Amygdala protein kinase C epsilon regulates corticotropin-releasing factor and anxiety-like behavior

Role of α6-Nicotinic Receptors in Alcohol-Induced GABAergic Synaptic Transmission and Plasticity to Cholinergic Interneurons in the Nucleus Accumbens

The prevailing view is that enhancement of dopamine (DA) transmission in the mesolimbic system, consisting of DA neurons in the ventral tegmental area (VTA) that project to the nucleus accumbens (NAc), underlies the reward properties of ethanol (EtOH) and nicotine (NIC). We have shown previously that EtOH and NIC modulation of DA release in the NAc is mediated by α6-containing nicotinic acetylcholine receptors (α6*-nAChRs), that α6*-nAChRs mediate low-dose EtOH effects on VTA GABA neurons and EtOH preference, and that α6*-nAChRs may be a molecular target for low-dose EtOH. However, the most sensitive target for reward-relevant EtOH modulation of mesolimbic DA transmission and the involvement of α6*-nAChRs in the mesolimbic DA reward system remains to be elucidated. The aim of this study was to evaluate EtOH effects on GABAergic modulation of VTA GABA neurons and VTA GABAergic input to cholinergic interneurons (CINs) in the NAc. Low-dose EtOH enhanced GABAergic input to VTA GABA neurons that was blocked by knockdown of α6*-nAChRs. Knockdown was achieved either by α6-miRNA injected into the VTA of VGAT-Cre/GAD67-GFP mice or by superfusion of the α-conotoxin MII[H9A;L15A] (MII). Superfusion of MII blocked EtOH inhibition of mIPSCs in NAc CINs. Concomitantly, EtOH enhanced CIN firing rate, which was blocked by knockdown of α6*-nAChRs with α6-miRNA injected into the VTA of VGAT-Cre/GAD67-GFP mice. The firing rate of CINs was not enhanced by EtOH in EtOH-dependent mice, and low-frequency stimulation (LFS; 1 Hz, 240 pulses) caused inhibitory long-term depression at this synapse (VTA-NAc CIN-iLTD) which was blocked by knockdown of α6*-nAChR and MII. Ethanol inhibition of CIN-mediated evoked DA release in the NAc was blocked by MII. Taken together, these findings suggest that α6*-nAChRs in the VTA-NAc pathway are sensitive to low-dose EtOH and play a role in plasticity associated with chronic EtOH.

Neuromedin B excites central lateral amygdala neurons and reduces cardiovascular output and fear-potentiated startle

Neuromedin B (NMB) and gastrin-releasing peptide (GRP) are the two mammalian analogs in the bombesin peptide family that exert a variety of actions including emotional processing, appetitive behaviors, cognition, and tumor growth. The bombesin-like peptides interact with three receptors: the NMB-preferring bombesin 1 (BB1) receptors, the GRP-preferring bombesin 2 (BB2) receptors and the orphan bombesin 3 (BB3) receptors. Whereas, injection of bombesin into the central amygdala reduces satiety and modulates blood pressure, the underlying cellular and molecular mechanisms have not been determined. As administration of bombesin induces the expression of Fos in the lateral nucleus of the central amygdala (CeL) which expresses BB1 receptors, we probed the effects of NMB on CeL neurons using in vitro and in vivo approaches. We showed that activation of the BB1 receptors increased action potential firing frequency recorded from CeL neurons via inhibition of the inwardly rectifying K+ (Kir) channels. Activities of phospholipase Cβ and protein kinase C were required, whereas intracellular Ca2+ release was unnecessary for BB1 receptor-elicited potentiation of neuronal excitability. Application of NMB directly into the CeA reduced blood pressure and heart rate and significantly reduced fear-potentiated startle. We may provide a cellular and molecular mechanism whereby bombesin-like peptides modulate anxiety and fear responses in the amygdala.

Chemical Genetic Identification of PKC Epsilon Substrates in Mouse Brain

PKC epsilon (PKCε) plays important roles in behavioral responses to alcohol and in anxiety-like behavior in rodents, making it a potential drug target for reducing alcohol consumption and anxiety. Identifying signals downstream of PKCε could reveal additional targets and strategies for interfering with PKCε signaling. We used a chemical genetic screen combined with mass spectrometry to identify direct substrates of PKCε in mouse brain and validated findings for 39 of them using peptide arrays and in vitro kinase assays. Prioritizing substrates with several public databases such as LINCS-L1000, STRING, GeneFriends, and GeneMAINA predicted interactions between these putative substrates and PKCε and identified substrates associated with alcohol-related behaviors, actions of benzodiazepines, and chronic stress. The 39 substrates could be broadly classified in three functional categories: cytoskeletal regulation, morphogenesis, and synaptic function. These results provide a list of brain PKCε substrates, many of which are novel, for future investigation to determine the role of PKCε signaling in alcohol responses, anxiety, responses to stress, and other related behaviors.

Current Perspectives on Selective Dopamine D3 Receptor Antagonists/Partial Agonists as Pharmacotherapeutics for Opioid and Psychostimulant Use Disorders

Over three decades of evidence indicate that dopamine (DA) D3 receptors (D3R) are involved in the control of drug-seeking behavior and may play an important role in the pathophysiology of substance use disorders (SUD). The expectation that a selective D3R antagonist/partial agonist would be efficacious for the treatment of SUD is based on the following key observations. First, D3R are distributed in strategic areas belonging to the mesolimbic DA system such as the ventral striatum, midbrain, and ventral pallidum, which have been associated with behaviors controlled by the presentation of drug-associated cues. Second, repeated exposure to drugs of abuse produces neuroadaptations in the D3R system. Third, the synthesis and characterization of highly potent and selective D3R antagonists/partial agonists have further strengthened the role of the D3R in SUD. Based on extensive preclinical and preliminary clinical evidence, the D3R shows promise as a target for the development of pharmacotherapies for SUD as reflected by their potential to (1) regulate the motivation to self-administer drugs and (2) disrupt the responsiveness to drug-associated stimuli that play a key role in reinstatement of drug-seeking behavior triggered by re-exposure to the drug itself, drug-associated environmental cues, or stress. The availability of PET ligands to assess clinically relevant receptor occupancy by selective D3R antagonists/partial agonists, the definition of reliable dosing, and the prospect of using human laboratory models may further guide the design of clinical proof of concept studies. Pivotal clinical trials for more rapid progression of this target toward regulatory approval are urgently required. Finally, the discovery that highly selective D3R antagonists, such as R-VK4-116 and R-VK4-40, do not adversely affect peripheral biometrics or cardiovascular effects alone or in the presence of oxycodone or cocaine suggests that this class of drugs has great potential in safely treating psychostimulant and/or opioid use disorders.

