Role Of Endogenous Cannabinoids Research Articles

Pathogenic Mechanisms and Therapeutic Approaches in Obesity-Related Knee Osteoarthritis.

The knee is the joint most frequently involved in osteoarthritis, a common joint disorder in the adult population that is associated with significant chronic joint pain, reduced mobility and quality of life. Recent studies have established an association between obesity and the development of knee osteoarthritis that goes beyond the increased mechanical load on the knees as weight-bearing joints. This link is based on the maintenance of a chronic low-grade inflammation, altered secretion of adipokines by the adipose tissue and development of sarcopenia. Major adipokines involved in the pathogenesis of obesity-related knee osteoarthritis include adiponectin, which appears to have a protective effect, as well as leptin, resistin and visfatin, which are associated with higher pain scores and more severe structural damage. Joint pain in knee osteoarthritis may be both nociceptive and neuropathic and is the result of complex mechanisms driven by nerve growth factor, calcitonin gene-related peptide and pro-inflammatory cytokines. The role of endogenous cannabinoids and gut microbiota in common mechanisms between obesity and knee pain has recently been studied. The aim of the present review is to highlight major pathogenic mechanisms in obesity-related knee osteoarthritis with special attention on pain and to comment on possible therapeutic approaches.

Expression and Kinetics of Endogenous Cannabinoids in the Brain and Spinal Cord of a Spare Nerve Injury (SNI) Model of Neuropathic Pain

The role of endogenous cannabinoids in neuropathic pain has been actively studied, among which 2-arachidonoyl glycerol (2-AG) has received the most attention. However, owing to its chemical properties, direct detection of 2-AG distribution in tissues is difficult. Moreover, although desorption electrospray ionization mass spectrometry imaging (DESI-MSI) has enabled the detection of 2-AG, its distribution in the brain and spinal cord of neuropathic pain models has not been reported. In this study, the expression and distribution of 2-AG in the brain and spinal cord of a spare nerve injury (SNI) mice model of neuropathic pain was examined using DESI-MSI. The brain and lumbar spinal cord were collected and analyzed on days 3, 7, and 21 after treatment. On days 3 and 7 after treatment, 2-AG expression in the SNI model was decreased in the hypothalamus, midbrain, and especially in the periaqueductal gray (PAG) region but increased in the lumbar spinal cord. On day 21, the SNI model showed decreased 2-AG expression in the hypothalamus, but the difference from the control was not significant. Furthermore, there were no differences in 2-AG expression between the lumbar spinal cord, midbrain, or PAG. These data suggest that 2-AG might be involved in pain control.

Enhanced Analgesic Effects and Gastrointestinal Safety of a Novel, Hydrogen Sulfide-Releasing Anti-Inflammatory Drug (ATB-352): A Role for Endogenous Cannabinoids.

Aims: The covalent linking of nonsteroidal anti-inflammatory drugs to a hydrogen sulfide (H2S)-releasing moiety has been shown to dramatically reduce gastrointestinal (GI) damage and bleeding, as well as increase anti-inflammatory and analgesic potency. We have tested the hypothesis that an H2S-releasing derivative of ketoprofen (ATB-352) would exhibit enhanced efficacy without significant GI damage in a mouse model of allodynia/hyperalgesia.Results: ATB-352 was significantly more potent and effective as an analgesic than ketoprofen and did not elicit GI damage. Pretreatment with an antagonist of the CB1 cannabinoid receptor (AM251) significantly reduced the analgesic effects of ATB-352. The CB1 antagonist exacerbated GI damage when coadministered with ketoprofen, but GI damage was not induced by the combination of ATB-352 and the CB1 antagonist. In vitro, ATB-352 was substantially more potent than ketoprofen as an inhibitor of fatty acid amide hydrolase, consistent with a contribution of endogenous cannabinoids to the analgesic effects of this drug. Blood anandamide levels were significantly depressed by ketoprofen, but remained unchanged after treatment with ATB-352.Innovation: Ketoprofen is a potent analgesic, but its clinical use, even in the short term, is significantly limited by its propensity to cause significant ulceration and bleeding in the GI tract. Covalently linking an H2S-releasing moiety to ketoprofen profoundly reduces the GI toxicity of the drug, while boosting analgesic effectiveness.Conclusion: This study demonstrates a marked enhancement of the potency and effectiveness of ATB-352, an H2S-releasing derivative of ketoprofen, in part, through the involvement of the endogenous cannabinoid system. This may have significant advantages for the control and management of pain, such as in a postoperative setting.

