“W hat’s your name?” I was slightly confused. Didn’t she already know? “Austin,” I replied. “Th at’s a nice name,”

she said. “It’s nice to meet you.” Th en she turned away from me.“She is your grandmother’s sister,” my mother had reminded me, “and she is very forget-

ful, so be patient.” I pondered this fact as I sat in the bright, sunny room of the nursing home. My thoughts were interrupted as my great-aunt turned back to me. “What’s your name?” she asked.

Th is was my fi rst encounter with Alzheimer’s disease, a debilitating condition that causes its victims to eventually

lose their memories of everything they know, even the names and faces of close family. It is always fatal. I was young when I’d visited my great-aunt at the nursing home, but because of my encounter with her, I grew up fascinated with the inner work-ings of the brain, our thoughts, and memories. So when, in eleventh grade, I had an opportunity to work on a project that might one day unravel the mysteries of the processes behind memory, I jumped at the chance.

seeking the right FitI sought an internship within the National Institutes of Health (NIH) on the advice of friends who had previously worked there. Th e National Institute of Neurological Disorders and Stroke (NINDS), an institute within the NIH, off ers a student training program in brain and nervous system research. Th e Summer Program in the Neurological Sciences, open to aca-demically talented high school, undergraduate, graduate, and medical students, seemed like a perfect fi t. Once I had applied to the program, I began contacting researchers and scheduling meetings to see if I was a good match for the lab. Th is some-what informal process, in which prospective interns contact researchers to discuss their work, is typical.

At NINDS, I met Dr. Xiaobing Chen, an NIH scientist specializing in biophysics. Dr. Chen’s research dealt with the postsynaptic density (PSD), a macromolecular structure composed of hundreds of specialized proteins located on the

dendritic spines of the neurons of synapses. In essence, it is the organizational structure that receives and processes sig-nals between neurons. Th e PSD plays an integral role in the processes behind learning and memory, including long-term potentiation—the synchronization of fi ring of nerve pulses between neurons that is the basis for new memory formation.

I was thrilled when, aft er an interview and several meetings with Dr. Chen, I was accepted into the NINDS Laboratory of Neurobiology’s Summer Internship Program. It was an amaz-ing opportunity to work alongside great scientists, performing cutting-edge research that seeks to understand the core of what makes us human: our brains.

How to build an unknown objectWhile we know that the PSD is important in learning and memory, we know very little about how it actively infl uences these processes. And although we can determine the proteins that compose the PSD, we don’t know much about its organizational structure and the role this structure plays in its function. Dr. Chen’s research focused on decoding this complex structure with the goal of understanding the way we learn—and maybe, one day, developing drugs that can cure memory-related diseases such as Alzheimer’s.

Th e size of the PSD—only around 30 nanometers thick and 300 nanometers wide—is an inherent obstacle to understand-ing it. (By comparison, a hair is about 100,000 nanometers wide.) So how do you decipher the organization of a nanoscale structure composed of thousands of proteins? The process we used, electron microscopic (EM) tomography, generates

by Austin Hou

 “W hat’s your name?” I was slightly confused. Didn’t she hat’s your name?” I was slightly confused. Didn’t she already know? “Austin,” I replied. “Th at’s a nice name,” already know? “Austin,” I replied. “Th at’s a nice name,”

she said. “It’s nice to meet you.” Th en she turned away from me.she said. “It’s nice to meet you.” Th en she turned away from me.“She is your grandmother’s sister,” my mother had reminded me, “and she is very forget-“She is your grandmother’s sister,” my mother had reminded me, “and she is very forget-

ful, so be patient.” I pondered this fact as I sat in the bright, sunny room of the nursing home. My ful, so be patient.” I pondered this fact as I sat in the bright, sunny room of the nursing home. My thoughts were interrupted as my great-aunt turned back to me. “What’s your name?” she asked.thoughts were interrupted as my great-aunt turned back to me. “What’s your name?” she asked.

Th is was my fi rst encounter with Alzheimer’s disease, Th is was my fi rst encounter with Alzheimer’s disease, a debilitating condition that causes its victims to eventually a debilitating condition that causes its victims to eventually

lose their memories of everything they know, even the names lose their memories of everything they know, even the names and faces of close family. It is always fatal. I was young when I’d and faces of close family. It is always fatal. I was young when I’d visited my great-aunt at the nursing home, but because of my visited my great-aunt at the nursing home, but because of my encounter with her, I grew up fascinated with the inner work-

dendritic spines of the neurons of synapses. In essence, it is the organizational structure that receives and processes sig-

by Austin Houby Austin Hou

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The bright spots in the neuron represent dendritic spines in this confocal microscope image, courtesy of Dr. Xiaobing Chen.