Targeting the cannabinoid system to counteract the deleterious effects of stress in Alzheimer’s disease

Alzheimer’s disease is a progressive neurodegenerative disorder characterized histologically in postmortem human brains by the presence of dense protein accumulations known as amyloid plaques and tau tangles. Plaques and tangles develop over decades of aberrant protein processing, post-translational modification, and misfolding throughout an individual’s lifetime. We present a foundation of evidence from the literature that suggests chronic stress is associated with increased disease severity in Alzheimer’s patient populations. Taken together with preclinical evidence that chronic stress signaling can precipitate cellular distress, we argue that chronic psychological stress renders select circuits more vulnerable to amyloid- and tau- related abnormalities. We discuss the ongoing investigation of systemic and cellular processes that maintain the integrity of protein homeostasis in health and in degenerative conditions such as Alzheimer’s disease that have revealed multiple potential therapeutic avenues. For example, the endogenous cannabinoid system traverses the central and peripheral neural systems while simultaneously exerting anti-inflammatory influence over the immune response in the brain and throughout the body. Moreover, the cannabinoid system converges on several stress-integrative neuronal circuits and critical regions of the hypothalamic-pituitary-adrenal axis, with the capacity to dampen responses to psychological and cellular stress. Targeting the cannabinoid system by influencing endogenous processes or exogenously stimulating cannabinoid receptors with natural or synthetic cannabis compounds has been identified as a promising route for Alzheimer’s Disease intervention. We build on our foundational framework focusing on the significance of chronic psychological and cellular stress on the development of Alzheimer’s neuropathology by integrating literature on cannabinoid function and dysfunction within Alzheimer’s Disease and conclude with remarks on optimal strategies for treatment potential.

Role of CRF and the hypothalamic-pituitary-adrenal axis in stroke: revisiting temporal considerations and targeting a new generation of therapeutics

Ischaemic neurovascular stroke represents a leading cause of death in the developed world. Preclinical and human epidemiological evidence implicates the corticotropin-releasing factor (CRF) family of neuropeptides as mediators of acute neurovascular injury pathology. Preclinical investigations of the role of CRF, CRF receptors and CRF-dependent activation of the hypothalamic-pituitary-adrenal (HPA) axis have pointed toward a tissue-specific and temporal relationship between activation of these pathways and physiological outcomes. Based on the literature, the major phases of ischaemic stroke aetiology may be separated into an acute phase in which CRF and anti-inflammatory stress signalling are beneficial and a chronic phase in which these contribute to neural degeneration, toxicity and apoptotic signalling. Significant gaps in knowledge remain regarding the pathway, temporality and systemic impact of CRF signalling and stress biology in neurovascular injury progression. Heterogeneity among experimental designs poses a challenge to defining the apparent reciprocal relationship between neurological injury and stress metabolism. Despite these challenges, it is our opinion that the elucidated temporality may be best matched with an antibody against CRF with a half-life of days to weeks as opposed to minutes to hours as with small-molecule CRF receptor antagonists. This state-of-the-art review will take a multipronged approach to explore the expected potential benefit of a CRF antibody by modulating CRF and corticotropin-releasing factor receptor 1 signalling, glucocorticoids and autonomic nervous system activity. Additionally, this review compares the modulation of CRF and HPA axis activity in neuropsychiatric diseases and their counterpart outcomes post-stroke and assess lessons learned from antibody therapies in neurodegenerative diseases.

Generalized and social anxiety disorder interactomes show distinctive overlaps with striosome and matrix interactomes

Mechanisms underlying anxiety disorders remain elusive despite the discovery of several associated genes. We constructed the protein-protein interaction networks (interactomes) of six anxiety disorders and noted enrichment for striatal expression among common genes in the interactomes. Five of these interactomes shared distinctive overlaps with the interactomes of genes that were differentially expressed in two striatal compartments (striosomes and matrix). Generalized anxiety disorder and social anxiety disorder interactomes showed exclusive and statistically significant overlaps with the striosome and matrix interactomes, respectively. Systematic gene expression analysis with the anxiety disorder interactomes constrained to contain only those genes that were shared with striatal compartment interactomes revealed a bifurcation among the disorders, which was influenced by the anterior cingulate cortex, nucleus accumbens, amygdala and hippocampus, and the dopaminergic signaling pathway. Our results indicate that the functionally distinct striatal pathways constituted by the striosome and the matrix may influence the etiological differentiation of various anxiety disorders.

