Presynaptic effects of anandamide and WIN55,212-2 on glutamatergic nerve endings isolated from rat hippocampus

Behavioral, biochemical and histopathological toxic profiles induced by sub-chronic cannabimimetic WIN55, 212-2 administration in mice

WIN55, 212-2 mesylate is a synthetic cannabinoid (SC) agonist of CB1 and CB2 receptors with much higher affinity to CB1 receptor than tetrahydrocannabinol and many potential therapeutic effects. Few studies have evaluated SCs effects on more complex animal behavior and sex differences in cannabinoids toxicology. The current study was undertaken for determination of behavioral (Open Field test), biochemical (liver and kidney function test plus GABA & Glutamate levels), histopathological and CB1 immunohistochemistry risks of sub-chronic administration of SC WIN55, 212-2 mesylate in male and female mice. A total of 40 healthy adult mice were randomly divided into four groups (5 mice each): a negative control group, a vehicle group, a low dose (0.05 mg/kg) group and a high dose group (0.1 mg/kg) for each gender.Open Field Test revealed dose and gender-dependent anxiogenic effect with reduced locomotor activity in both sexes especially the higher doses with female mice being less compromised. GABA and glutamate levels increased significantly in both dose groups compared to controls alongside female mice versus males. No significant biochemical alterations were found in all groups with minimal histopathological changes. The CB1 receptors immunohistochemistry revealed a significant increase in the number of CB1 positive neurons in both low and high dose groups against controls with higher expression in female brains.ConclusionsThere were sexual dimorphism effects induced by sub-chronic exposure to WIN55, 212-2 with lesser female mice affection and dose-dependent influences.

The Association of Tanacetum parthenium and Salix alba Extracts Reduces Cortex Serotonin Turnover, in an Ex Vivo Experimental Model of Migraine

The mixture of water extracts from Tanacetum parthenium and Salix alba was studied in an ex vivo assessment of neurotoxicity constituted by isolated mouse cortex specimens challenged with K+ 60 mM Krebs–Ringer buffer (neurotoxicity stimulus). The effects of the mixture on lactate dehydrogenase (LDH), nitrite and serotonin levels were investigated. The phytochemical profile of the mixture was also evaluated. A docking approach was conducted to predict, albeit partially, the putative mechanism underlying the observed effects. The extracts displayed a good profile of polyphenolic compounds (22 chromatographic peaks detected), with caftaric acid and epicatechin being the prominent phenols. In isolated cortex, the association of T. parthenium and S. alba extracts was effective in reducing the K+ 60 mM-induced levels of LDH and nitrites, whereas the neurotoxicity stimulus-induced serotonin depletion was prevented by the treatment. Regarding the inhibition of serotonin catabolism, epicatechin (44.65 µg/mg) and caftaric acid (10.51 µg/mg) were putatively the main compounds involved in the inhibition of monoamineoxidase-A, which is known to play a master role in serotonin turnover. Collectively, the results of the present study point to the efficacy of the present extract mixture as an innovative pharmacological tool to prevent the onset of migraine.

In utero Δ9-tetrahydrocannabinol exposure confers vulnerability towards cognitive impairments and alcohol drinking in the adolescent offspring: Is there a role for neuropeptide Y?

BACKGROUND

Cannabinoid consumption during pregnancy has been increasing on the wave of the broad-based legalisation of cannabis in Western countries, raising concern about the putative detrimental outcomes on foetal neurodevelopment. Indeed, since the endocannabinoid system regulates synaptic plasticity, emotional and cognitive processes from early stages of life interfering with it and other excitability endogenous modulators, such as neuropeptide Y (NPY), might contribute to the occurrence of a vulnerable phenotype later in life.

AIMS

This research investigated whether in utero exposure to Δ9-tetrahydrocannabinol (THC) may induce deficits in emotional/cognitive processes and alcohol vulnerability in adolescent offspring. NPY and excitatory postsynaptic density (PSD) machinery were measured as markers of neurobiological vulnerability.

