For example acetylcholine, which primarily reaches its receptors by volume transmission can evoke endocannabinoid signaling in several brain regions through M1 receptors, which are distributed throughout the somatodendritic surface of postsynaptic neurons (Kim et al., 2002; Uchigashima et al., 2007; Yamasaki et al., 2010). system in animals. Cannabis plants produce a unique mixture of chemical constituents, the most famous products being the C21 terpenophenolic compounds, which are collectively called (9-THC) was isolated from confiscated hashish by Yechiel Gaoni and Raphael Mechoulam (Fig. 1A-B) (Gaoni and Mechoulam, 1964), and was shown to account for the psychotropic effects of cannabis preparations in rhesus monkeys (Mechoulam et al., 1970). This seminal discovery transformed cannabinoid research from an anecdote-based practice into an evidence-based modern research field. The use of the chemically defined 9-THC molecule made it possible to obtain qualitatively and quantitatively reproducible pharmacological, physiological or behavioral data, which then helped to uncover the neurobiological substrates of psychoactive effects of cannabis. Open in a separate window Physique 1 A tribute to the discoveries unraveling the endocannabinoid systemA,B) First identification of the chemical structure with its complete configuration of the psychoactive compound in marijuana, 9-THC (Gaoni and Mechoulam 1967). C) First demonstration by competitive inhibition of the presence of a high affinity, stereoselective, pharmacologically unique cannabinoid receptor in brain tissue (Devane et al., 1988). D) The 3D molecular model of the 7-transmembrane CB1 receptor (Shim, 2009). E) Localization of CB1 by high affinity receptor binding and autoradiography in the rat (Herkenham et al 1990), and F) by PET in human brain (Burns up et al 2007). G) Mass spectra of anandamide (Devane 1992) and H-J) 2-AG, together with the chemical structures of the two major endocannabinoids (Mechoulam et al., 1995). The individual figures have been modified from the originals with permission from the authors. The second major breakthrough in cannabinoid research provided answer to the conceptual question of why our brain reacts to cannabis. Using [3H]-CP55,940, a potent radioactively-labeled synthetic cannabinoid, Bill Devane, Allyn Howlett and their colleagues obtained the first unequivocal evidence for the presence of a specific cannabinoid receptor, which inhibits adenylate cyclase via dJ223E5.2 Gi-protein signaling in the brain (Fig. Mupirocin 1C-D) (Devane et al., 1988; Bidaut-Russell et al., 1990). This discovery is also considered as the first direct evidence for existence of the endocannabinoid system. The subsequent qualitative and quantitative radioligand binding studies quickly revealed the distribution of cannabinoid receptors in the brain (Fig 1E) (Herkenham et al., 1990). First, lesion experiments showed that the vast majority of cannabinoid binding sites in the brain are on neurons, and most likely on their axonal bundles (Herkenham et al., 1991). Second, the quantitative distribution pattern fitted well with the brain regions underlying the behavioral effects of cannabis. Third, this pattern was remarkably similar across species indicating a conserved physiological function for cannabinoid receptors. Finally, and most importantly, the density of cannabinoid receptors in the brain was comparable to the levels of glutamate, GABA or striatal dopamine receptors (Herkenham et al., 1990). Thus, these observations collectively predicted in advance that cannabinoid receptors are as ubiquitous components of chemical synapses as conventional neurotransmitter receptors. This period was the golden age for the cloning of G-protein-coupled receptors, thus, the molecular identification of the first cannabinoid receptor has followed very soon (Matsuda et al. 1990). The CB1 cannabinoid receptor indeed turned out to be a class A G-protein-coupled receptor, and has a notably similar sequence (97-99% amino acid sequence identity) across mammalian species, supporting once again a phylogenetically conserved function for CB1. In situ hybridization confirmed neuronal expression and revealed a heterogeneous distribution pattern largely corresponding to the ligand binding sites (Matsuda et al. 1990). With the help of significant homology (44% at the amino acid level), a second cannabinoid receptor was also discovered thereafter (Munro et al., 1993). These two receptors originated from a common ancestor, and it is now fairly safe to conclude that a third, phylogenetically closely related third cannabinoid receptor is unlikely to be found (Pertwee et al., 2010). Compelling evidence shows that CB1 receptors are the major neurobiological substrates for 9-THC effects on the Mupirocin human brain. The acute psychological consequences of marijuana smoking such as the subjective high experience was efficiently blocked by pretreatment with the.The unfolding of the molecular, anatomical, physiological Mupirocin and behavioral