TY - JOUR T1 - Retinal Input Regulates the Timing of Corticogeniculate Innervation JF - The Journal of Neuroscience JO - J. Neurosci. SP - 10085 LP - 10097 DO - 10.1523/JNEUROSCI.5271-12.2013 VL - 33 IS - 24 AU - Tania A. Seabrook AU - Rana N. El-Danaf AU - Thomas E. Krahe AU - Michael A. Fox AU - William Guido Y1 - 2013/06/12 UR - http://www.jneurosci.org/content/33/24/10085.abstract N2 - Neurons in layer VI of visual cortex represent one of the largest sources of nonretinal input to the dorsal lateral geniculate nucleus (dLGN) and play a major role in modulating the gain of thalamic signal transmission. However, little is known about how and when these descending projections arrive and make functional connections with dLGN cells. Here we used a transgenic mouse to visualize corticogeniculate projections to examine the timing of cortical innervation in dLGN. Corticogeniculate innervation occurred at postnatal ages and was delayed compared with the arrival of retinal afferents. Cortical fibers began to enter dLGN at postnatal day 3 (P3) to P4, a time when retinogeniculate innervation is complete. However, cortical projections did not fully innervate dLGN until eye opening (P12), well after the time when retinal inputs from the two eyes segregate to form nonoverlapping eye-specific domains. In vitro thalamic slice recordings revealed that newly arriving cortical axons form functional connections with dLGN cells. However, adult-like responses that exhibited paired pulse facilitation did not fully emerge until 2 weeks of age. Finally, surgical or genetic elimination of retinal input greatly accelerated the rate of corticogeniculate innervation, with axons invading between P2 and P3 and fully innervating dLGN by P8 to P10. However, recordings in genetically deafferented mice showed that corticogeniculate synapses continued to mature at the same rate as controls. These studies suggest that retinal and cortical innervation of dLGN is highly coordinated and that input from retina plays an important role in regulating the rate of corticogeniculate innervation. ER -