Cannabinoid CB2 receptors and hypersensitivity to methamphetamine: Vulnerability to schizophrenia.

The human cannabinoid receptor 2 (CB2R) gene CNR2 has been associated with schizophrenia development. Inbred mice treated with the CB2R inverse agonist AM630 and challenged with methamphetamine (MAP) showed reduced prepulse inhibition (%PPI) response and locomotor hyperactivity, both behavioral measures in rodents that correlate with psychosis. Mice lacking CB2R on striatal dopaminergic neurons exhibit a hyperdopaminergic tone and a hyperactivity phenotype. Hyperdopaminergia plays a role in the etiology of schizophrenia. This study aimed to determine the direct role of CB2R, heterozygous Cnr2 gene knockout (Het) mice treated with MAP to induce behavioral sensitivity mimicking a schizophrenia-like human phenotype. Additionally, the study aims to explore the unique modulation of dopamine activity by neuronal CB2R. Conditional knockout DAT-Cnr2-/- mice were evaluated in response to MAP treatments for this purpose. Sensorimotor gating deficits in DAT-Cnr2-/- mice were also evaluated. Het mice developed reverse tolerance (RT) to MAP-enhanced locomotor activity, and RT reduced the %PPI compared to wild-type (WT) mice. DAT-Cnr2-/- mice showed an increased sensitivity to stereotypical behavior induced by MAP and developed RT to MAP. DAT-Cnr2-/- mice exhibit a reduction in %PPI and alter social interaction, another core symptom of schizophrenia. These results demonstrate that there is an interaction between neuronal CB2R and MAP treatment, which increases the risk of schizophrenia-like behavior in this mouse model. This finding provides evidence for further studies targeting CB2R as a potential schizophrenia therapy.

Cannabis: Drug of Abuse and Therapeutic Agent, Two Sides of the Same Coin.

The consumption of Cannabis sativa plant, known as marijuana in the Western world, for different purposes (therapeutic, intoxicating, and spiritual) due to its psychoactive effects, can be traced back to ancient times. Cannabis is the most used illicit drug worldwide; however, its legal status is changing rapidly. Cannabis regulation will allow a better understanding of its effects as a misused drug, including new challenges, such as the availability of highly potent Cannabis extracts. Furthermore, scientific research is making significant efforts to take advantage of the potential therapeutic uses of Cannabis active compounds. The science of Cannabis derivatives started with the identification of the phytocannabinoids Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), allowing the formal study of the complex set of effects triggered by Cannabis consumption and the deciphering of its pharmacology. Δ9-THC is recognized as the compound responsible for the psychoactive and intoxicating effects of Cannabis. Its study led to the discovery of the endocannabinoid system, a neuromodulatory system widespread in the human body. CBD does not induce intoxication and for that reason, it is the focus of the search for cannabinoid potential clinical applications. This review examines the current state of knowledge about contrasting perspectives on the effects of Cannabis, Δ9-THC, and CBD: their abuse liability and potential therapeutic use; two sides of the same coin.

The endogenous cannabinoid system modulates male sexual behavior expression.

The endocannabinoid system (ECS) plays a key neuromodulatory role in the brain. Main features of endocannabinoids (eCBs) are that they are produced on demand, in response to enhanced neuronal activity, act as retrograde messengers, and participate in the induction of brain plasticity processes. Sexual activity is a motivated behavior and therefore, the mesolimbic dopaminergic system (MSL) plays a central role in the control of its appetitive component (drive to engage in copulation). In turn, copulation activates mesolimbic dopamine neurons and repeated copulation produces the continuous activation of the MSL system. Sustained sexual activity leads to the achievement of sexual satiety, which main outcome is the transient transformation of sexually active male rats into sexually inhibited animals. Thus, 24 h after copulation to satiety, the sexually satiated males exhibit a decreased sexual motivation and do not respond to the presence of a sexually receptive female with sexual activity. Interestingly, blockade of cannabinoid receptor 1 (CB1R) during the copulation to satiety process, interferes with both the appearance of the long-lasting sexual inhibition and the decrease in sexual motivation in the sexually satiated males. This effect is reproduced when blocking CB1R at the ventral tegmental area evidencing the involvement of MSL eCBs in the induction of this sexual inhibitory state. Here we review the available evidence regarding the effects of cannabinoids, including exogenously administered eCBs, on male rodent sexual behavior of both sexually competent animals and rat sub populations spontaneously showing copulatory deficits, considered useful to model some human male sexual dysfunctions. We also include the effects of cannabis preparations on human male sexual activity. Finally, we review the role played by the ECS in the control of male sexual behavior expression with the aid of the sexual satiety phenomenon. Sexual satiety appears as a suitable model for the study of the relationship between eCB signaling, MSL synaptic plasticity and the modulation of male sexual motivation under physiological conditions that might be useful for the understanding of MSL functioning, eCB-mediated plasticity and their relationship with motivational processes.

