OHSU

2010 NGP Retreat

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By Stephani Sutherland, NGP Alumna and Science Writer

The 2010 Neuroscience Graduate Program Retreat at Timberline Lodge provided students, postdocs, and faculty a chance to gather in a beautiful setting and share some of the ideas and approaches that drive research in the laboratories throughout the NGP at Oregon Health & Science University. NGP director, Gary Westbrook, introduced the 10 new students in the program and thanked the upcoming 2nd year students who organized the retreat program. Each session featured a talk from a faculty member, a postdoc, an NGP student, and a faculty member new to the OHSU community. In addition to the 100 attendees, each session also featured an appearance by a member of the local animal community as well.

In the first session, titled Neurophysiology, Craig Jahr explored how individual neurons use analog signaling in axons to enhance the all-or-none action potential. He described experiments that showed that a sub-threshold influx of calcium leads to greater calcium influx during a subsequent action potential. Joe Trappani, a postdoc in Teresa Nicholson's lab, next showed us that hair cells of the lateral line organ in zebrafish produce spontaneous synaptic "noise" even in the absence of stimuli. His analysis suggested that spiking in the lateral line axons rely on two separate stochastic—or random—processes, which could be differentiated by their time courses. The spontaneous events provide a sort of white noise. Though it may seem counterintuitive that background chatter would make it easier to hear a whisper, it keeps the system on the "knife's edge" of picking up a signal. Aya Matsui, a student in John Williams's lab, went in search of opioid-sensitive GABAergic inputs to midbrain dopamine neurons in a little-studied area called the rostromedial tegmental area (RMTg). Aya also first introduced our animal visitors. "Oh. There's a mouse!" she offered nervously. Those with a better view of the furry critter assured us it was a chipmunk, which seemed to reassure everyone. Shane Tillo, a graduate student filling in for new faculty member Haining Zhong, valiantly presented us with a look at the lab's efforts to understand protein movements at the synapse. He likened the exercise to an alien watching a football game, in which you might try to identify the players, understand their positions, and then figure out how they move on the field. Zhong's strategy to visualize PKA subunits, which move on a tiny spatial scale, combines fluorescence resonance electron transfer (FRET) with photo-activated localization microscopy (PALM). Repeated iterations of photobleaching and imaging reveal a brighter signal associated with the tiny movements.

After lunch in the Raven's Nest, we reconvened to hear about Molecular, Cellular, and Developmental Neurobiology. John Brigande described an elegant endeavor in which in utero gene transfer yielded what look and act like functional auditory hair cells in the cochlea. The next challenge will be in guiding their inputs to higher order neurons, which seem to reject the supernumerary cells' axons, preventing the ultimate goal of rewiring the ear. Jon Oyer, a postdoc in Gail Mandel's lab, discussed how co-factors for the transcriptional suppressor REST keep non-neuronal cells from expressing neuronal proteins. Zev Einhorn, also working in Teresa Nicholson's lab, nabbed the prize for the best student talk with his look at the effects of rabconnectin mutations on synaptic vesicle acidification. And Jae Lee, a new faculty member in the Department of Pediatrics, gave us an intriguing look at why we might eat in response to stress. He examines the molecular effects of glucocorticoids at the AgRP gene in hypothalamic arcuate nucleus neurons, which direct food-seeking behaviors.

The Neurobiology of Disease session showed us a few of the brain's "disaster scenarios." Paco Herson focused on the NAD+-activated ion channel TRPM2 as a therapeutic target in central ischemia. The result was "good news, bad news"—knockdown of TRPM2 conferred protection, but only in males, which probably arises from a sexually dimorphic upstream regulation. Herson summed up the conundrum: "Life isn't always simple." Bryan Luikart, a postdoc in Gary Westbrook's lab, drove this point home with his presentation of the role of the phosphoinositide phophastase PTEN on the growth of newborn neurons in the dentate gyrus. With reduced levels of PTEN, the neurons grew larger and spread a wider array of spiny processes, an effect that may underlie megancephaly in a subset of autism patients. Derek Musashe, a student in Doris Kretzschmar's lab, tried to persuade us that the much-maligned amyloid precursor protein (APP) is simply "misunderstood." He showed that the APP-like protein (APPL) in Drosophila could actually protect against neurodegeneration in the fly model, an effect that required both full-length APPL and its secreted fragments. Mary Logan, a new faculty member in the Jungers Center discussed the ways that glial cells find, identify, and engulf dying neurons before they spill their guts, so to speak. Without a transmembrane receptor called Draper, glia localized to the site of dying neurons but failed to carry out phagocytosis, leaving the brain susceptible to secondary damage.

