Titration of synaptotagmin I expression differentially regulates release of norepinephrine and neuropeptide Y

Function of Drosophila Synaptotagmins in membrane trafficking at synapses

The Synaptotagmin (SYT) family of proteins play key roles in regulating membrane trafficking at neuronal synapses. Using both Ca²⁺-dependent and Ca²⁺-independent interactions, several SYT isoforms participate in synchronous and asynchronous fusion of synaptic vesicles (SVs) while preventing spontaneous release that occurs in the absence of stimulation. Changes in the function or abundance of the SYT1 and SYT7 isoforms alter the number and route by which SVs fuse at nerve terminals. Several SYT family members also regulate trafficking of other subcellular organelles at synapses, including dense core vesicles (DCV), exosomes, and postsynaptic vesicles. Although SYTs are linked to trafficking of multiple classes of synaptic membrane compartments, how and when they interact with lipids, the SNARE machinery and other release effectors are still being elucidated. Given mutations in the SYT family cause disorders in both the central and peripheral nervous system in humans, ongoing efforts are defining how these proteins regulate vesicle trafficking within distinct neuronal compartments. Here, we review the Drosophila SYT family and examine their role in synaptic communication. Studies in this invertebrate model have revealed key similarities and several differences with the predicted activity of their mammalian counterparts. In addition, we highlight the remaining areas of uncertainty in the field and describe outstanding questions on how the SYT family regulates membrane trafficking at nerve terminals.

Light Activation of Calcein Inhibits Vesicle Release of Catecholamines

Calcein, a fluorescent fluid phase marker, has been used to track and visualize cellular processes such as synaptic vesicle fusion. It is also the fluorophore for live cells in the commonly used Live/Dead viability assay. In pilot studies designed to determine fusion pore open size and vesicle movement in secretory cells, imaging analysis revealed that calcein reduced the number of vesicles released from the cells when stimulated with nicotine. Using amperometry to detect individual vesicle release events, we show that when calcein is present in the media, the number of vesicles that fuse with the cellular membrane is reduced when cells are stimulated with either nicotine or high K⁺. Experimentally, amperometric electrodes are not undergoing fouling in the presence of calcein. We hypothesized that calcein, when activated by light, releases reactive oxygen species that cause a reduction in secreted vesicles. We show that when calcein is protected from light during experimentation, little to no reduction of vesicle secretion occurred. Therefore, photoactivated calcein can cause deleterious results for measurements of cellular processes, likely to be the result of release of reactive oxygen species.

Contrasting Regulation of Catecholamine Neurotransmission in the Behaving Brain: Pharmacological Insights from an Electrochemical Perspective

Catecholamine neurotransmission plays a key role in regulating a variety of behavioral and physiologic processes, and its dysregulation is implicated in both neurodegenerative and neuropsychiatric disorders. Over the last four decades, in vivo electrochemistry has enabled the discovery of contrasting catecholamine regulation in the brain. These rapid and spatially resolved measurements have been conducted in brain slices, and in anesthetized and freely behaving animals. In this review, we describe the methods enabling in vivo measurements of dopamine and norepinephrine, and subsequent findings regarding their release and regulation in intact animals. We thereafter discuss key studies in awake animals, demonstrating that these catecholamines are not only differentially regulated, but are released in opposition of each other during appetitive and aversive stimuli.

Transcriptome Analysis Reveals Altered Expression of Memory and Neurotransmission Associated Genes in the REM Sleep Deprived Rat Brain

Sleep disorders are associated with cognitive impairment. Selective rapid eye movement sleep (REMS) deprivation (REMSD) alters several physiological processes and behaviors. By employing NGS platform we carried out transcriptomic analysis in brain samples of control rats and those exposed to REMSD. The expression of genes involved in chromatin assembly, methylation, learning, memory, regulation of synaptic transmission, neuronal plasticity and neurohypophysial hormone synthesis were altered. Increased transcription of BMP4, DBH and ATP1B2 genes after REMSD supports our earlier findings and hypothesis. Alteration in the transcripts encoding histone subtypes and important players in chromatin remodeling was observed. The mRNAs which transcribe neurotransmitters such as OXT, AVP, PMCH and LNPEP and two small non-coding RNAs, namely RMRP and BC1 were down regulated. At least some of these changes are likely to regulate REMS and may participate in the consequences of REMS loss. Thus, the findings of this study have identified key epigenetic regulators and neuronal plasticity genes associated to REMS and its loss. This analysis provides a background and opens up avenues for unraveling their specific roles in the complex behavioral network particularly in relation to sustained REMS-loss associated changes.

