Real-time electrochemical recording of dopamine release under optogenetic stimulation

Development of a Smart Wireless Multisensor Platform for an Optogenetic Brain Implant

Implantable cell replacement therapies promise to completely restore the function of neural structures, possibly changing how we currently perceive the onset of neurodegenerative diseases. One of the major clinical hurdles for the routine implementation of stem cell therapies is poor cell retention and survival, demanding the need to better understand these mechanisms while providing precise and scalable approaches to monitor these cell-based therapies in both pre-clinical and clinical scenarios. This poses significant multidisciplinary challenges regarding planning, defining the methodology and requirements, prototyping and different stages of testing. Aiming toward an optogenetic neural stem cell implant controlled by a smart wireless electronic frontend, we show how an iterative development methodology coupled with a modular design philosophy can mitigate some of these challenges. In this study, we present a miniaturized, wireless-controlled, modular multisensor platform with fully interfaced electronics featuring three different modules: an impedance analyzer, a potentiostat and an optical stimulator. We show the application of the platform for electrical impedance spectroscopy-based cell monitoring, optical stimulation to induce dopamine release from optogenetically modified neurons and a potentiostat for cyclic voltammetry and amperometric detection of dopamine release. The multisensor platform is designed to be used as an opto-electric headstage for future in vivo animal experiments.

Live-Cell Imaging of Neurotransmitter Release with a Cell-Surface-Anchored DNA-Nanoprism Fluorescent Sensor

Neurotransmitters are essential chemical mediators for neuronal communication in variable neuromodulations. However, the progress of neuroscience is hampered by the shortage of suitable sensors to track neurotransmitters with high spatial and temporal resolution. Here, we introduce a self-assembled DNA-nanoprism fluorescent probe capable of nongenetically engineering the cell surface for ultrasensitive imaging of the neurotransmitter release at a single live-cell level. The DNA-nanoprism structure conjugated with three cholesterol tails enables the probe to rapidly and stably anchor on the cell surface within 10 min. The in situ detection of neurotransmitters is achieved by equipping the DNA-nanoprism with an aptamer-based "turn-on" fluorescent sensory module for the transmitter of interest. In a proof-of-concept study, we directly visualized the transient dopamine (DA) release on the cell surface with selective responsivity and high spatiotemporal precision and further explored the dynamic correlation between DA release and calcium influx triggered by high K⁺. This study provides a robust and sensitive tool for cell-surface-targeted imaging of neuromodulations, which might open up a new avenue to improve the understanding of neurochemistry and advance neuroscience research.

A wireless, implantable optoelectrochemical probe for optogenetic stimulation and dopamine detection

Physical and chemical technologies have been continuously progressing advances in neuroscience research. The development of research tools for closed-loop control and monitoring neural activities in behaving animals is highly desirable. In this paper, we introduce a wirelessly operated, miniaturized microprobe system for optical interrogation and neurochemical sensing in the deep brain. Via epitaxial liftoff and transfer printing, microscale light-emitting diodes (micro-LEDs) as light sources and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-coated diamond films as electrochemical sensors are vertically assembled to form implantable optoelectrochemical probes for real-time optogenetic stimulation and dopamine detection capabilities. A customized, lightweight circuit module is employed for untethered, remote signal control, and data acquisition. After the probe is injected into the ventral tegmental area (VTA) of freely behaving mice, in vivo experiments clearly demonstrate the utilities of the multifunctional optoelectrochemical microprobe system for optogenetic interference of place preferences and detection of dopamine release. The presented options for material and device integrations provide a practical route to simultaneous optical control and electrochemical sensing of complex nervous systems.

Electrochemical Micropyramid Array-Based Sensor for In Situ Monitoring of Dopamine Released from Neuroblastoma Cells

Abnormal dopamine neurotransmission is associated with several neurological and psychiatric disorders such as Parkinson's disease, schizophrenia, attention deficiency and hyperactivity disorder, and addiction. Developing highly sensitive, selective, and fast dopamine monitoring methods is of high importance especially for the early diagnosis of these diseases. Herein, we report a new ultrasensitive electrochemical sensing platform for in situ monitoring of cell-secreted dopamine using Au-coated arrays of micropyramid structures integrated directly into a Petri dish. This approach enables the monitoring of dopamine released from cells in real-time without the need for relocating cultured cells. According to the electrochemical analyses, our dopamine sensing platform exhibits excellent analytical characteristics with a detection limit of 0.50 ± 0.08 nM, a wide linear range of 0.01-500 μM, and a sensitivity of 0.18 ± 0.01 μA/μM. The sensor also has remarkable selectivity toward DA in the presence of different potentially interfering small molecules. The developed electrochemical sensor has great potential for in vitro analysis of neuronal cells as well as early diagnosis of different neurological diseases related to abnormal levels of dopamine.

