Antagonism of cannabinoid 1 receptors reverses the anxiety-like behavior induced by central injections of corticotropin-releasing factor and cocaine withdrawal

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Cannabinoid receptor type 1 in the bed nucleus of the stria terminalis modulates cardiovascular responses to stress via local N-methyl-D-aspartate receptor/neuronal nitric oxide synthase/soluble guanylate cyclase/protein kinase G signaling

BACKGROUND

Endocannabinoid neurotransmission in the bed nucleus of the stria terminalis is involved in the control of cardiovascular responses to stress. However, the local mechanisms involved is this regulation are not known.

AIMS

The purpose of this study was to assess an interaction of bed nucleus of the stria terminalis endocannabinoid neurotransmission with local nitrergic signaling, as well as to investigate the involvement of local N-methyl-D-aspartate glutamate receptor and nitric oxide signaling in the control of cardiovascular responses to acute restraint stress by bed nucleus of the stria terminalis endocannabinoid neurotransmission in rats.

METHODS

The first protocol evaluated the effect of intra-bed nucleus of the stria terminalis microinjection of the selective cannabinoid receptor type 1 receptor antagonist AM251 in nitrite/nitrate content in the bed nucleus of the stria terminalis following restraint stress. The other protocols evaluated the impact of local pretreatment with the selective N-methyl-D-aspartate glutamate receptor antagonist LY235959, the selective neuronal nitric oxide synthase inhibitor N^ω-propyl-L-arginine, the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, or the protein kinase G inhibitor KT5823 in restraint-evoked cardiovascular changes following bed nucleus of the stria terminalis treatment with AM251.

RESULTS

Bilateral microinjection of AM251 into the bed nucleus of the stria terminalis increased local nitric oxide release during restraint stress. Bed nucleus of the stria terminalis treatment with the cannabinoid receptor type 1 receptor antagonist also enhanced the tachycardia caused by restraint stress, but without affecting arterial pressure increase and sympathetic-mediated cutaneous vasoconstriction. The facilitation of restraint-evoked tachycardia following bed nucleus of the stria terminalis treatment with the cannabinoid receptor type 1 receptor antagonist was completely inhibited by local pretreatment with LY235959, N^ω-propyl-L-arginine, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, or KT5823.

CONCLUSIONS

Our results provide evidence that bed nucleus of the stria terminalis endocannabinoid neurotransmission inhibits local N-methyl-D-aspartate/neuronal nitric oxide synthase/soluble guanylate cyclase/protein kinase G signaling, and this mechanism is involved in the control of the cardiovascular responses to stress.

Conditioned aversive responses produced by delayed, but not immediate, exposure to cocaine and morphine in male Sprague-Dawley rats

RATIONALE

To determine the conditions under which tastes paired with delayed access to experimenter-delivered cocaine and morphine elicit a conditionally aversive affective state.

OBJECTIVES AND METHODS

The potential of saccharin paired with immediate access to cocaine (5, 10, 20 mg/kg, sc and ip) and delayed (30 and 10 min) access to cocaine (20 mg/kg, sc and ip) and morphine (10 mg/kg, sc) to elicit a pattern of aversive responding in the taste reactivity test (Grill and Norgren 1978a) was evaluated. Cocaine-induced aversions were compared with those produced by a moderate dose of LiCl (50 mg/kg). Finally, as an independent measure of cocaine withdrawal, the potential of exposure to saccharin paired with delayed access to cocaine to produce anxiogenic-like responding in the Light-Dark Emersion test was evaluated.

RESULTS

Immediate access to cocaine did not produce conditioned aversion at any dose. Delayed (30 or 10 min) access to sc cocaine (20 mg/kg) produced robust conditioned aversion and delayed access to ip cocaine (20 mg/kg; 30 min) and to sc morphine (10 mg/kg; 10 min) produced weaker conditioned aversion. Yawning emerged as a potential withdrawal response in rats conditioned with delayed (30 min) access to 20 mg/kg, sc, cocaine. Contextual cues did not produce conditioned aversion when paired with delayed access to sc cocaine (20 mg/kg). Finally, exposure to saccharin paired with delayed access to cocaine produced anxiogenic-like responding in the Light-Dark Emersion test.

