Anxiety phenotype in mice that overexpress protein kinase A

Opportunities and Challenges of Kava in Lung Cancer Prevention

Lung cancer is the leading cause of cancer-related deaths due to its high incidence, late diagnosis, and limited success in clinical treatment. Prevention therefore is critical to help improve lung cancer management. Although tobacco control and tobacco cessation are effective strategies for lung cancer prevention, the numbers of current and former smokers in the USA and globally are not expected to decrease significantly in the near future. Chemoprevention and interception are needed to help high-risk individuals reduce their lung cancer risk or delay lung cancer development. This article will review the epidemiological data, pre-clinical animal data, and limited clinical data that support the potential of kava in reducing human lung cancer risk via its holistic polypharmacological effects. To facilitate its future clinical translation, advanced knowledge is needed with respect to its mechanisms of action and the development of mechanism-based non-invasive biomarkers in addition to safety and efficacy in more clinically relevant animal models.

Hesperidin Exerts Anxiolytic-like Effects in Rats with Streptozotocin- Induced Diabetes via PKA/CREB Signaling

BACKGROUND

The mechanisms underlying synaptic injury and anxiety-like behavioral changes caused by diabetes and the strategies to reverse these changes are not well understood.

OBJECTIVES

This study examined the neuroprotective effects of hesperidin on anxiety-like behaviors in diabetic rats and investigated the underlying mechanisms from the perspective of the PKA/CREB pathway.

METHODS

Rats with streptozotocin-induced diabetes were treated orally with hesperidin (50 and 150 mg/kg) for 10 weeks. The elevated plus maze (EPM), hole board test (HBT), and marbleburying test (MBT) were used to assess anxiety-like behaviors. We further examined the effects of hesperidin on the PKA/CREB pathway in vivo and in vitro.

RESULTS

The results show that supplementation with hesperidin exerted anxiolytic effects on the diabetic rats, as evidenced by increased percentages of open arm entries and time spent in the open arms in the EPM; decreased numbers of hole visits in the HBT; decreased numbers of marbles buried; and increased expression of PKA, CREB, BDNF, and synaptic proteins in the amygdala and hippocampus of diabetic rats. Hesperidin was found to reverse the imbalance in the PKA/CREB/BDNF pathway. In vitro, we found that the PKA inhibitor H89 reversed the protective effects of hesperidin against cell injury and reversed the HG-induced expression of PKA, pCREB/CREB, and BDNF.

CONCLUSION

Our results demonstrated that hesperidin could ameliorate the anxiety-like behaviors of diabetic rats and that activating the PKA/CREB/BDNF pathway contributed to the beneficial effects. This study may provide important insights into the mechanisms underlying anxiety-like behaviors in diabetes and identify new therapeutic targets for clinical treatment.

Anatomical Evidence for the Neural Connection from the Emotional Brain to Autonomic Innervation in the Anterior Chamber Structures of the Eye

OBJECTIVE

Previous studies have shown that the autonomic nervous system (ANS), which can be affected by emotions, is important in the occurrence or progression of glaucoma. The autonomic innervation distributed in the anterior chamber (AC) structures might play an efferent role in the neural regulation of intraocular pressure (IOP). This study aimed to investigate the anatomic neural connection from the emotional brain to autonomic innervation in the AC.

METHODS

A retrograde trans-multisynaptic pseudorabies virus encoded with an enhanced green fluorescent protein (PRV531) and non-trans-synaptic tracer FAST Dil were injected into the right eye of mice, respectively. Fluorescent localization in the emotional brain and preganglionic nuclei was studied. Five and a half days after PRV531 injection into the right AC, fluorescent signals were observed in several emotional brain regions, including the amygdala, agranular insular cortex, lateral septal nuclei, periaqueductal gray, and hypothalamus. Autonomic preganglionic nuclei, including Edinger-Westphal nucleus, superior salivatory nucleus, and intermediolateral nucleus, were labeled using PRV531.

