Long-term CB₁ receptor blockade enhances vulnerability to anxiogenic-like effects of cannabinoids

Feasibility and therapeutical potential of local intracerebral encapsulated cell biodelivery of BDNF to AppNL-G-F knock-in Alzheimer mice

BACKGROUND

Alzheimer's disease (AD) is an age-related disease characterized by altered cognition, neuroinflammation, and neurodegeneration against which there is presently no effective cure. Brain-derived neurotrophic factor (BDNF) is a key neurotrophin involved in the learning and memory process, with a crucial role in synaptic plasticity and neuronal survival. Several findings support that a reduced BDNF expression in the human brain is associated with AD pathogenesis. BDNF has been proposed as a potential therapy for AD, but BDNF has low brain penetration. In this study, we used an innovative encapsulated cell biodelivery (ECB) device, containing genetically modified cells capable of releasing BDNF and characterized its feasibility and therapeutic effects in the novel App knock-in AD mouse model (AppNL-G-F).

METHODS

ECB's containing human ARPE-19 cells genetically modified to release BDNF (ECB-BDNF devices) were stereotactically implanted bilaterally into hippocampus of 3-month-old AppNL-G-F mice. The stability of BDNF release and its effect on AD pathology were evaluated after 1, 2-, and 4-months post-implantation by immunohistochemical and biochemical analyses. Exploratory and memory performance using elevated plus maze (EPM) and Y-maze test were performed in the 4-months treatment group. Immunological reaction towards ECB-BDNF devices were studied under ex vivo and in vivo settings.

RESULTS

The surgery and the ECB-BDNF implants were well tolerated without any signs of unwanted side effects or weight loss. ECB-BDNF devices did not induce host-mediated immune response under ex vivo set-up but showed reduced immune cell attachment when explanted 4-months post-implantation. Elevated BDNF staining around ECB-BDNF device proximity was detected after 1, 2, and 4 months treatment, but the retrieved devices showed variable BDNF release. A reduction of amyloid-β (Aβ) plaque deposition was observed around ECB-BDNF device proximity after 2-months of BDNF delivery.

CONCLUSIONS

The result of this study supports the use of ECB device as a promising drug-delivery approach to locally administer BBB-impermeable factors for treating neurodegenerative conditions like AD. Optimization of the mouse-sized devices to reduce variability of BDNF release is needed to employ the ECB platform in future pre-clinical research and therapy development studies.

Effects of Δ9-THC and Type-1 Cannabinoid Receptor Agonists in the Elevated Plus Maze Test of Anxiety: A Systematic Review and Meta-Analysis

Δ⁹-THC (the main active compound from Cannabis sativa) and related cannabinoids have been used as drugs of abuse and as medications. They induce a complex set of emotional responses in humans and experimental animals, consisting of either anxiolysis or heightened anxiety. These discrepant effects pose a major challenge for data reproducibility and for developing new cannabinoid-based medicines. In this study, we review and analyze previous data on cannabinoids and anxiety-like behavior in experimental animals. Systematic review and meta-analysis on the effects of type-1 cannabinoid receptor agonists (full or partial, selective or not) in rodents exposed to the elevated plus maze, a widely used test of anxiety-like behavior. Cannabinoids tend to reduce anxiety-like behavior if administered at low doses. THC effects are moderated by the dose factor, with anxiolytic- and anxiogenic-like effects occurring at low-dose (0.075-1 mg/kg) and high-dose (1-10 mg/kg) ranges, respectively. However, some studies report no effect at all regardless of the dose tested. Finally, motor impairment represents a potential confounding factor when high doses are administered. The present analysis may contribute to elucidate the experimental factors underlying cannabinoid effects on anxiety-like behavior and facilitate data reproducibility in future studies.