CONCLUSION

Our results support the contention that a conditioned aversive state develops when a taste cue comes to predict the delayed availability of drugs of abuse.

Acupuncture modulates stress response by the mTOR signaling pathway in a rat post-traumatic stress disorder model

Post-traumatic stress disorder (PTSD) is a psychiatric disease that can form following exposure to a traumatic event. Acupuncture has been proposed as a beneficial treatment for PTSD, but the underlying mechanisms remain unclear. The present study investigated whether acupuncture improves depression- and anxiety-like behaviors induced using a single prolonged stress (SPS) as a PTSD rat model. In addition, we investigated whether the effects were mediated by increased mTOR activity and its downstream signaling components, which contribute to protein synthesis required for synaptic plasticity in the hippocampus. We found that acupuncture at HT8 significantly alleviated both depression- and anxiety-like behaviors induced by SPS in rats, as assessed by the forced swimming, elevated plus maze, and open field tests; this alleviation was blocked by rapamycin. The effects of acupuncture were equivalent to those exerted by fluoxetine. Acupuncture regulated protein translation in the mTOR signaling pathway and enhanced the activation of synaptic proteins, PSD95, Syn1, and GluR1 in the hippocampus. These results suggest that acupuncture exerts antidepressant and anxiolytic effects on PTSD-related symptoms by increasing protein synthesis required for synaptic plasticity via the mTOR pathway in the hippocampus. Acupuncture may be a promising treatment for patients with PTSD and play a role as an alternative PTSD treatment.

Epigenetic mechanisms associated with addiction-related behavioural effects of nicotine and/or cocaine: implication of the endocannabinoid system

The addictive use of nicotine (NC) and cocaine (COC) continues to be a major public health problem, and their combined use has been reported, particularly during adolescence. In neural plasticity, commonly induced by NC and COC, as well as behavioural plasticity related to the use of these two drugs, the involvement of epigenetic mechanisms, in which the reversible regulation of gene expression occurs independently of the DNA sequence, has recently been reported. Furthermore, on the basis of intense interactions with the target neurotransmitter systems, the endocannabinoid (ECB) system has been considered pivotal for eliciting the effects of NC or COC. The combined use of marijuana with NC and/or COC has also been reported. This article presents the addiction-related behavioural effects of NC and/or COC, based on the common behavioural/neural plasticity and combined use of NC/COC, and reviews the interacting role of the ECB system. The epigenetic processes inseparable from the effects of NC and/or COC (i.e. DNA methylation, histone modifications and alterations in microRNAs) and the putative therapeutic involvement of the ECB system at the epigenetic level are also discussed.

The novel cannabinoid receptor GPR55 mediates anxiolytic-like effects in the medial orbital cortex of mice with acute stress

The G protein-coupled receptor 55 (GPR55) is a novel cannabinoid receptor, whose exact role in anxiety remains unknown. The present study was conducted to explore the possible mechanisms by which GPR55 regulates anxiety and to evaluate the effectiveness of O-1602 in the treatment of anxiety-like symptoms. Mice were exposed to two types of acute stressors: restraint and forced swimming. Anxiety behavior was evaluated using the elevated plus maze and the open field test. We found that O-1602 alleviated anxiety-like behavior in acutely stressed mice. We used lentiviral shRNA to selective ly knockdown GPR55 in the medial orbital cortex and found that knockdown of GPR55 abolished the anxiolytic effect of O-1602. We also used Y-27632, a specific inhibitor of ROCK, and U73122, an inhibitor of PLC, and found that both inhibitors attenuated the effectiveness of O-1602. Western blot analysis revealed that O-1602 downregulated the expression of GluA1 and GluN2A in mice. Taken together, these results suggest that GPR55 plays an important role in anxiety and O-1602 may have therapeutic potential in treating anxiety-like symptoms.