RESULTS

The sensory trigeminal nuclei were not labeled using PRV531. The fluorescence signals in the nuclei mentioned above showed bilateral distribution, primarily on the ipsilateral side. Seven days after injecting FAST Dil into the AC, we observed no FAST Dil-labeled neurons in the central nervous system.

CONCLUSION

Our results indicate a neural connection from the emotional brain to autonomic innervation in the AC, which provides anatomical support for the emotional influence of IOP via the ANS.

The regulation of PKA signaling in obesity and in the maintenance of metabolic health

The cAMP-dependent protein kinase (PKA) system represents a primary cell-signaling pathway throughout systems and across species. PKA facilitates the actions of hormones, neurotransmitters and other signaling molecules that bind G-protein coupled receptors (GPCR) to modulate cAMP levels. Through its control of synaptic events, exocytosis, transcriptional regulation, and more, PKA signaling regulates cellular metabolism and emotional and stress responses making it integral in the maintenance and dysregulation of energy homeostasis. Neural PKA signaling is regulated by afferent and peripheral efferent signals that link specific neural cell populations to the regulation of metabolic processes in adipose tissue, liver, pancreas, adrenal, skeletal muscle, and gut. Mouse models have provided invaluable information on the roles for PKA subunits in brain and key metabolic organs. While limited, human studies infer differential regulation of the PKA system in obese compared to lean individuals. Variants identified in PKA subunit genes cause Cushing syndrome that is characterized by metabolic dysregulation associated with endogenous glucocorticoid excess. Under healthy physiologic conditions, the PKA system is exquisitely regulated by stimuli that activate GPCRs to alter intracellular cAMP concentrations, and by PKA cellular localization and holoenzyme stability. Adenylate cyclase activity generates cAMP while phosphodiesterase-mediated cAMP degradation to AMP decreases cAMP levels downstream of GPCRs. Chronic perturbations in PKA signaling appear to be capable of resetting PKA regulation at several levels; in addition, sex differences in PKA signaling regulation, while not well understood, impact the physiologic consequences of metabolic dysregulation and obesity. This review explores the roles for PKA signaling in the pathogenesis of metabolic diseases including obesity, type 2 diabetes mellitus and associated co-morbidities through neural-peripheral crosstalk and cAMP/PKA signaling pathway targets that hold therapeutic potential.

OUP accepted manuscript

Our earlier work demonstrated varying potency of dihydromethysticin (DHM) as the active kava phytochemical for prophylaxis of tobacco carcinogen nicotine-derived nitrosamine ketone (NNK)-induced mouse lung carcinogenesis. Efficacy was dependent on timing of DHM gavage ahead of NNK insult. In addition to DNA adducts in the lung tissues mitigated by DHM in a time-dependent manner, our in vivo data strongly implicated the existence of DNA damage-independent mechanism(s) in NNK-induced lung carcinogenesis targeted by DHM to fully exert its anti-initiation efficacy. In the present work, RNA seq transcriptomic profiling of NNK-exposed (2 h) lung tissues with/without a DHM (8 h) pretreatment revealed a snap shot of canonical acute phase tissue damage and stress response signaling pathways as well as an activation of protein kinase A (PKA) pathway induced by NNK and the restraining effects of DHM. The activation of the PKA pathway by NNK active metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) at a concentration incapable of promoting DNA adduct was confirmed in a lung cancer cell culture model, potentially through NNAL binding to and activation of the β-adrenergic receptor. Our in vitro and in vivo data overall support the hypothesis that DHM suppresses PKA activation as a key DNA damage-independent mechanistic lead, contributing to its effective prophylaxis of NNK-induced lung carcinogenesis. Systems biology approaches with a detailed temporal dissection of timing of DHM intake versus NNK exposure are warranted to fill the knowledge gaps concerning the DNA damage-driven mechanisms and DNA damage-independent mechanisms to optimize the implementation strategy for DHM to achieve maximal lung cancer chemoprevention.