Oligonucleotides as therapeutic tools for brain disorders: Focus on major depressive disorder and Parkinson's disease

Remarkable advances in understanding the role of RNA in health and disease have expanded considerably in the last decade. RNA is becoming an increasingly important target for therapeutic intervention; therefore, it is critical to develop strategies for therapeutic modulation of RNA function. Oligonucleotides, including antisense oligonucleotide (ASO), small interfering RNA (siRNA), microRNA mimic (miRNA), and anti-microRNA (antagomir) are perhaps the most direct therapeutic strategies for addressing RNA. Among other mechanisms, most oligonucleotide designs involve the formation of a hybrid with RNA that promotes its degradation by activation of endogenous enzymes such as RNase-H (e.g., ASO) or the RISC complex (e.g. RNA interference - RNAi for siRNA and miRNA). However, the use of oligonucleotides for the treatment of brain disorders is seriously compromised by two main limitations: i) how to deliver oligonucleotides to the brain compartment, avoiding the action of peripheral RNAses? and once there, ii) how to target specific neuronal populations? We review the main molecular pathways in major depressive disorder (MDD) and Parkinson's disease (PD), and discuss the challenges associated with the development of novel oligonucleotide therapeutics. We pay special attention to the use of conjugated ligand-oligonucleotide approach in which the oligonucleotide sequence is covalently bound to monoamine transporter inhibitors (e.g. sertraline, reboxetine, indatraline). This strategy allows their selective accumulation in the monoamine neurons of mice and monkeys after their intranasal or intracerebroventricular administration, evoking preclinical changes predictive of a clinical therapeutic action after knocking-down disease-related genes. In addition, recent advances in oligonucleotide therapeutic clinical trials are also reviewed.

Activation of V1a vasopressin receptors excite subicular pyramidal neurons by activating TRPV1 and depressing GIRK channels

Arginine vasopressin (AVP) is a nonapeptide that serves as a neuromodulator in the brain and a hormone in the periphery that regulates water homeostasis and vasoconstriction. The subiculum is the major output region of the hippocampus and an integral component in the networks that processes sensory and motor cues to form a cognitive map encoding spatial, contextual, and emotional information. Whereas the subiculum expresses high densities of AVP-binding sites and AVP has been shown to increase the synaptic excitability of subicular pyramidal neurons, the underlying cellular and molecular mechanisms have not been determined. We found that activation of V_1a receptors increased the excitability of subicular pyramidal neurons via activation of TRPV1 channels and depression of the GIRK channels. V_1a receptor-induced excitation of subicular pyramidal neurons required the function of phospholipase Cβ, but was independent of intracellular Ca²⁺ release. Protein kinase C was responsible for AVP-mediated depression of GIRK channels, whereas degradation of phosphatidylinositol 4,5-bisphosphate was involved in V_1a receptor-elicited activation of TRPV1 channels. Our results may provide one of the cellular and molecular mechanisms to explain the physiological functions of AVP in the brain.

The α1-adrenergic receptors in the amygdala regulate the induction of learned despair through protein kinase C-beta signaling

Hyperactivity of amygdala is observed in patients with major depressive disorder. Although the role of α1-adrenoceptor in amygdala on fear memory has been well studied, the role of α1-adrenoceptor in amygdala on depression-like behaviors remains unclear. Therefore, we investigated the effect of α1A-adrenoreceptor in amygdala on despair behavior, evaluated by the immobility time during tail suspension test (TST), pharmacological intervention, and immunohistological methods. C57BL6/J mice given a bilateral intra-amygdala injection of artificial cerebrospinal fluid exhibited an increased duration of immobility in the latter half of both trials of TST with a 24-h interval, a phenomenon known as learned despair. Intra-amygdala injection of WB4101 (1.7 nmol/0.1 µl), an α1 adrenoreceptor antagonist, but not propranolol (250 pmol/0.1 µl), a β-adrenoreceptor antagonist, blocked the induction of learned despair during TST. Immunostaining experiments revealed that ~61-75% of α1A-adrenoreceptor-positive neurons were colocalized with GAD65/67 in amygdala, implying that the α1-adrenoceptors in amygdala may enormously regulate the GABA release. Protein kinase C-beta (PKCβ) was predominantly expressed in the α1A-adrenoreceptor-positive neurons in the BLA, whereas protein kinase C-epsilon (PKCε) was highly expressed with the α1A-adrenoreceptor in the Central nucleus of amygdala. Intra-amygdala injection of ruboxistaurin (10 pmol/0.1 µl), a PKCβ inhibitor, blocked the induction of learned despair during TST, whereas neither TAT-εV1-2 (500 ng/0.1 μl), a cell-permeant PKCε inhibitory peptide, nor HBDDE (50 pmol/0.1 µl), an inhibitor of PKCα and -γ, affected the duration of immobility during TST. These data suggest that the α1-adrenoreceptor in amygdala regulates the induction of learned despair via PKCβ.

Activation of Oxytocin Receptors Excites Subicular Neurons by Multiple Signaling and Ionic Mechanisms

Oxytocin (OXT) is a nonapeptide that serves as a neuromodulator in the brain and a hormone participating in parturition and lactation in the periphery. The subiculum is the major output region of the hippocampus and an integral component in the networks that process sensory and motor cues to form a cognitive map encoding spatial, contextual, and emotional information. Whilst the subiculum expresses the highest OXT-binding sites and is the first brain region to be activated by peripheral application of OXT, the precise actions of OXT in the subiculum have not been determined. Our results demonstrate that application of the selective OXT receptor (OXTR) agonist, [Thr4,Gly7]-oxytocin (TGOT), excited subicular neurons via activation of TRPV1 channels, and depression of K+ channels. The OXTR-mediated excitation of subicular neurons required the functions of phospholipase Cβ, protein kinase C, and degradation of phosphatidylinositol 4,5-bisphosphate (PIP2). OXTR-elicited excitation of subicular neurons enhanced long-term potentiation via activation of TRPV1 channels. Our results provide a cellular and molecular mechanism to explain the physiological functions of OXT in the brain.

Oxytocin receptors excite lateral nucleus of central amygdala by phospholipase Cβ- and protein kinase C-dependent depression of inwardly rectifying K+ channels

KEY POINTS

Activation of oxytocin receptors (OXTRs) facilitates neuronal excitability in rat lateral nucleus of central amygdala (CeL). OXTR-induced excitation is mediated by inhibition of inwardly rectifying K⁺ (Kir) channels. Phospholipase Cβ is necessary for OXTR-mediated excitation of CeL neurons and depression of Kir channels. OXTR-elicited depression of Kir channels and excitation of CeL neurons require the function of Ca²⁺ -dependent protein kinase C.

