Conditional CRF receptor 1 knockout mice show altered neuronal activation pattern to mild anxiogenic challenge

Long-range inputome of cortical neurons containing corticotropin-releasing hormone

Dissection of the neural circuits of the cerebral cortex is essential for studying mechanisms underlying brain function. Herein, combining a retrograde rabies tracing system with fluorescent micro-optical sectional tomography, we investigated long-range input neurons of corticotropin-releasing hormone containing neurons in the six main cortical areas, including the prefrontal, somatosensory, motor, auditory, and visual cortices. The whole brain distribution of input neurons showed similar patterns to input neurons distributed mainly in the adjacent cortical areas, thalamus, and basal forebrain. Reconstruction of continuous three-dimensional datasets showed the anterior and middle thalamus projected mainly to the rostral cortex whereas the posterior and lateral projected to the caudal cortex. In the basal forebrain, immunohistochemical staining showed these cortical areas received afferent information from cholinergic neurons in the substantia innominata and lateral globus pallidus, whereas cholinergic neurons in the diagonal band nucleus projected strongly to the prefrontal and visual cortex. Additionally, dense neurons in the zona incerta and ventral hippocampus were found to project to the prefrontal cortex. These results showed general patterns of cortical input circuits and unique connection patterns of each individual area, allowing for valuable comparisons among the organisation of different cortical areas and new insight into cortical functions.

Elucidation of the neural circuits activated by a GABAB receptor positive modulator: Relevance to anxiety

Although there is much evidence for a role of GABA_B receptors in the pathophysiology of anxiety, the underlying neuronal mechanisms are largely unclear. The GABA_B receptor allosteric positive modulator, GS39783, exerts anxiolytic effects without interfering with GABA_B-mediated modulation of body temperature, cognitive performance and locomotor activity thus offering advantages over GABA_B receptor agonists. However, the precise neural circuits underlying the anxiolytic effects of GS39783 are unknown. The aim of the present study was to identify brain structures and associated neuronal circuits that are modulated by GS39783 under either basal or mild stress conditions. To this end, the expression pattern of c-Fos, a marker of neuronal activation, was examined in mice acutely treated with GS39783 under basal conditions or following a mild anxiogenic challenge induced by exposure to the Open Arm (OA) of an Elevated Plus Maze. OA exposure enhanced c-Fos expression in vehicle-treated animals in several brain regions, including the medial prefrontal cortex, lateral septum, amygdala, hippocampus, paraventricular nucleus of the hypothalamus and the periaqueductal gray (PAG). Under basal conditions, GS39783 increased c-Fos in a restricted panel of areas notably amygdala nuclei, cortical areas and PAG subregions, while it inhibited c-Fos expression in the dorsal raphe nucleus (DRN). Under stress conditions, GS39783 reversed OA-induced c-Fos expression in the granular cell layer of the dentate gyrus, no longer increased c-Fos expression in the amygdala nor reduced c-Fos expression in the DRN. These specific patterns of neural activation by GS39783 might explain the neurobiological correlates implicated in GABA_B-mediated anti-anxiety effects. This article is part of the "Special Issue Dedicated to Norman G. Bowery".

Inhibition of corticotropin releasing factor expression in the central nucleus of the amygdala attenuates stress-induced behavioral and endocrine responses

Corticotropin releasing factor (CRF) is a primary mediator of endocrine, autonomic and behavioral stress responses. Studies in both humans and animal models have implicated CRF in a wide-variety of psychiatric conditions including anxiety disorders such as post-traumatic stress disorder (PTSD), depression, sleep disorders and addiction among others. The central nucleus of the amygdala (CeA), a key limbic structure with one of the highest concentrations of CRF-producing cells outside of the hypothalamus, has been implicated in anxiety-like behavior and a number of stress-induced disorders. This study investigated the specific role of CRF in the CeA on both endocrine and behavioral responses to stress. We used RNA Interference (RNAi) techniques to locally and specifically knockdown CRF expression in CeA. Behavior was assessed using the elevated plus maze (EPM) and open field test (OF). Knocking down CRF expression in the CeA had no significant effect on measures of anxiety-like behavior in these tests. However, it did have an effect on grooming behavior, a CRF-induced behavior. Prior exposure to a stressor sensitized an amygdalar CRF effect on stress-induced HPA activation. In these stress-challenged animals silencing CRF in the CeA significantly attenuated corticosterone responses to a subsequent behavioral stressor. Thus, it appears that while CRF projecting from the CeA does not play a significant role in the expression stress-induced anxiety-like behaviors on the EPM and OF it does play a critical role in stress-induced HPA activation.

