Endocannabinoid structure-activity relationships for interaction at the cannabinoid receptors

Anandamide (N -arachidonoylethanolamine) was the first ligand to be identified as an endogenous ligand of the G-protein coupled cannabinoid CB1 receptor. Subsequently, two other fatty acid ethanolamides, N -homo- gamma -linolenylethanolamine and N -7,10,13,16-docosatetraenylethanolamine were identified as endogenous cannabinoid ligands. A fatty acid ester, 2-arachidonoylglycerol (2-AG), and a fatty acid ether, 2-arachidonyl glyceryl ether also have been isolated and shown to be endogenous cannabinoid ligands. Recent studies have postulated the existence of carrier-mediated anandamide transport that is essential for termination of the biological effects of anandamide. A membrane bound amidohydrolase (fatty acid amide hydrolase, FAAH), located intracellularly, hydrolyzes and inactivates anandamide and other endogenous cannabinoids such as 2-AG. 2-AG has also been proposed to be an endogenous CB2 ligand. Structure-activity relationships (SARs) for endocannabinoid interaction with the CB receptors are currently emerging in the literature. This review considers cannabinoid receptor SAR developed to date for the endocannabinoids with emphasis upon the conformational implications for endocannabinoid recognition at the cannabinoid receptors.     

The endocannabinoid-CB receptor system: Importance for development and in pediatric disease

Endogenous cannabinoids (endocannabinoids) and their cannabinoid CB1 and CB2 receptors, are present from the early stages of gestation and play a number of vital roles for the developing organism. Although most of these data are collected from animal studies, a role for cannabinoid receptors in the developing human brain has been suggested, based on the detection of "atypically" distributed CB1 receptors in several neural pathways of the fetal brain. In addition, a role for the endocannabinoid system for the human infant is likely, since the endocannabinoid 2-arachidonoyl glycerol has been detected in human milk. Animal research indicates that the Endocannabinoid-CB1 Receptor ('ECBR') system fulfills a number of roles in the developing organism: 1. embryonal implantation (requires a temporary and localized reduction in anandamide); 2. in neural development (by the transient presence of CB1 receptors in white matter areas of the nervous system); 3. as a neuroprotectant (anandamide protects the developing brain from trauma-induced neuronal loss); 4. in the initiation of suckling in the newborn (where activation of the CB1 receptors in the neonatal brain is critical for survival). 5. In addition, subtle but definite deficiencies have been described in memory, motor and addictive behaviors and in higher cognitive ('executive') function in the human offspring as result of prenatal exposure to marihuana. Therefore, the endocanabinoid-CB1 receptor system may play a role in the development of structures which control these functions, including the nigrostriatal pathway and the prefrontal cortex. From the multitude of roles of the endocannabinoids and their receptors in the developing organism, there are two distinct stages of development, during which proper functioning of the endocannabinoid system seems to be critical for survival: embryonal implantation and neonatal milk sucking. We propose that a dysfunctional Endocannabinoid-CB1 Receptor system in infants with growth failure resulting from an inability to ingest food, may resolve the enigma of "non-organic failure-to-thrive" (NOFTT). Developmental observations suggest further that CB1 receptors develop only gradually during the postnatal period, which correlates with an insensitivity to the psychoactive effects of cannabinoid treatment in the young organism. Therefore, it is suggested that children may respond positively to medicinal applications of cannabinoids without undesirable central effects. Excellent clinical results have previously been reported in pediatric oncology and in case studies of children with severe neurological disease or brain trauma. We suggest cannabinoid treatment for children or young adults with cystic fibrosis in order to achieve an improvement of their health condition including improved food intake and reduced inflammatory exacerbations.     

