Coexpression of the cannabinoid receptor type 1 with the corticotropin-releasing hormone receptor type 1 in distinct regions of the adult mouse forebrain

Endocannabinoid Signaling in the Central Amygdala and Bed Nucleus of the Stria Terminalis: Implications for the Pathophysiology and Treatment of Alcohol Use Disorder

High rates of relapse are a chronic and debilitating obstacle to effective treatment of alcohol use disorder (AUD); however, no effective treatments are available to treat symptoms induced by protracted abstinence. In the first part of this 2-part review series, we examine the literature supporting the effects of alcohol exposure within the extended amygdala (EA) neural circuitry. In Part 2, we focus on a potential way to combat negative affect associated with AUD, by exploring the therapeutic potential of the endogenous cannabinoid (eCB) system. The eCB system is a potent modulator of neural activity in the brain, and its ability to mitigate stress and negative affect has long been an area of interest for developing novel therapeutics. This review details the recent advances in our understanding of eCB signaling in 2 key regions of the EA, the central nucleus of the amygdala and the bed nucleus of the stria terminalis (BNST), and their role in regulating negative affect. Despite an established role for EA eCB signaling in reducing negative affect, few studies have examined the potential for eCB-based therapies to treat AUD-associated negative affect. In this review, we present an overview of studies focusing on eCB signaling in EA and cannabinoid modulation on EA synaptic activity. We further discuss studies suggesting dysregulation of eCB signaling in models of AUD and propose that pharmacological augmentation of eCB could be a novel approach to treat aspects of AUD. Lastly, future directions are proposed to advance our understanding of the relationship between AUD-associated negative affect and the EA eCB system that could yield new pharmacotherapies targeting negative affective symptoms associated with AUD.

Signaling pathways to and from the hypophysial pars tuberalis, an important center for the control of seasonal rhythms

Seasonal (circannual) rhythms play an important role for the control of body functions (reproduction, metabolism, immune responses) in nearly all living organisms. Also humans are affected by the seasons with regard to immune responses and mental functions, the seasonal affective disorder being one of the most prominent examples. The hypophysial pars tuberalis (PT), an important interface between the hypophysial pars distalis and neuroendocrine centers in the brain, plays an essential role in the regulation of seasonal functions and may even be the seat of the circannual clock. Photoperiodic signals provide a major input to the PT. While the perception of these signals involves extraocular photoreceptors in non-mammalian species (birds, fish), mammals perceive photoperiodic signals exclusively in the retina. A multisynaptic pathway connects the retina with the pineal organ where photoperiodic signals are translated into the neurohormone melatonin that is rhythmically produced night by night and encodes the length of the night. Melatonin controls the functional activity of the mammalian PT by acting upon MT1 melatonin receptors. The PT sends its output signals via retrograde and anterograde pathways. The retrograde pathway targetting the hypothalamus employs TSH as messenger and controls a local hypothalamic T3 system. As discovered in Japanese quail, TSH triggers molecular cascades mediating thyroid hormone conversion in the ependymal cell layer of the infundibular recess of the third ventricle. The local accumulation of T₃ in the mediobasal hypothalamus (MBH) appears to activate the gonadal axis by affecting the neuro-glial interaction between GnRH terminals and tanycytes in the median eminence. This retrograde pathway is conserved in photoperiodic mammals (sheep and hamsters), and even in non-photoperiodic laboratory mice provided that they are capable to synthesize melatonin. The anterograde pathway is implicated in the control of prolactin secretion, targets cells in the PD and supposedly employs small molecules as signal substances collectively denominated as "tuberalins". Several "tuberalin" candidates have been proposed, such as tachykinins, the secretory protein TAFA and endocannabinoids (EC). The PT-intrinsic EC system was first demonstrated in Syrian hamsters and shown to respond to photoperiodic changes. Subsequently, the EC system was also demonstrated in the PT of mice, rats and humans. To date, 2-arachidonoylglycerol (2-AG) appears as the most important endocannabinoid from the PT. Likely targets for the EC are folliculo-stellate cells that contain the CB1 receptor and appear to contact lactotroph cells. The CB1 receptor was also found on corticotroph cells which appear as a further target of the EC. Recently, the CB1 receptor was also localized to CRF-containing nerve fibers running in the outer zone of the median eminence. This finding suggests that the EC system of the PT contributes not only to the anterograde, but also to the retrograde pathway. Taken together, the results support the concept that the PT transmits its signals via a "cocktail" of messenger molecules which operate also in other brain areas and systems rather than through PT-specific "tuberalins". Furthermore, they may attribute a novel function to the PT, namely the modulation of the stress response and immune functions.

