Disturbance of serotonin 5HT2 receptors in remitted patients suffering from hereditary depressive disorder

Is treatment-resistance in unipolar melancholic depression characterized by decreased serotonin₂A receptors in the dorsal prefrontal - anterior cingulate cortex?

OBJECTIVES

Quite a number of patients diagnosed with major depression are resistant to several well carried-out psychopharmacological interventions. It remains unclear as to how the serotonergic system is implicated in the phenomenon of treatment-resistance.

METHODS

We examined the involvement of post-synaptic 5-HT(2A) receptors in the pathophysiology of treatment-resistance in unipolar melancholic major depression with (123)I-5-I-R91150 SPECT. 15 antidepressant-naïve (ADN) first-episode depressed patients, 15 antidepressant-free treatment-resistant depressed (TRD) patients and 15 never-depressed individuals, matched for age and gender were studied.

RESULTS

Compared to ADN patients and healthy controls, TRD patients displayed significantly lower 5-HT(2A) receptor binding index (BI) in the dorsal regions of the prefrontal and the anterior cingulate cortex. No significant 5-HT(2A) receptor BI differences between ADN patients and controls were observed.

CONCLUSIONS

At the cortical level, 5-HT(2A) receptor BI does not significantly differ in first-episode melancholic depressed patients compared to healthy controls. This observation might imply a limited short-term impact on the serotonergic system in first episode depression. Our results also suggest that when encountered with treatment-resistance, the 5-HT(2A) receptors in the DPFC-ACC axis are significantly down-regulated. However, whether this assumed underlying pathophysiological mechanism is due solely to abnormalities in the serotonergic system remains to be answered. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Serotonin polymorphisms and posttraumatic stress disorder in a trauma exposed African American population

BACKGROUND

Genetic polymorphisms that influence serotonin (5-hydroxytryptamine, 5HT) neurotransmission are candidates for contributing to susceptibility to posttraumatic stress disorder (PTSD). The objective of our study was to determine if a variable length polymorphism for the promoter regions of the 5HT transporter (5HTTLPR), and/or a substitution polymorphism in the promoter region for the 5HT2A receptor, would be associated with PTSD in a trauma exposed population of adult African-Americans.

METHODS

Using a case control design, 118 participants recruited from the primary care clinics and the campus of a historically black university who met inclusion criteria including trauma exposure provided blood samples for genomic DNA. PTSD criteria were determined by the Clinician Assessment of PTSD Scale (CAPS) and criteria for other psychiatric disorders by the Structured Clinical Interview for DSM-IV (SCID). 5HTTLPR and 5HT2A-1438A/G were genotyped using established methods. Associations of genotypes with lifetime PTSD, and models testing associations of allele "dose", were analyzed.

RESULTS

Fifty-five (47%) participants met lifetime criteria for PTSD and 26 (22%) met criteria for (mostly comorbid) major depression. The 5HT2A (lower expressing) G allele was significantly associated with PTSD. We did not find significant associations with 5HTTLPR.

CONCLUSIONS

Our findings suggest a relationship between genetic variation in the 5HT2A promoter region and PTSD.

Decreased hippocampal 5-HT(2A) receptor binding in older depressed patients using [18F]altanserin positron emission tomography

Serotonin receptor changes have been associated with the pathophysiology and treatment of major depression. Only one other study has investigated serotonin receptor changes in older depressed patients. We used positron emission tomography (PET) and [18F]altanserin, a ligand with high affinity for the 5-HT(2A) receptor, to examine the relationship between 5-HT(2A) receptor density and depression. Depressed subjects (n = 16), age > 50 years, were recruited as part of a larger study. Older depressed subjects consisted of early-onset recurrent depression (EORD, n = 11) and late-onset depression (LOD, n = 5). An age-matched control group (n = 9) was also recruited. All subjects were right-handed, nonsmokers and antidepressant-free. Regions of interest were determined on a summed MPRAGE scan transformed into Talairach space and coregistered with the PET images. Depressed subjects had less hippocampal 5-HT(2A) receptor binding than controls (p = 0.05). No significant differences in receptor binding were found between EORD and LOD subjects. Depressed subjects not previously treated for depression (n = 6) had less hippocampal 5-HT(2A) receptor binding (p = 0.04) than previously treated subjects (n = 10). It may be that prior medication treatment provides a compensatory upregulation of the 5-HT(2A) receptor.