Cannabinoid receptors and their ligands

There are at least two types of cannabinoid receptors, CB(1) and CB(2), both coupled to G proteins. CB(1) receptors exist primarily on central and peripheral neurons, one of their functions being to modulate neurotransmitter release. CB(2) receptors are present mainly on immune cells. Their roles are proving more difficult to establish but seem to include the modulation of cytokine release. Endogenous agonists for cannabinoid receptors (endocannabinoids) have also been discovered, the most important being arachidonoyl ethanolamide (anandamide), 2-arachidonoyl glycerol and 2-arachidonyl glyceryl ether. Other endocannabinoids and cannabinoid receptor types may also exist. Although anandamide can act through CB(1) and CB(2) receptors, it is also a vanilloid receptor agonist and some of its metabolites may possess yet other important modes of action. The discovery of the system of cannabinoid receptors and endocannabinoids that constitutes the "endocannabinoid system" has prompted the development of CB(1)- and CB(2)-selective agonists and antagonists/inverse agonists. CB(1)/CB(2) agonists are already used clinically, as anti-emetics or to stimulate appetite. Potential therapeutic uses of cannabinoid receptor agonists include the management of multiple sclerosis/spinal cord injury, pain, inflammatory disorders, glaucoma, bronchial asthma, vasodilation that accompanies advanced cirrhosis, and cancer. Following their release onto cannabinoid receptors, endocannabinoids are removed from the extracellular space by membrane transport and then degraded by intracellular enzymic hydrolysis. Inhibitors of both these processes have been developed. Such inhibitors have therapeutic potential as animal data suggest that released endocannabinoids mediate reductions both in inflammatory pain and in the spasticity and tremor of multiple sclerosis. So too have CB(1) receptor antagonists, for example for the suppression of appetite and the management of cognitive dysfunction or schizophrenia.     

Role of lipids and lipid signaling in the development of cannabinoid tolerance

Cannabinoid agonists such as Delta9-tetrahydrocannabinol (THC) produce a wide range of pharmacological effects both in the central nervous system and in the periphery. One of the most striking features of cannabinoids such as THC is the magnitude to tolerance that can be produced upon repetitive administration of this substance to animals. Relatively modest dosing regimens are capable of producing significant tolerance, whereas greater than 100-fold tolerance can be obtained with aggressive treatments. While cannabinoid tolerance has been studied quite extensively to establish its relevance to the health consequences of marijuana use, it has also proven to be a valuable strategy in understanding the mechanism of action of cannabinoids. The discovery of the endocannabinoid system that contains two receptor subtypes, CB1 and CB2, associated signaling pathways, endocannabinoids (anandamide and 2-arachidonoylglycerol) and their synthetic and degradative pathways has provided a means of systematically evaluating the mechanism of cannabinoid tolerance. It is well known that the CB1 cannabinoid receptor is down-regulated in states of cannabinoid tolerance along with uncoupling from its second messenger systems. Endocannabinoid levels are also altered in selected brain regions during the development of tolerance. While it is reasonable to speculate that a likely relationship exists between receptor and endocannabinoid levels, at present, little is known regarding the biological signal that leads to alterations in endocannabinoid levels. It is also unknown to what degree synthetic and degradative pathways for the endocannabinoids are altered in states of tolerance. The discovery that the brain is abundant in fatty acid amides and glycerols raises the question as to what roles these lipids contribute to the endocannabinoid system. Some of these lipids also utilize the endocannabinoid metabolic pathways, produce similar pharmacological effects, and are capable of modulating the actions of anandamide and 2-arachidonoylglycerol. In addition, there are dopamine, glycine, and serotonin conjugates of arachidonic acid that may also contribute to the actions of endocannabinoids. A systematic examination of these lipids in cannabinoid tolerance might shed light on their physiological relevance to the endocannabinoid system.     

The endocannabinoid system in the brain of Carassius auratus and its possible role in the control of food intake

Cannabinoid receptors and the endocannabinoids anandamide and 2-arachidonoylglycerol have been suggested to regulate food intake in several animal phyla. Orthologs of the mammalian cannabinoid CB(1) and CB(2) receptors have been identified in fish. We investigated the presence of this endocannabinoid system in the brain of the goldfish Carassius auratus and its role in food consumption. CB(1)-like immunoreactivity was distributed throughout the goldfish brain. The prosencephalon showed strong CB(1)-like immunoreactivity in the telencephalon and the inferior lobes of the posterior hypothalamus. Endocannabinoids were detected in all brain regions of C. auratus and an anandamide-hydrolysing enzymatic activity with features similar to those of mammalian fatty acid amide hydrolase was found. Food deprivation for 24 h was accompanied by a significant increase of anandamide, but not 2-arachidonoylglycerol, levels only in the telencephalon. Anandamide caused a dose-dependent effect on food intake within 2 h of intraperitoneal administration to satiated fish and significantly enhanced or reduced food intake at low (1 pg/g body weight) or intermediate (10 pg/g) doses, respectively, the highest dose tested (100 pg/g) being inactive. We suggest that endocannabinoids might variously contribute to adaptive responses to food shortage in fish.     

