin-releasing factor receptor 1-deficient mice, and corticotropin-releasing factor-transgenic mice overexpressing corticotropin-releasing factor. Heart rate was recorded by radio-telemetry during novelty exposure and auditory fear conditioning. Locomotor activity and freezing served as behavioral indices. Locomotor activity and heart rate were invariably increased in response to novelty exposure in both corticotropin-releasing factor receptor 1-deficient mice and littermate wild-type controls. The heart rate responses during retention of conditioned auditory fear and the exponential relationship between heart rate and heart rate variability were unaffected by genotype. Moreover, conditioned fear responses inferred from multiple behavioral measures including freezing did not differ between corticotropin-releasing factor receptor 1-deficient and corticotropin-releasing factor receptor 1 wild-type control mice. Corticotropin-releasing factor-transgenic mice exhibited markedly reduced locomotor activity during novelty exposure when compared with littermate wild-type controls. Baseline and novelty-driven heart rate was slightly elevated in corticotropin-releasing factor-transgenic mice, whereas the novelty-induced increase of heart rate was not different between genotypes. In contrast, corticotropin-releasing factor-transgenic mice did not display a heart rate response indicative of conditioned auditory fear. It is concluded that corticotropin-releasing factor receptor 1-deficiency does not affect heart rate adjustment and behavioral responses to acute fearful stimuli. The resiliency of behavioral and cardiovascular patterns elevation argues against the involvement of corticotropin-releasing factor receptor 1 in acute emotional regulation on these two functional levels despite an absent corticosterone elevation in corticotropin-releasing factor receptor 1-deficient mice. It is hypothesized that the lack of a conditioned heart rate response in corticotropin-releasing factor-transgenic mice is attributable to an impairment of cognitive function. The results are compared with those of corticotropin-releasing factor receptor 2-deficient mice, and the role of the corticotropin-releasing factor system in cardiovascular regulation is discussed.

Mutagenesis and knockout models: hypothalamic-pituitary-adrenocortical system

Hyperactivity of central neuropeptidergic circuits such as the corticotropin-releasing hormone (CRH) and vasopressin (AVP) neuronal systems is thought to play a causal role in the etiology and symptomatology of anxiety disorders. Indeed, there is increasing evidence from basic science that chronic stress-induced perturbation of CRH and AVP neurocircuitries may contribute to abnormal neuronal communication in conditions of pathological anxiety. Anxiety disorders aggregate in families, and accumulating evidence supports the notion that the major source of familial risk is genetic. In this context, refined molecular technologies and the creation of genetically engineered mice have allowed us to specifically target individual genes involved in the regulation of the elements of the CRH (e.g., CRH peptides, CRH-related peptides, their receptors, binding protein). During the past few years, studies performed in such mice have complemented and extended our knowledge. The cumulative evidence makes a strong case implicating dysfunction of CRH-related systems in the pathogenesis of anxiety disorders and depression and leads us beyond the monoaminergic synapse in search of eagerly anticipated strategies to discover and develop better therapies.

Listening to mutant mice: a spotlight on the role of CRF/CRF receptor systems in affective disorders

Genetically engineered mice were originally generated to delineate the role of a specific gene product in behavioral or neuroendocrine phenotypes, rather than to produce classic animal models of depression. To learn more about the neurobiological mechanisms underlying a clinical condition such as depression, it has proven worthwhile to investigate changes in behaviors characteristic of depressed humans, such as anxiety, regardless of whether or not these alterations may also occur in other disorders besides depression. The majority of patients with mood and anxiety disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have been increasingly translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) system elements (e.g. CRF and CRF-related peptides, their receptors, binding protein). Studies performed in such mice have complemented and extended our knowledge. The cumulative evidence makes a strong case implicating dysfunction of these systems in the pathogenesis of depression and leads us beyond the monoaminergic synapse in search of eagerly anticipated strategies to discover and develop better therapies 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.

Deficits in hippocampus-mediated Pavlovian conditioning in endogenous hypercortisolism

BACKGROUND

Elevated endogenous levels of corticosteroids cause neural dysfunction and loss, especially within the hippocampus, as well as cognitive impairment in hippocampus-mediated tasks. Because Cushing's syndrome patients suffer from hypercortisolism, they represent a unique opportunity to study the impact of elevated glucocorticoids on cognitive functions. The aim of this study was to examine the performance of Cushing's syndrome patients on trace eyeblink conditioning, a cross-species, hippocampal-mediated test of learning and memory.

METHODS

Eleven Cushing's syndrome patients and 11 healthy control subjects participated in an eyeblink trace conditioning test (1000-msec trace) and a task of declarative memory for words. Salivary cortisol was collected in both the patients and the control subjects, and urinary free cortisol was collected in the patients only.

RESULTS

The patients exhibited fewer conditional responses and remembered fewer words, compared with the control subjects. Cortisol levels correlated with immediate and delayed declarative memory only. Conditional response correlated with delayed recall after controlling for the magnitude of unconditional response.

