Gennady Sergeevich Cymbalyuk - US grants

In this proposal the PI will study the onset and control of bursting activity of neurons in the central pattern generator (CPG) that controls heart beating in the medicinal leech using neuron-computer interface (dynamic clamp and hybrid systems analysis). Neurons exhibit a variety of qualitatively different activity, such as bursting, tonic spiking, sub-threshold oscillations and rest potentials. Bursting is commonly involved in the control of rhythmic motor behaviors, it is associated with the sleep state of the brain in contrast to a vigilant state, and/or can be a distinguishing factor between pathological and normal dynamics of the central nervous system (CNS). Such medical conditions as sudden infant death syndrome, epilepsy and Parkinson's disease are examples of the medical conditions which are caused by malfunction in the dynamics of the CNS. The complexity of endogenous dynamics supporting bursting originates from the dynamical diversity of ionic currents. The PI will apply the analytical tools of the theory of dynamical systems to the analysis of stationary and oscillatory regimes of activity of living neurons to explain how bursting activity is generated and can be controlled. The dynamic clamp will be used to artificially reintroduce or augment a particular ionic current; while hybrid systems approach will be employed to create and study the interactions of two neurons, where one is the mathematical model running in real-time and the other is a living neuron. To identify physical mechanisms by which bursting can arise from other regimes and how it can be regulated, the PI proposes two goals. 1. To investigate the role of slow ionic currents in determining the characteristics of bursting activity. 2. To study the dynamics of a pair of mutually inhibitory neurons. The PI will also continue to recruit minority students to participate in research in his laboratory, and will continue to encourage them to pursue academic careers. The PI will continue to work with students in the Atlanta metro area schools to foster their interest in science. In the PIs laboratory, graduate and undergraduate students will be involved in the research projects using interdisciplinary methods from mathematics, physics and neuroscience.

Robust bursting activity of neurons is critical for motor pattern generation and brain rhythms, and depends on a subtle balance of inward and outward currents. A little recognized contributor is the outward current originating with the Na+/K+ pump. The pump not only maintains the Na+ and K+ gradients across neuronal membranes, but produces an inherent outward current, which is dynamic because the pump is regulated by the internal Na+ concentration up to saturation. As yet the actual dynamical mechanisms by which pump current contributes to bursting activity are not well understood. Much work on the functional contribution of pump current to rhythmic motor activity has emphasized a time scale of a minute affecting bouts of bursting, but our recent work shows that the pump can influence individual burst in a rhythmic motor system (time scale of seconds). The interplay of inward Na+ currents and outward Na+/K+ pump current can afford rich dynamics to bursting networks. We will study how pump dynamics contribute to bursting activity in the leech heartbeat central pattern generator (CPG) because of the unique accessibility of the neurons and the wealth of experimental and modeling analyses of the system. The premise of this proposal is that the Na+/K+ pump contributes to the dynamics of neurons on the time scale of the period of their rhythmic bursting activity (6-10 s). In the leech heartbeat CPG, the basic building blocks are half-center oscillators (HCOs), which are pairs of mutually inhibitory HN interneurons producing alternating bursting activity. Our central hypothesis is that the Na+/K+ pump current through its interaction with inward currents supports robust bursting in both individual neurons and in HCO networks that allows for control of burst characteristics through modulation. To test this hypothesis we must be able to directly control both the pump current and the currents with which it interacts. A critical barrier has been the lack of experimental tools to manipulate these currents independently and together. We are developing a real-time HN model with the pump included and a dynamic clamp implementation of the pump. We will be able to introduce pump current into living HN neurons, form hybrid systems between living and model HNs, and manipulate pump parameters on the fly to investigate the role of Na+/K+ pump in rhythm generation of a motor control circuit. Aim 1. Develop a real-time hybrid system (real time model and dynamic clamp implementation). Aim 2. Investigate how burst initiation, maintenance, and termination mechanisms interact to control burst duration, interburst interval, and spike frequency.

The long-term goal of this proposal is to understand the molecular and physiological bases of cold nociception. Thermosensory nociception is a specialized form of somatosensation essential to the survival of all metazoans. Thermosensory nociception alerts the organism to potential environmental dangers coupled with pain sensation thereby serving as a protective mechanism for driving adaptive behavioral responses to safeguard against incipient damage. Despite this importance, the fundamental molecular and biophysical bases of cold nociception remain poorly understood. Molecularly, transient receptor potential channels (i.e. thermoTRPs) play critical roles in thermosensation, however, relatively less is known regarding how thermoTRPs mechanistically function in regulating noxious cold detection. Neurologically, acute and chronic pain may manifest as altered thermosensory nociception whereby innocuous thermal stimuli erroneously engage nociceptive circuitry leading to neuropathic pain. Cold hypersensitivity is associated with multiple sclerosis, fibromyalgia, stroke, and chemotherapy-induced neuropathy resulting in neuropathic pain, however the mechanisms underlying cold sensitization are largely unknown. Here, we will investigate a fundamental problem of how multimodal sensory neurons discriminately detect noxious cold stimuli to elicit nocict9ptive behavior using Drosophila as a model system in combination with bi- directionally linked neurogenetic, neurogenomic, cellular imaging, electrophysiological, behavioral, computational modeling, and bifurcation analyses. We aim to uncover molecular and biophysical bases for cold-evoked nociceptive stimulus coding, including the functional properties of thermoTRPs and Ca2· signaling dynamics in this process. The project aims and outcomes of this research will significantly advance our knowledge of cold nociception by addressing three open questions: (1) What are the molecular and biophysical bases of cold nociceptive stimulus coding? (2) How do multimodal nociceptive neurons discriminately detect noxious stimuli (e.g. cold) to drive nocifensive behavior? (3) How do thermoTRPs and Ca2· signaling mechanisms mechanistically function in regulating noxious cold detection? More generally, the bi-directional integration of experimental and computational approaches in a closed- loop investigational strategy is well-suited to transform our understanding of cold nociception by elucidating potentially generalizable mechanisms of cold thermosensory coding, including roles of TRP channels and. Ca2· homeostasis in sensory-evoked neural activity. RELEVANCE (See instructions): The perception of noxious stimuli is often coupled to pain sensation as a protective mechanism, however altered temperature sensation may lead to neuropathic pain (e.g. in multiple sclerosis, fibromyalgia, and stroke) where patients experience pain due to cold hypersensitivity. By uncovering basic mechanisms of noxious cold perception, we develop important insights on neural integration of painful stimuli providing potential routes for understanding and treating neurological disease when this process is disrupted.