Adaptations in endocannabinoid signaling in response to repeated homotypic stress: a novel mechanism for stress habituation

Stress and visceral pain: from animal models to clinical therapies

Epidemiological studies have implicated stress (psychosocial and physical) as a trigger of first onset or exacerbation of irritable bowel syndrome (IBS) symptoms of which visceral pain is an integrant landmark. A number of experimental acute or chronic exteroceptive or interoceptive stressors induce visceral hyperalgesia in rodents although recent evidence also points to stress-related visceral analgesia as established in the somatic pain field. Underlying mechanisms of stress-related visceral hypersensitivity may involve a combination of sensitization of primary afferents, central sensitization in response to input from the viscera and dysregulation of descending pathways that modulate spinal nociceptive transmission or analgesic response. Biochemical coding of stress involves the recruitment of corticotropin releasing factor (CRF) signaling pathways. Experimental studies established that activation of brain and peripheral CRF receptor subtype 1 plays a primary role in the development of stress-related delayed visceral hyperalgesia while subtype 2 activation induces analgesic response. In line with stress pathways playing a role in IBS, non-pharmacologic and pharmacologic treatment modalities aimed at reducing stress perception using a broad range of evidence-based mind-body interventions and centrally-targeted medications to reduce anxiety impact on brain patterns activated by visceral stimuli and dampen visceral pain.

Late-life depression and Alzheimer's disease: the glutamatergic system inside of this mirror relationship

Late-life depressive syndromes often arise in the context of predementia, dementia syndromes, and Alzheimer's disease (AD). Conversely, patients with a history of mood disorders are at higher risk of developing cognitive impairment. The high rate of co-occurrence of these two disorders is becoming a major health problem in older subjects for both their epidemiological impact and the negative outcomes in terms of disability and increased mortality. In this perspective, it is possible to speculate on the presence of a mirror relationship between depressive and cognitive disorders in late-life. Indeed, although a causal contribution of genetic, environmental, and social factors is widely recognized in these disorders, the neurobiological links still remain largely unknown. l-glutamic acid and γ-aminobutyric acid are the principal excitatory and inhibitory neurotransmitters in the central nervous system, respectively, and increasing evidence suggests that alterations in this neurotransmitter system may contribute to the neurobiology linking depression and cognitive impairment. In the present review article, we examined the neurobiological bases of the relationship between late-life depressive syndromes and AD, with a particular attention to glutamatergic pathway signalling like a bridge connecting these two conditions. In addition, attempts have been made to explain changes in glutamatergic pathway, depression in older age, and dementia through the analysis of signal transduction mechanisms associated with these disabling disorders.

Social encounter with a novel partner in adolescent rats: activation of the central endocannabinoid system

The endocannabinoid system is critically involved in the modulation of affect, motivation, and emotion. Here, we investigated the hypothesis that changes in the content of endocannabinoid levels might underlie adaptation to positive social conditions during adolescence. To this aim, separate pairs of adolescent (postnatal days 32-35) male Wistar rats were allowed to interact in a neutral cage under two different testing conditions, i.e. familiar (FAM) and non-familiar (NFAM) social partners. We found that adolescent rats that encountered a NFAM partner spent significantly more time Sniffing and Following the companion than subjects exposed to a FAM partner, whereas no changes in levels of rough-and-tumble play were observed. Notably, the NFAM social encounter significantly increased striatal anandamide (AEA) levels compared to both non-social controls and animals that encountered a FAM partner. Changes in AEA levels appeared to be region-specific, since no changes were observed in the other brain regions analysed, neither were they observed in the activity of the AEA-hydrolase (FAAH) nor in the content of the other major endocannabinoid 2-arachidonylglycerol. In addition, animals that encountered a NFAM partner tended to explore less extensively the illuminated compartment of the light-dark box when compared to animals that had previously encountered a FAM companion. In conclusion, striatal AEA levels seem to participate in the emotional arousal resulting from a NFAM social encounter in adolescent rats, and to be particularly important for coping response to novel social contexts.

