Effects of chronic nicotine on the temporal structure of anxiety-related behavior in rats tested in hole-board.

The present study aimed to assess the behavioral effects of chronic treatments of different doses of nicotine by using both quantitative and multivariate T-pattern analysis (TPA), which can reveal hidden behavioral structures, in Sprague-Dawley rats tested in the hole-board apparatus. To this purpose, nicotine ditartrate was administered at the doses of 0.1, 0.5 and 1 mg/kg i.p., three times per day, for 14 consecutive days. As to quantitative evaluations, we observed significant reductions in the mean durations and mean frequencies of walking, climbing, immobile-sniffing and rearing in comparison to control. A significant reduction of edge-sniff and head-dip mean frequencies was also detected for all the doses tested. TPA revealed an increase in the number and the mean length of different T-patterns induced by the three doses of nicotine. On the other hand, a significant reduction of the mean occurrences of T-patterns was revealed. Overall, our results obtained by using both quantitative and T-pattern analyses indicate that chronic nicotine induces an anxiety condition characterized by a behavioral re-organization orbiting around the two main components of hole exploration, that is, head-dip and edge-sniff. A better understanding of the link between nicotine and anxiety might help to find new therapies for smoking cessation.