A brief guide to Serotonin

Medical Reviewer

A few years ago, if I mentioned serotonin to a class of 18 year olds, I would have been met by a wall of silence and maybe a question about how you spell that. Today things are different. Serotonin has found its way into the general vocabulary of many young people and we can only speculate why this might be so.

From the point of recognising the word serotonin I have found that knowledge of its role, and even what it is, varies greatly. I generally find that most student's think of it as the 'happy' stuff in the brain. I guess this isn't too bad a response and it helps to start a session. We quickly seem to establish that depression just might be something to do with a lack of whatever serotonin is. So, for the inquisitive, I thought it might be useful to post a few lines about serotonin and its role in depression.

The area of the brain associated with emotions is known as the limbic system. It is hardly surprising that a considerable amount of research has focused on the limbic system as a possible explanation for depression. Serotonin is actually one of three important chemicals called neurotransmitters that seem to have an important role in the limbic system. Incidentally, the other two neurotransmitters are called norepinephrine and dopamine. To date, most attention has been given to the role of serotonin in depression, but is worth mentioning that increased levels of dopamine are implicated in manic episodes.

Two possible processes seem to be responsible for variations in the levels of neurotransmitters. The first involves low levels of neurotransmitter being released, or too much reuptake following a nerve impulse (excess serotonin molecules are taken back up by the nerve cell and reprocessed). The second process involves the possibility of some breakdown at the junction point of nerves called the synapse. In either case the effect is that too little neurotransmitter is available.

Drugs such as fluoxetine (Prozac) work by blocking the re-uptake of serotonin. Prozac is often given as an example of an SSRI, or selective serotonin re-uptake inhibitor. In effect, it increases the levels of serotonin in the limbic system.

If depression was simply down to increasing the levels of serotonin, then a drug like Prozac should work quickly. In reality it can take a minimum of two weeks to achieve any kind of therapeutic effect, so it may be that the density or sensitivity of receptors needs to alter over time. Of course not everyone responds to a particular drug so it can take some trial and error to find if one will work for you.

Other examples of SSRIs:

Paroxetine (Paxil)

Sertraline (Zoloft)