Long-Term Plasticity in Amygdala Circuits: Implication of CB1-Dependent LTD in Stress

The amygdala mediates many forms of emotional learning, during which the central nucleus of amygdala (CeA) functions as a major output of the amygdala by converging inputs from the basolateral nucleus (BLA) and other amygdalar subregions. However, the contribution of BLA-CeA synaptic transmission and plasticity of this transmission after exposure to emotional stimuli remains to be completely understood. Using paired recording, we simultaneously recorded BLA and CeA neurons, and observed that BLA-CeA transmission was glutamatergic. In this transmission, high-frequency stimulation induced NMDA receptor (NMDAR)-dependent LTP, low-frequency stimulation induced NMDAR-dependent LTD, whereas modest-frequency stimulation induced cannabinoid receptor1 (CB1)-dependent LTD. After acute stress, CB1-dependent LTD of this transmission was selectively abolished. This effect of stress was mimicked by intra-CeA administration of CB1-selective agonists and prevented by CB1-selective antagonists. Furthermore, intra-CeA administration of CB1 antagonists prevented stress-induced reduction of explorative behaviors. These results indicate that CB1 signaling-mediated plasticity in local circuits of the amygdala plays a critical role in emotional responses.

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

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

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

BACKGROUND AND PURPOSE

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

EXPERIMENTAL APPROACH

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

KEY RESULTS

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

CONCLUSIONS AND IMPLICATIONS

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

Endocannabinoids and obesity

A safe and effective antiobesity drug is needed to combat the global obesity epidemic. The discovery of cannabinoids from medicinal herbs has revealed the endocannabinoid system (ECS) in animals and humans, which regulates various physiological activities such as feeding, thermogenesis, and body weight (BW). Although cannabinoid receptors 1 (CB1) antagonists have shown antiobesity efficacies in animal models and in the clinic, they failed to establish as a treatment due to their psychological side effects. Recent studies indicate that CB1 in various peripheral tissues may mediate some of the therapeutic effects of CB1 antagonists, such as improved lipid and glucose homeostasis. It rationalizes the development of compounds with limited brain penetration, for minimizing the side effects while retaining the therapeutic efficacies. A survey of the literature has revealed some controversies about how the ECS affects obesity. This review summarizes the research progresses and discusses some future perspectives.

Olfaction under metabolic influences

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin. In view of the worldwide health concern regarding the rising incidence of diabetes, obesity, and related metabolic disorders, we present a comprehensive review that addresses the current knowledge of hormonal modulation of olfactory perception and how disruption of hormonal signaling in the olfactory system can affect energy homeostasis.

The central cannabinoid CB1 receptor is required for diet-induced obesity and rimonabant's antiobesity effects in mice

