Acute Stress Suppresses Synaptic Inhibition and Increases Anxiety via Endocannabinoid Release in the Basolateral Amygdala

Glucocorticoid-induced enhancement of extinction-from animal models to clinical trials

Extensive evidence from both animal model and human research indicates that glucocorticoid hormones are crucially involved in modulating memory performance. Glucocorticoids, which are released during stressful or emotionally arousing experiences, enhance the consolidation of new memories, including extinction memory, but reduce the retrieval of previously stored memories. These memory-modulating properties of glucocorticoids have recently received considerable interest for translational purposes because strong aversive memories lie at the core of several fear-related disorders, including post-traumatic stress disorder and phobias. Moreover, exposure-based psychological treatment of these disorders relies on successful fear extinction. In this review, we argue that glucocorticoid-based interventions facilitate fear extinction by reducing the retrieval of aversive memories and enhancing the consolidation of extinction memories. Several clinical trials have already indicated that glucocorticoids might be indeed helpful in the treatment of fear-related disorders.

Distinct Proteomic, Transcriptomic, and Epigenetic Stress Responses in Dorsal and Ventral Hippocampus

BACKGROUND

Acutely stressful experiences can trigger neuropsychiatric disorders and impair cognitive processes by altering hippocampal function. Although the intrinsic organization of the hippocampus is highly conserved throughout its long dorsal-ventral axis, the dorsal (anterior) hippocampus mediates spatial navigation and memory formation, whereas the ventral (posterior) hippocampus is involved in emotion regulation. To understand the molecular consequences of stress, detailed genome-wide screens are necessary and need to distinguish between dorsal and ventral hippocampal regions. While transcriptomic screens have become a mainstay in basic and clinical research, proteomic methods are rapidly evolving and hold even greater promise to reveal biologically and clinically relevant biomarkers.

METHODS

Here, we provide the first combined transcriptomic (RNA sequencing) and proteomic (sequential window acquisition of all theoretical mass spectra [SWATH-MS]) profiling of dorsal and ventral hippocampus in mice. We used three different acute stressors (novelty, swim, and restraint) to assess the impact of stress on both regions.

RESULTS

We demonstrated that both hippocampal regions display radically distinct molecular responses and that the ventral hippocampus is particularly sensitive to the effects of stress. Separately analyzing these structures greatly increased the sensitivity to detect stress-induced changes. For example, protein interaction cluster analyses revealed a stress-responsive epigenetic network around histone demethylase Kdm6b restricted to the ventral hippocampus, and acute stress reduced methylation of its enzymatic target H3K27me3. Selective Kdm6b knockdown in the ventral hippocampus led to behavioral hyperactivity/hyperresponsiveness.

CONCLUSIONS

These findings underscore the importance of considering dorsal and ventral hippocampus separately when conducting high-throughput molecular analyses, which has important implications for fundamental research as well as clinical studies.

Cannabinoid receptor-1 signaling contributions to sign-tracking and conditioned reinforcement in rats

RATIONALE

Endocannabinoids (eCBs) are critical gatekeepers of dopaminergic signaling, and disrupting cannabinoid receptor-1 (CB1) signaling alters DA dynamics to attenuate cue-motivated behaviors. Prior studies suggest that dopamine (DA) release plays a critical role in driving sign-tracking.

OBJECTIVES

Here, we determine whether systemic injections of rimonabant, a CB1 receptor inverse agonist, during Pavlovian lever autoshaping impair the expression of sign-tracking. We next examine whether rimonabant blocks the reinforcing properties of the Pavlovian lever cue in a conditioned reinforcement test.

METHODS

In Exp. 1, we trained rats in Pavlovian lever autoshaping prior to systemic rimonabant injections (0, 1, 3 mg/kg) during early and late Pavlovian lever autoshaping sessions. In Exp. 2, we trained rats in Pavlovian lever autoshaping prior to systemic rimonabant injections (0, 1 mg/kg) during a conditioned reinforcement test.

RESULTS

Rimonabant dose-dependently decreased lever contact and probability, and increased sign-tracker's latency to approach the lever cue early in Pavlovian training. With extended training, many previously goal-tracking and intermediate rats shifted to lever approach, which remained dose-dependently sensitive to rimonabant. Rimonabant attenuated cue-evoked food cup approach early, but not late, in conditioning, and did not affect pellet retrieval or consumption. The inserted lever cue served as a robust conditioned reinforcer after Pavlovian lever autoshaping, and 1 mg/kg rimonabant blocked conditioned reinforcement.