Endogenous cannabinoid modulation of restraint stress-induced analgesia in thermal nociception.

It is thought that endogenous cannabinoids have a role in the analgesia induced by specific forms of stress. We examined if the role of endogenous cannabinoids is also dependent upon the mode of nociception, and whether this could be altered by drugs which block their enzymatic degradation. In C57BL/6 mice, restraint stress produced analgesia in the hot-plate and plantar tests, two thermal pain assays that engage distinct supraspinal and spinal nociceptive pathways. Stress-induced analgesia in the hot-plate test was abolished by pre-treatment with the opioid receptor antagonist naltrexone but was unaffected by the cannabinoid receptor antagonist 1-(2,4-Dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide(AM281). By contrast, stress-induced analgesia in the plantar test was abolished by pre-treatment with naltrexone plusAM281, but not by either antagonist individually. Remarkably, inhibiting the breakdown of endocannabinoids, with the dual fatty acid amide hydrolase and monoacylglycerol lipase inhibitor JZL195, rescued stress-induced analgesia in the hotplate test when endogenous opioid signalling was blocked by naltrexone. Furthermore, JZL195 recruited analgesia induced by sub-threshold restraint stress in both thermal pain assays. These findings indicate the role of endocannabinoids in stress-induced analgesia differs with the type of thermal pain behaviour. However, by inhibiting their breakdown, endocannabinoids can be recruited to substitute for endogenous opioid signalling when their activity is blocked, indicating a degree of redundancy between opioid and cannabinoid systems. Together these data suggest targeting endocannabinoid breakdown could provide an alternative, or adjuvant to mainstream analgesics such as opioids.

A novel role of cannabinoids in synaptogenesis

Synapses play a major role in signalling transduction in the nervous system. They display extensive activity-driven plasticity during development, learning and memory. Here we have explored a new role of endogenous cannabinoids and their CHI receptors in synapse formation, remodelling, and maintenance. Endogenous cannabinoids and their CHI receptors have been known to regulate neurotransmitter release at the level of the synapse and have also been implicated in several developmental events. Recent/y, if was reported that endogeneous cannabinoids decrease functional synapses in pyramidal neurons. We show here that endogenous cannabinoids and their CHI receptors regulate the dendritic and axonal filopodia formation (synapse precursors) and synaptogenesis obtained from embryonic mice cortical cultures. Stimulating the cortical cultures with the synthetic CHI receptor agonist, arachidonyl-2'-chloroethylamide (ACEA), produces a significant decrease in filopodia number at DIV8, and subsequently a lower synaptic contact density at DIV10 compared with the control group. On the other hand, inhibiting the action of endogenous cannabinoids and their CHI receptors by the inverse agonist AM251 or by the pure antagonist 02050 increases filopodia density at DIV8, and elevates synaptic density formation at DIV10. Furthermore, we found that this increase was reversed when cultures were pre-treated with H89, KT5720 (both inhibitors of Prote in Kinase A (PKA)) or DCCjb antibody, (an antibody which blocks the function of Deleted in Colorectal Cancer Receptor). Interestingly, a decrease of DCC receptors present at the surface of the neurons was observed when treated with ACEA. Conversely, an externalisation of DCC was observed when CHI receptors were antagonised by AM251 or 02050 and this effect was prevented when neurons were pretreated using H89, KT5720. This confirms the previous observations showing that the activation of adenylate cyclase and P KA pathway produces a netrinl-DCC dependent increase in synaptogenesis.