METHODS

Following in utero THC exposure (2 mg/kg delivered subcutaneously), preadolescent male rat offspring were assessed for: behavioural reactivity in the open field test, neutral declarative memory and aversive limbic memory in the Novel Object and Emotional Object Recognition tests, immunofluorescence for NPY neurons and the PSD proteins Homer-1, 1b/c and 2 in the prefrontal cortex, amygdala and nucleus accumbens at adolescence (cohort 1); and instrumental learning, alcohol taking, relapse and conflict behaviour in the operant chamber throughout adolescence until early adulthood (cohort 2).

RESULTS

In utero THC-exposed adolescent rats showed: (a) increased locomotor activity; (b) no alteration in neutral declarative memory; (c) impaired aversive limbic memory; (d) decreased NPY-positive neurons in limbic regions; (e) region-specific variations in Homer-1, 1b/c and 2 immunoreactivity; (f) decreased instrumental learning and increased alcohol drinking, relapse and conflict behaviour in the operant chamber.

CONCLUSION

Gestational THC impaired the formation of memory traces when integration between environmental encoding and emotional/motivational processing was required and promoted the development of alcohol-addictive behaviours. The abnormalities in NPY signalling and PSD make-up may represent the common neurobiological background, suggesting new targets for future research.

Targeting the Stress System During Gestation: Is Early Handling a Protective Strategy for the Offspring?

The perinatal window is a critical developmental time when abnormal gestational stimuli may alter the development of the stress system that, in turn, influences behavioral and physiological responses in the newborns. Individual differences in stress reactivity are also determined by variations in maternal care, resulting from environmental manipulations. Despite glucocorticoids are the primary programming factor for the offspring's stress response, therapeutic corticosteroids are commonly used during late gestation to prevent preterm negative outcomes, exposing the offspring to potentially aberrant stress reactivity later in life. Thus, in this study, we investigated the consequences of one daily s.c. injection of corticosterone (25 mg/kg), from gestational day (GD) 14-16, and its interaction with offspring early handling, consisting in a brief 15-min maternal separation until weaning, on: (i) maternal behavior; and (ii) behavioral reactivity, emotional state and depressive-like behavior in the adolescent offspring. Corticosterone plasma levels, under non-shock- and shock-induced conditions, were also assessed. Our results show that gestational exposure to corticosterone was associated with diminished maternal care, impaired behavioral reactivity, increased emotional state and depressive-like behavior in the offspring, associated with an aberrant corticosterone response. The early handling procedure, which resulted in increased maternal care, was able to counteract the detrimental effects induced by gestational corticosterone exposure both in the behavioral- and neurochemical parameters examined. These findings highlight the potentially detrimental consequences of targeting the stress system during pregnancy as a vulnerability factor for the occurrence of emotional and affective distress in the adolescent offspring. Maternal extra-care proves to be a protective strategy that confers resiliency and restores homeostasis.

The Ratio of 2-AG to Its Isomer 1-AG as an Intrinsic Fine Tuning Mechanism of CB1 Receptor Activation

Endocannabinoids are pleiotropic lipid messengers that play pro-homeostatic role in cellular physiology by strongly influencing intracellular Ca²⁺ concentration through the activation of cannabinoid receptors. One of the best-known endocannabinoid ‘2-AG’ is chemically unstable in aqueous solutions, thus its molecular rearrangement, resulting in the formation of 1-AG, may influence 2-AG-mediated signaling depending on the relative concentration and potency of the two isomers. To predict whether this molecular rearrangement may be relevant in physiological processes and in experiments with 2-AG, here we studied if isomerization of 2-AG has an impact on 2-AG-induced, CB1-mediated Ca²⁺ signaling in vitro. We found that the isomerization-dependent drop in effective 2-AG concentration caused only a weak diminution of Ca²⁺ signaling in CB1 transfected COS7 cells. We also found that 1-AG induces Ca²⁺ transients through the activation of CB1, but its working concentration is threefold higher than that of 2-AG. Decreasing the concentration of 2-AG in parallel to the prevention of 1-AG formation by rapid preparation of 2-AG solutions, caused a significant diminution of Ca²⁺ signals. However, various mixtures of the two isomers in a fix total concentration – mimicking the process of isomerization over time – attenuated the drop in 2-AG potency, resulting in a minor decrease in CB1 mediated Ca²⁺ transients. Our results indicate that release of 2-AG into aqueous medium is accompanied by its isomerization, resulting in a drop of 2-AG concentration and simultaneous formation of the similarly bioactive isomer 1-AG. Thus, the relative concentration of the two isomers with different potency and efficacy may influence CB1 activation and the consequent biological responses. In addition, our results suggest that 1-AG may play role in stabilizing the strength of cannabinoid signal in case of prolonged 2-AG dependent cannabinoid mechanisms.