Adolescent Exposure to the Synthetic Cannabinoid WIN 55212-2 Modifies Cocaine Withdrawal Symptoms in Adult Mice

Chronic cannabinoid consumption is an increasingly common behavior among teenagers and has been shown to cause long-lasting neurobehavioral alterations. Besides, it has been demonstrated that cocaine addiction in adulthood is highly correlated with cannabis abuse during adolescence. Cocaine consumption and subsequent abstinence from it can cause psychiatric symptoms, such as psychosis, cognitive impairment, anxiety, and depression. The aim of the present research was to study the consequences of adolescent exposure to cannabis on the psychiatric-like effects promoted by cocaine withdrawal in adult mice. We pre-treated juvenile mice with the cannabinoid CB1 receptor agonist WIN 55212-2 (WIN) and then subjected them to a chronic cocaine treatment during adulthood. Following these treatments, animals were tested under cocaine withdrawal in the following paradigms: pre-pulse inhibition, object recognition, elevated plus maze, and tail suspension. The long-term psychotic-like actions induced by WIN were not modified after cocaine cessation. Moreover, the memory impairments induced by cocaine withdrawal were not altered by previous adolescent WIN intake. However, WIN pre-treatment prevented the anxiogenic effects observed after cocaine abstinence, and led to greater depressive-like symptoms following cocaine removal in adulthood. This study is the first to show the long-lasting behavioral consequences of juvenile exposure to WIN on cocaine withdrawal in adult mice.

Adolescent but not adult ethanol binge drinking modulates cocaine withdrawal symptoms in mice

Background

Ethanol (EtOH) binge drinking is an increasingly common behavior among teenagers that induces long-lasting neurobehavioral alterations in adulthood. An early history of EtOH abuse during adolescence is highly correlated with cocaine addiction in adulthood. Abstinence of cocaine abuse can cause psychiatric symptoms, such as anxiety, psychosis, depression, and cognitive impairments. This study assessed the consequences of adolescent exposure to EtOH on the behavioral alterations promoted by cocaine withdrawal in adulthood.

Methods

We pretreated juvenile (34–47 days old) or adult (68–81 days old) mice with EtOH (1.25 g/kg) following a binge-drinking pattern. Then, after a three-week period without drug delivery, they were subjected to a chronic cocaine treatment in adulthood and tested under cocaine withdrawal by the ensuing paradigms: open field, elevated plus maze, prepulse inhibition, tail suspension test, and object recognition. Another set of mice were treated with the same EtOH binge-drinking procedure during adolescence and were tested immediately afterwards under the same behavioral paradigms.

Results

Adolescent EtOH pretreatment undermined the anxiogenic effects observed after cocaine abstinence, reduced prepulse inhibition, and increased immobility scores in the tail suspension test following cocaine withdrawal. Moreover, the memory deficits evoked by these substances when given separately were enhanced in cocaine-withdrawn mice exposed to EtOH during adolescence. EtOH binge drinking during adolescence also induced anxiety, depressive symptoms, and memory impairments when measured immediately afterwards. In contrast, neither EtOH nor cocaine alone or in combination altered any of these behaviors when given in adulthood.

Conclusions

EtOH binge drinking induces short- and long-term behavioral alterations and modulates cocaine withdrawal symptoms when given in adolescent mice.