Acute hypernatremia exerts an inhibitory oxytocinergic tone that is associated with anxiolytic mood in male rats

Anxiety disorders are the most common psychiatric illnesses and are associated with heightened stress responsiveness. The neuropeptide oxytocin (OT) has garnered significant attention for its potential as a treatment for anxiety disorders; however, the mechanism mediating its effects on stress responses and anxiety is not well understood. Here we used acute hypernatremia, a stimulus that elevates brain levels of OT, to discern the central oxytocinergic pathways mediating stress responsiveness and anxiety-like behavior. Rats were rendered hypernatremic by acute administration of 2.0 M NaCl and had increased plasma sodium concentration, plasma osmolality, and Fos induction in OT-containing neurons relative to 0.15 M NaCl-treated controls. Acute hypernatremia decreased restraint-induced elevations in corticosterone and created an inhibitory oxytocinergic tone on parvocellular neurosecretory neurons within the paraventricular nucleus of the hypothalamus. In contrast, evaluation of Fos immunohistochemistry determined that acute hypernatremia followed by restraint increased neuronal activation in brain regions receiving OT afferents that are also implicated in the expression of anxiety-like behavior. To determine whether these effects were predictive of altered anxiety-like behavior, rats were subjected to acute hypernatremia and then tested in the elevated plus maze. Relative to controls given 0.15 M NaCl, rats given 2.0 M NaCl spent more time in the open arms of the elevated plus maze, suggesting that acute hypernatremia is anxiolytic. Collectively the results suggest that acute elevations in plasma sodium concentration increase central levels of OT, which decreases anxiety by altering neuronal activity in hypothalamic and limbic nuclei.

Behavioral Studies and Genetic Alterations in Corticotropin-Releasing Hormone (CRH) Neurocircuitry: Insights into Human Psychiatric Disorders

To maintain well-being, all organisms require the ability to re-establish homeostasis in the presence of adverse physiological or psychological experiences. The regulation of the hypothalamic-pituitary adrenal (HPA) axis during stress is important in preventing maladaptive responses that may increase susceptibility to affective disorders. Corticotropin-releasing hormone (CRH) is a central stress hormone in the HPA axis pathway and has been implicated in stress-induced psychiatric disorders, reproductive and cardiac function, as well as energy metabolism. In the context of psychiatric disorders, CRH dysfunction is associated with the occurrence of post-traumatic stress disorder, major depression, anorexia nervosa, and anxiety disorders. Here, we review the synthesis, molecular signaling and regulation, as well as synaptic activity of CRH. We go on to summarize studies of altered CRH signaling in mutant animal models. This assembled data demonstrate an important role for CRH in neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation. Next, we present findings regarding human genetic polymorphisms in CRH pathway genes that are associated with stress and psychiatric disorders. Finally, we discuss a role for regulators of CRH activity as potential sites for therapeutic intervention aimed at treating maladaptive behaviors associated with stress.

Differential effects of diazepam and MPEP on habituation and neuro-behavioural processes in inbred mice

Background

Previous studies have demonstrated a profound lack of habituation in 129P3 mice compared to the habituating, but initially more anxious, BALB/c mice. The present study investigated whether this non-adaptive phenotype of 129P3 mice is primarily based on anxiety-related characteristics.

Methods

To test this hypothesis and extend our knowledge on the behavioural profile of 129P3 mice, the effects of the anxiolyticdiazepam (1, 3 and 5 mg/kg) and the putative anxiolytic metabotropic glutamate receptor 5 (mGlu5R) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP, 3, 10 and 30 mg/kg) treatment on within-trial (intrasession) habituation, object recognition (diazepam: 1 mg/kg; MPEP 10 mg/kg) and on the central-nervous expression of the immediate early gene c-Fos (diazepam: 1 mg/kg; MPEP 10 mg/kg) were investigated.