Phenotypic Trade-Offs: Deciphering the Impact of Neurodiversity on Drug Development in Fragile X Syndrome

Fragile X syndrome (FXS) is the most common single-gene cause of intellectual disability and autism spectrum disorder. Individuals with FXS present with a wide range of severity in multiple phenotypes including cognitive delay, behavioral challenges, sleep issues, epilepsy, and anxiety. These symptoms are also shared by many individuals with other neurodevelopmental disorders (NDDs). Since the discovery of the FXS gene, FMR1, FXS has been the focus of intense preclinical investigation and is placed at the forefront of clinical trials in the field of NDDs. So far, most studies have aimed to translate the rescue of specific phenotypes in animal models, for example, learning, or improving general cognitive or behavioral functioning in individuals with FXS. Trial design, selection of outcome measures, and interpretation of results of recent trials have shown limitations in this type of approach. We propose a new paradigm in which all phenotypes involved in individuals with FXS would be considered and, more importantly, the possible interactions between these phenotypes. This approach would be implemented both at the baseline, meaning when entering a trial or when studying a patient population, and also after the intervention when the study subjects have been exposed to the investigational product. This approach would allow us to further understand potential trade-offs underlying the varying effects of the treatment on different individuals in clinical trials, and to connect the results to individual genetic differences. To better understand the interplay between different phenotypes, we emphasize the need for preclinical studies to investigate various interrelated biological and behavioral outcomes when assessing a specific treatment. In this paper, we present how such a conceptual shift in preclinical design could shed new light on clinical trial results. Future clinical studies should take into account the rich neurodiversity of individuals with FXS specifically and NDDs in general, and incorporate the idea of trade-offs in their designs.

PKA functions in metabolism and resistance to obesity: lessons from mouse and human studies

Both direct and indirect evidence demonstrate a central role for the cAMP-dependent protein kinase (PKA) signaling pathway in the regulation of energy balance and metabolism across multiple systems. However, the ubiquitous pattern of PKA expression across cell types poses a challenge in pinpointing its tissue-specific regulatory functions and further characterizing its many downstream effects in certain organs or cells. Mouse models of PKA deficiency and over-expression and studies in living cells have helped clarify PKA function in adipose tissue (AT), liver, adrenal, pancreas, and specific brain nuclei, as they pertain to energy balance and metabolic dysregulation. Limited studies in humans suggest differential regulation of PKA in AT of obese compared to lean individuals and an overall dysregulation of PKA signaling in obesity. Despite its complexity, under normal physiologic conditions, the PKA system is tightly regulated by changes in cAMP concentrations upstream via adenylate cyclase and downstream by phosphodiesterase-mediated cAMP degradation to AMP and by changes in PKA holoenzyme stability. Adjustments in the PKA system appear to be important to the development and maintenance of the obese state and its associated metabolic perturbations. In this review we discuss the important role of PKA in obesity and its involvement in resistance to obesity, through studies in humans and in mouse models, with a focus on the regulation of PKA in energy expenditure, intake behavior, and lipid and glucose metabolism.

Haplotypes of coping behavior associated QTL regions reveal distinct transcript profiles in amygdala and hippocampus

Stress response and coping behavior in pigs are largely shaped by hypothalamic-pituitary-adrenal axis and sympatho-adrenomedullary system action. However, the dynamic interaction between amygdala and hippocampus crucially modulates the behavioral response towards significant emotional events. While this functional relationship is well documented, the molecular underpinnings still remain insufficiently understood. Our study used transcriptome profiling of porcine amygdala and hippocampus to identify molecular pathways that are differentially activated depending on the haplotype of a significantly coping behavior-associated region on pig chromosome 12 (SSC12). The pigs were classified into two groups based on the haplotype information of this QTL-region discovered in our previous genome-wide association study. Ten each of high- (HR) and low- (LR) reactive pigs (n = 20) were selected for differential gene expression analysis and weighted gene co-expression analysis with subsequent pathway analysis. Differentially expressed genes identified in the amygdala include SELL, CXCR7 and NTS, while TRAF3, PTGS2 and CFI were detected in the hippocampus indicating a role of neuroinflammation and immunological processes. Pathway analysis revealed IL-8 signaling, NF-κB signaling, glutamate and GABA metabolism, glucocorticoid receptor signaling and chemokine signaling in the amygdala and ephrin receptor signaling, as well as NF-κB signaling in the hippocampus. We discovered candidate genes in regions detected by genome-wide association study including ARRB2, ADRBK2, THRB, NEK7 and ACVR2B, which relate to dopaminergic and other monoaminergic neurotransmitter systems, neuroimmunomodulation, neuroinflammation and GABA-ergic neurotransmission. These findings provide insights into the molecular underpinning of divergent coping behavior and associated haplotypes in limbic forebrain system in pig.

