Biology subjects

Ridenour, M.

Publications and source records attributed to Ridenour, M..

5 recordsLinked to original sources

bioRxiv2026

High precision animal stereotaxis with 3D polychromic photogrammetry

Stereotaxic brain surgery is a foundational neurosurgical technique used to deliver chemical, pharmacological, or genetic material to specific brain regions, or to precisely implant electrodes and stimulators. Accurate targeting depends on reliable identification of skull landmarks, particularly bregma and lambda. Here we present a photogrammetry-based automated small animal stereotaxic platform that uses a single, freely handheld camera, such as a standard smartphone, to generate high-resolution, polychromatic 3D skull reconstructions. Because photogrammetry requires no fixed overhead hardware, the surgical field remains fully accessible for instruments, microscopes, and other equipment. The resulting color reconstructions substantially improve identification of bregma and lambda compared to monochromatic approaches, and the higher spatial resolution translates directly into improved targeting accuracy and surgical speed. The system operates by a user moving a handheld camera around the exposed skull. The platform automatically produces a detailed 3D mesh and computes stereotaxic coordinates without manual measurement. Together, these properties yield a practical, accessible yet accurate platform for automated small animal neurosurgery. We previously described a structured illumination approach in combination with a Steward platform; however, that system required a fixed projector and camera array that occupied critical surgical workspace and produced monochromatic meshes that complicated landmark identification. The photogrammetry-based method described here overcomes both limitations while retaining full compatibility with the Steward platform as a stereotaxic base.

neuroscience↗

bioRxiv2025

In-vivo optogenetic manipulation approach for gerbil medial nucleus of trapezoid body

PurposeThis study introduces an in-vivo optogenetic manipulation approach for the medial nucleus of the trapezoid body (MNTB) in Mongolian gerbils, a species with a hearing range similar to humans. The MNTB is crucial for sound localization, but traditional methods lack temporal precision and reversibility. The aim of this study is to develop a specific, reversible method for controlling MNTB activity with fast and precise temporal control, an approach vital for studying sound localization. MethodsWe stereotactically injected adeno-associated viral vectors encoding opsins into the gerbil MNTB. Precise targeting was achieved despite the MNTBs location in a deep, heavily myelinated area of the brainstem. Opsin expression was confirmed via confocal microscopy. In-vivo electrophysiology combined with optical stimulation was used to test optical activation and suppression of MNTB activity during sound stimuli. ResultsOpsin expression was strong and stable in MNTB neurons over weeks and months. Laser stimulation during in-vivo recordings successfully induced both activation and suppression of MNTB neurons, demonstrating fast and precise control over neural activity. ConclusionThis in-vivo optogenetic method provides specific, reversible control of MNTB activity in gerbils with rapid, real-time modulation. It offers a powerful tool for investigating sound localization and auditory processing with high temporal precision.

neuroscience↗

bioRxiv2024

Sapphire-Based Optrode for Low Noise Neural Recording and Optogenetic Manipulation

Electrophysiological recordings of neurons in deep brain regions using optogenetic stimulation are essential to understanding and regulating the role of complex neural activity in biological behavior and cognitive function. Optogenetic techniques have significantly advanced neuroscience research by enabling the optical manipulation of neural activities. Because of the significance of the technique, constant advancements in implantable optrodes that integrate optical stimulation with low-noise, large-scale electrophysiological recording are in demand to improve the spatiotemporal resolution for various experimental designs and future clinical applications. However, robust and easy-to-use neural optrodes that integrate neural recording arrays with high-intensity light emitting diodes (LEDs) are still lacking. Here, we propose a neural optrode based on Gallium Nitride (GaN) on sapphire technology, which integrates a high-intensity blue LED with a 5x2 recording array monolithically for simultaneous neural recording and optogenetic manipulation. To reduce the noise interference between the recording electrodes and the LED, which is in close physical proximity, three metal grounding interlayers were incorporated within the optrode, and their ability to reduce LED-induced artifacts during neural recording was confirmed through both electromagnetic simulations and experimental demonstrations. The capability of the sapphire optrode to record action potentials has been demonstrated by recording the firing of mitral/tuft cells in the olfactory bulbs of mice in vivo. Additionally, the elevation of action potential firing due to optogenetic stimulation observed using the sapphire probe in medial superior olive (MSO) neurons of the gerbil auditory brainstem confirms the capability of this sapphire optrode to precisely access neural activities in deep brain regions under complex experimental designs.

neuroscience↗

bioRxiv2024

Computational model for synthesizing auditory brainstem responses to assess neuronal alterations in aging and autistic animal models

PurposeThe auditory brainstem response (ABR) is a widely used objective electrophysiology measure for non-invasively assessing auditory function and neural activity in the auditory brainstem, but its ability to reflect detailed neuronal processing is limited due to the averaging nature of the electroencephalogram-type recordings. MethodThis study addresses this limitation by developing a computational model of the auditory brainstem which is capable of synthesizing ABR traces based on a large, population scale neural extrapolation of a spiking neuronal network of auditory brainstem circuitry. The model was able to recapitulate alterations in ABR waveform morphology that have been shown to be present in two medical conditions: animal models of autism and aging. Moreover, in both of these conditions, these ABR alterations are caused by known distinct changes in auditory brainstem physiology, and the model could recapitulate these changes. ResultsIn the autism model, the simulation revealed myelin deficits and hyperexcitability, which caused a decreased wave III amplitude and a prolonged wave III-V interval, consistent with experimentally recorded ABRs in Fmr1-KO mice. For the aging condition, the model recapitulated ABRs recorded in aged gerbils and indicated a reduction in activity in the medial nucleus of the trapezoid body (MNTB), a finding validated by confocal imaging data. ConclusionThese results demonstrate not only the models accuracy but also its capability of linking features of ABR morphology to underlying neuronal properties and suggesting follow-up physiological experiments.

neuroscience↗

bioRxiv2024

Age-related myelin deficits in the auditory brain stem contribute to cocktail party-deficits

Age-related hearing loss consists of both peripheral and central components and is an increasing global health concern. While peripheral hearing loss is well understood, central hearing loss-- age-related changes in the central auditory pathways resulting in a listeners inability to process sound correctly --remains poorly understood. In this study, we focus on the pathway from the cochlear nucleus to the medial nucleus of the trapezoid body (MNTB), which depends on heavily myelinated axons for microsecond-level temporal precision required for sound localization. Using a combination of auditory brainstem response recordings (ABR), advanced light and electron microscopy, and behavioral testing with prepulse inhibition of the acoustic startle response (PPI) we identified a correlation between oligodendrocyte loss, abnormal myelination in MNTB afferents, altered ABR wave III morphology indicating MNTB dysfunction, and deficits in spatial hearing behaviors in aging Mongolian gerbils. These findings provide a mechanistic explanation of how demyelination contributes to age-related dysfunction in the auditory brainstems sound localization pathway.

neuroscience↗