Are Endocannabinoids Neurotransmitters

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Failure In The Endocannabinoid System: Theory Or Reality?

However, results of this compound can nonetheless be blocked by the CB2 antagonist SR . Inhibition of FAAH by URB597 can also produce antinociceptive effects in inflammatory pain fashions that are mediated by the activation of PPAR-α receptors . Synergistic interactions between anandamide and GW7647 (PPAR-α agonist) have been demonstrated in the formalin test . Thus, modulation of the endocannabinoid system by FAAH/MGL/uptake inhibitors and their attainable interaction with non-cannabinoid receptors requires additional investigation. Thus, animal fashions of persistent ache are likely to be differentially delicate to CB2-mediated components of cannabinoid antinociception. Thus, manipulation of endocannabinoid accumulation through inhibition of metabolism or reuptake mechanisms may be employed to elucidate a task for cannabinoid CB2 receptors beneath conditions of inflammation or damage. Endocannabinoid signaling is restricted by efficient degradation processes involving enzymatic hydrolysis mediated by particular intracellular enzymes. THC is probably the most studied of all of the phytocannabinoids, as it binds to both the CB1 and CB2 cannabinoid receptors located all through the mind and physique. CBD binds weakly at both CB1 and CB2 receptors, with most of its therapeutic action thought to modulate the ECS through pathways together with a serotonin receptor. Thus, results of URB602 are only likely to be mediated by MGL under situations during which it's documented that local administration of URB602 will increase 2-AG accumulation with out altering ranges of AEA . Systemic administration of AM404 produces CB1-mediated antihyperalgesic effects in inflammatory ache fashions corresponding to full Freund’s adjuvant and formalin models but includes CB1/CB2 receptors in the CCI mannequin.

Endocannabinoid Synthesis, Release, And Degradation

However, Beaulieu and collaborators did not find a rise in AEA and a couple of-AG levels in the formalin test, measured 2 h after formalin injection when pain conduct has subsided . In a model of bone most cancers ache, intraplantar administration of exogenous AEA or the FAAH inhibitor URB597 increased the local level of AEA . These studies counsel that manipulation of peripheral endocannabinoids may be promising strategy for the management of ache. Indeed, the endocannabinoid system is localized all through the peripheral nervous system and CNS in a means that suggests that it performs a task in the modulation of ache processing.

Key Components Of The Endocannabinoid System

In some cases, functions of the endocannabinoid system are surmised following pharmacological inhibition of endocannabinoid deactivation. Thus, FAAH and MGL inhibitors enhance endocannabinoid accumulation (AEA and a pair of-AG, respectively) by inhibiting hydrolysis of fatty-acid amides and monoacylglycerols; these enzymes have multiple substrates. Both AEA and 2-AG are derivatives of arachidonic acid and bind to cannabinoid CB1 and CB2 receptors, though with completely different affinities and efficacies . However, the variable affinity for cannabinoid receptors may be due, partially, to the existence of distinct binding websites for the totally different ligands on cannabinoid receptors, as documented by molecular modeling studies . The plantar test measures the latency for animals to remove their paws from a radiant heat supply that is centered onto the plantar floor of the paw through the ground of a glass platform . Analgesia is obvious following injection of cannabinoid agonists locally into numerous mind regions including the periaqueductal grey (PAG), thalamus, and rostral ventromedial medulla (RVM), all critical mind regions involved in the ache processing. Furthermore, electrical stimulation of the dorsolateral PAG produced analgesia in the tail-flick take a look at and mobilized endogenous anandamide (AEA), as measured by microdialysis. Taken collectively, these findings strongly suggest that endogenous exercise performs an essential function in modulating pain beneath physiological situations. In this test, the FAAH inhibitor Compound 17 dose-dependently potentiates the consequences of exogenous AEA in the plantar check . Finally, exogenous administration of AEA also produces CB1-mediated antinociception within the paw stress test , assessed utilizing the tactic of Randall and Selitto (see Table 2). A position for cannabinoid CB2 receptors in antinociception in otherwise naive animals has been studied in an try to optimize the therapeutic potential of cannabinoid analgesic methods. CB2 agonists show therapeutic potential as a result of they're devoid of the unwanted central side-results attributed to activation of CB1 receptors ( for a evaluation). It is due to this fact acknowledged that solely certain assays (e.g. the plantar test) are likely to be sensitive to detection of CB2-mediated antinociceptive results in the absence of irritation or harm (for evaluation see ). Endocannabinoids serve as synaptic circuit breakers and regulate a number of physiological and pathological circumstances, e.g. regulation of food intake, immunomodulation, inflammation, analgesia, cancer, addictive behavior, epilepsy and others. This evaluation will focus on uncovering the roles of anandamide (AEA) and a couple of-arachidonoylglycerol (2-AG), the two greatest characterised endocannabinoids recognized thus far, in controlling nociceptive responding. The roles of AEA and 2-AG, released underneath physiological conditions, in modulating nociceptive responding at completely different levels of the neuraxis will be emphasized in this review. Effects of modulation of endocannabinoid ranges by way of inhibition of endocannabinoid hydrolysis and uptake can be compared with effects of exogenous administration of synthetic endocannabinoids in acute, inflammatory and neuropathic ache fashions. Finally, the therapeutic potential of the endocannabinoid signaling system is discussed within the context of identifying novel pharmacotherapies for the remedy of ache. Peripheral antinociceptive actions of cannabinoids have been demonstrated in numerous animal ache models (for evaluation see [123–125]). Harnessing these mechanisms exhibits considerable promise for separating the therapeutic results of cannabinoids from undesirable CNS aspect-results. Cannabinoid receptors are synthesized in dorsal root ganglion (DRG) cells, which are the source of major afferent input to the spinal twine [30, 31, 85, 165–167]. These afferent nerve fibers transmit information about sensory stimulation to the spinal twine, thereby enabling communication between the periphery and particular areas of the CNS that contribute to pain notion . Following the induction of neuropathy (by spinal nerve ligation), cannabinoid receptors and their endogenous ligands (AEA and a pair of-AG) are increased in the DRG on the ipsilateral facet of the injury .

