Involvement of the kappa-opioid receptor in the anxiogenic-like effect of CP 55,940 in male rats

β-caryophyllene inhibits heroin self-administration, but does not alter opioid-induced antinociception in rodents

A growing body of research indicates that β-caryophyllene (BCP), a constituent present in a large number of plants, possesses significant therapeutic properties against CNS disorders, including alcohol and psychostimulant use disorders. However, it is unknown whether BCP has similar therapeutic potential for opioid use disorders. In this study, we found that systemic administration of BCP dose-dependently reduced heroin self-administration in rats under an FR2 schedule of reinforcement and partially blocked heroin-enhanced brain stimulation reward in DAT-cre mice, maintained by optical stimulation of midbrain dopamine neurons at high frequencies. Acute administration of BCP failed to block heroin conditioned place preference (CPP) in male mice, but attenuated heroin-induced CPP in females. Furthermore, repeated dosing with BCP for 5 days facilitated the extinction of CPP in female but not male mice. In the hot plate assay, pretreatment with the same doses of BCP failed to enhance or prolong opioid antinociception. Lastly, in a substitution test, BCP replacement for heroin failed to maintain intravenous BCP self-administration, suggesting that BCP itself has no reinforcing properties. These findings suggest that BCP may have certain therapeutic effects against opioid use disorders with fewer unwanted side-effects by itself.

Should oncologists trust cannabinoids?

Cannabis enjoyed a "golden age" as a medicinal product in the late 19th, early 20th century, but the increased risk of overdose and abuse led to its criminalization. However, the 21st century have witnessed a resurgence of interest and a large body of literature regarding the benefits of cannabinoids have emerged. As legalization and decriminalization have spread around the world, cancer patients are increasingly interested in the potential utility of cannabinoids. Although eager to discuss cannabis use with their oncologist, patients often find them to be reluctant, mainly because clinicians are still not convinced by the existing evidence-based data to guide their treatment plans. Physicians should prescribe cannabis only if a careful explanation can be provided and follow up response evaluation ensured, making it mandatory for them to be up to date with the positive and also negative aspects of the cannabis in the case of cancer patients. Consequently, this article aims to bring some clarifications to clinicians regarding the sometimes-confusing various nomenclature under which this plant is mentioned, current legislation and the existing evidence (both preclinical and clinical) for the utility of cannabinoids in cancer patients, for either palliation of the associated symptoms or even the potential antitumor effects that cannabinoids may have.

A review of the effects of acute and chronic cannabinoid exposure on the stress response

While cannabis has been used for centuries for its stress-alleviating properties, the effects of acute and chronic cannabinoid exposure on responses to stress remain poorly understood. This review provides an overview of studies that measured stress-related endpoints following acute or chronic cannabinoid exposure in humans and animals. Acute cannabinoid exposure increases basal concentrations of stress hormones in rodents and humans and has dose-dependent effects on stress reactivity in humans and anxiety-like behavior in rodents. Chronic cannabis exposure is associated with dampened stress reactivity, a blunted cortisol awakening response (CAR), and flattened diurnal cortisol slope in humans. Sex differences in these effects remain underexamined, with limited evidence for sex differences in effects of cannabinoids on stress reactivity in rodents. Future research is needed to better understand sex differences in the effects of cannabis on the stress response, as well as downstream impacts on mental health and stress-related disorders.

Delta-Opioid Receptors Play a Role in the Control of Selected Parameters Related to Stress and Brain Plasticity Under Non-stress and/or Stress Conditions

There is some evidence that delta-opioid receptors may be involved in the brain processes related to neuroprotection. The aim of the present studies was to test the hypothesis that endogenous opioid peptides acting via delta-opioid receptors can protect against stress-induced changes in factors related to brain plasticity and stress hormone release. Forty male adult Wistar rats were used. Half of the animals were exposed to sustained partial restraint stress (hypokinesis) lasting 48 h. Rats were treated with vehicle (isotonic saline) or the delta-opioid receptor antagonist naltrindole (3 mg/kg/ml, s.c.) six times a day. The stressfulness of the model was confirmed by increased plasma concentrations of corticosterone and prolactin, the increase in anxiety behavior in the open field test, as well as the reduction of BrdU incorporation into newly formed DNA in the hippocampus. Treatment with naltrindole potentiated the stress-induced rise in aldosterone concentrations. The blockade of delta-opioid receptors resulted in a decrease in hippocampal BDNF gene expression independently of control or stress conditions. Treatment with naltrindole enhanced plasma concentrations of copeptin, a stable precursor of vasopressin. In conclusion, these results suggest that endogenous opioid peptides might play an inhibitory role in aldosterone release under stress conditions and in the control of vasopressin release independently of stress exposure. Endogenous opioids might stimulate hippocampal gene expression of the important neurotrophic factor BDNF via delta-opioid receptors.

Cannabis, a cause for anxiety? A critical appraisal of the anxiogenic and anxiolytic properties

BACKGROUND

Cannabis has been documented for use in alleviating anxiety. However, certain research has also shown that it can produce feelings of anxiety, panic, paranoia and psychosis. In humans, Δ9-tetrahydrocannabinol (THC) has been associated with an anxiogenic response, while anxiolytic activity has been attributed mainly to cannabidiol (CBD). In animal studies, the effects of THC are highly dose-dependent, and biphasic effects of cannabinoids on anxiety-related responses have been extensively documented. A more precise assessment is required of both the anxiolytic and anxiogenic potentials of phytocannabinoids, with an aim towards the development of the 'holy grail' in cannabis research, a medicinally-active formulation which may assist in the treatment of anxiety or mood disorders without eliciting any anxiogenic effects.

OBJECTIVES

To systematically review studies assessing cannabinoid interventions (e.g. THC or CBD or whole cannabis interventions) both in animals and humans, as well as recent epidemiological studies reporting on anxiolytic or anxiogenic effects from cannabis consumption.

METHOD

The articles selected for this review were identified up to January 2020 through searches in the electronic databases OVID MEDLINE, Cochrane Central Register of Controlled Trials, PubMed, and PsycINFO.

RESULTS

Acute doses of CBD were found to reduce anxiety both in animals and humans, without having an anxiogenic effect at higher doses. Epidemiological studies tend to support an anxiolytic effect from the consumption of either  CBD or THC, as well as whole plant cannabis. Conversely, the available human clinical studies demonstrate a common anxiogenic response to THC (especially at higher doses).

CONCLUSION

Based on current data, cannabinoid therapies (containing primarily CBD) may provide a more suitable treatment for people with pre-existing anxiety or as a potential adjunctive role in managing anxiety or stress-related disorders. However, further research is needed to explore other cannabinoids and phytochemical constituents present in cannabis (e.g. terpenes) as anxiolytic interventions. Future clinical trials involving patients with anxiety disorders are warranted due to the small number of available human studies.

