Fatty acid amide hydrolase is located preferentially in large neurons in the rat central nervous system as revealed by immunohistochemistry

Fatty acid amide hydrolase localization in the human central nervous system: an immunohistochemical study

Recent discoveries have opened new fields for research on the biochemistry and pharmacology of cannabinoids. Among them, and most importantly, are the characterization and molecular cloning of central and peripheral cannabinoid receptors as well as the isolation of the first putative endogenous ligands that bind to them, anandamide and 2-arachidonylglycerol. The enzyme that degrades these so-called "endocannabinoids" is an integral membrane protein, fatty acid amide hydrolase. Its distribution and biochemistry in rat brain suggest that it plays a critical role in the regulation of the endocannabinoid system. However, few data exist regarding its distribution and mechanism of action in human tissues. To that end, we have studied its cellular distribution in the human central nervous system by immunohistochemistry. Using an affinity-purified antibody, we report that fatty acid amide hydrolase is localized to specific and well-delimited cell populations, including cortical pyramidal neurons, subcortical white matter astrocytes, striatal and striatoefferent projecting neurons, hypothalamic and midbrain nuclei, granular and molecular layers of the cerebellum, Purkinje neurons, dentate cerebellar nucleus, inferior olivary nuclei and others. This distribution resembles that of the central cannabinoid receptors as well as that of the enzyme distribution in the rat brain. In summary, the cellular localization of the degradative enzyme of the endogenous cannabinoid ligands in human central nervous system reveals its presence on both neuronal and glial elements and shows a significant overlapping with that of central cannabinoid receptors, mainly in areas related with motor control, confirming the notion that the endocannabinoid system plays a critical role in the control of movement.

Localization of the CB1 type cannabinoid receptor in the rat basolateral amygdala: high concentrations in a subpopulation of cholecystokinin-containing interneurons

The neuronal localization of the CB1 cannabinoid receptor in the rat basolateral amygdala was studied using peroxidase and fluorescence immunohistochemical techniques. All nuclei of the basolateral amygdala contained a large number of lightly stained pyramidal neurons and a small number of more intensely stained non-pyramidal neurons. Most of the latter cells had medium-sized to large multipolar somata and three to four aspiny dendrites, but some exhibited smaller oval somata. The axon initial segments of some of these non-pyramidal neurons exhibited large swollen varicosities in colchicine-injected animals, suggesting that much of the CB1 receptor protein is transported down the axons of these cells. Double-labeling studies using immunofluorescence histochemistry combined with confocal laser scanning microscopy revealed that the great majority of non-pyramidal neurons with CB1 receptor immunoreactivity belonged to a cholecystokinin-containing subpopulation. Whereas none of the other subpopulations of non-pyramidal neurons (exhibiting immunoreactivity for calretinin, parvalbumin, or somatostatin) expressed high levels of CB1 receptor immunoreactivity, a small percentage of these cells exhibited low levels of immunoreactivity. The results indicate that cannabinoids may modulate the activity of pyramidal projection neurons as well as a subpopulation of cholecystokinin-containing non-pyramidal neurons in the basolateral amygdala. Previous studies indicate that most of the latter are inhibitory interneurons that utilize GABA as a neurotransmitter. The intense staining of the cholecystokinin-containing interneurons and the evidence that large amounts of CB1 receptor protein are transported down the axons of these cells suggests that, as in the hippocampus, cannabinoids may inhibit the release of GABA from the axon terminals of these neurons.

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.

Endocannabinoids and basal ganglia functionality

In recent years, our knowledge on the cannabinoid pharmacology has shown a significant rise in terms of both quantity (more compounds and more targets) and quality (more selective compounds). This allows to consider cannabinoids and related compounds as a promising new line of research for therapeutic treatment of a variety of conditions, such as brain injury, chronic pain, glaucoma, asthma, cancer and AIDS-associated effects and other pathologies. Motor disorders are another promising field for the therapeutic application of cannabinoid-related compounds, since the control of movement is one of the more relevant physiological roles of the endocannabinoid transmission in the brain. There are two pathologies, Parkinson's disease and Huntington's chorea, which are particularly interesting from a clinical point of view due to the direct relationship of endocannabinoids and their receptors with neurons that degenerate in those disorders. However, other neurological pathologies, such as Alzheimer's disease or multiple sclerosis, which are not motor disorders in origin, but present a strong alteration in the control of movement, have also been a subject of interesting research for a cannabinoid therapy. This review will summarize our current knowledge on the role of these endogenous substances in the control of movement and, in particular, on the possible therapeutic usefulness of these compounds in the treatment of motor pathologies.