Endocannabinoids and endocannabinoid-related mediators: Targets,metabolism and role in neurological disorders

The endocannabinoid system (ECS) is composed of two G protein-coupled receptors (GPCRs), the cannabinoid CB1 and CB2 receptors, and the two main endogenous lipid ligands of such receptors (also known as the “endocannabinoids”), anandamide and 2-arachidonoyl-glycerol. The ECS is a pleiotropic signalling system involved in all aspects of mammalian physiology and pathology, and for this reason it represents a potential target for the design and development of new therapeutic drugs. However, the endocannabinoids as well as some of their congeners also interact with a much wider range of receptors, including members of the Transient Receptor Potential (TRP) channels, Peroxisome Proliferator-Activated Receptors (PPARs), and other GPCRs. Indeed, following the discovery of the endocannabinoids, endocannabinoid-related lipid mediators, which often share the same metabolic pathways of the endocannabinoids, have also been identified or rediscovered. In this review article, we discuss the role of endocannabinoids and related lipids during physiological functions, as well as their involvement in some of the most common neurological disorders.     

Astrocytes in culture produce anandamide and other acylethanolamides

Anandamide (arachidonylethanolamide) is an endocannabinoid that belongs to the acylethanolamide lipid family. It is produced by neurons in a calcium-dependent manner and acts through cannabinoid CB1 receptors. Other members of the acylethanolamide lipid family are also produced by neurons and act through G-protein-coupled receptors: homo-gamma-linolenylethanolamide (HEA) and docosatetraenylethanolamide (DEA) act through CB1 receptors, palmitylethanolamide (PEA) acts through CB2-like receptors, and oleylethanolamide (OEA) acts through receptors that have not yet been cloned. Although it is clear that anandamide and other acylethanolamides play a major role in neuronal signaling, whether astrocytes also produce these lipids is unknown. We developed a chemical ionization gas chromatography/mass spectrometry method that allows femtomole detection and quantification of anandamide and other acylethanolamides. Using this method, we unambiguously detected and quantified anandamide, HEA, DEA, PEA, and OEA in mouse astrocytes in culture. Stimulation of mouse astrocytes with ionomycin, a calcium ionophore, enhanced the production of anandamide, HEA, and DEA, whereas PEA and OEA levels were unchanged. Endothelin-1, a peptide known to act on astrocytes, enhanced the production of anandamide, without affecting the levels of other acylethanolamides. These results show that astrocytes produce anandamide, HEA, and DEA in a calcium-dependent manner and that anandamide biosynthesis can be selectively stimulated under physiologically relevant conditions. The relative levels of acylethanolamides in astrocytes from rat and human were different from the relative levels of acylethanolamides in mouse astrocytes, indicating that the production of these lipids differs between species. Because astrocytes are known to express CB1 receptors and inactivate endocannabinoids, our finding strongly suggests the existence of a functional endocannabinoid signaling system in these cells.     

