An Adaptive Element-Level Impedance-Matched ASIC With Improved Acoustic Reflectivity for Medical Ultrasound Imaging

This paper presents an active impedance matching scheme that tries to optimize electrical power transfer and acoustic reflectivity in ultrasound transducers. Leveraging negative capacitance-based impedance matching would potentially improve the bandwidth and electrical power transfer while minimizing acoustic reflection of transducer elements and improve uniformity while reducing acoustic crosstalk of transducer arrays. A 16-element transceiver front-end is designed which employs an element-level active capacitive impedance cancellation scheme using an element-level negative impedance converter. The ASIC fabricated in 180-nm HVBCD technology provides high-voltage pulses up to 60 V consuming 3.6 mW and occupying 2.5 mm2. The front-end ASIC is used with a 1-D capacitive micromachined ultrasonic transducer (CMUT) array and its acoustical reflectivity reduction and imaging capabilities have successfully been demonstrated through pulse-echo measurements and acoustic imaging experiments.

A Highly Miniaturized, Chronically Implanted ASIC for Electrical Nerve Stimulation

We present a wireless, fully implantable device for electrical stimulation of peripheral nerves consisting of a powering coil, a tuning network, a Zener diode, selectable stimulation parameters, and a stimulator IC, all encapsulated in biocompatible silicone. A wireless RF signal at 13.56 MHz powers the implant through the on-chip rectifier. The ASIC, designed in TSMC's 180 nm MS RF G process, occupies an area of less than 1.2 mm². The IC enables externally selectable current-controlled stimulation through an on-chip read-only memory with a wide range of 32 stimulation parameters (90-750 µA amplitude, 100 µs or 1 ms pulse width, 15 or 50 Hz frequency). The IC generates the constant current waveform using an 8-bit binary weighted DAC and an H-Bridge. At the most power-hungry stimulation parameter, the average power consumption during a stimulus pulse is 2.6 mW with a power transfer efficiency of ∼5.2%. In addition to benchtop and acute testing, we chronically implanted two versions of the device (a design with leads and a leadless design) on two rats' sciatic nerves to verify the long-term efficacy of the IC and the full system. The leadless device had the following dimensions: height of 0.45 cm, major axis of 1.85 cm, and minor axis of 1.34 cm, with similar dimensions for the device with leads. Both devices were implanted and worked for experiments lasting from 21-90 days. To the best of our knowledge, the fabricated IC is the smallest constant-current stimulator that has been tested chronically.

A Wearable Ultrasonic Neurostimulator - Part I: A 1D CMUT Phased Array System for Chronic Implantation in Small Animals

In this work, we present a wireless ultrasonic neurostimulator, aiming at a truly wearable device for brain stimulation in small behaving animals. A 1D 5-MHz capacitive micromachined ultrasonic transducer (CMUT) array is adopted to implement a head-mounted stimulation device. A companion ASIC with integrated 16-channel high-voltage (60-V) pulsers was designed to drive the 16-element CMUT array. The ASIC can generate excitation signals with element-wise programmable phases and amplitudes: 1) programmable sixteen phase delays enable electrical beam focusing and steering, and 2) four scalable amplitude levels, implemented with a symmetric pulse-width-modulation technique, are sufficient to suppress unwanted sidelobes (apodization). The ASIC was fabricated in the TSMC 0.18- μm HV BCD process within a die size of 2.5 × 2.5 mm². To realize a completely wearable system, the system is partitioned into two parts for weight distribution: 1) a head unit (17 mg) with the CMUT array, 2) a backpack unit (19.7 g) that includes electronics such as the ASIC, a power management unit, a wireless module, and a battery. Hydrophone-based acoustic measurements were performed to demonstrate the focusing and beam steering capability of the proposed system. Also, we achieved a peak-to-peak pressure of 2.1 MPa, which corresponds to a spatial peak pulse average intensity ( I_SPPA) of 33.5 W/cm², with a lateral full width at half maximum (FWHM) of 0.6 mm at a depth of 3.5 mm.

