title: Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats.
abstract: Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: André
authors.initials: A
authors.lastname: de Macêdo Medeiros
authors.affiliation: Behavioral Genetics Laboratory, Universidade Federal de Santa Catarina, Florianópolis, Brazil.
authors.forename: Geison Souza
authors.initials: GS
authors.lastname: Izídio
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: Diego Silveira
authors.initials: DS
authors.lastname: Sousa
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: Priscila Tavares
authors.initials: PT
authors.lastname: Macedo
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: Anatildes Feitosa
authors.initials: AF
authors.lastname: Silva
authors.affiliation: Behavioral Endocrinology Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: Victor Kenji Medeiros
authors.initials: VK
authors.lastname: Shiramizu
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: Alicia
authors.initials: A
authors.lastname: Cabral
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil.
authors.forename: Alessandra Mussi
authors.initials: AM
authors.lastname: Ribeiro
authors.affiliation: Memory Studies Laboratory, Universidade Federal do Rio Grande do Norte, Natal, Brazil. Electronic address: reginahsilva@gmail.com.
authors.forename: Regina Helena
authors.initials: RH
authors.lastname: Silva
mesh_terms: D000647:Amnesia / Q000139:chemically induced* / Q000150:complications / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D001007:Anxiety / Q000209:etiology; D001362:Avoidance Learning / Q000187:drug effects; D018680:Cholinergic Antagonists / Q000633:toxicity*; D003270:Contraceptive Agents / Q000494:pharmacology; D004195:Disease Models, Animal; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004967:Estrogens / Q000378:metabolism*; D030762:Estrous Cycle / Q000187:drug effects; D005260:Female; D018782:Maze Learning / Q000187:drug effects; D009043:Motor Activity / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D012601:Scopolamine / Q000633:toxicity*; D013997:Time Factors
chemical_list: D018680:Cholinergic Antagonists; D003270:Contraceptive Agents; D004967:Estrogens; D004958:Estradiol; D012601:Scopolamine
keywords: Anxiety-like behavior; Cholinergic transmission; Discriminative avoidance task; Estrous cycle; Memory