Anandamide, but not 2-arachidonoylglycerol, accumulates during in vivo neurodegeneration

Endogenous cannabinoid receptor ligands (endocannabinoids) may rescue neurons from glutamate excitotoxicity. As these substances also accumulate in cultured immature neurons following neuronal damage, elevated endocannabinoid concentrations may be interpreted as a putative neuroprotective response. However, it is not known how glutamatergic insults affect in vivo endocannabinoid homeostasis, i.e. N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), as well as other constituents of their lipid families, N-acylethanolamines (NAEs) and 2-monoacylglycerols (2-MAGs), respectively. Here we employed three in vivo neonatal rat models characterized by widespread neurodegeneration as a consequence of altered glutamatergic neurotransmission and assessed changes in endocannabinoid homeostasis. A 46-fold increase of cortical NAE concentrations (anandamide, 13-fold) was noted 24 h after intracerebral NMDA injection, while less severe insults triggered by mild concussive head trauma or NMDA receptor blockade produced a less pronounced NAE accumulation. By contrast, levels of 2-AG and other 2-MAGs were virtually unaffected by the insults employed, rendering it likely that key enzymes in biosynthetic pathways of the two different endocannabinoid structures are not equally associated to intracellular events that cause neuronal damage in vivo. Analysis of cannabinoid CB(1) receptor mRNA expression and binding capacity revealed that cortical subfields exhibited an up-regulation of these parameters following mild concussive head trauma and exposure to NMDA receptor blockade. This may suggest that mild to moderate brain injury may trigger elevated endocannabinoid activity via concomitant increase of anandamide levels, but not 2-AG, and CB(1) receptor density.     

Endocannabinoids and the gut

In the digestive tract, there is evidence for the presence of high amounts of endocannabinoids (anandamide and 2-arachidonylglycerol) and of mechanisms for endocannabinoid metabolism and possibly endocannabinoid uptake. Pharmacological studies have shown that anandamide inhibits excitatory transmission and peristalsis in the isolated guinea-pig ileum and reduces intestinal motility in the mouse in vivo; all these effects are mediated by CB(1) receptors, which are located on enteric nerves. Conversely, the selective CB(1) receptor antagonist SR141716A increased intestinal motility and this effect is likely due to the displacement of endocannabinoids rather than to its inverse agonist properties. Interestingly, inhibitory effects of anandamide via non-CB(1) receptors and stimulatory effects via vanilloid receptors have also been proposed.     

Lipid rafts: A nexus for endocannabinoid signaling?

The endocannabinoids are endogenous agonists of the cannabinoid receptors and some members of the transient receptor potential, vanilloid type (TRPV), family of cation channels. Endocannabinoids along with their target receptors comprise a signaling system that is not well characterized. There have been many advances in our collective understanding of endocannabinoid signaling in the last decade and experimental evidence is mounting that pharmacological augmentation of endocannabinoid tone might have a significant therapeutic benefit in several disease states. However, the mechanisms responsible for the biosynthesis, cellular uptake, and intracellular processing of endocannabinoids are not well understood and have been the source of much debate. Recent studies have revealed a role for detergent insoluble membrane domains called lipid rafts in various aspects of signaling associated with the endocannabinoid anandamide. Intact detergent insoluble membrane domains appear to play a role in an anandamide-induced signaling cascade that is independent of G protein-coupled cannabinoid receptors or TRPV channels. Furthermore, detergent insoluble membrane domain-related endocytosis and recycling to lipid rafts appear to regulate the organization and localization of anandamide metabolites. We will discuss the implications that these findings have on the way we view endocannabinoid signaling, trafficking, and processing.     

Endocannabinoid modulation of sympathetic and cardiovascular responses to acute stress in the periaqueductal gray of the rat

Activation of the sympathetic nervous system is fundamental to the coordinated response to stress or danger. The midbrain periaqueductal gray (PAG) contains the neural substrate required to recruit the sympathetic nervous system and organize the physiological and behavioral responses required to respond to imposed challenges. Endocannabinoids have been shown to influence associated behavioral responses. The defense response was used in this study as a working model to examine endocannabinoid modulation of the sympathetic response to acute stress in the anesthetized rat. Microinjection of the cannabinoid 1 (CB1) receptor agonist anandamide into the defense pathway of the dorsal PAG could elicit an increase in renal sympathetic nerve activity and blood pressure, twitching of the whiskers, and movement of the limbs. The response was attenuated by prior microinjection of the CB1 receptor antagonist AM-281 at the same site. Electrical stimulation of the hypothalamic defense area could evoke similar sympathoexcitatory and pressor responses, which were significantly attenuated by microinjection of AM-281 into the dorsal PAG. These data indicate that endocannabinoids can modulate the sympathetic and cardiovascular components of the acute stress response via CB1 receptors at the level of the PAG.     