Cannabis: Drug of Abuse and Therapeutic Agent, Two Sides of the Same Coin

ABSTRACT The consumption of Cannabis sativa plant, known as marijuana in the Western world, for different purposes (therapeutic, intoxicating, and spiritual) due to its psychoactive effects, can be traced back to ancient times. Cannabis is the most used illicit drug worldwide; however, its legal status is changing rapidly. Cannabis regulation will allow a better understanding of its effects as a misused drug, including new challenges, such as the availability of highly potent Cannabis extracts. Furthermore, scientific research is making significant efforts to take advantage of the potential therapeutic uses of Cannabis active compounds. The science of Cannabis derivatives started with the identification of the phytocannabinoids Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), allowing the formal study of the complex set of effects triggered by Cannabis consumption and the deciphering of its pharmacology. Δ9-THC is recognized as the compound responsible for the psychoactive and intoxicating effects of Cannabis. Its study led to the discovery of the endocannabinoid system, a neuromodulatory system widespread in the human body. CBD does not induce intoxication and for that reason, it is the focus of the search for cannabinoid potential clinical applications. This review examines the current state of knowledge about contrasting perspectives on the effects of Cannabis, Δ9-THC, and CBD: their abuse liability and potential therapeutic use; two sides of the same coin.

Crosstalk between the endocannabinoid and mid-brain dopaminergic systems: Implication in dopamine dysregulation.

Endocannabinoids (eCBs) and the expanded endocannabinoid system (ECS)-"endocannabinoidome", consists of the endogenous ligands, eCBs, their canonical and non-canonical receptor subtypes, and their synthesizing and metabolizing enzymes. This system modulates a wide range of body functions and acts as a retrograde signaling system within the central nervous system (CNS) by inhibition of classical transmitters, and plays a vital modulatory function on dopamine, a major neurotransmitter in the CNS. Dopamine is involved in different behavioral processes and contributes to different brain disorders-including Parkinson's disease, schizophrenia, and drug addiction. After synthesis in the neuronal cytosol, dopamine is packaged into synaptic vesicles until released by extracellular signals. Calcium dependent neuronal activation results in the vesicular release of dopamine and interacts with different neurotransmitter systems. The ECS, among others, is involved in the regulation of dopamine release and the interaction occurs either through direct or indirect mechanisms. The cross-talk between the ECS and the dopaminergic system has important influence in various dopamine-related neurobiological and pathologic conditions and investigating this interaction might help identify therapeutic targets and options in disorders of the CNS associated with dopamine dysregulation.

The Polypharmacological Effects of Cannabidiol.

Cannabidiol (CBD) is a major phytocannabinoid present in Cannabis sativa (Linneo, 1753). This naturally occurring secondary metabolite does not induce intoxication or exhibit the characteristic profile of drugs of abuse from cannabis like Δ9-tetrahydrocannabinol (∆9-THC) does. In contrast to ∆9-THC, our knowledge of the neuro-molecular mechanisms of CBD is limited, and its pharmacology, which appears to be complex, has not yet been fully elucidated. The study of the pharmacological effects of CBD has grown exponentially in recent years, making it necessary to generate frequently updated reports on this important metabolite. In this article, a rationalized integration of the mechanisms of action of CBD on molecular targets and pharmacological implications in animal models and human diseases, such as epilepsy, pain, neuropsychiatric disorders, Alzheimer's disease, and inflammatory diseases, are presented. We identify around 56 different molecular targets for CBD, including enzymes and ion channels/metabotropic receptors involved in neurologic conditions. Herein, we compiled the knowledge found in the scientific literature on the multiple mechanisms of actions of CBD. The in vitro and in vivo findings are essential for fully understanding the polypharmacological nature of this natural product.

The nucleus accumbens dopamine increase, typically triggered by sexual stimuli in male rats, is no longer produced when animals are sexually inhibited due to sexual satiety.

