Ultrastructure of Synaptic Connectivity within Subregions of the Suprachiasmatic Nucleus Revealed by a Genetically Encoded Tag and Serial Blockface Electron Microscopy

• DOI: 10.1523/eneuro.0227-23.2023
• Publication Date: 2023-07-27T17:50:22Z
• Authors: Hugo Calligaro; Azarin Shoghi; Xinyue Chen; Keun-Young Kim; Hsin Liu Yu; Brian Khov; Benjamin Finander; Hiep Le; Mark H. Ellisman; Satchidananda Panda
• Keywords: Male; Retinal Ganglion Cells; Mice; Microscopy, Electron; Circadian Clocks; Animals; Suprachiasmatic Nucleus; Research Article: New Research; Circadian Rhythm

The hypothalamic suprachiasmatic nucleus (SCN) is the central circadian pacemaker in vertebrates. SCN receives photic information exclusively through melanopsin-expressing retinal ganglion cells (mRGCs) to synchronize rhythms with environmental light cycles. composed of two major peptidergic neuron types core and shell regions SCN. Determining how mRGCs interact network synaptic connections onto between neurons key understand regulates clock elucidate relevant local circuits within To map these connections, we used a newly developed Cre-dependent electron microscopy (EM) reporter, APEX2, label mitochondria mRGC axons. Serial blockface scanning was then resolve fine 3D structure axons boutons male mouse. resulting maps reveal patterns connectomic organization We show that are different neuronal subtypes differ regard pattern input, as denser input compared core. This finding challenges present view coming directly from retina received primarily by region