Antidepressant treatment effects on dopamine transporter availability in patients with major depression: a prospective 123I-FP-CIT SPECT imaging genetic study

Dopamine in major depressive disorder: A systematic review and meta-analysis of in vivo imaging studies

BACKGROUND

Major depressive disorder (MDD) is a leading cause of global disability. Several lines of evidence implicate the dopamine system in its pathophysiology. However, the magnitude and consistency of the findings are unknown. We address this by systematically reviewing in vivo imaging evidence for dopamine measures in MDD and meta-analysing these where there are sufficient studies.

METHODS

Studies investigating the dopaminergic system using positron emission tomography or single photon emission computed tomography in MDD and a control group were included. Demographic, clinical and imaging measures were extracted from each study, and meta-analyses and sensitivity analyses were conducted.

RESULTS

We identified 43 studies including 662 patients and 801 controls. Meta-analysis of 38 studies showed no difference in mean or mean variability of striatal D2/3 receptor availability (g = 0.06, p = 0.620), or combined dopamine synthesis and release capacity (g = 0.19, p = 0.309). Dopamine transporter (DAT) availability was lower in the MDD group in studies using DAT selective tracers (g = -0.56, p = 0.006), but not when tracers with an affinity for serotonin transporters were included (g = -0.21, p = 0.420). Subgroup analysis showed greater dopamine release (g = 0.49, p = 0.030), but no difference in dopamine synthesis capacity (g = -0.21, p = 0.434) in the MDD group. Striatal D1 receptor availability was lower in patients with MDD in two studies.

CONCLUSIONS

The meta-analysis indicates striatal DAT availability is lower, but D2/3 receptor availability is not altered in people with MDD compared to healthy controls. There may be greater dopamine release and lower striatal D1 receptors in MDD, although further studies are warranted. We discuss factors associated with these findings, discrepancies with preclinical literature and implications for future research.

The 3'UTR VNTR SLC6A3 Genetic Variant and Major Depressive Disorder: A Systematic Review

Major Depressive Disorder (MDD) is a disabling and particularly persistent mental disorder that is considered to be a priority public health problem. The active human dopamine transporter (DAT), which is encoded by the SLC6A3 gene, regulates the dopamine concentration in the synaptic cleft. In this sense, this neurotransmitter is primordial in modulating human emotions. This systematic review aims to verify the SLC6A3 (DAT1) 3'UTR VNTR (rs28363170) gene variant's SS (9R/9R) genotype and S (9R) allele frequency fluctuation and its influence on the modulation of pharmacotherapy in MDD. For this purpose, we searched different databases, and after applying the eligibility criteria, six articles were selected. Studies have shown an association between the SS (9R/9R) genotypic and S (9R) allelic presence with the risk of developing MDD, in addition to influencing the decrease in response to antidepressant therapy. However, despite the findings, disagreements were observed between other studies. For this reason, further studies with the SLC6A3 3'UTR VNTR (rs28363170) variant in different populations are necessary to understand this polymorphism's role in the onset of this disease.

Altered levels of dopamine transporter in the frontal pole and the striatum in mood disorders: A postmortem study

Dopamine dysregulation is known to play a major role in the pathophysiology of major depressive disorders (MDD) and bipolar disorders (BD). The dopamine transporter (DAT) plays a critical role in regulating dopamine concentration at the synaptic cleft and therefore could have an important role in the molecular pathology of MDD and BD. To test this hypothesis, we measured levels of [³H]mazindol binding to DAT in Brodmann's area (BA) 10, BA 17 as well as in the dorsal and ventral striatum from 15 controls, 15 patients with MDD and 15 patients with BD, obtained postmortem, using in situ radioligand binding with autoradiography. Compared to controls, levels of [³H]mazindol binding to DAT was significantly higher in BA10 from patients with MDD but not BD. There was no significant difference in [³H]mazindol binding to DAT in BA 17 or the dorsal and ventral striatum from patients with MDD or BD. In addition, levels of [³H]mazindol binding show no correlation with donor age, postmortem interval, tissue pH, sex or duration of illness. In conclusion, our data suggest that changes in levels of DAT may be selectively affecting dopamine homeostasis in BA 10 in patients with MDD.

Intrinsic Alertness Is Impaired in Patients with Nigrostriatal Degeneration: A Prospective Study with Reference to [123I]FP-CIT SPECT and [18F]FDG PET

BACKGROUND

Variations in alertness and attention are common in Lewy body diseases (LBD) and among the core features of dementia with Lewy bodies (DLB). Dopamine transporter SPECT is an accurate biomarker of nigrostriatal degeneration (NSD) in LBD.

OBJECTIVE

The present study investigated performance on a computerized alertness test as a potential measure of attention in patients with NSD compared to patients without NSD.

METHODS

Thirty-six patients with cognitive impairment plus at least one core feature of DLB referred for [123I]FP-CIT SPECT imaging were prospectively recruited. Performance in a computerized test of intrinsic alertness was compared between patients with and those without NSD as assessed by [123I]FP-CIT SPECT.

RESULTS

Reaction times to auditory stimuli (adjusted for age, sex, and education) were significantly longer in patients with NSD compared to those with a normal [123I]FP-CIT SPECT scan (p < 0.05). Statistical analyses revealed no significant differences comparing reaction times to visual stimuli or dispersion of reaction times between groups. Exploratory analysis in a subgroup of patients with available [18F]FDG PET revealed that longer reaction times were associated with decreased glucose metabolism in the prefrontal cortex (statistical parametric mapping, adjusted for age and sex; p < 0.005, cluster extent > 50 voxels).

CONCLUSION

Computerized assessment of auditory reaction times is able to detect alertness deficits in patients with NSD and might help to measure alertness deficits in patients with LBD and NSD. Future studies in larger samples are needed to evaluate the diagnostic utility of computerized alertness assessment for the differential diagnosis of LBD.

Update on PET imaging biomarkers in the diagnosis of neuropsychiatric disorders

PURPOSE OF REVIEW

To give an update on recent imaging studies probing positron emission tomography (PET) as a tool for improving biomarker-guided diagnosis of neuropsychiatric disorders.

RECENT FINDINGS

Several studies confirmed the value of imaging of regional neuronal activity and imaging of dopaminergic, serotonergic, and other neuroreceptor function in the diagnostic process of neuropsychiatric disorders, particularly schizophrenia, depression/bipolar disorder, substance use disorders, obsessive compulsive disorders (OCD), and attention-deficit/hyperactivity disorder. Additionally, imaging brain microglial activation using translocator protein 18 kDa (TSPO) radiotracer allows for unique in-vivo insights into pathophysiological neuroinflammatory changes underlying schizophrenia, affective disorders, and OCD.

SUMMARY

The role of PET imaging in the biomarker-guided diagnostic process of neuropsychiatric disorders has been increasingly acknowledged in recent years. Future prospective studies are needed to define the value of PET imaging for diagnosis, treatment decisions, and prognosis in neuropsychiatric disorders.