After the day of talks—sprinkled with appearances from our fuzzy friends—the crowd adjourned to Timberline Lodge's majestic lobby. There, attendees chatted about the posters set up around the perimeter of the grand fireplace while sipping on microbrews and local wines. After the happy hour, a delicious Pacific Northwest dinner of—you guessed it—salmon was served to a room abuzz with conversation. As the invited speaker, Bill Zagotta, PhD, was charged with the difficult job of engaging this rather comfortable crowd with an after-dinner presentation. He was more than up to the task.

Zagotta, a HHMI investigator at the University of Washington, gave us a glimpse of the questions that motivate him—which he described as "trying to understand ligand-induced conformational changes" in proteins—and how he approaches them. Specifically, Zagotta studies the conformational changes that occur in response to ligand binding at cyclic nucleotide-gated (CNG) ion channels. Most CNG channels are expressed in sensory tissues, most familiarly in the retina. The ligand-binding site in these channels lies, as Zagotta put it, "as far from the pore region as you could be and still be in the same protein." So how does the ligand affect the physical change that leads to pore opening?

It turns out there are two main models for ligand-gated channel opening: either the ligand causes a conformational change that "works" to open the pore, or the channel actually "works" to keep the pore closed in the unbound state, which is relieved by binding and results in channel opening. CNG channels use the second mechanism. Zagotta went on to describe an intricate latticework of b-rolls, b-strands, and helices, including "elbow" and "shoulder" regions where the  four channel subunits interact. In order to learn more about how the protein moves in response to ligand binding, Zagotta and his team (which, incidentally, is well represented by OHSU alums) used FRET technology. FRET can provide a look at the movements of proteins—by the transfer of energy from one fluorophore to an acceptor molecule—in the range of 50 angstroms (Å). But remember, Zagotta inhabits a world where 50Å is a giant chasm. He needed to see movements on an even smaller scale. To achieve this, the team used an alternative "crappy acceptor" molecule: metal ions, which need to be within 6-10Å in order to absorb donor electrons. From these and further investigations, Zagotta has formed a model of how they believe the protein subunits "work" to stay closed and then "pop open" in response to nucleotide binding. NGP student Zev Einhorn summed it up with this analogy: picture closing up a cardboard box, folding down one flap of the lid after another, until finally the fourth flap "locks" the lid shut. When you open the box, the flaps open all at once in a singular process. His analysis of the model earned him this comment from Zagotta: "I never thought of it quite that way. I'm going to use that!"

Larry Trussell began the wednesday morning's sessions with a history of inhibition in the nervous system. After receiving a legally binding assurance that the students did not invite him to address this topic based on his age, Trussell made clear to the audience that this was not a first-hand account. But it was insightful and entertaining. After the talk, NGP students answered "quiz questions" to earn free coffee and other swag. Trussell challenged us to consider not just the discoveries of pioneering scientists, but also how they thought about the questions  and what ideas were available to them at the time—words of wisdom even in these "modern" times.

Systems Neuroscience was represented in the retreat's final session. Christine Portfors, an OHSU adjunct faculty member at Washington State University Vancouver, described vocalizations by mice that lead female mice to pause their activity for mating behavior. Her question about the auditory signal was, "Why? What is the brain cueing in on that makes the female say, 'OK, I will stop and mate with you'?" Her lab's analysis has shown that the decision-making process begins in brainstem structures, long before information reaches the cortex. Perhaps not surprisingly, Portfors's talk also featured an appearance by a chipmunk, which she too mistook for a large mouse. Sowmya Venkataramani, a postdoc in the lab of Rowland Taylor, also showed how decisions could be made at a very early sensory processing level—here, in the retina. Experiments in which she recorded from neurons in an intact retinal preparation revealed that motion- and orientation-selectivity begin in the eye. Pierre Apostolides described his work in the Trussell lab, which focuses on co-packaging of GABA and glycine in the same synaptic vesicles. He hopes to uncover the ways that adjustments to this co-packaging might translate to activity-dependent modulation of the kinetics of inhibitory postsynaptic potentials, which vary depending on the predominantly released transmitter. Wolf Almers provided a wrap-up to the retreat with his presentation, Watching molecules in live cells. He described experiments with total internal reflection fluorescent (TIRF) microscopy to examine exocytosis using videos that the community fondly refers to as "Wolf's cool neuron movies."

If you missed the retreat this year, mark your calendars now for next year's retreat, which is scheduled for September 19 and 20, 2011 at Timberline Lodge.