Cannabinoid receptor CB1 is expressed abundantly in the brain and presumably in the peripheral tissues responsible for energy metabolism. It is unclear if the antiobesity effects of rimonabant, a CB1 antagonist, are mediated through the central or the peripheral CB1 receptors. To address this question, we generated transgenic mice with central nervous system (CNS)-specific knockdown (KD) of CB1, by expressing an artificial microRNA (AMIR) under the control of the neuronal Thy1.2 promoter. In the mutant mice, CB1 expression was reduced in the brain and spinal cord, whereas no change was observed in the superior cervical ganglia (SCG), sympathetic trunk, enteric nervous system, and pancreatic ganglia. In contrast to the neuronal tissues, CB1 was undetectable in the brown adipose tissue (BAT) or the liver. Consistent with the selective loss of central CB1, agonist-induced hypothermia was attenuated in the mutant mice, but the agonist-induced delay of gastrointestinal transit (GIT), a primarily peripheral nervous system-mediated effect, was not. Compared to wild-type (WT) littermates, the mutant mice displayed reduced body weight (BW), adiposity, and feeding efficiency, and when fed a high-fat diet (HFD), showed decreased plasma insulin, leptin, cholesterol, and triglyceride levels, and elevated adiponectin levels. Furthermore, the therapeutic effects of rimonabant on food intake (FI), BW, and serum parameters were markedly reduced and correlated with the degree of CB1 KD. Thus, KD of CB1 in the CNS recapitulates the metabolic phenotype of CB1 knockout (KO) mice and diminishes rimonabant's efficacy, indicating that blockade of central CB1 is required for rimonabant's antiobesity actions.

Endocannabinoid signaling in the amygdala: anatomy, synaptic signaling, behavior, and adaptations to stress

The molecular constituents of endocannabinoid (eCB) signaling are abundantly expressed within the mammalian amygdaloid complex, consistent with the robust role of eCB signaling in the modulation of emotional behavior, learning, and stress-response physiology. Here, we detail the anatomical distribution of eCB signaling machinery in the amygdala and the role of this system in the modulation of excitatory and inhibitory neuroplasticity in this region. We also summarize recent findings demonstrating dynamic alternations in eCB signaling that occur in response to stress exposure, as well as known behavioral consequences of eCB-mediated modulation of amygdala function. Finally, we discuss how integrating anatomical and physiological data regarding eCB signaling in the amygdala could help elucidate common functional motifs of this system in relation to broader forebrain function.

Ovarian hormones influence corticotropin releasing factor receptor colocalization with delta opioid receptors in CA1 pyramidal cell dendrites

Stress interacts with addictive processes to increase drug use, drug seeking, and relapse. The hippocampal formation (HF) is an important site at which stress circuits and endogenous opioid systems intersect and likely plays a critical role in the interaction between stress and drug addiction. Our prior studies demonstrate that the stress-related neuropeptide corticotropin-releasing factor (CRF) and the delta-opioid receptor (DOR) colocalize in interneuron populations in the hilus of the dentate gyrus and stratum oriens of CA1 and CA3. While independent ultrastructural studies of DORs and CRF receptors suggest that each receptor is found in CA1 pyramidal cell dendrites and dendritic spines, whether DORs and CRF receptors colocalize in CA1 neuronal profiles has not been investigated. Here, hippocampal sections of adult male and proestrus female Sprague-Dawley rats were processed for dual label pre-embedding immunoelectron microscopy using well-characterized antisera directed against the DOR for immunoperoxidase and against the CRF receptor for immunogold. DOR-immunoreactivity (-ir) was found presynaptically in axons and axon terminals as well as postsynaptically in somata, dendrites and dendritic spines in stratum radiatum of CA1. In contrast, CRF receptor-ir was predominantly found postsynaptically in CA1 somata, dendrites, and dendritic spines. CRF receptor-ir frequently was observed in DOR-labeled dendritic profiles and primarily was found in the cytoplasm rather than at or near the plasma membrane. Quantitative analysis of CRF receptor-ir colocalization with DOR-ir in pyramidal cell dendrites revealed that proestrus females and males show comparable levels of CRF receptor-ir per dendrite and similar cytoplasmic density of CRF receptor-ir. In contrast, proestrus females display an increased number of dual-labeled dendritic profiles and an increased membrane density of CRF receptor-ir in comparison to males. We further examined the functional consequences of CRF receptor-ir colocalization with DOR-ir in the same neuron using the hormone responsive neuronal cell line NG108-15, which endogenously expresses DORs, and assayed intracellular cAMP production in response to CRF receptor and DOR agonists. Results demonstrated that short-term application of DOR agonist SNC80 inhibited CRF-induced cAMP accumulation in NG108-15 cells transfected with the CRF receptor. These studies provide new insights on opioid-stress system interaction in the hippocampus of both males and females and establish potential mechanisms through which DOR activation may influence CRF receptor activity.