Short-term adaptation of conditioned fear responses through endocannabinoid signaling in the central amygdala

The cannabinoid receptor type 1 (CB1) and the central nucleus of the amygdala (CeA) are both known to have crucial roles in the processing of fear and anxiety, whereby they appear to be especially involved in the control of fear states. However, in contrast to many other brain regions including the cortical subregions of the amygdala, the existence of CB1 in the CeA remains enigmatic. In this study we show that CB1 is expressed in the CeA of mice and that CB1 in the CeA mediates short-term synaptic plasticity, namely depolarization-induced suppression of excitation (DSE) and inhibition (DSI). Moreover, the CB1 antagonist AM251 increased both excitatory and inhibitory postsynaptic responses in CeA neurons. Local application of AM251 in the CeA in vivo resulted in an acutely increased fear response in an auditory fear conditioning paradigm. Upon application of AM251 in the basolateral nucleus of the amygdala (BLA) in an otherwise identical protocol, no such acute behavioral effects were detected, but CB1 blockade resulted in increased fear responses during tone exposures on the subsequent days. Moreover, we observed that the efficacy of DSE and DSI in the CeA was increased on the day following fear conditioning, indicating that a single tone-shock pairing resulted in changes in endocannabinoid signaling in the CeA. Taken together, our data show the existence of CB1 proteins in the CeA, and their critical role for ensuring short-term adaptation of responses to fearful events, thereby suggesting a potential therapeutic target to accompany habituation-based therapies of post-traumatic symptoms.

Cannabinoids and Reproduction: A Lasting and Intriguing History

Starting from an historical overview of lasting Cannabis use over the centuries, we will focus on a description of the cannabinergic system, with a comprehensive analysis of chemical and pharmacological properties of endogenous and synthetic cannabimimetic analogues. The metabolic pathways and the signal transduction mechanisms, activated by cannabinoid receptors stimulation, will also be discussed. In particular, we will point out the action of cannabinoids and endocannabinoids on the different neuronal networks involved in reproductive axis, and locally, on male and female reproductive tracts, by emphasizing the pivotal role played by this system in the control of fertility.

Repeated stress impairs endocannabinoid signaling in the paraventricular nucleus of the hypothalamus

Endocannabinoids (eCBs) are ubiquitous retrograde signaling molecules in the nervous system that are recruited in response to robust neuronal activity or the activation of postsynaptic G-protein-coupled receptors. Physiologically, eCBs have been implicated as important mediators of the stress axis and they may contribute to the rapid feedback inhibition of the hypothalamic-pituitary-adrenal axis (HPA) by circulating corticosteroids (CORTs). Understanding the relationship between stress and eCBs, however, is complicated by observations that eCB signaling is itself sensitive to stress. The mechanisms that link stress to changes in synaptic eCB signaling and the impact of these changes on CORT-mediated negative feedback have not been resolved. Here, we show that repetitive immobilization stress, in juvenile male rats, causes a functional downregulation of CB(1) receptors in the paraventricular nucleus of the hypothalamus (PVN). This loss of CB(1) receptor signaling, which requires the activation of genomic glucocorticoid receptors, impairs both activity and receptor-dependent eCB signaling at GABA and glutamate synapses on parvocellular neuroendocrine cells in PVN. Our results provide a plausible mechanism for how stress can lead to alterations in CORT-mediated negative feedback and may contribute to the development of plasticity of HPA responses.

Endocannabinoid signaling in neurotoxicity and neuroprotection

The cannabis plant and products produced from it, such as marijuana and hashish, have been used for centuries for their psychoactive properties. The mechanism for how Delta(9)-tetrahydrocannabinol (THC), the active constituent of cannabis, elicits these neurological effects remained elusive until relatively recently, when specific G-protein coupled receptors were discovered that appeared to mediate cellular actions of THC. Shortly after discovery of these specific receptors, endogenous ligands (endocannabinoids) were identified. Since that time, an extensive number of papers have been published on the endocannabinoid signaling system, a widespread neuromodulatory mechanism that influences neurotransmission throughout the nervous system. This paper summarizes presentations given at the 12th International Neurotoxicology Association meeting that described the potential role of endocannabinoids in the expression of neurotoxicity. Dr. Raphael Mechoulam first gave an overview of the discovery of exogenous and endogenous cannabinoids and their potential for neuroprotection in a variety of conditions. Dr. Larry Parsons then described studies suggesting that endocannabinoid signaling may play a selective role in drug reinforcement. Dr. Carey Pope presented information on the role that endocannabinoid signaling may have in the expression of cholinergic toxicity following anticholinesterase exposures. Together, these presentations highlighted the diverse types of neurological insults that may be modulated by endocannabinoids and drugs/toxicants which might influence endocannabinoid signaling pathways.

