Selection of Laboratory Mice for the High Scores of Logic Task Solutions: The Correlated Changes in Behavior

Genetically heterogenous mouse population served as the basis for experiment designed to select mice for the high levels of extrapolation ability. Extrapolation task (which belongs to the category of cognitive tasks) was the following: hungry and thirsty mouse was placed in the experimental box facing the cup with milk which could be reached via the small opening in the frontal wall. After several seconds of drinking the food moved behind this wall to the right or to the left and disappeared from animal view. Mouse can find the food only if it moves in the direction of food movement. The direction could be chosen at random or based on animal apprehension of elementary logic of this task. Mice were selected not only for high scores of this task solution but also for lack of anxiety signs during test performance. Extrapolation task scores in selected strain mice were above the chance levels in F9 but non-significantly different from those of control unselected mouse population. The performance of F9 mice in the “puzzle box” cognitive test, based on animal tendency to avoid the brightly lit area in the dark compartment with increasing “difficulty” of reaching this compartment, was measured as mean escape latencies of the respective group. The latencies of mice from selected strain were significantly shorter than those of control animals. This fact is interpreted as the sign that the selection for one cognitive trait (yet still not efficient) resulted in positive changes in the ability to solve another cognitive task. The relationship of cognitive task solutions success and anxiety behavior scores in F9 is discussed.

Mice selected for large and small brain weight: The preservation of trait differences after the selection was discontinued

The selection for large and small relative brain weight (RBW) in mice, started in 1999, resulted in stable significant differences in the trait (16%). The selection was discontinued at F22, and both lines (Large Brain, LB and Small brain, SB) were maintained by random mating. In F25-F28 the significant differences in RBW were still present in spite of the lack of selection. In F28 ethanol injections (2.4 mg/kg, 12% ethanol, i.p.) were performed to animals of both lines. The ethanol effects were more intense in SB, than in LB line. Mice were tested in elevated and closed plus-mazes and in slip-funnel tests. Control LB mice explored new environment more actively and were less affected by stressful environment than SBs. SB ethanol mice were less anxious in elevated plus maze, initiated closed maze exploration earlier, moved more vividly and demonstrated lower anxiety level in elevated plus maze than saline injected mice, while changes in these behaviors after ethanol were not so clear in LB mice, although their locomotion level increased.