Abnormalities in social behavior are found in almost all psychiatric disorders, such as anxiety, depression, autism, and schizophrenia. Thus, comprehension of the neurobiological basis of social ...interaction is important for a better understanding of numerous pathologies and improved treatments. Several findings have suggested that an alteration of cannabinoid receptor type 1 (CB1) receptor function could be involved in the pathophysiology of such disorders. However, the role of CB1 receptors is still unclear, and their localisation on different neuronal subpopulations may produce distinct outcomes. To dissect the role of CB1 receptors in different neuronal populations, we used male knockout mice and their respective control littermates total deletion (CB1−/−); specific deletion on cortical glutamatergic neurons (Glu‐CB1−/−) or on GABAergic interneurons (GABA‐CB1−/−), and wild‐type (WT) mice treated with the CB1 antagonist/inverse agonist SR141716A (3 mg/kg). Mice were required to perform different social tasks – direct social interaction and social investigation. Direct interaction of two male mice was not modified in any group; however, when they were paired with females, Glu‐CB1−/− mice showed reduced interaction. Also, exploration of the male stimulus subject in the three‐chamber social investigation test was almost unaffected. The situation was completely different when a female was used as the stimulus subject. In this case, Glu‐CB1−/− mice showed reduced interest in the social stimulus, mimicking the phenotype of CB1−/− or WT mice treated with SR141716A. GABA‐CB1−/− mice showed the opposite phenotype, by spending more time investigating the social stimulus. In conclusion, we provide evidence that CB1 receptors specifically modulate the social investigation of female mice in a neuronal subtype‐specific manner.
To better dissect the role of CB1 receptor in different neuronal subpopulations on social behavior alterations observed in several psychiatry disorders, we submitted mice with pharmacological blockage or distinct CB1 receptors deletion to two different social paradigms ‐ animals could direct or indirectly investigate a male or ovariectomised female stimulus subject. Our results demonstrate an opposite role of CB1 receptors on glutamatergic versus GABAergic neurons in regulation of social interaction with female, but not male conspecifics.
Our current knowledge of the implications of endocannabinoids in fear and anxiety is largely based on fear conditioning paradigms and approach-avoidance conflicts. Here we establish the ...ethobehavioral beetle mania task (BMT), which confronts mice with an erratically moving robo-beetle. With the help of this task we demonstrate decreased tolerance yet increased avoidance responses to an approaching beetle in high-anxiety behavior (HAB) and BALBc mice compared to C57BL/6N, CD1 and normal-anxiety behavior (NAB) mice. Also DBA/2N mice showed decreased passive and increased active behavior, but followed the robo-beetle more often than HAB and BALBc mice. Treatment with diazepam (1 mg/kg) increased tolerance without affecting avoidance behavior in HAB mice. Treatment with the MAGL inhibitor JZL184 (8 mg/kg) increased flight behavior, but did not affect tolerance. The FAAH inhibitor URB597 (0.3 mg/kg), however, reduced flight behavior and enhanced tolerance to the robo-beetle. The latter effects were blocked by co-treatment with the CB1 receptor antagonist SR141716A (3 mg/kg), which failed to affect the behavior by itself. Taken together, we validate the BMT as a novel test for studying endocannabinoids beyond traditional paradigms and for assessing active fear responses in mice. Furthermore, we demonstrate panicolytic consequences of pharmacological enhancement of anandamide, but not 2-AG signaling.
•The new beetle mania task (BMT) allows the assessment of passive and active fear responses in mice.•High-anxiety behavior (HAB) and BALBc mice show exaggerated active fear.•MAGL inhibitor JZL184 increases flight behavior in HAB mice.•FAAH inhibitor URB597 exerts panicolytic effects in both HAB and BALBc mice.•The effects of URB597 depend on CB1 receptors.
PTSD can develop in the aftermath of traumatic incidents like combat, sexual abuse, or life threatening accidents. Unfortunately, there are still no biomarkers for this debilitating anxiety disorder ...in clinical use. Anyhow, there are numerous studies describing potential PTSD biomarkers, some of which might progress to the point of practical use in the future. Here, we outline and comment on some of the most prominent findings on potential imaging, psychological, endocrine, and molecular PTSD biomarkers and classify them into risk, disease, and therapy markers. Since for most of these potential PTSD markers a causal role in PTSD has been demonstrated or at least postulated, this review also gives an overview on the current state of research on PTSD pathobiology.
