title: Desensitization of cannabinoid-mediated presynaptic inhibition of neurotransmission between rat hippocampal neurons in culture.
abstract: Prolonged exposure to cannabinoids results in tolerance in vivo and desensitization of cannabinoid receptors in vitro. We show here that cannabinoid-induced presynaptic inhibition of glutamatergic neurotransmission desensitized after prolonged exposure to the cannabinoid receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo-[1,2,3-de]-1,4-benzoxazin-6-yl](1-napthalenyl)methanone monomethanesulfonate (Win55,212-2). Synaptic activity between hippocampal neurons in culture was determined from network-driven increases in intracellular Ca(2+) concentration ([Ca(2+)](i) spikes) and excitatory postsynaptic currents. Win55,212-2-induced (100 nM) inhibition partially desensitized after 2 h and completely desensitized after 18- to 24-h exposure. The desensitization could be overcome by higher concentrations of agonist as indicated by a parallel rightward shift of the concentration response curve from an EC(50) of 2.7 +/- 0.3 nM to 320 +/- 147 nM for inhibition of [Ca(2+)](i) spiking and from 43 +/- 17 nM to 4505 +/- 403 nM for inhibition of synaptic currents, suggesting that this phenomenon may underlie tolerance. Presynaptic expression of dominant negative G-protein-coupled-receptor kinase (GRK2-Lys220Arg) or beta-arrestin (319-418) reduced the desensitization produced by 18- to 24-h pretreatment with 100 nM, Win55,212-2 suggesting that desensitization followed the prototypical pathway for G-protein-coupled receptors. Prolonged treatment with Win55,212-2 produced a modest increase in the EC(50) for adenosine inhibition of synaptic transmission and pretreatment with cyclopentyladenosine produced a slight increase in the EC(50) for Win55,212-2, suggesting a reciprocal ability to produce heterologous desensitization. The long-term changes in synaptic function that accompany chronic cannabinoid exposure will be an important factor in evaluating the therapeutic potential of these drugs and will provide insight into the role of the endocannabinoid system.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Kouznetsova
authors.forename: Brooke
authors.initials: B
authors.lastname: Kelley
authors.forename: Maoxing
authors.initials: M
authors.lastname: Shen
authors.forename: Stanley A
authors.initials: SA
authors.lastname: Thayer
mesh_terms: D000818:Animals; D019390:Arrestins / Q000378:metabolism; D048588:Benzoxazines; D002121:Calcium Channel Blockers / Q000494:pharmacology; D063385:Cannabinoid Receptor Modulators; D002186:Cannabinoids / Q000494:pharmacology*; D002478:Cells, Cultured; D029721:Drosophila Proteins; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D019476:Insect Proteins / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D020239:Receptor Cross-Talk; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000378:metabolism*; D017470:Receptors, Glutamate / Q000378:metabolism; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects*; D016211:Transforming Growth Factor alpha; D015291:Transforming Growth Factors / Q000378:metabolism; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D048588:Benzoxazines; D002121:Calcium Channel Blockers; D063385:Cannabinoid Receptor Modulators; D002186:Cannabinoids; D029721:Drosophila Proteins; D018691:Excitatory Amino Acid Antagonists; D019476:Insect Proteins; D009025:Morpholines; D009281:Naphthalenes; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D017470:Receptors, Glutamate; D018047:Receptors, Purinergic P1; D016211:Transforming Growth Factor alpha; D000071557:beta-Arrestins; C083730:grk protein, Drosophila; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D015291:Transforming Growth Factors