Therapeutic potential of PIMSR, a novel CB1 receptor neutral antagonist, for cocaine use disorder: evidence from preclinical research

Cannabinoid CB1 receptors (CB1Rs) have been major targets in medication development for the treatment of substance use disorders. However, clinical trials with rimonabant, a CB1R antagonist/inverse agonist, failed due to severe side effects. Here, we evaluated the therapeutic potential of PIMSR, a neutral CB1R antagonist lacking an inverse agonist profile, against cocaine's behavioral effects in experimental animals. We found that systemic administration of PIMSR dose-dependently inhibited cocaine self-administration under fixed-ratio (FR5), but not FR1, reinforcement, shifted the cocaine self-administration dose-response curve downward, decreased incentive motivation to seek cocaine under progressive-ratio reinforcement, and reduced cue-induced reinstatement of cocaine seeking. PIMSR also inhibited oral sucrose self-administration. Importantly, PIMSR alone is neither rewarding nor aversive as assessed by place conditioning. We then used intracranial self-stimulation (ICSS) to explore the possible involvement of the mesolimbic dopamine system in PIMSR's action. We found that PIMSR dose-dependently attenuated cocaine-enhanced ICSS maintained by electrical stimulation of the medial forebrain bundle in rats. PIMSR itself failed to alter electrical ICSS, but dose-dependently inhibited ICSS maintained by optical stimulation of midbrain dopamine neurons in transgenic DAT-Cre mice, suggesting the involvement of dopamine-dependent mechanisms. Lastly, we examined the CB1R mechanisms underlying PIMSR's action. We found that PIMSR pretreatment attenuated Δ⁹-tetrahydrocannabinol (Δ⁹-THC)- or ACEA (a selective CB1R agonist)-induced reduction in optical ICSS. Together, our findings suggest that the neutral CB1R antagonist PIMSR deserves further research as a promising pharmacotherapeutic for cocaine use disorder.

Effects of endocannabinoid system modulation on social behaviour: A systematic review of animal studies

There is a clear link between psychiatric disorders and social behaviour, and evidence suggests the involvement of the endocannabinoid system (ECS). A systematic review of preclinical literature was conducted using MEDLINE (PubMed) and PsychINFO databases to examine whether pharmacological and/or genetic manipulations of the ECS alter social behaviours in wildtype (WT) animals or models of social impairment (SIM). Eighty studies were included. Risk of bias (RoB) was assessed using SYRCLE's RoB tool. While some variability was evident, studies most consistently found that direct cannabinoid receptor (CBR) agonism decreased social behaviours in WT animals, while indirect CBR activation via enzyme inhibition or gene-knockout increased social behaviours. Direct and, more consistently, indirect CBR activation reversed social deficits in SIM. These CBR-mediated effects were often sex- and developmental-phase-dependent and blocked by CBR antagonism. Overall, ECS enzyme inhibition may improve social behaviour in SIM, suggesting the potential usefulness of ECS enzyme inhibition as a therapeutic approach for social deficits. Future research should endeavour to elucidate ECS status in neuropsychiatric disorders characterized by social deficits.

The role of the endocannabinoid system as a therapeutic target for autism spectrum disorder: Lessons from behavioral studies on mouse models

Recent years have seen an impressive amount of research devoted to understanding the etiopathology of Autism Spectrum Disorder (ASD) and developing therapies for this syndrome. Because of the lack of biomarkers of ASD, this work has been largely based on the behavioral characterization of rodent models, based on a multitude of genetic and environmental manipulations. Here we highlight how the endocannabinoid system (ECS) has recently emerged within this context of mouse behavioral studies as an etiopathological factor in ASD and a valid potential therapeutic target. We summarize the most recent results showing alterations of the ECS in rodent models of ASD, and demonstrating ASD-like behaviors in mice with altered ECS, induced either by genetic or pharmacological manipulations. We also give a critical overview of the most relevant advances in designing treatments and novel mouse models for ASD targeting the ECS, highlighting the relevance of thorough and innovative behavioral approaches to investigate the mechanisms acting underneath the complex features of ASD.