CONCLUSIONS

Together, our results suggest that CB1 signaling mediates two critical properties of incentive stimuli; their ability to attract (Exp. 1) and their ability to reinforce (Exp. 2) behavior.

Factors promoting vulnerability to dysregulated stress reactivity and stress-related disease

Effective coordination of the biological stress response is integral for the behavioural well-being of an organism. Stress reactivity is coordinated by an interplay of the neuroendocrine system and the sympathetic nervous system. The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in orchestrating the bodily responses to stress, and the activity of the axis can be modified by a wide range of experiential events. This review focuses on several factors that influence subsequent HPA axis reactivity. Some of these factors include early-life adversity, exposure to chronic stress, immune activation and traumatic brain injury. The central premise is that each of these experiences serves as a general vulnerability factor that accelerates future HPA axis reactivity in ways that make individuals more sensitive to stress challenges, therefore feeding forward into the exacerbation of ongoing (or greater susceptibility toward) future stress-related disease states, especially as they pertain to negative affect and overall brain health.

Endocannabinoid regulation of homeostatic feeding and stress-induced alterations in food intake in male rats

BACKGROUND AND PURPOSE

Stress is known to reduce food intake. Many aspects of the stress response and feeding are regulated by the endocannabinoid system, but the roles of anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in stress-induced anorexia are unclear.

EXPERIMENTAL APPROACH

Effects of acute restraint stress on endocannabinoids were investigated in male Sprague-Dawley rats. Systemic and central pharmacological inhibition of fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL) was used to assess the effects of elevated AEA and 2-AG on homeostatic feeding and on food consumption after stress. Animals were pretreated with the FAAH inhibitor, PF-04457845, or the MAGL inhibitor, MJN110, before 2 h acute restraint stress or 2 h homecage period without food.

KEY RESULTS

Restraint stress decreased hypothalamic and circulating AEA, with no effect in the gastrointestinal tract, while 2-AG content in the jejunum (but not duodenum) was reduced. PF-04457845 (30 μg), given i.c.v., attenuated stress-induced anorexia via CB₁ receptors, but reduced homeostatic feeding in unstressed animals through an unknown mechanism. On the other hand, systemic administration of MJN110 (10 mg·kg^-1 ) reduced feeding, regardless of stress or feeding status and inhibited basal intestinal transit in unstressed rats. The ability of MAGL inhibition to reduce feeding in combination with stress was independent of CB₁ receptor signalling in the gut as the peripherally restricted CB₁ receptor antagonist, AM6545 did not block this effect.

CONCLUSIONS AND IMPLICATIONS

Our data reveal diverse roles for 2-AG and AEA in homeostatic feeding and changes in energy intake following stress.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Stress in Regulation of GABA Amygdala System and Relevance to Neuropsychiatric Diseases

The amygdala is an almond-shaped nucleus located deep and medially within the temporal lobe and is thought to play a crucial role in the regulation of emotional processes. GABAergic neurotransmission inhibits the amygdala and prevents us from generating inappropriate emotional and behavioral responses. Stress may cause the reduction of the GABAergic interneuronal network and the development of neuropsychological diseases. In this review, we summarize the recent evidence investigating the possible mechanisms underlying GABAergic control of the amygdala and its interaction with acute and chronic stress. Taken together, this study may contribute to future progress in finding new approaches to reverse the attenuation of GABAergic neurotransmission induced by stress in the amygdala.

Deficient endocannabinoid signaling in the central amygdala contributes to alcohol dependence-related anxiety-like behavior and excessive alcohol intake

Negative emotional states that are associated with excessive alcohol intake, particularly anxiety-like states, have been linked to opponent processes in the central nucleus of the amygdala (CeA), affecting stress-related transmitters and monoamines. This study extends these observations to include endocannabinoid signaling in alcohol-dependent animals. Rats and mice were exposed to chronic intermittent alcohol with vapor inhalation or liquid diet to induce dependence. In vivo microdialysis was used to estimate interstitial concentrations of endocannabinoids [N-arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG)] and amino acids (glutamate and GABA) in rat CeA. Additionally, we evaluated the inhibition of endocannabinoids clearance enzymes [monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase] on anxiety-like behavior and alcohol consumption in alcohol-dependent rats and mice. Results revealed that alcohol dependence produced decreases in baseline 2-AG dialysate levels and increases in baseline levels of glutamate and GABA. Acute alcohol abstinence induced an enhancement of these dependence-induced effects and the levels of 2-AG and GABA were restored upon alcohol re-exposure. Additional studies showed that the increased CeA 2-AG levels induced by restraint stress and alcohol self-administration were blunted in alcohol-dependent rats. Pharmacological studies in rats and mice showed that anxiety-like behavior and alcohol consumption were increased in alcohol-dependent animals, and these behavioral effects were attenuated mainly by MAGL inhibitors [MJN110 (10 and 20 mg/kg) in rats and JZL184 (1 and 3 mg/kg) in mice]. The present results suggest a key role for endocannabinoid signaling in motivational neuroadaptations during alcohol dependence, in which a deficiency in CeA 2-AG signaling in alcohol-dependent animals is linked to stress and excessive alcohol consumption.

