Figure 7
Ultrastructural analysis of retinal terminals in subnuclei of mouse visual thalamus. Retinal terminals were identified in serial block face scanning electron microscopy (SBFSEM) micrographs based upon their pale mitochondria and round, abundant synaptic vesicles. A,B. Retinal terminals in P42 dorsal lateral geniculate nucleus (dLGN). A’ shows non-pseudo-colored image depicted in A. C,D. Retinal terminals in P42 ventral lateral geniculate nucleus (vLGN). Each terminal and axon traced was given a unique color; therefore terminals labeled the same color belong to the same axonal arbor. Retinal terminals in dLGN contain a large number of processes from dendrites that extend into the nerve terminals (compare arrows in A,B with those in D). E. Retinal terminals in dLGN are statistically larger than those in vLGN (P <0.000001 by Student’s t-test; n = 3 datasets containing a total of 111 terminals in dLGN and 148 in vLGN). F. Quantification of the percent of terminals traced that contain postsynaptic intrusions (see arrows in A,B,D,G, and J). G-I. SBFSEM micrographs demonstrate the complex nature of terminal-dendrite interactions in dLGN. A single retinal terminal is labeled in pink and its dendritic partner is labeled in blue. In G’ and G”, arrows highlight dendritic projections into the retinal terminal. H and H’ depict 3D reconstructions of the retinal terminal and dendrite labeled in G. I,I’ represents a high magnification image of the terminal-dendrite interface in H. The retinal terminal has been made translucent in H’ and I’. 3 finger-like dendritic protrusions that invade a single terminal bouton are highlighted with arrows in I’. J-N. Multiple SBFSEM micrographs through two retinogeniculate synapses demonstrate the less complex nature of terminal-dendrite interactions in vLGN. K and M depict 3D reconstructions of the retinal terminals and dendrites traced in J and L respectively. Arrows in J and K’ indicate a small dendritic protrusion that extends into the retinal terminal. In M, 4 terminals from the same axon contact the purple dendrite and none contain dendritic protrusions. N shows a high magnification, rotated image of the terminal and dendrite in indicated by the arrow in M. Note the absence of dendritic protrusions into this terminal bouton. Retinal terminals and axons been made translucent in K’,M’ and N’. Scale bar in A = 1.5 μm for A-D, G, J, and L.