Angiotensin type 1a receptors in the paraventricular nucleus of the hypothalamus control cardiovascular reactivity and anxiety-like behavior in male mice

This study tested the hypothesis that deletion of angiotensin type 1a receptors (AT1a) from the paraventricular nucleus of hypothalamus (PVN) attenuates anxiety-like behavior, hypothalamic-pituitary-adrenal (HPA) axis activity, and cardiovascular reactivity. We used the Cre/LoxP system to generate male mice with AT1a specifically deleted from the PVN. Deletion of the AT1a from the PVN reduced anxiety-like behavior as indicated by increased time spent in the open arms of the elevated plus maze. In contrast, PVN AT1a deletion had no effect on HPA axis activation subsequent to an acute restraint challenge but did reduce hypothalamic mRNA expression for corticotropin-releasing hormone (CRH). To determine whether PVN AT1a deletion inhibits cardiovascular reactivity, we measured systolic blood pressure, heart rate, and heart rate variability (HRV) using telemetry and found that PVN AT1a deletion attenuated restraint-induced elevations in systolic blood pressure and elicited changes in HRV indicative of reduced sympathetic nervous activity. Consistent with the decreased HRV, PVN AT1a deletion also decreased adrenal weight, suggestive of decreased adrenal sympathetic outflow. Interestingly, the altered stress responsivity of mice with AT1a deleted from the PVN was associated with decreased hypothalamic microglia and proinflammatory cytokine expression. Collectively, these results suggest that deletion of AT1a from the PVN attenuates anxiety, CRH gene transcription, and cardiovascular reactivity and reduced brain inflammation may contribute to these effects.

Endocannabinoid CB1 receptor activation upon global ischemia adversely impact recovery of reward and stress signaling molecules, neuronal survival and behavioral impulsivity

Global cerebral ischemia in rodents, which mimics cardiac arrest in humans, is associated with a surge in endocannabinoids and increased transmission of dopamine and glutamate leading to excitotoxic cell death. The current study assessed the role of CB1 receptor activation at the moment of an ischemic insult on ensuing regulation of stress and reward signaling molecules, neuronal injury and anxiety-like behavior. Male Wistar rats were separated into 4 groups (n=10/group); sham and ischemic rats administered the CB1 endocannabinoid receptor antagonist AM251 (2mg/kg, i.p.) 30min prior to global cerebral ischemia, and vehicle-treated counterparts. The effects of CB1 receptor blockade on corticotropin-releasing hormone (CRH), vesicular glutamate transporter 2 (vGluT2), tyrosine hydroxylase (TH) and dopamine receptor 1 (DRD1) signaling expression, together with CA1 neuronal damage and anxiety-like behaviors were assessed. Our findings show attenuated CA1 injury and behavioral deficits in AM251-treated ischemic rats. AM251-pretreatment also partially or completely reversed ischemia-induced alterations in TH-ir expression at the hippocampus, ventral tegmental area (VTA), nucleus accumbens (NAc) and basolateral amygdala (BLA), normalized DRD1-ir at the medial forebrain bundle, and diminished BLA and PVN-CRH expression. All groups showed comparable vGluT2 expression at the BLA and PVN-parvocellular subdivision. These findings support a determinant role of CB1 receptor activation at time of ischemia on functional recovery. They also support "state-dependent" effects of endocannabinoids, raising considerations in the development of effective molecules to regulate HPA axis function and mood disorders following cardiac arrest and stroke.

Endocannabinoids, through opioids and prostaglandins, contribute to fever induced by key pyrogenic mediators

This study aims to explore the contribution of endocannabinoids on the cascade of mediators involved in LPS-induced fever and to verify the participation of prostaglandins and endogenous opioids in fever induced by anandamide (AEA). Body temperature (Tc) of male Wistar rats was recorded over 6h, using a thermistor probe. Cerebrospinal fluid concentration of PGE2 and β-endorphin were measured by ELISA after the administration of AEA. Intracerebroventricular administration of the CB1 receptor antagonist AM251 (5μg, i.c.v.), reduced the fever induced by IL-1β (3ng, i.c.v.), TNF-α (250ng, i.c.v.), IL-6 (300ng, i.c.v.), corticotrophin release factor (CRH; 2.5μg, i.c.v.) and endothelin (ET)-1 (1pmol, i.c.v.), but not the fever induced by PGE2 (250ng, i.c.v.) or PGF2α (250ng, i.c.v.). Systemic administration of indomethacin (2mgkg(-1), i.p.) or celecoxib (5mgkg(-1), p.o.) reduced the fever induced by AEA (1μg, i.c.v.), while naloxone (1mgkg(-1), s.c.) abolished it. The increases of PGE2 and β-endorphin concentration in the CSF induced by AEA were abolished by the pretreatment of rats with AM251. These results suggest that endocannabinoids are intrinsically involved in the pyretic activity of cytokines (IL-1β, TNF-α, IL-6), CRH and ET-1 but not the PGE2 or PGF2α induced fevers. However, anandamide via CB1 receptor activation induces fever that is dependent on the synthesis of prostaglandin and opioids.