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".

The fatty acid amide hydrolase (FAAH)

The fatty acid amide hydrolase (FAAH), is the enzyme responsible for the hydrolysis of anandamide, an endocannabinoid. The FAAH knockout, the assays for FAAH, the activity of its substrates, its reversibility and its cloning from rat, mouse, human, and pig are covered in this review. The conserved regions of FAAH are described in terms of sequence and function, including the domains that contains the serine catalytic nucleophile, the hydrophobic domain important for self-association, the proline rich domain region which may be important for subcellular localization and the fatty acid chain binding domain. The FAAH mouse promoter region was characterized in terms of its transcription start site and its activity in different cell types. The distribution of FAAH in the major organs in the body is described as well as regional distribution in the brain and its correlation with cannabinoid receptors. Since FAAH is recognized as a drug target, a large number of inhibitors have been synthesized and tested since 1994 and these are reviewed in terms of reversibility, potency, and specificity for FAAH.

Differing effects of the cannabinoid agonist, CP 55,940, in an alcohol or Tween 80 solvent, on prepulse inhibition of the acoustic startle reflex in the rat

It has been suggested that cannabinoid agonists increase dopamine (DA) transmission in the mesolimbic dopamine system. However, evidence for such an effect is inconsistent. Prepulse inhibition (PPI) of the acoustic startle reflex is a behavioural paradigm that is modulated by an increase of mesolimbic dopamine. This study sought to ascertain whether or not a cannabinoid agonist, CP 55,940, mimicked the effects of amphetamine (a drug which increases dopamine release) on PPI. The first experiment measured the PPI of 16 male Wistar rats injected (i.p.) with different doses of CP 55,940 in a Latin-square design. A second experiment replicated the effects of the first experiment in a between-subjects design, and also examined the effects of using a 5% alcohol solution as a solvent for cannabinoid agonists, in comparison to the more inert detergent, Tween 80. In both experiments, CP 55,940 in Tween 80 significantly reduced basal activity, increased startle onset latencies and increased PPI, effects opposite to those of amphetamine. These results suggest that the net behavioural effects of cannabinoids are opposite to those of amphetamine. In addition, it was found that 1 ml/kg of a 5% alcohol solution has significant behavioural effects on its own, and reverses the effects of CP 55,940 on PPI.

Relationships between CB1 cannabinoid receptors and pituitary endocrine cells in Xenopus laevis: an immunohistochemical study

The distribution of the cannabinoid CB1 receptor and its relationships with individual endocrine cell types were investigated by immunohistochemistry in the anterior lobe of the Xenopus adenohypophysis. By use of a specific primary antibody raised in rabbit against the amino terminus of the rat CB1, we have found numerous CB1-like-immunoreactive cells distributed throughout all of the pituitary anterior lobe with the exception of the ventrocranial area adjacent to the median eminence of the neurohypophysis. Aided by both double-immunostaining on consecutive serial sections and double-simultaneous immunofluorescence on the same section of the gland, the CB1-like immunoreactivity was compared to some specific hormone immunoreactive cells. CB1 labelings were mainly codistributed, and even colocalized, with lactotrophs and thyrotrophs. Gonadotrophs containing CB1 receptors were also observed. In contrast, corticotrophs, which are located mainly in the ventrocranial pole of the anterior lobe, were generally devoid of CB1. Since nerve terminals immunoreactive to the CB1 antibody were observed within the vascular zone of the median eminence, the possibility that endocannabinoids are involved in the control of some secretory activities of Xenopus pituitary, either indirectly via hypothalamic neurosecretory mechanisms or directly on the pituitary cells, was envisaged. In particular, the present study suggests the occurrence of a direct cannabinergic modulation of the prolactin, gonadotrophin, and thyrotrophin secretions through the CB1 receptor.

