A STORM of activity: Super-resolution imaging analysis of activity-dependent synaptic development in the circadian photoentrainment circuit

Abstract

Circadian rhythmicity is a subconscious process that controls for many of our daily behaviors such as appetite and sleep. Controlled by the Suprachiasmatic Nucleus (SCN), the circadian rhythm is entrained to environmental light by a unique retinal ganglion cell, the intrinsically photosensitive retinal ganglion cell (ipRGC). Experience-dependent activity has been shown to influence synaptogenesis and refinement of neural circuits. We utilized the ipRGC-SCN circuit to investigate activity-dependent changes in synaptic structure to understand the effect of activity on synaptogenesis throughout early development. We used the super-resolution microscopy technique, STochastic Optical Reconstruction Microscopy to quantify synaptic structural changes. We found reduced synaptic density and volume in activity manipulated animals compared to controls. These findings suggest ipRGC photoactivity is permissive to the proper development and signaling in ipRGC-SCN synapses. The proper activity-dependent maturation of synapses in SCN neurons are crucial to the ability to normally photoentrain and maintain rhythmic bodily functions.