Kara L. Stuhr

Disruption of Fatty Acid Amide Hydrolase Activity Prevents the Effects of Chronic Stress on Anxiety and Amygdalar Microstructure

Hyperactivation of the amygdala following chronic stress is believed to be one of the primary mechanisms underlying the increased propensity for anxiety-like behaviors and pathological states; however, the mechanisms by which chronic stress modulates amygdalar function are not well characterized. The aim of the current study was to determine the extent to which the endocannabinoid (eCB) system, which is known to regulate emotional behavior and neuroplasticity, contributes to changes in amygdalar structure and function following chronic stress. To examine the hypothesis, we have exposed C57/Bl6 mice to chronic restraint stress, which results in an increase in fatty acid amide hydrolase (FAAH) activity and a reduction in the concentration of the eCB N-arachidonylethanolamine (AEA) within the amygdala. Chronic restraint stress also increased dendritic arborization, complexity and spine density of pyramidal neurons in the basolateral nucleus of the amygdala (BLA) and increased anxiety-like behavior in wild-type mice. All of the stress-induced changes in amygdalar structure and function were absent in mice deficient in FAAH. Further, the anti-anxiety effect of FAAH deletion was recapitulated in rats treated orally with a novel pharmacological inhibitor of FAAH, JNJ5003 (50 mg per kg per day), during exposure to chronic stress. These studies suggest that FAAH is required for chronic stress to induce hyperactivity and structural remodeling of the amygdala. Collectively, these studies indicate that FAAH-mediated decreases in AEA occur following chronic stress and that this loss of AEA signaling is functionally relevant to the effects of chronic stress. These data support the hypothesis that inhibition of FAAH has therapeutic potential in the treatment of anxiety disorders, possibly by maintaining normal amygdalar function in the face of chronic stress.

Contributions of endocannabinoid signaling to psychiatric disorders in humans: genetic and biochemical evidence.

The endocannabinoid signaling system is a widespread, neuromodulatory system in brain and is also widely utilized in the periphery to modulate metabolic functions and the immune system. Preclinical data demonstrate that endocannabinoid signaling is an important stress buffer and modulates emotional and cognitive functions. These data suggest the hypothesis that endocannabinoid signaling could be dysfunctional in a number of mental disorders. Genetic polymorphisms in the human genes for two important proteins of the endocannabinoid signaling system, the CB1 cannabinoid receptor (CB1R) and fatty acid amide hydrolase (FAAH), have been explored in the context of normal and pathological conditions. In the case of the gene for FAAH, the mechanistic relationships among the common genetic polymorphism, the expression of the FAAH protein, and its likely impact on endocannabinoid signaling are understood. However, multiple polymorphisms in the gene for the CB1R occur and are associated with human phenotypic differences without an understanding of the functional relationships among the gene, mRNA, protein, and protein function. The endocannabinoid ligands are found in the circulation, and several studies have identified changes in their concentrations under various conditions. These data are reviewed for the purpose of generating hypotheses and to encourage further studies in this very interesting and important area.

Acute Stress Increases Circulating Anandamide and Other N-Acylethanolamines in Healthy Humans

Stress plays an important role in psychiatric disorders, and preclinical evidence indicates that the central endocannabinoid system modulates endocrine and neuronal responses to stress. This study aimed to investigate the effect of acute stress on circulating concentrations of endocannabinoids (eCBs) in healthy humans. A total of 71 adults participated in two sessions in which they were exposed to either a standardized psychosocial stress procedure (Trier Social Stress Test) or a control task. Blood samples for eCB and cortisol assays and cardiovascular and subjective measures were obtained before and at regular intervals after the tasks. Serum concentrations of the eCBs, N-arachidonylethanolamine (anandamide, AEA) and 2-arachidonoylglycerol (2-AG), as well as of the N-acylethanolamides (NAEs), N-palmitoylethanolamine (PEA) and N-oleoylethanolamine (OEA), and of the O-acylglycerol, 2-oleoylglycerol (2-OG), were determined. Compared with the control condition, stress increased serum concentrations of AEA and the other NAEs immediately after the stress period. Increases in PEA were positively correlated with increases in serum cortisol after stress. Furthermore, anxiety ratings at baseline were negatively correlated with baseline concentrations of AEA. The sex and menstrual cycle status of the subject affected the NAE responses to stress. Interestingly, subjects of Asian and African-American races exhibited different patterns of stress responses compared with the Caucasian subjects. These results indicate that stress increases circulating NAEs in healthy human volunteers. This finding supports a protective role for eCBs in anxiety. Further research is needed to elucidate the function of these lipid mediators, and to determine the mechanisms that regulate their appearance in the circulation.