Stress Promotes Drug Seeking Through Glucocorticoid-Dependent Endocannabinoid Mobilization in the Prelimbic Cortex

BACKGROUND

Clinical reports suggest that rather than directly driving cocaine use, stress may create a biological context within which other triggers for drug use become more potent. We hypothesize that stress-induced increases in corticosterone "set the stage" for relapse by promoting endocannabinoid-induced attenuation of inhibitory transmission in the prelimbic cortex (PL).

METHODS

We have established a rat model for these stage-setting effects of stress. In this model, neither a stressor (electric footshock) nor stress-level corticosterone treatment alone reinstates cocaine seeking following self-administration and extinction, but each treatment potentiates reinstatement in response to an otherwise subthreshold cocaine priming dose (2.5 mg/kg, intraperitoneal). The contributions of endocannabinoid signaling in the PL to the effects of stress-level corticosterone on PL neurotransmission and cocaine seeking were determined using intra-PL microinfusions. Endocannabinoid-dependent effects of corticosterone on inhibitory synaptic transmission in the rat PL were determined using whole-cell recordings in layer V pyramidal neurons.

RESULTS

Corticosterone application attenuated inhibitory synaptic transmission in the PL via cannabinoid receptor type 1 (CB₁R)- and 2-arachidonoylglycerol-dependent inhibition of gamma-aminobutyric acid release without altering postsynaptic responses. The ability of systemic stress-level corticosterone treatment to potentiate cocaine-primed reinstatement was recapitulated by intra-PL injection of corticosterone, the CB₁R agonist WIN 55,212-2, or the monoacylglycerol lipase inhibitor URB602. Corticosterone effects on reinstatement were attenuated by intra-PL injections of either the CB₁R antagonist, AM251, or the diacylglycerol lipase inhibitor, DO34.

CONCLUSIONS

These findings suggest that stress-induced increases in corticosterone promote cocaine seeking by mobilizing 2-arachidonoylglycerol in the PL, resulting in CB₁R-mediated attenuation of inhibitory transmission in this brain region.

2-Arachidonoylglycerol: A signaling lipid with manifold actions in the brain

2-Arachidonoylglycerol (2-AG) is a signaling lipid in the central nervous system that is a key regulator of neurotransmitter release. 2-AG is an endocannabinoid that activates the cannabinoid CB₁ receptor. It is involved in a wide array of (patho)physiological functions, such as emotion, cognition, energy balance, pain sensation and neuroinflammation. In this review, we describe the biosynthetic and metabolic pathways of 2-AG and how chemical and genetic perturbation of these pathways has led to insight in the biological role of this signaling lipid. Finally, we discuss the potential therapeutic benefits of modulating 2-AG levels in the brain.

Glucocorticoid-endocannabinoid uncoupling mediates fear suppression deficits after early - Life stress

Early-life stress (ELS) creates life-long vulnerability to stress-related anxiety disorders through altering stress and fear systems in the brain. The endocannabinoid system has emerged as an important regulator of the stress response through a crosstalk with the glucocorticoid system, yet whether it plays a role in the persistent effects of ELS remains unanswered. By combining, behavioral, pharmacological and biochemical approaches in adult male rats, we examined the impact of ELS on the regulation of endocannabinoid function by stress and glucocorticoids. We employed a postnatal limited-nesting/bedding induced ELS between postnatal days 2-9 in rats. Exposure to postnatal ELS compromised the ability of both acute stress and glucocorticoid administration to mobilize the endocannabinoid ligand 2-arachidonoyl glycerol (2-AG) in the hippocampus of adult male rats. These findings suggest that ELS compromises the coupling of the glucocorticoid and endocannabinoid systems in the hippocampus. Since 2-AG signaling is essential in mediating glucocorticoid-induced suppression of fear recall, we further examined the impact of ELS on the ability of glucocorticoids to suppress fear memory recall. While ELS did not affect normative fear recall, it impaired the ability of glucocorticoids to dampen fear recall. Notably, bypassing glucocorticoids and directly amplifying hippocampal 2-AG signaling with a monoacyl glycerol lipase inhibitor produced a suppression of fear memory recall in animals exposed to ELS. These findings suggest that ELS results in an uncoupling of glucocorticoid-endocannabinoid signaling in the hippocampus, which, in turn, relates to alterations in stress regulation of memory recall. These data provide compelling evidence that ELS-induced deficits in the glucocorticoid-endocannabinoid coupling following stress could predispose susceptibility to stress-related psychopathology.