Effects of early-life FGF2 on ultrasonic vocalizations (USVs) and the mu-opioid receptor in male Sprague-Dawley rats selectively-bred for differences in their response to novelty

In previous studies, early-life fibroblast growth factor-2 (FGF2) administration conferred resilience to developing anxiety-like behavior in vulnerable animals in adulthood. To follow up on this work, we administered FGF2 the day after birth to animals that differ in emotional behavior and further explored its long-term effects on affective behavior and circuitry. Selectively-bred "high responder" rats (bHRs) exhibit low levels of anxiety-like and depression-like behavior, whereas selectively-bred "low responders" (bLRs) display high levels of anxiety-like and depression-like behavior. We found that early-life administration of FGF2 decreased negative affect in bLRs during the early post-natal period, as indexed by 40 kHz ultrasonic vocalizations (USVs) in response to a brief maternal separation on PND11. FGF2 also increased positive affect during the juvenile period, as measured by 50 kHz USVs in response to heterospecific hand play ("tickling") after weaning. In general, we found that bHRs produced more 50 kHz USVs than bLRs. In adulthood, we measured opioid ligand and receptor expression in brain regions implicated in USV production and affect regulation by mRNA in situ hybridization. Within multiple affective brain regions, bHRs had greater expression of the mu opioid receptor than bLRs. FGF2 increased mu opioid expression in bLRs. The bLRs had more kappa and less delta receptor expression than bHRs, and FGF2 increased prodynorphin in bLRs. Our results provide support for further investigations into the role of growth factors and endogenous opioids in the treatment of disorders characterized by altered affect, such as anxiety and depression.

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

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

Buprenorphine, methadone, and morphine treatment during pregnancy: behavioral effects on the offspring in rats

Methadone and buprenorphine are widely used for treating people with opioid dependence, including pregnant women. Prenatal exposure to opioids has devastating effects on the development of human fetuses and may induce long-term physical and neurobehavioral changes during postnatal maturation. This study aimed at comparing the behavioral outcomes of young rats prenatally exposed to buprenorphine, methadone, and morphine. Pregnant Sprague-Dawley rats were administered saline, morphine, methadone, and buprenorphine during embryonic days 3-20. The cognitive function, social interaction, anxiety-like behaviors, and locomotor activity of offsprings were examined by novel object recognition test, social interaction test, light-dark transition test, elevated plus-maze, and open-field test between 6 weeks and 10 weeks of age. Prenatal exposure to methadone and buprenorphine did not affect locomotor activity, but significantly impaired novel object recognition and social interaction in both male and female offsprings in the same manner as morphine. Although prenatal exposure to methadone or buprenorphine increased anxiety-like behaviors in the light-dark transition in both male and female offsprings, the effects were less pronounced as compared to that of morphine. Methadone affected elevated plus-maze in both sex, but buprenorphine only affected the female offsprings. These findings suggest that buprenorphine and methadone maintenance therapy for pregnant women, like morphine, produced detrimental effects on cognitive function and social behaviors, whereas the offsprings of such women might have a lower risk of developing anxiety disorders.

The microinjection of a cannabinoid agonist into the accumbens shell induces anxiogenesis in the elevated plus-maze

This study investigated the effect of a cannabinoid agonist injected into the shell region of the nucleus accumbens (nAcb shell) on anxiety-related behaviors. The animals (male Wistar rats) were unilaterally microinjected with either ACEA (arachidonyl-2'-chloroethylamide a CB1 receptor agonist) at doses of 0.005, 0.05 or 0.5 pmol, or vehicle (ethanol 0.04% in saline 0.9%) and submitted to the elevated plus-maze (EPM), a pre-clinical test of anxiety. The data showed that rats microinjected with ACEA (0.05 pmol/0.2 μl) into the nAcb shell exhibited decreased % open arm time and open arm entries in comparison with the control group, which is compatible with an anxiogenic-like effect. To rule out the hypothesis that spread of the drug into the ventricle was responsible for the observed anxiogenic effect, 0.05 pmol ACEA was injected into the lateral ventricle and shown not to alter the responses representative of fear/anxiety and locomotion. The locomotor activity was not changed at the dose of 0.05 pmol ACEA microinjected into the nAcb shell. The present data suggest that activation of cannabinoid receptors in the nAcb shell may modulate fear/anxiety in the EPM.

Behavioral responses to acute and sub-chronic administration of the synthetic cannabinoid JWH-018 in adult mice prenatally exposed to corticosterone

Recent data indicate that both availability and consumption of synthetic and natural psychoactive substances, marketed under the name of "legal highs", has increased. Among them, the aminoalkylindole-derivative JWH-018 is widely distributed due to its capability of binding the cannabinoid receptors CB1 and CB2 thereby mimicking the effects of classical drug agonists. To address whether the behavioral effects of the synthetic compound JWH-018 are similar to those induced by classical cannabinoid agonists, we investigated, in outbred CD1 mice, the consequences of its acute and sub-chronic administration (0, 0.03, 0.1, or 0.3 mg/kg, IP) at the level of body temperature, pain perception, general locomotion, and anxiety. In order to address whether the exposure to precocious stressors-modified individual reactivity to this psychoactive substance, we also investigated its effects in adult mice previously exposed to prenatal stress in the form of corticosterone supplementation in the maternal drinking water (33 or 100 mg/L). In the absence of major effects on motor coordination, JWH-018-reduced body temperature, locomotion and pain reactivity, and increased indices of anxiety. Prenatal corticosterone administration-reduced individual sensitivity to the effects of JWH-018 administration in all the aforementioned parameters. This altered response is not due to variations in JWH-018 metabolism. Present data support the hypothesis that precocious stress may affect, in the long-term, the functional status, and reactivity of the endocannabinoid system.

Pharmacological effects of cannabinoids on the reference and working memory functions in mice

RATIONALE

Evidence indicates cannabinoid receptor agonists impair performance in procedures to assess memory that may also be confounded by motivational or motor effects, both of which occur with cannabinoids. Thus, convergence of evidence from a variety of procedures that differ in motivation, attention, arousal and response requirements, but share a common reliance on memory, is required. There are no current reports on cannabinoid effects on mice tested in the radial arm maze.

OBJECTIVES

The objective was to determine the effects of the cannabinoid agonist CP 55940 and the dependence of any such effects on the CB1 receptor using the CB1 receptor antagonist SR 141716A on two strains of mice in the eight-arm radial maze procedure.

METHODS

Male C57BL/6J (N = 36) and C3H/HEJ (N = 12) mice were trained to a criterion and then were treated (IP) with vehicle + vehicle, SR 141716A + vehicle, vehicle + CP 55940 and SR 141716A + CP 55940 in a fully balanced mixed design prior to further tests in the maze. Reference (long-term) and working (short-term) memory were assessed.

RESULTS

CP 55940 impaired performance of the reference memory task in the C57BL/6J strain but not the C3H/HEJ strain; SR 141716A reversed the effect of CP 55940 on these measures. CP 55940 also increased working memory errors in the C57BL/6J mice only, which was not affected by SR 141716A.

CONCLUSION

The present study provides evidence for a strain-specific effect of a dose of CP 55940 on reference memory. While the cannabinoid agonist also impaired working memory in one strain, this effect was apparently not mediated by CB1 receptors.

Case-control association analysis of polymorphisms in the δ-opioid receptor, OPRD1, with cocaine and opioid addicted populations

BACKGROUND

Addiction susceptibility and treatment responsiveness are greatly influenced by genetic factors. Sequence variation in genes involved in the mechanisms of drug action have the potential to influence addiction risk and treatment outcome. The opioid receptor system is involved in mediating the rewarding effects of cocaine and opioids. The μ-opioid receptor (MOR) has traditionally been considered the primary target for opioid addiction. The MOR, however, interacts with and is regulated by many known MOR interacting proteins (MORIPs), including the δ-opioid receptor (DOR).

METHODS

The present study evaluated the contribution of OPRD1, the gene encoding the DOR, to the risk of addiction to opioids and cocaine. The association of OPRD1 polymorphisms with both opioid addiction (OA) and cocaine addiction (CA) was analyzed in African American (OA n=336, CA n=503) and European American (OA n=1007, CA n=336) populations.