Increased tonic cannabinoid CB1R activity and brain region-specific desensitization of CB1R Gi/o signaling axis in mice with global genetic knockout of monoacylglycerol lipase

In mammalian brain, monoacylglycerol lipase (MAGL) is the primary enzyme responsible for terminating signaling function of the endocannabinoid 2-arachidonoylglycerol (2-AG). Previous in vivo studies with mice indicate that both genetic and chronic pharmacological inactivation of MAGL result in 8–30-fold increase of 2-AG concentration in the brain, causing desensitization and downregulation of cannabinoid CB1 receptor (CB1R) activity, leading to functional and behavioral tolerance. However, direct evidence for reduced CB1R activity in the brain is lacking. In this study, we used functional autoradiography to assess basal and agonist-stimulated CB1R-dependent Gi/o protein activity in multiple brain regions of MAGL-KO mice in comparison to their wild-type (WT) littermates. In addition, the role of endogenous cannabinoids in basal CB1R signaling was assessed after comprehensive pharmacological blockade of 2-AG hydrolysis by determining the contents of endocannabinoids (eCBs) in WT and MAGL-KO brain tissues by LC/MS/MS technology. To show whether lack of MAGL cause compensatory alterations in the serine hydrolase activity, we compared serine hydrolase pattern of WT and MAGL-KO using activity-based protein profiling. Consistent with studies using chronic pharmacological MAGL inactivation in vivo, we observed a statistically significant decrease of CB1R-Gi/o signaling in most of the studied brain regions. In MAGL-KO brain sections, elevated 2-AG levels were mirrored to heightened basal CB1R-dependent Gi/o-activity, as well as, dampened agonist-evoked responses in several brain regions. The non-selective serine hydrolase inhibitor methylarachidonoylfluorophosphonate (MAFP) was able to significantly elevate 2-AG levels in brain sections of MAGL-KO mice, indicating that additional serine hydrolases possess 2-AG hydrolytic activity in MAGL-KO brain sections.

Cannabinoid modification of cocaine action

lacking the neuronal cannabinoid CB1 receptor show a striking acceleration of the age-related cognitive decline, accompanied by an enhanced neuronal loss and increased neuroinflammation. A similar phenotype was also observed in mice lacking CB1 specifically on GABAergic neurons. The role of endogenous cannabinoids in age-related changes will also be addressed using knockout mouse models with deletions in endocannabinoid synthesizing and degrading enzymes.

Release of endogenous cannabinoids from ventral tegmental area dopamine neurons and the modulation of synaptic processes

Endogenous cannabinoids play important roles in a variety of functions in the mammalian brain, including the regulation reward-related information processing. The primary mechanism through which this is achieved is the presynaptic modulation of synaptic transmission. During reward- and reinforcement-related behavior dopamine levels increase in forebrain areas and this has recently been shown to be modulated by the endocannabinoid system. Therefore, understanding how endocannabinoids are mobilized to modulate synaptic inputs impinging on midbrain dopamine neurons is crucial to a complete understanding of the roles that these molecules play in reward behavior, drug abuse and addiction. Here we summarize the literature describing short-term and long-term regulation of afferent connections on dopamine neurons in the ventral tegmental area via endocannabinoid activation of cannabinoid CB1 receptors, and describe the mechanisms through which these molecules are released during reward-based behavior and exposure to abused drugs.