Corticotropin-releasing hormone drives anandamide hydrolysis in the amygdala to promote anxiety

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.

L-tetrahydropalmatine ameliorates development of anxiety and depression-related symptoms induced by single prolonged stress in rats

Abnormal adaptation of the stress-response system following traumatic stress can lead to alterations in the hypothalamic-pituitary-adrenal (HPA) axis that may contribute to the development of post-traumatic stress disorder (PTSD). The present study used several behavioral tests to investigate the anxiolytic-like and antidepressant activity of L-tetrahydropalmatine (L-THP) in an experimental rat model of anxiety and depression induced by single prolonged stress (SPS), an animal model of PTSD. Male rats were treated intraperitoneally (i.p.) with vehicle or varied doses of THP 30 min prior to SPS for 8 consecutive days. Daily THP (50 mg/kg) administration significantly increased the number and duration of open arm visits in the elevated plus maze (EPM) test, reduced the anxiety index, increased the risk assessment, and increased the number of head dips over the borders of the open arms after SPS. THP was also associated with increased time spent at the center of the open field, reduced grooming behaviors in the EPM test, and reduced time spent immobile in the forced swimming test (FST). It also blocked the decrease in neuropeptide Y (NPY) and the increase in corticotrophin-releasing factor (CRF) expression in the hypothalamus. This is the first study to determine that THP exerts pronounced anxiolytic-like and antidepressant effects on the development of the behavioral and biochemical symptoms associated with PTSD, indicating its prophylactic potential. Thus, THP reversed several behavioral impairments triggered by the traumatic stress of SPS and is a potential non-invasive therapeutic intervention for PTSD.

Alpha-Asarone, a Major Component of Acorus gramineus, Attenuates Corticosterone-Induced Anxiety-Like Behaviours via Modulating TrkB Signaling Process

We investigated the anxiolytic-like activity of α-asarone (AAS) from Acorus gramineus in an experimental rat model of anxiety induced by repeated administration of the exogenous stress hormone corticosterone (CORT). The putative anxiolytic effect of AAS was studied in behavioral tests of anxiety, such as the elevated plus maze (EPM) test and the hole-board test (HBT) in rats. For 21 consecutive days, male rats received 50, 100, or 200 mg/kg AAS (i.p.) 30 min prior to a daily injection of CORT. Dysregulation of the HPA axis in response to the repeated CORT injections was confirmed by measuring serum levels of CORT and the expression of corticotrophin-releasing factor (CRF) in the hypothalamus. Daily AAS (200 mg/kg) administration increased open-arm exploration significantly in the EPM test, and it increased the duration of head dipping activity in the HBT. It also blocked the increase in tyrosine hydroxylase (TH) expression in the locus coeruleus (LC) and decreased mRNA expression of brain-derived neurotrophic factor (BDNF) and its receptor, TrkB, in the hippocampus. These results indicated that the administration of AAS prior to high-dose exogenous CORT significantly improved anxiety-like behaviors, which are associated with modification of the central noradrenergic system and with BDNF function in rats. The current finding may improve understanding of the neurobiological mechanisms responsible for changes in emotions induced by repeated administration of high doses of CORT or by elevated levels of hormones associated with chronic stress. Thus, AAS did exhibit an anxiolytic-like effects in animal models of anxiety.

