The Influence of the Pretectum on the Visual Thalamus

PROJECT SUMMARY / ABSTRACT The pretectum (PT) is a relatively unexplored brain area in mammals, and it is currently unknown how the PT affects the visual properties of thalamic neurons that underly the complex integration of vision and movement. Here, a team of investigators propose a multifaceted approach - from synapse to behavior – to answer fundamental questions regarding PT circuits (Aim 1), the visual and/or motor response properties of identified PT neurons (Aim 2), the effects of PT input on the response properties of thalamic neurons (Aim 3), and the effects of the PT on visual behavior (Aim 4). Each aim will utilize a combination of novel intersectional circuit labeling techniques, neuronal activation, and recording strategies to probe two identified PT pathways: a GABAergic pathway to the lateral geniculate nucleus (LGN) and the visual sector of the thalamic reticular nucleus (vTRN), and a nonGABAergic pathway to the pulvinar nucleus (PUL) from PT neurons that contain parvalbumin. Aim 1 will use cre-dependent monosynaptic rabies tracing to induce the expression of the calcium indicator GCaMP to classify, using 2P imaging, the receptive field properties and morphology of retinal ganglion cells that innervate PT-LGN/TRN and PT-PUL neurons. Monosynaptic rabies tracing will also be used to characterize cortical and subcortical brain inputs to PT-LGN/TRN and PT-PUL cells; identified PT inputs will subsequently be studied using electron microscopy and in vitro whole cell recordings paired with optogenetic activation to characterize their ultrastructure and synaptic properties. Aim 2 will use in vivo extracellular recordings in awake animals paired with “opto-tagging” to determine the response properties of PT-LGN/TRN and PT-PUL neurons. Aim 3 will use in vivo extracellular recordings from awake animals paired with optogenetic activation of PT inputs to determine the effects of the PT inputs on LGN, vTRN and PUL response properties. Finally, Aim 4 will use cre- and flp-dependent chemogenetic activation of PT-LGN/TRN or PT-PUL neurons to determine if these cells affect stereopsis and/or optokinetic responses. Collectively, these 4 lines of inquiry will provide key information regarding the role of the PT in active vision.