Brain and Violence: New Clues
Researchers at the Hopkins University created mice with a missing gene, which is responsible for the synthesis of Nitric Oxide (NO). These animals were apparently normal, but they presented violent behavior, viciously attacking other mice. They also exhibited a high degree of sexual persistence toward females mice.
Nitric oxide (NO) is a neurotransmitter found in regions of the brain that, among other functions, regulates the emotional behavior. S. Snyder believes that NO imposes a break in the social behavior. Without this break, the mouse does not recognizes the signal of the female rejecting them, or of males that are not wanting to fight.
Nature 378, 383-386, 1995