Characterization of the 5'-sequence of the mouse fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH) is critical for degradation of several important fatty acid amides including anandamide, an endocannabinoid, as well as oleamide, a sleep-inducing factor. These compounds play roles in diverse physiological processes ranging from memory and learning to the regulation of blood pressure. The mechanisms that regulate FAAH expression have not been characterized. A 5'-region of the mouse FAAH with promoter activity was isolated from 1.8 kbp of genomic sequence. Characterization of +1 of transcription of FAAH by RNA ligase mediated-rapid amplification of cDNA ends showed that FAAH mRNA is transcribed from multiple transcription start sites lacking a TATA-box element. Functional analysis of the FAAH upstream sequence fused to a luciferase reporter gene revealed a FAAH-promoter construct with tissue specific activity. A 674-bp FAAH-promoter construct was active in N18TG2 (N18) neuroblastoma cells and C6 glioma cells, lines that have endogenous FAAH activity. The same 674-bp FAAH-promoter construct was not active in C2C12 or L6 myogenic cells, two lines that do not have FAAH activity.

Cannabinoids inhibit emesis through CB1 receptors in the brainstem of the ferret

BACKGROUND & AIMS

Marijuana and other cannabinoids are effective anti-emetics. Despite ongoing controversy over their usage, the receptor distribution and the site of the anti-emetic action of these compounds are not known. Our aim was to investigate whether the cannabinoid 1 receptor (CB1r) and endocannabinoids play a role in the anti-emetic action of cannabinoids.

METHODS

Ferrets were given an emetic stimulus and the number of episodes of retching and vomiting were observed after administration of CB1r agonists and a CB1r antagonist. CB1r and fatty acid amide hydrolase (FAAH), which degrades endocannabinoids, were localized by immunohistochemistry.

RESULTS

CB1r and FAAH were localized in the dorsal vagal complex, consisting of the area postrema, nucleus of the solitary tract, and the dorsal motor nucleus of the vagus in the brainstem. CB1r was found in the myenteric plexus of the stomach and duodenum. Activation of CB1r by the agonists (delta)(9)-tetrahydrocannabinol, WIN 55,212-2, and methanandamide inhibited emesis and their action was reversed by a selective CB1r antagonist, which alone had no effect, but potentiated vomiting in response to an emetic stimulus.

CONCLUSIONS

CB1r mediates the anti-emetic action of cannabinoids in the dorsal vagal complex. Endocannabinoids are a novel neuroregulatory system involved in the control of emesis.

Fatty acid amide hydrolase: biochemistry, pharmacology, and therapeutic possibilities for an enzyme hydrolyzing anandamide, 2-arachidonoylglycerol, palmitoylethanolamide, and oleamide

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of a number of important endogenous fatty acid amides, including the endogenous cannabimimetic agent anandamide (AEA), the sleep-inducing compound oleamide, and the putative anti-inflammatory agent palmitoylethanolamide (PEA). In recent years, there have been great advances in our understanding of the biochemical and pharmacological properties of the enzyme. In this commentary, the structure and biochemical properties of FAAH and the development of potent and selective FAAH inhibitors are reviewed, together with a brief discussion on the therapeutic possibilities for such compounds in the treatment of inflammatory pain and ischaemic states.

Supersensitivity to anandamide and enhanced endogenous cannabinoid signaling in mice lacking fatty acid amide hydrolase

The medicinal properties of marijuana have been recognized for centuries, but clinical and societal acceptance of this drug of abuse as a potential therapeutic agent remains fiercely debated. An attractive alternative to marijuana-based therapeutics would be to target the molecular pathways that mediate the effects of this drug. To date, these neural signaling pathways have been shown to comprise a cannabinoid receptor (CB(1)) that binds the active constituent of marijuana, tetrahydrocannabinol (THC), and a postulated endogenous CB(1) ligand anandamide. Although anandamide binds and activates the CB(1) receptor in vitro, this compound induces only weak and transient cannabinoid behavioral effects in vivo, possibly a result of its rapid catabolism. Here we show that mice lacking the enzyme fatty acid amide hydrolase (FAAH(-/-)) are severely impaired in their ability to degrade anandamide and when treated with this compound, exhibit an array of intense CB(1)-dependent behavioral responses, including hypomotility, analgesia, catalepsy, and hypothermia. FAAH(-/-)-mice possess 15-fold augmented endogenous brain levels of anandamide and display reduced pain sensation that is reversed by the CB(1) antagonist SR141716A. Collectively, these results indicate that FAAH is a key regulator of anandamide signaling in vivo, setting an endogenous cannabinoid tone that modulates pain perception. FAAH may therefore represent an attractive pharmaceutical target for the treatment of pain and neuropsychiatric disorders.

