Jennifer Viegas, Discovery News reports:




Jan. 25, 2008 -- Feline defensive rage, the aggressive cat behavior that recently led to the death of a California zoo visitor by a tiger that felt threatened, is comparable to human rage, both in the way that it emerges and unleashes in the brain, suggests a new study.


Because scientists are gaining a better understanding of the mammalian brain's recipe for rage, violent behavior in humans and other mammals may one day be quelled with improved drug therapies.


For cats, such a drug could prevent the hissing, back arching, ear retraction, claw extensions and fur standing-on-end that are typical indicators of feline defensive rage. In humans, related anger reveals itself with road rage, an impulsive form of anger that involves little or no thought.


"In road rage, the person never thinks about what he is doing but just acts in the way he does because he feels that he has been threatened by someone else and the impulsive behavior represents a way by which he can protect himself from such a threat," co-author Allan Siegel told Discovery News.


"In reality, his actions are usually much more dangerous to him than to the person whom he perceived cut him off on the road," added Siegel, a professor in the Department of Neurology & Neurosciences at New Jersey Medical School in Newark.


Prior studies have suggested that anger is centered in the medial hypothalamus region of the brain, more colloquially known as the midbrain's gray matter. Siegel and his team can even artificially induce anger in cats by electrically stimulating this brain region.


The researchers suspected that certain proteins help to control the process, so after electronically creating feline defensive rage in 10 adult female cats, they introduced a protein, called an interleukin, into the anger region of the cats' brains. As predicted, it fueled the felines' rage.


Siegel explained that the protein somehow attaches to a serotonin receptor. Serotonin is a critical neurotransmitter that helps inhibit everything from sleep to vomiting to sex and hunger in humans.


For anger, the interleukin reacts with the serotonin, causing the neuron to which the serotonin is attached to discharge. Before long, many neurons in the region start to discharge at a high rate, causing the individual to fall into a rage and behave defensively.



The findings have been accepted for publication in the journal Brain, Behavior, and Immunity.
Since scientists now have a better understanding of how anger manifests in the brain, the researchers can focus on developing drugs that prevent the rage process from erupting in the first place.


Illegal drugs like cocaine, however, may stimulate the development of anger in the brain, as may alcohol. In both instances, the substances cross the blood brain barrier that normally keeps infectious and dangerous things away from the brain, but isn't impervious to all materials.
Tumors or other brain disorders affecting the hypothalamus can also lead "to spontaneous and impulsive acts of violence and rage," according to Siegel, who added that he thought "there was nothing wrong with the brain of the tiger that attacked the teenagers."


Because wild cats are very territorial, he believes the zoo tiger felt threatened and acted aggressively in response, as it would have done in the wild if faced with intruders.


Hreday Sapru, director of Neurosurgical Laboratories at the New Jersey Medical School, who did not participate in the research, agreed with the findings outlined in the new study.
Because of these determinations, Sapru agreed "there is a possibility that new targets for therapeutic management of aggressive behavior in humans can be developed."


"In addition," Sapru added, "this discovery may provide a basis for future studies that will unravel the underlying mechanisms of aggression and other related behaviors in animals."