Search

Major depressive disorder (MDD) is a psychiatric condition that affects a large number of people in the world, and the treatment existents do not work for all individuals affected. Thus, it is believed that other systems or pathways which regulate brain networks involved in mood regulation and cognition are associated with MDD pathogenesis. Studies in humans and animal models have been shown that in MDD there are increased levels of inflammatory mediators, including cytokines and chemokines in both periphery and central nervous system (CNS). In addition, microglial activation appears to be a key event that triggers changes in signaling cascades and gene expression that would be determinant for the onset of depressive symptoms. Recent researches also point out that changes in the gut microbiota would lead to a systemic inflammation that in different ways would reach the CNS modulating inflammatory pathways and especially the microglia, which could influence responses to treatments. Moreover, pre‐ and probiotics have shown antidepressant responses and anti‐inflammatory effects. This review will focus on studies that show the relationship of inflammation with the gut microbiota–brain axis and its relation with MDD. [ABSTRACT FROM AUTHOR]

Several studies have found that the molecular mechanisms of mitochondrial energy metabolism are impaired in major depressive disorder (MDD). Classic antidepressants and atypical antipsychotics can alter the function of enzymes involved in adenosine triphosphate (ATP) metabolism. Quetiapine is an atypical antipsychotic that, in addition to having a therapeutic benefit in treating MDD, appears to exert antioxidant and neuroprotective effects. Therefore, we aimed to evaluate the acute and chronic effects of quetiapine on the activity of enzyme complexes I to IV of the mitochondrial respiratory chain and creatine kinase (CK) in brain regions involved with MDD. After a single dose or serial injections over 14 days of quetiapine (20, 40, and 80 mg) were administered, isolates from the pre- frontal cortex, hippocampus, amygdala and nucleus accumbens were analyzed for enzyme activity levels. The enzyme activity varied according to the dose, brain region, and acute or chronic dosing protocols. In general, complexes I-III activity was increased, especially after acute administration. Acute administration also increased the activity of complex IV and CK in the amygdala while complex I was inhibited in the prefrontal cortex and nucleus accumbens. These results suggest that quetiapine produces an increase in respiratory chain complex activity, which may be underlying its efficacy against psychiatric disorders and neuronal damage.

Studies have suggested that ketamine, a nonselective NMDA receptor antagonist, could be a new drug in the treatment of major depression, but the way ketamine presents such effects remains to be elucidated. Therefore, the objective of this paper was to evaluate the effects of ketamine treatment on parameters related to depression in the brain of adult rats subjected to an animal model of depression. The animals were divided into: non-deprived + saline; non-deprived + ketamine; deprived + saline; deprived + ketamine. Treatments involving ketamine (15 mg/kg) were administered once a day during 14 days in the animal's adult phase. After treatment, the brain derived-neurotrophic factor (BDNF) levels, oxidative stress and energy metabolism activity were evaluated in brain structures of rats involved in the circuit of depression. In the amygdala, hippocampus and nucleus accumbens (NAc), a reduction in BDNF levels was observed in deprived rats, but the animals treated with ketamine reversed the effects of this animal model only in the amygdala and NAc. In addition to this, the complex I activity, in deprived rats, was diminished in the prefrontal cortex (PFC) and amygdala; in the PFC and hippocampus, the complex II-III was diminished in deprived rats; still the administration of ketamine increased the complex IV activity in the PFC and amygdala of rats submitted to the maternal deprivation. In deprived rats, the creatine kinase activity was reduced in the PFC and amygdala, however the administration of ketamine reversed this decrease in the amygdala. The malondialdehyde (MDA) equivalents were increased in non-deprived rats treated with ketamine in the PFC and NAc. Carbonyl levels in the PFC were diminished in control rats that received saline. Though ketamine treatment reversed this effect in deprived rats in the PFC and hippocampus. Still, in NAc, the carbonyl levels were diminished in deprived rats. The superoxide dismutase (SOD) activity was increased in control rats that received ketamine in the PFC and NAc, and were diminished in deprived rats that received saline or ketamine in the PFC and hippocampus. These findings may help to explain that dysfunctions involving BDNF, oxidative stress and energy metabolism within specific brain areas, may be linked with the pathophysiology of depression, and antidepressant effects of ketamine can be positive, at least partially due to the control of these pathways.