Hypolocomotor effects in rats of capsaicin and two long chain capsaicin homologues
Introduction
Anandamide (N-arachidonoyl-ethanolamine) was the first endogenous ligand of cannabinoid receptors to be discovered (Devane et al., 1992). This compound binds with moderate affinity to cannabinoid CB1 and CB2 receptors (Pertwee, 1997), but is a preferential functional agonist only for the CB1 subtype. Anandamide exhibits a pharmacological profile (see Mechoulam et al., 1998, Di Marzo, 1998) similar, but not identical, to that of the psychotropic component of Cannabis sativa, (−)-Δ9-tetrahydro-cannabinol (Gaoni and Mechoulam, 1964). Differences in the pharmacology of anandamide and Δ9-tetrahydrocannabinol may be due to the facile degradation of the former compound in vivo (Willoughby et al., 1997), or also to its interactions with targets other than cannabinoid CB1 or CB2 receptors. Indeed, a selective antagonist of CB1 receptors, (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide.HCl (SR141716A, Rinaldi-Carmona et al., 1994), does not block the typical cannabimimetic neurobehavioral effects of anandamide in mice (Adams et al., 1998), which consist of suppression of spontaneous activity and induction of immobility, analgesia and hypothermia, and are known as the mouse “tetrad” of tests. Furthermore, some of these effects of anandamide are still observed in mutant mice where the CB1 receptor gene has been disrupted (“CB1 knockouts”) (Di Marzo et al., 2000a). Recent experiments Zygmunt et al., 1999, Smart et al., 2000 showed that anandamide is also a full agonist at the capsaicin receptor, a ligand and heat-activated non-selective cation channel named “vanilloid” VR1 receptor (Caterina et al., 1997). By acting in part through vanilloid receptors, anandamide relaxes both the buffer-perfused small artery preparations (Zygmunt et al., 1999) and the electrically contracted mouse vas deferens (Ross et al., 2001), and induces apoptosis of cancer cells (Maccarrone et al., 2000). Although vanilloid VR1 receptors have been identified in several areas of the rodent brain, e.g. the basal ganglia, hypothalamus and brainstem (Mezey et al., 2000), there is still no evidence for their participation either in central nervous system (CNS) functions other than body temperature control (Szallasi and Di Marzo, 2000). The involvement of vanilloid VR1 receptors in the control of spontaneous activity, body temperature and (supra)spinal nociception is supported by the observation that capsaicin exhibits moderate to strong activity in the four tests of the mouse “tetrad”, even though it was not possible to counteract these effects of capsaicin with the vanilloid VR1 receptor antagonist, capsazepine (Di Marzo et al., 2000b). Apart from VR1 receptors, anandamide interacts also with non-CB1, non-CB2 G-protein-coupled receptors in mouse brain (Di Marzo et al., 2000a) which are activated also by the cannabinoid receptor ligand R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl) methanone mesylate (WIN 55212-2) Sagan et al., 1999, Breivogel et al., 2001. Therefore, it is possible that the effects of anandamide in the mouse ‘tetrad’ are partly mediated by VR1 receptors or novel cannabinoid receptors, although these possibilities have not yet been fully investigated.
Arvanil (N-[3-methoxy-4-hydroxy-benzyl]-arachidonamide) is a recently developed anandamide/capsaicin structural “hybrid” (Melck et al., 1999) with an affinity for cannabinoid CB1 receptors comparable to that of anandamide, and an activity at vanilloid VR1 receptors that is stronger than that of capsaicin De Petrocellis et al., 2000, Ross et al., 2001. Arvanil is also a potent inhibitor of anandamide-facilitated transport into cells (Melck et al., 1999). Its actions at these multiple sites, and its higher metabolic stability as compared to anandamide, may explain in part why arvanil is more potent than either anandamide or capsaicin in the mouse ‘tetrad’, even though its effects, like for anandamide, are insensitive to SR141716A (Di Marzo et al., 2000b). Although the time-course of arvanil actions in mice seem to differ from that observed with capsaicin, it is possible that this novel compound acts in the CNS via VR1 receptors. Alternatively, since it induces potent analgesia in the tail-flick test in a manner insensitive to either SR141716A or capsazepine (Di Marzo et al., 2000b), arvanil may also activate non-CB1, non-CB2, and non-VR1 receptors.
Here, we have addressed the question of whether vanilloid VR1 receptors or non-CB1, non-VR1 sites of action are involved in the regulation of motor behavior in rats. We have studied the effect on locomotion of capsaicin, anandamide and of two arvanil analogues having weak activity, if any, at rat CB1 receptors. We report that the activation of either VR1 receptors or putative novel anandamide sites of action leads to suppression of motor behavior in rats, and suggest that vanilloid receptor stimulation may affect motor behavior also through the intermediacy of anandamide.
