title: A biphasic and brain-region selective down-regulation of cyclic adenosine monophosphate concentrations supports object recognition in the rat.
abstract: BACKGROUND
  We aimed to further understand the relationship between cAMP concentration and mnesic performance.
  
  
  RESULTS
  Rats were injected with milrinone (PDE3 inhibitor, 0.3 mg/kg, i.p.), rolipram (PDE4 inhibitor, 0.3 mg/kg, i.p.) and/or the selective 5-HT4R agonist RS 67333 (1 mg/kg, i.p.) before testing in the object recognition paradigm. Cyclic AMP concentrations were measured in brain structures linked to episodic-like memory (i.e. hippocampus, prefrontal and perirhinal cortices) before or after either the sample or the testing phase. Except in the hippocampus of rolipram treated-rats, all treatment increased cAMP levels in each brain sub-region studied before the sample phase. After the sample phase, cAMP levels were significantly increased in hippocampus (1.8 fold), prefrontal (1.3 fold) and perirhinal (1.3 fold) cortices from controls rat while decreased in prefrontal cortex (∼0.83 to 0.62 fold) from drug-treated rats (except for milrinone+RS 67333 treatment). After the testing phase, cAMP concentrations were still increased in both the hippocampus (2.76 fold) and the perirhinal cortex (2.1 fold) from controls animals. Minor increase were reported in hippocampus and perirhinal cortex from both rolipram (respectively, 1.44 fold and 1.70 fold) and milrinone (respectively 1.46 fold and 1.56 fold)-treated rat. Following the paradigm, cAMP levels were significantly lower in the hippocampus, prefrontal and perirhinal cortices from drug-treated rat when compared to controls animals, however, only drug-treated rats spent longer time exploring the novel object during the testing phase (inter-phase interval of 4 h).
  
  
  CONCLUSIONS
  Our results strongly suggest that a "pre-sample" early increase in cAMP levels followed by a specific lowering of cAMP concentrations in each brain sub-region linked to the object recognition paradigm support learning efficacy after a middle-term delay.
authors.affiliation: Université de Caen Basse-Normandie, Groupe Mémoire et Plasticité comportementale (GMPc), EA4259, IFR 146, Caen, France.
authors.forename: Maïte
authors.initials: M
authors.lastname: Hotte
authors.forename: François
authors.initials: F
authors.lastname: Dauphin
authors.forename: Thomas
authors.initials: T
authors.lastname: Freret
authors.forename: Michel
authors.initials: M
authors.lastname: Boulouard
authors.forename: Guenaëlle
authors.initials: G
authors.lastname: Levallet
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000502:physiology; D000242:Cyclic AMP / Q000032:analysis* / Q000502:physiology; D015536:Down-Regulation; D006624:Hippocampus; D008568:Memory; D017397:Prefrontal Cortex; D051381:Rats; D011930:Reaction Time; D021641:Recognition, Psychology; D013702:Temporal Lobe
chemical_list: D000242:Cyclic AMP