ABSTRACT

Oxytocin (OXT) is a nonapeptide that exerts anxiolytic effects in the brain. The amygdala is an important structure involved in the modulation of fear and anxiety. A high density of OXT receptors (OXTRs) has been detected in the capsular (CeC) and lateral (CeL) nucleus of the central amygdala (CeA). Previous studies have demonstrated that activation of OXTRs induces remarkable increases in neuronal excitability in the CeL/C. However, the signalling and ionic mechanisms underlying OXTR-induced facilitation of neuronal excitability have not been determined. We found that activation of OXTRs in the CeL increased action potential firing frequency recorded from neurons in this region via inhibition of the inwardly rectifying K⁺ channels. The functions of phospholipase Cβ and protein kinase C were required for OXTR-induced augmentation of neuronal excitability. Our results provide a cellular and molecular mechanism whereby activation of OXTRs exerts anxiolytic effects.

Genetic inhibition of PKCε attenuates neurodegeneration after global cerebral ischemia in male mice

Global cerebral ischemia that accompanies cardiac arrest is a major cause of morbidity and mortality. Protein Kinase C epsilon (PKCε) is a member of the novel PKC subfamily and plays a vital role in ischemic preconditioning. Pharmacological activation of PKCε before cerebral ischemia confers neuroprotection. The role of endogenous PKCε after cerebral ischemia remains elusive. Here we used male PKCε-null mice to assess the effects of PKCε deficiency on neurodegeneration after transient global cerebral ischemia (tGCI). We found that the cerebral vasculature, blood flow, and the expression of other PKC isozymes were not altered in the PKCε-null mice. Spatial learning and memory was impaired after tGCI, but the impairment was attenuated in male PKCε-null mice as compared to male wild-type controls. A significant reduction in Fluoro-Jade C labeling and mitochondrial release of cytochrome C in the hippocampus was found in male PKCε-null mice after tGCI. Male PKCε-null mice expressed increased levels of PKCδ in the mitochondria, which may prevent the translocation of PKCδ from the cytosol to the mitochondria after tGCI. Our results demonstrate the neuroprotective effects of PKCε deficiency on neurodegeneration after tGCI, and suggest that reduced mitochondrial translocation of PKCδ may contribute to the neuroprotective action in male PKCε-null mice.

Effect of electrical stimulation of the infralimbic and prelimbic cortices on anxiolytic-like behavior of rats during the elevated plus-maze test, with particular reference to multiunit recording of the behavior-associated neural activity

Fear and anxiety affect the activities of daily living and require concerted management, such as coping strategies, to preserve quality of life. The infralimbic (IL) and prelimbic (PL) medial prefrontal cortices have been implicated in the regulation of fear- and anxiety-like behavior, but their roles in overcoming fear- and anxiety-like behavior remain unknown. We investigated the anxiolytic-like effects of electrical stimulation of the IL and PL cortices in rats during the elevated plus-maze test. IL stimulation led to a significantly higher percentage of time spent and entries in the open arms, whereas PL stimulation did not have any significant behavioral effects. Subsequently, we recorded multiunit activity from the IL and PL cortices in rats using a wireless telemetry device, to determine whether activation of the IL occurs when rats enter the open arms in the elevated plus-maze test. The firing rate of IL neurons increased 1-3 s prior to entry from the closed arm to the open arm, whereas there were no corresponding changes in the firing rate of PL neurons. Taken together, the present findings suggest that the IL plays a key role in exerting active action to overcome anxiety-like behavior.

MARCKSL1 Regulates Spine Formation in the Amygdala and Controls the Hypothalamic-Pituitary-Adrenal Axis and Anxiety-Like Behaviors

Abnormalities in limbic neural circuits have been implicated in the onset of anxiety disorders. However, the molecular pathogenesis underlying anxiety disorders remains poorly elucidated. Here, we demonstrate that myristoylated alanine-rich C-kinase substrate like 1 (MARCKSL1) regulates amygdala circuitry to control the activity of the hypothalamic-pituitary-adrenal (HPA) axis, as well as induces anxiety-like behaviors in mice. MARCKSL1 expression was predominantly localized in the prefrontal cortex (PFC), hypothalamus, hippocampus, and amygdala of the adult mouse brain. MARCKSL1 transgenic (Tg) mice exhibited anxiety-like behaviors dependent on corticotropin-releasing hormone. MARCKSL1 increased spine formation in the central amygdala, and downregulation of MARCKSL1 in the amygdala normalized both increased HPA axis activity and elevated anxiety-like behaviors in Tg mice. Furthermore, MARCKSL1 expression was increased in the PFC and amygdala in a brain injury model associated with anxiety-like behaviors. Our findings suggest that MARCKSL1 expression in the amygdala plays an important role in anxiety-like behaviors.

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MARCKSL1 induces spine formation in the amygdala, HPA axis activation, and anxiety-like behaviors.

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Downregulation of MARCKSL1 in the amygdala ameliorates anxiety-like behaviors

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MARCKSL1 is increased in a brain injury model associated with anxiety.

The molecular pathogenesis underlying anxiety disorders is still unclear. Here, we demonstrate that myristoylated alanine-rich C-kinase substrate like 1 (MARCKSL1) overexpression in mice increases spine formation in the amygdala and induces stress hormone upregulation and anxiety-like behaviors. Suppression of MARCKSL1 in the amygdala ameliorates both the increase in stress hormones and the elevated anxiety-like behaviors. Our results indicate that MARCKSL1 expression in the amygdala plays an important role in anxiety-like behaviors.

Molecular mechanisms underlying alcohol-drinking behaviours

The main characteristic of alcohol use disorder is the consumption of large quantities of alcohol despite the negative consequences. The transition from the moderate use of alcohol to excessive, uncontrolled alcohol consumption results from neuroadaptations that cause aberrant motivational learning and memory processes. Here, we examine studies that have combined molecular and behavioural approaches in rodents to elucidate the molecular mechanisms that keep the social intake of alcohol in check, which we term 'stop pathways', and the neuroadaptations that underlie the transition from moderate to uncontrolled, excessive alcohol intake, which we term 'go pathways'. We also discuss post-transcriptional, genetic and epigenetic alterations that underlie both types of pathways.

