Single-Sided Multimodal Neural Probe Enabling Co-Localized Recording of Electrical and Chemical Signals.

The development of in vivo analytical tools and methods for recording electrical signals and accurately quantifying chemical signals is a key issue for a comprehensive understanding of brain events. The electrophysiological microelectrode was invented to monitor electrical signals in free-moving brains. On the other hand, electrochemical assays with excellent spatiotemporal resolution provide an effect way to monitor chemical signals in vivo. Unfortunately, the in vivo electrochemical biosensors still have three limitations. First, many biological species such as reactive oxygen species (ROS) and neurotransmitters demonstrate large overpotentials at conventional electrodes. Thus, it is hard to convert the chemical/electrochemical signals of these molecules into electric signals. Second, the interfacial properties of the recognition molecules assembled onto the electrode surfaces have a great influence on the transmission of electric charge through the interface and the stability of the modified recognition molecules. Meanwhile, the surface of biosensors implanted in the brain is easily absorbed by many proteins present in the brain, resulting in the loss of signals. Finally, activities in the brain including neuron discharges and electrophysiological signals may be affected by electrochemical measurements due to the application of extra potentials and/or currents.This Account presents a deep view of the fundamental design principles and solutions in response to the above challenges for developing in vivo biosensors with high performance while meeting the growing requirements, including high selectivity, long-time stability, and simultaneously monitoring electrical and chemical signals. We aim to highlight the basic criteria based on a double-recognition strategy for the selective biosensing of ROS, H2S, and HnS through the rational design of specific recognition molecules followed by electrochemical oxidation or reduction. Recent developments in designing functionalized surfaces through a systematic investigation of self-assembly with Au-S bonds, Au-Se bonds, and Au≡C bonds for facilitating electrochemical properties as well as improving the stability are summarized. More importantly, this Account highlights the novel methodologies for simultaneously monitoring electrical and chemical signals ascribed to the dynamic changes in K+, Na+, and Ca2+ and pH values in vivo. Additionally, SERS-based photophysiological microarray probes have been developed for quantitatively tracking chemical changes in the live brain together with recording electrophysiological signals.The design principles and novel strategies presented in this Account can be extended to the real-time tracking of electrical signals and the accurate quantification of more chemical signals such as amino acids, neurotransmitters, and proteins to understand the brain events. The final part also outlines potential future directions in constructing high-density microarrays, eventually enabling the large-scale dynamic recording of the chemical expression of multineuronal signals across the whole brain. There is still room to develop a multifiber microarray which can be coupled with photometric methods to record chemical signals both inside and outside neurons in the live brains of freely moving animals to understand physiological processes and screen drugs.

Short-term (up to 1 h) systemic responses of tobacco (Nicotiana tabacum cv. Samsun) plants to local burning of an upper leaf were studied by measuring the following variables in a distant leaf: extracellular electrical potentials (EEPs); gas exchange parameters; fast chlorophyll fluorescence induction; and endogenous concentrations of three putative chemical signaling compounds-abscisic (ABA), jasmonic (JA), and salicylic (SA) acids. The first detected response to local burning in the distant leaves was in EEP, which started to decline within 10-20 s of the beginning of the treatment, fell sharply for ca. 1-3 min, and then tended to recover within the following hour. The measured gasometric parameters (stomatal conductance and the rates of transpiration and CO(2) assimilation) started to decrease 5-7 min after local burning, suggesting that the electrical signals may induce stomatal closure. These changes were accompanied by systemic increases in the endogenous ABA concentration followed by huge systemic rises in endogenous JA levels started after ca. 15 min, providing the first evidence of short-term systemic accumulation of these plant hormones in responses to local burning. Furthermore, JA appears to have an inhibitory effect on CO(2) assimilation. The correlations between the kinetics of the systemic EEP, stomatal, photosynthetic, ABA, and JA responses suggest that (1) electrical signals (probably induced by a propagating hydraulic signal) may trigger chemical defense-related signaling pathways in tobacco plants; (2) both electrical and chemical signals are interactively involved in the induction of short-term systemic stomatal closure and subsequent reductions in the rate of transpiration and CO(2) assimilation after local burning events.