Results

Behavioural findings validated the initially high, but habituating phenotype of BALB/c mice, while 129P3 mice were characterized by impaired intrasession habituation. Diazepam had an anxiolytic effect in BALB/c mice, while in higher doses caused behavioural inactivity in 129P3 mice. MPEP revealed almost no anxiolytic effects on behaviour in both strains, but reduced stress-induced corticosterone responses only in 129P3 mice. These results were complemented by reduced expression of c-Fos after MPEP treatment in brain areas related to emotional processes, and increased c-Fos expression in higher integrating brain areas such as the prelimbic cortex compared to vehicle-treated 129P3 mice.

Conclusions

These results suggest that the strain differences observed in (non)adaptive anxiety behaviour are at least in part mediated by differences in gamma-aminobutyric acid- A and mGluR5 mediated transmission.

A test to identify judgement bias in mice

Emotional states are known to affect cognitive processes. For example highly anxious individuals interpret ambiguous stimuli more negatively than low anxious people, an effect called negative judgement bias. Recently, the measurement of judgement bias has been used to try and indicate emotional states in animals. In the present experiment a potential test for judgement bias in mice was examined. Mice were trained with two distinct odour cues (vanilla or apple) predicting either a palatable or an unpalatable almond piece. Subsequently their reaction to mixtures of both odours, the ambiguous stimuli, was investigated. Mice of the BALB/cJ and 129P3/J inbred mouse strains (high initial anxiety and low initial anxiety phenotypes respectively) were tested. While BALB/cJ mice showed odour association learning and showed intermediate reactions to the ambiguous cues, 129P3/J mice did not discriminate between the cues. Additionally BALB/cJ mice that were tested under more aversive white light conditions revealed a higher latency to approach the almond piece than mice tested under less aversive red light conditions. The ambiguous stimulus however was interpreted as negative under both test conditions. Brain c-Fos expression levels (a marker for neuronal activity) differed between the BALB/c/J and 129P3/J in the lateral amygdala and the prelimbic cortex, indicating differences in ambiguous information processing between the strains. The behavioural results suggest that the present judgement bias test might be used to assess emotional states in at least BALB/c mice, however further research on both behaviour and on the involved brain mechanisms is necessary to confirm this idea.

Sex differences in prenatally programmed anxiety behaviour in rats: differential corticotropin-releasing hormone receptor mRNA expression in the amygdaloid complex

We recently reported that male, but not female, offspring born to mothers exposed to social stress during late gestation show heightened anxiety-type behaviour in adulthood. The amygdala organises anxious behaviour, which involves actions of corticotropin-releasing hormone (CRH). CRH gene expression and/or its release are increased in the amygdala in prenatally stressed (PNS) rats. CRH type 1 receptor (CRH-R1) mediates actions of CRH and urocortin I to promote anxiety-like behaviour, whereas the CRH type 2 receptor (CRH-R2) may mediate anxiolytic actions, through actions of urocortins 2 and 3. Here, using quantitative in situ hybridisation, we investigated whether altered CRH receptor mRNA expression in the amygdaloid nuclei may explain the sex differences in anxiety behaviour in adult male and female PNS rats. CRH-R1 mRNA expression was significantly greater in the central amygdala and basolateral amygdala (BLA) in male PNS rats compared with controls, with no change in the basomedial amygdala (BMA) or medial amygdala (MeA). In PNS females, CRH-R1 mRNA expression was greater than controls only in the MeA. Conversely, CRH-R2 mRNA expression was significantly lower in the BMA of male PNS rats compared with controls, but greater in female PNS rats, with no change in the BLA or MeA in either sex. The ratio of CRH-R1:CRH-R2 mRNA in the amygdaloid nuclei was generally increased in PNS males, but not in the PNS females. In conclusion, sex differences in anxiety-type behaviour in PNS rats may be explained by differential mRNA expression for CRH-R1 (pro-anxiogenic) and CRH-R2 (pro-anxiolytic) in the amygdaloid complex.

