Further evidence for the role of nitric oxide in maternal aggression: effects of L-NAME on maternal aggression towards female intruders in Wistar rats

It has been shown that nitric oxide (NO) increases aggression inmale mice, whereas it decreases aggression in lactating femalemice and prairie voles. It is also known that aggression can beexhibited at different levels in rodent species, strain or subtypes.The aims of this study were to investigate the proportion ofaggressiveness in Wistar rats, the effect of intraperitoneallyadministered nonspecific nitric oxide synthase (NOS) inhibitorL-NAME (NG-nitro L-arginine methyl ester) on maternal aggressiontowards female intruders, and whether these effects are due to NOproduction or not. Rats were given saline intraperitoneally on thepostpartum Day 2 and aggression levels were recorded. The samerats were given 60 mg/kg L-NAME or D-NAME (NG-nitro D-arginine methyl ester) on the postpartum Day 3 and their effects onaggression levels were compared to saline. While L-NAMEadministration did not cause any differences in the total number ofaggressive behavior, aggression duration and aggression intensity,it reduced the proportion of animals showing aggressive behavior.In addition, the latency of the first aggression was significantlyincreased by L-NAME. In the D-NAME group, however, nosignificant change was found. Our results have shown that L-NAMEreduces maternal aggression towards female intruders in Wistarrats through inhibition of NO production. These results suggest thatthe role of NO in offensive and defensive maternal aggressionshares neural mechanisms.