The effects of acute ethanol administration on ethanol withdrawal-induced anxiety-like syndrome in rats: A biochemical study

Withdrawal from long-term ethanol consumption results in overexcitation of glutamatergic neurotransmission in the amygdala, which induces an anxiety-like syndrome. Most alcoholics that suffer from such symptoms frequently depend on habitual drinking as self-medication to alleviate their symptoms. Metabotropic glutamate receptor subtype 5 (mGlu5) and protein kinase C (PKC) epsilon have been reported to mediate acute and chronic effects of ethanol. This study explores the changes in mGlu5 and PKC epsilon in the amygdala following acute administration of ethanol during ethanol withdrawal (EW) induced anxiety. Male Wistar rats were fed a modified liquid diet containing low-fat cow milk, sucrose, and maltodextrin, with a gradual introduction of 2.4%, 4.8% and 7.2% ethanol for 20 days. Six hours into EW, the rats were intraperitoneally injected with normal saline and ethanol (2.5 g/kg, 20% v/v), and exposed to open-field and elevated plus maze tests. Then, amygdala tissue was dissected from the rat brain for Western blot and gene expression studies. EW-induced anxiety was accompanied by a significant increase in mGlu5, total PKC epsilon, and phosphorylated PKC epsilon protein levels, and also of mRNA of mGlu5 (GRM5) in the amygdala. Acute administration of ethanol significantly attenuated EW-induced anxiety as well as an EW-induced increase in GRM5. The acute challenge of ethanol to EW rats had little effect on the phosphorylated and total protein levels of PKC epsilon in the amygdala. Our results demonstrate that amygdala PKC epsilon may not be directly involved in the development of anxiety following EW.

A Transgenic Rat for Investigating the Anatomy and Function of Corticotrophin Releasing Factor Circuits

Corticotrophin-releasing factor (CRF) is a 41 amino acid neuropeptide that coordinates adaptive responses to stress. CRF projections from neurons in the central nucleus of the amygdala (CeA) to the brainstem are of particular interest for their role in motivated behavior. To directly examine the anatomy and function of CRF neurons, we generated a BAC transgenic Crh-Cre rat in which bacterial Cre recombinase is expressed from the Crh promoter. Using Cre-dependent reporters, we found that Cre expressing neurons in these rats are immunoreactive for CRF and are clustered in the lateral CeA (CeL) and the oval nucleus of the BNST. We detected major projections from CeA CRF neurons to parabrachial nuclei and the locus coeruleus, dorsal and ventral BNST, and more minor projections to lateral portions of the substantia nigra, ventral tegmental area, and lateral hypothalamus. Optogenetic stimulation of CeA CRF neurons evoked GABA-ergic responses in 11% of non-CRF neurons in the medial CeA (CeM) and 44% of non-CRF neurons in the CeL. Chemogenetic stimulation of CeA CRF neurons induced Fos in a similar proportion of non-CRF CeM neurons but a smaller proportion of non-CRF CeL neurons. The CRF1 receptor antagonist R121919 reduced this Fos induction by two-thirds in these regions. These results indicate that CeL CRF neurons provide both local inhibitory GABA and excitatory CRF signals to other CeA neurons, and demonstrate the value of the Crh-Cre rat as a tool for studying circuit function and physiology of CRF neurons.

The central amygdala as an integrative hub for anxiety and alcohol use disorders

The central amygdala (CeA) plays a central role in physiologic and behavioral responses to fearful stimuli, stressful stimuli, and drug-related stimuli. The CeA receives dense inputs from cortical regions, is the major output region of the amygdala, is primarily GABAergic (inhibitory), and expresses high levels of prostress and antistress peptides. The CeA is also a constituent region of a conceptual macrostructure called the extended amygdala that is recruited during the transition to alcohol dependence. We discuss neurotransmission in the CeA as a potential integrative hub between anxiety disorders and alcohol use disorder, which are commonly co-occurring in humans. Imaging studies in humans and multidisciplinary work in animals collectively suggest that CeA structure and function are altered in individuals with anxiety disorders and alcohol use disorder, the end result of which may be disinhibition of downstream "effector" regions that regulate anxiety-related and alcohol-related behaviors.

Neuronal excitation upregulates Tbr1, a high-confidence risk gene of autism, mediating Grin2b expression in the adult brain

The activity-regulated gene expression of transcription factors is required for neural plasticity and function in response to neuronal stimulation. T-brain-1 (TBR1), a critical neuron-specific transcription factor for forebrain development, has been recognized as a high-confidence risk gene for autism spectrum disorders. Here, we show that in addition to its role in brain development, Tbr1 responds to neuronal activation and further modulates the Grin2b expression in adult brains and mature neurons. The expression levels of Tbr1 were investigated using both immunostaining and quantitative reverse transcription polymerase chain reaction (RT-PCR) analyses. We found that the mRNA and protein expression levels of Tbr1 are induced by excitatory synaptic transmission driven by bicuculline or glutamate treatment in cultured mature neurons. The upregulation of Tbr1 expression requires the activation of both α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors. Furthermore, behavioral training triggers Tbr1 induction in the adult mouse brain. The elevation of Tbr1 expression is associated with Grin2b upregulation in both mature neurons and adult brains. Using Tbr1-deficient neurons, we further demonstrated that TBR1 is required for the induction of Grin2b upon neuronal activation. Taken together with the previous studies showing that TBR1 binds the Grin2b promoter and controls expression of luciferase reporter driven by Grin2b promoter, the evidence suggests that TBR1 directly controls Grin2b expression in mature neurons. We also found that the addition of the calcium/calmodulin-dependent protein kinase II (CaMKII) antagonist KN-93, but not the calcium-dependent phosphatase calcineurin antagonist cyclosporin A, to cultured mature neurons noticeably inhibited Tbr1 induction, indicating that neuronal activation upregulates Tbr1 expression in a CaMKII-dependent manner. In conclusion, our study suggests that Tbr1 plays an important role in adult mouse brains in response to neuronal activation to modulate the activity-regulated gene transcription required for neural plasticity.