RATIONALE: Exposure of male rats to an inaccessible receptive female and copulation increases dopamine (DA) levels in the nucleus accumbens (NAcc). Males copulating to satiety become sexually inhibited and most of them do not display sexual activity when presented with a sexually receptive female 24 h later. This inhibitory state can be pharmacologically reversed. There are no studies exploring NAcc DA levels during this sexual inhibitory state. OBJECTIVES: To characterize changes in NAcc DA and its metabolites' levels during sexual satiety development, during the well-established sexual inhibitory state 24 h later, and during its pharmacological reversal. METHODS: Changes in NAcc DA and its metabolites were measured in sexually experienced male rats, using in vivo microdialysis, during copulation to satiety, when presented to a new sexually receptive female 24 h later, and during the pharmacological reversal of the sexual inhibition by anandamide. RESULTS: NAcc DA levels remained increased during copulation to satiety. DA basal levels were significantly reduced 24 h after copulation to satiety, as compared to the initial basal levels. Presenting a receptive female behind a barrier 24 h after satiety did not induce the typical NAcc DA elevation in the sexually satiated males but there was a decrease that persisted when they got access to the female, with which they did not copulate. Anandamide injection slightly increased NAcc DA levels coinciding with sexual satiety reversal. CONCLUSIONS: Reduced NAcc DA concentrations coincide with the inhibition of an instinctive, natural rewarding behavior suggesting that there might be a DA concentration threshold needed to be responsive to a rewarding stimulus.

Cell-Type Specific Deletion of CB2 Cannabinoid Receptors in Dopamine Neurons Induced Hyperactivity Phenotype: Possible Relevance to Attention-Deficit Hyperactivity Disorder.

DAT-Cnr2 mice are conditional knockout (cKO) animals that do not express cannabinoid CB2 receptors (CB2R), in midbrain dopamine neurons. The hyperactivity phenotype of DAT-Cnr2 cKO mice were paradoxically reduced by low dose of amphetamine. Here, we report on the locomotor activity analysis in male and female adolescent (PND 30 ± 2) mice in basal conditions and in response to different doses of amphetamine, using the Open Field (OF), Elevated Plus-Maze (EPM) tests and the Novel Object Recognition (NOR) task as a putative model of attention deficit hyperactivity disorder (ADHD). Results showed that both male and female adolescent DAT-Cnr2 mice displayed significant increases in distance traveled in the OF test compared with WT mice. However, 2 mg/kg dose of amphetamine reduced the distance traveled by the DAT-Cnr2 but was increased in the WT mice. In the EPM test of anxiety-like behavioral responses, DAT-Cnr2 spent more time in the open arms of the maze than the WT mice, suggesting a reduction in anxiety-like response. DAT-Cnr2 mice showed significant increase in the number of unprotected head dips in the maze test and in the cliff avoidance reaction (CAR) test demonstrating impulsivity and risky behavior. DAT-Cnr2 mice also exhibited deficient response in the delay decision making (DDM), with impulsive choice. Both DAT-Cnr2 and WT were able to recognize the new object in the NOR task, but the exploration by the DAT-Cnr2 was less than that of the WT mice. Following the administration of 2 mg/kg of amphetamine, the similarities and differential performances of the DAT-Cnr2 and WT mice in the EPM test and NOR task was probably due to increase in attention. Microglia activation detected by Cd11b immunolabelling was enhanced in the hippocampus in DAT-Cnr2 cKO than in WT mice, implicating neuro-immune modulatory effects of CB2R. The results demonstrates that DAT-Cnr2 cKO mice with cell-type specific deletion of CB2R in midbrain dopaminergic neurons may represent a possible model for studying the neurobiological basis of ADHD.

Low Basal CB2R in Dopamine Neurons and Microglia Influences Cannabinoid Tetrad Effects.

