Component analyses differentiate between exploratory behaviour of spontaneously hypertensive rats and Wistar Kyoto rats in a two-compartment free-exploration open field

The present study investigated behaviour in a two-compartment free-exploration open field by means of a component analysis. Seven spontaneously hypertensive rats (SHR) and six normotensive Wistar Kyoto control rats (WKY) were tested repeatedly on eight behaviour parameters in this apparatus. A two-compartment free-exploration open field evokes less fear than the standard one-compartment forced-exploration open field, because it permits the rat to enter the field from its home cage. The data were subjected to principal component analysis and multivariate analysis of variance. The results showed that the recorded behaviour grouped into two independent components, encompassing behaviour in the cage and in the field, respectively. These components are interpreted as reflecting different kinds of exploration: (i) distant exploration when the rat explores from its home cage, and (ii) close exploration when the rat explores by entering the novel field. The SHR scored highest on both, although they mostly used close exploration. In the WKY rats, which mainly stayed in their cages, distant exploration was predominant. The present free-exploration open-field procedure discriminates between two different exploration strategies employed by SHR and WKY rats.