The Evolution of Senses: My Research Journey into the Nervous System of Cnidaria

Our understanding of the evolutionary history of animals is improving, but knowledge of the ancient sensory systems that early animals used to interact with their environments is still largely unknown. Using molecular cloning and in situ hybridization staining procedures, I was able to test the hypothesis that some senses evolved prior to the evolution of animals with bilateral symmetry. My data provides evidence that cnidarians can taste using genes that are closely related to human taste receptors. This finding changes our current understanding of when tasteevolved by hundreds of millions of years. The in situ hybridization results also demonstrated co-localization, or overlap, of the expression of taste and photosensitivity genes, which provides preliminary evidence that cnidarians use a polymodal sensory-motor (PSM) neuron to sense light and chemical cues (“tastes”) to coordinate their feeding behavior. The cDNA constructs I have produced will also provide further biochemical insights into their function. My long-term research projects have taught me about the process of making scientific discoveries, and I hope to continue conducting research throughout my career

Four-Dimensional Neuronal Signaling by Nitric Oxide: A Computational Analysis

Nitric oxide (NO) is now recognized as a transmitter of neurons that express the neuronal isoform of the enzyme nitric oxide synthase. NO, however, violates some of the key tenets of chemical transmission, which is classically regarded as occurring at points of close apposition between neurons. It is the ability of NO to diffuse isotropically in aqueous and lipid environments that has suggested a radically different form of signaling in which the transmitter acts four-dimensionally in space and time, affecting volumes of the brain containing many neurons and synapses. Although ¿volume signaling¿ clearly challenges simple connectionist models of neural processing, crucial to its understanding are the spatial and temporal dynamics of the spread of NO within the brain. Existing models of NO diffusion, however, have serious shortcomings because they represent solutions for ¿point-sources,¿ which have no physical dimensions. Methods for overcoming these difficulties are presented here, and results are described that show how NO spreads from realistic neural architectures with both simple symmetrical and irregular shapes. By highlighting the important influence of the geometry of NO sources, our results provide insights into the four-dimensional spread of a diffusing messenger. We show for example that reservoirs of NO that accumulate in volumes of the nervous system where NO is not synthesized contribute significantly to the temporal and spatial dynamics of NO spread

Arylthioamides and aryliminothioethers as new slow H2S-releasing agents

Hydrogen sulphide (H2S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H2S exhibits the antioxidant properties of inorganic and organic sulphides, behaving as a scavenger of reactive oxygen species. H2S is biosynthesized in mammalian tissues by cystathionine--synthase (CBS) and cystathionine--lyase (CSE) that is the main source of H2S in the CV. H2S trigger other important effects and the activation of ATP-sensitive potassium channel (KATP) accounts for its vasorelaxing and cardioprotective effects. Furthermore, H2S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H2S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H2S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H2S biosynthesis is involved in CV complications associated with diabetes mellitus. Many experiments suggest a cross-talk between the H2S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H2S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H2S have led several authors to look at this mediator as ‘‘the new NO’’, giving attractive opportunities to develop innovative classes of drugs. NaHS is the prototypical example of H2S-generating agent: it is a rapid H2S-donor and the most widely used H2S-donor for experimental purposes. However, this salt is not suitable for clinical applications, as the quick release of H2S may cause adverse effects, such as a rapid and excessive lowering of blood pressure. For a safer and effective pharmacological administration, ideal H2S-donors should generate H2S with slower releasing rates. Organic polysulphides of garlic, such as diallyl disulphide (DADS), act as H2S-releasing compounds, with a relatively slow mechanism that requires the presence of reduced glutathione. Other examples of original synthetic H2S-releasing agents have been described in the literature, including a number of aminothiol derivatives, and the phosphinodithioate derivative GYY4137. Furthermore, some H2S-releasing chemical moieties, such as the dithiolethione, the thioamide and the isothiocyanate, have been used for synthesizing multifunctional drugs. In this study, we report the synthesis and pharmacological evaluation of a series of new arylthioamide and aryliminothioether as “smart” H2S-releasing drugs