Abstract 416: Inhibition of Metabolism of Endogenous AEA and 2-AG Reduces Ang II Induced Uterine Artery Contraction at Early Pregnancy in a Transgenic Model of Preeclampsia

Recent evidence of interactions between the renin-angiotensin and the endocannabinoid systems suggests a regulatory role for endogenous cannabinoids (ECs) in modulating Ang II vascular responses. Endogenous levels of the ECs, AEA and 2-AG, are controlled by the hydrolytic enzymes FAAH and MAGL, respectively. We investigated the role of AEA and 2-AG as modulators of Ang II contraction in uterine arteries (UA) in a transgenic pregnant rat, in which the female expressing human angiotensinogen (AGT) is mated to the male with human renin (REN), producing a preeclamptic pregnancy. Uterine arteries were isolated from pregnant transgenic h AGTx h REN rats at 7 days of gestational age (n=4). Arterial segments were mounted in a wire myograph for determinations of isometric tension (DMT USA, 620M). Concentration response curves to Ang II (10 -11 -10 -8 M) were performed in control conditions and after preincubation with enzyme inhibitors: URB597 (FAAH) or JZL184 (MAGL) at 10 -6 M. Data were fitted to a dose response curve, maximal responses (Ang II MAX ) were expressed as percent of maximal response to 75 mM KCl (% K MAX ) and sensitivity as pD 2 (pD 2 = -Log [EC 50 ]). Inhibition of FAAH attenuated both maximal response and sensitivity (Ang II MAX 76±9 vs 105±3, p<0.05; pD 2 8.7±0.09 vs 9.1±0.04, p<0.05) and inhibition of MAGL lowered Ang II sensitivity (Ang II MAX 83±15; pD 2 8.8±0.01, p<0.05), Figure. Thus, by inhibiting the enzymes involved in breakdown of ECs, we demonstrate a functional EC system in the UA that counteracts Ang II contraction. Whether the buffering capacity of the EC system is altered in this model of preeclampsia relative to normal pregnancy is under investigation.

Lasting impacts of prenatal cannabis exposure and the role of endogenous cannabinoids in the developing brain.

Cannabis is the most commonly used illicit substance among pregnant women. Human epidemiological and animal studies have found that prenatal cannabis exposure influences brain development and can have long-lasting impacts on cognitive functions. Exploration of the therapeutic potential of cannabis-based medicines and synthetic cannabinoid compounds has given us much insight into the physiological roles of endogenous ligands (endocannabinoids) and their receptors. In this article, we examine human longitudinal cohort studies that document the long-term influence of prenatal exposure to cannabis, followed by an overview of the molecular composition of the endocannabinoid system and the temporal and spatial changes in their expression during brain development. How endocannabinoid signaling modulates fundamental developmental processes such as cell proliferation, neurogenesis, migration and axonal pathfinding are also summarized.

An endocannabinoid signal associated with desire for alcohol is suppressed in recently abstinent alcoholics

Alcoholics report persistent alcohol craving that is heightened by cognitive cues, stressful situations, and abstinence. The role of endogenous cannabinoids in human alcohol craving--though long suspected--remains elusive. We employed laboratory exposure to stress, alcohol cue, and neutral relaxed situations through guided imagery procedures to evoke alcohol desire and craving in healthy social drinkers (n = 11) and in treatment-engaged, recently abstinent alcoholic subjects (n = 12) and assessed alcohol craving, heart rate, and changes in circulating endocannabinoid levels. Subjective anxiety was also measured as a manipulation check for the procedures. In healthy social drinkers, alcohol cue imagery increased circulating levels of the endocannabinoid anandamide, whereas neutral and stress-related imagery had no such effect. Notably, baseline and response anandamide levels in these subjects were negatively and positively correlated with self-reported alcohol craving scores, respectively. Cue-induced increases in heart rate were also correlated with anandamide responses. By contrast, no imagery-induced anandamide mobilization was observed in alcoholics, whose baseline anandamide levels were markedly reduced compared to healthy drinkers and were uncorrelated to either alcohol craving or heart rate. The results suggest that plasma anandamide levels provide a marker of the desire for alcohol in social drinkers, which is suppressed in recently abstinent alcoholics.