There are two well-characterized cannabinoid receptors (CB1R and CB2R and other candidates): the central nervous system (CNS) enriched CB1R and peripheral tissue enriched CB2R with a wide dynamic range of expression levels in different cell types of human tissues. Hepatocytes and neurons express low baseline CB1R and CB2R, respectively, and their cell-type-specific functions are not well defined. Here we report inducible expression of CB1R in the liver by high-fat and high sugar diet and CB2R in cortical neurons by methamphetamine. While there is less controversy about hepatocyte CB1R, the presence of functional neuronal CB2R is still debated to date. We found that neuron CB2R basal expression was higher than that of hepatocyte CB1R by measuring mRNA levels of specific isoform CB2A in neurons isolated by fluorescence-activated cell sorting (FACS) and CB1A in hepatocytes isolated by collagenase perfusion of liver. For in vivo studies, we generated hepatocyte, dopaminergic neuron, and microglia-specific conditional knockout mice (Abl-Cnr1Δ, Dat-Cnr2Δ, and Cx3cr1-Cnr2Δ) of CB1R and CB2R by crossing Cnr1f/f and Cnr2f/f strains to Abl-Cre, Dat-Cre, and Cx3cr1-Cre deleter mouse strains, respectively. Our data reveals that neuron and microglia CB2Rs are involved in the "tetrad" effects of the mixed agonist WIN 55212-2, CB1R selective agonist arachidonyl-2'-chloroethylamide (ACEA), and CB2R selective agonist JWH133. Dat-Cnr2Δ and Cx3cr1-Cnr2Δ mice showed genotypic differences in hypomobility, hypothermia, analgesia, and catalepsy induced by the synthetic cannabinoids. Alcohol conditioned place preference was abolished in DAT-Cnr2Δ mice and remained intact in Cx3cr1-Cnr2Δ mice in comparison to WT mice. These Cre-loxP recombinant mouse lines provide unique approaches in cannabinoid research for dissecting the complex endocannabinoid system that is implicated in many chronic disorders.

Involvement of CB2 Receptors in the Neurobehavioral Effects of Catha Edulis (Vahl) Endl. (Khat) in Mice.

There is behavioral evidence for the interaction between crude khat extract and the endocannabinoid system, whereby the endocannabinoid system alters khat extract-mediated behavioral effects through modulation of the monoaminergic system. The objective of this study was to investigate the role of the endocannabinoid system on the neurobehavioral effect of khat extract in mice following concomitant administration of khat extract and the CB2R agonist, JWH133. Locomotor activity test, immunohistochemistry, and reverse transcriptase polymerase chain reaction technique were utilized to assess locomotor activity, tyrosine hydroxylase immunoreactivity, and expression of dopamine transporter mRNA gene. The results show sub-acute administration of khat extract alone increased locomotor activity in mice and co-administration of the CB2R agonist, JWH133, reduced khat extract induced hyperlocomotor activity. The data revealed that cell type specific deletion of CB2Rs on dopaminergic neurons increased the hyperlocomotor behavior of khat extract. Furthermore, the results revealed that khat extract attenuated MPTP induced motor deficits, which is enhanced by JWH133. Khat extract also increased expression of tyrosine hydroxylase positive cells and expression of dopamine transporter mRNA gene in wild type mice. Nevertheless, JWH133 did not alter the effect of khat extract on tyrosine hydroxylase immunoreactivity and dopamine transporter mRNA expression when given together with khat extract. Taken together, the results suggest that the CB2Rs selectively interact with khat extract-mediated locomotor effects and could be utilized as therapeutic target in central nervous system movement disorders associated with dopamine dysregulation.

Endocannabinoids Interact With the Dopaminergic System to Increase Sexual Motivation: Lessons From the Sexual Satiety Phenomenon.

In male rats, copulation to satiety induces a long-lasting sexual inhibitory state, considered to rely on a decreased sexual motivation. Dopaminergic transmission at the mesolimbic system plays a central role in the regulation of male sexual motivation. Endocannabinoids (eCBs) modulate the activity of the mesolimbic system and both dopamine (DA) and cannabinoid receptor activation reverses the sexual inhibition that characterizes sexually satiated rats. The eCB anandamide reverses sexual satiety when systemically administered or infused into the ventral tegmental area (VTA), the region where the activity of mesolimbic dopaminergic neurons is regulated. Thus, it could be thought that sexual motivation is diminished during the long-lasting sexual inhibition of sexually satiated rats and that eCBs reverse that inhibition through the modulation of the dopaminergic system. To test this hypothesis, we assessed the motivational state of sexually satiated male rats and determined if 2-arachidonoylglycerol (2-AG), the most abundant eCB and a full cannabinoid receptor agonist, also reversed the sexual inhibitory state. To establish the possible interaction between 2-AG and anandamide with the dopaminergic system for the reversal of sexual satiety, we analyzed the effects of the co-administration of each eCB and DA receptor agonists or antagonists. Results showed that 24-h after copulation to satiety, when the sexual inhibition is well established, the males' sexual motivation is diminished as measured in the sexual incentive motivation test. 2-AG, similarly to anandamide, reverses sexual satiety through the activation of CB1 receptors and both eCBs interact with the dopaminergic system to reverse the sexual inhibitory state. 2-AG effects are mediated by the modulation of the D2-like DA receptor family, whereas anandamide's effects are clearly mediated by the modulation of the D1-like DA receptor family and the activation of D2-like DA receptors. Present results evidence that a reduced sexual motivation underlies the sexual inhibitory state of sexually satiated rats and support the notion that eCBs reverse sexual satiety by modulating dopaminergic transmission, presumably at the mesolimbic system. Anandamide and 2-AG have a different interaction with D1-like and D2-like DA receptor families. Altogether present data endorse the association of the eCB system with the regulation of the motivational tone at the mesolimbic system.