Acetaldehyde, Motivation and Stress: Behavioral Evidence of an Addictive ménage à trois

Acetaldehyde (ACD) contributes to alcohol's psychoactive effects through its own rewarding properties. Recent studies shed light on the behavioral correlates of ACD administration and the possible interactions with key neurotransmitters for motivation, reward and stress-related response, such as dopamine and endocannabinoids. This mini review article critically examines ACD psychoactive properties, focusing on behavioral investigations able to unveil ACD motivational effects and their pharmacological modulation in vivo. Similarly to alcohol, rats spontaneously drink ACD, whose presence is detected in the brain following chronic self-administration paradigm. ACD motivational properties are demonstrated by operant paradigms tailored to model several drug-related behaviors, such as induction and maintenance of operant self-administration, extinction, relapse and punishment resistance. ACD-related addictive-like behaviors are sensitive to pharmacological manipulations of dopamine and endocannabinoid signaling. Interestingly, the ACD-dopamine-endocannabinoids relationship also contributes to neuroplastic alterations of the NPYergic system, a stress-related peptide critically involved in alcohol abuse. The understanding of the ménage-a-trois among ACD, reward- and stress-related circuits holds promising potential for the development of novel pharmacological approaches aimed at reducing alcohol abuse.

Peripheral chemerin administration modulates hypothalamic control of feeding

Chemerin is a recently identified adipokine that is involved in the regulation of adipogenesis, energy metabolism, and inflammation. The aim of the present study was to investigate the role of chemerin on food intake, body weight and hypothalamic peptidergic and aminergic modulators which play a pivotal role in feeding regulation in rats. Male adult Wistar rats were intraperitoneally injected, daily for 17 days at 9.00am, with either vehicle (saline; N=12) or chemerin (8μg/kg; N=12) and (16μg/kg; N=12). Food intake was recorded 24h after each administration. Animals were sacrificed 24h after the last injection. Total RNA was extracted from hypothalami and reverse transcribed to evaluate gene expression of agouti-related peptide (AgRP), neuropeptide Y (NPY), orexin-A, corticotrophin releasing hormone (CRH), pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART). Furthermore, we evaluated the effect of chemerin on dopamine, norepinephrine and serotonin steady state concentrations in rat hypothalamus homogenate, and monoamine release from rat hypothalamic synaptosomes. Chemerin administration (8 and 16μg/kg) decreased both food intake and body weight compared to vehicle, possibly associated with a significant increase in serotonin synthesis and release, in the hypothalamus. On the other hand, the pattern of gene expression following chemerin administration indicates a minor role played by chemerin as a peripheral appetite-regulating signal.

Presynaptic TRPV1 vanilloid receptor function is age- but not CB1 cannabinoid receptor-dependent in the rodent forebrain

