The treatment of depression was revolutionised in the 1980s by the introduction of drugs that increased levels of the neurotransmitter serotonin. At the time it was thought that such drugs would help 80-90% of depressed people. However this has not proved to be the case and a recent article in New Scientist reports that, if anything, such serotonin-boosting drugs appear to be becoming even less effective and untreatable depression is on the rise (you can read the article here, ‘A new understanding of depression’ by Samantha Murray).
The role of serotonin was challenged in a study that found depressed patients who did not received drug treatment had serotonin levels that were twice as high as those receiving drugs to boost serotonin levels.
One possible new candidate is the neurotransmitter ketamine, which has been found, in small scale studies, to have benefits for depressed patients. This may be because ketamine plays a key role in brain activity but most importantly it may help the brain’s neurons repair themselves. The usefulness of glutamate would fit with a theory that suggests that depression causes some dendrites to shrivel and what happens at the synapses of depressed individuals is that they fail to function – they are like broken bridges. Enhancing serotonin at synapses kind of works because it improves transmission across these ‘broken bridges’, however glutamate might be more effective because it would repair the broken bridges. A number of drug companies are currently investigating the usefulness of ketamine in treating depression.
The New Scientist article also discusses the use of transcranial magnetic stimulation.