Figure 1: Identification of virus-labeled and unlabeled synaptic profiles.

Montage images were collected to measure the size of all unlabeled synaptic terminals and postsynaptic dendrites in the Pl and Pcm. a) Low magnification montage of a coronal section through the pulvinar nucleus after collecting 4 high magnification montages in the Pl and 4 high magnification montages in the Pcm. For each high magnification montage, the electron beam caused the tissue to lighten relative to areas that were not montaged at high magnification. b) Pl montage #1. Examples of terminals labeled by a SV-HRP injection in the SC are indicated by black arrows. Examples of mitochondria labeled by a matrix-dAPEX2 virus injection in V1 are indicated with white arrows. c) Example of a labeled mitochondria (white asterisk) in a synaptic terminal resulting from the V1 injection of the matrix-dAPEX2 virus. Below is a synaptic terminal that does not contain mitochondria. The lumens of the vesicles in both terminals are clear. Black arrows indicate synapses. d) Pcm montage #1. Examples of terminals labeled by a SV-HRP injection in the SC are indicated by black arrows. Few labeled mitochondria resulting from a matrix-dAPEX2 virus injection in V1 are present in the Pcm. e) Examples of small unlabeled synaptic terminals that do not contain mitochondria. The lumens of the vesicles in both terminals are clear. Black arrows indicate synapses. f) Example of a large unlabeled terminal that contains unlabeled mitochondria (black asterisks) and vesicles with clear lumens. Black arrow indicates a synapse. g) Example of a synaptic terminal labeled with the SV-HRP virus. Note that the lumens of many of the synaptic vesicles contain a dark reaction product, while the mitochondria are unlabeled (black asterisks). Black arrow indicates a synapse. Scale bar in a = 30 μm. Scale bar in b = 5 μm and also applies to d. Scale bars in c,e,f and g = 400nm. OT, optic tract