Leaky Optoelectrical Fiber for Optogenetic Stimulation and Electrochemical Detection of Dopamine Exocytosis from Human Dopaminergic Neurons

In Parkinson's disease, the degeneration of dopaminergic neurons in substantia nigra leads to a decrease in the physiological levels of dopamine in striatum. The existing dopaminergic therapies effectively alleviate the symptoms, albeit they do not revert the disease progression and result in significant adverse effects. Transplanting dopaminergic neurons derived from stem cells could restore dopamine levels without additional motor complications. However, the transplanted cells disperse in vivo and it is not possible to stimulate them on demand to modulate dopamine release to prevent dyskinesia. In order to address these issues, this paper presents a multifunctional leaky optoelectrical fiber for potential neuromodulation and as a cell substrate for application in combined optogenetic stem cell therapy. Pyrolytic carbon coated optical fibers are laser ablated to pattern micro-optical windows to permit light leakage over a large area. The pyrolytic carbon acts as an excellent electrode for the electrochemical detection of dopamine. Human neural stem cells are genetically modified to express the light sensitive opsin channelrhodopsin-2 and are differentiated into dopaminergic neurons on the leaky optoelectrical fiber. Finally, light leaking from the micro-optical windows is used to stimulate the dopaminergic neurons resulting in the release of dopamine that is detected in real-time using chronoamperometry.

Modulation of epileptogenesis: A paradigm for the integration of enzyme-based microelectrode arrays and optogenetics

BACKGROUND

Genesis of acquired epilepsy includes transformations spanning genetic-to- network-level modifications, disrupting the regional excitatory/inhibitory balance. Methodology concurrently tracking changes at multiple levels is lacking. Here, viral vectors are used to differentially express two opsin proteins in neuronal populations within dentate gyrus (DG) of hippocampus. When activated, these opsins induced excitatory or inhibitory neural output that differentially affected neural networks and epileptogenesis. In vivo measures included behavioral observation coupled to real-time measures of regional glutamate flux using ceramic-based amperometric microelectrode arrays (MEAs).

RESULTS

Using MEA technology, phasic increases of extracellular glutamate were recorded immediately upon application of blue light/488 nm to DG of rats previously transfected with an AAV 2/5 vector containing an (excitatory) channelrhodopsin-2 transcript. Rats receiving twice-daily 30-sec light stimulation to DG ipsilateral to viral transfection progressed through Racine seizure stages. AAV 2/5 (inhibitory) halorhodopsin-transfected rats receiving concomitant amygdalar kindling and DG light stimuli were kindled significantly more slowly than non-stimulated controls. In in vitro slice preparations, both excitatory and inhibitory responses were independently evoked in dentate granule cells during appropriate light stimulation. Latency to response and sensitivity of responses suggest a degree of neuron subtype-selective functional expression of the transcripts.

CONCLUSIONS

This study demonstrates the potential for coupling MEA technology and optogenetics for real-time neurotransmitter release measures and modification of seizure susceptibility in animal models of epileptogenesis. This microelectrode/optogenetic technology could prove useful for characterization of network and system level dysfunction in diseases involving imbalanced excitatory/inhibitory control of neuron populations and guide development of future treatment strategies.

Optical excitation and detection of neuronal activity

Optogenetics has emerged as an exciting tool for manipulating neural activity, which in turn, can modulate behavior in live organisms. However, detecting the response to the optical stimulation requires electrophysiology with physical contact or fluorescent imaging at target locations, which is often limited by photobleaching and phototoxicity. In this paper, we show that phase imaging can report the intracellular transport induced by optogenetic stimulation. We developed a multimodal instrument that can both stimulate cells with subcellular spatial resolution and detect optical pathlength (OPL) changes with nanometer scale sensitivity. We found that OPL fluctuations following stimulation are consistent with active organelle transport. Furthermore, the results indicate a broadening in the transport velocity distribution, which is significantly higher in stimulated cells compared to optogenetically inactive cells. It is likely that this label-free, contactless measurement of optogenetic response will provide an enabling approach to neuroscience.