Neuroanatomical evidence for reciprocal regulation of the corticotrophin-releasing factor and oxytocin systems in the hypothalamus and the bed nucleus of the stria terminalis of the rat: Implications for balancing stress and affect

Activation of corticotrophin releasing factor (CRF) neurons in the paraventricular nucleus of the hypothalamus (PVN) is necessary for establishing the classic endocrine response to stress, while activation of forebrain CRF neurons mediates affective components of the stress response. Previous studies have reported that mRNA for CRF2 receptor (CRFR2) is expressed in the bed nucleus of the stria terminalis (BNST) as well as hypothalamic nuclei, but little is known about the localization and cellular distribution of CRFR2 in these regions. Using immunofluorescence with confocal microscopy, as well as electron microscopy, we demonstrate that in the BNST CRFR2-immunoreactive fibers represent moderate to strong labeling on axons terminals. Dual-immunofluorescence demonstrated that CRFR2-fibers co-localize oxytocin (OT), but not arginine-vasopressin (AVP), and make perisomatic contacts with CRF neurons. Dual-immunofluorescence and single cell RT-PCR demonstrate that in the hypothalamus, CRFR2 immunoreactivity and mRNA are found in OT, but not in CRF or AVP-neurons. Furthermore, CRF neurons of the PVN and BNST express mRNA for the oxytocin receptor, while the majority of OT/CRFR2 neurons in the hypothalamus do not. Finally, using adenoviral-based anterograde tracing of PVN neurons, we show that OT/CRFR2-immunoreactive fibers observed in the BNST originate in the PVN. Our results strongly suggest that CRFR2 located on oxytocinergic neurons and axon terminals might regulate the release of this neuropeptide and hence might be a crucial part of potential feedback loop between the hypothalamic oxytocin system and the forebrain CRF system that could significantly impact affective and social behaviors, in particular during times of stress.

Regulation of neuronal activation by Alpha2A adrenergic receptor agonist

Stress factors induce neuronal activation in brain areas that are related to anxiety and fear. High doses of caffeine induce neuronal activation with Ca2+ influx followed by expression of the immediate early gene c-fos. In the present study, we investigated c-Fos protein expression in stress-responsive brain areas induced by caffeine, as well as the role of alpha2A receptor in the regulation of neuronal activation. Immunohistochemical analysis showed that an acute effect of caffeine induced c-Fos protein expression in the hippocampus, the bed nucleus of stria terminalis (BNST), the lateral septum, the basolateral and central amygdala, the paraventricular hypothalamic nucleus (PVN), the locus coeruleus, and the lateral parabrachial nucleus (LPBN). However, c-Fos expression was attenuated after repeated treatment of caffeine, spaced 24 h apart, compared to a single acute effect. Alpha2A receptor activation with the agonist guanfacine attenuated the acute effect of caffeine in terms of c-Fos expression in neurons in the CA1-CA3 areas of hippocampus, the locus coeruleus and the LPBN as compared with effect of caffeine alone, whereas the number of c-Fos expressing neurons increased in the lateral septum, the dorsal BNST, the central amygdala, and the PVN, areas that are densely innervated by noradrenergic neurons. Guanfacine alone induced c-Fos protein expression in neurons in the central amygdala, the dorsal BNST, the PVN, the LPBN, and the caudal nucleus of the solitary tract. Guanfacine alone also induced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in neurons expressing c-Fos in the dorsal BNST, the central amygdala, and the LPBN. These results suggest that alpha2A receptor activation modulates synaptic transmission in neuronal circuits that are correlated with stress in vivo.

Susceptibility of a potential animal model for pathological anxiety to chronic mild stress