RESULTS

The primary finding of this study is an association of rs678849 with cocaine addiction in African Americans (allelic p=0.0086). For replication purposes, this SNP was analyzed in a larger independent population of cocaine addicted African Americans and controls and the association was confirmed (allelic p=4.53 × 10(-5); n=993). By performing a meta-analysis on the expanded populations, the statistical evidence for an association was substantially increased (allelic p=8.5 × 10(-7)) (p-values non-FDR corrected).

CONCLUSION

The present study suggests that polymorphisms in OPRD1 are relevant for cocaine addiction in the African American population and provides additional support for a broad role for OPRD1 variants in drug dependence.

Endocannabinoid system and psychiatry: in search of a neurobiological basis for detrimental and potential therapeutic effects

Public concern on mental health has noticeably increased given the high prevalence of neuropsychiatric disorders. Cognition and emotionality are the most affected functions in neuropsychiatric disorders, i.e., anxiety disorders, depression, and schizophrenia. In this review, most relevant literature on the role of the endocannabinoid (eCB) system in neuropsychiatric disorders will be presented. Evidence from clinical and animal studies is provided for the participation of CB1 and CB2 receptors (CB1R and CB2R) in the above mentioned neuropsychiatric disorders. CBRs are crucial in some of the emotional and cognitive impairments reported, although more research is required to understand the specific role of the eCB system in neuropsychiatric disorders. Cannabidiol (CBD), the main non-psychotropic component of the Cannabis sativa plant, has shown therapeutic potential in several neuropsychiatric disorders. Although further studies are needed, recent studies indicate that CBD therapeutic effects may partially depend on facilitation of eCB-mediated neurotransmission. Last but not least, this review includes recent findings on the role of the eCB system in eating disorders. A deregulation of the eCB system has been proposed to be in the bases of several neuropsychiatric disorders, including eating disorders. Cannabis consumption has been related to the appearance of psychotic symptoms and schizophrenia. In contrast, the pharmacological manipulation of this eCB system has been proposed as a potential strategy for the treatment of anxiety disorders, depression, and anorexia nervosa. In conclusion, the eCB system plays a critical role in psychiatry; however, detrimental consequences of manipulating this endogenous system cannot be underestimated over the potential and promising perspectives of its therapeutic manipulation.

Structure selectivity relationship studies of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)carboxamido]morphinan derivatives toward the development of the mu opioid receptor antagonists

Mu opioid receptor antagonists have been applied to target a variety of diseases clinically. The current study is designed to explore the structure selectivity relationship (SSR) of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)carboxamido]morphinan (NAP), a lead compound identified as a selective mu opioid receptor antagonist based on the previous study. Among a series of NAP derivatives synthesized, compounds 6 (NMP) and 9 (NGP) maintained comparable binding affinity, selectivity and efficacy to the lead compound. Particularly, the mu opioid receptor selectivity over kappa opioid receptor of NGP was considerably enhanced compared to that of NAP. Overall, the preliminary SSR supported our original hypothesis that an alternate 'address' domain may exist in the mu opioid receptor, which favors the ligands carrying a hydrogen bond acceptor and an aromatic system to selectively recognize the mu opioid receptor.

Methamphetamine neurotoxicity increases brain expression and alters behavioral functions of CB₁ cannabinoid receptors

Cannabis is the most common secondary illicit substance in methamphetamine (METH) users, yet the outcomes of the concurrent consumption of both substances remain elusive. Capitalizing on recent findings on the implication of CB₁ cannabinoid receptors in the behavioral effects of METH, we hypothesized that METH-induced neurotoxicity may alter the brain expression of CB₁, thereby affecting its role in behavioral functions. To test this possibility, we subjected rats to a well-characterized model of METH neurotoxicity (4 mg/kg, subcutaneous × 4 injections, 2 h apart), and analyzed their CB₁ receptor brain expression three weeks later. METH exposure resulted in significant enhancements of CB₁ receptor expression across several brain regions, including prefrontal cortex, caudate-putamen, basolateral amygdala, CA1 hippocampal region and perirhinal cortex. In parallel, a different group of METH-exposed rats was used to explore the responsiveness to the potent cannabinoid agonist WIN 55,212-2 (WIN) (0.5-1 mg/kg, intraperitoneal), within several paradigms for the assessment of emotional and cognitive functions, such as open field, object exploration and recognition, and startle reflex. WIN induced anxiolytic-like effects in METH-exposed rats and anxiogenic-like effects in saline-treated controls. Furthermore, METH-exposed animals exhibited a significantly lower impact of WIN on the attenuation of exploratory behaviors and short-term (90 min) recognition memory. Conversely, METH neurotoxicity did not significantly affect WIN-induced reductions in locomotor activity, exploration time and acoustic startle. These results suggest that METH neurotoxicity may alter the vulnerability to select behavioral effects of cannabis, by inducing distinct regional variations in the expression of CB₁ receptors.

Vulnerability Factors for the Psychiatric and Behavioral Effects of Cannabis

Cogent evidence shows that cannabis plays a variable role on behavioral regulation and the pathophysiology of most psychiatric conditions. Accordingly, cannabis has been alternatively shown to exacerbate or ameliorate mental symptoms, depending on its composition and route of consumption, as well as specific individual and contextual characteristics. The vulnerability to the psychological effects of cannabis is influenced by a complex constellation of genetic and environmental factors. In the present article, we will review the current evidence on the pharmacological, individual and situational factors that have been documented to affect the behavioral and psychiatric effects of cannabinoids.

Effects of delta9-tetrahydrocannabinol on reward and anxiety in rats exposed to chronic unpredictable stress

Although cannabis derivatives produce clear subjective motivational responses in humans leading to drug-seeking behaviour, the reinforcing attributes of these subjective effects are difficult to define in experimental animals. The aim of this study was to examine how exposure to chronic unpredictable stress (CUS) will affect reward function and anxiety after acute administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) in rats. Male rats were exposed to either 10 days of CUS or no stressor. Alterations in brain reward function were assessed with the intracranial self-stimulation (ICSS) paradigm, and anxiety responses were measured with the elevated plus maze. CUS did not affect baseline brain stimulation reward thresholds. Delta(9)-THC did not exhibit reinforcing actions in the ICSS paradigm neither in nonstressed nor in stressed animals. More importantly, in nonstressed animals, both the low and the high dose of Delta(9)-THC exerted anxiolytic-like effects. In stressed animals, however, only the high dose of THC induced an anxiolytic-like response, whereas the low dose induced anxiogenic effects. The present results provide clear evidence for an anxiolytic effect of Delta(9)-THC both in stressed and in nonstressed animals, and indicate that environmental conditions, such as stressful experiences, do not alter the behavioural effects of Delta( 9)-THC in the ICSS paradigm.

Cocaine withdrawal-induced anxiety in females: impact of circulating estrogen and potential use of delta-opioid receptor agonists for treatment

Sex differences in cocaine addiction warrants further research focused on examining the growing population of female cocaine addicts. As demonstrated in both clinical and preclinical research, females are more susceptible to drug relapse with anxiety being a contributing factor. In support of this, a recent clinical study from our laboratory highlights the importance of menstrual cycle phase and anxiety at treatment admission for cocaine addiction on treatment retention. In support of these trends in the clinical population, the purpose of the present study was to design an animal model to directly test the role of circulating hormone levels during cocaine withdrawal. To directly measure the influence of estrogen on anxiety-like behavior during early stages of withdrawal, both ovariectomized and intact female rodent models were employed. The elevated-plus maze and elevated-zero maze were used to assess anxiety-like behavior. Recent evidence in male rodents highlights a potential role for the delta opioid-receptor (DOR) system in the modulation of cocaine withdrawal-induced anxiety. In addition to the evaluation of hormonal effects, a potential anxiolytic specific for DOR was tested for its efficacy in females withdrawn from cocaine. Our results support the use of DOR agonists as a potential anxiolytic in females and highlight the importance of estrogen and other circulating hormones during all phases of cocaine addiction.