The cannabinoid receptor CB₁ inverse agonist AM251 potentiates the anxiogenic activity of urocortin I in the basolateral amygdala

The basolateral amygdala is reported to play an important role in the neural bases of emotional processing. Previous studies have shown that injections of urocortin I (UcnI) into the basolateral amygdala (BLA) elicit anxiety-like behaviors in animal models. The present study examined the anxiogenic effects of UcnI administered directly into the BLA of male Sprague-Dawley rats. UcnI was administered at doses of 0.1-10.0 pmol and rats were then placed in an elevated plus maze for 10 min. UcnI reliably decreased the percent time spent in the open arms of the elevated plus maze (EPM) as well as open arm entries. This effect was observed across all doses tested, indicating the induction of anxiety-like behavior. In separate groups of rats, the CB(1) inverse agonist AM251 was administered systemically (0.03-3.0 mg/kg IP) or directly into the BLA (0.25-25.0 pmol) and EPM performance assessed. Both routes of AM251 administration produced a reduction in open arm entries and in time spent in the open arms. Moreover, when rats were pretreated with AM251 either systemically or directly into the BLA, the anxiogenic effect of UcnI was potentiated. That is, co-administration of AM251 and UcnI produced a greater suppression of percent time spent in the open arms and open arm entries as compared to UcnI alone. Based on these findings, we propose that urocortin and endocannabinoid signaling are part of an integrated neural axis modulating anxiety states within the basolateral amygdala. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Cannabinoids and Reproduction: A Lasting and Intriguing History

Starting from an historical overview of lasting Cannabis use over the centuries, we will focus on a description of the cannabinergic system, with a comprehensive analysis of chemical and pharmacological properties of endogenous and synthetic cannabimimetic analogues. The metabolic pathways and the signal transduction mechanisms, activated by cannabinoid receptors stimulation, will also be discussed. In particular, we will point out the action of cannabinoids and endocannabinoids on the different neuronal networks involved in reproductive axis, and locally, on male and female reproductive tracts, by emphasizing the pivotal role played by this system in the control of fertility.

The endocannabinoid system tonically regulates inhibitory transmission and depresses the effect of ethanol in central amygdala

The central amygdala (CeA) has a major role in alcohol dependence and reinforcement, and behavioral and neurochemical evidence suggests a role for the endocannabinoid (eCB) system in ethanol binging and dependence. We used a slice preparation to investigate the physiological role of cannabinoids and their interaction with ethanol on inhibitory synaptic transmission in CeA. Superfusion of the cannabinoid receptor (CB1) agonist WIN55212-2 (WIN2) onto CeA neurons decreased evoked GABA(A) receptor-mediated inhibitory postsynaptic potentials (IPSPs) in a concentration-dependent manner, an effect prevented by the CB1 antagonists Rimonabant (SR141716, SR1) and AM251. SR1 or AM251 applied alone augmented IPSPs, revealing a tonic eCB activity that decreased inhibitory transmission in CeA. Paired-pulse analysis suggested a presynaptic CB1 mechanism. Intracellular BAPTA abolished the ability of AM251 to augment IPSPs, demonstrating the eCB-driven nature and postsynaptic origin of the tonic CB1-dependent control of GABA release. Superfusion of ethanol increased IPSPs and addition of WIN2 reversed the ethanol effect. Similarly, previous superfusion of WIN2 prevented subsequent ethanol effects on GABAergic transmission. The ethanol-induced augmentation of IPSPs was additive to CB1 blockade, ruling out a participation of CB1 in the action of acute ethanol. Our study points to an important role of CB1 in CeA in which the eCBs tonically regulate neuronal activity, and suggests a potent mechanism for modulating CeA tone during challenge with ethanol.