Prefrontal cortical anandamide signaling coordinates coping responses to stress through a serotonergic pathway

The endocannabinoid system has recently emerged as a vital component of the stress response and is an appealing target for the treatment of mood and anxiety disorders. Additionally, corticolimbic endocannabinoid signaling is important for stress-induced regulation of emotional behavior. However, the mechanism by which this occurs remains elusive. Combining biochemical and behavioral analyses within the forced swim test, we examined whether stress-induced regulation of endocannabinoid signaling in the medial prefrontal cortex contributes to behavioral responses to stress, and whether these responses are dependent on serotonergic neurotransmission. Forced swim stress produced a rapid and pronounced reduction in medial prefrontal anandamide content, but had no effect on 2-arachidonoylglycerol content within this region. Local administration of the anandamide hydrolysis inhibitor URB597 (0.01μg) into the ventromedial region of the prefrontal cortex decreased passive coping responses and increased active behavioral strategies, a phenomenon which was blocked by local antagonism of the CB(1) receptor. Furthermore, local inhibition of anandamide hydrolysis within the medial PFC increased the firing rate of serotonergic neurons within the dorsal raphe, suggesting that prefrontal cortical endocannabinoid signaling may modulate stress coping behaviors through a regulation of serotonergic neurotransmission. Accordingly, serotonin depletion prevented the ability of inhibition of anandamide hydrolysis within the medial PFC to promote active stress coping responses. Collectively, these data argue that stress-induced changes in endocannabinoid signaling within the medial PFC modulate stress-coping behaviors through a regulation of serotonergic neurotransmission and provide a neuroanatomical framework by which we may understand the mechanisms subserving the antidepressant potential of the endocannabinoid system.

Endocannabinoid signaling in hypothalamic-pituitary-adrenocortical axis recovery following stress: effects of indirect agonists and comparison of male and female mice.

Studies in male rodents have shown that stress-induced increases in circulating corticosterone are increased by both CB1 receptor (CB1R) antagonist treatment and genetic deletion. The purposes of the current study were to determine whether female mice respond in the same manner as males, and whether indirect CB1R agonists accelerate the return of corticosterone to baseline. In agreement with earlier studies, CB1R null and rimonabant-treated male mice had significantly increased circulating corticosterone 30 min following the end of a restraint episode compared to wild type and vehicle-treated, respectively. Females treated with rimonabant had significantly higher circulating corticosterone compared to vehicle. However, corticosterone concentrations were not different between CB1R null and wild type females at 30 min recovery, although CB1R null mice had higher corticosterone concentrations at 90 min of recovery. Female CB1R null mice exhibited greater serum binding capacity for corticosterone than wild type. The monoacylglycerol lipase inhibitor, JZL184, attenuated corticosterone concentrations at restraint offset in male, and at 30 min recovery in female mice compared to vehicle. Male mice treated with JZL184 exhibited greater concentrations of circulating corticosterone at 120 min recovery, even in the absence of restraint. JZL184 had no effect on corticosterone concentrations in CB1R null mice. The fatty acid amide hydrolase inhibitor, URB597, did not affect corticosterone responses to restraint in male or female, wild type or CB1R null mice. These data suggest that 2-arachidonoylglycerol is the primary endocannabinoid involved in CB1R regulation of the recovery of the HPA axis from restraint stress. These data support a role for endocannabinoid-CB1R signaling in the regulation of the corticosterone response to restraint stress and suggest that female mice with life-long loss of the CB1R undergo compensatory changes that minimize the impact of loss of endocannabinoid signaling on circulating corticosterone.

Inhibition of fatty acid amide hydrolase suppresses referred hyperalgesia induced by bladder inflammation

Study Type – Aetiology (case series)

Sleep Restriction Enhances the Daily Rhythm of Circulating Levels of Endocannabinoid 2-Arachidonoylglycerol.

STUDY OBJECTIVES Increasing evidence from laboratory and epidemiologic studies indicates that insufficient sleep may be a risk factor for obesity. Sleep curtailment results in stimulation of hunger and food intake that exceeds the energy cost of extended wakefulness, suggesting the involvement of reward mechanisms. The current study tested the hypothesis that sleep restriction is associated with activation of the endocannabinoid (eCB) system, a key component of hedonic pathways involved in modulating appetite and food intake. METHODS In a randomized crossover study comparing 4 nights of normal (8.5 h) versus restricted sleep (4.5 h) in healthy young adults, we examined the 24-h profiles of circulating concentrations of the endocannabinoid 2-arachidonoylglycerol (2-AG) and its structural analog 2-oleoylglycerol (2-OG). We concomitantly assessed hunger, appetite, and food intake under controlled conditions. RESULTS A robust daily variation of 2-AG concentrations with a nadir around the middle of the sleep/overnight fast, followed by a continuous increase culminating in the early afternoon, was evident under both sleep conditions but sleep restriction resulted in an amplification of this rhythm with delayed and extended maximum values. Concentrations of 2-OG followed a similar pattern, but with a lesser amplitude. When sleep deprived, participants reported increases in hunger and appetite concomitant with the afternoon elevation of 2-AG concentrations, and were less able to inhibit intake of palatable snacks. CONCLUSIONS Our findings suggest that activation of the eCB system may be involved in excessive food intake in a state of sleep debt and contribute to the increased risk of obesity associated with insufficient sleep. COMMENTARY A commentary on this article appears in this issue on page 495.