Neocortical and striatal TRPV1 (vanilloid or capsaicin) receptors (TRPV1Rs) are excitatory ligand-gated ion channels, and are implicated in psychiatric disorders. However, the purported presynaptic neuromodulator role of TRPV1Rs in glutamatergic, serotonergic or dopaminergic terminals of the rodent forebrain remains little understood. With the help of patch-clamp electrophysiology and neurochemical approaches, we mapped the age-dependence of presynaptic TRPV1R function, and furthermore, we aimed at exploring whether the presence of CB1 cannabinoid receptors (CB1Rs) influences the function of the TRPV1Rs, as both receptor types share endogenous ligands. We found that the major factor which affects presynaptic TRPV1R function is age: by post-natal day 13, the amplitude of capsaicin-induced release of dopamine and glutamate is halved in the rat striatum, and two weeks later, capsaicin already loses its effect. However, TRPV1R receptor function is not enhanced by chemical or genetic ablation of the CB1Rs in dopaminergic, glutamatergic and serotonergic terminals of the mouse brain. Altogether, our data indicate a possible neurodevelopmental role for presynaptic TRPV1Rs in the rodent brain, but we found no cross-talk between TRPV1Rs and CB1Rs in the same nerve terminal.

Orexigenic effects of omentin-1 related to decreased CART and CRH gene expression and increased norepinephrine synthesis and release in the hypothalamus

Omentin-1, a visceral fat depot-specific secretory protein, is inversely correlated with obesity and insulin resistance. We investigated, in rats, the effects of chronic omentin-1 administration (8 μg/kg, intraperitoneally, once daily for 14-days) on feeding behavior and related hypothalamic peptides and neurotransmitters. Food intake and body weight were recorded daily throughout the study. We found a significantly increased food intake compared to controls, but only in days 10-14, while body weight significantly increased since day 12 (P<0.05). Compared with vehicle, omentin-1 treatment led to a significant reduction in both cocaine and amphetamine-regulated transcript (CART) (P<0.05) and corticotrophin releasing hormone (CRH) (P<0.05) gene expression, while pro-opiomelanocortin (POMC), agouti-related peptide (AgRP), neuropeptide Y (NPY) and orexin-A gene expression were not modified with respect to vehicle-treated rats. We also found an increase in hypothalamic levodopa (l-dopa) (P<0.05) and norepinephrine (NE) (P<0.01) synthesis, without any effect on dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) metabolism. Furthermore, in hypothalamic synaptosomes, omentin-1 (10-100 ng/ml) stimulated basal NE release (ANOVA, P<0.0001; post hoc, P<0.001 vs. vehicle), in a dose-dependent manner, leaving unaffected both basal and depolarization-induced DA and 5-HT release. Finally, when synaptosomes were co-perfused with leptin and omentin-1, we observed that leptin was able to reverse omentin-1-induced stimulation of NE. In conclusion, the orexigenic effects of omentin-1 could be related, at least in part, to decreased CART and CRH gene expression and increased NE synthesis and release in the hypothalamus.

The cannabinoid CB1 receptor biphasically modulates motor activity and regulates dopamine and glutamate release region dependently

Cannabinoid administration modulates both dopaminergic and glutamatergic neurotransmission. The present study examines the effects of high and low dose WIN55,212-2, a CB1 receptor agonist, on extracellular dopamine and glutamate release in vivo via brain microdialysis in the nucleus accumbens (NAc), striatum and prefrontal cortex (PFC) in parallel to its effects on locomotor activity. WIN55,212-2 increased extracellular dopamine in the NAc (1 mg/kg i.p.), striatum (0.1 and 1 mg/kg i.p.) and PFC (1 mg/kg i.p.). Glutamate release was also elevated by WIN55,212-2 in the PFC (1 mg/kg i.p.) whereas in the NAc (0.1 and 1 mg/kg i.p.) and striatum, it was reduced (1 mg/kg i.p.). WIN55,212-2 administration produced hyperlocomotion at the lower dose (0.1 mg/kg i.p.) and hypolocomotion at the higher dose (1 mg/kg i.p.). Co-administration with the CB1 antagonist, SR-141716A (0.03 mg/kg i.p.), prevented the above effects. According to the present results, WIN55,212-2 affected locomotor activity biphasically while exerting converging effects on dopamine activity but diverging effects on glutamate release between cortical and subcortical regions, especially at the higher dose. These findings emphasize the involvement of the CB1 receptor in the simultaneous modulation of dopaminergic and glutamatergic neurotransmission in brain regions involved in reward and locomotion and suggest possible underlying mechanisms of acute cannabinoid exposure and its psychoactive and behavioural manifestations.