Tbr1 haploinsufficiency impairs amygdalar axonal projections and results in cognitive abnormality

The neuron-specific transcription factor T-box brain 1 (TBR1) regulates brain development. Disruptive mutations in the TBR1 gene have been repeatedly identified in patients with autism spectrum disorders (ASDs). Here, we show that Tbr1 haploinsufficiency results in defective axonal projections of amygdalar neurons and the impairment of social interaction, ultrasonic vocalization, associative memory and cognitive flexibility in mice. Loss of a copy of the Tbr1 gene altered the expression of Ntng1, Cntn2 and Cdh8 and reduced both inter- and intra-amygdalar connections. These developmental defects likely impair neuronal activation upon behavioral stimulation, which is indicated by fewer c-FOS-positive neurons and lack of GRIN2B induction in Tbr1(+/-) amygdalae. We also show that upregulation of amygdalar neuronal activity by local infusion of a partial NMDA receptor agonist, d-cycloserine, ameliorates the behavioral defects of Tbr1(+/-) mice. Our study suggests that TBR1 is important in the regulation of amygdalar axonal connections and cognition.

The role of PKC signaling in CRF-induced modulation of startle

RATIONALE

Hypersignaling of corticotropin releasing factor (CRF) has been implicated in stress disorders; however, many of its downstream mechanisms of action remain unclear. In vitro, CRF1 receptor activation initiates multiple cell signaling cascades, including protein kinase A (PKA), protein kinase C (PKC), and mitogen-activated protein kinase kinase MEK1/2 signaling. It is unclear, however, which of these signaling cascades mediate CRF-induced behaviors during stress.

OBJECTIVES

We examined the role of PKA, PKC, and MEK1/2 signaling pathways in CRF-induced anxiety as measured by startle hyperreactivity.

METHODS

Mice treated with intracerbroventricular (ICV) ovine CRF (oCRF) were pretreated with the PKA inhibitor Rp-cAMPS, PKC inhibitor bisindolylmaleimide (BIM), or MEK1/2 inhibitor PD98059 (ICV) and assessed for acoustic startle reactivity.

RESULTS

The PKC inhibitor BIM significantly attenuated CRF-induced increases in startle. BIM was also able to block startle increases induced by oCRF when both compounds were infused directly into the bed nucleus of stria terminalis (BNST). PKA and MEK1/2 inhibition had no significant effects on CRF-induced changes in startle at the dose ranges tested. CRF-induced disruption of prepulse inhibition was not significantly reversed by any of the three pretreatments at the dose ranges tested.

CONCLUSIONS

PKC signaling is required for CRF-induced increases in startle, and this effect is mediated at least in part at the BNST. These findings suggest that PKC signaling cascades (1) may be important for the acute effects of CRF to induce startle hyperreactivity and (2) support further research of the role of PKC signaling in startle abnormalities relevant to disorders such as posttraumatic stress disorder.

PKC-epsilon activation is required for recognition memory in the rat

Activation of PKCɛ, an abundant and developmentally regulated PKC isoform in the brain, has been implicated in memory throughout life and across species. Yet, direct evidence for a mechanistic role for PKCɛ in memory is still lacking. Hence, we sought to evaluate this in rats, using short-term treatments with two PKCɛ-selective peptides, the inhibitory ɛV1-2 and the activating ψɛRACK, and the novel object recognition task (NORT). Our results show that the PKCɛ-selective activator ψɛRACK, did not have a significant effect on recognition memory. In the short time frames used, however, inhibition of PKCɛ activation with the peptide inhibitor ɛV1-2 significantly impaired recognition memory. Moreover, when we addressed at the molecular level the immediate proximal signalling events of PKCɛ activation in acutely dissected rat hippocampi, we found that ψɛRACK increased in a time-dependent manner phosphorylation of MARCKS and activation of Src, Raf, and finally ERK1/2, whereas ɛV1-2 inhibited all basal activity of this pathway. Taken together, these findings present the first direct evidence that PKCɛ activation is an essential molecular component of recognition memory and point toward the use of systemically administered PKCɛ-regulating peptides as memory study tools and putative therapeutic agents.

Compulsive drug use and its neural substrates

Drug addiction is a chronic relapsing brain disease, characterized by compulsive drug use. Despite the fact that drug addiction affects millions of people worldwide, treatments for this disorder are limited in number and efficacy. In our opinion, understanding the neural underpinnings of drug addiction would open new avenues for the development of innovative treatments for this disorder. Based on an awareness that drug use and drug reward do not equal drug addiction, there has been increasing interest in developing animal models of addiction that mimick the loss of control over drug use more closely than existing models aimed at studying drug reward. The present review provides an overview of animal studies of compulsive drug use and the neural mechanisms involved. First, the employed models are summarized, with a particular emphasis on models of escalation of drug use and resistance to punishment. Next, we discuss mechanisms within the (ventral and dorsal) striatum and (central) amygdala that have recently been implicated in the compulsive seeking and taking of alcohol and cocaine. The studies discussed here provide a promising line of research that will advance our knowledge of the neural circuits involved in the self-destructive behavior that characterizes drug addiction.

