title: Acute, chronic and withdrawal effects of the cannabinoid receptor agonist WIN55212-2 on the sequential activation of MAPK/Raf-MEK-ERK signaling in the rat cerebral frontal cortex: short-term regulation by intrinsic and extrinsic pathways.
abstract: The cannabinoids (CB) modulate the extracellular signal-regulated kinase (ERK), leading to various forms of plasticity in the brain. Little is known, however, on the in vivo short- and long-term activation and regulation of the components of mitogen-activated protein kinase (MAPK)/ERK signaling by CB. The CB agonist WIN55212-2 (8 mg/kg) increased the immunodensities of phosphorylated c-Raf-1 (42%), MEK1/2 (63%), ERK1 (24%), and ERK2 (28%) in the rat cerebral frontal cortex. These effects were antagonized by SR141716A (rimonabant, 10 mg/kg), a selective CB(1) receptor antagonist. Repeated WIN55212-2 treatment (2-8 mg/kg for 5 days) resulted in tachyphylaxis to the acute activation of Raf-MEK-ERK signaling. Acute WIN55212-2 also induced a hypothermic effect in rats, which was reduced after repeated administration (tolerance). Treatment with SR141716A after chronic WIN55212-2 resulted in the expected cannabinoid withdrawal syndrome, without concomitant alterations in the phosphorylation state of c-Raf-1, MEK1/2, or ERK1/2. Pretreatment with SL327 (20 mg/kg, a MEK1/2 inhibitor) increased the basal phosphorylation of c-Raf-1 (40%) and MEK1/2 (74%; feedback regulation) and fully prevented the up-regulation of ERK1/2 (23-31%) induced by WIN55212-2. Pretreatment with MK801 (1 mg/kg, a NMDA receptor antagonist) effectively blocked the up-regulation c-Raf-1 (41%), MEK1/2 (57%) and ERK1/2 (25-30%) induced by the CB agonist. The main findings demonstrate that the acute stimulation of CB(1) receptors in the frontal cortex results in the sequential phosphorylation of Raf-MEK-ERK cascade, in which c-Raf-1 activation (rate-limiting process) plays a crucial role. Moreover, the in vivo stimulating effect of WIN55212-2 on Raf-MEK-ERK signaling is under the extrinsic regulation of an excitatory glutamatergic mechanism.
authors.affiliation: Laboratori de Neurofarmacologia, Institut Universitari d'Investigació en Ciències de la Salut (IUNICS), Universitat de les Illes Balears, Palma de Mallorca, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Moranta
authors.forename: Susana
authors.initials: S
authors.lastname: Esteban
authors.forename: Jesús A
authors.initials: JA
authors.lastname: García-Sevilla
mesh_terms: D000818:Animals; D048588:Benzoxazines / Q000494:pharmacology*; D063387:Cannabinoid Receptor Antagonists; D002186:Cannabinoids / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005625:Frontal Lobe / Q000187:drug effects / Q000502:physiology*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology*; D009281:Naphthalenes / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043882:Receptors, Cannabinoid / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D048490:raf Kinases / Q000378:metabolism
chemical_list: D048588:Benzoxazines; D063387:Cannabinoid Receptor Antagonists; D002186:Cannabinoids; D009025:Morpholines; D009281:Naphthalenes; D043882:Receptors, Cannabinoid; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases