Overview of the spectrometer optical fiber feed for the Habitable-zone Planet Finder

The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed precision radial velocity (RV) spectrograph working in the Near Infrared (NIR): 810 - 1280 nm . In this paper we present an overview of the preparation of the optical fibers for HPF. The entire fiber train from the telescope focus down to the cryostat is detailed. We also discuss the fiber polishing, splicing and its integration into the instrument using a fused silica puck. HPF was designed to be able to operate in two modes, High Resolution (HR- the only mode mode currently commissioned) and High Efficiency (HE). We discuss these fiber heads and the procedure we adopted to attach the slit on to the HR fibers.Comment: Presented at 2018 SPIE Astronomical Telescopes + Instrumentation, Austin, Texas, USA. 18 pages, 25 figures, and 2 table

Electrical Compartmentalization in Neurons

The dendritic tree of neurons plays an important role in information processing in the brain. While it is thought that dendrites require independent subunits to perform most of their computations, it is still not understood how they compartmentalize into functional subunits. Here, we show how these subunits can be deduced from the properties of dendrites. We devised a formalism that links the dendritic arborization to an impedance-based tree graph and show how the topology of this graph reveals independent subunits. This analysis reveals that cooperativity between synapses decreases slowly with increasing electrical separation and thus that few independent subunits coexist. We nevertheless find that balanced inputs or shunting inhibition can modify this topology and increase the number and size of the subunits in a context-dependent manner. We also find that this dynamic recompartmentalization can enable branch-specific learning of stimulus features. Analysis of dendritic patch-clamp recording experiments confirmed our theoretical predictions.Peer reviewe

A spinal organ of proprioception for integrated motor action feedback

Proprioception is essential for behavior and provides a sense of our body movements in physical space. Proprioceptor organs are thought to be only in the periphery. Whether the central nervous system can intrinsically sense its own movement remains unclear. Here we identify a segmental organ of proprioception in the adult zebrafish spinal cord, which is embedded by intraspinal mechanosensory neurons expressing Piezo2 channels. These cells are late-born, inhibitory, commissural neurons with unique molecular and physiological profiles reflecting a dual sensory and motor function. The central proprioceptive organ locally detects lateral body movements during locomotion and provides direct inhibitory feedback onto rhythm-generating interneurons responsible for the central motor program. This dynamically aligns central pattern generation with movement outcome for efficient locomotion. Our results demonstrate that a central proprioceptive organ monitors self-movement using hybrid neurons that merge sensory and motor entities into a unified network

ATP-Sensitive Potassium Channel-Mediated Lactate Effect on Orexin Neurons: Implications for Brain Energetics during Arousal

Active neurons have a high demand for energy substrate, which is thought to be mainly supplied as lactate by astrocytes. Heavy lactate dependence of neuronal activity suggests that there may be a mechanism that detects and controls lactate levels and/or gates brain activation accordingly. Here, we demonstrate that orexin neurons can behave as such lactate sensors. Using acute brain slice preparations and patch-clamp techniques, we show that the monocarboxylate transporter blocker α-cyano-4-hydroxycinnamate (4-CIN) inhibits the spontaneous activity of orexin neurons despite the presence of extracellular glucose. Furthermore, fluoroacetate, a glial toxin, inhibits orexin neurons in the presence of glucose but not lactate. Thus, orexin neurons specifically use astrocyte-derived lactate. The effect of lactate on firing activity is concentration dependent, an essential characteristic of lactate sensors. Furthermore, lactate disinhibits and sensitizes these neurons for subsequent excitation. 4-CIN has no effect on the activity of some arcuate neurons, indicating that lactate dependency is not universal. Orexin neurons show an indirect concentration-dependent sensitivity to glucose below 1mM, responding by hyperpolarization, which is mediated by ATP-sensitive potassium channels composed of Kir6.1 and SUR1 subunits. In conclusion, our study suggests that lactate is a critical energy substrate and a regulator of the orexin system. Together with the known effects of orexins in inducing arousal, food intake, and hepatic glucose production, as well as lactate release from astrocytes in response to neuronal activity, our study suggests that orexin neurons play an integral part in balancing brain activity and energy supply

Stimulus-specific adaptation at the synapse level in vitro

published_or_final_versio

A versatile and open-source rapid LED switching system for one-photon imaging and photo-activation

