Norepinephrine appears to be related to arousal and attention. When norepinephrine, also known as noradrenaline, is released into the brain of an animal, the animal becomes more alert and vigilant to its environment. Likewise, norepinephrine may be involved in attention deficit disorder (ADD). Norepinephrine also activates the autonomic nervous system during the fight/flight response, affecting activity in the cardiovascular, muscular, and digestive systems. In fact, beta blockers, a class of medication used to treat high blood pressure, act on the noradrenergic system, the tract of neurons that release norepinephrine. In addition, the noradrenergic system is targeted by a class of antidepressant medication known as tricyclics. This suggests that norepinephrine may also be involved in mood.