Endocannabinoid Receptor Types: Cb1 And Cb2

The combination of FAAH or MGL inhibitors with the exogenous administration of endocannabinoids (AEA or 2-AG) also enhances the antinociceptive results of the putative endocannabinoid , but the mechanism of motion stays to be determined. The combination of AEA with both ibuprofen or rofecoxib produces antinociception that's mediated solely by CB1 receptors, although the mechanism of action for these other combos remains to be investigated . AEA and a pair of-AG are also increased in the spinal wire following induction of a neuropathic pain state produced by CCI of the sciatic nerve . The endocannabinoid system is equally modulated in response to a spinal twine contusion in rats . The endocannabinoid system interacts with a number of neurotransmitters similar to acetylcholine, dopamine, GABA, histamine, serotonin, glutamate, norepinephrine, prostaglandins and opioid peptides. The interaction with these neurotransmitters is liable for a lot of the pharmacological results of cannabinoids. Both artificial cannabinoids and fitocannabinoids act because of the interplay between the cannabinoid receptors. Medical cannabis contains many cannabinoid molecules that mimic these endocannabinoids, making the plant a potentially useful medication. The enzymes which degrade endocannabinoids are quite nicely characterised and embody fatty-acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL) (, for a evaluate). Inhibitors for FAAH (AM374, URB597, URB532 and others) or MGL (URB602, OMDM169, JZL184 and Compound eleven) enzymes have been described (; see for a review), though selectivity of some brokers might differ considerably. FAAH, a membrane sure enzyme, hydrolyzes AEA in neurons and astrocytes into breakdown products arachidonic acid and ethanolamine . However, additional work is needed to fully characterize the function that the endocannabinoid system performs within the processing of physiological pain. The therapeutic potential of cannabinoids has been the topic of extensive investigation following the invention of cannabinoid receptors and their endogenous ligands. Cannabinoid receptors and their endogenous ligands are current at supraspinal, spinal and peripheral ranges. Cannabinoids suppress behavioral responses to noxious stimulation and suppress nociceptive processing via activation of cannabinoid CB1 and CB2 receptor subtypes. Endocannabinoids, the mind’s personal cannabis-like substances, share the identical molecular goal as Δ9-tetrahydrocannabinol, the primary psychoactive component in cannabis.