Selective alterations of the CB1 receptors and the fatty acid amide hydrolase in the ventral striatum of alcoholics and suicides

Recent studies in rodents have suggested a role for the central endocannabinoid system in the regulation of mood and alcohol related behaviors. Alcohol use disorder is often associated with suicidal behavior. In the present study, we examined whether abnormalities in the endocannabinoid system in the ventral striatum are associated with alcohol dependence and suicide. The levels of CB1 receptors, receptor-mediated G-protein signaling, and activity and level of the fatty acid amide hydrolase (FAAH) were analyzed postmortem in the ventral striatum of alcohol-dependent nonsuicides (CA, n=9), alcohol-dependent suicides (AS, n=9) and nonpsychiatric controls (C, n=9). All subjects underwent a psychological autopsy, and toxicological and neuropathological examinations. The levels of the CB1 receptors and the CB1 receptor-mediated G-protein signaling were significantly lower in the ventral striatum of CA compared to the control group. However, these parameters were elevated in AS when compared to CA group. The activity of FAAH enzyme was lower in CA compared to the control group while it was found to be significantly higher in AS compared with CA group. These findings suggest that alcohol dependence is associated with the downregulation of the CB1 receptors, while suicide is linked to the upregulation of these receptors in the ventral striatum. Alteration in the activity of FAAH enzyme that regulates the anandamide (AEA) content might in turn explain differences in the CB1 receptor function in alcohol dependence and suicide. These findings may have etiological and therapeutic implications for the treatment of alcohol addiction and suicidal behavior.

Repeated psychological stress-induced alterations of visceral sensitivity and colonic motor functions in mice: influence of surgery and postoperative single housing on visceromotor responses

Visceral pain modulation by chronic stress in mice has been little studied. Electromyography (EMG) recording of abdominal muscle contractions, as a proxy to the visceromotor response (VMR), requires electrode implantation and post-surgical single housing (SH) which could affect the VMR to stress. To test this hypothesis, male mice had electrode implantation surgery (S) plus SH, or no surgery and were group housed (NS-GH) or single housed (NS-SH) and exposed to either water avoidance stress (WAS, 1 h/day) or left undisturbed in their home cages for 10 days. The VMR to phasic ascending colorectal distension (CRD) was assessed before (basal) and 24 h after 10 days of WAS or no stress using a surgery-free method of intraluminal colonic pressure (ICP) recording (solid-state manometry). WAS heightened significantly the VMR to CRD at 30, 45, and 60 mmHg in S-SH vs. NS-GH, but not compared to NS-SH conscious mice. Compared to basal CRD, WAS increased VMR at 60 mmHg in the S-SH group and decreased it at 30-60 mmHg in NS-GH mice, while having no effect in NS-SH mice. The average defecation during the hour of repeated WAS over 10 days was 1.9 and 2.4 fold greater in S-SH vs. NS-GH and NS-SH mice, respectively. These data indicate that the combination of S-SH required for VMR monitoring with EMG is an important component of repeated WAS-induced post-stress visceral hypersensitivity and defecation in mice.

Involvement of the endocannabinoid system in the neurobehavioural effects of stress and glucocorticoids

The endocannabinoid system is a neuroactive lipid signaling system that functions to gate synaptic transmitter release. Accumulating evidence has demonstrated that this system is responsive to modulation by both stress and glucocorticoids within the hypothalamus and limbic structures; however, the nature of this regulation is more complex than initially assumed. The aim of the current review is to summarize the research to date which examines the effects of acute stress and glucocorticoid administration on endocannabinoid signaling in limbic-hypothalamic-pituitary-adrenal (LHPA) axis, and in turn the role endocannabinoid signaling plays in the neurobehavioural responses to acute stress and glucocorticoid administration. The majority of research suggests that acute stress produces a mobilization of the endocannabinoid 2-arachidonoylglycerol (2-AG) while concurrently reducing the tissue content of the other endocannabinoid ligand anandamide. Genetic and pharmacological studies demonstrate that the reduction in anandamide signaling may be involved in the initiation of HPA axis activation and the generation of changes in emotional behaviour, while the increase in 2-AG signaling may be involved in terminating the stress response, limiting neuronal activation and contributing to changes in motivated behaviours. Collectively, these studies reveal a complex interplay between endocannabinoids and the HPA axis, and further identify endocannabinoid signaling as a critical regulator of the stress response.

