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

Abstract

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.