In this article http://www.nature.com/neuro/journal/v17/n9/full/nn.3778.html it states that
Increased promoter methylation of the serotonin transporter gene predicted increased threat related amygdala activity.
I'm finding this somewhat difficult to understand. Increased promoter methylation would imply that the serotonin transporter gene is less expressed, so less serotonin is taken up by the presynaptic neuron, leading to increased serotonin levels in the synaptic cleft. Surely the increased serotonin levels would lead to decreased amygdala response to threat? After all, selective serotonin reputable inhibitors (SSRIs) are used to treat anxiety disorders and depression by reducing uptake of serotonin and increasing serotonin levels as well. It seems like these two are suggesting two contrasting effects for the same cause?
I would be grateful if someone could point out where I have misunderstood. Thank you in advance :)