A role for the endocannabinoid system in the increased motivation for cocaine in extended-access conditions

Extended access to cocaine produces an increase in cocaine self-administration in rats that mimics aspects of compulsive drug intake in human addicts. Although emerging evidence implicates the endogenous cannabinoid system in aspects of opioid and ethanol addiction, a role of the endocannabinoid system in cocaine addiction remains widely inconclusive. Here, we investigate the effects of systemic and intra-accumbal administration of the CB1 antagonist SR141716A (Rimonabant) on cocaine self-administration (0.5 mg/kg/infusion) under a progressive ratio (PR) schedule in rats with extended [long access (LgA); 6 h/d] or limited [short access (ShA); 1 h/d] access to cocaine. LgA rats, but not ShA rats, showed an increase in cocaine intake as previously reported, and responding for cocaine by LgA rats was higher than in ShA rats under a PR schedule. Systemic SR141716A induced a dramatic dose-dependent decrease in the breakpoint for cocaine by LgA rats, whereas only the highest dose of the antagonist had a significant effect in the ShA group. Anandamide levels in the nucleus accumbens (NAc) shell were decreased in ShA rats but unchanged in LgA rats during cocaine self-administration. Both phosphorylated and total CB1 receptor protein expression were upregulated in LgA rats in the NAc and the amygdala compared with ShA and drug-naive rats, 24 h after last cocaine session. Finally, intra-NAc infusions of SR141716A reduced cocaine breakpoints selectively in LgA animals. These results suggest that neuroadaptations in the endogenous cannabinoid system may be part of the neuroplasticity associated with the development of cocaine addiction.

Feeding disorders and obesity

The ability of the endocannabinoid (EC) system to control appetite, food intake and energy balance has recently received great attention, particularly in the light of the different modes of action underlying these functions. The EC system modulates rewarding properties of food by acting at specific mesolimbic areas in the brain. In the hypothalamus, cannabinoid type 1 receptors (CB1) and ECs are integrated components of the networks controlling appetite and food intake. Interestingly, the EC system has recently been shown to control several metabolic functions by acting on peripheral tissues, such as adipocytes, hepatocytes, the skeletal muscles and the endocrine pancreas. The relevance of the system is further strengthened by the notion that visceral obesity seems to be a condition in which an overactivation of the EC system occurs; therefore, drugs interfering with this overactivation by blocking CB1 receptors are considered valuable candidates for the treatment of obesity and related cardiometabolic risk factors.

The endocannabinoid system and energy metabolism

Many different regulatory actions have been attributed to endocannabinoids, and their involvement in several pathophysiological conditions is under intense scrutiny. Cannabinoid receptors [cannabinoid receptor type 1 (CB1) and CB2] participate in the physiological modulation of many central and peripheral functions. The ability of the endocannabinoid system to control appetite, food intake and energy balance has recently received considerable attention, particularly in the light of the different modes of action underlying these functions. The endocannabinoid system modulates rewarding properties of food by acting at specific mesolimbic areas in the brain. In the hypothalamus, CB1 receptors and endocannabinoids are integrated components of the networks controlling appetite and food intake. Interestingly, the endocannabinoid system was recently shown to control several metabolic functions by acting on peripheral tissues such as adipocytes, hepatocytes, the gastrointestinal tract, the skeletal muscles and the endocrine pancreas. The relevance of the system is further strengthened by the notion that visceral obesity seems to be a condition in which an overactivation of the endocannabinoid system occurs, and therefore drugs interfering with this overactivation by blocking CB1 receptors are considered as potentially valuable candidates for the treatment of obesity and related cardiometabolic risk factors.

Effects of chronic treatment with citalopram on cannabinoid and opioid receptor-mediated G-protein coupling in discrete rat brain regions

RATIONALE

There is growing interest in investigating the mechanisms of action of selective serotonin reuptake inhibitors (SSRIs), beyond their association with the serotonergic system, due to their wide therapeutic potential for disorders including depression, pain and addiction.

OBJECTIVE

The aim of this study was to investigate whether chronic treatment with the SSRI, citalopram, alters the functional coupling of G(i/o)-associated cannabinoid type 1 (CB(1)) and mu-opioid receptors in selected areas of rat brain implicated in psychiatric disorders and pain.