Cannabinoids prevent lipopolysaccharide-induced neurodegeneration in the rat substantia nigra in vivo through inhibition of microglial activation and NADPH oxidase

We investigated the effects of synthetic cannabinoids, WIN55,212-2 and HU210, on LPS-injected rat substantia nigra in vivo. Intranigral injection of LPS resulted in a significant loss of nigral dopaminergic (DA) neurons, as determined by Nissl staining and TH immunohistochemistry. LPS-induced neurotoxicity was accompanied by microglial activation, as demonstrated by OX-42 immunohistochemistry. In parallel, Western blot analysis, ELISA assay and hydroethidine histochemistry revealed activation of NADPH oxidase, as demonstrated by increased translocation of the cytosolic proteins p47(phox) and p67(phox), generation of reactive oxygen species (ROS) and increased level of proinflammatory cytokines (TNF-α and IL-1β), where degeneration of nigral DA neurons was evident. Interestingly, WIN55,212-2 and HU210 increased the survival of nigral DA neurons at 7days post-LPS treatment. Consistent with these results, cannabinoids inhibited activation of NADPH oxidase, ROS production and production of proinflammatory cytokines in the rat SN. The present data suggest that cannabinoids may be beneficial for the treatment of neurodegenerative diseases, such as PD, that are associated with microglial activation.

Cannabinoid receptor type 1 protects nigrostriatal dopaminergic neurons against MPTP neurotoxicity by inhibiting microglial activation

This study examined whether the cannabinoid receptor type 1 (CB(1)) receptor contributes to the survival of nigrostriatal dopaminergic (DA) neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. MPTP induced significant loss of nigrostriatal DA neurons and microglial activation in the substantia nigra (SN), visualized with tyrosine hydroxylase or macrophage Ag complex-1 immunohistochemistry. Real-time PCR, ELISA, Western blotting, and immunohistochemistry disclosed upregulation of proinflammatory cytokines, activation of microglial NADPH oxidase, and subsequent reactive oxygen species production and oxidative damage of DNA and proteins in MPTP-treated SN, resulting in degeneration of DA neurons. Conversely, treatment with nonselective cannabinoid receptor agonists (WIN55,212-2 and HU210) led to increased survival of DA neurons in the SN, their fibers and dopamine levels in the striatum, and improved motor function. This neuroprotection by cannabinoids was accompanied by suppression of NADPH oxidase reactive oxygen species production and reduced expression of proinflammatory cytokines from activated microglia. Interestingly, cannabinoids protected DA neurons against 1-methyl-4-phenyl-pyridinium neurotoxicity in cocultures of mesencephalic neurons and microglia, but not in neuron-enriched mesencephalic cultures devoid of microglia. The observed neuroprotection and inhibition of microglial activation were reversed upon treatment with CB(1) receptor selective antagonists AM251 and/or SR14,716A, confirming the involvement of the CB(1) receptor. The present in vivo and in vitro findings clearly indicate that the CB(1) receptor possesses anti-inflammatory properties and inhibits microglia-mediated oxidative stress. Our results collectively suggest that the cannabinoid system is beneficial for the treatment of Parkinson's disease and other disorders associated with neuroinflammation and microglia-derived oxidative damage.

Regulation of hippocampal cannabinoid CB1 receptor actions by adenosine A1 receptors and chronic caffeine administration: implications for the effects of Δ9-tetrahydrocannabinol on spatial memory

