Synthesis, Spectral Characterization and Photoluminescence of 3-chloro-6-methoxy-2-(methylsulfanyl)quinoxaline in Different Solvents: An Experimental and Theoretical Investigation Using DFT.

In the present work, we synthesized 3-chloro-6-methoxy-2-(methyl sulfanyl) quinoxaline (3MSQ) using a microwave-assisted synthesis method. The physicochemical structural analysis of the synthesized compound utilizing 1H-NMR, 13C-NMR, and FT-IR spectroscopy techniques. The photophysical properties of 3MSQ was examined through absorption and fluorescence spectroscopy. Spectroscopic analyses revealed a bathochromic shift in both absorption and fluorescence spectra, attributed to the π → π* transition. Ground and excited state dipole moments was experimentally determined using the solvatochromic shift method, employing various correlations such as Lippert's, Bakhshiev's, Kawski-Chamma-Viallet's equations, and solvent polarity parameters. Our findings indicate that the excited state dipole moments exceed those of the ground state, suggesting increased polarity in the excited state. Further, the while detailed bond length, bond angles, dihedral angles, Mulliken charge distribution, ground state dipole moments and HOMO-LUMO energy gap estimated through ab initio computations using Gaussian-09W. The value of energy band gap obtained from both the methods are in good agreement. Furthermore, employing DFT computational analysis, we identified reactive centers such as electrophilic and nucleophilic sites using molecular electrostatic potential (MESP) 3D plots. Additionally, CIE chromaticity analysis was performed to understand the photoluminescent properties of 3MSQ. The insights derived from these analyses contribute to a better understanding of the molecule's electronic structure, photophysical properties, and solute-solvent interactions, thus providing valuable information regarding its behaviour and characteristics under diverse conditions. These results contribute to a comprehensive understanding of the molecular structure and properties of 3-chloro-6-methoxy-2-(methyl sulfanyl) quinoxaline (3MSQ).

Inactivity produces increases in neurotransmitter release and synapse size.

When hippocampal synapses in culture are pharmacologically silenced for several days, synaptic strength increases. The structural correlate of this change in strength is an increase in the size of the synapses, with all synaptic components--active zone, postsynaptic density, and bouton--becoming larger. Further, the number of docked vesicles and the total number of vesicles per synapse increases, although the number of docked vesicles per area of active zone is unchanged. In parallel with these anatomical changes, the physiologically measured size of the readily releasable pool (RRP) and the release probability are increased. Ultrastructural analysis of individual synapses in which the RRP was previously measured reveals that, within measurement error, the same number of vesicles are docked as are estimated to be in the RRP.

Visualizing postendocytic traffic of synaptic vesicles at hippocampal synapses.

We have investigated mechanisms in postendocytic processing of synaptic vesicles at hippocampal synapses, using synaptobrevin/vesicle-associated membrane protein (VAMP) tagged with variants of the green fluorescent protein. Following exocytosis, VAMP is retrieved at synaptic and adjoining axonal regions. Retrieved VAMP-containing vesicles return to synaptic vesicle clusters at a rate slower than endocytosis. Vesicles containing a different protein, synaptophysin, recluster at a similar rate, suggesting common vesicular intermediates for the two proteins. Activity prolongs the time taken by endocytosed vesicles to return to synapses. Exogenous calcium buffers slow endocytosis but have no additional effect on the time course of reclustering. In contrast, the protein kinase inhibitor staurosporine does not affect endocytosis but slows reclustering. Finally, since VAMP can move freely on surface membranes, sustained synaptic activity leads to mixing of this vesicular component between adjacent synapses.

Synaptic plasticity: rush hour traffic in the AMPA lanes.

Recent experiments indicate that modification of synaptic strength may involve rapid regulation of vesicular traffic on the postsynaptic side of the synapse. The specific vesicular trafficking route taken by postsynaptic receptors appears to depend on the stimulus.

Calcium dynamics during fertilization in C. elegans.

BACKGROUND: Of the animals typically used to study fertilization-induced calcium dynamics, none is as accessible to genetics and molecular biology as the model organism Caenorhabditis elegans. Motivated by the experimental possibilities inherent in using such a well-established model organism, we have characterized fertilization-induced calcium dynamics in C. elegans. RESULTS: Owing to the transparency of the nematode, we have been able to study the calcium signal in C. elegans fertilization in vivo by monitoring the fluorescence of calcium indicator dyes that we introduce into the cytosol of oocytes. In C. elegans, fertilization induces a single calcium transient that is initiated soon after oocyte entry into the spermatheca, the compartment that contains sperm. Therefore, it is likely that the calcium transient is initiated by contact with sperm. This calcium elevation spreads throughout the oocyte, and decays monotonically after which the cytosolic calcium concentration returns to that preceding fertilization. Only this single calcium transient is observed. CONCLUSION: Development of a technique to study fertilization induced calcium transients opens several experimental possibilities, e.g., identification of the signaling events intervening sperm binding and calcium elevation, identifying the possible roles of the calcium elevation such as the completion of meiosis, the formation of the eggshell, and the establishing of the embryo's axis of symmetry.

Dynamics of dendritic calcium transients evoked by quantal release at excitatory hippocampal synapses.