Abstract The development of exaggerated avoidance behavior is largely responsible for the decreased quality of life in patients suffering from anxiety disorders. Studies using animal models have ...contributed to the understanding of the neural mechanisms underlying the acquisition of avoidance responses. However, much less is known about its extinction. Here we provide evidence in mice that learning about the safety of an environment (i.e., safety learning) rather than repeated execution of the avoided response in absence of negative consequences (i.e., response extinction) allowed the animals to overcome their avoidance behavior in a step-down avoidance task. This process was context-dependent and could be blocked by pharmacological (3 mg/kg, s.c.; SR141716) or genetic (lack of cannabinoid CB1 receptors in neurons expressing dopamine D1 receptors) inactivation of CB1 receptors. In turn, the endocannabinoid reuptake inhibitor AM404 (3 mg/kg, i.p.) facilitated safety learning in a CB1-dependent manner and attenuated the relapse of avoidance behavior 28 days after conditioning. Safety learning crucially depended on endocannabinoid signaling at level of the hippocampus, since intrahippocampal SR141716 treatment impaired, whereas AM404 facilitated safety learning. Other than AM404, treatment with diazepam (1 mg/kg, i.p.) impaired safety learning. Drug effects on behavior were directly mirrored by drug effects on evoked activity propagation through the hippocampal trisynaptic circuit in brain slices: As revealed by voltage-sensitive dye imaging, diazepam impaired whereas AM404 facilitated activity propagation to CA1 in a CB1-dependent manner. In line with this, systemic AM404 enhanced safety learning-induced expression of Egr1 at level of CA1. Together, our data render it likely that AM404 promotes safety learning by enhancing information flow through the trisynaptic circuit to CA1.
Corticotropin-releasing hormone (CRH) is a central integrator in the brain of endocrine and behavioral stress responses, whereas activation of the endocannabinoid CB1 receptor suppresses these ...responses. Although these systems regulate overlapping functions, few studies have investigated whether these systems interact. Here we demonstrate a novel mechanism of CRH-induced anxiety that relies on modulation of endocannabinoids. Specifically, we found that CRH, through activation of the CRH receptor type 1 (CRHR1), evokes a rapid induction of the enzyme fatty acid amide hydrolase (FAAH), which causes a reduction in the endocannabinoid anandamide (AEA), within the amygdala. Similarly, the ability of acute stress to modulate amygdala FAAH and AEA in both rats and mice is also mediated through CRHR1 activation. This interaction occurs specifically in amygdala pyramidal neurons and represents a novel mechanism of endocannabinoid-CRH interactions in regulating amygdala output. Functionally, we found that CRH signaling in the amygdala promotes an anxious phenotype that is prevented by FAAH inhibition. Together, this work suggests that rapid reductions in amygdala AEA signaling following stress may prime the amygdala and facilitate the generation of downstream stress-linked behaviors. Given that endocannabinoid signaling is thought to exert "tonic" regulation on stress and anxiety responses, these data suggest that CRH signaling coordinates a disruption of tonic AEA activity to promote a state of anxiety, which in turn may represent an endogenous mechanism by which stress enhances anxiety. These data suggest that FAAH inhibitors may represent a novel class of anxiolytics that specifically target stress-induced anxiety.
Abstract
Anxiety-like behavior of rodents is frequently accompanied by reduced exploration. Here, we identify dissociable components of anxiety, fear, and exploratory drive of sated and foraging ...mice. With the help of behavioral assays, including the open field task, elevated plus maze, dark–light transition task, and beetle mania task, we demonstrate a general increase in exploration by food restriction. Food-restricted mice bred for high anxiety behavior (HAB) showed ameliorated anxiety- but not fear-related behavior. By means of principal component analysis, we identified three independent components, which resemble the behavioral dimensions proposed by Gray’s Reinforcement Sensitivity Theory (approach behavior, avoidance behavior, and decision making). Taken together, we demonstrate anxiolytic consequences of food restriction in a mouse model of anxiety disorders that can be dissociated from a general increase in foraging behavior.
Mammals respond to challenging situations with characteristic changes in their behaviour as well as in autonomic and neuroendocrine parameters aimed at reinstating their disturbed homeostasis. Among ...such so-called coping strategies, alterations of the hypothalamic–pituitary–adrenal (HPA) axis play a crucial role. Today it is generally accepted that parvocellular neurones of the hypothalamic paraventricular nucleus control the secretion of corticotropin and corticosterone by synthesising and releasing both the corticotropin-releasing hormone and vasopressin (AVP). Recent evidence supports and embellishes the old hypothesis that AVP and the structurally related neuropeptide, oxytocin, originating from the hypothalamic–neurohypophysial system (HNS) might directly affect HPA axis activity. This review presents data supporting the concept of HNS effects on HPA axis activity and outlines their possible impact on some aspects of behavioural regulation and psychopathology.
