Object preference and nicotine consumption in rats with high vs. low rearing activity in a novel open field

Our previous work has shown that normal male wistar rats can differ systematically with respect to rearing activity in a novel open field: animals with high rearing activity (HRA rats) differed from those with low rearing activity (LRA rats) in dopaminergic and cholinergic brain activity, as well as in their behavioral responsiveness to a cholinergic antagonist, but not in measures of anxiety in the elevated plus-maze. Here, we tested (a) whether HRA vs. LRA reflects responsiveness to novelty, (b) whether such rats voluntarily consume different amounts of the cholinergic agonist nicotine and (c) whether these measures are related to those of anxiety in the plus-maze. Using a novel object test, we found that HRA showed a trend for more object exploration than LRA rats when confronted with two identical novel objects in a familiar open field. When subsequently confronted with a familiar vs. a new object, HRA rats showed substantially more exploration of the new but not of the familiar object than LRA rats. In a subsequent test, HRA vs. LRA rats did not differ in voluntary or forced consumption of oral nicotine, or water. In contrast to rearing activity in a novel open field, measures of anxiety in the plus-maze were neither related to behavior in the novel object test nor to voluntary oral consumption of nicotine, or water. Among others, these data are discussed with respect to dopaminergic and cholinergic forebrain mechanisms, which have previously been found to differ between HRA and LRA rats. Since forebrain dopamine and acetylcholine functions are critical for novelty processing, we suggest that they are also important for the differential behavioral patterns of HRA and LRA rats in the open field, and in the novel object test.