Project 1 Vertebrate Electrophysiology
Title: Otolith nerve response to short and longer duration hypergravity exposure and its re-adaptation to 1G.
Abstract from Society for Neurosciences 2010: The inner ear utricle senses the sum of inertial force due to head translation and head orientation with respect to gravity. An organism rapidly senses exposure to altered gravity and adaptive mechanisms are initiated. These processes in the nervous system might involve the peripheral otolith receptors, the brain or both. It is clear from space missions that humans adapt to the µG environment within 2-4 days and subsequently re-adapt upon return to 1G. Here we ask: does the transfer from 1G to 3G impart the opposite effects on changes of gravitational sensitivity seen following µG exposure? Do the effects accompanying transfer from the 3G to the 1G conditions resemble in part (as an analog) the transfer from 1G to the µG? Adult toadfish, Opsanus tau, were placed in groups and exposed to 3G for 1, 2, 3, 4, 5, 8, 16, 24, and 32 days and 1.5G for 4 and 16 days. Re-adaptation to 1G was studied in 3G exposure of 4- and 16-days following 1-8 days of recovery. Directional selectivity to translational and tilt stimuli were well characterized in typically >60 afferents in each fish. Afferent firing rates were also examined during electric shocks applied to the efferent vestibular pathway at rest and during motion tests. Since the 3G centrifugation includes a 228°/s constant velocity rotation, horizontal canal afferents are also studied to yaw rotation in each fish. Results show a biphasic pattern in response to 3G exposures: an initial sensitivity increase (3- and 4-day), similar to that observed in utricular afferents upon return to Earth, followed by a transition through normal sensitivity to a significant decrease at 16-32 day exposure. 1.5 G centrifugation also leads to an increase of sensitivity after 4 days and decrease after 16 days, but these changes are far less pronounced than 3G experiments. As an internal control horizontal canal afferents respond normally to yaw rotation. Afferent responses to efferent stimulation appear influenced by hyper-G exposures: on average efferent evoked rate increase was lower after 4-day in 3G than in ground control, and significantly higher after 16-day in 3G. Return to control values following 16-day exposure is on the order of 4-8 days. On-Center Controls (228°/s rotation about Earth vertical) at 4- and 16-days do not show any difference compare to ground controls. Utricular sensitivity is strongly regulated by altered gravity exposure, and transition from hyper-G to normal gravity seem to resemble the transfer from 1G to µG, and might be used as an analog ground-based model. Support Contributed By: NASA 03-OBPR-04
Project 2 Invertebrate Electrophysiology: Radiation
Title: Functional and Mechanistic Analysis of the Bystander Effect in the Gravi-sensing Nervous System Following Low-Dose Radiation.
Key Words: Organismal Biology; Nervous System; Gravity Receptors; Neuro-physiology and –pharmacology; Gap Junctions; Microbeam Radiation
Description: The primary objectives of this research are to (a) quantify bystander effects in the central nervous system of a model organism at doses below 0.10 Gy of low-LET radiation, (b) evaluate mechanisms associated with the bystander effect, and (c) compare with high-energy charged particles simulating space radiations important for risk assessment to astronauts. The experimental model is the land snail (Helix lucorum) that was studied on two previous orbital missions and will participate in the Bion M-1 mission in 2012. The strength of this model allows us to track over time both reflex motor and learned behaviors driven by the gravi-sensing organ in the intact organism, and allows direct hypothesis-driven tests to specify the mechanism(s) responsible for CNS damage in its highly organized neural system, the statocyst organ, in isolated, but living, neural preparations.
Project 3 Structural Physiology
Title: Role of Gravity in determining inner ear otoconial biomechanics
A widely considered mechanism by which the organism responds to a change in amplitude of the gravity vector is a change in the weight-lending otoconia (or statoconia in invertebrates). Structurally, these are minute calcareous particles surmounting the neural epithelium. . In µG, it is argued, the organism counters the loss of gravity by increasing CaCO3 production and its deposition onto otoconia, thereby seen as a means to increase the "system gain". In hypergravity, the converse is argued. In this study we apply electron microscopic techniques to image the otoconia mass of mice subjected to altered gravity levels in samples obtained from 1) The Mouse Drawer System (MDS) of the Italian Space Agency (ASI) housed 6 mice on the International Space Station (ISS) for 100 days, and returned in November 2009 on STS-131. The 100-day stay on the ISS was the longest duration of µG exposure of any subhuman mammal. In human terms, the mice lived approximately 7-8 years in space. 2) A recently completed study conducted at the University of Osaka (Japan) in which the same transgenic model and its wild-type counterparts in the MDS study were subjected to 2G centrifugation and hindlimb suspension. and 3) Samples obtained from STS-133 and -135 orbital shuttle missions.
Project 4 Invertebrate Electrophysiology: 30-day Orbital Space Mission
Title: Bion Receptor Study - Space Flight Impact on the behavior, peptide expression, and electrophysiology of the snail statocyst system.
In collaboration with Prof. Pavel Balaban and his team at the Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences (Moscow) we will extend our studies conducted on the Foton M-2 and M-3 orbital missions on the May 2012 Bion M-1 30-day orbital mission. We will study the influence of the space flight on sensory-motor behavior, such as the negative gravitaxis response to sudden shifts in orientation, and memory and retention to previously acquired skills, the genetic expression of neuropeptides and neuromodulators, and the electrophysiological responses of statocyst hair cells to controlled accelerations and inter-sensory interactions with photoreceptors.
Project 5 Modeling and Simulation
Title: Biologically Inspired Hardware: I. Adaptive, Learning Networks to Control the Spatial Orientation and Stabilization of Autonomous Explorers.
The long-term goal of our project is to apply a biologically valid model of the inner ear vestibular mechanisms, called the EarBot, to the design of balance and motor control of robotic explorers. The purpose of the EarBot is to provide more autonomy to robotic explorers, such as improving reliability and quality of acquired scientific data, enhancing navigation over varying terrains, and accessing difficult sites (e.g ocean caves). The vestibular system of the inner ear is the structure that detects sensations of equilibrium. The system coordinates gaze, head on shoulder stabilization and posture through an array of sensory input signals, constructive and destructive gain controllers, feedback and feedforward control signals, and adaptive mechanisms that compensate for the loss of signal through injury. For example, when the head is rotated in a counterclockwise fashion, signals are generated in the vestibular pathways and sent to the ocular motoneurons to help stabilize gaze, in this case a compensatory rotation of the eyes in a clockwise fashion. This ocular motor response to a head movement is called the vestibulo-ocular reflex (VOR). A more elaborate example is visually fixating on a point in space while walking, which requires feedback signals to compensate for movement of the neck and head in yaw, pitch and roll, as well as translation in x, y and z. Balance, the fundamental ability to stabilize the body in 3D space during self-movement, is a basic functionality expected of an autonomously controlled robotic vehicle. A sense of balance provides stability during complex movements such as climbing over uneven terrain, gait control for varying speeds, and avoidance of catastrophic movements (e.g., falling) in reaction to unanticipated external perturbations. A well-controlled system of balance must be able to differentiate a change in posture that is due to either a self-generated motion, a motion caused by an external perturbation, or both occurring simultaneously. Signals can be generated in tandem to optimize image stabilization from camera mounted vision data acquisition systems, much in the way the vestibular system controls the VOR. This is particularly critical where the robot is instructed to maintain a target fixation while walking or systematically shifting its gaze while in motion in an unpredictable environment.
Benchmarking and validation testing of the individual sensors and the configured device could be performed on many of Ames Acceleration Facility devices, such as the multi-axis centrifuge.