Converging action of alcohol consumption and cannabinoid receptor activation on adult hippocampal neurogenesis

Alcoholism is characterized by successive periods of abstinence and relapse, resulting from long-lasting changes in various circuits of the central nervous system. Accumulating evidence points to the endocannabinoid system as one of the most relevant biochemical systems mediating alcohol addiction. The endocannabinoid system regulates adult neurogenesis, a form of long-lasting adult plasticity that occurs in a few areas of the brain, including the dentate gyrus. Because exposure to psychotropic drugs regulates adult neurogenesis, it is possible that neurogenesis might be implicated in the pathophysiology, and hence treatment, of neurobiological illnesses related to drugs of abuse. Here, we investigated the sensitivity of adult hippocampal neurogenesis to alcohol and the cannabinoid receptor agonist WIN 55,212-2 (WIN). Specifically, we analysed the potential link between alcohol relapse, cannabinoid receptor activation, and adult neurogenesis. Adult rats were exposed to subchronic alcohol binge intoxication and received the cannabinoid receptor agonist WIN. Another group of rats were subjected to an alcohol operant self-administration task. Half of these latter animals had continuous access to alcohol, while the other half were subjected to alcohol deprivation, with or without WIN administration. WIN treatment, when administered during alcohol deprivation, resulted in the greatest increase in alcohol consumption during relapse. Together, forced alcohol binge intoxication and WIN administration dramatically reduced hippocampal neurogenesis. Furthermore, adult neurogenesis inversely correlated with voluntary consumption of alcohol. These findings suggest that adult hippocampal neurogenesis is a key factor involved in drug abuse and that it may provide a new strategy for the treatment of alcohol addiction and dependence.

30 years of dynorphins--new insights on their functions in neuropsychiatric diseases

Since the first description of their opioid properties three decades ago, dynorphins have increasingly been thought to play a regulatory role in numerous functional pathways of the brain. Dynorphins are members of the opioid peptide family and preferentially bind to kappa opioid receptors. In line with their localization in the hippocampus, amygdala, hypothalamus, striatum and spinal cord, their functions are related to learning and memory, emotional control, stress response and pain. Pathophysiological mechanisms that may involve dynorphins/kappa opioid receptors include epilepsy, addiction, depression and schizophrenia. Most of these functions were proposed in the 1980s and 1990s following histochemical, pharmacological and electrophysiological experiments using kappa receptor-specific or general opioid receptor agonists and antagonists in animal models. However, at that time, we had little information on the functional relevance of endogenous dynorphins. This was mainly due to the complexity of the opioid system. Besides actions of peptides from all three classical opioid precursors (proenkephalin, prodynorphin, proopiomelanocortin) on the three classical opioid receptors (delta, mu and kappa), dynorphins were also shown to exert non-opioid effects mainly through direct effects on NMDA receptors. Moreover, discrepancies between the distribution of opioid receptor binding sites and dynorphin immunoreactivity contributed to the difficulties in interpretation. In recent years, the generation of prodynorphin- and opioid receptor-deficient mice has provided the tools to investigate open questions on network effects of endogenous dynorphins. This article examines the physiological, pathophysiological and pharmacological implications of dynorphins in the light of new insights in part obtained from genetically modified animals.

Endocannabinoid-mediated control of synaptic transmission

The discovery of cannabinoid receptors and subsequent identification of their endogenous ligands (endocannabinoids) in early 1990s have greatly accelerated research on cannabinoid actions in the brain. Then, the discovery in 2001 that endocannabinoids mediate retrograde synaptic signaling has opened up a new era for cannabinoid research and also established a new concept how diffusible messengers modulate synaptic efficacy and neural activity. The last 7 years have witnessed remarkable advances in our understanding of the endocannabinoid system. It is now well accepted that endocannabinoids are released from postsynaptic neurons, activate presynaptic cannabinoid CB(1) receptors, and cause transient and long-lasting reduction of neurotransmitter release. In this review, we aim to integrate our current understanding of functions of the endocannabinoid system, especially focusing on the control of synaptic transmission in the brain. We summarize recent electrophysiological studies carried out on synapses of various brain regions and discuss how synaptic transmission is regulated by endocannabinoid signaling. Then we refer to recent anatomical studies on subcellular distribution of the molecules involved in endocannabinoid signaling and discuss how these signaling molecules are arranged around synapses. In addition, we make a brief overview of studies on cannabinoid receptors and their intracellular signaling, biochemical studies on endocannabinoid metabolism, and behavioral studies on the roles of the endocannabinoid system in various aspects of neural functions.

Chronic unpredictable stress enhances cocaine-conditioned place preference in type 1 cannabinoid receptor knockout mice

Cannabinoid signaling via the type 1 cannabinoid (CB1) receptor modulates the effects of drugs of abuse and the response to exposure to stressors. In addition, exposure to stressors can alter the effects of drugs of abuse. This study examined the effects of exposure to chronic unpredictable stress (CUS) in CB1 receptor knockout (CB1 KO) mice and their wild-type (WT) littermates, using cocaine-conditioned place preference (CPP) to compare their response to cocaine. Mice were untreated or exposed to 2 weeks of CUS. After this period, the acquisition of a cocaine CPP was examined with one of three doses (3.2, 10.0, or 17.0 mg/kg) of cocaine. Untreated CB1 KO and WT mice both acquired the cocaine CPP; however, exposure to CUS enhanced the acquisition of the cocaine CPP in CB1 KO mice, but did not significantly alter the effects of cocaine in WT mice. Taken together, these findings support earlier evidence suggesting a role for the CB1 receptor in the response to stress as well as in the effects of cocaine.

Antiaversive effects of cannabinoids: is the periaqueductal gray involved?

Cannabinoids play an important role in activity-dependent changes in synaptic activity and can interfere in several brain functions, including responses to aversive stimuli. The regions responsible for their effects, however, are still unclear. Cannabinoid type 1 (CB1) receptors are widely distributed in the central nervous system and are present in the periaqueductal gray (PAG), a midbrain structure closely involved in responses related to aversive states. Accordingly, exposure to stressful stimuli increases endocannabinoid (eCB) levels in the PAG, and local administration of CB1 agonists or drugs that facilitate eCB-mediated neurotransmission produces antinociceptive and antiaversive effects. To investigate if these drugs would also interfere in animal models that are sensitive to anxiolytic drugs, we verified the responses to intra-PAG injection of CB1 agonists in rats submitted to the elevated plus-maze, the Vogel punished licking test, or contextual aversive conditioning model. The drugs induced anxiolytic-like effects in all tests. The same was observed with the transient receptor potential vanilloid type 1 (TRPV1) antagonist capsazepine and with cannabidiol, a nonpsychotomimetic phytocannabinoid that produces anxiolytic-like effects after systemic administration in humans and laboratory animals. These results, therefore, suggest that the PAG could be an important site for the antiaversive effects of cannabinoids.

