Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Original Paper Neuroendocrinology 2005;82:306–319 DOI: 10.1159/000093129 Analysis of the Stress Response in Rats Trained in the Water-Maze: Differential Expression of Corticotropin-Releasing Hormone, CRH-R1, Glucocorticoid Receptors and Brain-Derived Neurotrophic Factor in Limbic Regions Argel Aguilar-Valles a Edith Sánchez a Patricia de Gortari b Israela Balderas c Víctor Ramírez-Amaya d Federico Bermúdez-Rattoni c Patricia Joseph-Bravo a a Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), b División de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatría Ramón de la Fuente Muñíz, México, c Departamento de Neurociencias, Instituto de Fisiología Celular, UNAM, and d Departamento de Neurobiología Conductual y Cognitiva, Instituto de Neurobiología, UNAM, Mexico hypothalamus and quantified serum corticosterone lev- els by radioimmunoassay at different stages of training. mRNA levels of brain-derived neurotrophic factor (BDNF) were also quantified due to its prominent role in learning and memory processes. Male Wistar rats trained for 1, 3 or 5 days in the Morris water-maze (10 trials/day) were sacrificed 5–60 min the after last trial. A strong stress re- sponse occurred at day one in both yoked and trained animals (increased corticosterone and hypothalamic pro-CRH and CRH-R1 mRNA levels); changes gradually diminished as the test progressed. In amygdala, pro-CRH mRNA levels decreased while those of BDNF augmented when stress was highest, in yoked and trained animals. Hippocampi, of both yoked and trained groups, had de- creased levels of GR mRNA on days 1 and 3, normalizing by day 5, while those of pro-CRH and CRH-R1 increased after the 3rd day. Increased gene expression, specifical- ly due to spatial learning, occurred only for hippocampal BDNF since day 3. These results show that the Morris water-maze paradigm induces a strong stress response Key Words Corticotropin-releasing hormone  Adrenal steroid receptor  Brain-derived neurotrophic factor  Hippocampus  Amygdala  Hypothalamus  Stress  Behavioral neuroendocrinology Abstract Glucocorticoids and corticotropin-releasing hormone (CRH) are key regulators of stress responses. Different types of stress activate the CRH system; in hypothala- mus, CRH expression and release are increased by phys- ical or psychological stressors while in amygdala, pref- erentially by psychological stress. Learning and memory processes are modulated by glucocorticoids and stress at different levels. To characterize the kind of stress pro- voked by a hippocampal-dependent task such as spatial learning, we compared the expression profile of gluco- corticoid receptor (GR), pro-CRH and CRH-R1 mRNAs (analyzed by RT-PCR), in amygdala, hippocampus and Received: December 13, 2005 Accepted after revision: March 14, 2006 Published online: May 4, 2006 Patricia Joseph-Bravo Instituto de Biotecnología, UNAM, AP510-3 Cuernavaca, Mor 62210 (Mexico) Tel. +52 555 622 7632, Fax +52 555 622 7622 E-Mail joseph@ibt.unam.mx © 2005 S. Karger AG, Basel 0028–3835/05/0826–0306$22.00/0 Accessible online at: www.karger.com/nen