Bidirectional Selective Breeding for Ethanol Effects on Locomotor Activity: Characterization of FAST and SLOW Mice Through Selection Generation 35

Increased recognition of the advantages of genetic animal models has led to heightened interest in their use and development. A replicated bidirectional selective breeding project has produced lines of mice that differ in their locomotor responses to 2.0 g/kg ethanol. FAST‐1 and FAST‐2 mice are highly stimulated by ethanol (EtOH), whereas SLOW‐1 and SLOW‐2 mice are either not affected or respond with locomotor depression. Current heritability estimates indicate that ±6–8% of the response variance in the FAST lines and 2–10% of the response variance in the SLOW lines is of additive genetic origin. Little systematic response to selection has occurred in recent generations, which implies that the limits of selection have been reached. Analysis of saline activity over 35 generations of selection indicates that baseline activities have not changed during the course of selection in three of the lines, whereas baseline activity of FAST‐1 mice has increased slightly. In EtOH dose‐response studies (0.5–3.0 g/kg), FAST mice had biphasic dose‐response curves, whereas the locomotor activity of SLOW mice was either unaffected or depressed by all doses of EtOH. In addition, FAST mice spent more time in motion, traveled farther per movement, traversed greater distances in the center of the test chamber, and ambulated more quickly than SLOW mice when given EtOH. FAST and SLOW mice differed in EtOH clearance rates; however, the differences were slight relative to the large difference in locomotor response. We encourage the use of FAST and SLOW mice to investigate neurophysiological factors underlying sensitivity to the behavioral effects of EtOH, with a view to further testing of the postulated homology between locomotor stimulant effects and addiction potential of drugs of abuse.