Role of endogenous cannabinoids in ischemia/reperfusion injury following testicular torsion in rats

The role of endogenous cannabinoids in ischemia/reperfusion induced germ cell apoptosis in rats was investigated. Baseline group was for basal normal values. The Sham operated group served as a control group. The torsion/detorsion (T/D) group underwent torsion (1 h) and detorsion; AN1, AN2, and AN3 groups received anandamide (10 mg/kg) 30 min before torsion, 30 min after torsion, and just after detorsion, respectively. In the AM251 group, AM251 (0.5 mg/kg) was injected 45 min before torsion and in the AN/AM group, AM251 and anandamide were injected 45 and 30 min before torsion, respectively. Lipid peroxidation, antioxidant enzymes, and germ cell apoptosis was determined. Malondialdehyde (MDA) levels in the T/D group were significantly higher than the control group. Moreover, MDA values in the AN1, AN2, and AN3 groups were significantly lower than T/D. There were significant decreases in catalase and superoxide dismutase activities in the T/D group versus the control group. These values in the AN1, AN2, and AN3 groups were significantly higher than T/D. It was also shown that MDA levels in the AN/AM group were significantly higher than the AN1 group. In the AN/AM group, catalase and superoxide dismutase activities were significantly lower versus the AN1 group. The mean germ cell apoptosis scores in all animals with testicular T/D were significantly higher than the control group. There was no difference between the apoptotic indices in the AN1, AN2, AN3, and T/D groups. Apoptosis scores in AM251 and AN/AM were significantly higher compared with the T/D and AN1 groups. Although anandamide increased antioxidant markers, it failed to reduce germ cell apoptosis. AM251 worsened the antioxidant defense system, which is reflected as higher germ cell apoptosis.

A role for ERp57 in the regulation of anandamide metabolism

The cannabinoid field is currently an active research area due to a proposed role for endogenous cannabinoids, such as anandamide (AEA), in various physiological processes. AEA is synthesized on‐demand and released into the extracellular space, where it acts as an agonist at both the central and peripheral nervous system cannabinoid receptors CB1 and CB2, respectively. To cease signaling, AEA is transported into cells, where it is metabolized by the enzyme fatty acid amide hydrolase (FAAH1). However, very little is known regarding AEA transport. Our lab has previously identified caveolae‐dependent endocytosis as a mechanism for AEA transport. We recently showed that the protein ERp57 localizes to caveolae during AEA transport. Interestingly, the transcription factor STAT3, which interacts with ERp57 and has been implicated in the regulation of FAAH1 gene expression, localizes to caveolae in its inactive form. We propose that in response to AEA transport, ERp57 and STAT3 work together to up‐regulate FAAH1 gene transcription. Such increases in FAAH1 expression levels have previously been associated with increased AEA transport. We are using RNAi technology to explore the role of ERp57 in STAT3‐regulated FAAH1 transcription. Additionally, we are using various techniques to identify changes in both FAAH1 expression and STAT3 activation in response to AEA uptake. Research funded by NIH Grant R21DA018844.

Potentiation of Electrical and Chemical Synaptic Transmission Mediated by Endocannabinoids

Endocannabinoids are well established as inhibitors of chemical synaptic transmission via presynaptic activation of the cannabinoid type 1 receptor (CB1R). Contrasting this notion, we show that dendritic release of endocannabinoids mediates potentiation of synaptic transmission at mixed (electrical and chemical) synaptic contacts on the goldfish Mauthner cell. Remarkably, the observed enhancement was not restricted to the glutamatergic component of the synaptic response but also included a parallel increase in electrical transmission. This effect involved the activation of CB1 receptors and was indirectly mediated via the release of dopamine from nearby varicosities, which in turn led to potentiation of the synaptic response via a cAMP-dependent protein kinase-mediated postsynaptic mechanism. Thus, endocannabinoid release can potentiate synaptic transmission, and its functional roles include the regulation of gap junction-mediated electrical synapses. Similar interactions between endocannabinoid and dopaminergic systems may be widespread and potentially relevant for the motor and rewarding effects of cannabis derivatives.