Intervention effect of gamma aminobutyric acid on anxiety behavior induced by phthalate (2-ethylhexyl ester) in rats

BACKGROUND

Di(2-ethylhexyl) phthalate (DEHP) is one of the most widely used phthalate esters. The application of DEHP has caused serious environmental pollution and posed a threat to human health.

METHODS

A total of 30 male Sprague-Dawley rats were randomly divided into control group, DEHP group (500 mg/kg DEHP), low GABA (Gama-aminobutyric acid) group (500 mg/kg DEHP and 1 mg/kg GABA), medium GABA group (500 mg/kg DEHP and 2 mg/kg GABA) and high GABA group (500 mg/kg DEHP and 4 mg/kg GABA). The interventions continued for 30 consecutive days. Open-field test and elevated plus-maze test were used to detect behavioral changes of rats before and after interventions.

RESULTS

The levels of nitric oxide and nitric oxide synthase in prefrontal cortex of rats were measured using enzyme-linked immunosorbent assay. DEHP and GABA treatment had no significant effects on the body weight of rats. GABA restored food utilization rate of rats impaired by DEHP to the level of healthy rats. According to open-field test and elevated plus-maze test, GABA alleviated the effects of DEHP on rat behaviors. Enzyme-linked immunosorbent assay showed that GABA was effective in reducing the levels of nitric oxide and nitric oxide synthase in rats treated with DEHP.

CONCLUSION

DEHP exposure induced anxiety in rats, which may be achieved through elevating nitric oxide and nitric oxide synthase levels in prefrontal cortex of rats. However, the effects caused by DEHP could be alleviated by GABA.

Anxiety-like behavior and other consequences of early life stress in mice with increased protein kinase A activity

Anxiety disorders are associated with abnormalities in fear-learning and bias to threat; early life experiences are influential to the development of an anxiety-like phenotype in adulthood. We recently reported that adult mice (Prkar1a+/-) with haploinsufficiency for the main regulatory subunit of the protein kinase A (PKA) exhibit an anxiety-like phenotype associated with increased PKA activity in the amygdala. PKA is the main effector of cyclic adenosine mono-phosphate signaling, a key pathway involved in the regulation of fear learning. Since anxiety has developmental and genetic components, we sought to examine the interaction of a genetic defect associated with anxiety phenotype and early life experiences. We investigated the effects of neonatal maternal separation or tactile stimulation on measures of behavior typical to adolescence as well as developmental changes in the behavioral phenotype between adolescent and adult wild-type (WT) and Prkar1a+/- mice. Our results showed developmental differences in assays of anxiety and novelty behavior for both genotypes. Adolescent mice showed increased exploratory and novelty seeking behavior compared to adult counterparts. However, early life experiences modulated behavior in adolescent WT differently than in adolescent Prkar1a+/- mice. Adolescent WT mice exposed to early life tactile stimulation showed attenuation of anxiety-like behavior, whereas an increase in exploratory behavior was found in Prkar1a+/- adolescent mice. The finding of behavioral differences that are apparent during adolescence in Prkar1a^+/- mice suggests that long-term exposure of the brain to increased PKA activity during critical developmental periods contributes to the anxiety-like phenotype noted in the adult animals with increased PKA activity.