Advances in the field of cannabinoid--opioid cross-talk

A remarkable amount of literature has been generated demonstrating the functional similarities between the endogenous opioid and cannabinoid systems. Anatomical, biochemical and molecular data support the existence of reciprocal interactions between these two systems related to several pharmacological responses including reward, cognitive effects, and the development of tolerance and dependence. However, the assessment of the bidirectionality of these effects has been difficult due to their variety and complexity. Reciprocal interactions have been well established for the development of physical dependence. Cross-tolerance and cross-sensitization, although not always bidirectional, are also supported by a number of evidence, while less data have been gathered regarding the relationship of these systems in cognition and emotion. Nevertheless, the most recent advances in cannabinoid-opioid cross-modulation have been made in the area of drug craving and relapse processes. The present review is focused on the latest developments in the cannabinoid-opioid cross-modulation of their behavioural effects and the possible neurobiological substrates involved.

Withdrawal from chronic administration of cocaine decreases delta opioid receptor signaling and increases anxiety- and depression-like behaviors in the rat

Chronic administration of cocaine has been shown to attenuate the functional capacity of delta opioid receptors to inhibit adenylyl cyclase activity. Abuse and withdrawal from cocaine in humans is associated with increases in anxiety and depression. Since recent research supports the role of delta opioid receptors in anxiety- and depression-like behaviors in rodents, we hypothesized that functional desensitization of delta opioid receptors contributes to anxiety- and depression-like behavioral phenotypes following short-term withdrawal from chronic administration of cocaine. To test this hypothesis, delta opioid receptor signaling and behaviors were evaluated 24h after 14days of binge-pattern cocaine administration (15mg/kg three times daily at 1h intervals) in male Sprague-Dawley rats. Results showed that the inhibition of adenylyl cyclase by delta opioid receptor agonists was attenuated in the frontal cortex, nucleus accumbens and caudate putamen 24h after cessation of cocaine administration. One day withdrawal from chronic administration of cocaine resulted in increased anxiety- and depression-like behaviors as measured by the elevated plus maze and the forced swim test respectively, and no change in locomotor activity. The anxiety- and depression-like behaviors were dose-dependently reduced by acute administration of the selective delta opioid receptor agonist, SNC80. These results demonstrate that early withdrawal from cocaine resulted in increased anxiety and depression, which accompanies the desensitization of delta opioid receptor function. Furthermore, cocaine-induced anxiety- and depression-like behaviors were reversible by the delta opioid receptor agonist SNC80.

Endocannabinoid system and synaptic plasticity: implications for emotional responses

The endocannabinoid system has been involved in the regulation of anxiety, and proposed as an inhibitory modulator of neuronal, behavioral and adrenocortical responses to stressful stimuli. Brain regions such as the amygdala, hippocampus and cortex, which are directly involved in the regulation of emotional behavior, contain high densities of cannabinoid CB1 receptors. Mutant mice lacking CB1 receptors show anxiogenic and depressive-like behaviors as well as an altered hypothalamus pituitary adrenal axis activity, whereas enhancement of endocannabinoid signaling produces anxiolytic and antidepressant-like effects. Genetic and pharmacological approaches also support an involvement of endocannabinoids in extinction of aversive memories. Thus, the endocannabinoid system appears to play a pivotal role in the regulation of emotional states. Endocannabinoids have emerged as mediators of short- and long-term synaptic plasticity in diverse brain structures. Despite the fact that most of the studies on this field have been performed using in vitro models, endocannabinoid-mediated plasticity might be considered as a plausible candidate underlying some of the diverse physiological functions of the endogenous cannabinoid system, including developmental, affective and cognitive processes. In this paper, we will focus on the functional relevance of endocannabinoid-mediated plasticity within the framework of emotional responses. Alterations of the endocannabinoid system may constitute an important factor in the aetiology of certain neuropsychiatric disorders, and, in turn, enhancers of endocannabinoid signaling could represent a potential therapeutical tool in the treatment of both anxiety and depressive symptoms.

The role of the hippocampus in mediating emotional responses to nicotine and cannabinoids: a possible neural substrate for functional interactions

The endocannabinoid system is involved in the regulation of behavioural and physiological stress-related responses. Nicotine exerts complex effects on emotional behaviour, and its withdrawal may result in depressive and anxiogenic-like symptoms. Cannabinoid receptor agonists and nicotine induce biphasic effects in diverse tests of unconditioned anxiety, alter adrenocortical activity and affect hippocampus-dependent contextual fear conditioning. Upon exposure to stressful stimuli, central endocannabinoid and cholinergic systems appear to be activated in key limbic areas such as hippocampus and amygdala, which might contribute to adaptive cognitive and emotional strategies to cope with aversive situations. Numerous studies indicate the existence of functional interactions between nicotine and cannabinoids, particularly in relation to anxiety-related processes. An overlapping distribution of CB1 and nicotinic acetylcholine receptors in the hippocampus is observed and the endocannabinoid system exerts a modulatory role over the hippocampal cholinergic system. In this review, we point to the hippocampus as a relevant neural substrate for cannabinoid-nicotine interactions, notably as regards emotional responses. After a general description of the cannabinoid and nicotinic systems, we review their implications in unconditioned anxiety, depressive-like behaviour and fear conditioning. Then we discuss the role of both systems in modulating stress-induced changes at cellular, endocrine and behavioural levels and their possible involvement in hippocampal neurogenesis. Although we mainly focus on animal data, some relevant human studies are also discussed.

Cellular mechanisms underlying the anxiolytic effect of low doses of peripheral Delta9-tetrahydrocannabinol in rats

We investigated the effect of low doses of intraperitoneal Delta(9)-tetrahydrocannabinol (THC) on anxiety behavior in rats using the elevated plus maze (EPM). An anxiolytic effect was obtained in a range of doses between 0.075 and 1.5 mg/kg, the 0.75 dose being the most effective. Pretreatment with the CB1 receptor antagonist AM251 fully reversed THC's effect, suggesting CB1 receptors were involved. In order to elucidate the neuroanatomical substrates underlying the effect of the maximal effective dose of THC, we investigated cFos expression in anxiety-related brain regions (prefrontal cortex, nucleus accumbens, amygdala, and hippocampus) of rats exposed to the EPM. THC significantly lowered the amount of cFos in prefrontal cortex and amygdala without affecting the other cerebral areas. As there is increasing evidence that CREB function regulates anxiety-like behavior in rats, the second biochemical parameter we measured was phosphorylated CREB in the same brain areas. Rats treated with THC showed a significant increase in CREB activation in the prefrontal cortex and hippocampus. In the prefrontal cortex this increased activation was linked to an increase in ERK activation, whereas in the hippocampus there was a drop in the activity of CAMKII, a kinase with inhibitory effect on CREB activation. All these effects were reversed by AM251 pretreatment, suggesting that stimulation of CB1 receptors is fundamental for triggering the biochemical events. Our results suggest that the stimulation of these receptors in the prefrontal cortex, amygdala, and hippocampus with the subsequent activation of different signaling pathways is the first event underlying the effects of cannabinoids on anxious states.