Motion sickness, stress and the endocannabinoid system

Background

A substantial number of individuals are at risk for the development of motion sickness induced nausea and vomiting (N&V) during road, air or sea travel. Motion sickness can be extremely stressful but the neurobiologic mechanisms leading to motion sickness are not clear. The endocannabinoid system (ECS) represents an important neuromodulator of stress and N&V. Inhibitory effects of the ECS on N&V are mediated by endocannabinoid-receptor activation.

Methodology/Principal Findings

We studied the activity of the ECS in human volunteers (n = 21) during parabolic flight maneuvers (PFs). During PFs, microgravity conditions (<10⁻² g) are generated for approximately 22 s which results in a profound kinetic stimulus. Blood endocannabinoids (anandamide and 2-arachidonoylglycerol, 2-AG) were measured from blood samples taken in-flight before start of the parabolic maneuvers, after 10, 20, and 30 parabolas, in-flight after termination of PFs and 24 h later. Volunteers who developed acute motion sickness (n = 7) showed significantly higher stress scores but lower endocannabinoid levels during PFs. After 20 parabolas, blood anandamide levels had dropped significantly in volunteers with motion sickness (from 0.39±0.40 to 0.22±0.25 ng/ml) but increased in participants without the condition (from 0.43±0.23 to 0.60±0.38 ng/ml) resulting in significantly higher anandamide levels in participants without motion sickness (p = 0.02). 2-AG levels in individuals with motion sickness were low and almost unchanged throughout the experiment but showed a robust increase in participants without motion sickness. Cannabinoid-receptor 1 (CB1) but not cannabinoid-receptor 2 (CB2) mRNA expression in leucocytes 4 h after the experiment was significantly lower in volunteers with motion sickness than in participants without N&V.

Conclusions/Significance

These findings demonstrate that stress and motion sickness in humans are associated with impaired endocannabinoid activity. Enhancing ECS signaling may represent an alternative therapeutic strategy for motion sickness in individuals who do not respond to currently available treatments.

Endogenous cannabinoid signaling is essential for stress adaptation

Secretion of glucocorticoid hormones during stress produces an array of physiological changes that are adaptive and beneficial in the short term. In the face of repeated stress exposure, however, habituation of the glucocorticoid response is essential as prolonged glucocorticoid secretion can produce deleterious effects on metabolic, immune, cardiovascular, and neurobiological function. Endocannabinoid signaling responds to and regulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis that governs the secretion of glucocorticoids; however, the role this system plays in adaptation of the neuroendocrine response to repeated stress is not well characterized. Herein, we demonstrate a divergent regulation of the two endocannabinoid ligands, N-arachidonylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG), following repeated stress such that AEA content is persistently decreased throughout the corticolimbic stress circuit, whereas 2-AG is exclusively elevated within the amygdala in a stress-dependent manner. Pharmacological studies demonstrate that this divergent regulation of AEA and 2-AG contribute to distinct forms of HPA axis habituation. Inhibition of AEA hydrolysis prevented the development of basal hypersecretion of corticosterone following repeated stress. In contrast, systemic or intra-amygdalar administration of a CB(1) receptor antagonist before the final stress exposure prevented the repeated stress-induced decline in corticosterone responses. The present findings demonstrate an important role for endocannabinoid signaling in the process of stress HPA habituation, and suggest that AEA and 2-AG modulate different components of the adrenocortical response to repeated stressor exposure.

Dissociation of within- and between-session extinction of conditioned fear

Recent findings obtained in patients with phobias or trauma-related anxiety disorders raise doubts concerning the interrelation between acute fear relief during an exposure-based therapeutic session and beneficial treatment progress. In a mouse model explicit for exposure therapy, we challenge the view that within-session fear reduction is the turning point for relearning of a stimulus-threat association. Even though within-session extinction of auditory-cued fear memory was identical for prolonged and spaced tone presentations, only the latter caused between-session extinction. Furthermore, spaced tone presentations led to between-session extinction even in the complete absence of within-session extinction, as observed for remote fear memories and in case of abolished cannabinoid receptor type 1 signaling. Induction of between-session extinction was accompanied by an increase in the number of c-Fos-positive neurons within the basolateral amygdala, the cingulate cortex, and the dentate gyrus, independent of the level of within-session extinction. Together, our findings demonstrate that within-session extinction is neither sufficient nor essential for between-session extinction, thus calling for a reconsideration of current concepts underlying exposure-based therapies.