When anxiety-related behaviour in animals appears to lack adaptive value, it might be defined as pathological. Adaptive behaviour can be assessed for example by changes in behavioural responses over time, i.e. habituation. Thus, non-adaptive anxiety would be reflected by a lack of habituation. Recently, we found that 129P3/J mice are characterised by non-adaptive avoidance behaviour after repeated test exposure. The present study was aimed at investigating the sensitivity of the behavioural profile of these animals to exposure to a chronic mild stress (CMS) paradigm followed by repeated exposure to the modified hole board test. If the behavioural profile of 129P3/J mice mirrors pathological anxiety, their behavioural habituation under repeated test exposure conditions should be affected by CMS treatment. The results confirm the profound lack of habituation with respect to anxiety-related behaviour in both control and CMS treated mice. Additionally, CMS treated animals revealed a lower exploratory behaviour, reduced locomotor activity and increased arousal-related behaviour over time when compared to control individuals, proving an extension of their impaired habituation behaviour. Although no effects of CMS treatment on plasma corticosterone levels were found, higher immediate early gene expression in the bed nucleus of the stria terminalis and the ventrolateral periaqueductal grey in CMS treated mice indicated that 129P3/J mice are susceptible to the negative effects of CMS treatment at both the behavioural and the functional level. These results support the hypothesis that 129P3/J mice might be an interesting model for pathological anxiety.

Identifying emotional adaptation: behavioural habituation to novelty and immediate early gene expression in two inbred mouse strains

Normal anxiety is an adaptive emotional response. However, when anxiety appears to lack adaptive value, it might be defined as pathological. Adaptation in animals can be assessed for example by changes in behavioural responses over time, i.e. habituation. We hypothesize that non-adaptive anxiety might be reflected by impaired habituation. To test our hypothesis, we repeatedly exposed male mice from two inbred strains to a novel environment, the modified hole board. BALB/cJ mice were found to be initially highly anxious, but subsequently habituated to the test environment. In contrast, 129P3/J mice initially showed less anxiety-related behaviour compared with the BALB/cJ mice but no habituation in anxiety-related behaviour was observed. Notably, anxiety-related behaviour even increased during the experimental period. Complementary, 129P3/J mice did not show habituation in other parameters such as locomotor and exploratory activity, whereas significant changes appeared in these behaviours in BALB/c mice. Finally, the expression of the immediate early gene c-fos differed between the two strains in distinct brain areas, known to regulate the integration of emotional and cognitive processes. These results suggest that 129P3/J mice might be a promising (neuro)-behavioural animal model for non-adaptive, i.e. pathological anxiety.

Identification of brain target neurons using a fluorescent conjugate of corticotropin-releasing factor

Corticotropin-releasing factor (CRF) is a peptide well known for its role in coordinating various neuroendocrine, autonomic, and behavioral components of the vertebrate stress response, including rapid enhancement of locomotor activity. Although CRF's locomotor enhancing properties are well documented, the neuronal mechanisms and specific target neurons that underlie the peptide's effect on locomotor behavior remain poorly understood. In the present study, we describe the synthesis and functional characteristics of a CRF rhodamine analogue TAMRA-X conjugate mixture (CRF-TAMRA 1), to be used for tracking this peptide's internalization into target neurons in the brainstem of an amphibian, the roughskin newt (Taricha granulosa). CRF-TAMRA 1 conjugate administration into the lateral cerebral ventricle resulted in a rapid, endosomal-like internalization of fluorescence into brainstem medullary neurons. In addition, central CRF-TAMRA 1 administration produced neurobehavioral effects comparable to the native peptide, effects that were blocked by pre-treatment with the CRF receptor antagonist, alpha-helical CRF. Taken together, our results show the efficacy of CRF-TAMRA 1 as a novel tool for tracking CRF internalization into targets neurons in vivo and ultimately, aiding in elucidating the neuronal mechanisms and circuitry underlying CRF's influence on behavioral and physiological responses to stress.

Region specific gene expression profile in mouse brain after chronic corticotropin releasing factor receptor 1 activation: the novel role for diazepam binding inhibitor in contextual fear conditioning

