Robert B. Renden, Ph.D. - US grants

DESCRIPTION (provided by applicant): The medial nucleus of the trapezoid body is an essential sign-inverting synapse in the binaural sound localization circuit. The major synapse in the MNTB is the calyx of Held, a. glutamatergic axosomatic synapse, with a uniquely large presynaptic terminal. This morphology allows paired pre-and postsynaptic intracellular recordings, allowing real-time measurements of presynaptic vesicle release, and postsynaptic receptor responses. The calyx shows activity-dependent functional synaptic plasticity, and also undergoes well-characterized postembryonic developmental changes. There are several modulatory transmitters and receptors present at the calyx of Held, that likely play a role in shaping the synpatic properties during development. 0f these, the metabotropic glutamate receptors, (mGluRs) are enigmatic, as they do not to date show a well-defined physiological role in either synaptic plasticity, or synaptic development. My interest lies in investigating the functional role of the group Ill mGluRs, which are located presynaptically at the calyx of Held. Using a combination of immunohistochemistry, electrophysiology, and murine genetics, I will determine the identity and role of group Ill mGluRs in synaptic plasticity and development of the calyx.

We request the funds to establish a new COBRE Magnetic Resonance Imaging Core on the campus of the University of Nevada Reno with additional resources located at the Nevada Cancer Institute (NVCI) and the Cleveland Clinic Lou Ruvo Center for Brain Health, both located in Las Vegas, NV. The core will be directed and managed by a open-rank tenure track faculty person to be hired pending the funding of this proposal. The core will provide for the first time, the infrastructure necessary to conduct human and animal magnetic resonance imaging (MRI research. The core will provide access to well-established cutting-edge human MRI scanning at the Ruvo Center of Brain Health and animal scanning at the NVCI. In addition the core will establish, on the UNR campus, a state-of-the-art computer laboratory equipped with workstations, digital storage, training and technical support, and software for the analysis of human and animal magnetic resonance data. This core will directly support the aims of COBRE projects 1 (Dr. Berryhill), 1 (Dr. Caplovitz) and 5 (Dr. Zhu) and will benefit any and all faculty and students interested in MRI research including members ofthe UNR School of Medicine who have recently invested in a comnpact small-animal MRI scanner. The computer laboratory will house eight Macintosh workstations installed with a variety of MRI analysis software packages including BrainVoyager, MATLAB, AFNI/SUMA, SPM and DTI Studio and will have direct links with the Nevada INBRE Bioinformatics Center. This core will also provide training and foster collaboration in the use of MRI data and data analyses. Funds are requested to provide annual tuition support for faculty and graduate students to attend the Athinoula A. Martinos Center: Functional MRI Visiting Fellowip program. In addition the core will sponsor tutorial workshops for facutly and students in the mehtods and applications of MRI technology. The core will host a monthly MRI Imaging Meeting to bring together faculty and students with interests in neuroimaging. This meeting will provide a mechansim for fostering collaboration and attracting new members into the UNR neuroscience research community.

This work is relevant to both normal aging and pathologies like Alzheimer?s disease, where brain function is impaired due to defective mitochondrial respiration and loss of cellular energy. The long-term goal of this project is to ameliorate neurotransmission defects due to mitochondrial dysfunction, as a way to stop disease progression to later degenerative stages, increasing healthspan in populations increasingly subject to age- related neurological diseases. Fundamental mechanisms underlying the bioenergetics of synaptic function in normal tissue must be resolved first, to cure these diseases. Our goals in this project are two-fold. First, the extent to which mitochondrial Ca2+ uptake facilitates ATP production in response to activity will be defined. Second, the extent that compensatory strategies are utilized at the presynaptic terminal to delay energy loss will be determined when mitochondrial function is impaired. Results from this project will provide clear mechanistic insight into the Ca2+-buffering and ATP-producing roles of synaptic mitochondria, an essential first step that is currently unclear. The PI has developed several novel approaches that allow us to dissect the bioenergetic strategies used to support transmission at the mouse calyx of Held, using a combination of electrophysiology, Ca2+ imaging, and ATP imaging. In contrast to small conventional synapses, giant ?calyx-like? excitatory synapses in the rodent auditory brainstem allow direct whole-cell recordings from the presynaptic terminal. This experimental accessibility permits manipulation of presynaptic [Ca2+] and [ATP], making it possible to dissect the interdependent Ca2+-buffering and energy-supporting roles of synaptic mitochondria. In the first Specific Aim, the extent that the mitochondrial calcium uniporter (MCU) facilitates mitochondrial respiration and ATP homeostasis following synaptic activity will be determined. The second Specific Aim will dissect the importance of mitochondrial Ca2+ uptake versus facilitated respiration on synaptic transmission and presynaptic short-term plasticity. Namely, is the MCU more important for Ca2+ buffering or ATP homeostasis at the synapse? In Specific Aim three, the consequence of metabolic switching between glycolysis and mitochondrial respiration in support of transmission will be examined in normal synapses, and in cases where MCU function is acutely or chronically impaired. This project will provide a detailed understanding of the range of metabolic strategies that are employed by synapses to support synaptic transmission in physiological and pathological settings. This knowledge will identify viable routes of intervention for restoring function to energy-deficient synapses that can be leveraged therapeutically to alleviate disease-related synaptic dysfunction.