Role of Endogenous Cannabinoids in Cognition and Emotionality

Novel pharmacological tools and the generation of null-mutants enabled the elucidation of the role of endocannabinoids in cognition and emotionality of rats and mice. Endocannabinoids seem to limit memory retention, to facilitate memory extinction and to ensure adequate coping with stressful situations. A selective potentiation of these actions may lead to novel pharmacotherapies for human anxiety disorders.

Cannabinoids and the human uterus during pregnancy

Objective The aim of this study was to investigate the expression of cannabinoid receptors in human uterine smooth muscle during pregnancy and to evaluate the effects of endogenous and exogenous cannabinoids on myometrial contractility in vitro. Study design Human myometrial biopsy specimens were obtained at elective cesarean delivery and snap frozen or mounted for isometric recording under physiologic conditions. Cumulative doses of the endogenous cannabinoid anandamide or the exogenous cannabinoid Δ 9 (indicates a double bond between carbons 9 and 10) tetrahydrocannabinol were added in the range 1 nmol/L to 100 μmol/L. Selectivity of the cannabinoid receptor agonists was investigated with specific antagonists for the CB 1 and the CB 2 receptors. Reverse transcription–polymerase chain reaction with primers for the CB 1 and CB 2 receptors was performed on messenger RNA that was isolated from human pregnant myometrium. Results Both anandamide and Δ 9-tetrahydrocannabinol exerted a direct relaxant effect on human pregnant myometrium in vitro, which was of equal potency for both compounds. This relaxant effect was antagonized by the specific CB 1 receptor antagonist, SR 141716, but not by the specific CB 2 receptor antagonist, SR 144528 (n = 6 specimens, P<.01). Both the CB 1 and CB 2 receptors are expressed in human myometrium. Conclusions Both endogenous and exogenous cannabinoids exert a potent and direct relaxant effect on human pregnant myometrium, which is mediated through the CB 1 receptor. This highlights a possible role for endogenous cannabinoids during human parturition and pregnancy. These results also support the view that the use of exogenous cannabinoids during pregnancy is not linked independently with preterm labor.

Role of endogenous cannabinoids in synaptic signaling.

Research of cannabinoid actions was boosted in the 1990s by remarkable discoveries including identification of endogenous compounds with cannabimimetic activity (endocannabinoids) and the cloning of their molecular targets, the CB1 and CB2 receptors. Although the existence of an endogenous cannabinoid signaling system has been established for a decade, its physiological roles have just begun to unfold. In addition, the behavioral effects of exogenous cannabinoids such as delta-9-tetrahydrocannabinol, the major active compound of hashish and marijuana, await explanation at the cellular and network levels. Recent physiological, pharmacological, and high-resolution anatomical studies provided evidence that the major physiological effect of cannabinoids is the regulation of neurotransmitter release via activation of presynaptic CB1 receptors located on distinct types of axon terminals throughout the brain. Subsequent discoveries shed light on the functional consequences of this localization by demonstrating the involvement of endocannabinoids in retrograde signaling at GABAergic and glutamatergic synapses. In this review, we aim to synthesize recent progress in our understanding of the physiological roles of endocannabinoids in the brain. First, the synthetic pathways of endocannabinoids are discussed, along with the putative mechanisms of their release, uptake, and degradation. The fine-grain anatomical distribution of the neuronal cannabinoid receptor CB1 is described in most brain areas, emphasizing its general presynaptic localization and role in controlling neurotransmitter release. Finally, the possible functions of endocannabinoids as retrograde synaptic signal molecules are discussed in relation to synaptic plasticity and network activity patterns.