Correlated species differences in the effects of cannabinoid ligands on anxiety and on GABAergic and glutamatergic synaptic transmission

Cannabinoid ligands show therapeutic potential in a variety of disorders including anxiety. However, the anxiety-related effects of cannabinoids remain controversial as agonists show opposite effects in mice and rats. Here we compared the effects of the cannabinoid agonist WIN-55,212 and the CB1 antagonist AM-251 in CD1 mice and Wistar rats. Special attention was paid to antagonist–agonist interactions, which had not yet been studied in rats. In mice, WIN-55,212 decreased whereas AM-251 increased anxiety. The antagonist abolished the effects of the agonist. In contrast, WIN-55,212 increased anxiety in rats. Surprisingly, the antagonist potentiated this effect. Cannabinoids affect both GABAergic and glutamatergic functions, which play opposite roles in anxiety. We hypothesized that discrepant findings resulted from species differences in the relative responsiveness of the two transmitter systems to cannabinoids. We investigated this hypothesis by studying the effects of WIN-55,212 on evoked hippocampal inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs). IPSCs were one order of magnitude more sensitive to WIN-55,212 in mice than in rats. In mice, IPSCs were more sensitive than EPSCs to WIN-55,212. This is the first study showing that the relative cannabinoid sensitivity of GABA and glutamate neurotransmission is species-dependent. Based on behavioural and electrophysiological findings, we hypothesize that WIN-55,212 reduced anxiety in mice by affecting GABA neurotransmission whereas it increased anxiety in rats via glutamatergic mechanisms. In rats, AM-251 potentiated this anxiogenic effect by inhibiting the anxiolytic GABAergic mechanism. We suggest that the anxiety-related effects of cannabinoids depend on the relative cannabinoid responsiveness of GABAergic and glutamatergic neurotransmission.

CB1 receptor stimulation in specific brain areas differently modulate anxiety-related behaviour

There is a general consensus that the effects of cannabinoid agonists on anxiety seem to be biphasic, with low doses being anxiolytic and high doses ineffective or possibly anxiogenic. Besides the behavioural effects of cannabinoids on anxiety, very few papers have dealt with the neuroanatomical sites of these effects. We investigated the effect on rat anxiety behavior of local administration of THC in the prefrontal cortex, basolateral amygdala and ventral hippocampus, brain regions belonging to the emotional circuit and containing high levels of CB1 receptors. THC microinjected at low doses in the prefrontal cortex (10 microg) and ventral hippocampus (5 microg) induced in rats an anxiolytic-like response tested in the elevated plus-maze, whilst higher doses lost the anxiolytic effect and even seemed to switch into an anxiogenic profile. Low THC doses (1 microg) in the basolateral amygdala produced an anxiogenic-like response whereas higher doses were ineffective. All these effects were CB1-dependent and closely linked to modulation of CREB activation. Specifically, THC anxiolytic activity in the prefrontal cortex and ventral hippocampus was paralleled by an increase in CREB activation, whilst THC anxiogenic response in the basolateral amygdala was paralleled by a decrease in CREB activation. Our results suggest that while a mild activation of CB1 receptors in the prefrontal cortex and ventral hippocampus attenuates anxiety, a slight CB1 receptor stimulation in the amygdala results in an anxiogenic-like response. The molecular underpinnings of these effects involve a direct stimulation of CB1 receptors ending in pCREB modulation and/or a possible alteration in the fine tuning of local neuromodulator release.

Previous exposure to THC alters the reinforcing efficacy and anxiety-related effects of cocaine in rats

The hypothesis that prior cannabis exposure increases the likelihood of becoming addicted to other drugs can be evaluated by giving rats a history of tetrahydrocannabinol (THC) exposure, then allowing them to self-administer other drugs. In Experiment 1, THC pre-exposure did not alter the acquisition of cocaine self-administration or the amount of cocaine taken under a fixed-ratio 1 (FR1) schedule, with one response required for each injection. Under a progressive-ratio schedule, with the response requirement increasing exponentially with each injection, cocaine-seeking was significantly reduced in THC-exposed rats, suggesting that the regimen of THC exposure used in the present study caused cocaine to be devalued as a reinforcer. In contrast, in an earlier study that used the same regimen, a history of THC exposure did not alter the value of heroin as a reinforcer under the progressive-ratio schedule, but it increased heroin self-administration under the FR1 schedule. Experiment 2 examined how this regimen of THC pre-exposure alters the locomotor effects of cocaine and heroin. THC pre-exposure produced cross-tolerance to the motor-depressant effects of heroin; this may explain the shortened post-injection pauses exhibited by THC-exposed rats under FR1 heroin self-administration. When given cocaine, THC-exposed rats exhibited normal increases in locomotion, but they avoided the center of the open field, suggesting that this THC pre-exposure regimen enhances the anxiogenic effects of cocaine. This enhanced anxiogenic effect-which was verified in Experiment 3 using another model of anxiety, the light-dark test-may explain the reduced reinforcing value of cocaine observed in THC-exposed rats in Experiment 1.

Delta opioid receptor ligands modulate anxiety-like behaviors in the rat

The role of the delta opioid receptor in regulating anxiety-like behavior in male Sprague-Dawley rats was examined. Using an elevated plus maze, the effects of the selective delta opioid receptor antagonist naltrindole (1 or 5 mg kg(-1)) and agonist SNC80 (1, 5 or 20 mg kg(-1)) on anxiety-like behavior were measured. Anxiety was also measured following administration of diazepam (3 mg kg(-1)) and amphetamine (1 mg kg(-1)) and compared to the effects of SNC80. Locomotor activity following administration of naltrindole, SNC80, diazepam, and amphetamine was measured. Finally, the defensive burying paradigm was used to confirm the findings from the elevated plus maze. Results demonstrated that SNC80 produced dose-dependent anxiolytic effects similar to that of the classical antianxiety agent, diazepam. Administration of naltrindole caused anxiogenic behavior in rats further supporting the involvement of the delta opioid receptor system in regulating anxiety. Naltrindole also blocked the anxiolytic effects of SNC80. Amphetamine had no effect on anxiety-like behavior. SNC80 induced hyperactivity similar to amphetamine at the doses tested, while naltrindole and diazepam did not significantly affect locomotor activity. Although SNC80 can increase locomotor activity, control experiments reported herein indicate that hyperlocomotion is not sufficient to produce an anxiolytic response on the elevated plus maze. Together with the results from the defensive burying paradigm, this suggests that the effects of SNC80 on reducing anxiety are independent of its effects on locomotion. Collectively these data show that the delta opioid receptor system can regulate anxiety-like behavior in an anxiolytic (agonist) and anxiogenic (antagonist) manner.

Interactions of buprenorphine and dipotassium clorazepate on anxiety and memory functions in the mouse

Buprenorphine, a partial mu-receptor agonist widely substituted for heroin in the treatment of addiction, is often misused in combination with benzodiazepines. Improved hedonic properties may result, but only at the cost of increased buprenorphine toxicity. In order to elucidate the appeal of the benzodiazepine-buprenorphine combination, the present study looked at its neuropsycho-pharmacological effects on various emotional and cognitive parameters in the mouse. On the basis of previous dose-response studies, the regimen used was buprenorphine 0.3mg/kg, s.c. plus dipotassium clorazepate 1, 4 and 16 mg/kg, i.p. Anxiety-like behaviour was assessed using the black and white test box, and memory processes were examined via the spontaneous alternation paradigm in the Y-maze, and passive avoidance tests. Spontaneous locomotor activity was also evaluated. High doses of clorazepate impaired buprenorphine-induced hyperactivity and anxiogenic-like effects. They also increased buprenorphine-induced spontaneous alternation impairment, but did not modify its impact on long-term memory processes. These results suggest that the positive reinforcement experienced with the buprenorphine-benzodiazepine combination may be attributable, at least in part, to an increase in buprenorphine's sedative effect associated with a decrease in anxiogenicity.

