title: Increased Contextual Fear Conditioning in iNOS Knockout Mice: Additional Evidence for the Involvement of Nitric Oxide in Stress-Related Disorders and Contribution of the Endocannabinoid System.
abstract: BACKGROUND
  Inducible or neuronal nitric oxide synthase gene deletion increases or decreases anxiety-like behavior in mice, respectively. Since nitric oxide and endocannabinoids interact to modulate defensive behavior, the former effect could involve a compensatory increase in basal brain nitric oxide synthase activity and/or changes in the endocannabinoid system. Thus, we investigated the expression and extinction of contextual fear conditioning of inducible nitric oxide knockout mice and possible involvement of endocannabinoids in these responses.
  
  
  METHODS
  We evaluated the effects of a preferential neuronal nitric oxide synthase inhibitor, 7-nitroindazol, nitric oxide synthase activity, and mRNA changes of nitrergic and endocannabinoid systems components in the medial prefrontal cortex and hippocampus of wild-type and knockout mice. The effects of URB597, an inhibitor of the fatty acid amide hydrolase enzyme, which metabolizes the endocannabinoid anandamide, WIN55,212-2, a nonselective cannabinoid agonist, and AM281, a selective CB1 antagonist, on contextual fear conditioning were also evaluated.
  
  
  RESULTS
  Contextual fear conditioning expression was similar in wild-type and knockout mice, but the latter presented extinction deficits and increased basal nitric oxide synthase activity in the medial prefrontal cortex. 7-Nitroindazol decreased fear expression and facilitated extinction in wild-type and knockout mice. URB597 decreased fear expression in wild-type and facilitated extinction in knockout mice, whereas WIN55,212-2 and AM281 increased it in wild-type mice. Nonconditioned knockout mice showed changes in the mRNA expression of nitrergic and endocannabinoid system components in the medial prefrontal cortex and hippocampus that were modified by fear conditioning.
  
  
  CONCLUSIONS
  These data reinforce the involvement of the nitric oxide and endocannabinoids (anandamide) in stress-related disorders and point to a deregulation of the endocannabinoid system in situations where nitric oxide signaling is increased.
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel). sabrinalisboa@usp.br.
authors.forename: Sabrina F
authors.initials: SF
authors.lastname: Lisboa
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Felipe V
authors.initials: FV
authors.lastname: Gomes
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Andréia L
authors.initials: AL
authors.lastname: Silva
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Daniela L
authors.initials: DL
authors.lastname: Uliana
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Laura H A
authors.initials: LH
authors.lastname: Camargo
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Francisco S
authors.initials: FS
authors.lastname: Guimarães
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Fernando Q
authors.initials: FQ
authors.lastname: Cunha
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Sâmia R L
authors.initials: SR
authors.lastname: Joca
authors.affiliation: Department of Pharmacology, Medical School of Ribeirão Preto (Drs Lisboa, Gomes, Silva, Cunha, and Resstel, Ms Uliana and Ms Camargo), Department of Pharmacology, School of Pharmaceutical Sciences of Ribeirão Preto (Dr Joca), and Center for Interdisciplinary Research on Applied Neurosciences, University of São Paulo, Brazil (Drs Lisboa, Gomes, Guimarães, Joca, and Resstel).
authors.forename: Leonardo B M
authors.initials: LB
authors.lastname: Resstel
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D001549:Benzamides / Q000494:pharmacology; D048588:Benzoxazines / Q000494:pharmacology; D063386:Cannabinoid Receptor Agonists / Q000494:pharmacology; D063387:Cannabinoid Receptor Antagonists / Q000494:pharmacology; D002219:Carbamates / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology*; D063388:Endocannabinoids / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D046352:Freezing Reaction, Cataleptic / Q000187:drug effects / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D007191:Indazoles / Q000494:pharmacology; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D053284:Polyunsaturated Alkamides / Q000378:metabolism*; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D013315:Stress, Psychological / Q000378:metabolism
chemical_list: D001095:Arachidonic Acids; D001549:Benzamides; D048588:Benzoxazines; D063386:Cannabinoid Receptor Agonists; D063387:Cannabinoid Receptor Antagonists; D002219:Carbamates; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D007191:Indazoles; D009025:Morpholines; D009281:Naphthalenes; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles; D012333:RNA, Messenger; D043884:Receptor, Cannabinoid, CB1; C500528:cyclohexyl carbamic acid 3'-carbamoylbiphenyl-3-yl ester; D009569:Nitric Oxide; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; C109925:AM 281; C078814:anandamide; C080122:7-nitroindazole
keywords: 212-2; 7-nitroindazole; AM281; CB1 receptors; URB597; WIN55; anandamide; extinction; fear conditioning; nitric oxide