Ligand-receptor signaling with endocannabinoids in preimplantation embryo development and implantation

Although adverse effects of cannabinoids on pregnancy have been indicated for many years, the mechanisms by which they exert their actions were not clearly understood. Only recently, molecular and biochemical approaches have led to the identification of two types of cannabinoid receptors, brain-type receptors (CB1-R) and spleen-type receptors (CB2-R), which mediate cannabinoid effects. These findings were followed by the discovery of endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG). The natural cannabinoids and endocannabinoids exert their effects via cannabinoid receptors and share similar pharmacological and physiological properties. Recent demonstration of expression of functional CB1-R in the preimplantation embryo and synthesis of anandamide in the pregnant uterus of mice suggests that cannabinoid ligand-receptor signaling is operative in the regulation of preimplantation embryo development and implantation. This review describes recent observations and their significance in embryo-uterine interactions during implantation and future research directions in this emerging area of interest.     

Release of Endocannabinoids into the Cerebrospinal Fluid during the Induction of the Trigemino-Hypoglossal Reflex in Rats

The endocannabinoid system (ECS) plays an important role in pain processing and modulation. Since the specific effects of endocannabinoids within the orofacial area are largely unknown, we aimed to determine whether an increase in the endocannabinoid concentration in the cerebrospinal fluid (CSF) caused by the peripheral administration of the FAAH inhibitor URB597 and tooth pulp stimulation would affect the transmission of impulses between the sensory and motor centers localized in the vicinity of the third and fourth cerebral ventricles. The study objectives were evaluated on rats using a method that allowed the recording of the amplitude of evoked tongue jerks (ETJ) in response to noxious tooth pulp stimulation and URB597 treatment. The amplitude of ETJ was a measure of the effect of endocannabinoids on the neural structures. The concentrations of the endocannabinoids tested (AEA and 2-AG) were determined in the CSF, along with the expression of the cannabinoid receptors (CB1 and CB2) in the tissues of the mesencephalon, thalamus, and hypothalamus. We demonstrated that anandamide (AEA), but not 2-arachidonoylglycerol (2-AG), was significantly increased in the CSF after treatment with a FAAH inhibitor, while tooth pulp stimulation had no effect on the AEA and 2-AG concentrations in the CSF. We also found positive correlations between the CSF AEA concentration and cannabinoid receptor type 1 (CB1R) expression in the brain, and between 2-AG and cannabinoid receptor type 2 (CB2R), and negative correlations between the CSF concentration of AEA and brain CB2R expression, and between 2-AG and CB1R. Our study shows that endogenous AEA, which diffuses through the cerebroventricular ependyma into CSF and exerts a modulatory effect mediated by CB1Rs, alters the properties of neurons in the trigeminal sensory nuclei, interneurons, and motoneurons of the hypoglossal nerve. In addition, our findings may be consistent with the emerging concept that AEA and 2-AG have different regulatory mechanisms because they are involved differently in orofacial pain. We also suggest that FAAH inhibition may offer a therapeutic approach to the treatment of orofacial pain.     

Endocannabinoids in the central nervous system--an overview

Many aspects of the physiology and pharmacology of anandamide (arachidonoyl ethanol amide), the first endogenous cannabinoid ligand ("endocannabinoid") isolated from pig brain, have been studied since its discovery in 1992. Ethanol amides from other fatty acids have also been identified as endocannabinoids with similar in vivo and in vitro pharmacological properties. 2-Arachidonoyl glycerol and noladin ether (2-arachidonyl glyceryl ether), isolated in 1995 and 2001, respectively, so far, display pharmacological properties in the central nervous system, similar to those of anandamide. The endocannabinoids are widely distributed in brain, they are synthesized and released upon neuronal stimulation, undergo reuptake and are hydrolyzed intracellularly by fatty acid amide hydrolase (FAAH). For therapeutic purposes, inhibitors of FAAH may provide more specific cannabinoid activities than direct agonists, and several such molecules have already been developed.Pharmacological effects of the endocannabinoids are very similar, yet not identical, to those of the plant-derived and synthetic cannabinoid receptor ligands. In addition to pharmacokinetic explanations, direct or indirect interactions with other receptors have been considered to explain some of these differences, including activities at serotonin and GABA receptors. Binding affinities for other receptors such as the vanilloid receptor, have to be taken into account in order to fully understand endocannabinoid physiology. Moreover, possible interactions with receptors for the lysophosphatidic acids deserve attention in future studies.Endocannabinoids have been implicated in a variety of physiological functions. The areas of central activities include pain reduction, motor regulation, learning/memory, and reward. Finally, the role of the endocannabinoid system in appetite stimulation in the adult organism, and perhaps more importantly, its critical involvement in milk ingestion and survival of the newborn, may not only further our understanding of the physiology of food intake and growth, but may also find therapeutic applications in wasting disease and infant's "failure to thrive".     