Proteins regulating the biosynthesis and inactivation of neuromodulatory fatty acid amides

Fatty acid amides (FAAs) represent a growing family of biologically active lipids implicated in a diverse range of cellular and physiological processes. At present, two general types of fatty acid amides, the N-acylethanolamines (NAEs) and the fatty acid primary amides (FAPAs), have been identified as potential physiological neuromodulators/neurotransmitters in mammals. Representative members of these two subfamilies include the endocannabinoid NAE anandamide and the sleep-inducing FAPA oleamide. In this Chapter, molecular mechanisms proposed for the biosynthesis and inactivation of FAAs are critically evaluated, with an emphasis placed on the biochemical and cell biological properties of proteins thought to mediate these processes.

Evidence for an endocannabinoid system in the central nervous system of the leech Hirudo medicinalis

In invertebrates, like Hydra and sea urchins, evidence for a functional cannabinoid system was described. The partial characterization of a putative CB1 cannabinoid receptor in the leech Hirudo medicinalis led us to investigate the presence of a complete endogenous cannabinoid system in this organism. By using gas chromatography-mass spectrometry, we demonstrate the presence of the endocannabinoids anandamide (N-arachidonoylethanolamine, 21.5+/-0.7 pmol/g) and 2-arachidonoyl-glycerol (147.4+/-42.7 pmol/g), and of the biosynthetic precursor of anandamide, N-arachidonylphosphatidyl-ethanolamine (16.5+/-3.3 pmol/g), in the leech central nervous system (CNS). Anandamide-related molecules such as N-palmitoylethanolamine (32.4+/-1.6 pmol/g) and N-linolenoylethanolamine (5.8 pmol/g) were also detected. We also found an anandamide amidase activity in the leech CNS cytosolic fraction with a maximal activity at pH 7 and little sensitivity to typical fatty acid amide hydrolase (FAAH) inhibitors. Using an antiserum directed against the amidase signature sequence, we focused on the identification and the localization of the leech amidase. Firstly, leech nervous system protein extract was subjected to Western blot analysis, which showed three immunoreactive bands at ca. approximately 42, approximately 46 and approximately 66 kDa. The former and latter bands were very faint and were also detected in whole homogenates from the coelenterate Hydra vulgaris, where the presence of CB1-like receptors, endocannabinoids and a FAAH-like activity was reported previously. Secondly, amidase immunocytochemical detection revealed numerous immunoreactive neurons in the CNS of three species of leeches. In addition, we observed that leech amidase-like immunoreactivity matches to a certain extent with CB1-like immunoreactivity. Finally, we also found that stimulation by anandamide of this receptor leads, as in mammals, to inhibition of cAMP formation, although this effect appeared to be occurring through the previously described anandamide-induced and CB1-mediated activation of nitric oxide release. Taken together, these results suggest the existence of a complete and functional cannabinoid system in leeches.

Levels, metabolism, and pharmacological activity of anandamide in CB(1) cannabinoid receptor knockout mice: evidence for non-CB(1), non-CB(2) receptor-mediated actions of anandamide in mouse brain