Modulation of ventral tegmental area dopamine receptors inhibit nicotine-induced anxiogenic-like behavior in the central amygdala

Nicotine, the major addictive substance in tobacco, increases the activity of the central amygdala (CeA). Amygdala is directly implicated in anxiety modulation and sends projections to the vicinity of the midbrain dopamine neurons, including the ventral tegmental area (VTA) which is a key area that controls nicotine dependence processes. In this study, the role of dopamine D(1) and D(2)/(3) receptors of the VTA on anxiogenic-like behavior induced with intra-CeA injection of nicotine has been investigated. Male Wistar rats with cannula aimed to the left CeA and the left VTA were submitted to the elevated plus-maze (EPM). The nicotine injection (1 μg/rat) into the CeA decreased the percentage of open arm time and open arm entries, but not locomotor activity, indicating an anxiogenic-like response. Intra-VTA injection of a dopamine D1 receptor antagonist, SCH23390 (0.25 μg/rat), and a dopamine D2/3 receptor antagonist, sulpiride (0.7 μg/rat), inhibited the anxiogenic-like response caused by intra-CeA injection of nicotine. These results suggest that the relationship between the VTA and the CeA may be involved in nicotine-induced anxiogenic-like behavior via dopamine D(1) and D(2)/(3) receptors. An understanding of these cellular processes will be crucial for the development of new intervention to combat nicotine effect.

Signaling pathways mediating alcohol effects

Ethanol's effects on intracellular signaling pathways contribute to acute effects of ethanol as well as to neuroadaptive responses to repeated ethanol exposure. In this chapter we review recent discoveries that demonstrate how ethanol alters signaling pathways involving several receptor tyrosine kinases and intracellular tyrosine and serine-threonine kinases, with consequences for regulation of cell surface receptor function, gene expression, protein translation, neuronal excitability and animal behavior. We also describe recent work that demonstrates a key role for ethanol in regulating the function of scaffolding proteins that organize signaling complexes into functional units. Finally, we review recent exciting studies demonstrating ethanol modulation of DNA and histone modification and the expression of microRNAs, indicating epigenetic mechanisms by which ethanol regulates neuronal gene expression and addictive behaviors.

Intracellular interaction of interleukin (IL)-32α with protein kinase Cε (PKCε ) and STAT3 protein augments IL-6 production in THP-1 promonocytic cells

IL-32α is known as a proinflammatory cytokine. However, several evidences implying its action in cells have been recently reported. In this study, we present for the first time that IL-32α plays an intracellular mediatory role in IL-6 production using constitutive expression systems for IL-32α in THP-1 cells. We show that phorbol 12-myristate 13-acetate (PMA)-induced increase in IL-6 production by IL-32α-expressing cells was higher than that by empty vector-expressing cells and that this increase occurred in a time- and dose-dependent manner. Treatment with MAPK inhibitors did not diminish this effect of IL-32α, and NF-κB signaling activity was similar in the two cell lines. Because the augmenting effect of IL-32α was dependent on the PKC activator PMA, we tested various PKC inhibitors. The pan-PKC inhibitor Gö6850 and the PKCε inhibitor Ro-31-8220 abrogated the augmenting effect of IL-32α on IL-6 production, whereas the classical PKC inhibitor Gö6976 and the PKCδ inhibitor rottlerin did not. In addition, IL-32α was co-immunoprecipitated with PMA-activated PKCε, and this interaction was totally inhibited by the PKCε inhibitor Ro-31-8220. PMA-induced enhancement of STAT3 phosphorylation was observed only in IL-32α-expressing cells, and this enhancement was inhibited by Ro-31-8220, but not by Gö6976. We demonstrate that IL-32α mediated STAT3 phosphorylation by forming a trimeric complex with PKCε and enhanced STAT3 localization onto the IL-6 promoter and thereby increased IL-6 expression. Thus, our data indicate that the intracellular interaction of IL-32α with PKCε and STAT3 promotes STAT3 binding to the IL-6 promoter by enforcing STAT3 phosphorylation, which results in increased production of IL-6.

Phosphorylation of h1 calponin by PKC epsilon may contribute to facilitate the contraction of uterine myometrium in mice during pregnancy and labor

BACKGROUND

The timely onset of powerful uterine contractions during parturition occurs through thick and thin filament interactions, similar to other smooth muscle tissues. Calponin is one of the thin filament proteins. Phosphorylation of calponin induced by PKC-epsilon can promote the contraction of vascular smooth muscle. While the mechanism by which calponin regulates the contraction of pregnant myometrium has rarely been explored. Here, we explore whether PKC-epsilon/h1 calponin pathway contribute to regulation of myometrial contractility and development of parturition.

METHODS

We detected the expression of h1 calponin, phosphorylated h1 calponin, PKC-epsilon and phosphorylated PKC-epsilon in the different stages of mice during pregnancy and in labor by the method of western blot and recorded the contraction activity of myometrium strips at the 19th day during pregnancy with different treatments by the organ bath experiments.

RESULTS

The level of the four proteins including h1 calponin, phosphorylated h1 calponin, PKC-epsilon and phosphorylated PKC-epsilon was significantly increased in pregnant mice myometrium as compared with that in nonpregnant mice. The ratios of phosphorylated h1 calponin/h1 calponin and phosphorylated PKC-epsilon/PKC-epsilon were reached the peak after the onset of labor in myometrium in the mice. After the treatment of more than 10(9-) mol/L Psi-RACK (PKC-epsilon activator), the contractility of myometrium strips from mice was reinforced and the level of phosphorylated h1 calponin increased at the same time which could be interrupted by the specific inhibitor of PKC-epsilon. Meanwhile, the change of the ratio of phosphorylated h1 calponin/h1 calponin was consistent with that of contraction force of mice myometrium strips.

CONCLUSIONS

These data suggest that in mice myometrium, phosphorylation of h1 calponin induced by the PKC-epsilon might facilitate the contraction of uterine in labor and regulate pregnant myometrial contractility.

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.

