Recent Submissions

  • Caveats of chronic exogenous corticosterone treatments in adolescent rats and effects on anxiety-like and depressive behavior and hypothalamic-pituitary-adrenal (HPA) axis function

    Waters, Patti; McCormick, Cheryl M (BioMed Central, 2011)
    Background: Administration of exogenous corticosterone is an effective preclinical model of depression, but its use has involved primarily adult rodents. Using two different procedures of administration drawn from the literature, we explored the possibility of exogenous corticosterone models in adolescence, a time of heightened risk for mood disorders in humans. Methods: In experiment 1, rats were injected with 40 mg/kg corticosterone or vehicle from postnatal days 30 to 45 and compared with no injection controls on behavior in the elevated plus maze (EPM) and the forced swim test (FST). Experiment 2 consisted of three treatments administered to rats from postnatal days 30 to 45 or as adults (days 70 to 85): either corticosterone (400 μg/ml) administered in the drinking water along with 2.5% ethanol, 2.5% ethanol or water only. In addition to testing on EPM, blood samples after the FST were obtained to measure plasma corticosterone. Analysis of variance (ANOVA) and alpha level of P < 0.05 were used to determine statistical significance. Results: In experiment 1, corticosterone treatment of adolescent rats increased anxiety in the EPM and decreased immobility in the FST compared to no injection control rats. However, vehicle injected rats were similar to corticosterone injected rats, suggesting that adolescent rats may be highly vulnerable to stress of injection. In experiment 2, the intake of treated water, and thus doses delivered, differed for adolescents and adults, but there were no effects of treatment on behavior in the EPM or FST. Rats that had ingested corticosterone had reduced corticosterone release after the FST. Ethanol vehicle also affected corticosterone release compared to those ingesting water only, but differently for adolescents than for adults. Conclusions: The results indicate that several challenges must be overcome before the exogenous corticosterone model can be used effectively in adolescents.
  • Peer pressures: Social instability stress in adolescence and social deficits in adulthood in a rodent model

    McCormick, Cheryl M; Hodges, Travis E; Simone, Jonathan J (Elsevier Ltd, 2014)
    Studies in animal models generate and test hypotheses regarding developmental stagespecific vulnerability that might inform research questions about human development. In both rats and humans, peer relationships are qualitatively different in adolescence than at other stages of development, and social experiences in adolescence are considered important determinants of adult social function. This review describes our adolescent rat social instability stress model and the long-lasting effects social instability has on social behaviour in adulthood as well as the possible neural underpinnings. Effects of other adolescent social stress experiences in rats on social behaviours in adulthood also are reviewed. We discuss the role of hypothalamic–pituitary–adrenal (HPA) function and glucocorticoid release in conferring differential susceptibility to social experiences in adolescents compared to adults. We propose that although differential perception of social experiences rather than immature HPA function may underlie the heightened vulnerability of adolescents to social instability, the changes in the trajectory of brain development and resultant social deficits likely are mediated by the heightened glucocorticoid release in response to repeated social stressors in adolescence compared to in adulthood.
  • Taking Control of Aggression: Perceptions of Aggression Suppress the Link Between Perceptions of Facial Masculinity and Attractiveness

    Geniole, Shawn N; McCormick, Cheryl M (SAGE Publishing, 2013)
    Women’s preferences for masculine-looking male faces are inconsistent across studies, with some studies finding a positive relationship between masculinity and attractiveness and others finding a negative relationship or no association. One possible reason for this inconsistency is that the perception of masculinity is also associated with perceptions of aggression, which may be viewed as particularly costly to women (aggressive individuals are more likely to experience injury or death). Based on the proposal that women’s preference for masculinity is in conflict with their aversion for aggression in male faces, we hypothesized that the bivariate associations between perceptions of masculinity and attractiveness would be weak or negative, but would be positive and significantly stronger after controlling statistically for perceptions of aggression. Across three studies involving three sets of faces (n = 25, 54, 24) and five sets of raters (n = 29, 30, 26, 16, 10), this hypothesis was supported with the average correlation between perceptions of masculinity and attractiveness (r = -.09) reversing in direction and substantially increasing in magnitude after perceptions of aggression were controlled statistically (r = .35). Perceived masculinity may thus involve both attractive and unattractive components, and women’s preferences for masculinity may involve weighing its relative costs and benefits.
  • Evidence from Meta-Analyses of the Facial Width-to-Height Ratio as an Evolved Cue of Threat