Stress regulates endocannabinoid-CB1 receptor signaling

The CB1 cannabinoid receptor is a G protein coupled receptor that is widely expressed throughout the brain. The endogenous ligands for the CB1 receptor (endocannabinoids) are N-arachidonylethanolamine and 2-arachidonoylglycerol; together the endocannabinoids and CB1R subserve activity dependent, retrograde inhibition of neurotransmitter release in the brain. Deficiency of CB1 receptor signaling is associated with anhedonia, anxiety, and persistence of negative memories. CB1 receptor-endocannabinoid signaling is activated by stress and functions to buffer or dampen the behavioral and endocrine effects of acute stress. Its role in regulation of neuronal responses is more complex. Chronic variable stress exposure reduces endocannabinoid-CB1 receptor signaling and it is hypothesized that the resultant deficiency in endocannabinoid signaling contributes to the negative consequences of chronic stress. On the other hand, repeated exposure to the same stress can sensitize CB1 receptor signaling, resulting in dampening of the stress response. Data are reviewed that support the hypothesis that CB1 receptor signaling is stress responsive and that maintaining robust endocannabinoid/CB1 receptor signaling provides resilience against the development of stress-related pathologies.

Rimonabant precipitates anxiety in rats withdrawn from palatable food: role of the central amygdala

The anti-obesity medication rimonabant, an antagonist of cannabinoid type-1 (CB(1)) receptor, was withdrawn from the market because of adverse psychiatric side effects, including a negative affective state. We investigated whether rimonabant precipitates a negative emotional state in rats withdrawn from palatable food cycling. The effects of systemic administration of rimonabant on anxiety-like behavior, food intake, body weight, and adrenocortical activation were assessed in female rats during withdrawal from chronic palatable diet cycling. The levels of the endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG), and the CB(1) receptor mRNA and the protein in the central nucleus of the amygdala (CeA) were also investigated. Finally, the effects of microinfusion of rimonabant in the CeA on anxiety-like behavior, and food intake were assessed. Systemic administration of rimonabant precipitated anxiety-like behavior and anorexia of the regular chow diet in rats withdrawn from palatable diet cycling, independently from the degree of adrenocortical activation. These behavioral observations were accompanied by increased 2-AG, CB(1) receptor mRNA, and protein levels selectively in the CeA. Finally, rimonabant, microinfused directly into the CeA, precipitated anxiety-like behavior and anorexia. Our data show that (i) the 2-AG-CB(1) receptor system within the CeA is recruited during abstinence from palatable diet cycling as a compensatory mechanism to dampen anxiety, and (ii) rimonabant precipitates a negative emotional state by blocking the beneficial heightened 2-AG-CB(1) receptor signaling in this brain area. These findings help elucidate the link between compulsive eating and anxiety, and it will be valuable to develop better pharmacological treatments for eating disorders and obesity.

Addiction and the adrenal cortex

Substantial evidence shows that the hypophyseal–pituitary–adrenal (HPA) axis and corticosteroids are involved in the process of addiction to a variety of agents, and the adrenal cortex has a key role. In general, plasma concentrations of cortisol (or corticosterone in rats or mice) increase on drug withdrawal in a manner that suggests correlation with the behavioural and symptomatic sequelae both in man and in experimental animals. Corticosteroid levels fall back to normal values in resumption of drug intake. The possible interactions between brain corticotrophin releasing hormone (CRH) and proopiomelanocortin (POMC) products and the systemic HPA, and additionally with the local CRH–POMC system in the adrenal gland itself, are complex. Nevertheless, the evidence increasingly suggests that all may be interlinked and that CRH in the brain and brain POMC products interact with the blood-borne HPA directly or indirectly. Corticosteroids themselves are known to affect mood profoundly and may themselves be addictive. Additionally, there is a heightened susceptibility for addicted subjects to relapse in conditions that are associated with change in HPA activity, such as in stress, or at different times of the day. Recent studies give compelling evidence that a significant part of the array of addictive symptoms is directly attributable to the secretory activity of the adrenal cortex and the actions of corticosteroids. Additionally, sex differences in addiction may also be attributable to adrenocortical function: in humans, males may be protected through higher secretion of DHEA (and DHEAS), and in rats, females may be more susceptible because of higher corticosterone secretion.

