Gαs, adenylyl cyclase, and their relationship to the diagnosis and treatment of depression

The therapeutic effects of saikosaponins on depression through the modulation of neuroplasticity: From molecular mechanisms to potential clinical applications

Depression is a major global health issue that urgently requires innovative and precise treatment options. In this context, saikosaponin has emerged as a promising candidate, offering a variety of therapeutic benefits that may be effective in combating depression. This review delves into the multifaceted potential of saikosaponins in alleviating depressive symptoms. We summarized the effects of saikosaponins on structural and functional neuroplasticity, elaborated the regulatory mechanism of saikosaponins in modulating key factors that affect neuroplasticity, such as inflammation, the hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, and the brain-gut axis. Moreover, this paper highlights existing gaps in current researches and outlines directions for future studies. A detailed plan is provided for the future clinical application of saikosaponins, advocating for more targeted researches to speed up its transition from preclinical trials to clinical practice.

Ketamine - A New Antidepressant Drug with Anti-Inflammatory Properties

Ketamine is a new, potent and rapid-acting antidepressant approved for therapy of treatment-resistant depression, which has a different mechanism of action than currently-available antidepressant therapies. It owes its uniquely potent antidepressant properties to a complex mechanism of action, which currently remains unclear. However, it is thought that it acts by modulating the functioning of the glutamatergic system, which plays an important role in the process of neuroplasticity associated with depression. However, preclinical and clinical studies have also found ketamine to reduce inflammation, either directly or indirectly (by activating neuroprotective branches of the kynurenine pathway), among patients exhibiting higher levels of inflammation. Inflammation and immune system activation are believed to play key roles in the development and course of depression. Therefore, the present work examines the role of the antidepressant effect of ketamine and its anti-inflammatory properties in the treatment of depression. SIGNIFICANCE STATEMENT: The present work examines the relationship between the antidepressant effect of ketamine and its anti-inflammatory properties, and the resulting benefits in treatment-resistant depression (TRD). The antidepressant mechanism of ketamine remains unclear, and there is an urgent need to develop new therapeutic strategies for treatment of depression, particularly TRD.

cAMP-dependent protein kinase signaling is required for (2R,6R)-hydroxynorketamine to potentiate hippocampal glutamatergic transmission

(2R,6R)-Hydroxynorketamine (HNK) is a ketamine metabolite that shows rapid antidepressant-like effects in preclinical studies and lacks the adverse N-methyl-d-aspartate receptor (NMDAR) inhibition-related properties of ketamine. Investigating how (2R,6R)-HNK exerts its antidepressant actions may be informative in the design of novel pharmacotherapies with improved safety and efficacy. We sought to identify the molecular substrates through which (2R,6R)-HNK induces functional changes at excitatory synapses, a prevailing hypothesis for how rapid antidepressant effects are initiated. We recorded excitatory postsynaptic potentials in hippocampal slices from male Wistar Kyoto rats, which have impaired hippocampal plasticity and are resistant to traditional antidepressants. (2R,6R)-HNK (10 µM) led to a rapid potentiation of electrically evoked excitatory postsynaptic potentials at Schaffer collateral CA1 stratum radiatum synapses. This potentiation was associated with a decrease in paired pulse facilitation, suggesting an increase in the probability of glutamate release. The (2R,6R)-HNK-induced potentiation was blocked by inhibiting either cyclic adenosine monophosphate (cAMP) or its downstream target, cAMP-dependent protein kinase (PKA). As cAMP is a potent regulator of brain-derived neurotrophic factor (BDNF) release, we assessed whether (2R,6R)-HNK exerts this acute potentiation through a rapid increase in cAMP-dependent BDNF-TrkB signaling. We found that the cAMP-PKA-dependent potentiation was not dependent on TrkB activation by BDNF, which functionally delimits the acute synaptic effects of (2R,6R)-HNK from its sustained BDNF-dependent actions in vivo. These results suggest that, by potentiating glutamate release via cAMP-PKA signaling, (2R,6R)-HNK initiates acute adaptations in fast excitatory synaptic transmission that promote structural plasticity leading to maintained antidepressant action.NEW & NOTEWORTHY Ketamine is a rapid-acting antidepressant and its preclinical effects are mimicked by its (2R,6R)-(HNK) metabolite. We found that (2R,6R)-HNK initiates acute adaptations in fast excitatory synaptic transmission by potentiating glutamate release via cAMP-PKA signaling at hippocampal Schaffer collateral synapses. This cAMP-PKA-dependent potentiation was not dependent on TrkB activation by BDNF, which functionally delimits the rapid synaptic effects of (2R,6R)-HNK from its sustained BDNF-dependent actions that are thought to maintain antidepressant action in vivo.

The Regulatory Roles of Cerebellar Glycosphingolipid Microdomains/Lipid Rafts

Lipid rafts are dynamic assemblies of glycosphingolipids, sphingomyelin, cholesterol, and specific proteins which are stabilized into platforms involved in the regulation of vital cellular processes. Cerebellar lipid rafts are cell surface ganglioside microdomains for the attachment of GPI-anchored neural adhesion molecules and downstream signaling molecules such as Src-family kinases and heterotrimeric G proteins. In this review, we summarize our recent findings on signaling in ganglioside GD3 rafts of cerebellar granule cells and several findings by other groups on the roles of lipid rafts in the cerebellum. TAG-1, of the contactin group of immunoglobulin superfamily cell adhesion molecules, is a phosphacan receptor. Phosphacan regulates the radial migration signaling of cerebellar granule cells, via Src-family kinase Lyn, by binding to TAG-1 on ganglioside GD3 rafts. Chemokine SDF-1α, which induces the tangential migration of cerebellar granule cells, causes heterotrimeric G protein Goα translocation to GD3 rafts. Furthermore, the functional roles of cerebellar raft-binding proteins including cell adhesion molecule L1, heterotrimeric G protein Gsα, and L-type voltage-dependent calcium channels are discussed.

Inhibition of Microglial GSK3β Activity Is Common to Different Kinds of Antidepressants: A Proposal for an In Vitro Screen to Detect Novel Antidepressant Principles

Depression is a major public health concern. Unfortunately, the present antidepressants often are insufficiently effective, whilst the discovery of more effective antidepressants has been extremely sluggish. The objective of this review was to combine the literature on depression with the pharmacology of antidepressant compounds, in order to formulate a conceivable pathophysiological process, allowing proposals how to accelerate the discovery process. Risk factors for depression initiate an infection-like inflammation in the brain that involves activation microglial Toll-like receptors and glycogen synthase kinase-3β (GSK3β). GSK3β activity alters the balance between two competing transcription factors, the pro-inflammatory/pro-oxidative transcription factor NFκB and the neuroprotective, anti-inflammatory and anti-oxidative transcription factor NRF2. The antidepressant activity of tricyclic antidepressants is assumed to involve activation of GS-coupled microglial receptors, raising intracellular cAMP levels and activation of protein kinase A (PKA). PKA and similar kinases inhibit the enzyme activity of GSK3β. Experimental antidepressant principles, including cannabinoid receptor-2 activation, opioid μ receptor agonists, 5HT2 agonists, valproate, ketamine and electrical stimulation of the Vagus nerve, all activate microglial pathways that result in GSK3β-inhibition. An in vitro screen for NRF2-activation in microglial cells with TLR-activated GSK3β activity, might therefore lead to the detection of totally novel antidepressant principles with, hopefully, an improved therapeutic efficacy.