Inhibitory influence of dihydroergosine on the aggressiveness of rats and mice.

Fifty mg/kg of ergot alkaloid dihydroergosine (DHESN) inhibited the mouse-killing behavior of isolated male rats, while 10 mg/kg did not. This effect of DHESN (50 mg/kg) lasted for 24 hr. When an additional injection of DHESN (50 mg/kg) was given to mouse-killer rats 6 days following the first, the mouse-killing behavior was again inhibited. The effect of the second drug injection also persisted for 24 hr and was accompanied by an increased concentration of 5-HT in the raphe nuclei and hypothalamus and by a decreased concentration of GABA in the olfactory bulbs. DHESN also inhibited aggressiveness in isolated mice. Two hr following the administration of 10 mg/kg DHESN the fighting was inhibited in 46% of pairs tested, while 50 mg/kg abolished it completely. The effect of 50 mg/kg lasted 24 hr. These results, showing the antiaggressive effects of DHESN, support our previous suggestion that DHESN might presumably be a new antidepressant, and suggest that besides the serotoninergic, the GABA-ergic system might also be involved in the modification of behavior induced by this drug.