Cannabinoid CB1 receptors mediate the effects of corticotropin-releasing factor on the reinstatement of cocaine seeking and expression of cocaine-induced behavioural sensitization

BACKGROUND AND PURPOSE

The endocannabinoid and corticotropin-releasing factor (CRF) systems have been implicated in several long-lasting behavioural effects of prior cocaine experience. The present experiments were designed to probe functional interactions between endocannabinoids and CRF by testing the role of cannabinoid CB(1) receptors in cocaine-related behaviours induced or mediated by CRF.

EXPERIMENTAL APPROACH

In Experiment 1, rats trained to self-administer cocaine were pretreated with the CB(1) receptor antagonist, AM251 (0, 10, 100 or 200 µg, i.c.v.), before tests for reinstatement in response to CRF (0, 0.5 µg, i.c.v.), intermittent footshock stress (0, 0.9 mA) or cocaine (0, 10 mg·kg(-1) , i.p.). In Experiment 2, rats pre-exposed to cocaine (15-30 mg·kg(-1) , i.p.) or saline for 7 days were pretreated with AM251 (0, 10 or 100 µg, i.c.v.) before tests for locomotion in response to CRF (0.5 µg, i.c.v.), cocaine (15 mg·kg(-1) , i.p.) or saline (i.c.v.).

KEY RESULTS

Pretreatment with AM251 selectively interfered with CRF-, but not footshock- or cocaine-induced reinstatement. AM251 blocked the expression of behavioural sensitization induced by challenge injections of both CRF and cocaine.

CONCLUSIONS AND IMPLICATIONS

These findings reveal a mediating role for CB(1) receptor transmission in the effects of CRF on cocaine-related behaviours.

Enhanced anxiety observed in cocaine withdrawn rats is associated with altered reactivity of the dorsomedial prefrontal cortex

Discontinuation of drug intake in cocaine abusers commonly produces a variety of adverse withdrawal symptoms among which anxiety and depression-related behavior are prevailing during the initial period of abstinence. The aim of this study was to provide further insight into the neurobiological dysregulations that might contribute to these pathological states. Rats were treated with cocaine or saline for 14 days (20 mg/kg; i.p) and anxiety-related behavior was assessed in different paradigms (elevated plus-maze (EPM), confinement to an open arm of the EPM and shock-probe burying tests) for up to 4 weeks after withdrawal. Depression-like behavior was assessed by the forced swim test and sucrose preference test. Altogether our results demonstrated that cocaine withdrawal induced persistent heightened levels of anxiety that last for at least 28 days but did not affect depression-like behavior. We then used Fos immunohistochemistry to map neuronal activation patterns in withdrawn rats confined to one open arm of an EPM, and a double labeling procedure using Fos immunohistochemistry and in situ hybridization of glutamic acid decarboxylase or vesicular glutamate transporter mRNAs to identify the phenotype of the activated neurons. Our data showed that the exacerbated anxiety observed in cocaine withdrawn rats exposed to an elevated open arm was accompanied by an altered reactivity of the dorsal part of the medial prefrontal cortex (anterior cingulate and dorsal prelimbic cortices), the paraventricular thalamic nucleus and the lateral and anterior areas of the hypothalamus. In the medial prefrontal cortex, we evidenced a negative correlation between Fos expression in its dorsal part and open arm-induced freezing in NaCl-treated rats but not in cocaine withdrawn rats. We also found that more than 65% of activated neurons were glutamatergic projection neurons. The present study provides new insights into the neuroanatomical regions and neuronal cell types that may underlie pathological anxiety during cocaine withdrawal.

Introduction to the special issue on stress, emotional behavior, and the endocannabinoid system: a decade of research

This article is part of a Special Issue entitled:Stress, Emotional Behavior, and the Endocannabinoid System.