Biology subjects

Gehr, C.

Publications and source records attributed to Gehr, C..

4 recordsLinked to original sources

bioRxiv2023

Retinal input integration in excitatory and inhibitory neurons in the mouse superior colliculus in vivo

The superior colliculus (SC) is a midbrain structure that contains one of the highest densities of inhibitory neurons in the brain and, together with the thalamocortical visual system, it plays a key role in visually guided behaviors. The SC receives direct inputs from retinal ganglion cells (RGCs) but whether excitatory and inhibitory SC neurons differentially integrate retinal activity in vivo is still largely unknown. We recently established an extracellular recording approach using high-density electrodes to measure the activity of RGCs simultaneously with their postsynaptic SC targets in vivo, that allows addressing how SC neurons integrate RGC activity. Here, we employ this method to study the functional properties and dynamics that govern retinocollicular signaling in a cell-type specific manner by identifying GABAergic SC neurons using optotagging in anesthetized VGAT- ChR2 mice. We measured 305 monosynaptically connected RGC-SC pairs, out of which approximately one third of retinal afferents connect onto inhibitory SC neurons. We show that both excitatory and inhibitory SC neurons receive comparably strong RGC inputs, with functionally similar RGC-SC pairs showing stronger connections. Our results demonstrate that similar wiring rules apply for RGCs innervation of both excitatory and inhibitory SC neurons, which is unlike the cell-type specific connectivity in the thalamocortical system. Contrasting the similar RGC-SC connection strength, we observed that RGC activity contributed more to the activity of postsynaptic excitatory SC neurons than to the activity of postsynaptic inhibitory SC neurons. This implies that the excitatory SC neurons are more specifically coupled to RGC afferent inputs, while inhibitory SC neurons may integrate additional inputs from other sources. Taken together, our study deepens the understanding of cell-type specific retinocollicular functional connectivity and emphasizes that the two major brain areas for visual processing, the visual cortex and the superior colliculus, differently integrate sensory afferent inputs.

neuroscience↗

bioRxiv2022

Efficient mapping of the thalamocortical monosynaptic connectivity in vivo by tangential insertions of high-density electrodes in cortex

Thalamus provides the principal input to cortex, thus understanding the mechanisms of cortical computations in behaving animals requires to characterize the thalamocortical connectivity in vivo. We show that tangential insertions of high-density electrodes into mouse cortex capture the activity of thalamocortical axons simultaneously with their synaptically connected cortical neurons. Multiple thalamic synaptic inputs to cortical neurons can be measured providing an efficient approach for mapping the thalamocortical connectivity in vivo.

neuroscience↗

bioRxiv2021

Strong and specific connections between retinal axon mosaics and midbrain neurons revealed by large scale paired recordings

The superior colliculus (SC) is a midbrain structure that plays important roles in visually guided behaviors. Neurons in the SC receive afferent inputs from retinal ganglion cells (RGC), the output cells of the retina, but how SC neurons integrate RGC activity in vivo is unknown. SC neurons might be driven by strong but sparse retinal inputs, thereby reliably transmitting specific retinal functional channels. Alternatively, SC neurons could sum numerous but weak inputs, thereby extracting new features by combining a diversity of retinal signals. Here, we discovered that high-density electrodes simultaneously capture the activity and the location of large populations of retinal axons and their postsynaptic SC target neurons, permitting us to investigate the retinocollicular circuit on a structural and functional level in vivo. We show that RGC axons in the mouse are organized in mosaics that provide a single cell precise representation of the retina as input to SC. This isomorphic mapping between retina and SC builds the scaffold for highly specific wiring in the retinocollicular circuit which we show is characterized by strong connections and limited functional convergence, established in log-normally distributed connection strength. Because our novel method of large-scale paired recordings is broadly applicable for investigating functional connectivity across brain regions, we were also able to identify retinal inputs to the avian optic tectum of the zebra finch. We found common wiring rules in mammals and birds that provide a precise and reliable representation of the visual world encoded in RGCs to neurons in retinorecipient areas. HIGHLIGHTSO_LIHigh-density electrodes capture the activity of afferent axons and target neurons in vivo C_LIO_LIRetinal ganglion cells axons are organized in mosaics C_LIO_LISingle cell precise isomorphism between dendritic and axonal RGC mosaics C_LIO_LIMidbrain neurons are driven by sparse but strong retinal inputs C_LIO_LIFunctional wiring of the retinotectal circuit is similar in mammals and birds C_LI

neuroscience↗

bioRxiv2021

Tangential high-density electrode insertions allow to simultaneously measure neuronal activity across an extended region of the visual field in mouse superior colliculus

The superior colliculus (SC) is a midbrain structure that plays a central role in visual processing. Although we have learned a considerable amount about the function of single SC neurons, the way in which sensory information is represented and processed on the population level in awake behaving animals and across a large region of the retinotopic map is still largely unknown. Partially because the SC is anatomically located below the cortical sheet and the transverse sinus, it is technically difficult to measure neuronal activity from a large population of neurons in SC. To address this, we propose a tangential recording configuration using high-density electrode probes (Neuropixels) in mouse SC in vivo that permits a large number of recording sites (~200) accessibility inside the SC circuitry. This approach thereby provides a unique opportunity to measure the activity of SC neuronal populations composing up to ~2 mm of SC tissue and characterized by receptive fields covering an extended region in the visual field. Here we describe how to perform tangential recordings along the anterior-posterior and the medio-lateral axis of the mouse SC in vivo and how to combine this approach with optogenetic tools for cell-type identification on the population level.

neuroscience↗