Figure 2. PC but not MC are directly innervated by the ATN.

(a) Channelrhodopsin-2-eYFP expression in ATN of SstCre::tdTomato mice 15 days after stereotaxic injections of an AAV vector. Injection site in AT and projecting thalamic axons in the ipsilateral presubiculum (horizontal brain section, 20° angle; dorso-ventral depth 2.5–3). Scale bar, 1 mm. (b) Enlarged view of the parahippocampal cortex. Thalamic axons specifically target the superficial layers of presubiculum. Scale bar, 200 μm. DG: dentate gyrus; S: subiculum; PrS: presubiculum, PaS: parasubiculum; EC: entorhinal cortex; (c) Presubicular responses to illumination (470 nm LED, 0.5 ms, 2 mW) of ChR2-expressing thalamic fibres, in simultaneous records from a PC and MC. Top, action potentials were evoked in three trials following a blue light flash in the PC but not in the MC. Below, light-evoked EPSCs from three trials, and average responses (40 trials) in red. (d) In TTX-4AP containing ACSF, EPSCs were still elicited in PCs, indicating that thalamic axons made direct synaptic contacts onto PCs. Responses were mostly abolished in MCs, suggesting indirect, disynaptic excitation of MCs. (e) Onset latencies of PC EPSCs are significantly shorter than for MC EPSCs. **Mann–Whitney U test , P<0.01. (f,g) Absolute charge transfer over 25 ms after the light stimulus in f standard and g TTX-4AP containing ACSF was significantly higher in PCs than MCs. *** and **Dunn’s multiple comparison test P<0.001 and P<0.01, respectively, performed after a significant (P<0.0001) Kruskal–Wallis test comparing responses in PC and MC from standard and TTX-4AP conditions. For PCs, the charge transfer was significantly reduced (****Wilcoxon-signed rank test P<0.0001) but still present in TTX/4AP condition. For MC cells, the measured charge transfer was also significantly reduced (**Wilcoxon-signed rank test P=0.0078) to values close to zero in TTX/4AP condition. Horizontal bars indicate median values. Data from n=14 PC (blue triangles) and 9 MCs (green circle) from 5 mice.