Mice deficient in AKAP13 (BRX) develop compulsive-like behavior and increased body weight

OBJECTIVE

Hormonal contributions to the sex-dependent development of both obsessive-compulsive disorder (OCD) and obesity have been described, but the underlying mechanisms are incompletely understood. A-kinase anchoring protein 13 (AKAP13) significantly augments ligand-dependent activation of estrogen receptors alpha and beta. The hypothalamus and pituitary gland are implicated in the development and exacerbation of OCD and obesity and have strong AKAP13 expression. The AKAP13 localization pattern observed in these key brain regions together with its effects on sex steroid action suggest a potential role for AKAP13 in compulsive-like behaviors. Here we tested the role of AKAP13 in compulsive-like behavior and body weight using an Akap13 haploinsufficient murine model.

MATERIALS AND METHODS

Targeted deletion of the Akap13 gene generated haploinsufficient (Akap13+/-) mice in a C57BL6/J genetic background. Established behavioral assays were conducted, video recorded, and scored blindly to assess compulsive-like behavior based on genotype and gender. Tests included: marble-burying, grooming, open- field and elevated plus-maze. Brain and body weights were also obtained. Mean levels of test outcomes were compared using multi-way ANOVA to test for genotype, sex, genotype*sex, and genotype*sex*age interaction effects with Bonferroni adjustment for multiple comparisons, to further explain any significant interactions.

RESULTS

The marble-burying and grooming assays revealed significant sex-dependent increases in perseverative, compulsive-like behaviors in female Akap13 haploinsufficient mice compared to female wild type (WT) mice by demonstrating increased marble-burying activity (p = .0025) and a trend towards increased grooming behavior (p = .06). Male Akap13 haploinsufficient mice exhibited no behavioral changes (p > 0.05). Elevated plus-maze and open-field test results showed no overt anxiety-like behavior in Akap13 haploinsufficient mice irrespective of sex (p > 0.05, both). No differences in brain weight were found in Akap13 haploinsufficient mice compared to WT mice (p > 0.05). However, female Akap13 haploinsufficient mice weighed more than female WT mice in the 4 to <7 months age range (p = .0051). Male Akap13 haploinsufficient mice showed no differences in weight compared to male WT mice (p = >0.05) at any age range examined.

CONCLUSION

Akap13 haploinsufficiency led to sex-dependent, compulsive-like behavioral changes in a murine model. Interestingly, Akap13 haploinsufficiency also led to a sex-dependent increase in body weight. These results revealed a requirement for AKAP13 in murine behavior, particularly in female mice, and is the first report of AKAP13 involvement in murine behavior. Future studies may examine the involvement of AKAP13 in the pathophysiology of OCD in female humans and may contribute to a better understanding of the role of AKAP13 and sex hormones in the development and exacerbation of OCD.

Studies of mice with cyclic AMP-dependent protein kinase (PKA) defects reveal the critical role of PKA's catalytic subunits in anxiety

Cyclic adenosine mono-phosphate-dependent protein kinase (PKA) is critically involved in the regulation of behavioral responses. Previous studies showed that PKA's main regulatory subunit, R1α, is involved in anxiety-like behaviors. The purpose of this study was to determine how the catalytic subunit, Cα, might affect R1α's function and determine its effects on anxiety-related behaviors. The marble bury (MB) and elevated plus maze (EPM) tests were used to assess anxiety-like behavior and the hotplate test to assess nociception in wild type (WT) mouse, a Prkar1a heterozygote (Prkar1a(+/-)) mouse with haploinsufficiency for the regulatory subunit (R1α), a Prkaca heterozygote (Prkaca(+/-)) mouse with haploinsufficiency for the catalytic subunit (Cα), and a double heterozygote mouse (Prkar1a(+/-)/Prkaca(+/-)) with haploinsufficiency for both R1α and Cα. We then examined specific brain nuclei involved in anxiety. Results of MB test showed a genotype effect, with increased anxiety-like behavior in Prkar1a(+/-) and Prkar1a(+/-)/Prkaca(+/-) compared to WT mice. In the EPM, Prkar1a(+/-) spent significantly less time in the open arms, while Prkaca(+/-) and Prkar1a(+/-)/Prkaca(+/-) mice displayed less exploratory behavior compared to WT mice. The loss of one Prkar1a allele was associated with a significant increase in PKA activity in the basolateral (BLA) and central (CeA) amygdala and ventromedial hypothalamus (VMH) in both Prkar1a(+/-) and Prkar1a(+/-)/Prkaca(+/-) mice. Alterations of PKA activity induced by haploinsufficiency of its main regulatory or most important catalytic subunits result in anxiety-like behaviors. The BLA, CeA, and VMH are implicated in mediating these PKA effects in brain.