Circadian Rhythm of Circulating Levels of the Endocannabinoid 2-Arachidonoylglycerol

CONTEXT The endocannabinoid (eCB) system is involved in the regulation of food intake and of peripheral metabolism. Although the cross talk between energy metabolism and the circadian system is well documented, little is known about a potential circadian modulation of human eCB activity. OBJECTIVE The objective of the study was to define the 24-hour profile of circulating levels of the most abundant endogenous ligand of the CB1 receptor, 2-arachidonoylglycerol (2-AG), in healthy young nonobese adults studied under controlled bedtime, dietary, and activity conditions. METHODS Fourteen subjects participated in this 4-day laboratory study with fixed light-dark cycles, standardized meals, and bedtimes. Sleep was recorded each night. On the third day, blood sampling at 15- to 30-minute intervals began at 9:30 pm and continued for 24 hours. Cortisol, leptin, and ghrelin were assayed on all samples, whereas the levels of 2-AG and its structural analog, 2-oleoylglycerol (2-OG), were measured at 60-minute intervals. RESULTS All participants exhibited a large circadian variation of 2-AG serum concentrations with a nadir around midsleep, coincident with the middle of the overnight fast. Levels of 2-AG increased continually across the morning, peaking in the early to midafternoon. Peak values represented, on average, a nearly 3-fold increase above nocturnal nadir levels. Concentrations of 2-OG followed a similar pattern, although with a shorter morning increase and lower amplitude. CONCLUSIONS The findings demonstrate that activity of the eCB system is profoundly modulated by circadian rhythmicity and suggest that its impact on the regulation of food intake is suppressed during sleep and is maximal during early to midafternoon.

Swim stress differentially affects limbic contents of 2-arachidonoylglycerol and 2-oleoylglycerol

UNLABELLED Restraint stress exposures evoke progressively larger increases in 2-arachidonoylglycerol (2-AG) in limbic brain regions as the number of repetitions increases. The Porsolt swim test usually involves two swim exposures separated by 24 h, and we asked whether the 2-AG response differed between the first and second exposures. METHODS Four groups of male C57/Bl6N mice were studied: control; exposed to a single 6 min swim and killed immediately; exposed to a single 6 min swim and killed 24 h later; and exposed to two swims, separated by 24 h, and killed after the second swim. Outcomes were swim behavior, serum corticosterone, and 2-AG and 2-oleoylglycerol (2-OG) contents in amygdala, hippocampus, and prefrontal cortex. RESULTS Mean 2-AG contents were not significantly different among the four treatment groups in any brain region and did not correlate with immobility in either forced swim exposure. However, 2-AG contents in all three brain regions only of the mice exposed to two swims were significantly, positively correlated with serum corticosterone concentrations measured at the same time. 2-OG is present in brain and exhibits a striking regional heterogeneity in control mice. 2-OG concentrations in prefrontal cortex were significantly reduced in the mice killed on the second day compared with the mice killed on the first day. As the target of 2-OG in brain is not known, the significance of these observations await further studies. CONCLUSIONS Although prior exposure to swim stress does not alter brain 2-AG contents upon re-exposure, 2-AG concentrations in brain become significantly correlated with the hypothalamic-pituitary-adrenal (HPA) axis response to stress when prior exposure to the stress has occurred. These data suggest that even a single exposure to a short period of intense stress sensitizes the 2-AG response to re-exposure to that situation and are consistent with a role for endocannabinoid signaling in modulating stress responses.

Endocannabinoid modulation of hyperaemia evoked by physiologically relevant stimuli in the rat primary somatosensory cortex

Background and purpose:  In vitro studies demonstrate that cannabinoid CB1 receptors subserve activity‐dependent suppression of inhibition in the neocortex. To examine this mechanism in vivo, we assessed the effects of local changes in CB1 receptor activity on somatosensory cortex neuronal activation by whisker movement in rats.