Therapeutic endocannabinoid augmentation for mood and anxiety disorders: comparative profiling of FAAH, MAGL and dual inhibitors

Recent studies have demonstrated anxiolytic potential of pharmacological endocannabinoid (eCB) augmentation approaches in a variety of preclinical models. Pharmacological inhibition of endocannabinoid-degrading enzymes, such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), elicit promising anxiolytic effects in rodent models with limited adverse behavioral effects, however, the efficacy of dual FAAH/MAGL inhibition has not been investigated. In the present study, we compared the effects of FAAH (PF-3845), MAGL (JZL184) and dual FAAH/MAGL (JZL195) inhibitors on (1) anxiety-like behaviors under non-stressed and stressed conditions, (2) locomotor activity and body temperature, (3) lipid levels in the brain and (4) cognitive functions. Behavioral analysis showed that PF-3845 or JZL184, but not JZL195, was able to prevent restraint stress-induced anxiety in the light-dark box assay when administered before stress exposure. Moreover, JZL195 treatment was not able to reverse foot shock-induced anxiety-like behavior in the elevated zero maze or light-dark box. JZL195, but not PF-3845 or JZL184, decreased body temperature and increased anxiety-like behavior in the open-field test. Overall, JZL195 did not show anxiolytic efficacy and the effects of JZL184 were more robust than that of PF-3845 in the models examined. These results showed that increasing either endogenous AEA or 2-AG separately produces anti-anxiety effects under stressful conditions but the same effects are not obtained from simultaneously increasing both AEA and 2-AG.

Prior stress promotes the generalization of contextual fear memories: Involvement of the gabaergic signaling within the basolateral amygdala complex

Fear generalization occurs when a response, previously acquired with a threatening stimulus, is transferred to a similar one. However, it could be maladaptive when stimuli that do not represent a real threat are appraised as dangerous, which is a hallmark of several anxiety disorders. Stress exposure is a major risk factor for the occurrence of anxiety disorders and it is well established that it influences different phases of fear memory; nevertheless, its impact on the generalization of contextual fear memories has been less studied. In the present work, we have characterized the impact of acute restraint stress prior to contextual fear conditioning on the generalization of this fear memory, and the role of the GABAergic signaling within the basolateral amygdala complex (BLA) on the stress modulatory effects. We have found that a single stress exposure promoted the generalization of this memory trace to a different context that was well discriminated in unstressed conditioned animals. Moreover, this effect was dependent on the formation of a contextual associative memory and on the testing order (i.e., conditioning context first vs generalization context first). Furthermore, we observed that increasing GABA-A signaling by intra-BLA midazolam administration prior to the stressful session exposure prevented the generalization of fear memory, whereas intra-BLA administration of the GABA-A antagonist (Bicuculline), prior to fear conditioning, induced the generalization of fear memory in unstressed rats. We concluded that stress exposure, prior to contextual fear conditioning, promotes the generalization of fear memory and that the GABAergic transmission within the BLA has a critical role in this phenomenon.

Periaqueductal Gray Glutamatergic Transmission Governs Chronic Stress-Induced Depression

The mechanisms underlying chronic stress-induced dysfunction of glutamatergic transmission that contribute to helplessness-associated depressive disorder are unknown. We investigated the relationship of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and stress, and the neuroplastic changes of stress-induced depression-like behavior in the ventrolateral periaqueductal gray (vlPAG). We conducted whole-cell patch-clamp electrophysiological recordings in the vlPAG neurons. Depression-like behavior was assayed using tail suspension test and sucrose preference test. Surface and cytosolic glutamate receptor 1 (GluR1) AMPA receptor expression was analyzed using western blotting. Phosphorylated GluR1 expression was quantified using western blotting and immunohistochemical analysis. Unpredictable inescapable foot shock stress caused reduction in glutamatergic transmission originating from both presynaptic and postsynaptic loci in the vlPAG that was associated with behavioral despair and anhedonia in chronic stress-induced depression. Pharmacological inhibition of GluR1 function in the vlPAG caused depression-like behavior. Diminished glutamatergic transmission was due to reduced glutamate release presynaptically and enhanced GluR1-endocytosis from the cell surface postsynaptically. Chronic stress-induced neuroplastic changes and maladaptive behavior were reversed and mimicked by administration of glucocorticoid receptor (GR) antagonist and agonist, respectively. However, chronic stress did not affect γ-aminobutyric acid (GABA)-mediated inhibitory synaptic transmission in the vlPAG. These results demonstrate that depression-like behavior is associated with remarkable reduction in glutamatergic, but not GABAergic, transmission in the vlPAG. These neuroplastic changes and maladaptive behavior are attributed to GR-dependent mechanisms. As reduced GluR1-associated responses in the vlPAG contribute to chronic stress-induced neuroplastic changes, this cellular mechanism may be a critical component in the pathogenesis of stress-associated neuropsychiatric disorders.