The cannabinoid CB(1) receptor-mediated modulation of γ-aminobutyric acid (GABA) release from inhibitory interneurons is important for the integrity of hippocampal-dependent spatial memory. Although adenosine A(1) receptors have a central role in fine-tuning excitatory transmission in the hippocampus, A(1) receptors localized in GABAergic cells do not directly influence GABA release. CB(1) and A(1) receptors are the main targets for the effects of two of the most heavily consumed psychoactive substances worldwide: Δ(9)-tetrahydrocannabinol (THC, a CB(1) receptor agonist) and caffeine (an adenosine receptor antagonist). We first tested the hypothesis that an A(1)-CB(1) interaction influences GABA and glutamate release in the hippocampus. We found that A(1) receptor activation attenuated the CB(1)-mediated inhibition of GABA and glutamate release and this interaction was manifested at the level of G-protein activation. Using in vivo and in vitro approaches, we then investigated the functional implications of the adenosine-cannabinoid interplay that may arise following chronic caffeine consumption. Chronic administration of caffeine in mice (intraperitoneally, 3 mg/kg/day, for 15 days, >12 h before trials) led to an A(1)-mediated enhancement of the CB(1)-dependent acute disruptive effects of THC on a short-term spatial memory task, despite inducing a reduction in cortical and hippocampal CB(1) receptor number and an attenuation of CB(1) coupling with G protein. A(1) receptor levels were increased following chronic caffeine administration. This study shows that A(1) receptors exert a negative modulatory effect on CB(1)-mediated inhibition of GABA and glutamate release, and provides the first evidence of chronic caffeine-induced alterations on the cannabinoid system in the cortex and hippocampus, with functional implications in spatial memory.

Cannabinoid agonist WIN55,212 in vitro inhibits interleukin-6 (IL-6) and monocyte chemo-attractant protein-1 (MCP-1) release by rat pancreatic acini and in vivo induces dual effects on the course of acute pancreatitis

BACKGROUND

Cannabinoids (CBs) evoke their effects by activating the cannabinoid receptor subtypes CB1-r and CB2-r and exert anti-inflammatory effects altering chemokine and cytokine expression. Various cytokines and chemokines are produced and released by rodent pancreatic acini in acute pancreatitis. Although CB1-r and CB2-r expressed in rat exocrine pancreatic acinar cells do not modulate digestive enzyme release, whether they modulate inflammatory mediators remains unclear. We investigated the CB-r system role on exocrine pancreas in unstimulated conditions and during acute pancreatitis.

METHODS

We evaluated in vitro and in vivo changes induced by WIN55,212 on the inflammatory variables amylasemia, pancreatic edema and morphology, and on acinar release and content of the cytokine interleukin-6 (IL-6) and chemokine monocyte chemo-attractant protein-1 (MCP-1) in untreated rats and rats with caerulein (CK)-induced pancreatitis.

KEY RESULTS

In the in vitro experiments, WIN55,212 (10(-6) mol L(-1)) inhibited IL-6 and MCP-1 release from acinar cells of unstimulated rats and after CK-induced pancreatitis. In vivo, when rats were pretreated with WIN55,212 (2 mg kg(-1), intraperitoneally) before experimentally-induced pancreatitis, serum amylase, pancreatic edema and IL-6 and MCP-1 acinar content diminished and pancreatic morphology improved. Conversely, when rats with experimentally-induced pancreatitis were post-treated with WIN55,212, pancreatitis worsened.

CONCLUSIONS & INFERENCES

These findings provide new evidence showing that the pancreatic CB1-r/CB2-r system modulates pro-inflammatory factor levels in rat exocrine pancreatic acinar cells. The dual, time-dependent WIN55,212-induced changes in the development and course of acute pancreatitis support the idea that the role of the endogenous CB receptor system differs according to the local inflammatory status.

Interactions between CB(1) receptors and TRPV1 channels mediated by 12-HPETE are cytotoxic to mesencephalic dopaminergic neurons

BACKGROUND AND PURPOSES

We recently proposed the existence of neurotoxic interactions between the cannabinoid type 1 (CB(1)) receptor and transient receptor potential vanilloid 1 (TRPV1) channels in rat mesencephalic cultures. This study seeks evidence for the mediator(s) and mechanisms underlying the neurotoxic interactions between CB(1) receptors and TRPV1 in vitro and in vivo.

EXPERIMENTAL APPROACH

The mediator(s) and mechanism(s) for the interactions between CB(1) receptors and TRPV1 were evaluated by cell viability assays, immunocytochemistry, Fura-2 calcium imaging, mitochondrial morphology assay, ELISA and Western blot assay in vitro in neuron-enriched mesencephalic cultures. Injections into the substantia nigra and subsequent cell counts were also used to confirm these interactions in vivo.

