Social attraction between rats in open field: long-term consequences of kindled seizures

Kindling of the amygdaloid complex in rats results in an enhanced emotionality frequently expressed by an elevated anxiety and defensive attitude toward other animals. Defensive attitude may have important consequences in social context and if tested in a large space it may eventually lead to social withdrawal. To test this hypothesis, rats were subjected to daily kindling sessions and their behavior was compared to implanted-sham and intact rats. Blood was collected after selected kindling trials for assessment of corticosterone response. Behavioral tests started 1 month after the last kindling trial and consisted of two open field sessions. A solitary rat was tested in the 1st session and pair of rats was tested simultaneously in the second session. Results showed that kindling changed the balance between exploration and occupation of a home base (HB) in the open field, in favor of higher preference of the home base occupancy. These results were apparent only during the social session leading to the conclusion that rats preferred to stay in the home base to maximize the proximity to a partner rat. This was supported by the observation that by increasing the occupancy of the HB, the kindled rats accomplished the longest concurrent presence with the partner rat in the common HB. We discuss the level of inter-rats aggression as a factor defining whether the anxious kindled rats will respond with increased or decreased social attraction in the open field test.