Cannabidiol inhibits sucrose self-administration by CB1 and CB2 receptor mechanisms in rodents

A growing number of studies suggest therapeutic applications of cannabidiol (CBD), a recently U.S. Food and Drug Administration (FDA)-approved medication for epilepsy, in treatment of many other neuropsychological disorders. However, pharmacological action and the mechanisms by which CBD exerts its effects are not fully understood. Here, we examined the effects of CBD on oral sucrose self-administration in rodents and explored the receptor mechanisms underlying CBD-induced behavioral effects using pharmacological and transgenic approaches. Systemic administration of CBD (10, 20, and 40 mg/kg, ip) produced a dose-dependent reduction in sucrose self-administration in rats and in wild-type (WT) and CB1-/- mice but not in CB2-/- mice. CBD appeared to be more efficacious in CB1-/- mice than in WT mice. Similarly, pretreatment with AM251, a CB1R antagonist, potentiated, while AM630, a selective CB2R antagonist, blocked CBD-induced reduction in sucrose self-administration, suggesting the involvement of CB1 and CB2 receptors. Furthermore, systemic administration of JWH133, a selective CB2R agonist, also produced a dose-dependent reduction in sucrose self-administration in WT and CB1-/- mice, but not in CB2-/- mice. Pretreatment with AM251 enhanced, while AM630 blocked JWH133-induced reduction in sucrose self-administration in WT mice, suggesting that CBD inhibits sucrose self-administration likely by CB1 receptor antagonism and CB2 receptor agonism. Taken together, the present findings suggest that CBD may have therapeutic potential in reducing binge eating and the development of obesity.

Cannabis Use as a Risk Factor for Depression, Anxiety, and Suicidality: Epidemiological Associations and Implications for Nurses

Psychiatric disorders and substance use disorders commonly co-occur and are major public health concerns given the morbidity and mortality associated with them. Globally, cannabis is among the most commonly used drugs, and cannabis use frequently begins in adolescence or emerging adulthood, both important periods of development and periods in which psychiatric symptoms and disorders frequently emerge. Thus, the relationships between cannabis use and mental illnesses are essential for nurses and other healthcare professionals and researchers to explore and understand. This literature review examines the relationships between cannabis use and depression, anxiety, and suicide. It includes a primer on the neurobiology of cannabis effects; an overview on the epidemiological evidence on the associations between cannabis use and depression, anxiety, and suicide; and a discussion of implications for nurses, particularly important given changes in the medical and recreational cannabis legislation in North America. Overall, this review found consistent evidence showing a cross-sectional association between recreational cannabis use and depression, anxiety, and suicide, despite some limitations and conflicts in the literature. In addition, most evidence from longitudinal or case control studies suggested cannabis use preceded the development of depressive symptoms and suicidal behaviors, although the quality of this evidence was mixed. Implications for future research and nursing practice are discussed.

Endocannabinoids and Fear-Related Behavior in Mice Selectively Bred for High or Low Alcohol Preference

Alcohol use disorders (AUDs) have a high incidence of co-morbidity with stress-related psychopathologies, such as post-traumatic stress disorder (PTSD). Genetic and pharmacological studies support a prominent role for the endocannabinoid system (ECS) in modulating stress-related behaviors relevant to AUDs and PTSD. Mouse lines selectively bred for high (HAP) and low (LAP) alcohol preference show reproducible differences in fear-potentiated startle (FPS), a model for PTSD-related behavior. The first experiment in this study assessed levels of the endocannabinoids, anandamide (AEA) and sn-2 arachidonylglycerol (2-AG), in the prefrontal cortex (PFC), amygdala (AMG), and hippocampus (HIP) of male and female HAP1 and LAP1 mice following the expression of FPS to determine whether ECS responses to conditioned-fear stress (FPS) were correlated with genetic propensity toward high or low alcohol preference. The second experiment examined effects of a cannabinoid receptor type 1 agonist (CP55940) and antagonist (rimonabant) on the expression of FPS in HAP1 and LAP1 male and female mice. The estrous cycle of females was monitored throughout the experiments to determine if the expression of FPS differed by stage of the cycle. FPS was greater in male and female HAP1 than LAP1 mice, as previously reported. In both experiments, LAP1 females in diestrus displayed greater FPS than LAP1 females in metestrus and estrus. In the AMG and HIP, AEA levels were greater in male fear-conditioned HAP1 mice than LAP1 mice. There were no line or sex differences in effects of CP55940 or rimonabant on the expression of FPS. However, surprisingly, evidence for anxiogenic effects of prior treatment with CP55940 were seen in all mice during the third drug-free FPS test. These findings suggest that genetic differences in ECS function in response to fear-conditioning stress may underlie differences in FPS expression in HAP1 and LAP1 selected lines.

