Serum estradiol levels and ethanol-induced aggression

The biological mechanisms behind ethanol-induced aggression are not known. Because gonadal hormones are linked both to aggression and ethanol, the present study examined relationships among the levels of serum estradiol (E₂), testosterone (T), and aggressive behavior in ethanol-treated male mice. We found that among group-housed male mice, serum E₂ levels were significantly elevated 30 min after a single injection of 0.6 g/kg ethanol. Serum T levels showed a nonsignificant decrease by ethanol. The E₂/T ratio, an index of aromatization of T to E₂, was significantly higher in the ethanol-treated animals when compared with the vehicle-treated animals. We also determined aggressive behavior in the resident-intruder test among isolated male mice at baseline (after a vehicle), and after an injection of 0.6 g/kg ethanol. The mice were grouped accordingly to those that increased, decreased, or remained nonaggressive in response to ethanol administration. We found that at baseline, neither serum T or E₂ levels, nor E₂/T ratio differed significantly between the increased or reduced aggressor mice. In contrast to the increase in serum E₂ levels seen in the nonaggressive mice, ethanol significantly reduced circulating E₂ levels, but did not affect aromatization of E₂ from T in the mice that became aggressive following an ethanol injection. These data suggest that mice who exhibit a paradoxical decrease in serum E₂ levels by ethanol may be particularly prone to ethanol-induced aggression.