Immune System

They are generated within the cell membrane from phospholipid precursors and possess cannabimimetic properties as a result of they bind and activate one or more cannabinoid receptor subtypes . Endocannabinoids are implicated in numerous physiological and pathological capabilities (regulation of meals consumption, immunomodulation, inflammation, analgesia, most cancers, addictive behavior, epilepsy and others) . The two greatest-studied endocannabinoids isolated so far are arachidonoylethanolamine (anandamide or AEA) and 2-arachidonoylglycerol (2-AG). AEA is hydrolyzed by the enzyme fatty-acid amide hydrolase (FAAH) whereas 2-AG is degraded by the enzyme monoacylglycerol lipase (MGL) . Electrical stimulation of the dorsolateral PAG produced antinociception in the tail-flick check and mobilized endogenous AEA, as measured by microdialysis. Importantly, this stimulation-produced analgesia was blocked by the CB1 antagonist SR141716A, demonstrating mediation by CB1. CB1 and CB2 receptors are present in giant myelinated and small unmyelinated human cutaneous nerve fibers . Both cannabinoid receptor subtypes have additionally been discovered in several layers of the pores and skin, and in some adnexal constructions (sweat glands, sebaceous cells and others) which can contribute to peripheral antinociceptive actions [166, 172–one hundred seventy five]. Endocannabinoid ranges and FAAH exercise have also been measured in rodent paw skin [176–179]. AEA is observed in paw tissue [177–178] whereas a decrease in FAAH activity is observed within the inflamed paw following carrageenan-induced irritation . In the formalin model, 2-AG hydrolysis inhibitor, OMDM169, elevated levels of two-AG, but not AEA, within the ipsilateral paw . Endocannabinoids are taken up by a transporter on the glial cell and degraded by fatty acid amide hydrolase (FAAH), which cleaves anandamide into arachidonic acid and ethanolamine or monoacylglycerol lipase (MAGL), and 2-AG into arachidonic acid and glycerol. While arachidonic acid is a substrate for leukotriene and prostaglandin synthesis, it is unclear whether or not this degradative byproduct has distinctive features within the central nervous system. A neuropharmacological examine demonstrated that an inhibitor of FAAH (URB597) selectively increases anandamide ranges within the brain of rodents and primates. Such approaches may lead to the development of new medicine with analgesic, anxiolytic-like and antidepressant-like results, which are not accompanied by overt indicators of abuse liability. Moroever, a role for CB2 receptors cannot be discounted from contributing to the antinociceptive results of exogenous administration of AEA, as a result of mediation by CB2 receptors was not assessed in these studies. In these studies, cannabinoid receptor antagonists directed at CB1 (AA-5-HT, PTK, URB597 and URB602 ) or at CB1/CB2 (URB597 ) have been used to identify the receptor mechanism underlying these results. This pathway is implicated in the transmission of nociceptive info to the mind (for evaluate see ). FAAH has also been present in Lissauer’s tract, in neurons of the superficial dorsal horn of the spinal cord and in dorsal root ganglion cells. Although FAAH can hydrolyze 2-AG in vitro , MGL is the predominant enzyme which controls 2-AG hydrolysis. Its excessive density within the basal ganglia is related to the results on the locomotor activity already mentioned. The presence of the receptor in the hippocampus and cortex are related to the effects in studying and memory, and with the psychotropic and antiepileptic properties. The low toxicity and lethality are associated with the low expression of receptors in the brain stem. DRG cells additionally transport CB receptors to peripheral terminals of major afferents, and both CB1 and CB2 receptors are found in large myelinated and small unmyelinated human cutaneous nerve fibers. Cannabinoid receptors have been localized to pre- and postsynaptic websites inside the spinal cord as properly, utilizing receptor binding and quantitative autoradiography. In the dorsal horn, CB1 receptors have been discovered on interneurons and on astrocytes. Exposure to stress increases 2-AG and anandamide accumulation in the spinal wire, and these ranges correlate extremely with the appearance of stress-induced analgesia. Cannabinoid-related analgesia is attenuated following spinal transection, implicating an necessary function for supraspinal sites of action as properly.