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Battefeld, A., Popovic, M. A., van der Werf, D., & Kole, M. H. P. (2019). A versatile and open-source rapid LED switching system for one-photon imaging and photo-activation. Frontiers in Cellular Neuroscience, 12, (2019): 530. doi:10.3389/fncel.2018.00530.Combining fluorescence and transmitted light sources for microscopy is an invaluable method in cellular neuroscience to probe the molecular and cellular mechanisms of cells. This approach enables the targeted recording from fluorescent reporter protein expressing neurons or glial cells in brain slices and fluorescence-assisted electrophysiological recordings from subcellular structures. However, the existing tools to mix multiple light sources in one-photon microscopy are limited. Here, we present the development of several microcontroller devices that provide temporal and intensity control of light emitting diodes (LEDs) for computer controlled microscopy illumination. We interfaced one microcontroller with μManager for rapid and dynamic overlay of transmitted and fluorescent images. Moreover, on the basis of this illumination system we implemented an electronic circuit to combine two pulsed LED light sources for fast (up to 1 kHz) ratiometric calcium (Ca2+) imaging. This microcontroller enabled the calibration of intracellular Ca2+ concentration and furthermore the combination of Ca2+ imaging with optogenetic activation. The devices are based on affordable components and open-source hardware and software. Integration into existing bright-field microscope systems will take ∼1 day. The microcontroller based LED imaging substantially advances conventional illumination methods by limiting light exposure and adding versatility and speed.This work was supported by grants to MK: European Research Council (FP7/2007-2013)/ERC grant agreement P261114, National Multiple Sclerosis Society grant (RG 4924A1/1) and a NWO-Vici grant 865.17.003. AB received a Grass Fellowship from the Grass Foundation

Cellular mechanisms underlying burst firing in substantia nigra dopamine neurons

Burst firing of substantia nigra dopamine (SN DA) neurons is believed to represent an important teaching signal that instructs synaptic plasticity and associative learning. However, the mechanisms through which synaptic excitation overcomes the limiting effects of somatic Ca2+-dependent K+ current to generate burst firing are controversial. Modeling studies suggest that synaptic excitation sufficiently amplifies oscillatory dendritic Ca2+ and Na+ channel currents to lead to the initiation of high-frequency firing in SN DA neuron dendrites. To test this model, visually guided compartment-specific patch-clamp recording and ion channel manipulation were applied to rodent SN DA neurons in vitro. As suggested previously, the axon of SN DA neurons was typically found to originate from a large-diameter dendrite that was proximal to the soma. However, in contrast to the predictions of the model, (1) somatic current injection generated firing that was similar in frequency and form to burst firing in vivo, (2) the efficacy of glutamatergic excitation was inversely related to the distance of excitation from the axon, (3) pharmacological blockade or genetic deletion of Ca2+ channels did not prevent high-frequency firing, (4) action potential bursts were invariably detected first at sites that were proximal to the axon, and (5) pharmacological blockade of Na+ channels in the vicinity of the axon/soma but not dendritic excitation impaired burst firing. Together, these data suggest that SN DA neurons integrate their synaptic input in a more conventional manner than was hypothesized previously

Phase 1 repolarization rate defines Ca2+ dynamics and contractility on intact mouse hearts.

In the heart, Ca2+ influx through L-type Ca2+ channels triggers Ca2+ release from the sarcoplasmic reticulum. In most mammals, this influx occurs during the ventricular action potential (AP) plateau phase 2. However, in murine models, the influx through L-type Ca2+ channels happens in early repolarizing phase 1. The aim of this work is to assess if changes in the open probability of 4-aminopyridine (4-AP)-sensitive Kv channels defining the outward K+ current during phase 1 can modulate Ca2+ currents, Ca2+ transients, and systolic pressure during the cardiac cycle in intact perfused beating hearts. Pulsed local-field fluorescence microscopy and loose-patch photolysis were used to test the hypothesis that a decrease in a transient K+ current (Ito) will enhance Ca2+ influx and promote a larger Ca2+ transient. Simultaneous recordings of Ca2+ transients and APs by pulsed local-field fluorescence microscopy and loose-patch photolysis showed that a reduction in the phase 1 repolarization rate increases the amplitude of Ca2+ transients due to an increase in Ca2+ influx through L-type Ca2+ channels. Moreover, 4-AP induced an increase in the time required for AP to reach 30% repolarization, and the amplitude of Ca2+ transients was larger in epicardium than endocardium. On the other hand, the activation of Ito with NS5806 resulted in a reduction of Ca2+ current amplitude that led to a reduction of the amplitude of Ca2+ transients. Finally, the 4-AP effect on AP phase 1 was significantly smaller when the L-type Ca2+ current was partially blocked with nifedipine, indicating that the phase 1 rate of repolarization is defined by the competition between an outward K+ current and an inward Ca2+ current