Activation of protein kinase A in the amygdala modulates anxiety-like behaviors in social defeat exposed mice

Background

Social defeat (SD) stress induces social avoidance and anxiety-like phenotypes. Amygdala is recognized as an emotion-related brain region such as fear, aversion and anxiety. It is conceivable to hypothesize that activation of amygdala is involved in SD-dependent behavioral defects.

Results

SD model was established using C57BL/6J mice that were physically defeated by different CD-1 mice for 10 days. Stressed mice exhibited decreased social interaction level in social interaction test and significant anxiety-like behaviors in elevated plus maze and open field tests. Meanwhile, a higher phosphorylation of PKA and CREB with a mutually linear correlation, and increased Fos labeled cells in the basolateral amygdala (BLA) were observed. Activation of PKA in the BLA by 8-Br-cAMP, a PKA activitor, significantly upregulated pCREB and Fos expression. To address the role of PKA activation on SD stress-induced social avoidance and anxiety-like behaviors, 8-Br-cAMP or H-89, a PKA inhibitor, was continuously administered into the bilateral BLA by a micro-osmotic pump system during the 10-day SD period. Neither H-89 nor 8-Br-cAMP affected the social behavior. Differently, 8-Br-cAMP significantly relieved anxiety-like behaviors in both general and moderate SD protocols. H-89 per se did not have anxiogenic effect in naïve mice, but aggravated moderate SD stress-induced anxiety-like behaviors. The antidepressant clomipramine reduced SD-induced anxiety and up-regulated pPKA level in the BLA.

Conclusions

These results suggest that SD-driven PKA activation in the basolateral amygdala is actually a compensatory rather than pathogenic response in the homeostasis, and modulating amygdaloid PKA may exhibit potency in the therapy of social derived disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-015-0181-3) contains supplementary material, which is available to authorized users.

The Role of Protein Kinase A in Anxiety Behaviors

This review focuses on the genetic and other evidence supporting the notion that the cyclic AMP (cAMP) signaling pathway and its mediator, the protein kinase A (PKA) enzyme, which respond to environmental stressors and regulate stress responses, are central to the pathogenesis of disorders related to anxiety. We describe the PKA pathway and review in vitro animal studies (mouse) and other evidence that support the importance of PKA in regulating behaviors that lead to anxiety. Since cAMP signaling and PKA have been pharmacologically exploited since the 1940s (even before the identification of cAMP as a second messenger with PKA as its mediator) for a number of disorders from asthma to cardiovascular diseases, there is ample opportunity to develop therapies using this new knowledge about cAMP, PKA, and anxiety disorders.

