Brain-wide changes in excitation-inhibition balance of major depressive disorder: a systematic review of topographic patterns of GABA- and glutamatergic alterations.

The excitation-inhibition (E/I) imbalance is an important molecular pathological feature of major depressive disorder (MDD) as altered GABA and glutamate levels have been found in multiple brain regions in patients. Healthy subjects show topographic organization of the E/I balance (EIB) across various brain regions. We here raise the question of whether such EIB topography is altered in MDD. Therefore, we systematically review the gene and protein expressions of inhibitory GABAergic and excitatory glutamatergic signaling-related molecules in postmortem MDD brain studies as proxies for EIB topography. Searches were conducted through PubMed and 45 research articles were finally included. We found: i) brain-wide GABA- and glutamatergic alterations; ii) attenuated GABAergic with enhanced glutamatergic signaling in the cortical-subcortical limbic system; iii) that GABAergic signaling is decreased in regions comprising the default mode network (DMN) while it is increased in lateral prefrontal cortex (LPFC). These together demonstrate abnormal GABA- and glutamatergic signaling-based EIB topographies in MDD. This enhances our pathophysiological understanding of MDD and carries important therapeutic implications for stimulation treatment.

From Molecular to Behavior: Higher Order Occipital Cortex in Major Depressive Disorder.

Medial prefrontal cortex (MPFC) and other regions like the occipital cortex (OC) exhibit abnormal neural activity in major depressive disorder (MDD). Their relationship to specific biochemical, psychophysical, and psychopathological changes remains unclear, though. For that purpose, we focus on a particular subregion in OC, namely middle temporal (MT) visual area that is known to mediate the perception of visual motion. Using high-field 7 T magnetic resonance imaging (MRI), including resting state functional MRI and proton magnetic resonance spectroscopy, the amplitude of low-frequency fluctuations (ALFF) of the blood oxygen level-dependent signal in MT, MT-seeded functional connectivity (FC), and gamma-aminobutyric acid (GABA) in MT were investigated. Applying the vision motion psychophysical task, the motion suppression index of subjects was also examined. We demonstrate significantly elevated neural variability (as measured by ALFF) in MT together with decreases in both MT GABA and motion suppression in our MDD sample. Unlike in healthy subjects, MT neural variability no longer modulates the relationship of MT GABA and motion suppression in MDD. MT also exhibits reduction in global inter-regional FC to MPFC in MDD. Finally, elevated MT ALFF relates to specifically retardation in behavior as measured by the Hamilton subscore. Together, MT provides a strong candidate for biomarker in MDD.

Childhood trauma mediates repetitive transcranial magnetic stimulation efficacy in major depressive disorder.

Childhood trauma is one of the most prominent risk factors in developing major depressive disorder (MDD) and may lead to unfavorable outcomes of pharmacotherapy and psychotherapy in MDD. While how it modulates the treatment outcome of the repetitive transcranial magnetic stimulation (rTMS) and how sex difference may play a role in mediating this relationship remain unknown. To evaluate this question, 51 (37 women) MDD patients were treated with 10 Hz rTMS to the left dorsolateral prefrontal cortex (lDLPFC). The experience of childhood trauma was quantified by the Childhood Traumatic Questionnaire (CTQ). The depressive severity was assessed by Hamilton Depression Scale (HAMD) and Beck Depression Inventory (BDI) as the primary and secondary assessments. Beck Hopelessness Scale (BHS) and Hamilton Anxiety Scale (HAMA) were also assessed for further confirmation. Thirty-six (70.6%) participants showed a response including 17 (33.3%) achieving remission to the rTMS treatment. The alleviation of depressive symptoms was negatively correlated with the CTQ scores, specifically in women but not men, in subjective BDI and BHS, but not objective HAMD or HAMA. We demonstrate that childhood trauma negatively affects the subjective perception of rTMS-lDLPFC treatment outcomes in female MDD patients. This highlights the importance of measuring childhood trauma-related symptoms in routine clinical rTMS treatment, as they may impact perceived efficacy.

Reduction of higher-order occipital GABA and impaired visual perception in acute major depressive disorder.