Brain is complex organ composed of numerous glial cells and neurons to convey information using chemical and electrical signals. Neural interface technology using the electrical brain signals has attracted great attention for the clinical and experimental applications. Electrode as the neural interface is the most important part in stimulating neural cells or recording neural activities. In this paper, we provide an overview of electrodes for recording the electrical brain signal. The noninvasive electrodes are primarily used to capture electroencephalogram (EEG) from outside the skull while the implantable electrodes are employed to measure electrocorticogram (ECoG), local field potential (LFP) or spike activity. Recent progress in microfabrication technology enables the development of on-board electrode that combines the entire signal processing including amplification, filtering, and digitization. This will contribute to diagnostic and therapeutic application of the neural interface for restoring physical, psychological and social functions by improving motor, sensory or cognitive abilities.

To have a profound understanding of the physiological and pathological processes in a brain, both chemical and electrical signals need to be recorded, but this is still very challenging. Herein, micrometer‐ to nanometer‐sized SERS optophysiological probes were created to determine both the CO32− concentration and the pH in live brains and neurons because both species play important roles in regulating the acid–base balance in the brain. A ratiometric SERS microarray of eight microprobes with tip sizes of 5 μm was established and used for the first time for real‐time mapping and simultaneous quantification of CO32− and pH in a live brain. We found that both the CO32− concentration and the pH value dramatically decreased under ischemic conditions. The present SERS technique can be combined with electrophysiology without cross‐talk to record both electrical and chemical signals in brains. To deepen our understanding of the mechanism of ischemia on the single‐cell level, a SERS nanoprobe with a tip size of 200 nm was developed for use in a single neuron.

To have a profound understanding of the physiological and pathological processes in a brain, both chemical and electrical signals need to be recorded, but this is still very challenging. Herein, micrometer- to nanometer-sized SERS optophysiological probes were created to determine both the CO32- concentration and the pH in live brains and neurons because both species play important roles in regulating the acid-base balance in the brain. A ratiometric SERS microarray of eight microprobes with tip sizes of 5 μm was established and used for the first time for real-time mapping and simultaneous quantification of CO32- and pH in a live brain. We found that both the CO32- concentration and the pH value dramatically decreased under ischemic conditions. The present SERS technique can be combined with electrophysiology without cross-talk to record both electrical and chemical signals in brains. To deepen our understanding of the mechanism of ischemia on the single-cell level, a SERS nanoprobe with a tip size of 200 nm was developed for use in a single neuron.