An optimized and automated approach to quantifying channelrhodopsin photocurrent kinetics

Channelrhodopsins are light-activated ion channels that enable targetable activation or inhibition of excitable cells with light. Ion conductance can generally be described by a four step photocycle, which includes two open and two closed states. While a complete understanding of channelrhodopsin function cannot be understood in the absence of kinetic modeling, model fitting requires manual fitting, which is laborious and technically complicated for non-experts. To enhance analysis of photocurrent data, this manuscript describes a fitting program where electrophysiology data can be automatically and quantitatively analyzed. Significant improvement in this program when compared to our previous version includes 1) the ability to automatically find the experiment start time using the derivative of the current signal, 2) utilizing the Object Oriented Programing (OPP) paradigm which is significantly more reliable if the code is used by people with little to no programming experience and 3) the distribution of the code is simplified to sharing a single MATLAB file, including rigorous comments throughout. To demonstrate the utility of this program, we show automated fitting of photocurrents from two member proteins: channelrhodopsin-2 and a chimera between channelrhodopsin-1 and channelrhodopsin-2 (C1C2).

An Optogenetic Approach for Investigation of Excitatory and Inhibitory Network GABA Actions in Mice Expressing Channelrhodopsin-2 in GABAergic Neurons

To investigate excitatory and inhibitory GABA actions in cortical neuronal networks, we present a novel optogenetic approach using a mouse knock-in line with conditional expression of channelrhodopsin-2 (ChR2) in GABAergic interneurons. During whole-cell recordings from hippocampal and neocortical slices from postnatal day (P) 2-P15 mice, photostimulation caused depolarization and excitation of interneurons and evoked barrages of postsynaptic GABAergic currents. Excitatory/inhibitory GABA actions on pyramidal cells were assessed by monitoring the alteration in the frequency of EPSCs during photostimulation of interneurons. We found that in slices from P2-P8 mice, photostimulation evoked an increase in EPSC frequency, whereas in P9-P15 mice the response switched to a reduction in EPSC frequency, indicating a developmental excitatory-to-inhibitory switch in GABA actions on glutamatergic neurons. Using a similar approach in urethane-anesthetized animals in vivo, we found that photostimulation of interneurons reduces EPSC frequency at ages P3-P9. Thus, expression of ChR2 in GABAergic interneurons of mice enables selective photostimulation of interneurons during the early postnatal period, and these mice display a developmental excitatory-to-inhibitory switch in GABA action in cortical slices in vitro, but so far show mainly inhibitory GABA actions on spontaneous EPSCs in the immature hippocampus and neocortex in vivo

SIGNIFICANCE STATEMENT

We report a novel optogenetic approach for investigating excitatory and inhibitory GABA actions in mice with conditional expression of channelrhodopsin-2 in GABAergic interneurons. This approach shows a developmental excitatory-to-inhibitory switch in the actions of GABA on glutamatergic neurons in neocortical and hippocampal slices from neonatal mouse pups in vitro, but also reveals inhibitory GABA actions in the neonatal mouse neocortex and hippocampus in vivo.

The Effects of Electrical and Optical Stimulation of Midbrain Dopaminergic Neurons on Rat 50-kHz Ultrasonic Vocalizations

Rationale: Adult rats emit ultrasonic vocalizations (USVs) at around 50-kHz; these commonly occur in contexts that putatively engender positive affect. While several reports indicate that dopaminergic (DAergic) transmission plays a role in the emission of 50-kHz calls, the pharmacological evidence is mixed. Different modes of dopamine (DA) release (i.e., tonic and phasic) could potentially explain this discrepancy.

Objective: To investigate the potential role of phasic DA release in 50-kHz call emission.

Methods: In Experiment 1, USVs were recorded in adult male rats following unexpected electrical stimulation of the medial forebrain bundle (MFB). In parallel, phasic DA release in the nucleus accumbens (NAcc) was recorded using fast-scan cyclic voltammetry. In Experiment 2, USVs were recorded following response-contingent or non-contingent optogenetic stimulation of midbrain DAergic neurons. Four 20-s schedules of optogenetic stimulation were used: fixed-interval, fixed-time, variable-interval, and variable-time.

Results: Brief electrical stimulation of the MFB increased both 50-kHz call rate and phasic DA release in the NAcc. During optogenetic stimulation sessions, rats initially called at a high rate comparable to that observed following reinforcers such as psychostimulants. Although optogenetic stimulation maintained reinforced responding throughout the 2-h session, the call rate declined to near zero within the first 30 min. The trill call subtype predominated following both electrical and optical stimulation.

Conclusion: The occurrence of electrically-evoked 50-kHz calls, time-locked to phasic DA (Experiment 1), provides correlational evidence supporting a role for phasic DA in USV production. However, in Experiment 2, the temporal dissociation between calling and optogenetic stimulation of midbrain DAergic neurons suggests that phasic mesolimbic DA release is not sufficient to produce 50-kHz calls. The emission of the trill subtype of 50-kHz calls potentially provides a marker distinguishing positive affect from positive reinforcement.