Effects of nicotine on target biting and resident-intruder attack.

The effects of acute administration of nicotine on target biting (defensive) and resident-intruder (offensive) attack of male mice were assessed. In the target biting procedure confined mice received tail shock on a fixed time, 2-min schedule. Under baseline conditions, biting attack directed toward an inanimate target occurred at three distinct rates. A high target biting rate (13.5 +/- 3.8 bites/15 sec) followed shock delivery, an intermediate biting rate (9.6 +/- 4.1 bites/15 sec) occurred during the inter-shock interval, and a low biting rate (1.0 +/- 0.5 bites/15 sec) occurred during a tone stimulus which signalled the impending shock. Nicotine (administered IP, 15 min presession) reduced post-shock and inter-shock interval target biting in a dose-dependent manner (ED50 values estimated at 0.13 and 0.14 mg/kg, respectively) but exerted more variable effects on target biting during the tone. In the resident-intruder paradigm the same mice were exposed to an intruder introduced into its home cage for a 10-min test session. Under baseline conditions, residents directed 20 +/- 3.2 biting attacks toward the intruder during the session with an average latency of 89 +/- 40 sec to the first attack. Nicotine caused a dose-dependent decrease in this attack behavior (ED50 values estimated to be 0.48 and 0.49 mg/kg, respectively). These observations are interpreted to indicate that nicotine has an increased potency at reducing "defensive" aggression.