    Geniole, Shawn N; Denson, Thomas F; Dixson, Barnaby J; Carré, Justin M; McCormick, Cheryl M (2015)
    The facial width-to-height ratio (FWHR) is the width of the face divided by the height of the upper face. There is mixed evidence for the hypothesis that the FWHR is a cue of threat and dominance in the human face. We conducted a systematic review and meta-analyses of all peer-reviewed studies (and 2 unpublished studies) to estimate the magnitude of the sex difference in the FWHR, and the magnitude of the relationship between the FWHR and threatening and dominant behaviours and perceptions. Studies were eligible for inclusion if the authors reported an analysis involving the FWHR. Our analyses revealed that the FWHR was larger in men than in women (d = .11, n = 10,853), cued judgements of masculinity in men ( r = .35, n of faces = 487; n of observers = 339), and was related to body mass index ( r = .31, n = 2,506). Further, the FWHR predicted both threat behaviour in men ( r = .16, n = 4,603) and dominance behaviour in both sexes ( r = .12, n = 948) across a variety of indices. Individuals with larger FWHRs were judged by observers as more threatening ( r = .46, n of faces = 1,691; n of observers = 2,076) and more dominant ( r = .20, n of faces = 603; n of observers = 236) than those with smaller FWHRs. Individuals with larger FWHRs were also judged as less attractive ( r = -.26, n of faces = 721; n of observers = 335), especially when women made the judgements. These findings provide some support for the hypothesis that the FWHR is part of an evolved cueing system of intra-sexual threat and dominance in men. A limitation of the meta-analyses on perceptions of threat and dominance were the low number of stimuli involving female and older adult faces.
  • Facing Aggression: Cues Differ for Female versus Male Faces

    Geniole, Shawn N; Keyes, Amanda E; Mondloch, Catherine J; Carré, Justin M; McCormick, Cheryl M (2012)
    The facial width-to-height ratio (face ratio), is a sexually dimorphic metric associated with actual aggression in men and with observers’ judgements of aggression in male faces. Here, we sought to determine if observers’ judgements of aggression were associated with the face ratio in female faces. In three studies, participants rated photographs of female and male faces on aggression, femininity, masculinity, attractiveness, and nurturing. In Studies 1 and 2, for female and male faces, judgements of aggression were associated with the face ratio even when other cues in the face related to masculinity were controlled statistically. Nevertheless, correlations between the face ratio and judgements of aggression were smaller for female than for male faces (F1,36 = 7.43, p = 0.01). In Study 1, there was no significant relationship between judgements of femininity and of aggression in female faces. In Study 2, the association between judgements of masculinity and aggression was weaker in female faces than for male faces in Study 1. The weaker association in female faces may be because aggression and masculinity are stereotypically male traits. Thus, in Study 3, observers rated faces on nurturing (a stereotypically female trait) and on femininity. Judgements of nurturing were associated with femininity (positively) and masculinity (negatively) ratings in both female and male faces. In summary, the perception of aggression differs in female versus male faces. The sex difference was not simply because aggression is a gendered construct; the relationships between masculinity/femininity and nurturing were similar for male and female faces even though nurturing is also a gendered construct. Masculinity and femininity ratings are not associated with aggression ratings nor with the face ratio for female faces. In contrast, all four variables are highly inter-correlated in male faces, likely because these cues in male faces serve as ‘‘honest signals’’.