Developmental and behavioral effects in neonatal and adult mice following prenatal activation of endocannabinoid receptors by capsaicin.

Despite the apparent abundance of ligand-gated transient receptor potential vanilloid type 1 (TRPV1) and possible cross talk between the endocannabinoid and endovanilloid systems in the central nervous system (CNS), it is unclear what role TRPV1 receptor activation in CNS plays in neurobehavioral development. We previously reported that capsaicin or WIN55212-2 induces risk aversion in the plus-maze test, which was dependent on the gender and mouse strain used. In this study, pregnant BALBc mice were administered capsaicin (1.0 or 4.0 mg/kg, i.p.) during the second week of gestation. Developmental effects of prenatal exposure to capsaicin were assessed in neonates, and behavioral effects were assessed in adult offspring. Gender- and dose-specific variations in ultrasonic vocalizations, weight gain, righting reflex, and general activity of the pups were observed. Prenatal exposure to capsaicin altered plus-maze performance, especially with further exogenous capsaicin challenge. Furthermore, dose- and gender-specific effects were evident in the conditioned place preference/aversion paradigm following conditioning with capsaicin in adult animals. The capsaicin-induced aversion in the plus-maze test was enhanced by WIN55212-2 and blocked by pretreatment with vanilloid antagonist capsazepine or the CB1 receptor antagonist rimonabant, demonstrating an interaction between the endocannabinoid and endovanilloid systems in CNS. Taken together, the interaction between the endocannabinoid and endovanilloid signaling systems can be exploited for therapeutic applications in health and disease.

Behavioral effects of psychostimulants in mutant mice with cell-type specific deletion of CB2 cannabinoid receptors in dopamine neurons.

Activation of the endocannabinoid system modulate dopaminergic pathways that are involved in the effects of psychostimulants including amphetamine, cocaine, nicotine and other drugs of abuse. Genetic deletion or pharmacological activation of CB2 cannabinoid receptor is involved in the modulation of the effects of psychostimulants and their rewarding properties. Here we report on the behavioral effects of psychostimulants in DAT-Cnr2 conditional knockout (cKO) mice with selective deletion of type 2 cannabinoid receptors in dopamine neurons. There was enhanced psychostimulant induced hyperactivity in DAT-Cnr2 cKO mice, but the psychostimulant-induced sensitization was absent in DAT-Cnr2 cKO compared to the WT mice. Intriguingly, lower doses of amphetamine reduced locomotor activity of the DAT-Cnr2 cKO mice. While cocaine, amphetamine and methamphetamine produced robust conditioned place preference (CPP) in both DAT-Cnr2 cKO and WT mice, nicotine at the dose used induced CPP only in the WT but not in the DAT-Cn2 cKO mice. However, pre-treatment with the CB2R selective agonist JWH133, blocked cocaine and nicotine induced CPP in the WT mice. The deletion of CB2Rs in dopamine neurons modified the levels of tyrosine hydroxylase, and reduced the expression of dopamine transporter gene expression in DAT-Cnr2 cKO midbrain region. Taken together, our data suggest that CB2Rs play a role in the modulation of dopamine-related effects of psychostimulants and could be exploited as therapeutic target in psychostimulant addiction and other psychiatric disorders associated with dopamine dysregulation.

Sexual interaction is essential for the transformation of non-copulating rats into sexually active animals by the endocannabinoid anandamide.