Protein Kinase A and Anxiety-Related Behaviors: A Mini-Review

This review focuses on the anxiety related to cyclic AMP/protein kinase A (PKA) signaling pathway that regulates stress responses. PKA regulates an array of diverse signals that interact with various neurotransmitter systems associated with alertness, mood, and acute and social anxiety-like states. Recent mouse studies support the involvement of the PKA pathway in common neuropsychiatric disorders characterized by heightened activation of the amygdala. The amygdala is critical for adaptive responses leading to fear learning and aberrant fear memory and its heightened activation is widely thought to underpin various anxiety disorders. Stress-induced plasticity within the amygdala is involved in the transition from normal vigilance responses to emotional reactivity, fear over-generalization, and deficits in fear inhibition resulting in pathological anxiety and conditions, such as panic and depression. Human studies of PKA signaling defects also report an increased incidence of psychiatric disorders, including anxiety, depression, bipolar disorder, learning disorders, and attention deficit hyperactivity disorder. We speculate that the PKA system is uniquely suited for selective, molecularly targeted intervention that may be proven effective in anxiolytic therapy.

Analysis of the effects of depression associated polymorphisms on the activity of the BICC1 promoter in amygdala neurones

The Bicaudal C Homolog 1 (BICC1) gene, which encodes an RNA binding protein, has been identified by genome wide association studies (GWAS) as a candidate gene associated with major depressive disorder (MDD). We explored the hypothesis that MDD associated single-nucleotide polymorphisms (SNPs) affected the ability of cis-regulatory elements within intron 3 of the BICC1 gene to modulate the activity of the BICC1 promoter region. We initially established that the BICC1 promoter drove BICC1 mRNA expression in amygdala, hippocampus and hypothalamus. Intriguingly, we provide evidence that MDD associated polymorphisms alter the ability of the BICC1 promoter to respond to PKA signalling within amygdala neurones. Considering the known role of amygdala PKA pathways in fear learning and mood these observations suggest a possible mechanism through which allelic changes in the regulation of the BICC1 gene in amygdala neurones may contribute to mood disorders. Our findings also suggest a novel direction for the identification of novel drug targets and the design of future personalised therapeutics.

Adenosine through the A2A adenosine receptor increases IL-1β in the brain contributing to anxiety

Anxiety is one of the most commonly reported psychiatric conditions, but its pathogenesis is poorly understood. Ailments associated with activation of the innate immune system, however, are increasingly linked to anxiety disorders. In adult male mice, we found that adenosine doubled caspase-1 activity in brain by a pathway reliant on ATP-sensitive potassium (KATP) channels, protein kinase A (PKA) and the A2A adenosine receptor (AR). In addition, adenosine-dependent activation of caspase-1 increased interleukin (IL)-1β in the brain by 2-fold. Peripheral administration of adenosine in wild-type (WT) mice led to a 2.3-fold increase in caspase-1 activity in the amygdala and to a 33% and 42% reduction in spontaneous locomotor activity and food intake, respectively, that were not observed in caspase-1 knockout (KO), IL-1 receptor type 1 (IL-1R1) KO and A2A AR KO mice or in mice administered a caspase-1 inhibitor centrally. Finally, adenosine administration increased anxiety-like behaviors in WT mice by 28% in the open field test and by 55% in the elevated zero-maze. Caspase-1 KO mice, IL-1R1 KO mice, A2A AR KO mice and WT mice treated with the KATP channel blocker, glyburide, were resistant to adenosine-induced anxiety-like behaviors. Thus, our results indicate that adenosine can act as an anxiogenic by activating caspase-1 and increasing IL-1β in the brain.