Effects of early tooth loss on the hippocampus in senescence-accelerated mice

Neuroplasticity, the ability of the brain to form new neural pathways and synaptic connections, is gaining renewed interest for therapeutic purposes in stroke or spinal cord injury patients. Earlier work in this area in animal models has shown that behavior modulation was associated with the release of serotonin that subsequently leads to changes in gene expression and new neural growth [1]. A separate work has also demonstrated that using serotonin 1A agonists in rats with respiratory dysfunction due spinal cord injury results in better respiratory function [2]. Taken together, these studies indicate that neurotransmitters such as serotonin are closely linked to neuroplasticity, suggesting that changes in levels of these neurotransmitters can be correlated to synaptic changes. Currently, there is growing interest in the use of electrical stimulation as a means for inducing neuroplasticity in stroke and spinal cord injury patients [3]. However, while the data suggests that plasticity could be induced by electrical stimulation, neither the mechanism nor the protocols of stimulation are understood. We submit that a possible path to understanding these mechanisms involves simultaneous real-time monitoring of neurotransmitters such as serotonin electrochemically and electrical signals during stimulation and finding a correlation between these electrical signals and neurotransmitters. In cases where detection of several key electroactive neurotransmitters like serotonin and dopamine is sought, fast scan cyclic voltammetry (FSCV) with its high temporal resolution is the preferred electrochemical method of obtaining real time data [4]. Now, to be able to simultaneously monitor these electrochemical signals along with electrical signals, new approaches in neural probe material and architecture selection are required, as almost all neural probes currently in use are capable of recording only electrical or chemical signals, but not both. Thus, implementation of electrochemical monitoring techniques in animal models requires an integrated electrode array with a size suitable for an animal containing a counter electrode, working electrodes and a reference electrode. Furthermore, electrode materials capable of electrochemically detecting the presence of neurotransmitters without undergoing non-reversible reactions are sought. To meet this need, we investigate and report on the use of glassy carbon, a form of carbon that has been demonstrated to possess ideal characteristics, such as a wide electrochemical window with no irreversible reactions as a coupled electrical and electrochemical sensing platform. In this particular study, we introduce a 12-channel glassy carbon (GC) microelectrode array fabricated on a flexible substrate. The specific design introduced here consists of electrodes supported on a polyimide substrate with penetrating probes at their edges that can penetrate up to 1.25 mm into an animal's cortex or spinal cord. Each probe contains a glassy carbon electrode that can be used to detect serotonin, stimulate a neuron, or read an electrophysiological signal. Our preliminary results show that serotonin can be detected using a polyimide-glassy carbon device down to at least 1 uM in vitro by stimulating through one portion of the device and reading through another (Figure 1). Furthermore, we have shown that our electrodes can read electrophysiological data in-vivo. Figure 2b shows the Fourier Transform of a few seconds of electrical brain signals from a song bird without stimulus. In this graph low frequency alpha waves are most prominent. Figure 2c, the stimulus graph, on the other hand, shows that the beta and gamma waves became more prominent under external, audio stimulation. We believe that the ability to couple this kind of electrical signal detection with electrochemical sensing through FSCV (fast-scan CV) in a single device for in-vivostudies give promise for the disambiguation behind the mechanisms involved in neuroplasticity. Figure 1: Background subtracted cyclic voltagramms for various concentrations of serotonin Figure2: In vivo ECoG signals recorded with carbon electrodes. (a) Time lapse of the audio stimulus (b) Amplitude spectra of the animal during quiet time (c) Amplitude spectra of the signal during the stimulus phase. [1] Kandel, Eric R. Science 294, no. 5544 (2001): 1030-1038. [2] Choi, Howard, Wei-Lee Liao, Kimberly M. Newton, Renna C. Onario, Allyson M. King, Federico C. Desilets, Eric J. Woodard et al. The Journal of neuroscience 25, no. 18 (2005): 4550-4559. [3] Dimyan, Michael A., and Leonardo G. Cohen. Nature Reviews Neurology 7, no. 2 (2011): 76-85. [4] Lama, Rinchen D., Karl Charlson, Arun Anantharam, and Parastoo Hashemi. Analytical chemistry 84, no. 19 (2012): 8096-8101. Figure 1

Chapter 35 - Overview: Function and Three-Dimensional Structures of Ion Channels

Leaf damage by herbivores inNicotiana sylvestris Spegazzini and Comes (Solanaceae) produces a damage signal that dramatically increasesde novo nicotine synthesis in the roots. The increased synthesis leads to increases in whole-plant nicotine pools, which in turn make plants more resistant to further herbivore attack. Because signal production and the response to the signal occur in widely separated tissues, the speed with which different damage signals exit a damaged leaf can be studied. We propose that electrical damage signals should exit a leaf faster (less than 60 min) than chemical damage signals. Excision of a leaf induces a smaller increase in nicotine production than does puncture damage, so we examined our proposition by excising previously punctured leaves at 1, 60, and 960 min after leaf puncture and quantifying the induced whole-plant nicotine pools six days later when the induced nicotine production had reached a maximum. Significant induced nicotine production occurred only if punctured leaves were excised more than 1 hr after puncture, which is consistent with the characteristics of a slow-moving chemical signal rather than a fast-moving electrical signal. We explore the nature of the chemical signal and demonstrate that additions of 90µg or more of methyl jasmonate (MJ) in an aqueous solution to the roots of hydroponically grown plants inducede novo nicotine synthesis from(15)NO3 in a manner similar to that induced by leaf damage. We examine the hypothesis that jasmonic acid (JA) functions in the transfer of the damage signal from shoot to root. Using GC-MS techniques to quantify whole-plant JA pools, we demonstrate that leaf damage rapidly (<0.5 hr) increases shoot JA pools and, more slowly (<2 hr), root JA pools. JA levels subsequently decay to levels found in undamaged plants within 24 hr and 10 hr for shoots and roots, respectively. The addition of sufficient quantities (186µg) of MJ in a lanolin paste to leaves from hydroponically grown plants significantly increased endogenous root JA pools and increasedde novo nicotine synthesis in these plants. However, the addition of 93µg or less of MJ did not significantly increase endogenous root JA pools and did not significantly affectde novo nicotine synthesis. We propose that wounding increases shoot JA pools, which either directly through transport or indirectly through a systemin-like signal increase root JA pools, which, in turn, stimulate root nicotine synthesis and increase whole-plant nicotine pools.