Dibenzo[1,2,5]thiadiazepines are non-competitive GABAA receptor antagonists

"A new process for obtaining dibenzo[c,f][1,2,5]thiadiazepines (DBTDs) and their effects on GABAA receptors of guinea pig myenteric neurons are described. Synthesis of DBTD derivatives began with two commercial aromatic compounds. An azide group was obtained after two sequential reactions, and the central ring was closed via a nitrene to obtain the tricyclic sulfonamides (DBTDs). Whole-cell recordings showed that DBTDs application did not affect the holding current but inhibited the currents induced by GABA (IGABA), which are mediated by GABAA receptors. These DBTDs effects reached their maximum 3 min after application and were: (i) reversible, (ii) concentration-dependent (with a rank order of potency of 2c = 2d > 2b), (iii) mediated by a non-competitive antagonism, and (iv) only observed when applied extracellularly. Picrotoxin (which binds in the channel mouth) and DBTDs effects were not modified when both substances were simultaneous applied. Our results indicate that DBTD acted on the extracellular domain of GABAA channels but independent of the picrotoxin, benzodiazepine, and GABA binding sites. DBTDs used here could be the initial model for synthesizing new GABAA receptor inhibitors with a potential to be used as antidotes for positive modulators of these receptors or to induce experimental epilepsy.

Toward Synthesizing a Selective Dopamine Binding Magnetic Resonance Contrast Agent

Magnetic resonance imaging (MRI) is a non-invasive diagnostic methodology used to provide a two-dimensional view of an internal organ or structure, especially the brain and spinal cord. Magnetic resonance contrast agents are usually injected into necessary parts of the body prior to imaging to increase the differences between different tissues or between normal and abnormal tissue, making it easier for a radiologist or doctor to interpret the image that is taken. The development of new and more efficient, effective, and selective contrast agents for various biological processes or chemicals is a growing field of research and study. My project allowed me to engage in undergraduate chemistry research in an academic setting under the supervision of an organic chemistry professor, Dr. DeBoef. He designed a molecule that will be developed further to be a magnetic resonance contrast agent, also referred to as an MRI probe. Reactions were carried out that were the beginning steps of the multi-step synthesis, or recipe, if you will, to make the target molecule which also binds gadolinium, making it MRI active (Figure 1). The entire multi-step synthesis is not included in this paper. The purpose of his design is for the molecule to selectively bind dopamine (Figure 2), a neurotransmitter that has been found to be associated with Parkinson’s Disease in humans. His molecule’s design is based on existing contrast agent structures published in chemical literature but is a new molecule after changes and additions were made. It can be years later before it will be tested for use in MRI as a contrast agent that is safe for use in humans

Robust Digital Molecular Design of Binarized Neural Networks

Molecular programming - a paradigm wherein molecules are engineered to perform computation - shows great potential for applications in nanotechnology, disease diagnostics and smart therapeutics. A key challenge is to identify systematic approaches for compiling abstract models of computation to molecules. Due to their wide applicability, one of the most useful abstractions to realize is neural networks. In prior work, real-valued weights were achieved by individually controlling the concentrations of the corresponding "weight" molecules. However, large-scale preparation of reactants with precise concentrations quickly becomes intractable. Here, we propose to bypass this fundamental problem using Binarized Neural Networks (BNNs), a model that is highly scalable in a molecular setting due to the small number of distinct weight values. We devise a noise-tolerant digital molecular circuit that compactly implements a majority voting operation on binary-valued inputs to compute the neuron output. The network is also rate-independent, meaning the speed at which individual reactions occur does not affect the computation, further increasing robustness to noise. We first demonstrate our design on the MNIST classification task by simulating the system as idealized chemical reactions. Next, we map the reactions to DNA strand displacement cascades, providing simulation results that demonstrate the practical feasibility of our approach. We perform extensive noise tolerance simulations, showing that digital molecular neurons are notably more robust to noise in the concentrations of chemical reactants compared to their analog counterparts. Finally, we provide initial experimental results of a single binarized neuron. Our work suggests a solid framework for building even more complex neural network computation