Endocannabinoid and Muscarinic Signaling Crosstalk in the 3xTg-AD Mouse Model of Alzheimer's Disease

The endocannabinoid system, which modulates emotional learning and memory through CB1 receptors, has been found to be deregulated in Alzheimer's disease (AD). AD is characterized by a progressive decline in memory associated with selective impairment of cholinergic neurotransmission. The functional interplay of endocannabinoid and muscarinic signaling was analyzed in seven-month-old 3xTg-AD mice following the evaluation of learning and memory of an aversive stimulus. Neurochemical correlates were simultaneously studied with both receptor and functional autoradiography for CB1 and muscarinic receptors, and regulations at the cellular level were depicted by immunofluorescence. 3xTg-AD mice exhibited increased acquisition latencies and impaired memory retention compared to age-matched non-transgenic mice. Neurochemical analyses showed changes in CB1 receptor density and functional coupling of CB1 and muscarinic receptors to Gi/o proteins in several brain areas, highlighting that observed in the basolateral amygdala. The subchronic (seven days) stimulation of the endocannabinoid system following repeated WIN55,212-2 (1 mg/kg) or JZL184 (8 mg/kg) administration induced a CB1 receptor downregulation and CB1-mediated signaling desensitization, normalizing acquisition latencies to control levels. However, the observed modulation of cholinergic neurotransmission in limbic areas did not modify learning and memory outcomes. A CB1 receptor-mediated decrease of GABAergic tone in the basolateral amygdala may be controlling the limbic component of learning and memory in 3xTg-AD mice. CB1 receptor desensitization may be a plausible strategy to improve behavior alterations associated with genetic risk factors for developing AD.

Altered motor development following late gestational alcohol and cannabinoid exposure in rats

Cannabis is the most commonly used illicit drug among pregnant women, and rates are likely to increase given recent legalization. In addition, half of pregnant women who report consuming cannabis also report drinking alcohol. However, little is known about the consequences of prenatal cannabis alone or in combination with alcohol, particularly with cannabis products that are continually increasing in potency of the primary psychoactive constituent in cannabis, Δ9-tetrahydrocannabinol (THC). The current study investigated the effects of early exposure to cannabinoids during the brain growth spurt on early physical and motor development alone (Experiment 1) or in combination with alcohol (Experiment 2). In Experiment 1, Sprague-Dawley rat pups were exposed to a cannabinoid receptor agonist (CP-55,940 [CP]; 0.1, 0.25, 0.4 mg/kg/day), the drug vehicle, or a saline control from postnatal days (PD) 4-9. In Experiment 2, rat pups were exposed to CP (0.4 mg/kg/day) or the vehicle, and were additionally intubated with alcohol (11.9% v/v; 5.25 g/kg/day) or received a sham intubation. Subjects in both experiments were tested on a motor development task (PD 12-20) and a motor coordination task during adolescence (PD 30-32). Both developmental cannabinoid and alcohol exposure separately decreased body growth throughout development, and combined exposure exacerbated these effects, although only alcohol exposure induced long-term body weight reductions. Developmental cannabinoid exposure advanced early motor development, whereas alcohol exposure delayed development, and subjects given combined exposure did not differ from controls on some measures. Alcohol exposure impaired motor coordination later in life. In contrast, cannabinoid exposure, by itself, did not significantly affect long-term motor coordination, but did exacerbate alcohol-related impairments in motor coordination among females. These results suggest that cannabinoid exposure may not only alter development by itself, but may exacerbate alcohol's teratogenic effects in specific behavioral domains. These findings have important implications not only for individuals affected by prenatal exposure, but also for establishing public policy for women regarding cannabis use during pregnancy.

