Extended Data Fig. 5: Optogenetic circuit mapping reveals functional hippocampal feedback to ECL2/3 and ECL5 with pathway specific synaptic excitation-inhibition ratio and plasticity.
From: Hippocampus shapes entorhinal cortical output through a direct feedback circuit
a. Schematic of direct and indirect circuits overlaid on a representative confocal image of a horizontal brain slice (10 animals, similar results). Green CA1 axons project to both ECL5 and ECL2/3. EC: entorhinal cortex, PrS: presubiculum, PaS: parasubiculum. b – e. Functional channelrhodopsin 2 (ChR2) expression restricted to hippocampal neurons. Top: Intrinsic firing and sag properties of CA1 pyramidal (b), ECL2/3 stellate (c), ECL2/3 pyramidal (d), and ECL5 pyramidal (e) neurons in response to current steps. Bottom: A 500 ms, 470 nm light pulse evokes sustained photocurrents in CA1 pyramidal neurons only, confirming no off-target ChR2 expression in ECL2/3 or ECL5 neurons. f. Representative voltage clamp recordings from ECL2/3 neuron to record excitatory and inhibitory postsynaptic currents (EPSC and IPSC respectively) at -80 mV and +10 mV respectively. Insets show parts of the trace enclosed in the dotted box. g. IPSC amplitudes in ECL2/3 neurons increase with LED intensity. Each blue trace: individual neuron (n = 10, N = 7 mice); bold red: mean ± SEM. h. EPSC amplitudes in ECL2/3 neurons as LED intensity increases. Each blue trace: individual neuron (n = 12, N = 6 mice); bold green: mean ± SEM. i. Same f. but for ECL5 neurons. j. IPSC amplitudes in ECL5 neurons. Gray traces: individual neurons (n = 10, N = 5 mice); bold red: mean ± SEM. k. EPSC amplitudes in ECL5 neurons. Gray traces: individual neurons (n = 9, N = 6 mice); bold green: mean ± SEM. l. Schematic of hippocampal feedback (green) to ECL2/3 (blue) and ECL5 (black), with multimodal input arriving at ECL1. Hippocampal input is optically stimulated, and ECL1 input is electrically stimulated. m. Example traces of post-synaptic potentials recorded in ECL2/3 pyramidal neuron in response to (from left to right) –: baseline ECL1 stimulation, paired ECL1 + HC inputs (20 ms interval, 1 Hz, 90 s), and ECL1 stimulation at 5 and 20 min post-pairing show long-term potentiation. n. Time window tuning for LTP induction in ECL2/3 neurons. Pairing intervals of 0, 5, 10, 20, 30, 40, 50 ms tested. Maximal LTP at 20 ms. Data: mean ± SEM. Number of neurons tested for each pairing interval (n) was as follows: 0 (n = 3), 5 (n = 5), 10 (n = 4), 20 (n = 7), 30 (n = 4), 40 (n = 4), and, 50 (n = 3) ms.