Recent Advances in Pineal Cytochemistry. Evidence of the Production of Indoleamines and Proteinaceous Substances by Rudimentary Photoreceptor Cells and Pinealocytes of Amniota

Brains are composed of networks of an enormous number of neurons interconnected with synapses. Neural information is carried by the electrical signals within neurons and the chemical signals among neurons. Generating these electrical and chemical signals is metabolically expensive. The fundamental issue raised here is whether brains have evolved efficient ways of developing an energy-efficient neural code from the molecular level to the circuit level. Here, we summarize the factors and biophysical mechanisms that could contribute to the energy-efficient neural code for processing input signals. The factors range from ion channel kinetics, body temperature, axonal propagation of action potentials, low-probability release of synaptic neurotransmitters, optimal input and noise, the size of neurons and neuronal clusters, excitation/inhibition balance, coding strategy, cortical wiring, and the organization of functional connectivity. Both experimental and computational evidence suggests that neural systems may use these factors to maximize the efficiency of energy consumption in processing neural signals. Studies indicate that efficient energy utilization may be universal in neuronal systems as an evolutionary consequence of the pressure of limited energy. As a result, neuronal connections may be wired in a highly economical manner to lower energy costs and space. Individual neurons within a network may encode independent stimulus components to allow a minimal number of neurons to represent whole stimulus characteristics efficiently. This basic principle may fundamentally change our view of how billions of neurons organize themselves into complex circuits to operate and generate the most powerful intelligent cognition in nature. © 2017 Wiley Periodicals, Inc.

Signal processing over the molecular domain is critical for analysing, modifying, and synthesising chemical signals in molecular communication systems. However, the lack of chemical signal processing blocks and the wide use of electronic devices to process electrical signals in existing molecular communication platforms can hardly meet the biocompatible, non-invasive, and size-miniaturised requirements of applications in various fields, e.g., medicine, biology, and environment sciences. To tackle this, here we design and construct a liquid-based microfluidic molecular communication platform for performing chemical concentration signal processing and digital signal transmission over distances. By specifically designing chemical reactions and microfluidic geometry, the transmitter of our platform is capable of shaping the emitted signals, and the receiver is able to threshold, amplify, and detect the chemical signals after propagation. By encoding bit information into the concentration of sodium hydroxide, we demonstrate that our platform can achieve molecular signal modulation and demodulation functionalities, and reliably transmit text messages over long distances. This platform is further optimised to maximise data rate while minimising communication error. The presented methodology for real-time chemical signal processing can enable the implementation of signal processing units in biological settings and then unleash its potential for interdisciplinary applications.

Ever since the seminal discovery of systemic wound signaling in tomato and potato plants by Green and Ryan (Science 1972), a number of candidate systemic wound signals have been proposed. These can be classified into three groups: (1) Chemical signals, including the alarm hormone systemin and other peptide hormones, jasmonic acid is a phytohormone, as well as reactive oxygen species (ROS); (2) physical signals, including electrical and hydraulic signals; and (3) herbivore-induced volatile compounds, including green leafy volatiles and terpenes. These signals are generated at or close to the site of herbivore-inflicted injury and systemically move to target tissues where they induce defense responses. Chemical and physical signals depend on the connectivity of the plant body, whereas volatile compounds are released into the airspace. Different plants with different morphologies and ecological niches employ different modes of systemic signaling.

We demonstrate a novel feedback mechanism to implement closed loop neuromodulation based on a combination of electrical and chemical neural signal recording. The platform consists of our custom designed multi-channel amplifier for recording electrical and chemical signals (such as pH), data processing unit and the stimulator IC unit. A novelty of our approach is that the neural chemical signals are used to initiate stimulation and electrical compound action potentials (CAPs) to determine stimulation dosage. The proposed adaptive stimulation platform has been implemented in the context of Vagus Nerve Stimulation (VNS) for obesity therapy. The demonstration is based on externally generated signals derived from our in vivo experiments on physiological stimulation of the gastric branch of vagus nerve by injection of gut hormone cholecystokinin (CCK).

Integration of biomolecular logic gates with field-effect transducers