Y. De Koninck

Remote Optogenetic Activation and Sensitization of Pain Pathways in Freely Moving Mice

We report a novel model in which remote activation of peripheral nociceptive pathways in transgenic mice is achieved optogenetically, without any external noxious stimulus or injury. Taking advantage of a binary genetic approach, we selectively targeted Nav1.8+ sensory neurons for conditional expression of channelrhodopsin-2 (ChR2) channels. Acute blue light illumination of the skin produced robust nocifensive behaviors, evoked by the remote stimulation of both peptidergic and nonpeptidergic nociceptive fibers as indicated by c-Fos labeling in laminae I and II of the dorsal horn of the spinal cord. A non-nociceptive component also contributes to the observed behaviors, as shown by c-Fos expression in lamina III of the dorsal horn and the expression of ChR2–EYFP in a subpopulation of large-diameter Nav1.8+ dorsal root ganglion neurons. Selective activation of Nav1.8+ afferents in vivo induced central sensitization and conditioned place aversion, thus providing a novel paradigm to investigate plasticity in the pain circuitry. Long-term potentiation was similarly evoked by light activation of the same afferents in isolated spinal cord preparations. These findings demonstrate, for the first time, the optical control of nociception and central sensitization in behaving mammals and enables selective activation of the same class of afferents in both in vivo and ex vivo preparations. Our results provide a proof-of-concept demonstration that optical dissection of the contribution of specific classes of afferents to central sensitization is possible. The high spatiotemporal precision offered by this non-invasive model will facilitate drug development and target validation for pain therapeutics.

Quantitative myelin imaging with coherent anti-Stokes Raman scattering microscopy: alleviating the excitation polarization dependence with circularly polarized laser beams

The use of coherent anti-Stokes Raman scattering microscopy tuned to the lipid vibration for quantitative myelin imaging suffers from the excitation polarization dependence of this third-order nonlinear optical effect. The contrast obtained depends on the orientation of the myelin membrane, which in turn affects the morphometric parameters that can be extracted with image analysis. We show how circularly polarized laser beams can be used to avoid this complication, leading to images free of excitation polarization dependence. The technique promises to be optimal for in vivo imaging and the resulting images can be used for coherent anti-Stokes Raman scattering optical histology on native state tissue.

Coxsackievirus Adenovirus Receptor Loss Impairs Adult Neurogenesis, Synapse Content, and Hippocampus Plasticity.

Although we are beginning to understand the late stage of neurodegenerative diseases, the molecular defects associated with the initiation of impaired cognition are poorly characterized. Here, we demonstrate that in the adult brain, the coxsackievirus and adenovirus receptor (CAR) is located on neuron projections, at the presynapse in mature neurons, and on the soma of immature neurons in the hippocampus. In a proinflammatory or diseased environment, CAR is lost from immature neurons in the hippocampus. Strikingly, in hippocampi of patients at early stages of late-onset Alzheimers disease (AD), CAR levels are significantly reduced. Similarly, in triple-transgenic AD mice, CAR levels in hippocampi are low and further reduced after systemic inflammation. Genetic deletion of CAR from the mouse brain triggers deficits in adult neurogenesis and synapse homeostasis that lead to impaired hippocampal plasticity and cognitive deficits. We propose that post-translational CAR loss of function contributes to cognitive defects in healthy and diseased-primed brains. SIGNIFICANCE STATEMENT This study addressed the role of the coxsackievirus and adenovirus receptor (CAR), a single-pass cell adhesion molecule, in the adult brain. Our results demonstrate that CAR is expressed by mature neurons throughout the brain. In addition, we propose divergent roles for CAR in immature neurons, during neurogenesis, and at the mature synapse. Notably, CAR loss of function also affects hippocampal plasticity.

A wireless optogenetic headstage with multichannel neural signal compression

This paper presents a multichannel wireless op-togenetic headstage providing neural recording and optical stimulation capabilities simultaneously. The proposed headstage, which is entirely built using commercial off-the-shelf components, includes 32 electrophysiological recording channels and up to 32 high-power optical stimulation channels. It can process 32 neuronal signals in real-time with high compression ratio using an embedded digital signal processor performing spike detection and data compression in-situ. The presented headstage is small and lightweight rendering it suitable for conducting in-vivo experiments with freely moving transgenic rodents. We report results obtained from in-vivo experiments showing that the proposed wireless headstage can collect, detect and compress the microvolts amplitude neuronal signals evoked by light stimulation with a high averaged peak-signal-to-noise ratio of 22.4 dB and a high averaged signal-to-noise distortion ratio of 17.0 dB. The design of this headstage is using a rigid-flex printed circuit board, resulting into a lightweight (2.8 g) and compact device (17×18×10 mm3).

A CMOS lock-in-amplifier with semi-digital automatic phase tuning

A new low-power custom integrated lock-in amplifier (LIA) with semi-digital automatic phase tuning is presented. The proposed LIA leverages a new semi-digital phase tuning peripheral loop to automatically align the relative phase of a low-amplitude input signal of known carrier with that of a reference signal to increase sensitivity while decreasing the power consumption of the LIA compared with previous solutions. The proposed LIA is designed for a specific reference frequency of 1.024 KHz which is suitable for most biomedical fiber photometry applications. The proposed LIA is implemented in a 0.18-μm CMOS technology with power supply voltage of 1.8 V. The proposed LIA consumes 60 μW at an operating frequency of 1.024 KHz, and presents a dynamic reserve of 33 dB for a detection bandwidth of 100 Hz and a FOM of 1.77 nW/Hz.

