Background Stress precipitates mood disorders, characterized by a range of symptoms present in different combinations, suggesting the existence of disease subtypes. Using an animal model, we previously described that repetitive stress via restraint or immobilization induced depressive-like behaviors in rats that were differentially reverted by a serotonin- or noradrenaline-based antidepressant drug, indicating that different neurobiological mechanisms may be involved. The forebrain astrocyte protein aldolase C, contained in small extracellular vesicles, was identified as a potential biomarker in the cerebrospinal fluid; however, its specific origin remains unknown. Here, we propose to investigate whether serum small extracellular vesicles contain a stress-specific protein cargo and whether serum aldolase C has a brain origin. Methods We isolated and characterized serum small extracellular vesicles from rats exposed to restraint, immobilization, or no stress, and their proteomes were identified by mass spectrometry. Data available via ProteomeXchange with identifier PXD009085 were validated, in part, by western blot. In utero electroporation was performed to study the direct transfer of recombinant aldolase C-GFP from brain cells to blood small extracellular vesicles. Results A differential proteome was identified among the experimental groups, including aldolase C, astrocytic glial fibrillary acidic protein, synaptophysin, and reelin. Additionally, we observed that, when expressed in the brain, aldolase C tagged with green fluorescent protein could be recovered in serum small extracellular vesicles. Conclusion The protein cargo of serum small extracellular vesicles constitutes a valuable source of biomarkers of stress-induced diseases, including those characterized by depressive-like behaviors. Brain-to-periphery signaling mediated by a differential molecular cargo of small extracellular vesicles is a novel and challenging mechanism by which the brain might communicate health and disease states to the rest of the body.

4-Methylthioamphetamine (MTA) is a phenylisopropylamine derivative whose use has been associated with severe intoxications. MTA is usually regarded as a selective serotonin-releasing agent. Nevertheless, previous data have suggested that its mechanism of action probably involves a catecholaminergic component. As little is known about dopaminergic effects of this drug, in this work the actions of MTA upon the dopamine (DA) transporter (DAT) were studied in vitro, in vivo and in silico. Also, the possible abuse liability of MTA was behaviourally assessed. MTA exhibited an in vitro affinity for the rat DAT in the low micromolar range (6.01 lM) and induced a significant, dose-dependent increase in striatal DA. MTA significantly increased c-Fos-positive cells in striatum and nucleus accumbens, induced conditioned place preference and increased locomotor activity. Docking experiments were performed in a homology model of the DAT. In conclusion, our results show that MTA is able to increase extracellular striatal DA levels and that its administration has rewarding properties. These effects were observed at concentrations or doses that can be relevant to its use in human beings.4-Methylthioamphetamine (MTA) is a phenylisopropylamine derivative originally synthesized and evaluated as an anorectic drug more than 40 years ago [1]. Subsequently, it was demonstrated that MTA is a potent, selective and non-neurotoxic serotonin (5-HT)-releasing agent in vitro [2,3] and in vivo [4], an effect that is mediated via the 5-HT transporter (SERT) [5,6]. MTA gained notoriety in the late 1990s as a street drug commonly known as 'flatliner', and its use has been associated with severe intoxications and several deaths [7][8][9][10]. Even though MTA is usually regarded as a selective serotonergic agent, it also potently inhibits monoamine oxidase-A (MAO-A) [4,11], and both hyperthermia [12] and aortic contraction [13] induced by MTA in rodent models can be blocked by a-adrenergic antagonists. In addition, it has been shown that MTA induces dopamine (DA) release from rat striatal synaptosomes pre-loaded with [ 3