Blood-brain and blood-cerebrospinal fluid passage of BRICHOS domains from two molecular chaperones in mice

Targeting toxicity associated with β-amyloid (Aβ) misfolding and aggregation is a promising therapeutic strategy for preventing or managing Alzheimer's disease. The BRICHOS domains from human prosurfactant protein C (proSP-C) and integral membrane protein 2B (Bri2) efficiently reduce neurotoxicity associated with Aβ42 fibril formation both in vitro and in vivo In this study, we evaluated the serum half-lives and permeability into the brain and cerebrospinal fluid (CSF) of recombinant human (rh) proSP-C and Bri2 BRICHOS domains injected intravenously into WT mice. We found that rh proSP-C BRICHOS has a longer blood serum half-life compared with rh Bri2 BRICHOS and passed into the CSF but not into the brain parenchyma. As judged by Western blotting, immunohistochemistry, and ELISA, rh Bri2 BRICHOS passed into both the CSF and brain. Intracellular immunostaining for rh Bri2 BRICHOS was observed in the choroid plexus epithelium as well as in the cerebral cortex. Our results indicate that intravenously administered rh proSP-C and Bri2 BRICHOS domains have different pharmacokinetic properties and blood-brain/blood-CSF permeability in mice. The finding that rh Bri2 BRICHOS can reach the brain parenchyma after peripheral administration may be harnessed in the search for new therapeutic strategies for managing Alzheimer's disease.

Sex-specific effects of CB1 receptor antagonism and stress in adolescence on anxiety, corticosterone concentrations, and contextual fear in adulthood in rats

There is a paucity of research regarding the role of endogenous cannabinoid signalling in adolescence on brain and behaviour development. We previously demonstrated effects of repeated CB1 receptor antagonism in adolescence on socioemotional behaviours and neural protein expression 24-48 h after the last drug administration in female rats, with no effect in males. Here we investigate whether greater effects would be manifested after a lengthier delay. In Experiment 1, male and female rats were administered either 1 mg / kg of the CB1 receptor-selective antagonist AM251, vehicle (VEH), or did not receive injections (NoINJ) daily on postnatal days (PND) 30-44 either alone (no adolescent confinement stress; noACS), or in tandem with 1 h ACS. On PND 70, adolescent AM251 exposure reduced anxiety in an elevated plus maze in males, irrespective of ACS, with no effects in females. On PND 73, there were no group differences in either sex in plasma corticosterone concentrations before or after 30 min of restraint stress, although injection stress resulted in higher baseline concentrations in males. Brains were collected on PND 74, with negligible effects of either AM251 or ACS on protein markers of synaptic plasticity and of the endocannabinoid system in the hippocampus and medial prefrontal cortex. In Experiment 2, rats from both sexes were treated with vehicle or AM251 on PND 30-44 and were tested for contextual fear conditioning and extinction in adulthood. AM251 females had greater fear recall than VEH females 24 h after conditioning, with no group differences in within- or between-session fear extinction. There were no group differences in long-term extinction memory, although AM251 females froze more during a reconditioning trial compared with VEH females. There were no group differences on any of the fear conditioning measures in males. Together, these findings indicate a modest, sex-specific role of CB1 receptor signalling in adolescence on anxiety-like behaviour in males and conditioned fear behaviour in females.

