ORIGINAL RESEARCH published: 06 October 2015 doi: 10.3389/fnins.2015.00336 Avoidance and contextual learning induced by a kairomone, a pheromone and a common odorant in female CD1 mice Lluís Fortes-Marco 1, 2 †, Enrique Lanuza 2, Fernando Martínez-García 1 and 1 Edited by: Carmen Agustín-Pavón * Thomas Endres, 1 Unitat Pre-departamental de Medicina, Facultad de Ciencias de la Salud, Universitat Jaume I, Castelló de la Plana, Spain, Otto-von-Guericke University, 2 Departament de Biologia Cel·lular, Facultat de Ciències Biològiques, Universitat de València, València, Spain Germany Reviewed by: Jeffrey B Rosen, Chemosignals mediate both intra- and inter-specific communication in most mammals. University of Delaware, USA Pheromones elicit stereotyped reactions in conspecifics, whereas kairomones provoke Pablo Chamero, University of Saarland, Germany a reaction in an allospecific animal. For instance, predator kairomones elicit anticipated *Correspondence: defensive responses in preys. The aim of this work was to test the behavioral responses Carmen Agustín-Pavón, of female mice to two chemosignals: 2-heptanone (2-HP), a putative alarm pheromone, Unitat Pre-departamental de and 2,4,5-trimethylthiazoline (TMT), a fox-derived putative kairomone, widely used to Medicina, Universitat Jaume I, Av. de Vicent Sos Baynat, s/n, 12071 investigate fear and anxiety in rodents. The banana-like odorant isoamyl acetate (IA), Castelló de la Plana, Spain unlikely to act as a chemosignal, served as a control odorant. We first presented [email protected] increasing amounts of these odorants in consecutive days, in a test box in which mice †Present Address: Lluís Fortes-Marco, could explore or avoid them. Female mice avoided the highest amounts of all three Departamento de Neurobiología compounds, with TMT and IA eliciting avoidance at lower amounts (3.8 pmol and Molecular, Celular y del Desarrollo. 0.35 µmol, respectively) than 2-HP (35 µmol). All three compounds induced minimal Instituto Cajal, Madrid, Spain effects in global locomotion and immobility in this set up. Further, mice detected 3.5 Specialty section: pmol of TMT and IA in a habituation–dishabituation test, so avoidance of IA started This article was submitted to well beyond the detection threshold. Finally, both TMT and IA, but not 2-HP, induced Systems Biology, a section of the journal conditioned place avoidance and increased immobility in the neutral compartment during Frontiers in Neuroscience a contextual memory test. These data suggest that intense odors can induce contextual Received: 25 June 2015 learning irrespective of their putative biological significance. Our results support that Accepted: 07 September 2015 synthetic predator-related compounds (like TMT) or other intense odorants are useful Published: 06 October 2015 Citation: to investigate the neurobiological basis of emotional behaviors in rodents. Since intense Fortes-Marco L, Lanuza E, odorants unlikely to act as chemosignals can elicit similar behavioral reactions than Martínez-García F and chemosignals, we stress the importance of using behavioral measures in combination Agustín-Pavón C (2015) Avoidance and contextual learning induced by a with other physiological (e.g., hormonal levels) or neural measures (e.g., immediate early kairomone, a pheromone and a gene expression) to establish the ethological significance of odorants. common odorant in female CD1 mice. Front. Neurosci. 9:336. Keywords: aversion, isoamyl acetate, 2,4,5-trimethylthiazoline, 2-heptanone, kairomones, pheromones, place doi: 10.3389/fnins.2015.00336 conditioning, vomeronasal Frontiers in Neuroscience | www.frontiersin.org 1 October 2015 | Volume 9 | Article 336 Fortes-Marco et al. Odor-induced contextual avoidance Introduction activates brain regions related to stress and anxiety, although the activation pattern differs from that induced by cat odor Rodents are widely used in studies on the neurobiological (Dielenberg et al., 2001; Staples et al., 2008; Janitzky et al., 2015; basis of emotional behaviors. Chemical signals are the most Pérez-Gómez et al., 2015). This fact, together with the fact that relevant sensory cues for rodents, capable of eliciting strong both unconditioned responses to TMT and its ability to support emotional responses in them. For example, chemical signals such conditioning are dependent on the environment and protocol as alarm pheromones and predator kairomones are anxiogenic used (Wallace and Rosen, 2000; Morrow et al., 2002; Blanchard for mice and rats. Alarm pheromones are substances released et al., 2003; Endres and Fendt, 2007), have led to some debate on by an injured or threatened animal and detected by conspecifics the kairomonal or simply aversive nature of this molecule (Fendt (Gutiérrez-García et al., 2007; Brechbühl