Functional Convergence at the Mouse Retinogeniculate Synapse
Litvina, Elizabeth Yakovlevna
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CitationLitvina, Elizabeth Yakovlevna. 2017. Functional Convergence at the Mouse Retinogeniculate Synapse. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractThe basic wiring diagram of a mammalian sensory circuit can illuminate the synaptic underpinnings of its function. The mammalian retina possesses a diversity retinal ganglion cell (RGC) types that encode different features of the visual scene. We do not yet fully understand how the visual system uses these features to support vision. According to the leading view, these diverse RGCs form separate channels of information that remain segregated as parallel lines that are relayed through the dorsoLateral Geniculate Nucleus (dLGN) to the visual cortex, where they finally converge in different combinations to form the basis of complex visual feature extraction.
In this dissertation, I interrogate the degree to which the functional organization of the mouse retinogeniculate synapse—the site of synaptic contact between a RGC axon and a thalamocortical (TC) neuron—conforms to this view. In the first study, I demonstrate that developmental refinement continues past p30, following the closure of the thalamic and cortical critical periods. This refinement coincides with the pruning of the broad RGC axonal arbor. Earlier in development, an arbor retains the potential to contact new geniculate partners through the reorganization of synaptic boutons along its scaffold, which exhibits plasticity in response to visual manipulation. Retinogeniculate connectivity thus remains morphologically and functionally plastic into adulthood in mice. In the second study, I optogenetically label RGCs in order to quantify the number of RGCs that innervate TC neurons in mice. In contrast to prior functional estimates, I show that an average of 10 RGCs converge onto a geniculate neuron, though only 30% of these contacts may strongly drive postsynaptic spiking. My final study asks whether retinogeniculate connectivity maintains functional segregation of visual information despite this surprisingly high degree of convergence; I use optogenetics to test if multiple types of RGCs can provide substantial inputs to the same TC neuron. Evidence from three groups of direction- selective RGCs shows that mature TC neurons often receive functional synaptic input from more than one RGC type. Together, these studies show the retinogeniculate functional organization in mice may support the computation of complex visual features at the level of the dLGN.
Citable link to this pagehttps://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37364826
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