Genetically selected winner and loser rats: what was selected?

Throughout the 6--12th generation, genetically selected winner and loser rats in the straight runway test, were studied, in relation to weight, open field behavior, behavioral responses to footshock and adrenocortical response following stimulation. The results showed that the Loser Runway Strain (LRS) when compared to the Winner Runway Strain (WRS), were (1) lighter in weight, (2) defecated less, ambulated more and showed higher frequency of rearing-up when submitted to an open field (3) defecated less and jumped more in reaction to footshock and (14) had a higher rise of corticosterone levels following handling or footshock. These differences between WRS--LRS are the same found between male-female rats. This conclusion does not favor the validity of the runway test as a social measure, and suggests that WSR--LRS were selected according to male-female characteristics instead of a winning or losing trait.