Remote memories are enhanced by COMT activity through dysregulation of the endocannabinoid system in the prefrontal cortex

The prefrontal cortex (PFC) is a crucial hub for the flexible modulation of recent memories (executive functions) as well as for the stable organization of remote memories. Dopamine in the PFC is implicated in both these processes and genetic variants affecting its neurotransmission might control the unique balance between cognitive stability and flexibility present in each individual. Functional genetic variants in the catechol-O-methyltransferase (COMT) gene result in a different catabolism of dopamine in the PFC. However, despite the established role played by COMT genetic variation in executive functions, its impact on remote memory formation and recall is still poorly explored. Here we report that transgenic mice overexpressing the human COMT-Val gene (COMT-Val-tg) present exaggerated remote memories (>50 days) while having unaltered recent memories (<24 h). COMT selectively and reversibly modulated the recall of remote memories as silencing COMT Val overexpression starting from 30 days after the initial aversive conditioning normalized remote memories. COMT genetic overactivity produced a selective overdrive of the endocannabinoid system within the PFC, but not in the striatum and hippocampus, which was associated with enhanced remote memories. Indeed, acute pharmacological blockade of CB1 receptors was sufficient to rescue the altered remote memory recall in COMT-Val-tg mice and increased PFC dopamine levels. These results demonstrate that COMT genetic variations modulate the retrieval of remote memories through the dysregulation of the endocannabinoid system in the PFC.

Effects of CB1 receptor antagonism and stress exposures in adolescence on socioemotional behaviours, neuroendocrine stress responses, and expression of relevant proteins in the hippocampus and prefrontal cortex in rats

Little is known about the consequences of altered endocannabinoid signalling in adolescence. We hypothesized that CB1 receptor antagonism (AM251, 1 mg/kg) and stress exposures (1 h confinement stress) in adolescence (daily, postnatal days 30-44) would interact to increase neuroendocrine stress responses and anxiety when investigated a minimum of 24 h after drug and stress treatments; these treatment effects were independent of each other. Changes in homecage behaviour and in weight gain confirmed that both males and females were sensitive to the treatments. Nevertheless, in males, repeated AM251 administration was without effect on any of the measures investigated in days post-treatment. Males had reduced corticosterone release to the repeated stress and had increased GAD67 expression in the ventral hippocampus under baseline conditions. In females, AM251 also reduced weight gain and increased stereotypic behaviours in the homecage; these same females showed increased sociality, reduced CB1 receptor expression in the dorsal hippocampus, and increased GAD67 expression in the prefrontal cortex. Further, females exposed to repeated stress had enhanced recovery to baseline corticosterone concentrations after stress. The inclusion of a non-injected comparison group also revealed stress of injection effects in both sexes that otherwise would have been masked. Together, the findings demonstrate effects of CB1 receptor antagonism and stress that were more evident in females than males, suggesting that females may be more vulnerable to the consequences of disrupted endocannabinoid signalling during adolescence.

Disruption of peri-adolescent endocannabinoid signaling modulates adult neuroendocrine and behavioral responses to stress in male rats

The endocannabinoid (eCB) system is known to regulate neural, endocrine and behavioral responses to stress in adults; however there is little knowledge regarding how this system governs the development and maturation of these responses. Previous work has reported dynamic and time-specific changes in CB1 receptor expression, N-arachidonylethanolamine (AEA) content and fatty acid amide hydrolase (FAAH) activity within corticolimbic structures throughout the peri-adolescent period. To examine whether fluctuations in adolescent eCB activity contribute to the development of adult stress responsivity and emotionality, we treated male Sprague-Dawley rats daily with the CB1R antagonist, AM-251 (5 mg/kg), or vehicle between post-natal days (PND) 35-45. Following this treatment, emotional behavior, HPA axis stress reactivity and habituation to repeated restraint stress, as well as corticolimbic eCB content were examined in adulthood (PND 75). Behaviorally, AM-251-treated males exhibited more active stress-coping behavior in the forced swim test, greater risk assessment behavior in the elevated plus maze and no significant differences in general motor activity. Peri-adolescent AM-251 treatment modified corticosterone habituation to repeated restraint exposure compared to vehicle. Peri-adolescent CB1R antagonism induced moderate changes in adult corticolimbic eCB signaling, with a significant decrease in amygdalar AEA, an increase in hypothalamic AEA and an increase in prefrontal cortical CB1R expression. Together, these data indicate that peri-adolescent endocannabinoid signaling contributes to the maturation of adult neurobehavioral responses to stress.