A database of [18F]-altanserin binding to 5-HT2A receptors in normal volunteers: normative data and relationship to physiological and demographic variables

This study presents the results of an analysis of 5-hydroxytryptamine (5-HT)(2A) receptors in 52 healthy subjects. Thirty men and twenty-two women aged between 21 and 79 years were investigated with magnetic resonance imaging (MRI) and [(18)F]-altanserin positron emission tomography (PET). The distribution volumes of specific tracer binding (DV(3)') was calculated for 15 brain regions using either cerebellum or pons as reference regions and correlations between DV(3)' and physiological and demographic variables were made. The regional distribution of [(18)F]-altanserin binding in the healthy human brain was in agreement with existing in vitro post-mortem human 5-HT(2A) data. Apart from nonspecific cerebellar binding (DV(2)), there was no gender difference in 5-HT(2A) binding. A positive correlation between cerebellar binding and age was observed and negative correlations between age and DV(3)' were found in all cortical regions, except occipital cortex, corresponding to a decrease in DV(3)' of 6% or 4% per decade with cerebellum or pons as reference regions, respectively. In several temporal and frontal cortical regions, positive correlations were found between body mass index (BMI) and DV(3)'. Our findings provide a resource to aid design of clinical studies of the 5-HT(2A) receptors. [(18)F]-altanserin binding appears to be unaffected by gender, but the effects of ageing must be considered for clinical studies. The correlations between different cortical regions' 5-HT(2A) binding and BMI should be explored in future studies.

Decreased hippocampal 5-HT2A receptor binding in major depressive disorder: in vivo measurement with [18F]altanserin positron emission tomography

BACKGROUND

Serotonin 5-HT(2A) receptors play an important role in the regulation of many functions that are disturbed in patients with major depressive disorder. Postmortem and positron emission tomography studies have reported both increased and decreased 5-HT(2A) receptor binding in different limbic and paralimbic regions.

METHODS

We conducted a quantitative 5-HT(2A) receptor binding study using positron emission tomography and [(18)F]altanserin of four regions hypothesized to have altered levels of 5-HT(2A) receptors in major depressive disorder. Using a four-compartment model, the 5-HT(2A) receptor distribution was estimated by calculating the regional [(18)F]altanserin k(3)/k(4) ratio in which k(3) is the rate of binding to the receptor and k(4) is the rate of dissociation from the receptor. Forty-six antidepressant-free patients with major depressive disorder and 29 healthy control subjects were enrolled.

RESULTS

5-HT(2A) receptor binding in the hippocampus was reduced by 29% in depressed subjects (p =.004). In other regions, 5-HT(2A) receptor binding was decreased (averaging 15%) but not significantly. Both groups had similar age-dependent decreases in 5-HT(2A) receptors throughout all brain regions.

CONCLUSIONS

Altered serotoninergic function in the hippocampus is likely involved in the disturbances of mood regulation in major depressive disorder, although the specific role of the 5-HT(2A) receptor changes is still unclear.

Epilepsy and depression: imaging potential common factors

Patients with seizure disorders have an increased incidence of depression. This may be due in part to psychosocial factors; or side effects of antiepileptic drugs. However, there may be underlying physiologic mechanisms for the relationship. Neuroimaging studies, including structural magnetic resonance imaging, positron emission tomography measurements of cerebral glucose metabolism, and, more recently, imaging of serotonin 1A receptors, may provide additional data to explain overlapping clinical manifestations of epilepsy and depression.

Involvement of serotonin in depression: evidence from postmortem and imaging studies of serotonin receptors and the serotonin transporter

Definitive conclusions on the role of serotonin receptors and transporter in suicide and depression have been elusive in studies of postmortem brain tissue. A number of methodological differences in these studies have made it difficult to reach a consensus, but crucial issues are being identified and incorporated into newer studies. This review will follow the evolution of serotonin receptor and transporter studies in postmortem tissues that initially focused on suicide and gradually incorporated depressive disorders as psychiatric assessments were increasingly performed. Studies in postmortem tissues on the serotonin-1A and serotonin-2A receptors and the serotonin transporter will be reviewed and compared with imaging studies of the same sites in depressed subjects. Critical issues to control in future studies of serotonin receptors in postmortem tissues include variables such as the cause of death (i.e. suicide), the specific psychiatric diagnoses of the subjects, whether the disorder was in remission at the time of death, long-term medication histories, psychoactive substance use disorders, the smoking history, the hemisphere from which tissues were dissected, and the specific cytoarchitectonic region to be evaluated. Carefully controlled studies in postmortem tissues will ensure a greater likelihood of reaching a consensus on the involvement of monoamine measures in the etiology of depression.