Endocannabinoids in the central nervous system

The major psychoactive component of cannabis derivatives, delta9-THC, activates two G-protein coupled receptors: CB1 and CB2. Soon after the discovery of these receptors, their endogenous ligands were identified: lipid metabolites of arachidonic acid, named endocannabinoids. The two major main and most studied endocannabinoids are anandamide and 2-arachidonyl-glycerol. The CB1 receptor is massively expressed through-out the central nervous system whereas CB2 expression seems restricted to immune cells. Following endocannabinoid binding, CB1 receptors modulate second messenger cascades (inhibition of adenylate cyclase, activation of mitogen-activated protein kinases and of focal-adhesion kinases) as well as ionic conductances (inhibition of voltage-dependent calcium channels, activation of several potassium channels). Endocannabinoids transiently silence synapses by decreasing neurotransmitter release, play major parts in various forms of synaptic plasticity because of their ability to behave as retrograde messengers and activate non-cannabinoid receptors (such as vanilloid receptor type-1), illustrating the complexity of the endocannabinoid system. The diverse cellular targets of endocannabinoids are at the origin of the promising therapeutic potentials of the endocannabinoid system.     

Cannabinoid receptors CB1 and CB2 form functional heteromers in brain

Exploring the role of cannabinoid CB(2) receptors in the brain, we present evidence of CB(2) receptor molecular and functional interaction with cannabinoid CB(1) receptors. Using biophysical and biochemical approaches, we discovered that CB(2) receptors can form heteromers with CB(1) receptors in transfected neuronal cells and in rat brain pineal gland, nucleus accumbens, and globus pallidus. Within CB(1)-CB(2) receptor heteromers expressed in a neuronal cell model, agonist co-activation of CB(1) and CB(2) receptors resulted in a negative cross-talk in Akt phosphorylation and neurite outgrowth. Moreover, one specific characteristic of CB(1)-CB(2) receptor heteromers consists of both the ability of CB(1) receptor antagonists to block the effect of CB(2) receptor agonists and, conversely, the ability of CB(2) receptor antagonists to block the effect of CB(1) receptor agonists, showing a bidirectional cross-antagonism phenomenon. Taken together, these data illuminate the mechanism by which CB(2) receptors can negatively modulate CB(1) receptor function.     

Endocannabinoids in the immune system and cancer

The present review focuses on the role of the endogenous cannabinoid system in the modulation of immune response and control of cancer cell proliferation. The involvement of cannabinoid receptors, endogenous ligands and enzymes for their biosynthesis and degradation, as well as of cannabinoid receptor-independent events is discussed. The picture arising from the recent literature appears very complex, indicating that the effects elicited by the stimulation of the endocannabinoid system are strictly dependent on the specific compounds and cell types considered. Both the endocannabinoid anandamide and its congener palmitoylethanolamide, exert a negative action in the onset of a variety of parameters of the immune response. However, 2-arachidonoylglycerol appears to be the true endogenous ligand for peripheral cannabinoid receptors, although its action as an immunomodulatory molecule requires further characterization. Modulation of the endocannabinoid system interferes with cancer cell proliferation either by inhibiting mitogenic autocrine/paracrine loops or by directly inducing apoptosis; however, the proapoptotic effect of anandamide is not shared by other endocannabinoids and suggests the involvement of non-cannabinoid receptors, namely the VR1 class of vanilloid receptors. In conclusion, further investigations are needed to elucidate the function of endocannabinoids as immunosuppressant and antiproliferative/cytotoxic agents. The experimental evidence reviewed in this article argues in favor of the therapeutic potential of these compounds in immune disorders and cancer.     