Synaptic N-methyl-D-aspartate (NMDA) receptors detect coincident pre- and postsynaptic activity and play a critical role in triggering changes in synaptic strength at central synapses. Despite intensive study of synaptic plasticity, relatively little is known about the magnitude and duration of calcium accumulation caused by unitary events at individual synapses. We used fluorescence imaging to detect NMDA receptor-mediated miniature synaptic calcium transients (MSCTs) caused by spontaneous release of synaptic vesicles in dendrites of cultured hippocampal neurons. MSCTs originated focally in dendritic regions <1 microm in length and decayed with a time constant of 0.35 +/- 0.03 s. Multiple occurrences of MSCTs recorded at single sites had fluctuating amplitudes, with a coefficient of variation of 0.34. From the reduction in the spatial spread of MSCTs with decreasing concentration of indicator dye, we estimated that the dominant endogenous calcium buffer in dendrites is relatively immobile (diffusion coefficient between 10 and 50 microm(2)/s). We conclude that calcium rise caused by spontaneous quantal synaptic NMDA receptor activation (i) is variable, (ii) lasts for a time period briefer than previous measurements indicate, and (iii) is confined by endogenous calcium buffers to local dendritic regions even when synapses are not on spines.

Synaptic interactions mediating synchrony and oscillations in primate sensorimotor cortex.

The appearance of oscillatory modes of 'gamma' activity in many cortical areas of different species has generated interest in understanding their underlying mechanisms and possible functions. This paper reviews evidence from studies on primate motor cortex showing that oscillatory activity entrains many neurons during periods of exploratory manipulative behavior. These oscillatory episodes synchronize widely spread neurons in sensorimotor cortex bilaterally, including descending corticospinal neurons, as evidenced by correlated modulations in EMG activity. The resulting neural synchronization involves task-related and -unrelated neurons similarly, suggesting that it is more likely to play some global role in attention than mediating any obvious interactions involved in coordinating movements. Intracellular recordings have elucidated the strength and types of synaptic interactions between motor cortical neurons that are involved in both normal and oscillatory activity. Spike-triggered averages (STAs) of intracellular membrane potentials have revealed serial connections in the form of unitary excitatory and inhibitory post-synaptic potentials (EPSPs and IPSPs). More commonly, STAs showed large synchronous excitatory or inhibitory potentials (ASEPs and ASIPs) beginning before the trigger spike and composed of multiple unitary events. ASEPs involved synchronous activity in a larger and more widespread group of presynaptic neurons than ASIPs. During oscillatory episodes synchronized excitatory and inhibitory synaptic potentials occurred in varying proportions. EPSPs evoked by stimulating neighboring cortical sites during the depolarizing phase of spontaneous oscillations showed evidence of transient potentiation. These observations are consistent with several functional hypotheses, but fit best with a possible role in attention or arousal.

Reversal of synaptic vesicle docking at central synapses.

We used quantitative fluorescence imaging of vesicles labeled with membrane-soluble dyes to determine rates of undocking and spontaneous exocytosis of vesicles docked to the active zone of hippocampal synapses in culture. Individual vesicles undock about once per two minutes and spontaneously exocytose about once per eight minutes. Thus, not only does undocking occur, but it is over threefold faster than spontaneous fusion.

Optical detection of synaptic vesicle exocytosis and endocytosis.

Recent advances in optical methods have catalyzed a detailed study of individual visualized synapses in several model systems. Quantal events at small central synapses, as well as single granule exocytosis in secretory cells, have been detected using quantitative fluorescence imaging. Sensitive detection of exocytosis and endocytosis at individual synapses has advanced our knowledge of synaptic vesicle trafficking.

Synaptic plasticity: step-wise strengthening.

Recent studies suggest that the strength of synapses in the brain may change in a step-wise manner, rather than continuously.

Synaptic vesicles retain their identity through the endocytic cycle.

After fusion of synaptic vesicles with presynaptic membrane and secretion of the contents of the vesicles into the synaptic cleft (a process known as exocytosis), the vesicular membrane is retrieved by endocytosis (internalization) for re-use. Several issues regarding endocytosis at central synapses are unresolved, including the location of membrane retrieval (relative to the active zone, where exocytosis occurs), the time course of various endocytic steps, and the recycling path taken by newly endocytosed membranes. The classical model of synaptic-vesicle recycling, proposed by analogy to other cellular endocytic pathways, involves retrieval of the membrane, fusion of the membrane with endosome-like compartments and, finally, budding of new synaptic vesicles from endosomes, although the endosomal station may not be obligatory. Here we test the classical model by using the fluorescent membrane dye FM1-43 with quantitative fluorescence microscopy. We find that the amount of dye per vesicle taken up by endocytosis equals the amount of dye a vesicle releases on exocytosis; therefore, we conclude that the internalized vesicles do not, as the classical picture suggests, communicate with intermediate endosome-like compartments during the recycling process.

Synaptic plasticity: neighborhood influences.

Recent studies indicate that, when the strengths of specific synapses are modified by activity, changes in strengths also occur at neighboring synapses; this neighborhood influence has important implications for how synaptic modifications implement learning and memory.

Heterogeneous release properties of visualized individual hippocampal synapses.

We have used endocytotic uptake of the styryl dye FM1-43 at synaptic terminals (Betz and Bewick, 1992) to study properties of individual synapses formed by axons of single hippocampal neurons in tissue culture. The distribution of values for probability of evoked transmitter release p estimated by dye uptake is continuous, with a preponderance of low p synapses and a broad spread of probabilities. We have validated this method by demonstrating that the optically estimated distribution of p at autapses in single-neuron microislands predicts, with no free parameters, the rate of blocking of NMDA responses by the noncompetitive antagonist MK-801 at the same synapses. Different synapses made by a single axon exhibited varying amounts of paired-pulse modulation; synapses with low p tended to be facilitated more than those with high p. The increment in release probability produced by increasing external calcium ion concentration also depended on a synapse's initial p value. The size of the recycling pool of vesicles was strongly correlated with p as well, suggesting that synapses with higher release probabilities had more vesicles. Finally, p values of neighboring synapses were correlated, indicating local interactions in the dendrite or axon, or both.