Genetically selected winner and loser rats: what was selected?

Area of Science:

• Behavioral neuroscience
• Animal behavior genetics
• Stress physiology

Background:

• The straight runway test is used to select for behavioral traits in rats.
• Previous studies have not fully characterized the physiological and behavioral differences between selected strains.

Purpose of the Study:

• To investigate the phenotypic differences between genetically selected Winner Runway Strain (WRS) and Loser Runway Strain (LRS) rats.
• To assess if selection for runway performance reflects social dominance or sex-linked characteristics.

Main Methods:

• Generations 6-12 of WRS and LRS rats were studied.
• Evaluations included body weight, open field behavior, responses to footshock, and adrenocortical (corticosterone) levels.

Main Results:

• Loser Runway Strain (LRS) rats were lighter than Winner Runway Strain (WRS) rats.
• LRS rats displayed increased ambulation and rearing in open fields, and reduced defecation.
• LRS rats showed increased jumping behavior and elevated corticosterone levels following stress (footshock or handling) compared to WRS rats.

Conclusions:

• The observed differences between WRS and LRS rats mirror those typically found between male and female rats.
• The runway test may select for sex-linked traits rather than true 'winning' or 'losing' characteristics.
• The validity of the runway test as a measure of social behavior is questioned.