Integrating Endocannabinoid Signaling and Cannabinoids into the Biology and Treatment of Posttraumatic Stress Disorder

Exposure to stress is an undeniable, but in most cases surmountable, part of life. However, in certain individuals, exposure to severe or cumulative stressors can lead to an array of pathological conditions including posttraumatic stress disorder (PTSD), characterized by debilitating trauma-related intrusive thoughts, avoidance behaviors, hyperarousal, as well as depressed mood and anxiety. In the context of the rapidly changing political and legal landscape surrounding use of cannabis products in the USA, there has been a surge of public and research interest in the role of cannabinoids in the regulation of stress-related biological processes and in their potential therapeutic application for stress-related psychopathology. Here we review the current state of knowledge regarding the effects of cannabis and cannabinoids in PTSD and the preclinical and clinical literature on the effects of cannabinoids and endogenous cannabinoid signaling systems in the regulation of biological processes related to the pathogenesis of PTSD. Potential therapeutic implications of the reviewed literature are also discussed. Finally, we propose that a state of endocannabinoid deficiency could represent a stress susceptibility endophenotype predisposing to the development of trauma-related psychopathology and provide biologically plausible support for the self-medication hypotheses used to explain high rates of cannabis use in patients with trauma-related disorders.

Cannabinoid Modulation of the Stressed Hippocampus

Exposure to stressful situations is one of the risk factors for the precipitation of several psychiatric disorders, including Major Depressive Disorder, Posttraumatic Stress Disorder and Schizophrenia. The hippocampal formation is a forebrain structure highly associated with emotional, learning and memory processes; being particularly vulnerable to stress. Exposure to stressful stimuli leads to neuroplastic changes and imbalance between inhibitory/excitatory networks. These changes have been associated with an impaired hippocampal function. Endocannabinoids (eCB) are one of the main systems controlling both excitatory and inhibitory neurotransmission, as well as neuroplasticity within the hippocampus. Cannabinoids receptors are highly expressed in the hippocampus, and several lines of evidence suggest that facilitation of cannabinoid signaling within this brain region prevents stress-induced behavioral changes. Also, chronic stress modulates hippocampal CB₁ receptors expression and endocannabinoid levels. Moreover, cannabinoids participate in mechanisms related to synaptic plasticity and adult neurogenesis. Here, we discussed the main findings supporting the involvement of hippocampal cannabinoid neurotransmission in stress-induced behavioral and neuroplastic changes.

Intrauterine inflammation induces sex-specific effects on neuroinflammation, white matter, and behavior

Exposure to inflammation during pregnancy has been linked to adverse neurodevelopmental consequences for the offspring. One common route through which a developing fetus is exposed to inflammation is with intrauterine inflammation. To that end, we utilized an animal model of intrauterine inflammation (IUI; intrauterine lipopolysaccharide (LPS) administration, 50µg, E15) to assess placental and fetal brain inflammatory responses, white matter integrity, anxiety-related behaviors (elevated zero maze, light dark box, open field), microglial counts, and the CNS cytokine response to an acute injection of LPS in both males and females. These studies revealed that for multiple endpoints (fetal brain cytokine levels, cytokine response to adult LPS challenge) male IUI offspring were uniquely affected by intrauterine inflammation, while for other endpoints (behavior, microglial number) both sexes were similarly affected. These data advance our understanding of sex-specific effects of early life exposure to inflammation in a translationally- relevant model.

