Refinement of spatial receptive fields in the developing mouse LGN is coordinated with excitatory and inhibitory remodeling

Receptive field properties of individual visual neurons are dictated by the precise patterns of synaptic connections they receive, including the arrangement of inputs in visual space and features such as polarity (On versus Off). The inputs from retina to the lateral geniculate nucleus (LGN) in the mouse undergo significant refinement over development, however it is unknown how this corresponds to the establishment of functional visual response properties. Here we conducted in vivo and in vitro recordings in mouse LGN, beginning just after natural eye opening to determine how receptive fields develop as excitatory and feed-forward inhibitory retinal afferents refine. Experiments used both male and female subjects. For in vivo assessment of receptive fields, we performed multisite extracellular recordings in awake mice. Spatial receptive fields were over twice as large at eye-opening as in adults, and then reduced in size over the subsequent week. This topographic refinement was accompanied by other spatial changes such as a decrease in spot size preference and an increase in surround suppression. Notably, the degree of specificity in terms of On/Off and sustained/transient responses appeared to be established already at eye opening and did not change. During the same time, in vitro recordings of the synaptic responses evoked by optic tract stimulation revealed a pairing of decreased excitatory and increased feed-forward inhibitory convergence, providing a potential mechanism to explain the spatial receptive field refinement. SIGNIFICANCE STATEMENT The development of precise patterns of retinogeniculate connectivity has been a powerful model system for understanding the mechanisms underlying the activity dependent refinement of sensory systems. Here we link the maturation of spatial receptive field properties in dLGN to the remodeling of retinal and inhibitory feed-forward convergence onto dLGN neurons. These findings should thus provide a foundation to test the cell-type specific plasticity mechanisms that lead to refinement of different excitatory and inhibitory inputs, and their impact on the establishment of mature receptive fields in the LGN.