Selective targeting of peripheral cannabinoid receptors prevents behavioral symptoms and sensitization of trigeminal neurons in mouse models of migraine and medication overuse headache

ABSTRACT

Migraine affects ∼15% of the world's population greatly diminishing their quality of life. Current preventative treatments are effective in only a subset of migraine patients, and although cannabinoids seem beneficial in alleviating migraine symptoms, central nervous system side effects limit their widespread use. We developed peripherally restricted cannabinoids (PRCBs) that relieve chronic pain symptoms of cancer and neuropathies, without appreciable central nervous system side effects or tolerance development. Here, we determined PRCB effectiveness in alleviating hypersensitivity symptoms in mouse models of migraine and medication overuse headache. Long-term glyceryl trinitrate (GTN, 10 mg/kg) administration led to increased sensitivity to mechanical stimuli and increased expression of phosphorylated protein kinase A, neuronal nitric oxide synthase, and transient receptor potential ankyrin 1 proteins in trigeminal ganglia. Peripherally restricted cannabinoid pretreatment, but not posttreatment, prevented behavioral and biochemical correlates of GTN-induced sensitization. Low pH-activated and allyl isothiocyanate-activated currents in acutely isolated trigeminal neurons were reversibly attenuated by PRCB application. Long-term GTN treatment significantly enhanced these currents. Long-term sumatriptan treatment also led to the development of allodynia to mechanical and cold stimuli that was slowly reversible after sumatriptan discontinuation. Subsequent challenge with a previously ineffective low-dose GTN (0.1-0.3 mg/kg) revealed latent behavioral sensitization and increased expression of phosphorylated protein kinase A, neuronal nitric oxide synthase, and transient receptor potential ankyrin 1 proteins in trigeminal ganglia. Peripherally restricted cannabinoid pretreatment prevented all behavioral and biochemical correlates of allodynia and latent sensitization. Importantly, long-term PRCB treatment alone did not produce any behavioral or biochemical signs of sensitization. These data validate peripheral cannabinoid receptors as potential therapeutic targets in migraine and medication overuse headache.

Co-Integrated PIN-PMN-PT 2-D Array and Transceiver Electronics by Direct Assembly Using a 3-D Printed Interposer Grid Frame

Tiled modular 2-D ultrasound arrays have the potential for realizing large apertures for novel diagnostic applications. This work presents an architecture for fabrication of tileable 2-D array modules implemented using 1-3 composites of high-bandwidth (BW) PIN-PMN-PT single-crystal piezoelectric material closely coupled with high-voltage CMOS application-specific integrated circuit (ASIC) electronics for buffering and multiplexing functions. The module, which is designed to be operated as a λ -pitch 1.75-D array, benefits from an improved electromechanical coupling coefficient and increased Curie temperature and is assembled directly on top of the ASIC silicon substrate using an interposer backing. The interposer consists of a novel 3-D printed acrylic frame that is filled with conducting and acoustically absorbing silver epoxy material. The ASIC comprises a high-voltage switching matrix with locally integrated buffering and is interfaced to a Verasonics Vantage 128, using a local field programmable gate array (FPGA) controller. Multiple prototype 5 ×6 element array modules have been fabricated by this process. The combined acoustic array and ASIC module was configured electronically by programming the switches to operate as a 1-D array with elements grouped in elevation for imaging and pulse-echo testing. The resulting array configuration had an average center frequency of 4.55 MHz, azimuthal element pitch of [Formula: see text], and exhibited average -20-dB pulsewidth of 592 ns and average -6-dB fractional BW of 77%.

New discoveries in migraine mechanisms and therapeutic targets

Migraine is among the most common and most disabling disorders worldwide, yet its underlying pathophysiology is among the most poorly understood. New information continues to emerge on mechanisms within the central and peripheral nervous systems that may contribute to migraine attacks. Additionally, new therapeutics have recently become available and along with much needed relief for many patients, these drugs provide insight into the disorder based on their mechanism of action. This review will cover new findings within the last several years that add to the understanding of migraine pathophysiology, including those related to the vasculature, calcitonin gene-related peptide (CGRP), and mechanisms within the cortex and meninges that may contribute to attacks. Discussion will also cover recent findings on novel therapeutic targets, several of which continue to show promise in new preclinical studies, including acid-sensing ion channels (ASICs) and the delta-opioid receptor (DOR).

