Serotonin is part of the brain's internal communication system. It's a neurotransmitter, meaning it helps the brain cells, or neurons, send information to each other. Specifically, serotonin signals brain cells that an individual feels relaxed and happy. When the brain produces low levels of serotonin, such signals become much more infrequent and shorter-lived, producing psychiatric disease processes including depression and anxiety, obsessive-compulsive disorder, and addiction.
Depression and Anxiety
Among the earliest-recognized of the serotonin-related disease processes was depression. While low serotonin levels don't necessarily mean that an individual will be depressed, Bryn Mawr University points out that researchers have found that low levels of the neurotransmitter predispose individuals toward depression. Pharmaceutical researchers treat such depression with drugs that help to increase the lifetime of serotonin in the neural synapses of the brain, or spaces between the neurons. Older drugs prevent enzymes called monoamine oxidases from breaking down serotonin, while newer drugs, like Prozac, prevent neurons from taking serotonin out of the synapses for recycling purposes. Macalester University notes that serotonin also plays a role in anxiety; individuals with low serotonin levels are more likely to experience anxiety to an unusual or troubling degree, and psychiatric diagnoses such as social anxiety disorder may be treatable using serotonin-increasing drugs.
The American Academy of Family Physicians points out that another of the major psychiatric disease processes that occurs as a result of serotonin imbalances in the brain is obsessive-compulsive disorder. Serotonin doesn't just produce feelings of happiness; it also helps individuals feel content and secure in their environments. It appears that in the absence of appropriate concentrations of serotonin, patients can feel very uncomfortable in the world, leading them to obsess about particular issues or concerns. Common obsessions include, for instance, numbers or cleanliness. The obsession results in a compulsive behavior. Patients obsessed with numbers might count sounds, times a light is turned on or off, or times they open or close a door. Patients typically feel they have to count a certain number of sounds before they can enter or exit a room. Cleanliness compulsion might lead to obsessive hand washing or cleaning.
One of the most recent of the disorders to be identified as related to serotonin is addiction. Wellesley University notes that recent research has revealed a connection between serotonin and a process once thought to be related strictly to concentrations of another neurotransmitter, dopamine. In fact, researchers, are determining, serotonin and dopamine work closely with one another in many psychological processes. While dopamine-deficient mice have long been known to be predisposed to addiction, serotonin-deficient mice share the same traits, leading researchers to conjecture that individuals born with "addictive personalities" might well be serotonin deficient, dopamine deficient, or both.