RT Journal Article
SR Electronic
T1 Ultrastructure of Synaptic Connectivity within Subregions of the Suprachiasmatic Nucleus Revealed by a Genetically Encoded Tag and Serial Blockface Electron Microscopy
JF eneuro
JO eNeuro
FD Society for Neuroscience
SP ENEURO.0227-23.2023
DO 10.1523/ENEURO.0227-23.2023
VO 10
IS 8
A1 Calligaro, Hugo
A1 Shoghi, Azarin
A1 Chen, Xinyue
A1 Kim, Keun-Young
A1 Yu, Hsin Liu
A1 Khov, Brian
A1 Finander, Benjamin
A1 Le, Hiep
A1 Ellisman, Mark H.
A1 Panda, Satchidananda
YR 2023
UL http://www.eneuro.org/content/10/8/ENEURO.0227-23.2023.abstract
AB The hypothalamic suprachiasmatic nucleus (SCN) is the central circadian pacemaker in vertebrates. The SCN receives photic information exclusively through melanopsin-expressing retinal ganglion cells (mRGCs) to synchronize circadian rhythms with the environmental light cycles. The SCN is composed of two major peptidergic neuron types in the core and shell regions of the SCN. Determining how mRGCs interact with the network of synaptic connections onto and between SCN neurons is key to understand how light regulates the circadian clock and to elucidate the relevant local circuits within the SCN. To map these connections, we used a newly developed Cre-dependent electron microscopy (EM) reporter, APEX2, to label the mitochondria of mRGC axons. Serial blockface scanning electron microscopy was then used to resolve the fine 3D structure of mRGC axons and synaptic boutons in the SCN of a male mouse. The resulting maps reveal patterns of connectomic organization in the core and shell of the SCN. We show that these regions are composed of different neuronal subtypes and differ with regard to the pattern of mRGC input, as the shell receives denser mRGC synaptic input compared with the core. This finding challenges the present view that photic information coming directly from the retina is received primarily by the core region of the SCN.