Increased Seizure Susceptibility and Proconvulsant Activity of Anandamide in Mice Lacking Fatty Acid Amide Hydrolase

A number of recent in vitro studies have described a role for endogenous cannabinoids ("endocannabinoids") as transsynaptic modulators of neuronal activity in the hippocampus and other brain regions. However, the impact that endocannabinoid signals may have on activity-dependent neural events in vivo remains mostly unknown and technically challenging to address because of the short half-life of these chemical messengers in the brain. Mice lacking the enzyme fatty acid amide hydrolase [FAAH (-/-) mice] are severely impaired in their ability to degrade the endocannabinoid anandamide and therefore represent a unique animal model in which to examine the function of this signaling lipid in vivo. Here, we show that the administration of anandamide dramatically augments the severity of chemically induced seizures in FAAH (-/-) mice but not in wild-type mice. Anandamide-enhanced seizures in FAAH (-/-) mice resulted in significant neuronal damage in the CA1 and CA3 regions of the hippocampus for the bicuculline and kainate models, respectively. Notably, in the absence of anandamide treatment, FAAH (-/-) mice exhibited enhanced seizure responses to high doses of kainate that correlated with greatly elevated endogenous levels of anandamide in the hippocampus of these animals. Collectively, these studies suggest that both exogenously administered and endogenously produced anandamide display FAAH-regulated proconvulsant activity and do not support a general neuroprotective role for this endocannabinoid in response to excitotoxic stimuli in vivo. More generally, these findings demonstrate that the disinhibitory actions of endocannabinoids observed in hippocampal slices in vitro may also occur in vivo.

Down-regulation of cannabinoid-1 (CB-1) receptors in specific extrahypothalamic regions of rats with dietary obesity: a role for endogenous cannabinoids in driving appetite for palatable food?

Agonists at cannabinoid-1 (CB-1) receptors stimulate feeding and particularly enhance the reward aspects of eating. To investigate whether endogenous cannabinoids might influence appetite for palatable food, we compared CB-1 receptor density in the forebrain and hypothalamus, between rats fed standard chow ( n=8) and others given palatable food ( n=8) for 10 weeks to induce dietary obesity. CB-1 receptor density was significantly decreased by 30–50% ( P<0.05) in the hippocampus, cortex, nucleus accumbens and entopeduncular nucleus of diet-fed rats. Furthermore, CB-1 receptor density in the hippocampus, nucleus accumbens and entopeduncular nucleus was significantly inversely correlated with intake of palatable food ( r 2=0.25–0.35; all P<0.05). By contrast, CB-1 receptor binding in the hypothalamus was low and not altered in diet-fed rats. CB-1 receptor down-regulation is consistent with increased activation of these receptors by endogenous cannabinoids. Acting in areas such as the nucleus accumbens and hippocampus, which are involved in the hedonic aspects of eating, cannabinoids may therefore drive appetite for palatable food and thus determine total energy intake and the severity of diet-induced obesity. However, cannabinoids in the hypothalamus do not appear to influence this aspect of eating behaviour.

Cannabinoid inhibition of capsaicin-sensitive sensory neurotransmission in the rat mesenteric arterial bed

The present study investigated whether cannabinoids can modulate neurotransmission mediated by capsaicin-sensitive sensory nerves in the rat isolated mesenteric arterial bed. Sensory neurogenic vasorelaxation mediated by electrical field stimulation was concentration-dependently attenuated by HU210 (0.1–3 μM), a cannabinoid receptor agonist (from 62±8.3% to 6±2.1% at 3 μM HU210). HU210 had no effect on relaxation to exogenous calcitonin gene-related peptide, indicating a prejunctional action. The action of HU210 (1 μM) was not affected by LY320135 (1 μM) or SR144528 (1 μM), cannabinoid CB 1 and CB 2 receptor antagonists, respectively. SR141716A (0.01–1 μM), a cannabinoid CB 1 receptor antagonist, concentration-dependently augmented vasorelaxation to electrical field stimulation, but had no effect on responses to calcitonin gene-related peptide and capsaicin, indicating a possible role of endogenous cannabinoids in sensory neurotransmission in rat mesenteric arteries. These data show that the cannabinoid receptor agonist HU210 inhibits prejunctionally sensory neurotransmission in rat mesenteric arteries and that this action is independent of cannabinoid CB 1- or CB 2-like receptors.