5-HT(1B) receptors, ventral orbitofrontal cortex, and aggressive behavior in mice.

RATIONALE: Systemic injections of 5-HT(1B) receptor agonists have been shown to have specific anti-aggressive effects in aggressive individuals. One site of action for these drugs is the 5-HT(1B) receptors in the ventral orbitofrontal cortex (VO PFC), an area that has been implicated in the inhibitory control of behavior and is a terminal region for 5-HT projections. OBJECTIVE: To assess the anti-aggressive effects of the 5-HT(1B) receptor agonist CP-94,253 when microinjected into the VO PFC (0.1, 0.56, and 1.0 microg/0.2 microl) or into the infralimbic prefrontal cortex (IL PFC; 1.0 microg/0.2 microl) in separate groups of aggressive resident male mice. To confirm the 5-HT(1B) receptor as the critical site of action for the anti-aggressive effects, the 5-HT(1B/D) antagonist GR-127,935 was microinjected at 10.0 microg/0.2 microl into the VO PFC. After recovery from surgery, the anti-aggressive effects of microinjected CP-94,253 were studied during 5-min resident-intruder confrontations that were recorded and analyzed. RESULTS: Microinjections of CP-94,253 (0.56 and 1.0 microg/0.2 microl) dose-dependently reduced the frequency of attack bites and sideways threats. This effect was behaviorally specific because non-aggressive motor activities were not significantly altered by the drug. In the IL vmPFC or in an area lateral to the VO PFC, CP-94,253 (1.0 microg/0.2 microl) did not have significant behavioral effects. CONCLUSIONS: The results highlight the 5-HT(1B) receptors in the VO PFC as a particularly important site for the inhibition of species-typical aggressive behavior in male mice.

Flunitrazepam in combination with alcohol engenders high levels of aggression in mice and rats.

RATIONALE: Higher doses of benzodiazepines and alcohol induce sedation and sleep; however, in low to moderate doses these drugs can increase aggressive behavior. OBJECTIVES: To assess firstly the effects of ethanol, secondly the effects of flunitrazepam, a so-called club drug, and thirdly the effects of flunitrazepam plus alcohol on aggression in mice and rats. METHODS: Exhaustive behavioral records of confrontations between a male resident and a male intruder were obtained twice a week, using CF-1 mice and Wistar rats. The salient aggressive and non-aggressive elements in the resident's repertoire were analyzed. Initially, the effects of ethanol (1.0g/kg), and secondly flunitrazepam (0; 0.01; 0.1; and 0.3mg/kg) were determined in all mice and rats; subsequently, flunitrazepam or vehicle, given intraperitoneally (0; 0.01; 0.1; and 0.3mg/kg) was administered plus ethanol 1.0g/kg or vehicle via gavage. RESULTS: The most significant finding is the escalation of aggression after a moderate dose of ethanol, and a low dose of flunitrazepam. The largest increase in aggressive behavior occurred after combined flunitrazepam plus ethanol treatment in mice and rats. CONCLUSIONS: Ethanol can heighten aggressive behavior and flunitrazepam further increases this effect in male mice and rats.