features of endocannabinoid signaling in the last decade fully justifies this expectation, because it has led to our appreciation of the fundamental role of retrograde communication in the brain. L.) and the discovery of the endocannabinoid system in animals. Cannabis plants produce a unique mixture of chemical constituents, the most famous products being the C21 terpenophenolic compounds, which are collectively called (9-THC) was isolated from confiscated hashish by Yechiel Gaoni and Raphael Mechoulam (Fig. 1A-B) (Gaoni and Mechoulam, 1964), and was shown to account for the psychotropic effects of cannabis preparations in rhesus monkeys (Mechoulam et al., 1970). This seminal discovery transformed cannabinoid research from an anecdote-based practice into an evidence-based Mupirocin modern research field. The use of the chemically defined 9-THC molecule made it possible to obtain qualitatively and quantitatively reproducible pharmacological, physiological or behavioral data, which then helped to uncover the neurobiological substrates of psychoactive effects of cannabis. Open in a separate window Figure 1 A tribute to the discoveries unraveling the endocannabinoid systemA,B) Mupirocin First identification of the chemical structure with its absolute configuration of the psychoactive compound in marijuana, 9-THC (Gaoni and Mechoulam 1967). C) First demonstration by competitive inhibition of the existence of a high affinity, stereoselective, pharmacologically distinct cannabinoid receptor in brain tissue (Devane et al., 1988). D) The 3D molecular model of the 7-transmembrane CB1 receptor (Shim, 2009). E) Localization of CB1 by high affinity receptor binding and autoradiography in the rat (Herkenham et al 1990), and F) by PET in human brain (Burns et al 2007). G) Mass spectra of anandamide (Devane 1992) and H-J) 2-AG, together with the chemical structures of the two major endocannabinoids (Mechoulam et al., 1995). The individual figures have been modified from the originals with permission from the authors. The second major breakthrough in cannabinoid research provided answer to the conceptual question of why our brain reacts to cannabis. Using [3H]-CP55,940, a potent radioactively-labeled synthetic cannabinoid, Bill Devane, Allyn Howlett and their colleagues obtained the first unequivocal evidence for the presence of a specific cannabinoid receptor, which inhibits adenylate cyclase via Gi-protein signaling in the brain (Fig. 1C-D) (Devane et al., 1988; Bidaut-Russell et al., 1990). This discovery is also considered as the first direct evidence for existence of the endocannabinoid system. The subsequent qualitative and quantitative radioligand binding studies quickly revealed the distribution of cannabinoid receptors in the brain (Fig 1E) (Herkenham et al., 1990). First, lesion experiments showed that the vast majority of cannabinoid binding sites in the brain are on neurons, and most likely on their axonal bundles (Herkenham et al., 1991). Second, the quantitative distribution pattern fitted well with the brain regions underlying the behavioral effects of cannabis. Third, this pattern was remarkably similar across varieties indicating a conserved physiological function for cannabinoid receptors. Finally, and most importantly, the denseness of cannabinoid receptors in the brain was comparable to the levels of glutamate, GABA or striatal dopamine receptors (Herkenham et al., 1990). Therefore, these observations collectively expected in advance that cannabinoid receptors are as ubiquitous components of chemical synapses as standard neurotransmitter receptors. This period was the golden age for the cloning of G-protein-coupled receptors, therefore, the molecular recognition of the 1st cannabinoid receptor offers followed very soon (Matsuda et al. 1990). The CB1 cannabinoid receptor indeed turned out to be a class A G-protein-coupled receptor, and has a notably related sequence (97-99% amino acid sequence identity) across mammalian varieties, supporting once again a phylogenetically conserved function for CB1. In situ hybridization confirmed neuronal manifestation and exposed a heterogeneous distribution pattern largely corresponding to the ligand binding sites (Matsuda et al. 1990). With the help of significant homology (44% in the amino acid level), a second cannabinoid receptor was also found out thereafter (Munro et al., 1993). These two receptors originated from a common ancestor, and it is right now fairly safe to conclude that a third, phylogenetically closely related third cannabinoid receptor is definitely unlikely to be found (Pertwee et al., 2010). Convincing evidence demonstrates CB1 receptors are the major neurobiological substrates for 9-THC effects on the human brain. The acute mental consequences of cannabis smoking such as the subjective high encounter was efficiently clogged by pretreatment with the CB1 antagonist, rimonabant in healthy human subjects (Huestis et al., 2001). Moreover, the development of novel inverse agonist radioligands for positron emission.