Maternal dietary fat determines metabolic profile and the magnitude of endocannabinoid inhibition of the stress response in neonatal rat offspring

Endocannabinoids (eCBs) are products of phospholipid (PL)-derived arachidonic acid (AA) that regulate hypothalamus-pituitary-adrenal axis activity. We hypothesized that differences in the quality and quantity of maternal dietary fat would modulate the PL AA content in the neonatal brain affecting stress responsiveness via differences in eCB production and activity in stress-activated brain areas. Pregnant rats were fed a 5% [control (C)] or 30% fat [high fat (HF)] diet rich in either n-6 (HF-n-6) or n-3 (HF-n-3) fat during the last week of gestation and lactation. Postnatal d 10 offspring were tested for metabolic hormones, AA (n-6) and eCB brain content, and hormonal effects of eCB receptor antagonism (AM251, 1 or 3 mg/kg ip) on stress responses. Like maternal diet, milk from HF-n-3 mothers had a reduced n-6/n-3 fat ratio compared with that of C and HF-n-6 mothers. Hypothalamic and hippocampal levels of PL AA were diet specific, reflecting the maternal milk and dietary n-6/n-3 ratio, with HF-n-3 offspring displaying reduced AA content relative to C and HF-n-6 offspring. Plasma corticosterone and insulin were elevated in HF-fed pups, whereas leptin was increased only in HF-n-6 pups. Basal eCB concentrations were also diet and brain region specific. In C pups, eCB receptor antagonist pretreatment increased stress-induced ACTH secretion, but not in the HF groups. Stress-induced corticosterone secretion was not sensitive to AM251 treatment in HF-n-3 pups. Thus, the nature of preweaning dietary fat differentially influences neonatal metabolic hormones, brain PL AA levels, and eCB, with functional consequences on hypothalamus-pituitary-adrenal axis modulation in developing rat pups.

Cannabinoids and anxiety

The term cannabinoids encompasses compounds produced by the plant Cannabis sativa, such as delta9-tetrahydrocannabinol, and synthetic counterparts. Their actions occur mainly through activation of cannabinoid type 1 (CB1) receptors. Arachidonoyl ethanolamide (anandamide) and 2-arachidonoyl glycerol (2-AG) serve as major endogenous ligands (endocannabinoids) of CB1 receptors. Hence, the cannabinoid receptors, the endocannabinoids, and their metabolizing enzymes comprise the endocannabinoid system. Cannabinoids induce diverse responses on anxiety- and fear-related behaviors. Generally, low doses tend to induce anxiolytic-like effects, whereas high doses often cause the opposite. Inhibition of endocannabinoid degradation seems to circumvent these biphasic effects by enhancing CB1 receptor signaling in a temporarily and spatially restricted manner, thus reducing anxiety-like behaviors. Pharmacological blockade or genetic deletion of CB1 receptors, in turn, primarily exerts anxiogenic-like effects and impairments in extinction of aversive memories. Interestingly, pharmacological blockade of Transient Receptor Potential Vanilloid Type-1 (TRPV1) channel, which can be activated by anandamide as well, has diametrically opposite consequences. This book chapter summarizes and conceptualizes our current knowledge about the role of (endo)cannabinoids in fear and anxiety and outlines implications for an exploitation of the endocannabinoid system as a target for new anxiolytic drugs.

Repeated homotypic stress elevates 2-arachidonoylglycerol levels and enhances short-term endocannabinoid signaling at inhibitory synapses in basolateral amygdala

Psychosocial stress is a risk factor for development and exacerbation of neuropsychiatric illness. Repeated stress causes biochemical adaptations in endocannabinoid (eCB) signaling that contribute to stress-response habituation, however, the synaptic correlates of these adaptations have not been examined. Here, we show that the synthetic enzyme for the eCB 2-arachidonoylglycerol (2-AG), diacylglycerol (DAG) lipase alpha, is heterogeneously expressed in the amygdala, and that levels of 2-AG and precursor DAGs are increased in the basolateral amygdala (BLA) after 10 days, but not 1 day, of restraint stress. In contrast, arachidonic acid was decreased after both 1 and 10 days of restraint stress. To examine the synaptic correlates of these alterations in 2-AG metabolism, we used whole-cell electrophysiology to determine the effects of restraint stress on depolarization-induced suppression of inhibition (DSI) in the BLA. A single restraint stress exposure did not alter DSI compared with control mice. However, after 10 days of restraint stress, DSI duration, but not magnitude, was significantly prolonged. Inhibition of 2-AG degradation with MAFP also prolonged DSI duration; the effects of repeated restraint stress and MAFP were mutually occlusive. These data indicate that exposure to repeated, but not acute, stress produces neuroadaptations that confer BLA neurons with an enhanced capacity to elevate 2-AG content and engage in 2-AG-mediated short-term retrograde synaptic signaling. We suggest stress-induced enhancement of eCB-mediated suppression of inhibitory transmission in the BLA could contribute to affective dysregulation associated with chronic stress.

