Recent Research
Recent years have seen researchers looking at genes that may play a role in depression.
Hundreds of genes on a wide range of chromosomes have been investigated.
Unfortunately it has not been possible to identify areas that increase the risk of depression with any degree of certainty.
Still, the gene for the actual serotonin transporter is still the subject of immense interest in research circles.
Antidepressant medications
Here you can read about the two main types of antidepressant medication:
- Tricyclic antidepressants (the original drugs)
- SSRIs (Selective Serotonin Reuptake Inhibitors)
The first antidepressants were discovered by chance in the late 1950s and are known as the tricyclic antidepressants.
At that time it was not known how they worked. After a few years of research it was discovered that tricyclic antidepressants:
- Inhibited a sodium transport mechanism in the cells of the heart
- Inhibited histaminergic, cholinergic and adrenergic receptors
- Acted on the serotonergic and adrenergic nerve endings to inhibit the reuptake mechanisms that cleared serotonin and noradrenaline from the synaptic cleft
It was not possible to know beforehand which of these actions were related to the antidepressant effect. But it has since emerged that the following played the key role in the antidepressant effect:
- The inhibition of the reuptake of serotonin and noradrenaline
- The other actions led to side effects.
The side effects of tricyclic antidepressants are as follows:
- Reduced saliva production
- Unpleasantly dry mouth
- Inhibition of the muscles in the eye, making it difficult to focus
- Inhibition of movement in the intestine, resulting in constipation
- Inhibition of the histaminergic receptors, resulting in drowsiness and weight gain
- Inhibition of the adrenergic receptors, leading to sudden drops in blood pressure when moving from a sitting or lying position, dizziness and fainting, and contributing to falls in the elderly
- Inhibition of sodium transport in the heart cells, which is the most dangerous side effect and can disrupt the normal rhythm of the heart - a side-effect that has unfortunately led to death in overdose.