Section snippets
Compounds
Capsaicin and capsazepine were purchased from Alexis Biochemicals or Sigma-Aldrich, and anandamide for in vivo studies from Tocris. Anandamide, N-linoleoyl-vanillyl-amine (livanil) and N-α-linolenoyl-vanillyl-amine (linvanil) (Fig. 1) were synthesized from the condensation of the corresponding fatty acids and amines as described previously (Melck et al., 1999). SR141716A was a kind gift from Sanofi Recherche (Montpellier, France). Δ9-Tetrahydrocannabinol was kindly provided by the National
Affinity of the compounds for cannabinoid CB1 receptors
The two long chain, polyunsaturated capsaicin analogues synthesized here were chosen instead of arvanil because of their lower affinity for mouse cannabinoid CB1 receptors and less potent inhibitory effect on the anandamide membrane transporter in rat cells (Melck et al., 1999). In a binding assay carried out with rat brain membranes, and, therefore, more relevant to the in vivo studies described here, we found that livanil and linvanil were very weak ligands of these receptors (Table 1). In
Discussion
Vanilloid VR1 receptors have been identified in several nuclei of rat brain, including the substantia nigra compacta and the striatum, which are involved in the control of motor behavior (Mezey et al., 2000). Furthermore, it was also shown that i.v. administration of capsaicin to mice caused inhibition of spontaneous activity (ED50=0.3 mg/kg) and, to a lesser extent, immobility on a ring (ED50∼1 mg/kg) (Di Marzo et al., 2000b). In mice, it was not possible to counteract capsaicin effects with
Acknowledgements
The authors wish to thank A. Schiano-Moriello for assistance. This work was partly funded by the MURST (grant 3933 and Fondi Strutturali) to VDM and by CAM-PRI (08.5/0029/98) to JJFR.
References (40)
- et al.
Isolation and expression of a mouse CB1 cannabinoid receptor gene. Comparison of binding properties with those of native CB1 receptors in mouse brain and N18TG2 neuroblastoma cells
Biochem. Pharmacol.
(1997) - et al.
Biosynthesis, uptake, and degradation of anandamide and palmitoylethanolamide in leukocytes
J. Biol. Chem.
(1997) - et al.
Intranigral injection of capsaicin enhances motor activity and depletes nigral 5-hydroxytryptamine but not substance P
Neuropharmacology
(1981) - et al.
Finding of the endocannabinoid signalling system in Hydra, a very primitive organism: possible role in the feeding response
Neuroscience
(1999) - et al.
Overlap between the ligand recognition properties of the anandamide transporter and the VR1 vanilloid receptor: inhibitors of anandamide uptake with negligible capsaicin-like activity
FEBS Lett.
(2000) - et al.
The activity of anandamide at vanilloid VR1 receptors requires facilitated transport across the cell membrane and is limited by intracellular metabolism
J. Biol. Chem.
(2001) ‘Endocannabinoids’ and other fatty acid derivatives with cannabimimetic properties: biochemistry and possible physiopathological relevance
Biochim. Biophys. Acta
(1998)- et al.
Neurobehavioral activity in mice of N-vanillyl-arachidonyl-amide
Eur. J. Pharmacol.
(2000) - et al.
Elevated circulating levels of anandamide after administration of the transport inhibitor, AM404
Eur. J. Pharmacol.
(2000) - et al.
Anandamide induces apoptosis in human cells via vanilloid receptors. Evidence for a protective role of cannabinoid receptors
J. Biol. Chem.
(2000)
Endocannabinoids
Eur. J. Pharmacol.
Unsaturated long-chain N-acyl-vanillyl-amides (N-AVAMs): vanilloid receptor ligands that inhibit anandamide-facilitated transport and bind to CB1 cannabinoid receptors
Biochem. Biophys. Res. Commun.
Pharmacology of cannabinoid CB1 and CB2 receptors
Pharmacol. Ther.
SR141716A, a potent and selective antagonist of the brain cannabinoid receptor
FEBS Lett.
Motor actions of cannabinoids in the basal ganglia output nuclei
Life Sci.
New perspectives on enigmatic vanilloid receptors
Trends Neurosci.
The anandamide transport inhibitor AM404 activates vanilloid receptors
Eur. J. Pharmacol.
Assessment of anandamide interaction with the cannabinoid brain receptor: SR 141716A antagonism studies in mice and autoradiographic analysis of receptor binding in rat brain
J. Pharmacol. Exp. Ther.
Evidence for a new G-protein-coupled cannabinoid receptor in mouse brain
Mol. Pharmacol.
SR141716A antagonizes the disruptive effects of cannabinoid ligands on learning in rats
J. Pharmacol. Exp. Ther.
Cited by (113)
Parkinson's disease related alterations in cannabinoid transmission
2022, Brain Research BulletinAcute acetaminophen intoxication induces direct neurotoxicity in rats manifested as astrogliosis and decreased dopaminergic markers in brain areas associated with locomotor regulation
2019, Biochemical PharmacologyCitation Excerpt :The involvement of the vanilloid system in the regulation dopaminergic neurons has been also demonstrated [65]. Capsaicin and other potent ligands of the TRPV1 receptor produce hypokinesia in rats [66], and its specific blockage with antagonists restores motor activity. Prior to the current investigations, the direct toxic effects of APAP on the brain, specific region and cell types was an area that received little attention.
Capsaicin produces antidepressant-like effects in the forced swimming test and enhances the response of a sub-effective dose of amitriptyline in rats
2018, Physiology and BehaviorCitation Excerpt :Thus, the potentiation found between Ami and Cap to reduce the immobility of rats in the FST opens the possibility of minimizing the adverse effects of tricyclic antidepressants by administering lower doses in combination with low doses of TRPV1 agonists. It has been reported that TRPV1 activation does not increase general locomotion in the OFT [5,7,42,46], which is in line with our results. The fact that Cap alone and combined with Ami did not augment the ambulation in the OFT, reinforces the idea that the anti-immobility effect of Cap in the FST is not a false positive but a real antidepressant property of the TRPV1 agonist.
Emotional disorders induced by Hemopressin and RVD-hemopressin(α) administration in rats
2017, Pharmacological ReportsCapsaicin protects cortical neurons against ischemia/reperfusion injury via down-regulating NMDA receptors
2017, Experimental Neurology