Anandamide [arachidonylethanolamide (AEA)] appears to be an endogenous agonist of brain cannabinoid receptors (CB(1)), yet some of the neurobehavioral effects of this compound in mice are unaffected by a selective CB(1) antagonist. We studied the levels, pharmacological actions, and degradation of AEA in transgenic mice lacking the CB(1) gene. We quantified AEA and the other endocannabinoid, 2-arachidonoyl glycerol, in six brain regions and the spinal cord by isotope-dilution liquid chromatography-mass spectrometry. The distribution of endocannabinoids and their inactivating enzyme, fatty acid amide hydrolase, were found to overlap with CB(1) distribution only in part. In CB(1) knockout homozygotes (CB(1)-/-), the hippocampus and, to a lesser extent, the striatum exhibited lower AEA levels as compared with wild-type (CB(1)+/+) controls. These data suggest a ligand/receptor relationship between AEA and CB(1) in these two brain regions, where tonic activation of the receptor may tightly regulate the biosynthesis of its endogenous ligand. 2-Arachidonoyl glycerol levels and fatty acid amide hydrolase activity were unchanged in CB(1)-/- with respect to CB(1)+/+ mice in all regions. AEA and Delta(9)-tetrahydrocannabinol (THC) were tested in CB(1)-/- mice for their capability of inducing analgesia and catalepsy and decreasing spontaneous activity. The effects of AEA, unlike THC, were not decreased in CB(1)-/- mice. AEA, but not THC, stimulated GTPgammaS binding in brain membranes from CB(1)-/- mice, and this stimulation was insensitive to CB(1) and CB(2) antagonists. We suggest that non-CB(1), non-CB(2) G protein-coupled receptors might mediate in mice some of the neuro-behavioral actions of AEA.

The movement of N-arachidonoylethanolamine (anandamide) across cellular membranes

This review presents and explores the hypothesis that N-arachidonoylethanolamine (AEA, also called anandamide) is transported across cellular membranes by a process that is protein-mediated. Support for this hypothesis comes from experiments demonstrating that cellular accumulation of extracellularly applied AEA is saturable, time and temperature dependent and exhibits selective inhibition by various structural analogs of AEA. The accumulation of AEA is cell specific; data is presented demonstrating that several cell types, including the bovine adrenal zona glomerulosa cell, exhibit very high capacity for AEA accumulation while others, such as the HeLa cell, have a very low capacity. The transport process has the characteristics of facilitated diffusion; it is bi-directional, not dependent on either ATP or extracellular sodium and exhibits the trans effect of flux coupling. Several important questions remain to be answered regarding the carrier, including its molecular structure and its role in the release and inactivation of endogenously produced AEA.

The fatty acid amide hydrolase (FAAH)

The topic of this review is fatty acid amide hydrolase (FAAH), one of the best-characterized enzymes involved in the hydrolysis of bioactive lipids such as anandamide, 2-arachidonoylglycerol (2-AG), and oleamide. Herein, we discuss the nomenclature, the various assays that have been developed, the relative activity of the various substrates and the reversibility of the enzyme reactions catalyzed by FAAH. We also describe the cloning of the enzyme from rat and subsequent cDNA isolation from mouse, human, and pig. The proteins and the mRNAs from different species are compared. Cloning the enzyme permitted the purification and characterization of recombinant FAAH. The conserved regions of FAAH are described in terms of sequence and function, including the amidase domain which contains the serine catalytic nucleophile, the hydrophobic domain important for self association, and the proline rich domain region, which may be important for subcellular localization. The distribution of FAAH in the major organs of the body is described as well as regional distribution in the brain and its correlation with cannabinoid receptors. Since FAAH is recognized as a drug target, a large number of inhibitors have been synthesized and tested since 1994 and these are reviewed in terms of reversibility, potency, and specificity for FAAH and cannabinoid receptors.

Differences in the pharmacological properties of rat and chicken brain fatty acid amidohydrolase

The pharmacological properties of fatty acid amidohydrolase (FAAH) were investigated in brains of 35-day-old chickens, since nothing is known about the enzyme in avian species. FAAH activity towards both [(3)H]-palmitoylethanolamide (PEA) [K(M)=1.5 microM] and [(3)H]-anandamide (AEA) [K(M)=5.4 microM] was demonstrated in the chicken brains. The chicken FAAH was inhibited by the substrate analogues oleyl trifluoromethylketone (OTMK) and diazomethylarachidonyl ketone (DAK) with similar potencies to the rat FAAH. However, in contrast to the rat brain, phenylmethylsulphonyl fluoride (PMSF) and the enantiomers of ibuprofen had very weak effects on chicken brain FAAH. Indomethacin and niflumic acid were found to inhibit rat brain AEA hydrolysis. The inhibition by indomethacin was reversible and competitive, with a K(i) value of 120 microM. Chicken FAAH was less sensitive to indomethacin than its rodent counterpart, but the inhibition was also competitive (K(i)). It is concluded that chicken FAAH activity has different pharmacological properties to its rodent counterpart.

