Summary: Researchers have created a highly selective fluorescent probe that images serotonin inside cells and in animal models, providing new insight into its role in depression. The study shows that overall serotonin levels in normal and depression-model cells are similar, but cells modeling depression release markedly less serotonin when stimulated.
The ability of cells to release serotonin correlates with the activity of mTOR, a key signaling protein. These results indicate that serotonin release — not just its steady-state concentration — is a critical factor to consider in understanding and treating depression.
Key Facts:
- The new fluorescent probe detects serotonin selectively and sensitively, even within living cells.
- Cells modeling depression exhibit a reduced capacity to release serotonin, and this deficit correlates with mTOR activity.
- These findings open pathways for developing treatments that target serotonin release mechanisms and mTOR signaling.
Source: Wiley
Serotonin’s role in depression matters for diagnosis, therapy, and drug discovery. To advance research in this area, a Chinese research team has developed a fluorescent molecular probe that is both highly sensitive and highly selective for serotonin.
Their findings, reported in the journal Angewandte Chemie, include preliminary imaging results from neuronal cell models and live animal experiments that clarify how serotonin dynamics relate to depressive states.
Depression is a major global health challenge, and existing treatments do not always provide reliable relief, in part because the underlying mechanisms remain incompletely understood. Although serotonin has long been implicated in depression, emerging evidence suggests that reduced serotonin concentration alone does not fully explain the disorder.
Led by Weiying Lin at Guangxi University (China), the research team set out to design a molecular fluorescent probe that responds specifically to serotonin inside biological systems. Designing such a probe is challenging because serotonin’s chemical structure is similar to other biomolecules like melatonin and tryptophan, which can cause cross-reactivity.
By analyzing subtle differences in chemical reactivity, the researchers created a novel reactive moiety, 3-mercaptopropionate, which undergoes a thiol-ene click cascade nucleophilic reaction that is highly selective for serotonin. They linked this reactive unit to a fluorescent dye based on a dicyanomethylene-benzopyran derivative.
In the probe’s initial state, the attached reactive unit suppresses fluorescence. When the probe encounters serotonin, a two-step cascade occurs: first, the thiol group reacts with a double bond in serotonin via a thiol-ene reaction; next, proximity enables a nucleophilic attack by serotonin’s amino group on a carbonyl in the reactive unit. This cascade removes the blocking appendage and restores fluorescence, producing a robust, selective fluorescence signal where serotonin is present.
The team applied this probe, named SJ-5-HT, to a neuronal cell line and to mouse brain tissue. They created a cellular depression model by treating neurons with corticosterone, a stress-related hormone. Imaging revealed that baseline serotonin concentrations were comparable between normal and depression-model cells, but the depressed-model cells released substantially less serotonin when stimulated. Treatment with selective serotonin reuptake inhibitors (SSRIs) produced only modest increases in release.
The researchers explored the role of mTOR (mechanistic target of rapamycin), a central regulator of cell signaling, and found a strong correlation between mTOR activity and serotonin release capacity. Activating mTOR in the depression-model cells significantly improved serotonin release, while inhibiting mTOR in normal cells reduced release. These relationships were confirmed across both neuronal cultures and mouse models.
Altogether, the imaging results imply that impaired serotonin release, rather than an absolute deficiency in serotonin levels, may play a more decisive role in certain forms of depression. The tight correlation between release ability and mTOR activity suggests mTOR signaling as a promising direction for future antidepressant strategies and for refining diagnostic approaches.
About this depression and serotonin research news
Author: Mario Mueller
Source: Wiley
Contact: Mario Mueller – Wiley
Image: The image is credited to Neuroscience News
Original Research: Closed access.
Title: “Development of a Fluorescent Probe with High Selectivity based on Thiol-ene Click Nucleophilic Cascade Reactions for Delving into the Action Mechanism of Serotonin in Depression” by Weiying Lin et al., Angewandte Chemie International Edition
Abstract
Development of a Fluorescent Probe with High Selectivity based on Thiol-ene Click Nucleophilic Cascade Reactions for Delving into the Action Mechanism of Serotonin in Depression
The relationship between depression and serotonin (5-HT) remains a central and debated issue with major implications for diagnosis, treatment, and development of neurological therapeutics. To clarify serotonin’s role, it is essential to visualize its dynamics in living cells and tissues using fluorescence imaging.
Progress has been limited by the lack of molecular probes that combine sensitivity with high selectivity for serotonin. Here, the authors report the design of a first highly selective serotonin-responsive unit, 3-mercaptopropionate, which leverages thiol-ene click cascade nucleophilic chemistry. This responsive unit was incorporated into the molecular probe SJ-5-HT to image serotonin changes in depression-model cells and brain tissues.
Imaging data indicate that serotonin concentration alone may not be the primary determinant in depression models. Instead, the neurons’ capacity to release serotonin appears substantially more important, and this release capability corresponds closely with intracellular mTOR levels. These findings provide mechanistic insight into depression and highlight mTOR signaling as a potential target for developing novel antidepressant treatments.