Open Field Behaviors Correlated with Reward Availability and Reward Shift in Three Rat Strains

Abstract

Rats derived from Wistar (W), Sprague-Dawley (SD), and Long-Evans hooded (LE) strains were placed in an open field for 5 min per day under three conditions: habituation (4 days), preshift (10 days), in which half of each strain was given access to a 32% sucrose solution and half to 4% solution, and postshift (4 days) in which all rats received the 4% solution. Individual and multivariate analyses of 10 dependent variables indicated reliable strain differences in the way the animals allocated their time in various stages of the experiment. In particular, the availability of different sucrose solutions exerted the greatest effect on the response patterns of the SD rats and the least on the W rats, the SD rats tended to ambulate more when sucrose was not available, and the LE rats engaged in the most rearing behavior. Some behavioral categories were sensitive to the stage of the experiment but not to the strain differences. All strains responded similarly to a shift in sucrose solutions and to the availability of sucrose in novel locations during the postshift period. Implications of these data for strain differences and similarities, obtained in operant and other situations, were considered.