Biochemistry and pharmacology of the endocannabinoids arachidonylethanolamide and 2-arachidonylglycerol

The purpose of this review is to discuss the cellular synthesis and inactivation of two putative endogenous ligands of the cannabinoid receptor, N-arachidonylethanolamine (AEA) and 2-arachidonylglycerol (2-AG). Both ligands are synthesized by neurons and brain tissue in response to increased intracellular calcium concentrations. Both ligands are substrates for fatty acid amide hydrolase (FAAH). Both AEA and 2-AG bind to the neuronal form of the cannabinoid receptor (CB1). AEA binds the receptor with moderate affinity and has the characteristics of a partial agonist, whereas, 2-AG binds with low affinity but exhibits full efficacy. Two possible physiological roles of the endocannabinoids and the CB1 receptor are discussed: the regulation of gestation and the regulation of gastrointestinal motility.

Anandamide amidohydrolase (fatty acid amide hydrolase)

Anandamide (N-arachidonoylethanolamine) loses its cannabimimetic activity when it is hydrolyzed to arachidonic acid and ethanolamine by the catalysis of an enzyme referred to as anandamide amidohydrolase or fatty acid amide hydrolase. Cravatt's group and our group cloned cDNA of the enzyme from rat, human, mouse and pig, and the primary structures revealed that the enzymes belong to an amidase family characterized by the amidase signature sequence. The recombinant enzyme acted not only as an amidase for anandamide and oleamide, but also as an esterase for 2-arachidonoylglycerol. The reversibility of the enzymatic anandamide hydrolysis and synthesis was also confirmed with a purified recombinant enzyme. Several fatty acid derivatives like methyl arachidonyl fluorophosphonate potently inhibited the enzyme. The enzyme was distributed widely in mammalian organs such as liver, small intestine and brain. However, the anandamide hydrolyzing enzyme found in human megakaryoblastic cells was catalytically distinct from the previously known enzyme.

Fatty acid amide hydrolase expression in rat choroid plexus: possible role in regulation of the sleep-inducing action of oleamide

The enzyme fatty acid amide hydrolase (FAAH) catalyses hydrolysis of oleamide, a sleep-inducing lipid whose concentration in the cerebrospinal fluid (CSF) is elevated in sleep-deprived mammals. Previous studies have reported expression of FAAH by distinct populations of neurons in the rat brain. Here we demonstrate using immunocytochemical methods that FAAH is also expressed by non-neuronal epithelial cells of the rat choroid plexus. The choroid plexus is formed by invaginations of the pia mater into the ventricle cavities of the brain and an important function of the choroidal epithelium is to regulate production and composition of CSF. Therefore, the role of FAAH in epithelial cells of the choroid plexus may be to control the concentration of oleamide in the CSF and as such FAAH may exert an important regulatory role in shaping the duration and magnitude of the sleep-inducing effect of endogenously or exogenously derived oleamide.

Activational role of cannabinoids on movement

Cannabinoid's major effect on movement is hypoactivity. Nevertheless, a biphasic excitatory/inhibitory effect of cannabinoids on movement has been repeatedly acknowledged. However, the literature is lacking a detailed description of such an effect. In this study, we performed a dose-response study of the effects of Delta(9)-tetrahydrocannabinol on movement. Immediately after the administration of vehicle or a dose of Delta(9)-tetrahydrocannabinol (0.2, 0.5, 1, 1.5, 2, 2.5, 3, 4, or 5 mg/kg), the animal was placed in an activity monitor and observed for 1 h. Several parameters were recorded. The horizontal and vertical activities were measured as the number of photobeams broken between the photocells on the walls of an activity monitor. The number of wet dog shakes, scratches with hindpaw, mouth movements, forepaw flutters were also recorded, as was the amount of time in minutes that each subject spent grooming. The number of fecal boluses was recorded as an index of autonomic activity. Each animal was subsequently tested for catalepsy in the bar test. A triphasic effect was observed: low doses of the cannabinoid receptor agonist Delta(9)-tetrahydrocannabinol (0.2 mg/kg) decreased locomotor activity while higher doses (1-2 mg/kg) dose-dependently stimulated movement until catalepsy emerged (2.5 mg/kg) accompanied by decreases in activity.

