Figure 6.

Asymmetric NMDAR Activity between Two Convergent Inputs Redirects Branch Growth

(A) Schematic of the experimental design. Top: Animals with a dually innervated optic tectum and single labeled retinotectal axons were used. NMDAR activity in one retinal pathway, ipsilateral or contralateral to the tectum with the labeled axon, was attenuated by stimulating the eye with flickering LED in the presence of 2 μM MK801 for 15 min (IPSI Block and CONTRA Block, respectively). To prevent the activation of the other eye by the flicker, the other side was illuminated with constant light from the LED. Bottom: After washing out MK801, both eyes were stimulated simultaneously and branch dynamics were quantified using in vivo time-lapse imaging.

(B) Left: Plot of NMDAR current normalized to AMPAR current recorded at specified times after MK801 treatment. Right: Plot of average NMDAR/AMPAR current ratios binned over time.

(C) In vivo time-lapse confocal z series images of axon arbors imaged on Day 0 and Day 1 in animals under IPSI Block and CONTRA Block conditions superimposed on differential interference contrast images of the tectum.

(D) Histograms of the amplitudes of branch tip movement toward the rostral or caudal tectal poles for axons imaged under IPSI (blue) and CONTRA (red) Block conditions. Bin = 2 μm. Bootstrap (N = 10,000) was used for statistics. ∗∗p < 0.01. (N (IPSI) = 144 branches in 6 axons, N (CONT) = 237 branches in 6 axons.