A High-Resolution Opto-Electrophysiology System With a Miniature Integrated Headstage

This work presents a fully integrated neural interface system in a small form factor (1.9 g), consisting of a μLED silicon optoelectrode (12 μLEDs and 32 recording sites in a 4-shank configuration), an Intan 32-channel recording chip, and a custom optical stimulation chip for controlling 12 μLEDs. High-resolution optical stimulation with approximately 68.5 nW radiant flux resolution is achieved by a custom LED driver ASIC, which enables individual control of up to 48 channels with a current precision of 1 μA, a maximum current of 1.024 mA, and an update rate of >10 kHz. Recording is performed by an off-the-shelf 32-channel digitizing front-end ASIC from Intan. Two compact custom interface printed circuit boards were designed to link the headstage with a PC. The prototype system demonstrates precise current generation, sufficient optical radiant flux generation , and fast turn-on of μLEDs . Single animal in vivo experiments validated the headstage's capability to precisely modulate single neuronal activity and independently modulate activities of separate neuronal populations near neighboring optoelectrode shanks.

Electrostatic charge at position 552 affects the activation and permeation of FMRFamide-gated Na+ channels

The FMRFamide-gated Na(+) channel (FaNaC) is a unique peptide-gated sodium channel and a member of the epithelial sodium channel/degenerin family. Previous studies have shown that an aspartate residue (Asp(552)) in the second transmembrane domain is involved in activation of the FaNaC. To examine the significance of a negative charge at position 552, we used a cysteine-modification method. Macroscopic currents of a cysteine mutant (D552C) were potentiated or inhibited by use of positively or negatively charged sulfhydryl reagents ([2-(trimethylammonium)ethyl]methanethiosulfonate bromide, MTSET, and sodium (2-sulfonatoethyl)methanethiosulfonate, MTSES, respectively). Dose-response analysis showed that treatment with MTSET increased the potency of the FMRFamide in the FaNaC whereas treatment with MTSES reduced the maximum response. Negative charge at position 552 was necessary for the characteristic inward rectification of the FaNaC. These results suggest that negative electric charge at position 552 is important to the activation and permeation properties of the FaNaC.

Inhibition of voltage-gated Na(+) currents in sensory neurones by the sea anemone toxin APETx2

BACKGROUND AND PURPOSE

APETx2, a toxin from the sea anemone Anthropleura elegantissima, inhibits acid-sensing ion channel 3 (ASIC3)-containing homo- and heterotrimeric channels with IC(50) values < 100 nM and 0.1-2 µM respectively. ASIC3 channels mediate acute acid-induced and inflammatory pain response and APETx2 has been used as a selective pharmacological tool in animal studies. Toxins from sea anemones also modulate voltage-gated Na(+) channel (Na(v) ) function. Here we tested the effects of APETx2 on Na(v) function in sensory neurones.

EXPERIMENTAL APPROACH

Effects of APETx2 on Na(v) function were studied in rat dorsal root ganglion (DRG) neurones by whole-cell patch clamp.

KEY RESULTS

APETx2 inhibited the tetrodotoxin (TTX)-resistant Na(v) 1.8 currents of DRG neurones (IC(50) , 2.6 µM). TTX-sensitive currents were less inhibited. The inhibition of Na(v) 1.8 currents was due to a rightward shift in the voltage dependence of activation and a reduction of the maximal macroscopic conductance. The inhibition of Na(v) 1.8 currents by APETx2 was confirmed with cloned channels expressed in Xenopus oocytes. In current-clamp experiments in DRG neurones, the number of action potentials induced by injection of a current ramp was reduced by APETx2.

CONCLUSIONS AND IMPLICATIONS

APETx2 inhibited Na(v) 1.8 channels, in addition to ASIC3 channels, at concentrations used in in vivo studies. The limited specificity of this toxin should be taken into account when using APETx2 as a pharmacological tool. Its dual action will be an advantage for the use of APETx2 or its derivatives as analgesic drugs.

Release of ATP from rat urinary bladder mucosa: role of acid, vanilloids and stretch

BACKGROUND AND PURPOSE

ATP, released from urothelial cells, modulates afferent nerve firing from the urinary bladder. Here, we have characterized ATP release from the rat bladder mucosa in response to acid, capsaicin, electrical field stimulation (EFS) and stretch, using agonists and antagonists at transient receptor potential vanilloid receptor 1 (TRPV1) and acid-sensing ion channels (ASICs).

EXPERIMENTAL APPROACH

Rat mucosal strips (containing urothelium and lamina propria) in Perspex microbaths were superfused with Krebs solution. ATP was measured after exposure of matched strips to acid (pH 6.6-5.0), capsaicin (0.1-10 microM), EFS or stretch (150% of original length).