The endocannabinoid anandamide (AEA) transforms half of the population of previously non-copulating (NC) rats into sexually active animals in a long-lasting manner. The aim of this work was to explore the nature of this transformation. We identified the dose range in which AEA induces mating behavior in previously NC rats, which evidenced a dose-based, biphasic profile for AEA to induce the transformation of NC rats. We demonstrate that the sexual interaction with a receptive female, involving at least an intromission, is essential for AEA to induce the transformation of NC rats. This AEA-induced conversion is centrally mediated and involves the activation of CB1 receptors. Results indicate that the sexual impairment of this population of NC rats relies on their incapacity to initiate sexual activity and that an unidentified brain inhibitory influence on sexual behavior expression is removed by AEA treatment, allowing previously NC rats to show copulatory behavior in a long-lasting manner. The inhibitory influence is not removed by AEA treatment when animals are not allowed to have sexual contact with the female immediately after AEA injection. The same result was found for the opioid receptor antagonist naloxone, the other treatment reported to induce copulation in rats classified as NC. These data suggest that sexual behavior expression could depend on two different neural mechanisms at two different moments: one involved in the display of the first copulatory response and another responsible for maintaining subsequent sexual behavior responding.

Behavioral Evaluation of Seeking and Preference of Alcohol in Mice Subjected to Stress.

The alcohol preference model is one of the most widely used animal models relevant to alcoholism. Stressors increase alcohol consumption. Here we present a protocol for a rapid and useful tool to test alcohol preference and stress-induced alcohol consumption in mice. In this model, animals are given two bottles, one with a diluted solution of ethanol in water, and the other with tap water. Consumption from each bottle is monitored over a 24-h period over several days to assess the animal's relative preference for the ethanol solution over water. In the second phase, animals are stressed by restraining them for an hour daily and their subsequent preference of tap water or the ethanol solution is evaluated. Preference is measured by the volume and/or weight or liquid consumed daily, which is then converted to a preference ratio. The alcohol preference model was combined with the conditioned place preference paradigm to determine alcohol conditioning and preference following the deletion of CB2 cannabinoid receptors in dopaminergic neurons in the DAT-Cnr2 Cre-recombinant conditional knockout (cKO) mice in comparison with the wild-type control mice.

Cannabinoid type 2 receptors in dopamine neurons inhibits psychomotor behaviors, alters anxiety, depression and alcohol preference.

Cannabinoid CB2 receptors (CB2Rs) are expressed in mouse brain dopamine (DA) neurons and are involved in several DA-related disorders. However, the cell type-specific mechanisms are unclear since the CB2R gene knockout mice are constitutive gene knockout. Therefore, we generated Cnr2-floxed mice that were crossed with DAT-Cre mice, in which Cre- recombinase expression is under dopamine transporter gene (DAT) promoter control to ablate Cnr2 gene in midbrain DA neurons of DAT-Cnr2 conditional knockout (cKO) mice. Using a novel sensitive RNAscope in situ hybridization, we detected CB2R mRNA expression in VTA DA neurons in wildtype and DAT-Cnr2 cKO heterozygous but not in the homozygous DAT-Cnr2 cKO mice. Here we report that the deletion of CB2Rs in dopamine neurons enhances motor activities, modulates anxiety and depression-like behaviors and reduces the rewarding properties of alcohol. Our data reveals that CB2Rs are involved in the tetrad assay induced by cannabinoids which had been associated with CB1R agonism. GWAS studies indicates that the CNR2 gene is associated with Parkinson's disease and substance use disorders. These results suggest that CB2Rs in dopaminergic neurons may play important roles in the modulation of psychomotor behaviors, anxiety, depression, and pain sensation and in the rewarding effects of alcohol and cocaine.

A new role for GABAergic transmission in the control of male rat sexual behavior expression.

GABAergic transmission in the ventral tegmental area (VTA) exerts a tonic inhibitory influence on mesolimbic dopaminergic neurons' activity. Blockade of VTA GABAA receptors increases dopamine release in the nucleus accumbens (NAcc). Increases in NAcc dopamine levels typically accompany sexual behavior display. Copulation to satiety is characterized by the instatement of a long lasting (72h) sexual behavior inhibition and the mesolimbic system appears to be involved in this phenomenon. GABAergic transmission in the VTA might play a role in the maintenance of this long lasting sexual inhibitory state. To test this hypothesis, in the present work we investigated the effect of GABAA receptor blockade in sexually exhausted males 24h after copulation to satiety, once the sexual inhibitory state is established, and compared it with its effect in sexually experienced rats. Results showed that low doses of systemically administered bicuculline induced sexual behavior expression in sexually exhausted rats, but lacked an effect on copulation of sexually experienced animals. Intra-VTA bilateral infusion of bicuculline did not modify sexual behavior of sexually experienced rats, but induced sexual behavior expression in all the sexually exhausted males. Hence, GABA plays a role in the control of sexual behavior expression at the VTA. The role played by GABAergic transmission in male sexual behavior expression of animals with distinct sexual behavior conditions is discussed.

