CIL:50585, fine structure and quantified the distribution of melanopsin-expressing retinal ganglion cell (ipRGC) projections within multiple brain regions. In Cell Image Library

Using a variant of miniSOG, a genetic probe for correlated light and electron microscopy (CLEM), we determined the form, fine structure and quantified the distribution of melanopsin-expressing retinal ganglion cell (ipRGC) projections within multiple brain regions. The method developed labels the entire neuron, including its axonal arbors in retinorecipient brain regions. Here the ‘synapto-projectome’ of these cells was charted in the suprachiasmatic nucleus (SCN), olivary pretectal nucleus (OPN), and subregions of the lateral geniculate. Each ipRGC axonal arbor synapsed on multiple target neurons in the SCN and OPN. Although the only direct retinal input to the OPN and SCN is from ipRGCs, the terminal arbors and boutons were different in each brain region. Also, a network of dendro-dendritic chemical synapses (DDCS) was discovered in the SCN; with ipRGC axons preferentially targeting the DDCS-linked cells. Methods used for this analysis should facilitate other CLEM studies of brain circuits at high resolution.