Selective breeding for negative contrast in consummatory behavior.

Rats showing either large or small reductions in licking following a shift from 32% to 4% sucrose were selectively bred for 7 generations. Rats from the 2 resulting lines reliably differed in successive negative contrast and in activity (radial-arm maze and open field). Differences in activity and contrast were not correlated. Heritability (h2) of the reaction to sucrose shift was reliable in the last 6 filial generations and equaled 0.64 in the F7 generation. The 2 lines did not differ (a) in response to the absolute rewarding value of sucrose or cocaine; (b) in open-field defecations or thigmotaxis; (c) in anticipatory contrast; or (d) in responsivity to midazolam. Responsivity to reward reduction may involve a relatively delimited psychological process that is amenable to selection.