Our lab develop and apply novel biomedical optics tools and techniques for Neuroceuticals, Congenital Heart Defects and Other applications.
Neuroceuticals are devices (e.g., electrodes) used to modulate nerve activity in order to treat disease as an alternative to pharmaceuticals.
In recent years, it has been become clear that modulating the autonomic nervous system has great potential for treating diseases. Neuromodulation of the vagus nerve has shown potential to treat several diseases including rheumatoid arthritis, hypertension, obesity, and coma. Neuroceuticals potentially have several advantages over pharmaceuticals including reduced side effects and more spatially targeted treatment. Neuromodulation is typically achieved with electrodes, but the development of alternative or complementary neuromodulation devices that produce unique physiologic responses are needed to realize the full potential of neuroceuticals. We have recently shown that infrared neuromodulation (IRN) induces unique patterns of physiological responses that cannot be elicited by electrical current or drugs when applied to peripheral structures (e.g., ganglia). We are currently investigating whether IRN has the potential to map/decode autonomic circuitry, and as a clinical neuroceutical device. Below are examples from recent papers.
Infrared inhibition increases the baseline temperature to create a heat block. Our group is the first to demonstrate that infrared light can block electrical activity in nerves and in cardiac tissue. The figure below demonstrates spatially selective block using infrared light.
Figure 1| Infrared inhibition
(a) A micropipette providing supra-threshold extracellular electrical stimulation to BN2 is flanked by two optical fibers. Extracellular nerve recordings were obtained from the three distal branches. (b) Nerve cross-section schematic at the site of inhibition. (c) Neural recordings from branches of BN2 showing selective inhibition (arrows) of AP generation. Each laser inhibits initiation of an AP projecting to a single nerve branch. Laser 1 (4.43 ± 0.30 J/cm2) inhibits an AP projecting to BN2c, whereas Laser 2 (8.34 ± 0.78 J/cm2) inhibits an AP projecting to BN2b. Upon removal of the infrared pulse, electrically evoked APs return, indicating reversibility.
Selective inhibition of small-diameter axons using infrared light
Infrared light can selectively and reversibly inhibit small-diameter axons at lower radiant exposures than large-diameter axons. Application of extracellular current to peripheral nerves generally has a bigger effect on larger-diameter axons, because current induced within the axon is proportional to axonal cross-section. Small-diameter fibers play critical roles in sensory and motor systems. Controlling the activity of these small fibers has great potential for treating diseases (e.g., pain).
Figure 2. Selective block of an individual slower-conducting axon in Aplysia californica.
Infrared light induces large physiologic responses – Coming Soon
Congenital Heart Defects
A congenital heart defect (CHD) is an evident structural anomaly of the heart or thoracic great vessels with real or potential functional impact. Among all birth defects, CHDs are one of the most common and devastating, afflicting 32,000 babies born in the United States each year and over 1 million Americans alive today. Our group develops new technology to study structure/function relationships in the developing heart. We aim to answer difficult questions such as how abnormal blood flow alters heart development and how this may manifest in common CHDs? In particular, we are interested in CHDs induced by prenatal ethanol exposure (PAE) and have identified several new compounds that protect against defects induced by PAE. Below is a list of technology we have developed for studying heart development.
Optical pacing (OP)
OP uses pulsed infrared light to pace the heart without adding any exogenous agents to the tissue. OP creates a thermal gradient in the tissue which depolarizes the cells. Our group was the first to demonstrate OP (see movie below). OP has several advantages over electrical pacing which include higher spatial specificity, no contact required, no electrical artifacts, and no interference from magnetic fields. OP allows us to noninvasively perturb blood flow to see how altered flow influences heart development and can be used as a point source (electrical pacing cannot be used in small tissues because of electrical artifacts) for electrophysiology studies of the embryonic heart.
Movie 1| Pacing of the embryonic quail heart as the frequency is modulated.
The top left panel depicts a real-time video of a stage 14 quail embryo commencing just before optical pacing begins. The top right panel shows a magnified region of interest around the heart. The fiber at the bottom delivers pacing pulses to the inflow region of the heart tube. The bottom panel presents a real-time update of the timing of the laser pulses (blue) superimposed on a trace showing the heart rate (red). It can be seen that the embryonic heart is able to follow the pulse frequency as it is varied.
Optical coherence tomography (OCT)
OCT achieves range-gated, sub-surface microscopic imaging of biological samples by use of low-coherence interferometry. It is well suited for imaging embryonic development due to its high spatial resolution (2-20 µm), high temporal resolution (> 100 kHz line rates), deep penetration (1-3 mm in embryonic tissues), and Doppler flow sensing. Our group has developed high-speed gated algorithms to capture cardiac dynamics in 4D; an environmental chamber to ensure imaging under physiological conditions; and visualization and measurement algorithms to accurately assess cardiac function.
Movie 2| OCT images the developing embryonic heart tube over 24 hours.
Transparent blue is the myocardium and red is the endocardium. The endocardium starts out smooth and develops more folds and ridges as time passes.
Optical mapping (OM)
OM uses potentiometric fluorescent dyes and fast cameras to image cardiac conduction over large fields of view. Our group has combined OM with OP for electrophysiology studies of the embryonic heart; developed new algorithms to quantify conduction velocity in the developing heart; and built a high-speed light-sheet microscopy setup capable of volumetric OM of the early embryonic heart (see below).
Movie 3| Volume rendering of 4D transmembrane potentials of a looping embryonic heart
Optical clearing uses compounds to render tissue transparent and increase imaging depth. Optical clearing can be utilized with any optical imaging modality. We have employed optical clearing to increase imaging depth in OCT images and enable phenotyping of late-stage embryonic hearts. We are currently working a new optical clearing protocol that achieves high transparency, low tissue distortion, is easy to use, and cost effective.
Movie 4| Optical clearing of a heart.
The heart was stained with dapi which is seen every time the blue light is turned on. Otherwise the heart is completely transparent
Scatter labeled imaging of microvasculature in excised tissues (SLIME) – Coming Soon
An infrared optical pacing system for screening cardiac electrophysiology in human cardiomyocytes
Optical pacing, optical mapping, and human cardiomyocytes are utilized to demonstrate a potential high-throughput system to screen out arrhythmogenic drugs.
Fig 7. System validation using Flecainide and Quinidine.
Activation time (top) and APD (bottom) contour maps measured at baseline (left) and after 0.3 μM Flecainide (right) in a single well of a 96-well plate. Mean local conduction velocity and APD for each map are shown below. Site of optical pacing is shown by red spot in activation contours. Flecainide decreased conduction velocity and increased APD. To the right are summary data for mean local conduction velocity (top) and APD (bottom) before (CNTL) and after Flecainide (n = 7, n = 6) and Quinidine (1.0 μM, n = 7).