Endocannabinoid and nitric oxide interaction mediates food intake in neonatal chicken

The aim of the current study was to investigate the interaction of the nitric oxide and cannabinoidergic systems on feeding behaviour in neonatal chicken. A total of 6 experiments were designed to evaluate the interaction between cannabinoidergic and nitrergic systems on food intake in 3-h food-deprived (FD3) neonatal chickens. In Experiment 1, chickens received intracerebroventricular (ICV) injections of saline, 2-arachidonoylglycerol (2-AG) (a CB1 receptor agonist, 2 µg), l-arginine (nitric oxide precursor, 200 nmol) and co-administration of 2-AG + l-arginine. In Experiment 2, ICV injection of saline, 2-AG (2 µg), l-NAME (a nitric oxide synthesis inhibitor, 100 nmol) and their combination (2-AG + l-NAME) were applied to the birds. In Experiment 3, injections were saline, CB65 (a CB2 receptor agonist, 1.25 µg), l-arginine (200 nmol) and CB65 + l-arginine. In Experiment 4, birds received ICV injection of saline, CB65 (1.25 µg), l-NAME (100 nmol) and CB65 + l-NAME. In Experiment 5, chickens were ICV injected with saline, l-arginine (800 nmol), SR141716A (a selective CB1 receptor antagonist, 6.25 µg) and l-arginine + SR141716A. In Experiment 6, birds were injected with saline, l-arginine (800 nmol), AM630 (a selective CB2 receptor antagonist, 5 µg) and l-arginine + AM630. Cumulative food intake was recorded until 2-h post injection. ICV injection of CB1 and CB2 receptor agonists increased food intake. Co-injection of 2-AG + l-NAME increased the hyperphagic effects of CB1 receptors. CB2 receptor-induced food intake was not affected by co-administration of CB65 + l-NAME. l-Arginine decreased food intake and this effect was amplified by co-injection of l-arginine + SR141716A. However; CB2 receptor antagonists had no effect on l-arginine-induced hypophagia. The results suggest that there is an interaction between endogenous nitric oxide and the cannabinoidergic system on feeding behaviour which is mediated via CB1 receptors in the neonatal chicken.

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.

Role of NPY Y1 receptor on acquisition, consolidation and extinction on contextual fear conditioning: dissociation between anxiety, locomotion and non-emotional memory behavior

Neuropeptide Y (NPY) is the most abundant peptide in the central nervous system (CNS) and is densely localized in the brain regions involved in stress, memory, fear and anxiety. Although previous research supports a role for NPY in the mediation of rodent and human emotional behavior, there is currently a lack of information on the effects of low doses of NPY that could have a potential therapeutic advantage, minimizing side-effects such as cognition impairment or sedation. Herein, we assessed the effects of intracerebroventricular (i.c.v.) administration of low doses of NPY, and of the Y1-agonist Leu31Pro34-NPY (LP-NPY) on contextual fear conditioning (CFC), as they have no effect on unconditioned anxiety-like, locomotor activity and non-emotional memory. NPY (3 pmol) and LP-NPY (1 pmol) inhibited freezing behavior when administered in the acquisition or consolidation stages, indicating a reduction of fear. When injected in the extinction phase, only NPY inhibited freezing behavior on CFC. Pre-treatment with the Y1-antagonist BIBO3304 before NPY and LP-NPY was able to prevent the inhibition of fear responses induced by both NPY agonists. Taken together, our results demonstrate robust fear-inhibiting effects of i.c.v. injection of NPY on contextual fear conditioning in rats, a response that is mediated, at least in part, by the Y1 receptor. Moreover, these treatments were unable to change locomotor activity or to show an anxiolytic-like effect, as evaluated in an open-field and an elevated plus-maze. This specific fear reduction effect may underlie resilience systems in the CNS and has potential therapeutic relevance in PTSD.