GABAB receptor intracellular signaling: novel pathways for depressive disorder treatment?

Shared Mechanisms of GABAergic and Opioidergic Transmission Regulate Corticolimbic Reward Systems and Cognitive Aspects of Motivational Behaviors

The functional interplay between the corticolimbic GABAergic and opioidergic systems plays a crucial role in regulating the reward system and cognitive aspects of motivational behaviors leading to the development of addictive behaviors and disorders. This review provides a summary of the shared mechanisms of GABAergic and opioidergic transmission, which modulate the activity of dopaminergic neurons located in the ventral tegmental area (VTA), the central hub of the reward mechanisms. This review comprehensively covers the neuroanatomical and neurobiological aspects of corticolimbic inhibitory neurons that express opioid receptors, which act as modulators of corticolimbic GABAergic transmission. The presence of opioid and GABA receptors on the same neurons allows for the modulation of the activity of dopaminergic neurons in the ventral tegmental area, which plays a key role in the reward mechanisms of the brain. This colocalization of receptors and their immunochemical markers can provide a comprehensive understanding for clinicians and researchers, revealing the neuronal circuits that contribute to the reward system. Moreover, this review highlights the importance of GABAergic transmission-induced neuroplasticity under the modulation of opioid receptors. It discusses their interactive role in reinforcement learning, network oscillation, aversive behaviors, and local feedback or feedforward inhibitions in reward mechanisms. Understanding the shared mechanisms of these systems may lead to the development of new therapeutic approaches for addiction, reward-related disorders, and drug-induced cognitive impairment.

GPCR-mediated calcium and cAMP signaling determines psychosocial stress susceptibility and resiliency

Chronic stress increases the risk of developing psychiatric disorders, including mood and anxiety disorders. Although behavioral responses to repeated stress vary across individuals, the underlying mechanisms remain unclear. Here, we perform a genome-wide transcriptome analysis of an animal model of depression and patients with clinical depression and report that dysfunction of the Fos-mediated transcription network in the anterior cingulate cortex (ACC) confers a stress-induced social interaction deficit. Critically, CRISPR-Cas9-mediated ACC Fos knockdown causes social interaction deficits under stressful situation. Moreover, two classical second messenger pathways, calcium and cyclic AMP, in the ACC during stress differentially modulate Fos expression and regulate stress-induced changes in social behaviors. Our findings highlight a behaviorally relevant mechanism for the regulation of calcium- and cAMP-mediated Fos expression that has potential as a therapeutic target for psychiatric disorders related to stressful environments.

A role of GABAA receptor α1 subunit in the hippocampus for rapid-acting antidepressant-like effects of ketamine

Ketamine can produce rapid-acting antidepressant effects in treatment-resistant patients with depression. Although alterations in glutamatergic and GABAergic neurotransmission in the brain play a role in depression, the precise molecular mechanisms in these neurotransmission underlying ketamine's antidepressant actions remain largely unknown. Mice exposed to FSS (forced swimming stress) showed depression-like behavior and decreased levels of GABA (γ-aminobutyric acid), but not glutamate, in the hippocampus. Ketamine increased GABA levels and decreased glutamate levels in the hippocampus of mice exposed to FSS. There was a correlation between GABA levels and depression-like behavior. Furthermore, ketamine increased the levels of enzymes and transporters on the GABAergic neurons (SAT1, GAD67, GAD65, VGAT and GAT1) and astrocytes (EAAT2 and GAT3), without affecting the levels of enzymes and transporters (SAT2, VGluT1 and GABA_AR γ2) on glutamatergic neurons. Moreover, ketamine caused a decreased expression of GABA_AR α1 subunit, which was specifically expressed on GABAergic neurons and astrocytes, an increased GABA synthesis and metabolism in GABAergic neurons, a plasticity change in astrocytes, and an increase in ATP (adenosine triphosphate) contents. Finally, GABA_AR antagonist bicuculline or ATP exerted a rapid antidepressant-like effect whereas pretreatment with GABA_AR agonist muscimol blocked the antidepressant-like effects of ketamine. In addition, pharmacological activation and inhibition of GABA_AR modulated the synthesis and metabolism of GABA, and the plasticity of astrocytes in the hippocampus. The present data suggest that ketamine could increase GABA synthesis and astrocyte plasticity through downregulation of GABA_AR α1, increases in GABA, and conversion of GABA into ATP, resulting in a rapid-acting antidepressant-like action. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Propofol Protects Against Erastin-Induced Ferroptosis in HT-22 Cells

Propofol is a short-acting intravenous anesthetic that is widely used in clinical treatment. Previous articles have indicated that propofol is a therapeutic target for anti-apoptosis, anti-inflammation, anti-lipid peroxidation, and anti-reactive oxygen species (ROS). Moreover, cell ferroptosis is strongly correlated with cellular ROS, inflammatory responses, and lipid peroxidation. However, the mechanisms by which propofol attenuates neuronal injury by reducing ferroptosis remain unknown. Hence, we hypothesized that propofol could protect neurons by reducing ferroptosis. To test this hypothesis, HT-22 cells were treated with a specific ferroptosis activator (erastin) in the presence of propofol (50 μM). We found that propofol reduced erastin-induced high Fe²⁺ concentrations, lipid peroxides, and excess ROS. Western blotting results also suggested that propofol could rescue erastin-induced low expression of GXP4 and system Xc^-. Further experiments indicated that propofol attenuated p-ALOX5 expression at Ser663 independent of ERK. In addition, we built two transient transfection cell lines, ALOX5 OE and Ser663Ala-ALOX5 OE, to confirm the target of propofol. We found that the Ser663 point is the critical role of propofol in rescuing erastin-induced cell injury/lipid peroxidation. In conclusion, propofol may help attenuate ferroptosis, which may provide a new therapeutic method to treat neuronal injury or the brain inflammatory response.

Childhood maltreatment history for guiding personalized antidepressant choice in major depressive disorder: Preliminary results from a systematic review

Childhood maltreatment (CM) is a predictor of poor outcome across treatments for major depressive disorder (MDD), while its potential role as a predictor of differential responses to specific antidepressants has received little attention. The present systematic review examined pharmacological studies (published up to June 30th, 2020) that included head-to-head comparisons of antidepressant treatments among adult MDD patients with a reported history of CM or no history to evaluate if CM may help clinicians choose antidepressants with greatest likelihood of successful outcome. Only three studies were included, providing limited and provisional results. These preliminary findings suggest that sustained-release bupropion (alone or in combination) or aripiprazole-augmentation as next-step intervention did not demonstrate differential outcome among MDD patients with or without a history of childhood adversity. Further, sertraline and the group of antidepressants with low affinity for the serotonin transporter may be less suitable for MDD patients with childhood abuse history than escitalopram, venlafaxine-XR, or antidepressants with high affinity for the serotonin transporter. The critical question of the most potentially efficacious treatment regimens for adult MDD with CM history requires further large-sample studies involving a greater number of medications, specifically designed to analyse the moderating effects of different types of CM, and possibly including objective biomarkers.