A well-defined readily releasable pool with fixed capacity for storing vesicles at calyx of Held.

The readily releasable pool (RRP) of vesicles is a core concept in studies of presynaptic function. However, operating principles lack consensus definition and the utility for quantitative analysis has been questioned. Here we confirm that RRPs at calyces of Held from 14 to 21 day old mice have a fixed capacity for storing vesicles that is not modulated by Ca2+. Discrepancies with previous studies are explained by a dynamic flow-through pool, established during heavy use, containing vesicles that are released with low probability despite being immediately releasable. Quantitative analysis ruled out a posteriori explanations for the vesicles with low release probability, such as Ca2+-channel inactivation, and established unexpected boundary conditions for remaining alternatives. Vesicles in the flow-through pool could be incompletely primed, in which case the full sequence of priming steps downstream of recruitment to the RRP would have an average unitary rate of at least 9/s during heavy use. Alternatively, vesicles with low and high release probability could be recruited to distinct types of release sites; in this case the timing of recruitment would be similar at the two types, and the downstream transition from recruited to fully primed would be much faster. In either case, further analysis showed that activity accelerates the upstream step where vesicles are initially recruited to the RRP. Overall, our results show that the RRP can be well defined in the mathematical sense, and support the concept that the defining mechanism is a stable group of autonomous release sites

Determining the neurotransmitter concentration profile at active synapses

Establishing the temporal and concentration profiles of neurotransmitters during synaptic release is an essential step towards understanding the basic properties of inter-neuronal communication in the central nervous system. A variety of ingenious attempts has been made to gain insights into this process, but the general inaccessibility of central synapses, intrinsic limitations of the techniques used, and natural variety of different synaptic environments have hindered a comprehensive description of this fundamental phenomenon. Here, we describe a number of experimental and theoretical findings that has been instrumental for advancing our knowledge of various features of neurotransmitter release, as well as newly developed tools that could overcome some limits of traditional pharmacological approaches and bring new impetus to the description of the complex mechanisms of synaptic transmission

Observational Behavior Assessment for Psychological Competencies in Police Officers:A Proposed Methodology for Instrument Development

This paper proposes and showcases a methodology to develop an observational behavior assessment instrument to assess psychological competencies of police officers. We outline a step-by-step methodology for police organizations to measure and evaluate behavior in a meaningful way to assess these competencies. We illustrate the proposed methodology with a practical example. We posit that direct behavioral observation can be key in measuring the expression of psychological competence in practice, and that psychological competence in practice is what police organizations should care about. We hope this paper offers police organizations a methodology to perform scientifically informed observational behavior assessment of their police officers’ psychological competencies and inspires additional research efforts into this important area

Presynaptic ATP Decreases During Physiological-Like Activity in Neurons Tuned for High-Frequency Transmission

Recent evidence indicates that the concentration of ATP remains stable during neuronal activity due to activity-dependent ATP production. However, the mechanisms of activity-dependent ATP production remain controversial. To stabilize the ATP concentration, feedforward mechanisms, which may rely on calcium or the sodium-potassium pump, do not require changes in the ATP and ADP concentrations. On the other hand, feedback mechanisms could be triggered by changes in the concentration of the adenine nucleotides. To test the possibility of feedback mechanisms, we quantified the ATP concentration in presynaptic terminals during synaptic activity in acute brain slices from mice stably expressing a genetically encoded ATP sensor. We first focused on the cerebellar mossy fiber bouton (cMFB) as a large presynaptic terminal that is specialized for high-frequency synaptic transmission. At physiological temperature and metabolite concentrations, the resting ATP concentration was in the range of approximately 2.5–2.7 mM. During strong, presumably non-physiological activity, the ATP concentration decreased within a few seconds. Experiments with blockade of ATP production indicated that ATP production increased ~10-fold during neuronal activity. Weaker stimulation resembling physiological activity at this synapse caused a decrease in ATP concentration by ~150 μM. We found similar results with in vivo-recorded spike sequences at the calyx of Held, another central glutamatergic synapse tuned for high-frequency synaptic activity. At conventional small synapses of cultured hippocampal neurons, weak stimulations also caused a decrease in ATP concentrations. Finally, quantitative modeling indicated that a pure ADP-based feedback mechanism can explain the activity-dependent ATP production when assuming a three-times higher maximal rate of ATP production compared to our measured rate of ATP production during high-frequency transmission. Our data reveal ATP reduction in presynaptic terminals during physiological-like activity, provide quantitative constraints on feedback mechanisms, and suggest that the ATP concentration can decrease during signaling, at least in some neuronal compartments of our brain

Two distinct secretory vesicle–priming steps in adrenal chromaffin cells

The calcium-dependent activator proteins for secretion, CAPS1 and CAPS2, facilitate syntaxin opening during synaptic vesicle priming

Neural dynamics of shooting decisions and the switch from freeze to fight

Real-life shooting decisions typically occur under acute threat and require fast switching between vigilant situational assessment and immediate fight-or-flight actions. Recent studies suggested that freezing facilitates action preparation and decision-making but the neurocognitive mechanisms remain unclear. We applied functional magnetic resonance imaging, posturographic and autonomic measurements while participants performed a shooting task under threat of shock. two independent studies, in unselected civilians (N = 22) and police recruits (N = 54), revealed that preparation for shooting decisions under threat is associated with postural freezing, bradycardia, midbrain activity (including the periaqueductal gray-PAG) and PAG-amygdala connectivity. Crucially, stronger activity in the midbrain/pAG during this preparatory stage of freezing predicted faster subsequent accurate shooting. Finally, the switch from preparation to active shooting was associated with tachycardia, perigenual anterior cingulate cortex (pgACC) activity and pgACC-amygdala connectivity. These findings suggest that threat-anticipatory midbrain activity centred around the PAG supports decision-making by facilitating action preparation and highlight the role of the pgACC when switching from preparation to action. These results translate animal models of the neural switch from freeze-to-action. In addition, they reveal a core neural circuit for shooting performance under threat and provide empirical evidence for the role of defensive reactions such as freezing in subsequent action decision-making

Profiling Synaptic Proteins Identifies Regulators of Insulin Secretion and Lifespan

Cells are organized into distinct compartments to perform specific tasks with spatial precision. In neurons, presynaptic specializations are biochemically complex subcellular structures dedicated to neurotransmitter secretion. Activity-dependent changes in the abundance of presynaptic proteins are thought to endow synapses with different functional states; however, relatively little is known about the rules that govern changes in the composition of presynaptic terminals. We describe a genetic strategy to systematically analyze protein localization at Caenorhabditis elegans presynaptic specializations. Nine presynaptic proteins were GFP-tagged, allowing visualization of multiple presynaptic structures. Changes in the distribution and abundance of these proteins were quantified in 25 mutants that alter different aspects of neurotransmission. Global analysis of these data identified novel relationships between particular presynaptic components and provides a new method to compare gene functions by identifying shared protein localization phenotypes. Using this strategy, we identified several genes that regulate secretion of insulin-like growth factors (IGFs) and influence lifespan in a manner dependent on insulin/IGF signaling