Pharmacological properties of rat brain fatty acid amidohydrolase in different subcellular fractions using palmitoylethanolamide as substrate

In the present study, the pharmacological properties of fatty acid amide hydrolase (FAAH) in subcellular fractions of rat brain were investigated using palmitoylethanolamide (PEA) and arachidonyl ethanolamide (anandamide, AEA) as substrates. FAAH hydrolysed [(3)H]PEA in crude homogenates with median K(m) and V(max) values of 2.9 microM and 2.14 nmol.(mg protein)(-1).min(-1), respectively. [(3)H]PEA hydrolysis was inhibited both by non-radioactive AEA (with a K(i) value very similar to the K(m) value for [(3)H]AEA as substrate using the same assay) and by R(-)ibuprofen (mixed-type inhibition K(i) and K'(i) values 88 and 720 microM, respectively). FAAH activity towards both [(3)H]PEA and [(3) myelin = cytosol, but there were no differences between the relative activities towards the two substrates in any of the fractions. [(3)H]PEA hydrolysis in mitochondrial, myelin, microsomal, and synaptosomal fractions was inhibited by oleyl trifluoromethylketone, phenylmethylsulphonyl fluoride, and the R(-)- and S(+)-enantiomers of the nonsteroidal anti-inflammatory drug ibuprofen, with mean IC(50) values in the ranges 0.028-0.041, 0.37-0.52, 67-110, and 130-260 microM, respectively. It is concluded that the pharmacological properties of FAAH in the different subcellular fractions are very similar.

Role of the superior colliculus in the motor effects of cannabinoids and dopamine

We studied the cellular distribution of CB1 cannabinoid receptors in the superior colliculus of the rat using an antibody raised against the N-terminal of the receptor. The effect of unilateral cannabinoid receptor stimulation in the intermediate layers of the superior colliculus on rotational behavior in rats was also explored. The antibody against CB1 receptors outlined the crossed descending system of the superior colliculus (predorsal bundle output system) as well as the collicular commisure. The potent cannabinoid agonist CP55,940 (5 microgram/0.25 microliter) induced strong contralateral turning when microinjected unilaterally into the lateral intermediate layers of the superior colliculus. The levels of turning obtained with the intracollicular administration of the cannabinoid were comparable to the highest levels obtained with dopamine agonists in the basal ganglia. The D(2) dopamine agonist quinpirole or the D(1) dopamine agonist SKF82958 reversed this contralateral rotation but failed to affect motor behavior on their own. A new motor pathway for cannabinoids is discussed.

Immunocytochemical localization of cannabinoid CB1 receptor and fatty acid amide hydrolase in rat retina

Cannabinoids have major effects on central nervous system function. Recent studies indicate that cannabinoid effects on the visual system have a retinal component. Immunocytochemical methods were used to localize cannabinoid CB1 receptor immunoreactivity (CB1R-IR) and an endocannabinoid (anandamide and 2-arachidonylglycerol) degradative enzyme, fatty acid amide hydrolase (FAAH)-IR, in the rat retina. Double labeling with neuron-specific markers permitted identification of cells that were labeled with CB1R-IR and FAAH-IR. CB1R-IR was observed in all cells that were protein kinase C-immunoreactive (rod bipolar cells and a subtype of GABA-amacrine cell) as well as horizontal cells (identified by calbindin-IR). There was also punctate CB1R-IR in the distal one-third of the inner plexiform layer (IPL) that could not be assigned to a cell type. FAAH-IR was most prominent in large ganglion cells, whose dendrites projected to a narrow band in the proximal IPL. Weaker FAAH-IR was observed in the soma of horizontal cells (identified by calbindin-IR); the soma of large, but not small, dopamine amacrine cells (identified by tyrosine hydroxylase-IR); and dendrites of orthotopic- and displaced-starburst amacrine cells (identified by choline acetyltransferase-IR) but in less than 50% of the starburst amacrine cell somata. The extensive distribution of CB1R-IR on horizontal cells and rod bipolar cells indicates a role of endocannabinoids in scotopic vision, whereas the more widespread distribution of FAAH-IR indicates a complex control of endocannabinoid release and degradation in the retina.

