Biology subjects

Robinson, J. C.

Publications and source records attributed to Robinson, J. C..

5 recordsLinked to original sources

bioRxiv2026

Medial septum glutamatergic neurons support speed coding and grid cell spatial stability in the medial entorhinal cortex

Successful navigation requires the integration of self-motion signals with spatial representations, yet the circuits that provide velocity information necessary for stable grid cell firing remain incompletely understood. Here, we identify medial septal (MS) glutamatergic neurons as a critical component of this pathway. Using cell-type-specific optogenetic silencing combined with in vivo electrophysiology in freely moving mice, we show that MS glutamatergic neurons support the fidelity of firing rate-based speed coding in the medial entorhinal cortex (MEC). Silencing this population reduced grid cell spatial periodicity and stability and produced distortions of grid firing fields. Silencing also reduced theta phase-locking strength in strongly theta-modulated MEC neurons. Model simulations of a hybrid oscillatory interference-continuous attractor network with reductions in speed-signal fidelity disrupted grid periodicity and reproduced features of the spatial distortions observed in vivo. Together, these findings identify a septo-entorhinal circuit that coordinates self-motion information with the spatial and temporal organization of MEC activity to maintain a stable neural representation of space.

neuroscience↗

bioRxiv2025

Comparative genomics of Sympodiorosea identifies genome evolution mediated through selective pressure on the metabolic gene repertoire

Biological interactions involving host-associated fungi are manifestations of chemistry shaped over evolutionary time. For antagonistic fungi, specialization to host fungi is often facilitated through the acquisition of genes encoding novel secretions, including proteins and specialized metabolites that shape interactions with host defenses, as well the acquisition of nutrients. Alternatively, novel function may arise from diversifying selection eliciting evolutionary innovation in inert secretions. Through specialization, fungal metabolic capacity can serve as an imprint of the selective forces imposed on the antagonist and provide insights into its natural history and occupied niche. Here, we conduct a phylogenomic investigation of antagonistic ascomycetes in the genus Sympodiorosea, which are commonly found in basal fungus-growing ant gardens. Sympodiorosea and closely related genera of Escovopsis, Luteomyces, and Escovopsioides are canonically referenced as virulent mycoparasites, however, recent work has illuminated the possibility for diverse, non-virulent species to emerge within these attine-associated fungi. We explored genomic variation in Sympodiorosea to gain insight into the genomic potential for alternative lifestyles, focusing on diversity and evolution of metabolic genes. Our study revealed a constrained selective landscape across the Sympodiorosea genome. However, outcomes of in vitro interactions with host fungi are diverse and predictable based on the antagonists ant-species-of-origin, suggesting functional diversification. Phylogenomics reveals that gain/loss events of genes involved in secretions (secretome) are potential drivers of diversification. Additionally, we demonstrate that purifying selection acts more intensely on secretome-related genes relative to other genes. In contrast, few genes from the secretome experience diversifying selection, suggesting a mechanistic role for driving both functional differences between strains and host-specialization. Comparative genomics including other fungi within the family Hypocreales reveals that Sympodiorosea has experienced expansions and contractions in proteases genes that are discordant from expectations under a strictly mycoparasitic lifestyle, indicating either the potential for an alternative lifestyle within ant gardens, or that Sympodiorosea recently evolved from other niches. These results provide novel insight into genomic evolution of these fungi and inform future experimental studies of the ecology and chemistry of interactions within the complex fungus-growing ant symbiosis.

evolutionary biology↗

bioRxiv2025

How do egocentric boundary cells depend upon the coordinate system of environmental features?

Neurons in the retrosplenial (RSC) (Alexander et al 2020a, LaChance & Hasselmo 2024) and postrhinal cortex (POR) respond to environmental boundaries and configurations using egocentric coordinates relative to an animals current position. Neurons in these structures and adjacent structures also respond to spatial dimensions of self-motion such as running velocity (Carstensen et al 2021, Robinson et al 2023). Experimental and modeling data suggest that these responses could be essential for guiding behaviors such as obstacle avoidance and goal-directed navigation (Erdem & Hasselmo 2012, Erdem & Hasselmo 2014). However, these findings still leave the unanswered question: What specific features, and in what coordinate frames, drive these egocentric neural responses? Here we present models of the potential circuit mechanisms generating egocentric responses in RSC. One model posits that neurons encode internal representations of barriers in head-centered coordinates, defined by distance and angle, which are modulated by running velocity to enable trajectory planning and obstacle avoidance. We contrast this with a complementary hypothesis in which neurons respond to retinotopic features--such as the top, bottom, or edges of walls, which may serve as precursors to head-centered representations. Additional hypotheses include trajectory-based forward scanning (e.g., ray tracing) for barrier detection or comparing optic flow across the visual field. These hypotheses generate complementary modeling predictions about how changes in environmental parameters could alter the neural responses of egocentric boundary cells that are presented here.

neuroscience↗

bioRxiv2023

Optogenetic Silencing of Medial Septal GABAergic Neurons Disrupts Grid Cell Spatial and Temporal Coding in the Medial Entorhinal Cortex

The hippocampus and medial entorhinal cortex (MEC) form a cognitive map that facilitates spatial navigation. As part of this map, MEC grid cells fire in a repeating hexagonal pattern across an environment. This grid pattern relies on inputs from the medial septum (MS). The MS, and specifically its GABAergic neurons, are essential for theta rhythm oscillations in the entorhinal-hippocampal network, however, it is unknown if this subpopulation is also essential for grid cell function. To investigate this, we used optogenetics to inhibit MS-GABAergic neurons during grid cell recordings. We found that MS-GABAergic inhibition disrupted grid cell spatial periodicity both during optogenetic inhibition and during short 30-second recovery periods. Longer recovery periods of 60 seconds between the optogenetic inhibition periods allowed for the recovery of grid cell spatial firing. Grid cell temporal coding was also disrupted, as observed by a significant attenuation of theta phase precession. Together, these results demonstrate that MS-GABAergic neurons are critical for grid cell spatial and temporal coding in the MEC.

neuroscience↗

bioRxiv2019

DG-CA3 circuitry mediates hippocampal representations of latent information

Survival in complex environments necessitates a flexible navigation system that incorporates memory of recent behavior and associations. Yet, how the hippocampal spatial circuit represents latent information independent of sensory inputs and future goals has not been determined. To address this, we imaged the activity of large ensembles in subregion CA1 via wide-field fluorescent microscopy during a novel behavioral paradigm. Our results demonstrated that latent information is represented through reliable firing rate changes during unconstrained navigation. We then hypothesized that the representation of latent information in CA1 is mediated by pattern separation/completion processes instantiated upstream within the dentate gyrus (DG) and CA3 subregions. Indeed, CA3 ensemble recordings revealed an analogous code for latent information. Moreover, selective chemogenetic inactivation of DG-CA3 circuitry completely and reversibly abolished the CA1 representation of latent information. These results reveal a causal and specific role of DG-CA3 circuitry in the maintenance of latent information within the hippocampus.

neuroscience↗