Intra-VTA anandamide infusion produces dose-based biphasic effects on male rat sexual behavior expression.

Sexual behavior is a natural reward and the mesolimbic (MSL) system is involved in the processing of its motivational component and reinforcing properties. Endocannabinoids control rewarding behaviors through the modulation of MSL system's activity. The endocannabinoid anandamide (AEA), systemically administered, produces dose-based, biphasic effects on male rat copulation, facilitating its expression at low doses in both, sexually experienced and sexually exhausted male rats. We hypothesized that AEA's sexual facilitative effects might be exerted at the MSL circuit. Therefore, in this work different AEA doses were bilaterally infused into the VTA of sexually experienced or sexually exhausted animals and their copulatory behavior recorded. Results showed that the lowest AEA dose tested lacked an effect, intermediate doses facilitated specific sexual parameters, and the highest dose inhibited copulation of sexually experienced males. In sexually exhausted animals low AEA doses reversed the sexual inhibition that characterizes sexual satiety, but this effect was lost at higher doses. Together, these data show that the VTA is a target for AEA's biphasic sexual effects suggesting a role of the MLS system in the actions of endocannabinoids on male rat sexual behavior.

Biphasic effects of anandamide on behavioural responses: emphasis on copulatory behaviour.

Endocannabinoids have emerged as important modulators of different neurotransmitter systems in the brain by acting as retrograde messengers. They are released from postsynaptic cell bodies, travel backwards across the synapsis and bind to their receptors located at the presynaptic terminal to inhibit neurotransmitter release. The fatty acid amide, arachidonoylethanolamide (anandamide), is an important endogenous ligand of the G-protein-coupled cannabinoid receptors CB1 and CB2. The aim of this mini-review is to outline the recent literature on the biphasic nature of the behavioural actions of anandamide, with particular focus on male rat sexual behaviour, and to examine whether dose-related activation of distinct receptors plays a role in the biphasic effects of this prototypical endocannabinoid.

Anandamide reduces the ejaculatory threshold of sexually sluggish male rats: possible relevance for human lifelong delayed ejaculation disorder.

INTRODUCTION: The sexually sluggish (SLG) male rat has been proposed as an animal model for the study of lifelong delayed ejaculation, a sexual dysfunction for which no treatment is available. Low endocannabinoid anandamide (AEA) doses facilitate sexual behavior display in normal sexually active and in noncopulating male rats through the activation of CB1 receptors. AIM: To establish whether low AEA doses reduced the ejaculatory threshold of SLG male rats by acting at CB1 receptors. METHODS: SLG male rats were intraperitoneally injected with different doses of AEA (0.1-3.0 mg/kg), the CB1 receptor antagonist AM251 (0.1-3.0 mg/kg), or their vehicles and tested for copulatory behavior during 60 minutes. Animals receiving AEA effective doses were subjected to a second sexual behavior test, 7 days later under drug-free conditions. To determine the participation of CB1 receptors in AEA-induced actions, SLG rats were pretreated with AM251 prior to AEA. MAIN OUTCOME MEASURES: The sexual parameters, intromission latency, number of mounts and intromissions, ejaculation latency, and interintromission interval. RESULTS: All sexual behavior parameters of SLG rats were significantly increased when compared with normal sexually experienced animals. Low AEA doses (0.3 and 1 mg/kg) significantly lowered the ejaculatory threshold of SLG rats, reducing the number of pre-ejaculatory intromissions and ejaculation latency. IL, M number, and locomotor activity were unaffected by AEA. Facilitation of the ejaculatory response of SLG rats disappeared 7 days after AEA injection. AM251 lacked an effect on copulation of SLG rats but blocked the AEA-induced lowering of the ejaculatory threshold. CONCLUSIONS: AEA appears to specifically target the ejaculatory threshold of SLG rats through the activation of CB1 receptors. This specificity along with the fact that AEA's effects are exerted acutely and at low doses makes this drug emerge as a promising treatment for the improvement of the ejaculatory response in men with primary delayed ejaculation.