Effects of rearing in different environments on subsequent environmental preference in rats

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Abstract
Environmental preference of male rats reared during 2 months after weaning either in a complex and changing environment (EC) or in empty laboratory cages (SC) was assessed in 4 different experiments. For 2 weeks after differential rearing, rats were placed in groups of 6 in testing cages which were divided into 2 compartments with communicating holes. One of these compartments was empty; the other contained 6 objects (complex compartment). Daily, 3 objects were moved from 1 compartment to the other and replaced by new ones. The preference for any of the compartments was chiefly assessed by the localization of feces (Experiments I and II) and directly by the localization of the animals through videorecording (Experiments III and II) and directly by the localization of the animals through videorecording (Experiments III and IV). Both EC and SC rats showed a significant preference for the empty compartment during both light and dark portions of the daily cycle, but particularly during the light portion. Moreover, EC and SC animals differed from one another in that the SC rats showed a stronger preference for the empty compartment than the EC rats, especially when active. General preference for the empty compartment seemed to diminish slowly, but EC and SC rats tended to remain distinct in habitat selection, at least during the period tested. This behavioral difference, tentatively interpreted in terms of neophobia, might constitute a possible mechanism for automaintenance of differential rearing effects.