Amygdala circuitry mediating reversible and bidirectional control of anxiety

Anxiety--a sustained state of heightened apprehension in the absence of immediate threat--becomes severely debilitating in disease states. Anxiety disorders represent the most common of psychiatric diseases (28% lifetime prevalence) and contribute to the aetiology of major depression and substance abuse. Although it has been proposed that the amygdala, a brain region important for emotional processing, has a role in anxiety, the neural mechanisms that control anxiety remain unclear. Here we explore the neural circuits underlying anxiety-related behaviours by using optogenetics with two-photon microscopy, anxiety assays in freely moving mice, and electrophysiology. With the capability of optogenetics to control not only cell types but also specific connections between cells, we observed that temporally precise optogenetic stimulation of basolateral amygdala (BLA) terminals in the central nucleus of the amygdala (CeA)--achieved by viral transduction of the BLA with a codon-optimized channelrhodopsin followed by restricted illumination in the downstream CeA--exerted an acute, reversible anxiolytic effect. Conversely, selective optogenetic inhibition of the same projection with a third-generation halorhodopsin (eNpHR3.0) increased anxiety-related behaviours. Importantly, these effects were not observed with direct optogenetic control of BLA somata, possibly owing to recruitment of antagonistic downstream structures. Together, these results implicate specific BLA-CeA projections as critical circuit elements for acute anxiety control in the mammalian brain, and demonstrate the importance of optogenetically targeting defined projections, beyond simply targeting cell types, in the study of circuit function relevant to neuropsychiatric disease.

Protein kinase C isozymes as regulators of sensitivity to and self-administration of drugs of abuse-studies with genetically modified mice

Studies using targeted gene deletion in mice have revealed distinct roles for individual isozymes of the protein kinase C (PKC) family of enzymes in regulating sensitivity to various drugs of abuse. These changes in drug sensitivity are associated with altered patterns of drug self-administration. The purpose of this review is to summarize behavioral studies conducted on mice carrying targeted deletions of genes encoding specific PKC isozymes (namely the beta, gamma, delta, and epsilon isozymes), and to critically evaluate the possibility of using pharmacological inhibitors of specific PKC isozymes as modulators of the sensitivity to various drugs of abuse, as well as potential aids in the treatment of substance use disorders.

The substrates and binding partners of protein kinase Cepsilon

The epsilon isoform of protein kinase C (PKCepsilon) has important roles in the function of the cardiac, immune and nervous systems. As a result of its diverse actions, PKCepsilon is the target of active drug-discovery programmes. A major research focus is to identify signalling cascades that include PKCepsilon and the substrates that PKCepsilon regulates. In the present review, we identify and discuss those proteins that have been conclusively shown to be direct substrates of PKCepsilon by the best currently available means. We will also describe binding partners that anchor PKCepsilon near its substrates. We review the consequences of substrate phosphorylation and discuss cellular mechanisms by which target specificity is achieved. We begin with a brief overview of the biology of PKCepsilon and methods for substrate identification, and proceed with a discussion of substrate categories to identify common themes that emerge and how these may be used to guide future studies.

Virus-delivered RNA interference in mouse brain to study addiction-related behaviors

The use of viral vectors for gene transfer to specific brain regions is a powerful tool for determining gene function in mouse behavioral models. We have employed a lentiviral vector to deliver small-hairpin RNAs to areas of mouse brain implicated in behaviors relevant to drug addiction, such as the nucleus accumbens and ventral tegmental area. Delivery of virus expressing small-hairpin RNAs results in sustained target gene knockdown by RNA interference. Mice can subsequently be tested for behavioral responses to various drugs of abuse over the course of several weeks or months. Here we describe a method for stereotaxic delivery of lentivirus to mouse brain. This method is widely applicable to any behavioral experiment in which the role of a specific gene in a particular brain region is to be elucidated.

Critical role of nociceptor plasticity in chronic pain

The transition from acute to chronic pain states might be the most important challenge in research to improve clinical treatment of debilitating pain. We describe a recently identified mechanism of neuronal plasticity in primary afferent nociceptive nerve fibers (nociceptors) by which an acute inflammatory insult or environmental stressor can trigger long-lasting hypersensitivity of nociceptors to inflammatory cytokines. This phenomenon, "hyperalgesic priming," depends on the epsilon isoform of protein kinase C (PKCepsilon) and a switch in intracellular signaling pathways that mediate cytokine-induced nociceptor hyperexcitability. We discuss the impact of this discovery on our understanding of, and ultimately our ability to treat, a variety of enigmatic and debilitating pain conditions, including those associated with repetitive injury, and generalized pain conditions, such as fibromyalgia.

Amygdala protein kinase C epsilon controls alcohol consumption

Alcoholism is a progressive disorder that involves the amygdala. Mice lacking protein kinase C epsilon (PKCepsilon) show reduced ethanol consumption, sensitivity and reward. We therefore investigated whether PKCepsilon signaling in the amygdala is involved in ethanol consumption. Local knockdown of PKCepsilon in the amygdala reduced ethanol consumption and preference in a limited-access paradigm. Further, mice that are heterozygous for the PKCepsilon allele consume less ethanol compared with wild-type mice in this paradigm. These mice have a >50% reduction in the abundance of PKCepsilon in the amygdala compared with wild-type mice. We conclude that amygdala PKCepsilon is important for ethanol consumption in mice.

Acute corticosterone treatment is sufficient to induce anxiety and amygdaloid dendritic hypertrophy

Stress is known to induce dendritic hypertrophy in the basolateral amygdala (BLA) and to enhance anxiety. Stress also leads to secretion of glucocorticoids (GC), and the BLA has a high concentration of glucocorticoid receptors. This raises the possibility that stress-induced elevation in GC secretion might directly affect amygdaloid neurons. To address the possible effects of GC on neurons of amygdala and on anxiety, we used rats treated either acutely with a single dose or chronically with 10 daily doses of high physiological levels of corticosterone (the rat-specific glucocorticoid). Behavior and morphological changes in neurons of BLA were measured 12 days after the initiation of treatment in both groups. A single acute dose of corticosterone was sufficient to induce dendritic hypertrophy in the BLA and heightened anxiety, as measured on an elevated plus maze. Moreover, this form of dendritic hypertrophy after acute treatment was of a magnitude similar to that caused by chronic treatment. Thus, plasticity of BLA neurons is sufficiently sensitive so as to be saturated by a single day of stress. The effects of corticosterone were specific to anxiety, as neither acute nor chronic treatment caused any change in conditioned fear or in general locomotor activity in these animals.