KEY RESULTS

Median basal ATP release was 3.46 nmol g(-1). The mucosal strips responded to stimuli with potency order (median, IQR): acid (pH 5.6-6.0) 286 (103-555) > 10 microM capsaicin 188 (117-431) > 10 Hz EFS 63.0 (13.3-96.4) > stretch 24.4 (6.73-55.1) nmol ATP g(-1). ATP release in response to acid was pH dependent (P < 0.05). Responses to capsaicin did not desensitize nor were they concentration dependent. TRPV1 antagonist, capsazepine (10 microM) abolished capsaicin-evoked ATP release, and reduced acid-evoked (pH 6.5) release to 30% (P < 0.001). The ASIC channel antagonists gadolinium (0.1 mM) and amiloride (0.3 microM) reduced (P < 0.05) the acid-evoked (pH 6.5) release to 40 and 6.5% respectively. ASIC (ASIC1, ASIC2a, ASIC2b, ASIC3) and two TRPV1 gene products were detected in mucosal and detrusor extracts.

CONCLUSIONS AND IMPLICATIONS

Capsaicin (at TRPV1) and acid (at both TRPV1 and ASIC) induce ATP release from the rat bladder mucosa. This ATP appears to be principally of urothelial origin. This study highlights the importance of ATP and acid as signalling molecules in modulating bladder function.

Nociceptors: a phylogenetic view

The ability to react to environmental change is crucial for the survival of an organism and an essential prerequisite is the capacity to detect and respond to aversive stimuli. The importance of having an inbuilt "detect and protect" system is illustrated by the fact that most animals have dedicated sensory afferents which respond to noxious stimuli called nociceptors. Should injury occur there is often sensitization, whereby increased nociceptor sensitivity and/or plasticity of nociceptor-related neural circuits acts as a protection mechanism for the afflicted body part. Studying nociception and nociceptors in different model organisms has demonstrated that there are similarities from invertebrates right through to humans. The development of technology to genetically manipulate organisms, especially mice, has led to an understanding of some of the key molecular players in nociceptor function. This review will focus on what is known about nociceptors throughout the Animalia kingdom and what similarities exist across phyla; especially at the molecular level of ion channels.

Acid-sensing ion channels: A new target for pain and CNS diseases

Low pH in tissue can evoke pain in animals and humans, and is an important factor in hyperalgesia. Research has also implicated acidosis in psychiatric and neurological diseases. One emerging class of pH-detecting receptors is that of the acid-sensing ion channels (ASICs). Advances in ASIC research have improved the understanding of the role played by pH dynamics in physiological and pathophysiological processes. Increasing evidence suggests that targeting ASICs with pharmacological agents may offer an effective and novel approach for treating pain and diseases of the CNS. However, the development of pharmaceuticals that target ASICs and are suitable for clinical use remains an obstacle. This review provides an update on ASICs and their potential for therapeutic modification in pain and CNS diseases.

Recombinant production and solution structure of PcTx1, the specific peptide inhibitor of ASIC1a proton-gated cation channels

Acid-sensing ion channels (ASICs) are thought to be important ion channels, particularly for the perception of pain. Some of them may also contribute to synaptic plasticity, learning, and memory. Psalmotoxin 1 (PcTx1), the first potent and specific blocker of the ASIC1a proton-sensing channel, has been successfully expressed in the Drosophila melanogaster S2 cell recombinant expression system used here for the first time to produce a spider toxin. The recombinant toxin was identical in all respects to the native peptide, and its three-dimensional structure in solution was determined by means of (1)H 2D NMR spectroscopy. Surface characteristics of PcTx1 provide insights on key structural elements involved in the binding of PcTx1 to ASIC1a channels. They appear to be localized in the beta-sheet and the beta-turn linking the strands, as indicated by electrostatic anisotropy calculations, surface charge distribution, and the presence of residues known to be implicated in channel recognition by other inhibitor cystine knot (ICK) toxins.