Endocannabinoids: Effectors of glucocorticoid signaling

For decades, there has been speculation regarding the interaction of cannabinoids with glucocorticoid systems. Given the functional redundancy between many of the physiological effects of glucocorticoids and cannabinoids, it was originally speculated that the biological mechanisms of cannabinoids were mediated by direct interactions with glucocorticoid systems. With the discovery of the endocannabinoid system, additional research demonstrated that it was actually the opposite; glucocorticoids recruit endocannabinoid signaling, and that the engagement of endocannabinoid signaling mediated many of the neurobiological and physiological effects of glucocorticoids. With the development of advances in pharmacology and genetics, significant advances in this area have been made, and it is now clear that functional interactions between these systems are critical for a wide array of physiological processes. The current review acts a comprehensive summary of the contemporary state of knowledge regarding the biological interactions between glucocorticoids and endocannabinoids, and their potential role in health and disease.

Functional Redundancy Between Canonical Endocannabinoid Signaling Systems in the Modulation of Anxiety

BACKGROUND

Increasing the available repertoire of effective treatments for mood and anxiety disorders represents a critical unmet need. Pharmacological augmentation of endogenous cannabinoid (eCB) signaling has been suggested to represent a novel approach to the treatment of anxiety disorders; however, the functional interactions between two canonical eCB pathways mediated via anandamide (N-arachidonylethanolamine [AEA]) and 2-arachidonoylglycerol (2-AG) in the regulation of anxiety are not well understood.

METHODS

We utilized pharmacological augmentation and depletion combined with behavioral and electrophysiological approaches to probe the role of 2-AG signaling in the modulation of stress-induced anxiety and the functional redundancy between AEA and 2-AG signaling in the modulation of anxiety-like behaviors in mice.

RESULTS

Selective 2-AG augmentation reduced anxiety in the light/dark box assay and prevented stress-induced increases in anxiety associated with limbic AEA deficiency. In contrast, acute 2-AG depletion increased anxiety-like behaviors, which was normalized by selective pharmacological augmentation of AEA signaling and via direct cannabinoid receptor 1 stimulation with Δ⁹-tetrahydrocannabinol. Electrophysiological studies revealed 2-AG modulation of amygdala glutamatergic transmission as a key synaptic correlate of the anxiolytic effects of 2-AG augmentation.

CONCLUSIONS

Although AEA and 2-AG likely subserve distinct physiological roles, a pharmacological and functional redundancy between these canonical eCB signaling pathways exists in the modulation of anxiety-like behaviors. These data support development of eCB-based treatment approaches for mood and anxiety disorders and suggest a potentially wider therapeutic overlap between AEA and 2-AG augmentation approaches than was previously appreciated.

The effects of cannabinoid receptors activation and glucocorticoid receptors deactivation in the amygdala and hippocampus on the consolidation of a traumatic event

Ample evidence demonstrates that fear learning contributes significantly to many anxiety pathologies including post-traumatic stress disorder (PTSD). The endocannabinoid (eCB) system may offer therapeutic benefits for PTSD and it is a modulator of the hypothalamic pituitary adrenal (HPA) axis. Here we compared the separated and combined effects of blocking glucocorticoid receptors (GRs) using the GR antagonist RU486 and enhancing CB1r signaling using the CB1/2 receptor agonist WIN55,212-2 in the CA1 and basolateral amygdala (BLA) on the consolidation of traumatic memory. Traumatic memory was formed by exposure to a severe footshock in an inhibitory avoidance apparatus followed by exposure to trauma reminders. Intra-BLA RU486 (10ng/side) and WIN55,212-2 (5μg/side) administered immediately after shock exposure dampened the consolidation of the memory about the traumatic event and attenuated the increase in acoustic startle response in rats exposed to shock and reminders. In the CA1, WIN55,212-2 impaired consolidation and attenuated the increase in acoustic startle response whereas RU486 had no effect. The effects of WIN55,212-2 were found to be mediated by CB1 receptors, but not by GRs. Moreover, post-shock systemic WIN55,212-2 (0.5mg/kg) administration prevented the increase in GRs and CB1 receptor levels in the CA1 and BLA in rats exposed to shock and reminders. The findings suggest that the BLA is a locus of action of cannabinoids and glucocorticoids in modulating consolidation of traumatic memory in a rat model of PTSD. Also, the findings highlight novel targets for the treatment of emotional disorders and PTSD in particular.