METHODS

Using an autoradiographic approach, the effects of the cannabinoid receptor agonist, HU210 (in the presence or absence of the CB(1) receptor antagonist AM251), or the mu-opioid receptor agonist, [D: -Ala(2),N-Me-Phe4,Gly(5)-ol]-enkephalin (DAMGO; in the presence or absence of the mu-opioid receptor antagonist D: -Phe-Cys-Tyr-D: -Trp-Orn-Thr-Pen-Thr-NH(2)), on [(35)S]GTPgammaS binding in discrete brain regions of citalopram-treated (10 mg kg(-1) day(-1) for 14 days by subcutaneous minipump) and control rats were investigated.

RESULTS

The HU210-induced increase in [(35)S]GTPgammaS binding observed in the hypothalamic paraventricular nucleus of control rats was abolished after chronic treatment with citalopram. Reduced response to HU210 in rats receiving chronic treatment with citalopram was also observed in the hippocampus and medial geniculate nucleus. Citalopram had no significant effect on DAMGO-induced [(35)S]GTPgammaS binding in the brain regions investigated, with the exception of the medial geniculate nucleus where a modest impairment was observed.

CONCLUSIONS

These data provide evidence for reduced cannabinoid receptor-mediated G-protein coupling in the hypothalamus, hippocampus and medial geniculate nucleus of rats chronically treated with citalopram, effects which may, in part, underlie the mechanism of action of SSRIs.

Synaptic physiology of central CRH system

Corticotropin-Releasing Hormone (CRH) or Corticotropin-Releasing Factor (CRF) and its family of related naturally occurring endogenous peptides and receptors are becoming recognized for their actions within central (CNS) and peripheral (PNS) nervous systems. It should be recognized that the term 'CRH' has been displaced by 'CRF' [Guillemin, R., 2005. Hypothalamic hormones a.k.a. hypothalamic releasing factors. J. Endocrinol. 184, 11-28]. However, to maintain uniformity among contributions to this special issue we have used the original term, CRH. The term 'CRF' has been associated recently with CRH receptors and designated with subscripts by the IUPHAR nomenclature committee [Hauger, R.L., Grigoriadis, D.E., Dallman, M.F., Plotsky, P.M., Vale, W.W., Dautzenberg, F.M., 2003. International Union of Pharmacology. XXXVI. Corticotrophin-releasing factor and their ligands. Pharmacol. Rev. 55, 21-26] to denote the type and subtype of receptors activated or antagonized by CRH ligands. CRH, as a hormone, has long been identified as the regulator of basal and stress-induced ACTH release within the hypothalamo-pituitary-adrenal axis (HPA axis). But the concept, that CRH and its related endogenous peptides and receptor ligands have non-HPA axis actions to regulate CNS synaptic transmission outside the HPA axis, is just beginning to be recognized and identified [Orozco-Cabal, L., Pollandt, S., Liu, J., Shinnick-Gallagher, P., Gallagher, J.P., 2006a. Regulation of Synaptic Transmission by CRF Receptors. Rev. Neurosci. 17, 279-307; Orozco-Cabal, L., Pollandt, S., Liu, J., Vergara, L., Shinnick-Gallagher, P., Gallagher, J.P., 2006b. A novel rat medial prefrontal cortical slice preparation to investigate synaptic transmission from amygdala to layer V prelimbic pyramidal neurons. J. Neurosci. Methods 151, 148-158] is especially noteworthy since this synapse has become a prime focus for a variety of mental diseases, e.g. schizophrenia [Fischbach, G.D., 2007. NRG1 and synaptic function in the CNS. Neuron 54, 497-497], and neurological disorders, e.g., Alzheimer's disease [Bell, K.F., Cuello, C.A., 2006. Altered synaptic function in Alzheimer's disease. Eur. J. Pharmacol. 545, 11-21]. We suggest that "The Stressed Synapse" has been overlooked [c.f., Kim, J.J., Diamond, D.M. 2002. The stressed hippocampus, synaptic plasticity and lost memories. Nat. Rev., Neurosci. 3, 453-462; Radley, J.J., Morrison, J.H., 2005. Repeated stress and structural plasticity in the brain. Ageing Res. Rev. 4, 271-287] as a major contributor to many CNS disorders. We present data demonstrating CRH neuroregulatory and neuromodulatory actions at three limbic synapses, the basolateral amygdala to central amygdala synapse; the basolateral amygdala to medial prefrontal cortex synapse, and the lateral septum mediolateral nucleus synapse. A novel stress circuit is presented involving these three synapses. We suggest that CRH ligands and their receptors are significant etiological factors that need to be considered in the pharmacotherapy of mental diseases associated with CNS synaptic transmission.