Major depressive disorder (MDD) is a complex state-dependent psychiatric illness for which biomarkers linking psychophysical, biochemical, and psychopathological changes remain yet elusive, though. Earlier studies demonstrate reduced GABA in lower-order occipital cortex in acute MDD leaving open its validity and significance for higher-order visual perception, though. The goal of our study is to fill that gap by combining psychophysical investigation of visual perception with measurement of GABA concentration in middle temporal visual area (hMT+) in acute depressed MDD. Psychophysically, we observe a highly specific deficit in visual surround motion suppression in a large sample of acute MDD subjects which, importantly, correlates with symptom severity. Both visual deficit and its relation to symptom severity are replicated in the smaller MDD sample that received MRS. Using high-field 7T proton Magnetic resonance spectroscopy (1H-MRS), acute MDD subjects exhibit decreased GABA concentration in visual MT+ which, unlike in healthy subjects, no longer correlates with their visual motion performance, i.e., impaired SI. In sum, our combined psychophysical-biochemical study demonstrates an important role of reduced occipital GABA for altered visual perception and psychopathological symptoms in acute MDD. Bridging the gap from the biochemical level of occipital GABA over visual-perceptual changes to psychopathological symptoms, our findings point to the importance of the occipital cortex in acute depressed MDD including its role as candidate biomarker.

Cultured rat cortical astrocytes synthesize melatonin: absence of a diurnal rhythm.

Melatonin not only plays a major role in the regulation of circadian rhythms, but is also involved in antioxidative defense and immunomodulation. Circulating melatonin levels are derived primarily from the pineal gland while other sources of melatonin have also been reported. Here, we show for the first time that astrocytes from the rat cortex and glioma C6 cell line synthesize melatonin in vitro. In addition, we show the presence of serotonin, the precursor of melatonin and the two key enzymes in the pathway of melatonin synthesis, i.e. N-acetyltransferase and hydroxyndole-O-methyltransferase in the cultured rat cortical astrocytes. Release of melatonin into the culture medium showed no diurnal changes. These point to astrocytes as a local source of melatonin in the rat brain. Its exact physiological function remains a topic for future studies.

Circadian rhythm of salivary serotonin in patients with major depressive disorder.

OBJECTIVES: The present study aimed to explore the circadian rhythm of salivary serotonin in patients with major depressive disorder before and after treatment with fluoxetine and its relationship with clinical therapeutic effect. METHODS: This study investigated salivary serotonin in 13 outpatients with major depressive disorder and age- and sex-matched healthy controls. Depressed patients received six weeks fluoxetine treatment (20 mg/day), saliva was collected before and four weeks after treatment. A total of 8 time-point salivary serotonin was measured across the whole day. Multi-oscillator cosinor model was used to fit the rhythms. RESULTS: Serotonin concentration in saliva ranged from 0.32 ng/ml to 9.62 ng/ml. Salivary serotonin showed prominent circadian rhythm in 91% depressed patients and 92% healthy subjects. Circadian amplitude tend to be higher after fluoxetine treatment in depressed patients, so as the ultradian cycle amplitude. The serotonin circadian amplitude (After minus Before) was positively correlated with the decrease of Zung Self-Rating Depression Scale(SDS) scores at day 42 whereas there was no such correlation at day 28. There was no significant difference in the parameters of mesor, acrophase, harmonic and area under curve among three groups. CONCLUSIONS: Salivary serotonin in patients with major depressive disorder showed clear circadian rhythm. The relationship between the increase of salivary serotonin amplitude and clinical response deserve further study.

Effect of fluoxetine on circadian rhythm of melatonin in patients with major depressive disorder.

OBJECTIVES: The purpose of this study is to explore the response of melatonin circadian rhythm to fluoxetine treatment and its relationship with clinical therapeutic effect. METHODS: This study investigated salivary melatonin in 13 outpatients with major depressive disorder and age- and sex-matched healthy controls. Depressed patients received six weeks fluoxetine (20 mg/day) treatment, and saliva was collected before and four weeks after treatment. In sampling days, a total of 12 time-point salivary melatonin was measured over 24-hours. Multioscillator cosinor model was used to fit the rhythms. RESULTS: There was no difference of circadian melatonin rhythms in depressed patients, and melatonin was not significantly lower after fluoxetine treatment. To our surprise, the melatonin amplitude (Before minus After) was positively correlated with the improvement in Hamilton Depression Rating Scale (HDRS) scores at day 42 whereas there was no such correlation at day 28. CONCLUSIONS: Melatonin rhythms were similar between depressed patients and matched healthy controls. The interesting finding that the difference of salivary melatonin amplitude was correlated with the clinical improvement after six weeks fluoxetine treatment deserve further study.