Actions of Steroids: New Neurotransmitters

Over the past two decades, the classical understanding of steroid action has been updated to include rapid, membrane-initiated, neurotransmitter-like functions. While steroids were known to function on very short time spans to induce physiological and behavioral changes, the mechanisms by which these changes occur are now becoming more clear. In avian systems, rapid estradiol effects can be mediated via local alterations in aromatase activity, which precisely regulates the temporal and spatial availability of estrogens. Acute regulation of brain-derived estrogens has been shown to rapidly affect sensorimotor function and sexual motivation in birds. In rodents, estrogens and progesterone are critical for reproduction, including preovulatory events and female sexual receptivity. Membrane progesterone receptor as well as classical progesterone receptor trafficked to the membrane mediate reproductive-related hypothalamic physiology, via second messenger systems with dopamine-induced cell signals. In addition to these relatively rapid actions, estrogen membrane-initiated signaling elicits changes in morphology. In the arcuate nucleus of the hypothalamus, these changes are needed for lordosis behavior. Recent evidence also demonstrates that membrane glucocorticoid receptor is present in numerous cell types and species, including mammals. Further, membrane glucocorticoid receptor influences glucocorticoid receptor translocation to the nucleus effecting transcriptional activity. The studies presented here underscore the evidence that steroids behave like neurotransmitters to regulate CNS functions. In the future, we hope to fully characterize steroid receptor-specific functions in the brain.

Sucrose-induced plasticity in the basolateral amygdala in a 'comfort' feeding paradigm

A history of intermittent, limited sucrose intake (LSI) attenuates the hypothalamic-pituitary-adrenocortical (HPA) axis stress response, and neuronal activity in the basolateral amygdala (BLA) is necessary for this HPA-dampening. LSI increases the expression of plasticity-associated genes in the BLA; however, the nature of this plasticity is unknown. As BLA principal neuron activity normally promotes HPA responses, the present study tests the hypothesis that LSI decreases stress-excitatory BLA output by decreasing glutamatergic and/or increasing GABAergic inputs to BLA principal neurons. Male rats with unlimited access to chow and water were given additional access to 4 ml of sucrose (30%) or water twice daily for 14 days, and BLA structural and functional plasticity was assessed by quantitative dual immunolabeling and whole-cell recordings in brain slices. LSI increased vesicular glutamate transporter 1-positive (glutamatergic) appositions onto parvalbumin-positive inhibitory interneurons, and this was accompanied by increased expression of pCREB, a marker of neuronal activation that is mechanistically linked with plasticity, within parvalbumin interneurons. LSI also increased the paired-pulse facilitation of excitatory, but not inhibitory synaptic inputs to BLA principal neurons, without affecting postsynaptic excitatory or miniature excitatory and inhibitory postsynaptic currents, suggesting a targeted decrease in the probability of evoked synaptic excitation onto these neurons. Collectively, these results suggest that LSI decreases BLA principal neuron output by increasing the excitatory drive to parvalbumin inhibitory interneurons, and decreasing the probability of evoked presynaptic glutamate release onto principal neurons. Our data further imply that palatable food consumption blunts HPA stress responses by decreasing the excitation-inhibition balance and attenuating BLA output.

Sex- and hormone-dependent alterations in alcohol withdrawal-induced anxiety and corticolimbic endocannabinoid signaling

Alcohol dependence is associated with anxiety during withdrawal. The endocannabinoid (ECB) system participates in the neuroendocrine and behavioral response to stress and changes in corticolimbic ECB signaling may contribute to alcohol withdrawal-induced anxiety. Moreover, symptoms of alcohol withdrawal differ between sexes and sexual dimorphism in withdrawal-induced ECB recruitment may be a contributing factor. Herein, we exposed intact male and female rats and ovariectomized (OVX) female rats with or without estradiol (E₂) replacement to 6 weeks of chronic intermittent alcohol vapor and measured anxiety-like behavior, ECB content, and ECB-related mRNA in the basolateral amygdala (BLA) and ventromedial prefrontal cortex (vmPFC). Acute alcohol withdrawal increased anxiety-like behavior, produced widespread disturbances in ECB-related mRNA, and reduced anandamide (AEA) content in the BLA and 2-arachidonoylglycerol (2-AG) content in the vmPFC of male, but not female rats. Similar to males, alcohol-exposed OVX females showed reductions in Napepld mRNA in the BLA, decreased AEA content in the BLA and vmPFC, and reductions in all ECB-related genes measured in the vmPFC. Importantly, E₂ replacement prevented withdrawal-induced alterations in ECB content (but not mRNA) in OVX females, and although alcohol-exposed OVX females failed to exhibit more anxiety compared to their respective control, chronic alcohol exposure abolished the anxiolytic properties of E₂ in OVX rats. These data indicate that ovarian sex hormones (but not E₂ alone) protect against withdrawal-induced alterations in corticolimbic ECB signaling but do not impart resilience to withdrawal-induced anxiety. Thus, the mechanisms implicated in the manifestation of alcohol withdrawal-induced anxiety are most likely sex-specific. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Emotional Modulation of Learning and Memory: Pharmacological Implications

