Clinical SPECT Studies of Depression

Serotonin and dopamine transporters

Drugs targeted at the synaptic reuptake sites (transporters) for serotonin and noradrenaline are highly effective treatments for the majority of patients with unipolar depression. Nevertheless, following the first year of treatment 20% of depressed patients remain ill, 30% experience residual symptoms and ultimately 30% of all those treated remain symptomatic and disabled. The cause of treatment resistance is not known and treatment resistant depression remains a significant mental health problem. A greater understanding of the biological mechanisms of response to currently available drugs in the human brain is required. We are using SPECT imaging with tracers specifically targeted at transporters to investigate treatment-resistant depression.

[123 I] beta-carbomethoxy-3beta-(4 iodophenyl)tropane - [123 I] beta-CIT, is a tracer that has been validated for imaging serotonin transporters (SERT). We have used this tracer to investigate treatment responders and non-responders during long-term antidepressant treatment

Patient with high [123 I] beta-CIT availability

Patient with high [123 I] beta-CIT availability

There was no difference in SERT availability between responders and non-responders. However, there was considerable variability in SERT availability in both groups of patients, all of whom were receiving antidepressant medication.

Nicotinic receptors

123I-5IA85380 in a depressed patient : a pilot study is currently underway.

The distribution of 123I-5IA85380 in vivo concords with our previous characterisation in human postmortem brain by autoradiography binding levels being highest in the midbrain.