• Harnessing these mechanisms exhibits appreciable promise for separating the therapeutic effects of cannabinoids from unwanted CNS aspect-effects.
• These afferent nerve fibers transmit details about sensory stimulation to the spinal twine, thereby enabling communication between the periphery and particular areas of the CNS that contribute to pain perception .
• Peripheral antinociceptive actions of cannabinoids have been demonstrated in numerous animal pain models (for evaluate see [123–125]).
• DRG cells synthesize cannabinoid receptors, and transport them to peripheral terminals of major afferents .
• Following the induction of neuropathy (by spinal nerve ligation), cannabinoid receptors and their endogenous ligands (AEA and 2-AG) are increased in the DRG on the ipsilateral aspect of the damage .
• Cannabinoid receptors are synthesized in dorsal root ganglion (DRG) cells, which are the source of primary afferent input to the spinal twine [30, 31, eighty five, one hundred sixty five–167].

DRG cells synthesize cannabinoid receptors, and transport them to peripheral terminals of major afferents . Multiple approaches assist the presence of cannabinoid receptors on major afferent neurons . The distribution of FAAH in organs of the rat has been described in detail; its activity is highest in the liver followed by the small intestine, mind, and testis (see for a evaluation). FAAH is found in the termination zone of the spinothalamic tract in the ventral posterior lateral nucleus of the thalamus [one hundred ten–112]. It can also be essential to emphasise that inhibitors of FAAH elevate ranges of fatty-acid amides that do not bind to cannabinoid receptors (e.g. palmitoylethanolamine) and have targets (e.g. PPAR-α) that are distinct from CB1 and CB2 receptors. Thus, the contribution of non-cannabinoid receptor mechanisms of motion within the in vivo pharmacological effects of FAAH and MGL inhibitors must also be thought of. Walker’s group first identified a task for endogenous AEA, released beneath physiological situations, in ache modulation . The early stages are marked by increases in AEA levels, upregulation of the artificial enzyme NAPE-PLD, and downregulation of the degradative enzyme FAAH. The delayed stages are marked by increases in 2-AG, a marked upregulation of the 2-AG synthesizing enzyme DAGL-α (i.e. in neurons, astrocytes and immune infiltrates), and a average enhance in ranges of the degradative enzyme MGL . In this research, CB1 receptors have been expressed in neurons, oligodendrocytes, and astrocytes, whereas CB2 receptors have been strongly upregulated after the lesion and expressed mainly in immune infiltrates and astrocytes . These research highlight the significance of the endocannabinoid system as a potential therapeutic goal for remedy of both spinal wire harm and neuropathic pain. Cannabis has been used for greater CBD Oil for Pets than twelve thousand years and for a lot of completely different purposes (i.e. fiber, medicinal, recreational). However, the endocannabinoid signaling system has solely just lately been the focus of medical analysis and thought of a potential therapeutic goal [1–3]. Endocannabinoids mimic the pharmacological actions of the psychoactive precept of marijuana, Δ9-tetrahydrocannabinol (Δ9-THC) . AEA biosynthesis was initially believed to happen from enzymatic cleavage of a phospholipid precursor, N-arachidonoyl-phosphatidylethanolamine (NAPE). NAPE is synthesized by the enzymatic transfer of arachidonic acid within the sn-1 place of a phosphatidylcholine to the amide group of a phosphatidylethanolamine under the supervision of the calcium-impartial N-acyl-transferase (NAT) . NAPE is then hydrolyzed to AEA by a specific phospholipase D (NAPE-PLD) which has recently been cloned and molecularly characterised [eight, 63–sixty five]. However, NAPE-PLD knockout mice present no deficit in AEA production, a discovering which questions the position of this enzyme in anandamide biosynthesis . Thus, a number of enzymatic pathways could also be concerned within the biosynthesis of anandamide and NAPE-PLD is unlikely to exclusively management its’ biosynthesis . Indeed, there is evidence for the metabolism of AEA and a couple of-AG by cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 enzymes, further including to the complexity of endocannabinoid signalling mechanisms . Moreover, increasing specific endocannabinoids (e.g. anandamide) or fatty-acid amides (e.g. palmiotylethanolamine) can activate different non-cannabinoid receptors (e.g. TRPV1 or PPAR-α, respectively). Entourage results may be produced by manipulations that elevate ranges of endogenous lipid mediators that don't bind to cannabinoid receptors however, nonetheless, compete for a similar enzymes for hydrolysis . Thus, not all effects of those modulators could be attributed to actions at cannabinoid receptors, and evaluation of pharmacological specificity is important for interpretation of in vivo actions of any compound. Palmitoylethanolamide (PEA), an