Threat bias in mice with inactivating mutations of Prkar1a

Anxiety disorders are associated with abnormalities in the neural processing of threat-related stimuli. However, the neurobiological mechanisms underlying threat bias in anxiety are not well understood. We recently reported that a Prkar1a heterozygote (Prkar1a(+/-)) mouse with haploinsufficiency for the main regulatory subunit (R1α) of protein kinase A (PKA) exhibits an anxiety-like phenotype associated with increased cAMP signaling in the amygdala. Prkar1a(+/-) mice provide a novel model to test the direct effect of altered PKA expression and subsequent anxiety-like behavioral phenotype on the response to threat. We hypothesized that Prkar1a(+/-)mice would exhibit a bias in threat detection since increased amygdala activity during emotional stimuli is associated with a maladaptive response. We measured behavior and PKA activity in brain areas after exposure to predator or control odor exposure in male Prkar1a(+/-) and wild-type (WT) littermates. Indeed, there were significant differences in the behavioral response to threat detection; WT mice showed the expected response of decrease in exploratory behavior during predator vs. control odor exposure, while Prkar1a(+/-) mice did not alter their behavior between conditions. Basal and total PKA activity was independently associated with genotype, with an interaction between genotype and threat condition. Prkar1a(+/-) mice had higher PKA activity in amygdala and ventromedial hypothalamus in response to predator odor. In contrast, WT mice had higher PKA activity in amygdala and orbitofrontal cortex after exposure to control odor. Dysregulated PKA activity in the amygdala-prefrontal cortex circuitry in Prkar1a(+/-) mice is associated with behavioral phenotype of anxiety and a bias for threat. This is likely related to a failure to inhibit the amydgala response, which is an effect of the genotype. These results suggest that the alteration in PKA signaling in Prkar1a(+/-) mice is not ubiquitous in the brain; tissue-specific effects of the cAMP/PKA pathway are related to threat detection and fear sensitization.

Synaptic plasticity in depression: molecular, cellular and functional correlates

Synaptic plasticity confers environmental adaptability through modification of the connectivity between neurons and neuronal circuits. This is achieved through changes to synapse-associated signaling systems and supported by complementary changes to cellular morphology and metabolism within the tripartite synapse. Mounting evidence suggests region-specific changes to synaptic form and function occur as a result of chronic stress and in depression. Within subregions of the prefrontal cortex (PFC) and hippocampus structural and synapse-related findings seem consistent with a deficit in long-term potentiation (LTP) and facilitation of long-term depression (LTD), particularly at excitatory pyramidal synapses. Other brain regions are less well-studied; however the amygdala may feature a somewhat opposite synaptic pathology including reduced inhibitory tone. Changes to synaptic plasticity in stress and depression may correlate those to several signal transduction pathways (e.g. NOS-NO, cAMP-PKA, Ras-ERK, PI3K-Akt, GSK-3, mTOR and CREB) and upstream receptors (e.g. NMDAR, TrkB and p75NTR). Deficits in synaptic plasticity may further correlate disrupted brain redox and bioenergetics. Finally, at a functional level region-specific changes to synaptic plasticity in depression may relate to maladapted neurocircuitry and parallel reduced cognitive control over negative emotion.

Sex differences in stress-related receptors: ″micro″ differences with ″macro″ implications for mood and anxiety disorders

Stress-related psychiatric disorders, such as unipolar depression and post-traumatic stress disorder (PTSD), occur more frequently in women than in men. Emerging research suggests that sex differences in receptors for the stress hormones, corticotropin releasing factor (CRF) and glucocorticoids, contribute to this disparity. For example, sex differences in CRF receptor binding in the amygdala of rats may predispose females to greater anxiety following stressful events. Additionally, sex differences in CRF receptor signaling and trafficking in the locus coeruleus arousal center combine to make females more sensitive to low levels of CRF, and less adaptable to high levels. These receptor differences in females could lead to hyperarousal, a dysregulated state associated with symptoms of depression and PTSD. Similar to the sex differences observed in CRF receptors, sex differences in glucocorticoid receptor (GR) function also appear to make females more susceptible to dysregulation after a stressful event. Following hypothalamic pituitary adrenal axis activation, GRs are critical to the negative feedback process that inhibits additional glucocorticoid release. Compared to males, female rats have fewer GRs and impaired GR translocation following chronic adolescent stress, effects linked to slower glucocorticoid negative feedback. Thus, under conditions of chronic stress, attenuated negative feedback in females would result in hypercortisolemia, an endocrine state thought to cause depression. Together, these studies suggest that sex differences in stress-related receptors shift females more easily into a dysregulated state of stress reactivity, linked to the development of mood and anxiety disorders. The implications of these receptor sex differences for the development of novel pharmacotherapies are also discussed.