KEY RESULTS

The neurotoxic interactions were mediated by 12(S)-hydroperoxyeicosatetraenoic acid (12(S)-HPETE), an endogenous TRPV1 agonist. CB(1) receptor agonists (HU210 and WIN55,212-2) increased the level of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a downstream metabolite of 12(S)-HPETE, which stimulates TRPV1-mediated death of mesencephalic neurons, both in vitro and in vivo. The neurotoxicity was mediated by increased intracellular Ca(2+) concentration ([Ca(2+)](i)) through TRPV1, consequently leading to mitochondrial damage and was attenuated by baicalein, a 12-lipoxygenase inhibitor.

CONCLUSION AND IMPLICATIONS

Activation of CB(1) receptors in rat mesencephalic neurons was associated with biosynthesis of 12(S)-HPETE, which in turn stimulated TRPV1 activity, leading to increased [Ca(2+)](i), mitochondrial damage and neuronal death.

The pharmacology of the endocannabinoid system: functional and structural interactions with other neurotransmitter systems and their repercussions in behavioral addiction

Addiction is a chronic, recurring and complex disorder. It is characterized by anomalous behaviors that are linked to permanent or long-lasting neurobiological alterations. Furthermore, the endocannabinoid system has a crucial role in mediating neurotransmitter release as one of the main neuromodulators of the mammalian central nervous system. The purpose of the present review is to instruct readers about the functional and structural interactions between the endocannabinoid system and the main neurotransmitter systems of the central nervous system in the context of drug addiction. With this aim, we have systematically reviewed the main findings of most of the existing literature that explores cross-talk in the five brain areas that are most traditionally implicated in addiction: amygdala, prefrontal cortex, nucleus accumbens, hippocampus and ventral tegmental area (VTA). The neurotransmission systems influenced by the pharmacology of the endocannabinoid system in these brain areas, which are reviewed here, are gamma-aminobutyric acid (GABA), glutamate, the main biogenic amines (dopamine, noradrenaline and serotonin), acetylcholine and opioids. We show that all of these neurotransmitter systems can be modulated differentially in each brain area by the activation or deactivation of cannabinoid CB1 brain receptors. Specifically, most of the studies relate to the hippocampus and nucleus accumbens. Moreover, the neurotransmitter with the fewest number of related studies is acetylcholine (excepting in the hippocampus), whereas there is a large number that evaluates GABA, glutamate and dopamine. Finally, we propose a possible interpretation of the role of the endocannabinoid system in the phenomenon of addiction.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.

Symptom-related changes of endocannabinoid and palmitoylethanolamide levels in brain areas of R6/2 mice, a transgenic model of Huntington's disease

Previous studies have shown an impairment of the endocannabinoid system in experimental models of Huntington's disease. In transgenic R6/2 mice, created by inserting exon 1 of the human IT15 mutant gene into the mouse, and exhibiting 150 CAG repeats as well as signs of HD, a progressive decline of CB(1) receptor expression and an abnormal sensitivity to CB(1) receptor stimulation have been reported. Here, by using isotope-dilution liquid chromatography-mass spectrometry, we investigated whether the levels of three endogenous neuroprotective substances, the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and palmitoylethanolamide (PEA), are altered in different brain areas of transgenic R6/2 versus wild-type (WT) mice at two different disease phases, i.e. in pre-symptomatic (4.5 weeks) or overtly symptomatic (10 weeks) R6/2 mice versus age-matched WT mice (n=4/group). Except for a approximately 25% decrease in 2-AG levels in the cortex, no significant changes in endocannabinoid and PEA levels were observed in pre-symptomatic R6/2 versus WT mice. By contrast, in symptomatic R6/2 mice the levels of all three compounds were significantly (approximately 30-60%) decreased in the striatum, whereas little changes were observed in the hippocampus, and a approximately 28% decrease of 2-AG levels, accompanied by a approximately 50% increase of AEA levels, was found in the cortex. These findings show that endocannabinoid levels change in a disease phase- and region-specific way in the brain of R6/2 mice and indicate that an impaired endocannabinoid system is a hallmark of symptomatic HD, thus suggesting that drugs inhibiting endocannabinoid degradation might be used to treat this disease.

