The Organization of Synapses on Visual Thalamus Dendrites in the Mouse: A 3D-Connectomics Approach

The lateral geniculate nucleus (LGN) of the thalamus modulates and relays visual information from the retina to the visual cortex. Synapses onto LGN neurons include input from the retina, the brainstem, the cortex, the thalamic reticular nucleus (TRN), and local inhibitory interneurons and these inputs shape the signal that is sent out of the LGN by relay cells. Previous studies of the LGN have described the organization of these inputs onto geniculate dendrites. However, key information is missing describing how inputs from different origins organize onto different LGN neuron dendrites subtypes and neuronal dendrite segments. The experiments in this dissertation sought to use a connectomics approach to characterize inputs onto LGN relay cell dendrites and interneuron dendrites with the goal of describing their organization in order to further explore how the setup of inputs into the LGN modulate visual information. Chapter II describes a method for determining putative terminal origin in the LGN through normal distribution based modeling of terminal volumes. This method was then used to study the organization of terminals onto different segments of LGN relay cell dendrites. Terminals from different origins show selectivity for different segments of relay cell dendrites based on both dendrite size and branch order. These terminals also show a selectivity for interactions with other distinct terminals on dendrite segments. Chapter III describes input selectivity onto LGN interneuron dendrites inside and outside of glomerular arrangements. Triadic motifs described in this chapter provide anatomical data that demonstrates how inputs onto interneurons affect inhibition of relay cells and therefore, the information that is sent by relay cells to the cortex. The results of these experiments detail the organization of terminals onto dendrites in a volume of LGN tissue and allows for more accurate speculation as to how this organization serves to modify visual information before it reaches the cortex.