Temporal Changes of CB1 Cannabinoid Receptor in the Basal Ganglia as a Possible Structure-Specific Plasticity Process in 6-OHDA Lesioned Rats

The endocannabinoid system has been implicated in several neurobiological processes, including neurodegeneration, neuroprotection and neuronal plasticity. The CB1 cannabinoid receptors are abundantly expressed in the basal ganglia, the circuitry that is mostly affected in Parkinson’s Disease (PD). Some studies show variation of CB1 expression in basal ganglia in different animal models of PD, however the results are quite controversial, due to the differences in the procedures employed to induce the parkinsonism and the periods analyzed after the lesion. The present study evaluated the CB1 expression in four basal ganglia structures, namely striatum, external globus pallidus (EGP), internal globus pallidus (IGP) and substantia nigra pars reticulata (SNpr) of rats 1, 5, 10, 20, and 60 days after unilateral intrastriatal 6-hydroxydopamine injections, that causes retrograde dopaminergic degeneration. We also investigated tyrosine hydroxylase (TH), parvalbumin, calbindin and glutamic acid decarboxylase (GAD) expression to verify the status of dopaminergic and GABAergic systems. We observed a structure-specific modulation of CB1 expression at different periods after lesions. In general, there were no changes in the striatum, decreased CB1 in IGP and SNpr and increased CB1 in EGP, but this increase was not sustained over time. No changes in GAD and parvalbumin expression were observed in basal ganglia, whereas TH levels were decreased and the calbindin increased in striatum in short periods after lesion. We believe that the structure-specific variation of CB1 in basal ganglia in the 6-hydroxydopamine PD model could be related to a compensatory process involving the GABAergic transmission, which is impaired due to the lack of dopamine. Our data, therefore, suggest that the changes of CB1 and calbindin expression may represent a plasticity process in this PD model.     

Enhancement of endocannabinoid signaling by fatty acid amide hydrolase inhibition: A neuroprotective therapeutic modality

AimsThis review posits that fatty acid amide hydrolase (FAAH) inhibition has therapeutic potential against neuropathological states including traumatic brain injury; Alzheimer's, Huntington's, and Parkinson's diseases; and stroke.Main methodsThis proposition is supported by data from numerous in vitro and in vivo experiments establishing metabolic and pharmacological contexts for the neuroprotective role of the endogenous cannabinoid (“endocannabinoid”) system and selective FAAH inhibitors.Key findingsThe systems biology of endocannabinoid signaling involves two main cannabinoid receptors, the principal endocannabinoid lipid mediators N-arachidonoylethanolamine (“anandamide”) (AEA) and 2-arachidonoyl glycerol (2-AG), related metabolites, and the proteins involved in endocannabinoid biosynthesis, biotransformation, and transit. The endocannabinoid system is capable of activating distinct signaling pathways on-demand in response to pathogenic events or stimuli, thereby enhancing cell survival and promoting tissue repair. Accumulating data suggest that endocannabinoid system modulation at discrete targets is a promising pharmacotherapeutic strategy for treating various medical conditions. In particular, neuronal injury activates cannabinoid signaling in the central nervous system as an intrinsic neuroprotective response. Indirect potentiation of this salutary response through pharmacological inhibition of FAAH, an endocannabinoid-deactivating enzyme, and consequent activation of signaling pathways downstream from cannabinoid receptors have been shown to promote neuronal maintenance and function.SignificanceThis therapeutic modality has the potential to offer site- and event-specific neuroprotection under conditions where endocannabinoids are being produced as part of a physiological protective mechanism. In contrast, direct application of cannabinoid receptor agonists to the central nervous system may activate CB receptors indiscriminately and invite unwanted psychotrophic effects.