24 imagine sept/oct 2012

a three-dimensional model of the object—in this case the PSD—through the use of back projections: First, silhouettes of the object are imaged at various angles with an electron micro-scope. Th en, through computation, the images are assembled to create a complete three-dimensional model.

Th e process is not completely straightforward, though. Using an electron microscope involves bombarding the sample (in this case, slices of hippocampal neuron from a rat brain) with a high-intensity electron beam, which causes the sample to degrade extremely quickly. To address this problem, we used freeze substitution, wherein the sample undergoes high-pressure freezing to prevent the formation of large ice crystals that can damage the cellular structures. Th e cellular H₂O is then removed and replaced with a durable resin, which is more resistant to irradiation by an electron beam. Th is process allows the cellular structures to withstand the stress that occurs when hundreds of images are taken with an electron microscope.

Once the problem of preserving the cellular structures was solved, we used EM tomography to study the core structural organization of the PSD, and in particular, the molecule PSD-95. Th is molecule was chosen because it had been detected in high concentrations within the PSD, and also because Dr. Chen’s previous work showed that PSD-95 tends to organize in a network of membrane-associated, vertically oriented fi la-ments—that is, fi laments perpendicular to the cell membrane. Our goal was to see how these fi laments interacted with other proteins within the PSD.

A surprising discoveryOver a two-month period, we examined the tomograms closely, identifying and classifying structures by their structural and associative properties. Slice by slice, cross-section by cross-section, we pored over the tomograms in order to observe the relationships between proteins in three dimensions. Because the work was progressing well, I returned the following summer to continue the research with Dr. Chen. By the end of the second summer, we had identifi ed a number of trends in the models. And as we worked, we made a surprising discovery.

In addition to the core vertical network of filaments

that formed the foundation of the PSD, we identified several other structural networks that associated with the verti-cal fi laments. Together, these networks created a cascading framework of scaf-folding proteins that formed the core of the PSD. We found clear trends in how these networks interacted, both with each other and with the PSD’s general structure. Perhaps most surprisingly, some of these proteins bound to each other in highly regular patterns. Th e PSD is incredibly complex, and the fact that it is highly ordered is fascinating. More interesting still, the proteins themselves are organized very regularly. We are cur-rently working to establish the identities of these proteins in hopes of creating a more realistic molecular picture of the fundamental structure of the PSD.

I am truly thankful for the chance to work with Dr. Chen on neurosci-ence research at NINDS. Through my experience, I’ve learned that within great complexity lies simplicity. I’m thrilled that I have been able to contribute to research that may one day help decipher the myster-ies behind memory and hopefully lead to a cure for diseases such as Alzheimer’s.

Austin Hou won a 2011 Exceptional summer student Award for his work at ninds. he is currently studying physics and electrical engineering at the University of maryland under a Banneker-key scholarship, and is continuing his work in the lab with dr.

chen. Austin plans to continue to do research in the future, most likely in the engineering fi eld.

a three-dimensional model of the object—in this case the PSD—through the use of back projections: First, silhouettes of the object are imaged at various angles with an electron micro-scope. Th en, through computation, the images are assembled to create a complete three-dimensional model.to create a complete three-dimensional model.

Th e process is not completely straightforward, though. Using an electron microscope involves bombarding the sample (in this case, slices of hippocampal neuron from a rat brain) with a high-intensity electron beam, which causes the sample to degrade extremely quickly. To address this problem,

that formed the foundation of the PSD, we identified several other structural networks that associated with the verti-cal fi laments. Together, these networks created a cascading framework of scaf-created a cascading framework of scaf-folding proteins that formed the core of

For more information on the ninds summer Program in the neurological sciences, see www.ninds.nih.gov/jobs_and_training/summer.

A raw image from the electron microscope depicting one of the “silhouettes” of a rat hippocampal neuron. Many images would be assembled to create a three-dimensional tomogram.

A cross-section of the tomogram produced from the raw EM images. The transposed colored model shows the fi laments of PSD-95 (red) interacting with other proteins in the PSD.

www.cty.jhu.edu/imagine imagine 25