2002). In this regard studies have demonstrated that laboratory mice express such

2002). In this regard studies have demonstrated that laboratory mice express such `endophenotypes’ (Langford, Aprotinin web Crager, Shehzad, Smith, Sotocinal, Levenstadt et al., 2006; Chen, Panksepp Lahvis, 2009; Jeon, Kim, order Vesnarinone Chetana, Jo, Ruley, Lin et al., 2010; Sanders, Mayford, Jeste, 2013; GonzalezLiencres, Juckel, Tas, Friebe, Br e, 2014). For example, observer C57BL/6J mice exhibit vicarious behavioral (Chen et al., 2009; Jeon et al., 2010), physiological (Chen et al., 2009) and neural responses (Jeon et al., 2010) to other’s expressions of fear. These studies and others using laboratory rats (Atsak, Orre, Bakker, Cerliani, Roozendaal, Gazzola et al., 2011; Jones, Riha, Gore, Monfils, 2013; Ben-Ami Bartal, Rodgers, Bernardez Sarria, Decety, Mason, 2014) additionally support the notion that social relationships, sexual characteristics, stress and prior experience are potent modulators of empathic responsiveness (Christov-Moore, Simpson, Coud? Grigaityte, Iacoboni Ferrari, 2014; Freidin, Carballo, Bentosela, 2015; Martin, Hathaway, Isbester, Mirali, Acland, Niederstrasser et al., 2015). Social exclusion can also influence empathy (Twenge, Baumeister, DeWall, Ciarocco Bartels, 2007) particularly during adolescent development (Eisenberg, 1982). In rodents, manipulation of the social housing environment is used as an experimental procedure to restrict or augment social interaction during adolescence, and can profoundly affect maturation of the brain and behavior (Yang, Perry, Weber, Katz, Crawley, 2010; Liu, Dietz, DeLoyht, Pedre, Kelkar, Kaur et al. 2012; Makinodan, Rosen, Ito, Corfas, 2012; Gan, Bowline, Lourenco, Pickel, 2014; Adams Rosenkranz, 2015). In the present study, we hypothesized that social housing during mouse adolescence would have a supportive effect on vicarious fear relative to isolate housing. Females and males were also compared because sexual identity can influence empathic responding. Moreover, responses were assessed 15-min and 24-h post-conditioning to distinguish between `short-term and `long-term’ memories, respectively, the latter of which may be less sensitive to the acute experience associated with conditioning.Author Manuscript Author Manuscript Author Manuscript Author Manuscript MethodsMice from the BALB/cJ (`BALB’) and C57BL/6J (`B6′) mice were bred within our own colony. At weaning B6 mice were pooled from 2-4 litters (Figure 1A), and then randomly selected for housing in either a social group of 2 males and 2 females (see Panksepp, Jochman, Kim, Koy, Wilson, Chen et al., 2007 for rationale) or in complete social isolation (Figure 1B). These B6 mice then became observers of target mice undergoing fear conditioning (i.e., vicarious fear) or were directly conditioned (see Figure 1C and below). Mice remained in their respective housing conditions throughout conditioning and testing. To control for familiarity with strain-specific communication modalities, such as vocalizations or volatile odorants, target mice during vicarious fear conditioning were age matched male-female pairs of unfamiliar mice derived from reciprocal BALB ?B6 (F1) crosses (see Chen et al., 2009 for rationale). On Day 1, B6 observers and targets were allowed 300-s to freely explore the fearconditioning compartment of the experimental apparatus (www.cleversysinc.com/products/ hardware). To familiarize observers with a distressful stimulus, they were exposed to a single, unconditioned stimulus (US; 3-s, 1mA scrambled shock) halfw.2002). In this regard studies have demonstrated that laboratory mice express such `endophenotypes’ (Langford, Crager, Shehzad, Smith, Sotocinal, Levenstadt et al., 2006; Chen, Panksepp Lahvis, 2009; Jeon, Kim, Chetana, Jo, Ruley, Lin et al., 2010; Sanders, Mayford, Jeste, 2013; GonzalezLiencres, Juckel, Tas, Friebe, Br e, 2014). For example, observer C57BL/6J mice exhibit vicarious behavioral (Chen et al., 2009; Jeon et al., 2010), physiological (Chen et al., 2009) and neural responses (Jeon et al., 2010) to other’s expressions of fear. These studies and others using laboratory rats (Atsak, Orre, Bakker, Cerliani, Roozendaal, Gazzola et al., 2011; Jones, Riha, Gore, Monfils, 2013; Ben-Ami Bartal, Rodgers, Bernardez Sarria, Decety, Mason, 2014) additionally support the notion that social relationships, sexual characteristics, stress and prior experience are potent modulators of empathic responsiveness (Christov-Moore, Simpson, Coud? Grigaityte, Iacoboni Ferrari, 2014; Freidin, Carballo, Bentosela, 2015; Martin, Hathaway, Isbester, Mirali, Acland, Niederstrasser et al., 2015). Social exclusion can also influence empathy (Twenge, Baumeister, DeWall, Ciarocco Bartels, 2007) particularly during adolescent development (Eisenberg, 1982). In rodents, manipulation of the social housing environment is used as an experimental procedure to restrict or augment social interaction during adolescence, and can profoundly affect maturation of the brain and behavior (Yang, Perry, Weber, Katz, Crawley, 2010; Liu, Dietz, DeLoyht, Pedre, Kelkar, Kaur et al. 2012; Makinodan, Rosen, Ito, Corfas, 2012; Gan, Bowline, Lourenco, Pickel, 2014; Adams Rosenkranz, 2015). In the present study, we hypothesized that social housing during mouse adolescence would have a supportive effect on vicarious fear relative to isolate housing. Females and males were also compared because sexual identity can influence empathic responding. Moreover, responses were assessed 15-min and 24-h post-conditioning to distinguish between `short-term and `long-term’ memories, respectively, the latter of which may be less sensitive to the acute experience associated with conditioning.Author Manuscript Author Manuscript Author Manuscript Author Manuscript MethodsMice from the BALB/cJ (`BALB’) and C57BL/6J (`B6′) mice were bred within our own colony. At weaning B6 mice were pooled from 2-4 litters (Figure 1A), and then randomly selected for housing in either a social group of 2 males and 2 females (see Panksepp, Jochman, Kim, Koy, Wilson, Chen et al., 2007 for rationale) or in complete social isolation (Figure 1B). These B6 mice then became observers of target mice undergoing fear conditioning (i.e., vicarious fear) or were directly conditioned (see Figure 1C and below). Mice remained in their respective housing conditions throughout conditioning and testing. To control for familiarity with strain-specific communication modalities, such as vocalizations or volatile odorants, target mice during vicarious fear conditioning were age matched male-female pairs of unfamiliar mice derived from reciprocal BALB ?B6 (F1) crosses (see Chen et al., 2009 for rationale). On Day 1, B6 observers and targets were allowed 300-s to freely explore the fearconditioning compartment of the experimental apparatus (www.cleversysinc.com/products/ hardware). To familiarize observers with a distressful stimulus, they were exposed to a single, unconditioned stimulus (US; 3-s, 1mA scrambled shock) halfw.