Memory consolidation involves the process by which newly acquired information becomes stored in a long-lasting fashion. Evidence acquired over the past several decades, especially from studies using post-training drug administration, indicates that emotional arousal during the consolidation period influences and enhances the strength of the memory and that multiple different chemical signaling systems participate in this process. The mechanisms underlying the emotional influences on memory involve the release of stress hormones and activation of the basolateral amygdala, which work together to modulate memory consolidation. Moreover, work suggests that this amygdala-based memory modulation occurs with numerous types of learning and involves interactions with many different brain regions to alter consolidation. Additionally, studies suggest that emotional arousal and amygdala activity in particular influence synaptic plasticity and associated proteins in downstream brain regions. This review considers the historical understanding for memory modulation and cellular consolidation processes and examines several research areas currently using this foundational knowledge to develop therapeutic treatments.

Acute stress enhances the glutamatergic transmission onto basoamygdala neurons embedded in distinct microcircuits

Amygdala activation is known to be critical for the processing of stressful events in brain. Recent studies have shown that the projection neurons (PNs) in amygdala, although architecturally intermingled, are integrated into distinct microcircuits and thus play divergent roles in amygdala-related behaviors. It remains unknown how stress regulates the individual amygdala PNs embedded in distinct microcircuits. Here, by using retrograde tracing and electrophysiological recording in in vitro slices, we explored the modulation of acute immobilization stress (AIS) on the basoamygdala (BA) PNs projecting either to medial prefrontal cortex (mPFC) or elsewhere, which we designated as BA-mPFC and non-BA-mPFC PNs respectively. The results showed that in the control mice, both the excitatory and inhibitory postsynaptic currents (sEPSCs/sIPSCs) were comparable between these two subsets of BA PNs. The influences of AIS on sEPSCs and sIPSCs were overall similar between the two neuronal populations. It markedly increased the sEPSCs amplitude but left unaltered their frequency as well as the sIPSCs amplitude and frequency. Despite this, several differences emerged between the effects of AIS on the distribution of sEPSCs/sIPSCs frequency in these two groups of BA PNs. Similar changes were also observed in the sEPSCs/sIPSCs of the two PN populations from mice experiencing forced swimming stress. Their intrinsic excitability, on the other hand, was nearly unaltered following AIS. Our results thus suggest that acute stress recruit both BA-mPFC and non-BA-mPFC PNs mainly through enhancing the glutamatergic transmission they receive.

Exposure of mother rats to chronic unpredictable stress before pregnancy alters the metabolism of gamma-aminobutyric acid and glutamate in the right hippocampus of offspring in early adolescence in a sexually dimorphic manner

There is increasing evidence that mothers' exposure to stress before or during pregnancy is linked to an incidence of psychiatric disorders in offspring. However, a few studies have estimated the role of sex in the detrimental effects of pre-gestational stress on the offspring rats at early adolescence. Sex differences regarding the metabolism of gamma-aminobutyric acid and glutamate in the right hippocampus were investigated by MRS when the offspring rats reached 30 days. Additionally, the impact of pre-gestational stress exposed on an additional short-term acute stressor, such as forced swim, was examined in the male and female offspring rats. Our findings showed female offspring rats were more vulnerable to stressful conditions for either pre-gestational stress or acute stress in early adolescence, and had decreased GABA/Cr+PCr and Glu/Cr+PCr in the right hippocampus. Interestingly, in response to forced swim, male offspring rats whose mothers were exposed to pre-gestational stress were more affected by the short-term acute stressor and this was manifested by change of Glu/GABA and Glu/Gln in the right hippocampus. These data indicated that although female offspring rats were more vulnerable to pre-gestational stress from their mothers than males, in response to an additional acute stressor they showed better response. Therefore, both sexually dimorphic manner and combination of stressful procedures should be carefully considered in the study of stress-related psychiatric disorders in early adolescence.

Stress, glucocorticoids and memory: implications for treating fear-related disorders

Glucocorticoid stress hormones are crucially involved in modulating mnemonic processing of emotionally arousing experiences. They enhance the consolidation of new memories, including those that extinguish older memories, but impair the retrieval of information stored in long-term memory. As strong aversive memories lie at the core of several fear-related disorders, including post-traumatic stress disorder and phobias, the memory-modulating properties of glucocorticoids have recently become of considerable translational interest. Clinical trials have provided the first evidence that glucocorticoid-based pharmacotherapies aimed at attenuating aversive memories might be helpful in the treatment of fear-related disorders. Here, we review important advances in the understanding of how glucocorticoids mediate stress effects on memory processes, and discuss the translational potential of these new conceptual insights.