Pattern formation by retinal afferents in the ferret lateral geniculate nucleus: Developmental segregation and the role of N-methyl-D-aspartate receptors

The projection from the retina to the lateral geniculate nucleus (LGN) in f errets segregates during development into eye-specific layers and ON/OFF su blayers. The projection pattern and the morphology of single axons was exam ined at several postnatal ages. The axons progress from a simple, sparsely branched morphology at birth to crude arbors at postnatal day 7 (P7). At P1 4-P15, axons have terminal arbors that span one eye-specific layer. By P19- P21, retinal afferents in the A layers have segregated into inner and outer sublaminae that correspond to ON- and OFF-center cells. Sublaminae form ma inly by directed growth of terminal arbors in appropriately positioned regi ons of the LGN, along with elimination of extraneous branches in inappropri ate regions. From P28 to P35, the LGN assumes an adult-like shape, and reti nogeniculate axons form terminal boutons on branch endings. During the peri od between P14 and P21, when retinogeniculate axons segregate into ON/OFF s ublaminae, N-methyl-D-aspartate (NMDA) receptors were blocked with chronic infusion of specific antagonists into the LGN. NMDA receptor blockade preve nts the retinal afferent segregation into ON/OFF sublaminae. Some individua l retinogeniculate axons have arbors that are not restricted appropriately, and most are restricted in size but are located inappropriately within the eye-specific laminae. Thus, NMDA receptor blockade prevents the positionin g of retinogeniculate arbors that lead to the formation of ON/OFF sublamina e in the LGN. These results indicate that the activity of postsynaptic cell s, and the activation of NMDA receptors in particular, can influence signif icantly the patterning of inputs and the structure of presynaptic afferents during development. (C) 1999 Wiley-Liss, Inc.