Cannabinoid receptor activation in the basolateral amygdala blocks the effects of stress on the conditioning and extinction of inhibitory avoidance

Despite the efficacy of behavior therapy for human anxiety disorders, extinction-like treatments require repeated cue exposures and are vulnerable to reversal by a number of environmental factors, particularly stress. The endocannabinoid system has recently emerged as important in the regulation of extinction learning and in the regulation of the hypothalamic-pituitary-adrenal axis. Here, we aimed to examine the involvement of the cannabinoid CB(1) receptor in the basolateral amygdala (BLA) in inhibitory avoidance (IA) conditioning and extinction and to test whether cannabinoid activation would reverse the effects of stress on these memory processes. The synthetic full agonist of the CB(1)/CB(2) receptor WIN55,212-2 [R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol[1,2,3-de]-1,4- benzoxazin-6-yl)(1-naphthalenyl) methanone monomethanesulfonate] (5 microg/0.5 microl) microinjected into the BLA had no effect on IA conditioning or extinction by itself. However, microinjecting WIN55,212-2 into the BLA before exposing the rats to a stressor reversed the enhancing effects of the stressor on IA conditioning and its impairing effects on IA extinction. Importantly, WIN55,212-2 microinjected into the BLA reduced stress-induced elevations in corticosterone levels. Control experiments demonstrated the following: (1) the effects of WIN55,212-2 could not be attributed to sensorimotor deficits, because these parameters seemed unchanged by WIN55,212-2 microinjected into the BLA; and (2) the CB(1) receptor in the BLA is crucially involved in the extinction of IA, because the CB(1) receptor antagonist AM251 [N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide] (6 ng/0.5 microl) microinjected into the BLA significantly blocked extinction. Together, our findings may support a wide therapeutic application for cannabinoids in the treatment of conditions associated with the inappropriate retention of aversive memories and stress-related disorders.

Central side-effects of therapies based on CB1 cannabinoid receptor agonists and antagonists: focus on anxiety and depression

Both agonists (e.g. Delta(9)-tetrahydrocannabinol, nabilone) and antagonists (e.g. rimonabant, taranabant) of the cannabinoid type-1 (CB(1)) receptor have been explored as therapeutic agents in diverse fields of medicine such as pain management and obesity with associated metabolic dysregulation, respectively. CB(1) receptors are widely distributed in the central nervous system and are involved in the modulation of emotion, stress and habituation responses, behaviours that are thought to be dysregulated in human psychiatric disorders. Accordingly, CB(1) receptor activation may, in some cases, precipitate episodes of psychosis and panic, while its inhibition may lead to behaviours reminiscent of depression and anxiety-related disorders. The present review discusses these side-effects, which have to be taken into account in the therapeutic exploitation of the endocannabinoid system.

Role of endocannabinoid signaling in anxiety and depression

Cannabinoid receptors and their endogenous ligands are located throughout the limbic, or "emotional," brain, where they modulate synaptic neurotransmission. Converging preclinical and clinical data suggest a role for endogenous cannabinoid signaling in the modulation of anxiety and depression. Augmentation of endocannabinoid signaling (ECS) has anxiolytic effects, whereas blockade or genetic deletion of CB₁ receptors has anxiogenic properties. Augmentation of ECS also appears to have anti-depressant actions, and in some assays blockade and genetic deletion of CB₁ receptors produces depressive phenotypes. These data provide evidence that ECS serves in an anxiolytic, and possibly anti-depressant, role. These data suggest novel approaches to treatment of affective disorders which could include enhancement of endogenous cannabinoid signaling, and warrant cautious use of CB₁ receptor antagonists in patients with pre-existing affective disorders.