Mugnaini, M. | bioRxiv Science

bioRxiv2022

Unique potential of immature adult-born neurons for the remodeling of CA3 spatial maps

Mammalian hippocampal circuits undergo extensive remodeling through adult neurogenesis. While this process has been widely studied, the specific contribution of adult-born granule cells (aGCs) to spatial operations in the hippocampus remains unknown. Here we show that optogenetic activation of 4-week-old (young) aGCs in free-foraging mice produces a non- reversible reconfiguration of spatial maps in proximal CA3, while rarely evoking neural activity. Stimulation of the same neuronal cohort on subsequent days recruits CA3 neurons with increased efficacy but fails to induce further remapping. In contrast, stimulation of 8- week-old (mature) aGCs can reliably activate CA3 cells but produce no alterations in spatial maps. Our results reveal a unique role of young aGCs in remodeling CA3 representations, a potential that can be depleted and is lost with maturation. This ability could contribute to generate orthogonalized downstream codes supporting pattern separation.

neuroscience↗

bioRxiv2022

Supraorbital whiskers act as wind-antennae in rat anemotaxis

We know little about mammalian anemotaxis, wind-sensing. Recently, however, Hartmann and colleagues showed whisker-based anemotaxis in rats. To investigate how whiskers sense airflow, we tracked whisker tips in anesthetized or cadaver rats under no airflow, low airflow and high (fan-blowing) airflow. Whisker tips showed little movement under no airflow conditions and all whisker tips moved during high airflow. Low airflow conditions - most similar to naturally occurring wind stimuli - engaged whisker tips differentially. Most whiskers moved little, the long supraorbital whisker showed maximal displacement and , A1, {beta}, and {gamma} whiskers also showed movements. The long supraorbital whisker differs from other whiskers in its exposed dorsal position, upward bending, length and thin diameter. Ex vivo extracted long supraorbital whiskers also showed exceptional airflow displacement, suggesting whisker-intrinsic biomechanics mediate the unique airflow-sensitivity. Micro computed tomography revealed that the ring-wulst - the follicle structure receiving the most sensitive afferents - was more complete/ closed in supraorbital and other wind-sensitive whiskers than in non-wind-sensitive whiskers, suggesting specialization of the supraorbital for omni-directional sensing. We localized and targeted the cortical supraorbital whisker representation in simultaneous Neuropixels recordings with D/E-row whisker barrels. Responses to wind-stimuli were stronger in the supraorbital whisker representation than in D/E-row barrel cortex. We assessed the behavioral significance of whiskers in an airflow-sensing paradigm. We observed that rats spontaneously turn towards airflow stimuli in complete darkness. Selective trimming of wind-responsive whiskers diminished airflow turning responses more than trimming of non-wind-responsive whiskers. Lidocaine injections targeted to supraorbital whisker follicles also diminished airflow turning responses compared to control injections. We conclude that supraorbital whiskers act as wind antennae. New and NoteworthyAnimals rely on sensory processing of airflow (anemotaxis) to guide navigation and survival. We examined mechanisms of rat anemotaxis by combining whisker tracking, biomechanical analysis, micro computed tomography of follicle structure, Neuropixels recordings in the barrel field, behavior of airflow turning and whisker interference by trimming and lidocaine injections. This diversity of methods led to a coherent pattern of results. Whiskers greatly differ in their airflow sensitivity and strongly wind-responsive whiskers - in particular long supraorbital whiskers - determine behavioral responses to airflow stimuli in rats.

neuroscience↗