The endocannabinoid system in the regulation of cardiometabolic risk factors

Obesity has increased at a striking rate over the last 3 decades in the Western world. This negative trend dramatically affects physical health and, ultimately, cardiovascular risks. In fact, particularly at the visceral level, obesity is strongly associated with an increased risk for life-threatening conditions, such as type 2 diabetes mellitus, hypertension, dyslipidemia, and cardiovascular disease. Although nutritional changes and physical activity are commonly thought of as the core treatments for obesity, it is necessary to further support obese patients with a pharmacologic approach for 2 reasons: to reduce the metabolic risk profile, and to avoid the regaining of weight. Among the various pharmacologic targets explored in recent years, the endocannabinoid (EC) system now constitutes the most promising proposal so far. In this review, after focusing on the central and peripheral signaling pathways that preserve energy homeostasis, we review the role of the EC system in regulating food's rewarding properties, controlling caloric intake by acting in hypothalamic pathways, and in modulating metabolic functions of several peripheral organs. In addition, we provide evidence that supports the recently proposed hypothesis that a close association exists between obesity and overactivation of the EC system.

Endocannabinoids and related N-acylethanolamines in the control of appetite and energy metabolism: emergence of new molecular players

PURPOSE OF REVIEW

Endocannabinoids (anandamide and 2-arachidonoylgycerol) and related N-acylethanolamines (N-oleoylethanolamine) exhibit opposite effects in the control of appetite. The purpose of this review is to highlight the similarities and differences of three major lipid-signaling molecules by focusing on their mode of action and the proteins involved in the control of food intake and energy metabolism.

RECENT FINDINGS

Anandamide and 2-arachidonoylglycerol promote food intake and are the main endogenous ligands of the cannabinoid receptors. One of them, the cannabinoid receptor 1, is responsible for the control of food intake and energy expenditure both at a central and a peripheral level, affecting numerous anorexigenic and orexigenic mediators (leptin, neuropeptide Y, ghrelin, orexin, endogenous opioids, corticotropin-releasing hormone, alpha-melanocyte stimulating hormone, cocaine and amphetamine-related transcript). In the gut, N-oleoylethanolamine plays an opposite role in food regulation, by interacting with two molecular targets different from the cannabinoid receptors: the nuclear receptor peroxisome proliferator-activated receptor alpha and a G-protein coupled receptor GPR119.

SUMMARY

Recent findings on the molecular mechanisms underlying the promotion of food intake or, in contrast, the suppression of food intake by anandamide and N-oleoylethanolamine, are summarized. Potential strategies for treating overweight, metabolic syndrome, and type II diabetes are briefly outlined.

Blocking the Cannabinoid Receptors: Drug Candidates and Therapeutic Promises

The CB1 and CB2 cannabinoid receptors have been described as two prime sites of action for endocannabinoids. Both the localization and pharmacology of these two G-protein-coupled receptors are well-described, and numerous selective ligands have been characterized. The physiological effects of Cannabis sativa (cannabis) and a throughout study of the endocannabinoid system allowed for the identification of several pathophysiological conditions--including obesity, dyslipidemia, addictions, inflammation, and allergies--in which blocking the cannabinoid receptors might be beneficial. Many CB1 receptor antagonists are now in clinical trials, and the results of several studies involving the CB1 antagonist lead compound rimonabant (SR141716A) are now available. This review describes the pharmacological tools that are currently available and the animal studies supporting the therapeutic use of cannabinoid receptor antagonists and inverse agonists. The data available from the clinical trials are also discussed.