Proinflammatory mediators, stimulators of sensory neuron excitability via the expression of acid-sensing ion channels

Tissue acidosis is an important feature of inflammation. It is a direct cause of pain and hyperalgesia. Protons activate sensory neurons mainly through acid-sensing ion channels (ASICs) and the subsequent membrane depolarization that leads to action potential generation. We had previously shown that ASIC transcript levels were increased in inflammatory conditions in vivo. We have now found that this increase is caused by the proinflammatory mediators NGF, serotonin, interleukin-1, and bradykinin. A mixture of these mediators increases ASIC-like current amplitude on sensory neurons as well as the number of ASIC-expressing neurons and leads to a higher sensory neuron excitability. An analysis of the promoter region of the ASIC3 encoding gene, an ASIC specifically expressed in sensory neurons and associated with chest pain that accompanies cardiac ischemia, reveals that gene transcription is controlled by NGF and serotonin.

Single channel properties of rat acid-sensitive ion channel-1alpha, -2a, and -3 expressed in Xenopus oocytes

The mammalian nervous system expresses proton-gated ion channels known as acid-sensing ion channels (ASICs). Depending on their location and specialization some neurons express more than one type of ASIC where they may form homo- or heteromeric channels. Macroscopic characteristics of the ASIC currents have been described, but little is known at the single channel level. Here, we have examined the properties of unitary currents of homomeric rat ASIC1alpha, ASIC2a, and ASIC3 expressed in Xenopus oocytes with the patch clamp technique. We describe and characterize properties unique to each of these channels that can be used to distinguish the various types of ASIC channels expressed in mammalian neurons. The amplitudes of the unitary currents in symmetrical Na(+) are similar for the three types of channels (23-18 pS) and are not voltage dependent. However, ASIC1alpha exhibits three subconductance states, ASIC2a exhibits only one, and ASIC3 none. The kinetics of the three types of channels are different: ASIC1alpha and ASIC2a shift between modes of activity, each mode has different open probability and kinetics. In contrast, the kinetics of ASIC3 are uniform throughout the burst of activity. ASIC1alpha, ASIC2a, and ASIC3 are activated by external protons with apparent pH(50) of 5.9, 5.0, and 5.4, respectively. Desensitization in the continual presence of protons is fast and complete in ASIC1alpha and ASIC3 (2.0 and 4.5 s(-1), respectively) but slow and only partial in ASIC2a (0.045 s(-1)). The response to external Ca(2+) also differs: micro M concentrations of extracellular Ca(2+) are necessary for proton gating of ASIC3 (EC(50) = 0.28 micro M), whereas ASIC1alpha and ASIC2a do not require Ca(2+). In addition, Ca(2+) inhibits ASIC1alpha (K(D) = 9.2 +/- 2 mM) by several mechanisms: decrease in the amplitude of unitary currents, shortening of the burst of activity, and decrease in the number of activated channels. Contrary to previous reports, our results indicate that the Ca(2+) permeability of ASIC1alpha is very small.

Neuronal expression of an FMRFamide-gated Na+ channel and its modulation by acid pH

The molluscan Phe-Met-Arg-Phe-amide (FMRFamide)-gated sodium channels (FaNaCs) show both structural and functional similarities to the mammalian acid-sensing ion channels (ASICs). Both channel types are related to the epithelial sodium channels and, although the neuropeptide FMRFamide directly gates the FaNaCs, it also modulates the proton-gating properties of ASICs. It is not yet known whether protons can alter the gating properties of the FaNaCs. We chose to examine this possibility at a site of FaNaC expression in the nervous system of the mollusk Lymnaea stagnalis. We cloned a putative L. stagnalis FaNaC (LsFaNaC) that exhibited a high degree of sequence identity to the Helix aspersa FaNaC (HaFaNaC, 60%), and a weaker homology to the ASICs (ASIC3, 22%). In situ hybridization was used to map the LsFaNaC expression pattern in the brain and to identify the right pedal giant1 (RPeD1) neuron as a site where the properties of the endogenous channel could be studied. In RPeD1 neurons isolated in culture, we demonstrated the presence of an FMRFamide-gated sodium current with features expected for a FaNaC: amiloride sensitivity, sodium selectivity, specificity for FMRFamide and Phe-Leu-Arg-Phe-amide (FLRFamide), and no dependency on G-protein coupling. The sodium current also exhibited rapid desensitization in response to repeated FMRFamide applications. Lowering of the pH of the bathing solution reduced the amplitude of the FMRFamide-gated inward current, while also activating an additional sustained weak inward current that was apparently not mediated by the FaNaC. Acidification also prevented the desensitization of the FMRFamide-induced inward current. The acid sensitivity of LsFaNaC is consistent with the hypothesis that FaNaCs share a common ancestry with the ASICs.