endogenous fatty-acid ethanolamide, is an agonist at PPAR-α receptors, however doesn't bind to cannabinoid receptors . In these studies, the tail-flick test was used to quantify the impression of electrical brain stimulation or publicity to footshock stress on antinociception. Thus, it is very important emphasize that tail-flick stimulation is not the set off for endocannabinoid mobilization in these studies, and antagonists do not alter basal nociceptive thresholds underneath testing situations. A position for CB2 was not evaluated in studies of endocannabinoid-mediated stimulation-produced analgesia, presumably because of the lack of availability of a CB2 antagonist at the time the work was performed . The existence of a cross-tolerance and cross-sensitization between exogenous cannabinoid antinociception and endocannabinoid-mediated stress-induced analgesia suggests that these phenomena are linked by a standard mechanism . Therefore, the reader ought to pay attention to these limitations when interpreting the results of any specific study. Pharmacological modulation of endocannabinoid levels also suppresses neuropathic pain habits in other models of surgically-induced traumatic nerve injury. For instance, AM404 produces CB1-dependent antinociception in a model of unilateral hind limb neuropathy induced by partial sciatic nerve ligation (PSNL) . Exogenous administration of anandamide similarly produces CB1-dependent antinociceptive effects whereas the antinociceptive results of two-AG, administered by way of the same route, are CB1/CB2 mediated (see Table 5). The endocannabinoid system plays an necessary position in multiple elements of the neuronal features, together with studying and reminiscence, emotion, addictive like behaviour, feeding and metabolism, ache and neuroprotection. It can also be involved within the modulation of different processes at the cardiovascular and immunological ranges, among others. The distribution of the CB1 receptors within the brain correlates with the pharmacological actions of the cannabinoids. Exogenous administration of endocannabinoids or their modulation by way of inhibition of endocannabinoid deactivation or uptake can produce antinociception in acute pain models (see Table 1 and Table 2). The magnitude of the observed antinociceptive effect could differ depending upon the assay, the endocannabinoid used and/or the mechanism employed to alter endocannabinoid levels. The tail flick check examines the latency for a rodent to “flick” its tail away from a radiant heat source , or to take away the tail following immersion in scorching water (see Table 1). Moreover, native exogenous administrations of two-AG produce CB2-mediated antinociception in the formalin check and CB1/CB2-mediated antinociception in the partial sciatic nerve ligation mannequin. However, native administration of AEA produces CB1-mediated antinociception in each of these models (see Table 3–Table 5). A local route of agonist administration might unmask CB2-mediated components in the antinociceptive results produced by pharmacological inhibitors of endocannabinoid uptake and degradation. However, URB597 produces antinociceptive effects with largely consistent pharamacological specificity following either systemic or local routes of administration. The primary goal of this evaluation might be to uncover the position of AEA and a pair of-AG in ache modulation. This shall be completed by reviewing studies analyzing mobilization of endocannabinoids underneath physiological situations or through the use of pharmacological instruments that inhibit their uptake or degradation. This evaluate may even think about research using exogenous administration of artificial endocannabinoids in combination with different pharmacological approaches aimed toward regulating their uptake or degradation. The general aim is to know the physiological function of the endogenous ligands at totally different ranges of the ache pathway and in several models of pathological pain. Once released into the extracellular space by a putative endocannabinoid transporter, messengers are vulnerable to glial cell inactivation. The discovery of AEA , the primary endocannabinoid isolated from mind, was adopted a number of years later by the identification of 2-AG . Since then, several putative endocannabinoids have been isolated which embody noladin ether , virodhamine and N-arachidonoyldopamine (NADA) . Much much less information is thought concerning the endocannabinoid-like properties of those latter putative endogenous ligands (see for a evaluate). Indeed, elucidation of the endogenous function of these compounds in several physiological processes and their precise mechanisms of motion requires additional investigation . Here, we'll contemplate the roles of various cannabinoid receptors, different endocannabinoids and the equipment responsible for their synthesis and degradation. AEA preferentially binds to CB1 receptors in vitro, and reveals low affinity for the transient