et al., 2013), whereas and Endres, 2008; Fortes-Marco et al., 2013). predator kairomones elicit defensive responses in preys (for In this vein, we have previously hypothesized that the a review, see Fortes-Marco et al., 2013). Thus, experiments exposure to intense odorants might be indeed very aversive, so exposing mice and rats to alarm pheromones and kairomones it could elicit similar anxiety-like responses to the ones elicited are valuable to investigate the neural circuits controlling fear and by kairomones and alarm pheromones in mice—not necessarily anxiety, key features of pathologies such as generalized anxiety accompanied by behavioral components of fear i.e., freezing disorder, depression, or post-traumatic stress disorder. (Fortes-Marco et al., 2013). The volatile chemical 2-heptanone (2-HP) has been proposed Thus, we sought to compare the behavioral reactions of to act as an alarm substance in bees (Collins et al., 1989) and female mice to increasing amounts of TMT, 2-HP and isoamyl rats (Gutiérrez-García et al., 2007). This ketone is a component acetate (IA), a banana-like odorant frequently used as a control of the urine of rats, and its concentration is higher in stressed odor (Wallace and Rosen, 2000; Root et al., 2014) in two- individuals. Urine from stressed rats or 2-HP alone induce stress- choice tests. Previous studies from our lab have validated like reactions in recipient subjects (Gutiérrez-García et al., 2006), these tests to investigate the attractive properties of male and despair in rats subjected to the forced swim paradigm pheromones for female mice (Agustín-Pavón et al., 2007, 2014; (Gutiérrez-García et al., 2007). In mice, the concentration of 2- Martínez-Ricós et al., 2007). We hypothesized that the putative HP in urine is dependent on the adrenal gland (Novotny et al., kairomone TMT would be avoided at detectable concentrations. 1986), and it acts as a puberty modulator in females in a blend The putative pheromone 2-HP might be either attractive or with other chemicals (Novotny et al., 1986; Jemiolo et al., 1989). aversive depending on its role—alarm pheromone or puberty Thus, 2-HP might be classified as a trigger pheromone for rats modulator, see above. Finally, the control odorant should not and a primer pheromone for mice, following the definition by elicit avoidance, except perhaps at high concentrations. We McClintock (2002). To our knowledge, the behavioral responses also hypothesized that sufficiently aversive olfactory stimulation of mice to 2-HP have not been characterized yet, and most of the might be able to support learning in the animals. Thus, we studies using 2-HP have focused on the mechanism of detection tested whether repeated exposure to the concentrations eliciting (Boschat et al., 2002; Thompson et al., 2004). Interestingly, a the maximum behavioral reaction could induce a conditioned recent paper suggests that, in mice, some substances proposed contextual avoidance in mice. as alarm pheromones, like 2-sec-butyl-4,5-dihydrothiazole, share structural similarity with kairomones (but see Jemiolo et al., 1985 Materials and Methods on the possible role of this chemical as a sexual pheromone). Thus, alarm pheromones and kairomones might act using the Animals same neural circuits conveying signals of danger (Brechbühl et al., For the present experiments, we used 125 adult female CD1 2013). mice (8–18 weeks old, Janvier SAS, St Berthevin Cedex, Cat fur and feces are potential sources of kairomones for France). Animals were housed under controlled temperature rodents. Indeed, cat odors consistently induce biochemical and (22–24◦C) and a light-dark cycle 12:12 (light from 08:00 to behavioral measures of stress in mice and rats, such as elevation 20:00), with food and water ad libitum. Animals were treated of plasma glucocorticoids, fear responses such as freezing, throughout according to the European Communities Council avoidance, and contextual memory (Berton et al., 1998; Muñoz- Directive of (86/609/EEC), and the protocols were approved Abellán et al., 2008, 2009). However, the components of cat by the Committee of Ethics on Animal Experimentation of the fur odor and feces are diverse, not yet fully characterized, and University of Valencia. the reaction to cat odor depends on the donor cat (Muñoz- Abellán et al., 2008) and its diet (Berton et al., 1998; Ferrero Odorants et al., 2011). Conversely, specific odorants derived from predator We used three odorants: 2,5-dihydro-2,4,5-trimethylthiazoline sources would offer the advantage of a controllable presentation (TMT; Contech, Victoria, Canada), a putative kairomone found to produce reproducible results. in fox feces and detected by the main olfactory system and the The synthetic molecule 2,5-dihydro-2,4,5-trimethylthiazoline