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

Concept article: Antidepressant-induced destabilization in bipolar illness mediated by serotonin 3 receptor (5HT3)

OBJECTIVES

Antidepressants used by patients with bipolar disorder have been associated with destabilization with an increase in mania, depression, and cycling. The most commonly proposed mechanism, that antidepressants 'overshoot' their antidepressant effect to create a manic or mixed state, is unlikely since antidepressants have actually been found to be ineffective in treating bipolar depression. Beginning with known bipolar-specific pathophysiologic abnormalities provides the greatest likelihood of insight.

METHODS

PubMed was queried with 'bipolar', 'sodium', 'intracellular sodium', 'serotonin 3', '5HT3', '5-hydroxytryptamine type 3 receptors', and 'antidepressant' either individually or in combination.

RESULTS

Pathologic mood states (both mania and depression) are associated with increased intracellular sodium (Na) concentrations that depolarize the resting membrane potential to increase cellular excitability (mania) or cause depolarization block (depression). Stimulation of the serotonin (5HT) receptors depolarizes the post-synaptic neuron. Stimulation of 5HT3 may be of particular importance since it is coupled to a cation channel that directly depolarizes the membrane. These effects directly impact the physiology of patients with bipolar disorder to alter neuronal excitability in a fashion that worsens both mania and depression.

PROPOSED CONCEPT

The most consistently observed biological abnormality in individuals going through mania or bipolar depression involves a decline in Na pump activity, with consequent elevation of intracellular Na levels. Antidepressant treatment potentiates this, particularly by activation of 5HT3. This hypothesis can be tested by coadministering a 5HT3 antagonist (e.g., vortioxetine or ondansetron) to achieve blockade of that receptor while treating bipolar depression with a serotoninergic antidepressant.

The Effects of Nanoplastics on the Dopamine System of Cerebrocortical Neurons

Nanoplastics (NPx) can enter living organisms, including humans, through ecosystems, inhalation, and dermal contact and can be found from the intestine to the brain. However, it is unclear whether NPx accumulates and affects the dopamine system. In this study, we investigated the effects of NPx on the dopamine system in cultured murine cerebral cortex neurons. Cultured cerebrocortical neurons were treated with 100 nm NPx at the following concentrations for 24 h: 1.896 × 105, 3.791 × 106, 7.583 × 107, 1.571 × 109, 3.033 × 1010, and 3.033 × 1011 particles/mL. Dopamine-associated proteins were analyzed using immunofluorescence staining. NPx treatment induced its accumulation in neurons in a dose-dependent manner and increased the levels of dopamine receptors D1 and D2 and their co-expression. However, NPx treatment did not affect the levels of other dopamine receptors, dopamine transporters, tyrosine hydroxylase, and microtubule-associated protein 2, or synaptophysin in neuronal structures. This study demonstrated that NPx is a potential modulator of the dopamine system via its receptors rather than its synthesis and reuptake in neurons and may be associated with dopamine-based psychiatric disorders.

Interactions of Oxytocin and Dopamine-Effects on Behavior in Health and Disease

The hypothalamic neuropeptide and hormone oxytocin are of fundamental importance for maternal, social, and sexual behavior. Deviations in oxytocin levels have also been associated with anxiety, autism spectrum disorders (ASD), depression, ADHD (attention deficit hyperactivity disorder), and schizophrenia. Both oxytocin and dopamine are often considered reward- and feel-good hormones, and dopamine is associated with the above-mentioned behaviors and, and dopamine is also associated with the above-mentioned behaviors and disorders. Although being structurally totally different, oxytocin, a peptide, and dopamine, a monoamine, they have a number of similar effects. They are synthesized both in the brain and in the periphery, and they affect each other's release and receptors. In addition, oxytocin and dopamine are released in response to, for example, social interaction, sex, feeding, and massage. This review discusses interactions between oxytocin and dopamine with a specific focus on behavioral effects and possible roles of oxytocin and dopamine in various mental disorders and functional diversities.

PI3K/AKT signaling pathway: Molecular mechanisms and therapeutic potential in depression

Depression is a serious global mental disorder. Numerous studies have found that depression may be closely related to decreased neurogenesis, neuroinflammation, neurotransmitter imbalance, and synaptic plasticity dysfunction. The pathogenesis of depression is complex and involves multiple signal transduction pathways and molecular changes. The PI3K/AKT pathway is an essential signaling pathways in neurons, which is widely expressed in emotion-related regions of the brain. Therefore, the PI3K/AKT pathway may play a moderating role in mood disorders. However, the role and mechanism of the PI3K/AKT signaling pathway in depression have not been fully described. This review systematically summarized the role of the PI3K/AKT signaling pathway in the pathogenesis of depression and discussed its potential in the treatment of depression. This will help in the treatment of depression and the development of antidepressants.