Labyrinth exploration, emotional reactivity, and conditioned fear in young Roman/Verh inbred rats.

An inbreeding program has been carried out with the Swiss sublines of Roman high- and low-avoidance rats since 1993. The present study reports the first experiments conducted with young animals of those inbred strains (RHA-I/Verh and RLA-I/Verh, respectively) from the sixth and seventh inbreeding generations. The results confirmed expected behavioral profiles. Compared to the RHA-I/Verh strain, RLA-I/Verh rats showed decreased entries into the illuminated central arena of an hexagonal tunnel maze, as well as decreased spontaneous locomotor activity and increased defecations, in two independent experiments. Young RLA-I/Verh females explored less than did their RHA-I/Verh counterparts during session 1 of a conditioned-fear experiment preceding shock administration, and in session 2 (conducted 24 h after the application of three footshocks), they showed greater conditioned behavioral inhibition (i.e., reduced amount of rearing), as well as higher defecation scores, than did RHA-I/Verh females.