5-HT1A receptors are involved in the anxiolytic effect of Delta9-tetrahydrocannabinol and AM 404, the anandamide transport inhibitor, in Sprague-Dawley rats

The mechanism mediating the effects of cannabinoids on anxiety-related responses appear to involve cannabinoid CB1 and non-CB1 receptors. However, other neurotransmitters may play a role in such effect. This study shows evidence of an interaction between endocannabinoid system and serotonin (5-HT), 1A receptor subtype on anxiety-like behavior in Sprague-Dawley rats. The exogenous cannabinoid agonist, Delta9-tetrahydrocannabinol (THC), and N-(4-hydroxyphenyl)-arachidonylamide, the anandamide transporter inhibitor (AM 404) were evaluated in the elevated plus maze test. THC (0.075-0.75 mg/kg i.p.), given 30 min and AM 404 (0.75-1.25 mg/kg i. p.), given 60 min before the test, exhibited a dose-response anxiolytic effect evaluated in terms of increase in the percentage of total entries and time spent in the open and decrease of total entries and time spent in the closed arms. The anxiolytic effect obtained with the maximal active dose of both THC (0.75 mg/kg) and AM 404 (1.25 mg/kg) was blocked by the 5-HT1A receptor antagonist, N-[2-[4-(2-methoxyphenyl) piperazin-1-yl]ethyl]-N-pyridin-2-yl-cyclohexanecarboxamide dihydro chloride (WAY-100635 (300 microg/kg, s.c.), given 30 min before THC or 15 min before AM 404. The combination of an ineffective dose of THC (0.015 mg/kg) or AM 404 (0.015 mg/kg) on anxiety-related responses with an ineffective dose of the 5HT(1A) receptor agonist, 8-Hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT) (7.5 microg/kg, i.p.), led to a synergistic effect. No interference with spontaneous motor activity, evaluated in an activity cage for 5 min, in rats given the drugs alone or in combination, was found. These data suggest that the anxiolytic effect produced by endo- and eso-cannabinoids is modulated by 5-HT1A receptors.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Involvement of kappa/dynorphin system in WIN 55,212-2 self-administration in mice

Self-administration procedures have not yet provided evidence that freely moving mice can reliably acquire and maintain an operant behavior to self-administer cannabinoid agonists. The aim of the present work was to establish a model of cannabinoid operant intravenous self-administration in freely moving mice given the relevance of this species for the use of genetically modified animals. In addition, the possible involvement of the kappa/dynorphin system in cannabinoid self-administration was evaluated by using pro-dynorphin knockout mice. Outbred CD1 wild-type mice as well as pro-dynorphin knockout and wild-type mice were trained to self-administer the cannabinoid receptor agonist WIN 55,212-2 under an FR1 schedule of reinforcement. Two cannabinoid training doses (6.25 and 12.5 microg/kg/infusion) were used in the acquisition studies in outbred mice. Animals acquired a reliable operant responding to self-administer WIN 55,212-2 (12.5 microg/kg/infusion), but required as many as 15 sessions to attain this behavior. Interestingly, when a previous injection of WIN 55,212-2 (0.1 mg/kg, i.p.) was administered in the home-cage 24 h before the first session, mice acquired operant responding for cannabinoid self-administration by the fourth session. When the kappa-opioid agonist antagonist nor-binaltorphimine (5 mg/kg s.c.) was administered 4 h before the first session, the time required to acquire a reliable cannabinoid self-administration was also significantly reduced. Finally, a shift to the left in the dose-intake curve to self-administer WIN 55,212-2 was observed in pro-dynorphin knockout mice when compared to wild-type mice. These results indicate that the activation of the kappa/dynorphin opioid system after WIN 55,212-2 administration could counteract cannabinoid rewarding effects.

Adolescent exposure to nicotine modifies acute functional responses to cannabinoid agonists in rats

We have studied functional interactions between nicotine and the cannabinoid receptor agonist CP 55,940 (CP) in the modulation of behavioural and corticosterone responses of male and female adolescent Wistar rats. The animals underwent a subchronic nicotine treatment (0.4 mg/kg i.p., once daily) during the periadolescent period (postnatal days 34-43). Twenty-four hours after the last injection of nicotine an acute dose of CP (1 or 100 microg/kg i.p.) was administered. Thirty minutes after the cannabinoid injection, the animals were tested individually in the holeboard immediately followed by the elevated plus-maze. We also measured corticosterone levels by radioimmunoassay. In males, neither CP (1 microg/kg) nor nicotine induced any modification in anxiety when administered alone. However, the combination of the two drugs resulted in a significant anxiogenic-like effect. In females, the lower dose of CP was anxiogenic and nicotine, which did not induce any effect per se, prevented this response. In the holeboard, subchronic nicotine and the acute cannabinoid treatment interacted in the modulation of horizontal activity and the nature of this interaction also showed a clear sexual dimorphism. Both, the cannabinoid agonist and nicotine increased corticosterone concentrations and the animals receiving the two drugs showed higher levels than the animals receiving the cannabinoid alone. The data provide evidence for the existence of functional interactions between nicotine and cannabinoids in the modulation of behavioural responses and adrenocortical activity in adolescent rats.

Atypical anxiolytic-like response to naloxone in benzodiazepine-resistant 129S2/SvHsd mice: role of opioid receptor subtypes

RATIONALE

Mice of many 129 substrains respond to environmental novelty with behavioural suppression and high levels of anxiety-like behaviour. Although resistant to conventional anxiolytics, this behavioural phenotype may involve stress-induced release of endogenous opioids.

OBJECTIVES

To assess the effects of opioid receptor blockade on behavioural reactions to novelty stress in a chlordiazepoxide-resistant 129 substrain.

MATERIALS AND METHODS

Experiment 1 contrasted the effects of the broad-spectrum opioid receptor antagonist naloxone (1.0-10.0 mg/kg) in C57BL/6JOlaHsd and 129S2/SvHsd mice exposed to the elevated plus-maze. Experiments 2-4 examined the responses of 129S2/SvHsd mice to the mu-selective opioid receptor antagonist beta-funaltrexamine (2.5-10.0 mg/kg), the delta-selective antagonist naltrindole (2.5-10.0 mg/kg) and the kappa-selective antagonist nor-binaltorphimine (2.5-5.0 mg/kg).

RESULTS

129 mice displayed higher levels of anxiety-like behaviour and lower levels of general exploration relative to their C57 counterparts. Although naloxone failed to alter the behaviour of C57 mice, both doses of this antagonist produced behaviourally selective reductions in open-arm avoidance in 129 mice. Surprisingly, none of the more selective opioid receptor antagonists replicated this effect of naloxone: beta-funaltrexamine was devoid of behavioural activity, naltrindole suppressed rearing (all doses) and increased immobility (10 mg/kg), while nor-binaltorphimine (5 mg/kg) nonspecifically increased percent open arm entries.

CONCLUSIONS

Recent evidence suggests differential involvement of opioid receptor subtypes in the anxiolytic efficacy of diverse compounds including conventional benzodiazepines. The insensitivity of 129 mice to the anxiolytic action of chlordiazepoxide, coupled with their atypical anxiolytic response to naloxone (but not more selective opioid receptor antagonists), suggests an abnormality in anxiety-related neurocircuitry involving opioid-GABA interactions.