Abstract Some, but not all studies in patients with posttraumatic stress disorder (PTSD), report reduced hippocampus (HPC) volume. In particular it is unclear, whether smaller hippocampal volume ...represents a susceptibility factor for PTSD rather than a consequence of the trauma. To gain insight into the relationship of brain morphology and trauma exposure, we investigated volumetric and molecular changes of the HPC in a mouse model of PTSD by means of in vivo Manganese Enhanced Magnetic Resonance Imaging (MEMRI) and ex vivo ultramicroscopic measurements. Exposure to a brief inescapable foot shock led to a volume reduction in both left HPC and right central amygdala two months later. This volume loss was mirrored by a down-regulation of growth-associated protein-43 (GAP43) in the HPC. Enriched housing decreased the intensity of trauma-associated contextual fear, independently of whether it was provided before or after the shock. Beyond that, enriched housing led to an increase in intracranial volume, including the lateral ventricles and the hippocampus, and to an up-regulation of GAP43 as revealed by MEMRI and Western blot analysis, thus partially compensating for trauma-related HPC volume loss and down-regulation of GAP43 expression. Together these data demonstrate that traumatic experience in mice causes a reduction in HPC and central amygdala volume possibly due to a shrinkage of axonal protrusions. Enriched housing might induce trophic changes, which may contribute to the amelioration of trauma-associated PTSD-like symptoms at behavioural, morphological and molecular levels.
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Cannabinoid receptor type 1 (CB1R) is widely distributed in the substantia nigra pars reticulata (SNpr). However, the role of CB1R at the SNpr level in threatening situations is ...poorly understood. We investigated the role of CB1R in the SNpr on the expression of fear responses in mice confronted with urutu-cruzeiro pit vipers. First, a bidirectional neurotracer was injected into the SNpr; then, immunostaining of the vesicular GABA transporter was conducted at the levels of the striatum (CPu) and deep layers of the superior colliculus (dlSC). In addition, CB1R immunostaining and GABA labelling were performed in the SNpr. Using a prey-versus-snake paradigm, mice were pretreated with the CB1R antagonist AM251 (100 pmol) and treated with the endocannabinoid anandamide (AEA, 5 pmol) in the SNpr, followed by bicuculline (40 ng) in the dlSC, and were then confronted with a snake. Bidirectional neural tract tracers associated with immunofluorescence showed the GABAergic striatonigral disinhibitory and nigrotectal inhibitory pathways. Furthermore, we showed that CB1R labelling was restricted to axonal fibres surrounding SNpr GABAergic cells. We also demonstrated a decrease in the defensive behaviours of mice treated with AEA in the SNpr, but this effect was blocked by pre-treatment with AM251 in this structure. Taken together, our results show that the panicolytic consequences of the AEA enhancement in the SNpr are signalled by CB1R, suggesting that CB1R localised in axon terminals of CPu GABAergic neurons in the SNpr modulates the activity of the nigrotectal GABAergic pathway during the expression of defensive behaviours in threatening situations.
Marijuana and its main psychotropic ingredient Delta(9)-tetrahydrocannabinol (THC) exert a plethora of psychoactive effects through the activation of the neuronal cannabinoid receptor type 1 (CB1), ...which is expressed by different neuronal subpopulations in the central nervous system. The exact neuroanatomical substrates underlying each effect of THC are, however, not known. We tested locomotor, hypothermic, analgesic, and cataleptic effects of THC in conditional knockout mouse lines, which lack the expression of CB1 in different neuronal subpopulations, including principal brain neurons, GABAergic neurons (those that release gamma aminobutyric acid), cortical glutamatergic neurons, and neurons expressing the dopamine receptor D1, respectively. Surprisingly, mice lacking CB1 in GABAergic neurons responded to THC similarly as wild-type littermates did, whereas deletion of the receptor in all principal neurons abolished or strongly reduced the behavioural and autonomic responses to the drug. Moreover, locomotor and hypothermic effects of THC depend on cortical glutamatergic neurons, whereas the deletion of CB1 from the majority of striatal neurons and a subpopulation of cortical glutamatergic neurons blocked the cataleptic effect of the drug. These data show that several important pharmacological actions of THC do not depend on functional expression of CB1 on GABAergic interneurons, but on other neuronal populations, and pave the way to a refined interpretation of the pharmacological effects of cannabinoids on neuronal functions.
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