Behavior and the balance between norepinephrine and serotonin

The functions of the central monoamines Norepinephrine (NE) and Serotonin (5HT) can be clarified by the study of behaviors of rats administered selective monoamine toxins. In his home environment the low NE rat has drive deficits and is lethargic, tending to remain in his burrow, but in novel environments this animal acts less frightened than Controls. The low 5HT rat is conversely active and exploratory in familiar environments but frightened in novel environments. These two animals model aspects of depression and anxiety, respectively. 5HT can be thought of as placing the brain into a state of consciousness appropriate for an animal in his nest (i.e., 5HT neurons act as relaxers), and as involved in a type of positive affect related to security, whereas NE neurons are dominant when an animal is vigilant, foraging out in the environment and are involved in a type of positive affect related to goal-directed approach arousal. Monoamine toxins may be produced when the behaviors elicited by these central neuronal systems are negatively reinforced (extinguished).