Cannabinoids in eating disorders and obesity

Cannabinoid system is a crucial mechanism in regulating food intake and energy metabolism. It is involved in central and peripheral mechanisms regulating such behavior, interacting with many other signaling systems with a role in metabolic regulation. Cannabinoid agonists promote food intake, and soon a cannabinoid antagonist, rimonabant, will be marketed for the treatment of obesity. It not only causes weight loss, but also alleviates metabolic syndrome. We present a review of current knowledge on this subject, along with data from our own research: genetic studies on this system in eating disorders and obesity and studies locating cannabinoid receptors in areas related to food intake. Such studies suggest cannabinoid hyperactivity in obesity, and this excessive activity may have prognostic implications.

The endocannabinoid system as an emerging target of pharmacotherapy

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

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Endocannabinoids in the regulation of appetite and body weight

The discovery of cannabinoid receptors, together with the development of selective cannabinoid receptor antagonists, has encouraged a resurgence of cannabinoid pharmacology. With the identification of endogenous agonists, such as anandamide, scientists have sought to uncover the biological role of endocannabinoid systems; initially guided by the long-established actions of cannabis and exogenous cannabinoids such as delta9-tetrahydrocannabinol (THC). In particular, considerable research has examined endocannabinoid involvement in appetite, eating behaviour and body weight regulation. It is now confirmed that endocannabinoids, acting at brain CB1 cannabinoid receptors, stimulate appetite and ingestive behaviours, partly through interactions with more established orexigenic and anorexigenic signals. Key structures such as the nucleus accumbens and hypothalamic nuclei are sensitive sites for the hyperphagic actions of these substances, and endocannabinoid activity in these regions varies in relation to nutritional status and feeding expression. Behavioural studies indicate that endocannabinoids increase eating motivation by enhancing the incentive salience and hedonic evaluation of ingesta. Moreover, there is strong evidence of an endocannabinoid role in energy metabolism and fuel storage. Recent developments point to potential clinical benefits of cannabinoid receptor antagonists in the management of obesity, and of agonists in the treatment of other disorders of eating and body weight regulation.

Cocaine- and amphetamine-related transcript is involved in the orexigenic effect of endogenous anandamide

Endocannabinoids acting at CB1 cannabinoid receptors (CB1) increase appetite. In view of the predominant presynaptic localization of CB1 in the brain, we tested the hypothesis that the orexigenic effect of endocannabinoids involves inhibition of the release of a tonically active anorexigenic mediator, such as the peptide product of the cocaine- and amphetamine-related transcript (CART). The CB1 antagonist rimonabant inhibited food intake in food-restricted wild-type mice, but not in their CART-deficient littermates. Mice deficient in fatty acid amide hydrolase (FAAH), the enzyme responsible for the in vivo metabolism of the endocannabinoid anandamide, have reduced levels of CART-immunoreactive nerve fibers and terminals in several brain regions implicated in appetite control, including the arcuate, dorsomedial and periventricular nuclei of the hypothalamus, the amygdala, the bed nucleus of the stria terminalis and the nucleus accumbens, and treatment of FAAH(-/-) mice with rimonabant, 3 mg/kg/day for 7 days, increased CART levels toward those seen in FAAH(+/+) wild-type controls. In contrast, no difference in the density of CART-immunoreactive fibers was observed in the median eminence and the paraventricular nucleus of FAAH(+/+) and FAAH(-/-) mice. Acute treatment of wild-type mice with the cannabinoid agonist HU-210 resulted in elevated CART levels in the dorsomedial nucleus and the shell portion of the nucleus accumbens. These observations are compatible with CART being a downstream mediator of the CB1-mediated orexigenic effect of endogenous anandamide.