Anandamide amidohydrolase of porcine brain: cDNA cloning, functional expression and site-directed mutagenesis(1)

Anandamide (arachidonoylethanolamide) is an endogenous ligand for cannabinoid receptors, and its cannabimimetic activities are lost when the compound is hydrolyzed to arachidonic acid and ethanolamine by an enzyme referred to as anandamide amidohydrolase. We cloned a cDNA for the enzyme of porcine brain, and the cDNA encoded a protein of 579 amino acids with a molecular mass of 62.9 kDa. The amino acid sequence was 81, 80 and 85% identical with the enzymes previously cloned from the liver of rat, mouse, and human, respectively. When the enzyme protein was overexpressed in COS-7 cells, the particulate fraction of the cells showed an anandamide hydrolyzing activity and also catalyzed the reverse reaction synthesizing anandamide from arachidonic acid and ethanolamine both with a specific activity of 0. 2-0.3 micromol/min/mg protein at 37 degrees C. The brain enzyme exhibited a wide substrate specificity hydrolyzing oleamide, 2-arachidonoylglycerol, and methyl arachidonate. The point mutation of Ser-217, Asp-237, Ser-241, or Cys-249 completely abolished the hydrolyses of all the above-mentioned substrates as well as the synthesis of anandamide in the reverse reaction.

Pain modulation by release of the endogenous cannabinoid anandamide

Synthetic cannabinoids produce behavioral analgesia and suppress pain neurotransmission, raising the possibility that endogenous cannabinoids serve naturally to modulate pain. Here, the development of a sensitive method for measuring cannabinoids by atmospheric pressure-chemical ionization mass spectrometry permitted measurement of the release of the endogenous cannabinoid anandamide in the periaqueductal gray (PAG) by in vivo microdialysis in the rat. Electrical stimulation of the dorsal and lateral PAG produced CB1 cannabinoid receptor-mediated analgesia accompanied by a marked increase in the release of anandamide in the PAG, suggesting that endogenous anandamide mediates the behavioral analgesia. Furthermore, pain triggered by subcutaneous injections of the chemical irritant formalin substantially increased the release of anandamide in the PAG. These findings indicate that the endogenous cannabinoid anandamide plays an important role in a cannabinergic pain-suppression system existing within the dorsal and lateral PAG. The existence of a cannabinergic pain-modulatory system may have relevance for the treatment of pain, particularly in instances where opiates are ineffective.

Cannabinoid CB1 receptors are localized primarily on cholecystokinin-containing GABAergic interneurons in the rat hippocampal formation

Localization of cannabinoid CB 1 receptors on GABAergic interneurons in the rat hippocampal formation was studied by double-labeling immunohistochemistry with confocal microscopy. Virtually all CB1-immunoreactive neurons (95%) are GABAergic. CB 1 fluorescence showed a punctate pattern. In contrast, the GABA fluorescence was distributed homogeneously, suggesting that while CB 1 receptors and GABA exist in the same cells they are not localized in the same subcellular compartments. Although virtually all CB1 neurons were GABAergic, many GABAergic neurons did not contain CB1 receptors. GABAergic interneurons in the hippocampal formation can be further divided into subpopulations with distinct connections and functions, using cell markers such as neuropeptides and calcium binding proteins. CB1 receptors were highly co-localized with cholecystokinin and partially co-localized with calretinin and calbindin, but not with parvalbumin. This suggests that cannabinoids may modulate GABAergic neurotransmission at the synapses on the soma and at synapses on the proximal dendrites of the principal neurons, as well as at synapses on other GABAergic interneurons.

Biosynthesis and inactivation of endocannabinoids: relevance to their proposed role as neuromodulators

The two putative endogenous ligands of cannabinoid receptors, anandamide and 2-arachidonoylglycerol, are synthesized by and released from neurons in a Ca2+-dependent fashion, and re-uptaken and catabolized by both neurons and astrocytes. These biochemical features of the endocannabinoids, as well as some of their pharmacological effects in both central and peripheral nervous systems, suggest a role as neuromodulators for these metabolites. This neuromodulatory role is supported by the brain regional distribution of anandamide, its biosynthetic precursor and its major inactivating enzyme, and by the existence of possible regulatory mechanisms for the biosynthesis and inactivation of endocannabinoids, which are reviewed in this article.