Cat odor causes long-lasting contextual fear conditioning and increased pituitary-adrenal activation, without modifying anxiety Cristina Muñoz-Abellán a,b , Nuria Daviu a,b , Cristina Rabasa a,b , Roser Nadal a,c , Antonio Armario a,b, ⁎ a Institute of Neurosciences, Autonomous University of Barcelona, Bellaterra 08193, Spain b Animal Physiology (School of Biosciences), Autonomous University of Barcelona, Bellaterra 08193, Spain c Psychobiology (School of Psychology), Autonomous University of Barcelona, Bellaterra 08193, Spain abstract article info Article history: Received 3 June 2009 Revised 11 August 2009 Accepted 12 August 2009 Available online 20 August 2009 Keywords: Predator odor Stress ACTH Corticosterone, Animal PTSD models, Long- term effects Hypothalamic-pituitary-adrenal axis A single exposure to a cat or cat odors has been reported by some groups to induce contextual and auditory fear conditioning and long-lasting changes in anxiety-like behaviour, but there is no evidence for parallel changes in biological stress markers. In the present study we demonstrated in male rats that exposure to a novel environment containing a cloth impregnated with cat fur odor resulted in avoidance of the odor, lower levels of activity and higher pituitary-adrenal (PA) response as compared to those exposed to the novel environment containing a clean cloth, suggesting increased levels of stress in the former animals. When re- exposed 9 days later to the same environment with a clean cloth, previously cat fur exposed rats again showed avoidance of the cloth area and lower levels of activity, suggesting development of contextual fear conditioning, which again was associated with a higher PA activation. In contrast, unaltered both anxiety-like behaviour and PA responsiveness to an elevated plus-maze were found 7 days after cat odor exposure. It is concluded that: (i) PA activation is able to reflect both the stressful properties of cat fur odor and odor- induced contextual fear conditioning; (ii) development of cat odor-induced contextual fear conditioning is independent of the induction of long-lasting changes in anxiety-like behaviour; and (iii) greater PA activation during exposure to the odor context is not explained by non-specific sensitization of the PA axis caused by previous exposure to cat fur odor. © 2009 Elsevier Inc. All rights reserved. Introduction Exposure of rats or mice to cats has been reported to induce not only immediate defensive responses (Blanchard et al., 1990a), but long-lasting (weeks) increases in anxiety-like behaviour as evaluated in the elevated plus-maze (EPM), a classical test of anxiety in rodents (i.e. Adamec et al., 1997, 2005; Adamec and Shallow, 1993; Cohen et al., 1996, 2003, 2004). In some experiments, enhancement of acoustic startle responses, another index of anxiety, was also found (Adamec et al., 2004; Cohen et al., 2004). Since cats are potential predators for rats and mice, such exposure may represent a life- threatening stimulus and, therefore, this stressor has been proposed as an animal model for post-traumatic stress disorder (PTSD). If rats are exposed to cloths or collars impregnated with cat fur odor instead of directly to the predator, the immediate response appears to be at least qualitatively similar in some respect, with increased immobility/freezing, reduced overall activity and avoidance of the area where the odor is located (i.e. Dielenberg et al., 2001; Dielenberg and McGregor, 1999; Koks et al., 2002; Li et al., 2004). Most of these behaviours are markedly attenuated by administration of anxiolytics (Blanchard et al., 1990b; Dielenberg et al., 1999; McGregor and Dielenberg, 1999). A single exposure to cat fur odors is also enough to induce effective contextual or contextual plus cue (cloth or collar) fear conditioning (Blanchard et al., 2001; Dielenberg et al., 1999, 2001; McGregor and Dielenberg, 1999) and more recently auditory fear conditioning (Takahashi et al., 2008). Apparently not all types of predator odors have similar properties and some authors argue that fur-derived odors are the most relevant to induce anxiety during the presence of the odor and contextual fear conditioning, whereas 2,4,5 trimetylthiazoline (TMT), a compound from the fox urine, or cat urine/feces may be merely aversive but not anxiogenic (Blanchard et al., 2003b; McGregor et al., 2002). Despite the consistency of fear conditioning after exposure to cat fur odors from a behavioural point of view, there is no evidence that conditioning is reflected in an altered physiological response, with the exception of the results reported by Dielenberg et al. (2001). Using telemetry and previous exposure to a worn collar as the odor-related stimulus, they found a small and transient increase in blood pressure after exposure to the context and the presentation of a clean (unworn) collar. However, their procedure was not specifically de- signed to differentiate between conditioning and non-specific sensitization of the physiological response to any novel environment. In addition, it is not known to what extent other physiological systems are able to reflect conditioning. On this regard, it is particularly Hormones and Behavior 56 (2009) 465–471 ⁎ Corresponding author. Fax: +34 935812390. E-mail address: Antonio.armario@uab.es (A. Armario). 0018-506X/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2009.08.002 Contents lists available at ScienceDirect Hormones and Behavior journal homepage: www.elsevier.com/locate/yhbeh