Jodie G. Pope

Synaptic pathology and therapeutic repair in adult retinoschisis mouse by AAV-RS1 transfer

Strategies aimed at invoking synaptic plasticity have therapeutic potential for several neurological conditions. The human retinal synaptic disease X-linked retinoschisis (XLRS) is characterized by impaired visual signal transmission through the retina and progressive visual acuity loss, and mice lacking retinoschisin (RS1) recapitulate human disease. Here, we demonstrate that restoration of RS1 via retina-specific delivery of adeno-associated virus type 8-RS1 (AAV8-RS1) vector rescues molecular pathology at the photoreceptor-depolarizing bipolar cell (photoreceptor-DBC) synapse and restores function in adult Rs1-KO animals. Initial development of the photoreceptor-DBC synapse was normal in the Rs1-KO retina; however, the metabotropic glutamate receptor 6/transient receptor potential melastatin subfamily M member 1-signaling (mGluR6/TRPM1-signaling) cascade was not properly maintained. Specifically, the TRPM1 channel and G proteins Gαo, Gβ5, and RGS11 were progressively lost from postsynaptic DBC dendritic tips, whereas the mGluR6 receptor and RGS7 maintained proper synaptic position. This postsynaptic disruption differed from other murine night-blindness models with an electronegative electroretinogram response, which is also characteristic of murine and human XLRS disease. Upon AAV8-RS1 gene transfer to the retina of adult XLRS mice, TRPM1 and the signaling molecules returned to their proper dendritic tip location, and the DBC resting membrane potential was restored. These findings provide insight into the molecular plasticity of a critical synapse in the visual system and demonstrate potential therapeutic avenues for some diseases involving synaptic pathology.

Determining the mass of gas in large collection volumes with acoustic and microwave resonances

We characterized a 1.8 m3, quasi-spherical resonator, a pressure vessel informally known as the “big blue ball” or “BBB.” The BBB will be the collection volume of a NIST-designed gas-flow standard that will operate at pressures up to 7 MPa. Using microwave resonance frequencies, we determined the volume of the BBB filled with argon as a function of pressure (up to 7 MPa) and temperature (near ambient). The measured pressure- and temperature-dependences of the BBB’s volume are consistent with the published properties of carbon steels. We filled the BBB with 220 kg of argon in weighed increments of approximately 20 kg. We also determined the mass m acoust of argon in the BBB by measuring the pressure, the acoustic resonance frequencies f acoust of 3 modes, and using the known thermophysical properties of argon. The values of m acoust were within ±0.03 % of the gravimetrically determined masses. In a typical application, the BBB will never be isothermal. Nevertheless, the acoustic resonance frequencies quickly and accurately determine the average temperature and mass of the gas in the BBB despite significant, long-lived thermal gradients that are created by pressure changes. A theoretical model for effect of temperature gradients on the acoustic resonance frequencies is presented.We characterized a 1.8 m3, quasi-spherical resonator, a pressure vessel informally known as the “big blue ball” or “BBB.” The BBB will be the collection volume of a NIST-designed gas-flow standard that will operate at pressures up to 7 MPa. Using microwave resonance frequencies, we determined the volume of the BBB filled with argon as a function of pressure (up to 7 MPa) and temperature (near ambient). The measured pressure- and temperature-dependences of the BBB’s volume are consistent with the published properties of carbon steels. We filled the BBB with 220 kg of argon in weighed increments of approximately 20 kg. We also determined the mass m acoust of argon in the BBB by measuring the pressure, the acoustic resonance frequencies f acoust of 3 modes, and using the known thermophysical properties of argon. The values of m acoust were within ±0.03 % of the gravimetrically determined masses. In a typical application, the BBB will never be isothermal. Nevertheless, the acoustic resonance frequencies quick...

Fast tracking of acoustic resonance frequencies in collection volumes to measure flow

Previously, we demonstrated accurate determinations of the mass of gas in a large collection vessel of known volume from measurements of the pressure and the resonance frequencies of a few acoustic modes. We achieved accurate mass measurements even when linear temperature gradients persisted after adding or removing gas. The change in mass Δm from before and after flow and the collection time Δt may be used to calibrate mass flowmeters. Because the resonance quality factors Q are very high (up to 30000), measuring the complex-valued frequency response using a lock-in amplifier to determine the resonance frequency is slow. This static measurement of mass requires sufficient time to elapse for transient non-linear gradients to dissipate through convection and diffusion. Here, we demonstrate a method to dynamically track the resonance frequency of a large, gas-filled collection vessel while gas is flowing into or out of the vessel. We use positive feedback to excite sustained oscillations at the desired resonance frequency without a lock-in amplifier or frequency synthesizer. As the speed of sound changes, the sustained oscillations track the changing resonance frequency f with response time ~1/f. Preliminary mass flow measurements using this technique agree with a flow standard within their combined uncertainties.Previously, we demonstrated accurate determinations of the mass of gas in a large collection vessel of known volume from measurements of the pressure and the resonance frequencies of a few acoustic modes. We achieved accurate mass measurements even when linear temperature gradients persisted after adding or removing gas. The change in mass Δm from before and after flow and the collection time Δt may be used to calibrate mass flowmeters. Because the resonance quality factors Q are very high (up to 30000), measuring the complex-valued frequency response using a lock-in amplifier to determine the resonance frequency is slow. This static measurement of mass requires sufficient time to elapse for transient non-linear gradients to dissipate through convection and diffusion. Here, we demonstrate a method to dynamically track the resonance frequency of a large, gas-filled collection vessel while gas is flowing into or out of the vessel. We use positive feedback to excite sustained oscillations at the desired reso...