Acute, chronic and withdrawal effects of the cannabinoid receptor agonist WIN55212-2 on the sequential activation of MAPK/Raf-MEK-ERK signaling in the rat cerebral frontal cortex: short-term regulation by intrinsic and extrinsic pathways

The cannabinoids (CB) modulate the extracellular signal-regulated kinase (ERK), leading to various forms of plasticity in the brain. Little is known, however, on the in vivo short- and long-term activation and regulation of the components of mitogen-activated protein kinase (MAPK)/ERK signaling by CB. The CB agonist WIN55212-2 (8 mg/kg) increased the immunodensities of phosphorylated c-Raf-1 (42%), MEK1/2 (63%), ERK1 (24%), and ERK2 (28%) in the rat cerebral frontal cortex. These effects were antagonized by SR141716A (rimonabant, 10 mg/kg), a selective CB(1) receptor antagonist. Repeated WIN55212-2 treatment (2-8 mg/kg for 5 days) resulted in tachyphylaxis to the acute activation of Raf-MEK-ERK signaling. Acute WIN55212-2 also induced a hypothermic effect in rats, which was reduced after repeated administration (tolerance). Treatment with SR141716A after chronic WIN55212-2 resulted in the expected cannabinoid withdrawal syndrome, without concomitant alterations in the phosphorylation state of c-Raf-1, MEK1/2, or ERK1/2. Pretreatment with SL327 (20 mg/kg, a MEK1/2 inhibitor) increased the basal phosphorylation of c-Raf-1 (40%) and MEK1/2 (74%; feedback regulation) and fully prevented the up-regulation of ERK1/2 (23-31%) induced by WIN55212-2. Pretreatment with MK801 (1 mg/kg, a NMDA receptor antagonist) effectively blocked the up-regulation c-Raf-1 (41%), MEK1/2 (57%) and ERK1/2 (25-30%) induced by the CB agonist. The main findings demonstrate that the acute stimulation of CB(1) receptors in the frontal cortex results in the sequential phosphorylation of Raf-MEK-ERK cascade, in which c-Raf-1 activation (rate-limiting process) plays a crucial role. Moreover, the in vivo stimulating effect of WIN55212-2 on Raf-MEK-ERK signaling is under the extrinsic regulation of an excitatory glutamatergic mechanism.

CB(1) cannabinoid receptors inhibit the glutamatergic component of KCl-evoked excitation of locus coeruleus neurons in rat brain slices

CB(1) cannabinoid receptors located at presynaptic sites suppress synaptic transmission in the rat brain. The aim of this work was to examine by single-unit extracellular techniques the effect of the synthetic cannabinoid receptor agonist WIN 55212-2 on KCl-evoked excitation of locus coeruleus neurons in rat brain slices. Short applications of KCl (30 mM) increased by 9-fold the firing rate of locus coeruleus cells. Perfusion with the GABA(A) receptor antagonist picrotoxin (100 microM) increased KCl-evoked effect, whereas NMDA and non-NMDA glutamate receptor antagonists (D-AP5 100 microM and CNQX 30 microM, respectively) were able to decrease KCl-evoked effect only in the presence of picrotoxin (100 microM). Bath application of WIN 55212-2 (10 microM) inhibited KCl-evoked effect; this inhibition was blocked by the CB(1) receptor antagonist AM 251 (1 microM). However, a lower concentration of WIN 55212-2 (1 microM) did not significantly change KCl effect. In the presence of picrotoxin (100 microM), perfusion with D-AP5 (100 microM) or CNQX (30 microM) blocked WIN 55212-2-induced inhibition, although picrotoxin (100 microM) itself failed to affect cannabinoid effect. In conclusion, GABAergic and glutamatergic components are both involved in KCl-evoked excitation of LC neurons, although CB(1) receptors only seem to inhibit the glutamatergic component of KCl effect in the locus coeruleus.