Mice selectively bred for open-field thigmotaxis: life span and stability of the selction traint (2005)

Selander, R.-K.

Abstract

THE OPEN-FIELD (OF) TEST, originally developed by Hall (Hall & Ballachey, 1932), is one of the most widely used methods in the study of emotionality in rodents. The test is conducted in an enclosed open area in which the animal is confronted with a strange and potentially threatening situation. The OF apparatus provides a number of psychological stimuli in a novel environment that evoke unconditioned fear and multiple spontaneous behavioral responses (Castanon & Mormede, 1994; Clement, Calatayud, & Belzung, 2002; Gershenfeld & Paul, 1997).One of the most prominent fear-related OF responses is thigmotactic or wall-seeking behavior, which refers to the propensity of a rodent to stay in close contact with the OF wall because of the underlying tendency to avoid open, unknown, and potentially dangerous places (see Choleris, Thomas, Kavaliers, & Prato, 2001). Researchers have demonstrated the validity of thigmotaxis in measuring emotionality in mice (Choleris et al; Simon, Dupuis, & Costentin, 1994) as well as in rats (Treit & Fundytus, 1989; van der Staay, Kerbusch, & Raaijmakers, 1990).In addition to thigmotaxis, researchers have used many other OF parameters to measure emotionality in rodents, with the most traditional index being defecation (Broadhurst, 1976; Gray, 1987, p. 51; Walsh & Cummins, 1976). In particular, a high level of defecation has been interpreted as an indicator of a high level of emotionality. However, some researchers have questioned the validity of this index in mice (e.g., Archer, 1973; Ramos & Mormede, 1998).The terms emotionality and anxiety are commonly used as synonyms (see Ramos & Mormede, 1998). The traditional OF test is supposed to measure primarily state anxiety (provoked by an anxiogenic stimulus; Belzung & Griebel, 200l; Lister, 1990). In contrast, trait anxiety (an enduring feature of an animal; Lister) should be measured in the absence of novelty or other aversive stimuli, for example, in the animal's home cage (see Ramos & Mormede). Until now, the thigmotactic behavior of the HOFT and LOFT mice has been measured only in an anxiety-provoking, traditional OF. Therefore, in the present study, we investigated whether the mice differ in a home-cage condition as well.