receptor potential vanilloid 1 (TRPV1) [seventy three–seventy six]. This compound is found in the brain in concentrations one hundred seventy-fold larger than those of anandamide . Cannabinoids are a category of molecules characterized by their ability to activate cannabinoid receptors like CB1 and CB2. Anandamide and a couple of-AG are the two major endocannabinoids produced naturally in the physique. All three of these cannabinoids can activate CB1 and CB2 receptors, though each one has a special potency at every receptor. FAAH inhibitors (URB597, Ibuprofen, Rofecoxib) are also antinociceptive in this mannequin . URB597 produces antinociception via an area peripheral mechanism that is mediated by CB1/CB2 cannabinoid receptors . However, systemic administration of the same compound does not reliably produce antinociception . Moreover, antinociception produced by native injection of ibuprofen and rofecoxib within the paw does not contain CB1 or CB2 cannabinoid receptors . Local administration of URB602 also produces a CB1/CB2 antinociception in this model . First, the 2-AG precursor diacylglycerol (DAG) is fashioned from enzymatic cleavage of membrane phospholipid precursors by the enzyme phospholipase C (PLC) (for evaluation see ). DAG is subsequently hydrolyzed by a diacylglycerol lipase (DAGL) selective for the sn-1 position to generate 2-AG . Subsequent to their on-demand synthesis, endocannabinoids might activate cannabinoid receptors following their release into the extracellular area or their movement directly into the cell membrane . MGL, a serine hydrolase, hydrolyzes 2-AG into breakdown merchandise (arachidonic acid and glycerol). By contrast, FAAH is a postsynaptic enzyme and should regulate AEA ranges near sites of synthesis . Although the biosynthesis and metabolism of AEA and 2-AG have been simplified right here to maintain the main focus of this review, it is important to mention that, in addition to hydrolysis, alternative metabolic pathways exist [67, 116–118]. For instance, along with present process hydrolysis, endocannabinoids endure oxidative metabolism, through which they're reworked into other biologically active mediators . Endocannabinoids are produced on demand either by activity-dependent or receptor-stimulated cleavage of membrane phospholipid precursors. Endocannabinoids may be released immediately from cells after their production since they're extremely lipophilic and thus are poorly fitted to storage (for review see ). Endocannabinoid signaling is regulated by synthesis, release, uptake and degradation. Membrane depolarization, will increase in intracellular calcium ranges and receptor stimulation can all activate enzymatic processes leading to the cleavage of membrane phospholipids precursors and subsequent synthesis of endocannabinoids (see for a review). Intraplantar administration of formalin was also proven to extend levels of endogenous AEA in the dorsolateral PAG. Exposure to an environmental stressor (transient continous footshock) additionally produces endocannabinoid-mediated stress-induced analgesia that CBD Vape Oil is related to mobilization of endogenous 2-AG and anandamide . Endocannabinoid mobilization was most pronounced in dorsal midbrain fragments containing the intact PAG . In this check, the endocannabinoid uptake inhibitors (VDM-11 and UCM707) produce CB1-mediated antinociception underneath conditions during which the endocannabinoid system is activated . Exogenous administration of AEA produces antinociception [188–191], though few studies have evaluated whether or not this impact is mediated by cannabinoid receptors. Several teams have evaluated a CB1 element in exogenous AEA antinociception [192–194], but other studies have suggested that anandamide produces antinociception via a CB1-unbiased mechanism . All these research assessed pharmacological specificity using the CB1 antagonist/inverse agonist SR141716A antagonist. Thus, you will need to emphasize that SR141716A acts as an inverse agonist at CB1 receptors and may activate both CB2 and vanilloid TRPV1 receptors, albeit with low affinity (for evaluation see ).

Modulation Of The Endocannabinoid System In Animal Models

Indeed, studies employing FAAH knockout mice additionally corroborate the earlier outcomes; a CB1-mediated part is noticed in each the tail immersion and sizzling plate exams under circumstances in which both CB1 and CB2 antagonists were evaluated . The mixture of exogenous AEA with FAAH (ibuprofen, indomethacin, PMSF, URB597) inhibitors also produces antinociception that's mediated by CB1 receptors . Therefore, documentation of intrinsic results of endocannabinoids launched beneath physiological conditions is important for understanding the functional roles of endocannabinoids in nociceptive processing. As described above, studies employing stimulation-produced analgesia and stress-induced analgesia provide direct support for the hypothesis that endogenous AEA and a pair of-AG suppress pain by way of a CB1-dependent mechanism.