Supplementary Figure 6: Array tomography of retrogradely labeled EC→CA1 synaptic connections; related to Fig. 6.
From: Single excitatory axons form clustered synapses onto CA1 pyramidal cell dendrites
(a) A retrograde strategy to label EC→CA1 afferent projections. AAV2retro-Cre virus was injected into the SLM area of Thy1 YFP-H mice to drive Cre expression in neurons projecting to the ipsilateral hippocampus. Cre-dependent virus encoding the V5 construct was injected locally into the MEC or LEC to label hippocampal-projecting EC neurons. Note that the axons of EC neurons projecting to the dentate gyrus were also infected in this preparation. (b) Left, maximum intensity projection of the MEC→CA1 array (YFP pyramidal cells in green, MEC axons in magenta). Right, maximum intensity projection of the LEC→CA1 array (YFP pyramidal cells in green, LEC axons in magenta) (from n = 1 large volume array for each projection, though these data replicate the data using the anterograde strategy shown in Fig. 6). Note the reciprocal proximal-distal gradient of axon density in CA1 SLM and the reciprocal labeling in the molecular layers of the dentate gyrus. (c) Similar to the anterograde strategy, the occurrence of compound synapses from retrograde labeling of MEC and LEC afferents differed (n = 149 identified MEC synapses and n = 66 identified LEC synapses: *two-sided Fisher’s exact test, p = 0.018).