Increased sensitivity to restraint stress and novelty-induced emotionality following long-term, high dose cannabinoid exposure

Cannabinoids have long been known to affect anxiety, emotionality and stress responsivity; however, the direction of this effect has been controversial. This research aimed to compare the effects of chronic administration of both a very low dose (5 microg/kg) and a very high dose (100 microg/kg) of the potent cannabinoid CB(1) receptor agonist HU-210 on emotionality and stress responsivity. Twelve day administration of the high dose of HU-210 increased anxiety-like behavior as indicated by a significant reduction in time spent in the central quadrant and an increase in fecal boli in the open field test. However, neither dose of HU-210 elicited any significant behavioral effect in the elevated plus maze. Stress responsivity appeared to be sensitized in animals that had received high dose HU-210 treatment, as 30 min of restraint resulted in significantly higher plasma corticosterone levels in these subjects than in stressed controls or those receiving the low dose treatment. Furthermore, restraint stress elicited a non-significant increase in c-fos induction in the central amygdala, which was significantly potentiated following high-dose treatment with HU-210. This interaction was not seen in the basolateral amygdala. Together, these findings suggest that chronic high dose, but not low dose, cannabinoid administration may result in increased emotionality and sensitization of the stress axis.

Role of delta-opioid receptor subtypes in anxiety-related behaviors in the elevated plus-maze in rats

RATIONALE

Recent studies have shown that endogenous opioid systems are associated with the regulation of emotional responses. In particular, it has been reported that delta-opioid receptors act naturally to inhibit stress and anxiety.

OBJECTIVE

The present study was designed to examine the possible involvement of opioid delta-receptor subtypes in the anxiety-related behavior in the elevated-plus-maze test.

METHODS

Six-week-old male Lewis rats were used. The total numbers of visits to the closed and open arms and the cumulative time spent and visits in the open arms were determined. Plasma corticosterone levels were measured by enzyme immunoassay.

RESULTS

Naltrindole (NTI), a delta-opioid receptor antagonist (3 mg/kg s.c.), induced a significant decrease in the percentages of time spent and visits in the open arms. Naltriben (NTB), a delta2-opioid receptor antagonist (3 mg/kg s.c.), but not 7-benzylidenenaltrexone, a delta1-opioid receptor antagonist, produced similar anxiety-related behaviors in the elevated plus-maze. These effects of NTI and NTB were antagonized by pretreatment with (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80), a delta-opioid receptor agonist. Furthermore, after exposure to the elevated plus-maze, the maximal increase in the plasma corticosterone level in NTI-treated rats was clearly higher than that in vehicle-treated rats. However, when NTI and SNC80 were coadministered, higher levels of plasma corticosterone were not seen after exposure to the elevated plus-maze.

CONCLUSION

These results suggest that endogenous delta2-opioid-receptor-mediated systems are involved in the regulation of anxiety-related behaviors and might play a physiologically important role in the regulation of adrenocortical activity.

Cannabinoids promote embryonic and adult hippocampus neurogenesis and produce anxiolytic- and antidepressant-like effects

The hippocampal dentate gyrus in the adult mammalian brain contains neural stem/progenitor cells (NS/PCs) capable of generating new neurons, i.e., neurogenesis. Most drugs of abuse examined to date decrease adult hippocampal neurogenesis, but the effects of cannabis (marijuana or cannabinoids) on hippocampal neurogenesis remain unknown. This study aimed at investigating the potential regulatory capacity of the potent synthetic cannabinoid HU210 on hippocampal neurogenesis and its possible correlation with behavioral change. We show that both embryonic and adult rat hippocampal NS/PCs are immunoreactive for CB1 cannabinoid receptors, indicating that cannabinoids could act on CB1 receptors to regulate neurogenesis. This hypothesis is supported by further findings that HU210 promotes proliferation, but not differentiation, of cultured embryonic hippocampal NS/PCs likely via a sequential activation of CB1 receptors, G(i/o) proteins, and ERK signaling. Chronic, but not acute, HU210 treatment promoted neurogenesis in the hippocampal dentate gyrus of adult rats and exerted anxiolytic- and antidepressant-like effects. X-irradiation of the hippocampus blocked both the neurogenic and behavioral effects of chronic HU210 treatment, suggesting that chronic HU210 treatment produces anxiolytic- and antidepressant-like effects likely via promotion of hippocampal neurogenesis.

The κ-opioid receptor is involved in the stimulating effect of nicotine on adrenocortical activity but not in nicotine induced anxiety

The kappa (kappa) opioid system appears to interact with nicotine in the modulation of locomotion and addiction related processes. In this study we have investigated the possible implication of the kappa-opioid system in the effects of nicotine on anxiety and adrenocortical activity. In two different experiments, we analysed the possible interaction between nicotine (0.5 mg/kg i.p.) and either the kappa-opioid receptor antagonist nor-binaltorphimine (5 mg/kg i.p.) or the kappa-opioid receptor agonist U50,488H (1 mg/kg s.c.). Behavioural and endocrine experiments were performed in different groups of animals. Animals were exposed to the holeboard immediately followed by the plus-maze. Serum corticosterone levels were determined by radioimmunoassay. Nicotine induced an anxiogenic-like effect in the plus-maze and a significant decrease of holeboard activity. The anxiogenic-like effect in the plus-maze was not modified by any of the kappa-opioid receptor ligands. Nicotine also induced a significant increase in the corticosterone levels, and the kappa antagonist, which did not exert any effect per se, antagonised this effect. The kappa-agonist U50,488H induced a significant increase in corticosterone concentration when administered alone. We provide the first evidence for the involvement of the kappa-opioid receptor in the stimulatory effect of nicotine on adrenocortical activity.

Behavioural and neuroendocrine effects of cannabinoids in critical developmental periods

The present article focuses on psychoneuroendocrine effects of cannabinoids in developing animals, with special emphasis on the perinatal, periweanling and periadolescent periods. We describe and discuss published data dealing with acute and long-term effects of exposure to cannabinoid agonists in such critical periods. Human studies have demonstrated that the consumption of marijuana by women during pregnancy affects the neurobehavioural development of their children. Investigations using animal models provide useful information for a better understanding of the long-lasting deleterious consequences of cannabis exposure during pregnancy and lactation. The increasing use of cannabis among adolescents and its associated public health problems have led to a parallel increase in basic research on appropriate animal models. Chronic administration of cannabinoid agonists during the periadolescent period causes persistent behavioural alterations in adult animals. Some of these alterations may be related to a possible increased risk of psychosis and other neuropsychiatric disorders in early onset cannabis users.

A role for cannabinoid CB1 receptors in mood and anxiety disorders

Mood and anxiety disorders, the most prevalent of the psychiatric disorders, cause immeasurable suffering worldwide. Despite impressive advances in pharmacological therapies, improvements in efficacy and side-effect profiles are needed. The present literature review examines the role that the endocannabinoid system may play in these disorders and the potential value of targeting this system in the search for novel and improved medications. Cannabis and its major psychoactive component (-)-trans-delta9-tetrahydrocannabinol, have profound effects on mood and can modulate anxiety and mood states. Cannabinoid receptors and other protein targets in the central nervous system (CNS) that modulate endocannabinoid function have been described. The discovery of selective modulators of some of these sites that increase or decrease endocannabinoid neurotransmission, primarily through the most prominent of the cannabinoid receptors in the CNS, the CB1 receptors, combined with transgenic mouse technology, has enabled detailed investigations into the role of these CNS sites in the regulation of mood and anxiety states. Although data point to the involvement of the endocannabinoid system in anxiety states, the pharmacological evidence seems contradictory: both anxiolytic- and anxiogenic-like effects have been reported with both endocannabinoid neurotransmission enhancers and blockers. Due to advances in the development of selective compounds directed at the CB1 receptors, significant progress has been made on this target. Recent biochemical and behavioural findings have demonstrated that blockade of CB1 receptors engenders antidepressant-like neurochemical changes (increases in extracellular levels of monoamines in cortical but not subcortical brain regions) and behavioural effects consistent with antidepressant/antistress activity in rodents.