An optimized adaptive spike detector for behavioural experiments

This paper presents the in vivo performances of a resource-optimized digital action potential (AP) detector featuring an adaptive threshold based on a new Sigma-delta control loop. The proposed AP detector is optimized for utilizing low hardware resources, which makes it suitable for real-time implementation on most common low-power microcontroller units (MCU). The adaptive threshold is calculated using a digital control loop based on a Sigma-delta modulator that precisely estimates the standard deviation of the neuronal signal amplitude. The detector was demonstrated using a common MCU from MSP430 family, incorporated into a small wireless platform for combined optogenetics and neura recording. The system has been fully characterized experimentally within in vivo experiments on a freely-moving transgenic mouse expressing ChannelRhodospin (Thy1::ChR2-YFP line4. The results demonstrate that the proposed AP detector can be used to achieve overall data reduction ratios above 11 hen transmitting only the detected APs. A comparison of the obtained results with other thresholding approaches shows that the pr posed detector provides similar performances to those significantly more resource demanding approaches.

Live demonstration: A wireless headstage enabling combined optogenetics and multichannel electrophysiological recording

The demonstration will presents a battery powered multichannel wireless optogenetic headstage providing neural recording and optical stimulation capabilities simultaneously. The proposed headstage, which is entirely built using commercial off-the-shelf components, includes 32 electrophysiological recording channels and up to 32 high-power optical stimulation channels. It can process 32 neuronal signals in real-time with high compression ratio using an FPGA performing spike detection and data compression in-situ for fitting 32 channels over a low-power 2.4-GHz ISM data link (compression ratio > 500), hence greatly decreasing power and complexity. The presented headstage is small and lightweight enough for enabling optogenetic in-vivo experiments with freely moving transgenic rodents.

A fully implantable multichip neural interface with a new scalable current-reuse front-end

This paper presents a fully implantable brain machine interface based on a new CMOS system-on-a-chip (SOC) including a low-power multi-channel current-reuse analog front-end (AFE), a multi-band wireless transceiver and a power management unit retrieving power from a 13.56 MHz carrier through a new 5-coil inductive link. In addition to this SOC, the proposed interface includes a low-power microcontroller, a wideband antenna and a double-sided power recovery coil. All components are bonded on a thin flexible printed circuit board. The AFE uses a new current-reuse circuit topology based on a current-mirror opamp which is scalable to very large number of recording channels, thanks to its small implementation area and its low-power consumption. It includes a low-noise amplifier (LNA) and a programmable gain amplifier (PGA) presenting tree selectable gains of 35 dB, 43.1 dB and 49.5 dB. The SOC is fabricated in a CMOS 180-nm process and has a size of 1.3 mm × 1.8 mm. The AFE has a low-power consumption of 9 µW (4.5 µw for LNA and 4.5 µw for PGA) per channel, for an input referred noise of 3.2 µV. A 5-coil wireless power link is utilized with an efficiency of 28% and a maximum power delivered to the load of 81 mW through a 1 cm2 flexible coil. The ultra wideband edge combining BPSK transmitter reaches a maximum data rate of 800 Mbps at 6.7 pJ/bit, and the 2.4-GHz OOK receiver reaches a maximum data rate of 100 Mbps. The whole system consumes 12.3 mW and weights 0.163 g. Finally, we present biological results obtained in-vivo from the cortex of an anesthetized mouse.

A wireless photostimulator for optogenetics with live animals

In this paper, we present a wireless photostimulator providing high output power from small 1.5-V Zinc-Air coin battery to stimulate light sensitized neurons. To overcome the limits of such a small energy source e.g. discharging current and voltage, the proposed photostimulator is based on a DC/DC converter and a switched capacitor circuit to provide high voltage (4 V) and high current (maximum 20 mA) to the stimulating μLEDs. These LED driving voltages and currents are modulated by a PWM signal, and designed to provide a stimulation pulsewidth of 5-ms at a period of 500 ms. A charge pump circuit is used to boost the battery voltage level up to 4 V from the aforementioned low-voltage coin battery. The output current of the proposed LED driver circuit is adjustable to provide different output light power levels output. The post layout simulation results in IBM CMRF8SF 130-nm process shows a variation of less than 1 % of the output LED driver current of the across all PVT corners. The efficiency of the proposed photostimulator, including the charge pump and the LED driver, is of 66 %.

A high-precision CMOS biophotometry sensor with noise cancellation and two-step A/D conversion

Fluorescence biophotometry measurements require wide dynamic range (DR) and high sensitivity laboratory apparatus. Indeed, it is often very challenging to accurately resolve the small fluorescence variations in presence of high background tissue autofluorescence. There is a great need for smaller detectors combining high linearity, high sensitivity, and high-energy efficiency. This paper presents a new high-dynamic range CMOS photodetector embedding a photosensor and a high-precision two-step analog-to-digital converter (ADC) with a noise cancellation scheme. In this system, a 16-bit two-step ADC sucessivley uses an integrating ADC and a successive approximation register (SAR) ADC enabling wide dynamic range and high energy-efficiency photocurrent quantization. Noise cancellation is achieved through a SAR digital-to-analog (DAC) capacitor bank to store and subtract the low-frequency noise from the output of a capacitive transimpedance amplifier (CTIA) throughout each data conversion. The 6-most significant bits are resolved through the integrating ADC, while the 10-least significant bits are extracted by the SAR ADC. The two-step data converter uses a hardware sharing scheme to decrease the chip size and to improve energy-efficiency. The proposed optoelectronic detector is implemented in a 0.18-µm CMOS technology, consuming 60 µW from a 3.3-V supply voltage while achieving a DR of 94 dB, a minimum detectable current of 200-ƒArms, at 1-kS/s sampling rate. The proposed biosensor presents a FOM of 1.46 pJ/conv. which is among the best reported performance among similar systems.