Maternal separation modulates short-term behavioral and physiological indices of the stress response Yoav Litvin a,b,d, ⁎, Philip Tovote d , Nathan S. Pentkowski a,b,d , Thomas Zeyda d , Lanikea B. King b , Amy J. Vasconcellos b , Christopher Dunlap b , Joachim Spiess d , D. Caroline Blanchard b,c,d , Robert J. Blanchard a,b,d a Department of Psychology, University of Hawaii, 2430 Campus Rd., Honolulu, HI 96822, USA b Pacific Biosciences Research Center, University of Hawaii, 1993 East-West Road, Honolulu, HI 96822, USA c John A. Burns School of Medicine, University of Hawaii, Department of Genetics and Molecular Biology, 651 Ilalo St, Honolulu, HI 96813, USA d Specialized Neuroscience Research Program, John A. Burns School of Medicine, University of Hawaii, 651 Ilalo St, Honolulu, HI 96813, USA abstract article info Article history: Received 4 November 2009 Revised 26 February 2010 Accepted 8 March 2010 Available online 15 March 2010 Keywords: Defense Anxiety Corticosterone Hippocampus Corticotropin-releasing factor GR Stress Trauma freezing Early-life stress produces an anxiogenic profile in adulthood, presumably by activating the otherwise quiescent hypothalamic–pituitary–adrenal (HPA) axis during the vulnerable ‘stress hyporesponsive period’. While the long-term effects of such early-life manipulations have been extensively characterized, little is known of the short-term effects. Here, we compared the short-term effects of two durations of maternal separation stress and one unseparated group (US) on behavioral and physiological indices of the stress response in rat pups. Separations included 3 h on each of 12 days, from postnatal day (PND) 2 to 13 (MS2–13) and 3 days of daily, 6- h separation from PND11–13 (MS11–13). On PND14 (Experiment 1), both MS2–13 and MS11–13 produced marked reductions in freezing toward an adult male conspecific along with reduced levels of glucocorticoid type 2 (GR) and CRF type-1 (CRF 1 ) receptor mRNA in the hippocampus. Group MS2–13 but not MS11–13 produced deficits in stressor-induced corticosterone secretion, accompanied by reductions in body weight. Our results suggest that GR and/or CRF 1 levels, not solely the magnitude of corticosterone secretion, may be involved in the modulation of freezing. In a second experiment, we aimed to extend these findings by testing male and female separated and unseparated pups' unconditioned defensive behaviors to cat odor on PND26, and subsequent cue + context conditioning and extinction throughout postnatal days 27–32. Our results show that maternal separation produced reductions in unconditioned freezing on PND26, with MS2–13 showing stronger deficits than MS11–13. However, separation did not affect any other defensive behaviors. Furthermore, separated rats failed to show conditioned freezing, although they did avoid the no-odor block conditioned cue. There were no sex differences other than weight. We suggest that maternal separation may have produced these changes by disrupting normal development of hippocampal regions involved in olfactory-mediated freezing, not in mechanisms of learning and memory per se. These findings may have direct relevance for understanding the mechanisms by which early-life adverse experiences produce short-term and lasting psychopathologies. © 2010 Elsevier Inc. All rights reserved. Introduction Early-life trauma has been shown to affect neurobiological structure and function associated with psychopathology. Manipula- tions such as prolonged maternal separation of pups from the dam have been used as an animal model of early-life trauma (Lehmann and Feldon, 2000). In the rat, these separations are typically carried out during the stress-hypo-responsive-period (SHRP), a period between postnatal day (PND) 4–14 in which the presence of the dam suppresses pups' basal and stress-induced circulating corticosterone, the principal rat glucocorticoid hormone (Walker et al., 2001). Corticosterone actions are predominantly catabolic, and suppress neurogeneration and proliferation (Tanapat et al., 2001), thus its relative inhibition is adaptive during development, a period charac- terized by anabolic processes: during the SHRP, low levels of corticosterone mediate a delicate balance between rapid cell death, birth, migration and proliferation in the dentate gyrus region of the hippocampus (Gould, 1994). The hippocampal formation has been the focus of much attention as a site which may be involved in the effects of early-life trauma on pathology; it shows structural and functional changes in patients suffering from a number of stress-related pathologies (Sheline et al., 1999; Bremner, 2006), shows epigeneti- cally mediated structural and functional plasticity (Mirescu et al., 2004; McGowan et al., 2009), is involved in defensive behaviors Hormones and Behavior 58 (2010) 241–249 ⁎ Corresponding author. 2430 Campus Rd., Honolulu, HI 96822, USA. Fax: + 1 808 9569612. E-mail address: litvin@hawaii.edu (Y. Litvin). 0018-506X/$ – see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2010.03.010 Contents lists available at ScienceDirect Hormones and Behavior journal homepage: www.elsevier.com/locate/yhbeh