Chapter 4.8 Measuring aggression in the mouse

Identification of Quantitative Trait Loci That Affect Aggressive Behavior in Mice

“…Moreover, the QTL we identified on chromosome X does not cover the pseudoautosomal region of chromosomes X and Y, which contains Sts. Our results may differ from those of previous investigators because we crossed NZB mice to a different mouse strain from those used previously (to A rather than CBA/H) (Roubertoux et al, 1994), we socially isolated the mice for longer than many other groups, and we used a modified version of the dangler test of aggression rather than the resident-intruder test used by some other groups (Maxson, 1992;Roubertoux et al, 1999). Also, it is worth noting that the use of inbred strains simplifies QTL mapping, because the number of genes that account for a phenotypic difference between two strains is likely to be smaller than the number of genes that cause phenotypic variation among outbred mice.…”

“…Residents that attacked the opponent in at least two of three tests were classified as being aggressive; those residents that either attacked in only one of three tests or never attacked were classified as being unaggressive. Aggression was thus analyzed as a threshold trait (Lynch and Walsh, 1998), i.e., a binary variable, that was defined by the presence or absence of reproducible attack behavior; we chose not to measure aggression as a score based on a composite of various behaviors, because other behaviors, such as tail rattling, are only weakly correlated with attack behavior and may have a different underlying genetics (Roubertoux et al, 1999). The test was stopped in 300 sec or within 3 sec of the start of an attack, whichever came sooner.…”

“…Second, to reduce the variability among opponent mice used for aggression testing, we used males of a relatively nonaggressive inbred strain, the 129T2/SvEmsJ strain, as standard opponents (Roubertoux and Carlier, 1987;Maxson, 1992) in aggression tests, and we measured aggressive behavior using a modification of the dangler paradigm (Kessler et al, 1977), in which the opponent mouse is restricted to one part of the cage and thus restricted in its ability to provoke an attack. Aggression was analyzed as a threshold trait (Lynch and Walsh, 1998), i.e., a binary variable that was defined by the presence or absence of reproducible attack behavior; we chose not to measure aggression as a score based on a composite of various behaviors, because other behaviors, such as tail rattling, are only weakly correlated with attack behavior and may have a different underlying genetics (Roubertoux et al, 1999). Only unequivocal bites and/or lunges of at least moderate intensity were considered to be attacks, whereas small nips that occurred during grooming or lower-intensity pushes were not considered to be attacks.…”

“…Using these tests, and variants of them, investigators have clearly demonstrated that genes influence aggressive behavior in mice. There are robust differences among inbred mouse strains in levels of aggressive behavior; for example, NZ B/ B1NJ (NZ B) mice are extremely aggressive, A /J (A) mice are markedly unaggressive, and other strains show intermediate levels of aggression (Roubertoux et al, 1999). Moreover, knock-out of any of a number of genes, including genes encoding nitric oxide synthase 1, monoamine oxidase A, the 5-hydroxytryptamine (serotonin) 1B receptor, and regulator of G-protein signaling 2 protein (RGS2), has marked affects on levels of aggressive behavior in mice (Maxson, 2000;Oliveira-Dos-Santos et al, 2000).…”

Effect of Domestication on Aggression in Gray Norway Rats

“…Taking this into account, the aggressive line of gray rats developed at the IC&G may be a good model for the consideration of the neurobiological mechanisms of aggression. It is relevant to note that aggressive behavioral responses either are weakly expressed in many inbred and outbred lines of rats and mice (De Boer et al 2003, Robertoux et al 1999Parmigiani et al 1999;Guillot and Chapouthier 1996) or are accompanied by general disturbances in social behavior .…”