Differential Releases of Dopamine and Neuropeptide Y from Histamine-Stimulated PC12 Cells Detected by an Aptamer-Modified Nanowire Transistor

Silicon nanowire field-effect transistors modified with specific aptamers can directly detect the minute dopamine and neuropeptide Y released from cells. The binding of these molecules to the aptamers results in a conductance change of the transistor biosensor and illustrates the differential releasing mechanisms of these molecules stored in various vesicle pools.

PC12 cells that lack synaptotagmin I exhibit loss of a subpool of small dense core vesicles

Neurons communicate by releasing neurotransmitters that are stored in intracellular vesicular compartments. PC12 cells are frequently used as a model secretory cell line that is described to have two subpools of vesicles: small clear vesicles and dense core vesicles. We measured transmitter molecules released from vesicles in NGF-differentiated PC12 cells using carbon-fiber amperometry, and relative diameters of individual vesicles using electron microscopy. Both amperometry and electron micrograph data were analyzed by statistical and machine learning methods for Gaussian mixture models. An electron microscopy size correction algorithm was used to predict and correct for observation bias of vesicle size due to tangential slices through some vesicles. Expectation maximization algorithms were used to perform maximum likelihood estimation for the Gaussian parameters of different populations of vesicles, and were shown to be better than histogram and cumulative distribution function methods for analyzing mixed populations. The Bayesian information criterion was used to determine the most likely number of vesicle subpools observed in the amperometric and electron microscopy data. From this analysis, we show that there are three major subpools, not two, of vesicles stored and released from PC12 cells. The three subpools of vesicles include small clear vesicles and two subpools of dense core vesicles, a small and a large dense core vesicle subpool. Using PC12 cells stably transfected with short-hairpin RNA targeted to synaptotagmin I, an exocytotic Ca(2+) sensor, we show that the presence and release of the small dense core vesicle subpool is dependent on synaptotagmin I. Furthermore, synaptotagmin I also plays a role in the formation and/or maintenance of the small dense core vesicle subpool in PC12 cells.

Depression-like Behavior Induced by Nesfatin-1 in Rats: Involvement of Increased Immune Activation and Imbalance of Synaptic Vesicle Proteins

Depression is a multicausal disorder and has been associated with metabolism regulation and immuno-inflammatory reaction. The anorectic molecule nesfatin-1 has recently been characterized as a potential mood regulator, but its precise effect on depression and the possible mechanisms remain unknown, especially when given peripherally. In the present study, nesfatin-1 was intraperitoneally injected to the rats and the depression-like behavior and activity of the hypothalamic-pituitary-adrenal (HPA) axis were evaluated. The plasma concentrations of nesfatin-1, interleukin 6 (IL-6), and C-reactive protein (CRP); and the hypothalamic expression levels of nesfatin-1, synapsin I, and synaptotagmin I mRNA were evaluated in nesfatin-1 chronically treated rats. The results showed that both acute and chronic administration of nesfatin-1 increased immobility in the forced swimming test (FST), and resulted in the hyperactivity of HPA axis, as indicated by the increase of plasma corticosterone concentration and hypothalamic expression of corticotropin-releasing hormone (CRH) mRNA. Moreover, after chronic nesfatin-1 administration, the rats exhibited decreased activity and exploratory behavior in the open field test (OFT) and increased mRNA expression of synapsin I and synaptotagmin I in the hypothalamus. Furthermore, chronic administration of nesfatin-1 elevated plasma concentrations of IL-6 and CRP, which were positively correlated with despair behavior, plasma corticosterone level, and the hypothalamic mRNA expression of synapsin I and synaptotagmin I. These results indicated that exogenous nesfatin-1 could induce the immune-inflammatory activation, which might be a central hug linking the depression-like behavior and the imbalanced mRNA expression of synaptic vesicle proteins in the hypothalamus.