CONCLUSIONS

The integrity of the hippocampus seems to be compromised in Cushing's syndrome patients. Trace eyeblink conditioning might be useful both as a clinical tool to examine changes in hippocampus function in Cushing's disease patients and as a translational tool of research on the impact of chronic exposure of glucocorticoids.

Corticotropin-releasing factor overexpression decreases ethanol drinking and increases sensitivity to the sedative effects of ethanol

RATIONALE

Corticotropin-releasing factor (CRF) may play a significant role in drug and alcohol abuse.

OBJECTIVE

To evaluate the role of CRF in these processes, we examined several ethanol (EtOH) related behaviors in mice that carry a transgene that causes overexpression of CRF.

METHODS

We examined voluntary EtOH drinking, loss of the righting reflex (LORR), EtOH-induced conditioned taste aversion (CTA), and EtOH clearance in littermate transgenic (TG) and non-transgenic (non-TG) mice. In addition, because preliminary results indicated that age exacerbated differences in EtOH consumption between the two genotypes, we performed a cross-sectional and longitudinal evaluation of this trait at two ages ( approximately 100 and 200 days old).

RESULTS

We found that TG mice consumed significantly less EtOH and had a lower preference for EtOH-containing solutions compared with their non-TG littermates. We also found that the older drug-naive TG mice drank less EtOH as compared with the younger mice of the same genotype; however, the same relationship did not exist for drug-naive non-TG mice. Prior experience in drinking EtOH when 100 days old led to decreased EtOH drinking when 200 days old in both genotypes. Duration of LORR was longer in the TG mice, EtOH-induced CTA was marginally greater in non-TG mice at the highest dose tested, and there were significant but small differences in EtOH clearance parameters.

CONCLUSIONS

These data show that CRF overexpressing mice voluntarily consume less EtOH. This difference is associated with greater sensitivity to the sedative-hypnotic effects of EtOH, but not with increased sensitivity to the aversive effects of EtOH.

Corticotropin-Releasing Factor in Brain: A Role in Activation, Arousal, and Affect Regulation

Organisms exposed to challenging stimuli that alter the status quo inside or outside of the body are required for survival purposes to generate appropriate coping responses that counteract departures from homeostasis. Identification of an executive control mechanism within the brain capable of coordinating the multitude of endocrine, physiological, and functional coping responses has high utility for understanding the response of the organism to stressor exposure under normal or pathological conditions. The corticotropin-releasing factor (CRF)/urocortin family of neuropeptides and receptors constitutes an affective regulatory system due to the integral role it plays in controlling neural substrates of arousal, emotionality, and aversive processes. In particular, available evidence from pharmacological intervention in multiple species and phenotyping of mutant mice shows that CRF/urocortin systems mediate motor and psychic activation, stimulus avoidance, and threat recognition responses to aversive stimulus exposure. It is suggested that affective regulation is exerted by CRF/urocortin systems within the brain based upon the sensitivity of local brain sites to CRF/urocortin ligand administration and the appearance of hypothalamo-pituitary-adrenocortical activation following stressor exposure. Moreover, these same stress neuropeptides may constitute a mechanism for learning to avoid noxious stimuli by facilitating the formation of so-called emotional memories. A conceptual framework is provided for extrapolation of animal model findings to humans and for viewing CRF/urocortin activation as a continuum measure linking normal and pathological states.

Reduced attention in mice overproducing corticotropin-releasing hormone

Data from several studies suggest that unrestrained secretion of corticotropin-releasing hormone in the CNS produces several signs and symptoms of depression. Recent evidence indicates that blockade of the CRH receptor 1 reduced depression scores in depressed patients. One of the symptoms that occur is depression is impairment in attentional processes. Whether these impairments are due to alterations in the CRH system are so far unknown. In order to investigate whether overproduction of CRH alters attentional process, transgenic mice overproducing CRH were tested on an operant five choice serial reaction time task, a task which taxes sustained and divided attention. Mutants showed impaired autoshaping. During initial discrimination learning, transgenics performed below wildtype level, but with extended training with long stimulus durations, transgenic animals reached similar accuracy levels as wildtype mice. When animals were tested at shortest stimulus duration (0.5s), a mild but significant impairment in accurate responding emerged in transgenics. This was accompanied by longer correct response latencies, while incorrect latencies did not differ between groups, suggesting attentional impairment in CRH transgenics. Because these animals have been reported to also show increased anxiety-related behaviour, animals were treated with the anxiolytic benzodiazepine diazepam. Diazepam failed to affect accuracy, but transgenic mice showed a stronger behavioural disinhibition. This suggests that the attentional impairment seen in CRH overexpressors is independent of alterations in anxiety-like behaviour. These findings may have implications for understanding the pathophysiology of psychiatric disorders such as depression, where it has been suggested that an overactivity of the CRH system accounts for a variety of symptoms, including hyper-arousal and attentional impairment.