We have previously reported that repeated central administration of sub-anxiogenic doses of the corticotropin releasing factor 1 (CRF(1)) agonist Cortagine, termed "priming," elicits a phenotype of increased anxiety-like behaviors in the elevated plus maze (EPM) and open-field test, and enhanced retention of contextual conditioned fear in C57BL/6J mice. Observed behavioral changes were functionally coupled to CRF(1)-mediated elevated central cholecystokinin (CCK) tone in discrete brain regions. However, the changes in gene expression that mediated "priming"-induced behavioral and concurrent molecular changes in specific brain regions remained unknown. In the present study, a complementary DNA microarray analysis was used to investigate gene expression profiles in the hippocampus and prefrontal cortex (PFC) of C57BL/6J mice following the "priming" procedure. Here, we report that chronic stimulation of CRF(1), by i.c.v. administration of 10 ng Cortagine for five days, brought about alterations in the expression of a wide range of hippocampal (31 genes) and PFC (18 genes) genes, implicated in anxiety and aversive memory formation. These expression changes involved genes associated with signal transduction, neurotransmitter secretion, synaptic transmission, myelination, and others involved in the transport, biosynthesis, and binding of proteins. In particular, several genes of the protein kinase A (PKA) and protein kinase C (PKC) signaling cascades, known to be involved in synaptic plasticity, such as neurogranin, calmodulin 3, and the PKA regulatory subunit 1 b were found to be upregulated in the PFC and hippocampus of CRF(1) agonist "primed" mice. Moreover, we show pharmacologically that one of the newly implicated memory regulatory elements, diazepam-binding inhibitor (DBI) is functionally involved in hippocampus-dependent enhancement of contextual fear, a cardinal phenotypic feature of the "primed" mice. Finally, an interaction network mapping of the altered genes and their known interacting partners identified additional molecular candidates responsible for CRF(1)-mediated hypersensitive fear circuitry.

Effect of neuropeptide Y Y2 receptor deletion on emotional stress-induced neuronal activation in mice

In different behavioral paradigms including the elevated plus maze (EPM), it was observed previously that deletion of the neuropeptide Y Y2 receptor subtype results in potent suppression of anxiety-related and stress-related behaviors. To identify neurobiological correlates underlying this behavioral reactivtiy, expression of c-Fos, an established early marker of neuronal activation, was examined in Y2 receptor knockout (Y2(-/-)) vs. wildtype (WT) mice. Mice were placed on the open arm (OA) or closed arm (CA) of the EPM for 10 min and the effect on regional c-Fos expression in the brain was investigated. The number of c-Fos positive neurons was significantly increased in both WT and Y2(-/-) lines after OA and CA exposure in 51 of 54 regions quantified. These regions included various cortical, limbic, thalamic, hypothalamic, and hindbrain regions. Genotype influenced c-Fos responses to arm exposures in 6 of the 51 activated regions: the cingulate cortex, barrel field of the primary somatosensory cortex, nucleus accumbens, dorsal lateral septum, amygdala and lateral periaqueductal gray. These differences in neuronal activity responses to the novel environments were more pronounced after OA than after CA exposure. Mice lacking Y2 receptors exhibited reduced neuronal activation when compared to WT animals in response to the emotional stressors. Reduced neuronal excitability in the identified brain areas relevant to the processing of motivated, explorative as well as anxiety-related behaviors is suggested to contribute to the reduced anxiety-related behavior observed in Y2(-/-) mice.

Neuropeptide Y in the amygdala induces long-term resilience to stress-induced reductions in social responses but not hypothalamic-adrenal-pituitary axis activity or hyperthermia

Resilience to mental and physical stress is a key determinant for the survival and functioning of mammals. Although the importance of stress resilience has been recognized, the underlying neural mediators have not yet been identified. Neuropeptide Y (NPY) is a peptide known for its anti-anxiety-like effects mediated via the amygdala. The results of our current study demonstrate, for the first time that repeated administration of NPY directly into the basolateral nucleus of the amygdala (BLA) produces selective stress-resilient behavioral responses to an acute restraint challenge as measured in the social interaction test, but has no effect on hypothalamic-adrenal-pituitary axis activity or stress-induced hyperthermia. More importantly, the resilient behaviors observed in the NPY-treated animals were present for up to 8 weeks. Antagonizing the activity of calcineurin, a protein phosphatase involved in neuronal remodeling and present in NPY receptor containing neurons within the BLA, blocked the development of long-term, but not the acute increases in social interaction responses induced by NPY administration. This suggests that the NPY-induced long-term behavioral resilience to restraint stress may occur via mechanisms involving neuronal plasticity. These studies suggest one putative physiologic mechanism underlying stress resilience and could identify novel targets for development of therapies that can augment the ability to cope with stress.