Figure 5

Stiff substrate facilitates excitatory synaptic connectivity and transmission in the neural networks of hippocampal neurons.

(a) Experimental setting of paired recording; one (presynaptic) neuron was stimulated by the electrode in current-clamp configuration to evoke APs and the unitary postsynaptic currents in the other (postsynaptic) neuron were detected by the electrode in voltage-clamp configuration. Example unitary EPSC and IPSC with distinct kinetics are illustrated at the bottom. (b) Summary of percentage of pairs of neurons that exhibited synaptic connectivity or transmission on soft and stiff substrates. In total, 181 pairs of neurons on soft and stiff substrates each from three independent preparations respectively were examined. (c) Summary of the percentage of pairs of neurons on soft and stiff substrates that showed excitatory and inhibitory synaptic connectivity (from (b)). (d) Paired recording from a pair of electrically coupled neurons. The experimental protocol is illustrated on top: a hyperpolarizing step current was injected to the presynaptic neuron C1 and changes in membrane potential were recorded from both presynaptic neuron and postsynaptic neuron (C2). Representative recordings of changes in membrane potential in C1 and C2 cells are shown below. (e) Summary of the percentage of electrically coupled neurons on soft and stiff substrates. In total, 54 pairs of neurons on soft substrates and 46 pairs of neurons on stiff substrates from 8 independent preparations were examined. (f) Summary of the coupling coefficient values for electrically coupled neurons. (g) The cumulative distribution of AP-evoked EPSC recorded in 18 neurons from seven independent preparations in each case. Insert: evoked EPSC traces from neurons on soft and stiff substrates. (h) Mean PPF value for 18 neurons on soft and stiff substrates from seven independent preparations. (i) The cumulative distribution of AP-evoked IPSC recorded in 16 neurons from seven independent preparations. Insert: evoked IPSC traces in neurons on soft and stiff substrates. (j) Mean PPD value for 16 neurons on soft and stiff substrates each from seven independent preparations. The numbers shown in parenthesis indicate neuron preparations (b–c and e) or neurons examined (f–j) in each case. *, p < 0.05 denotes significant difference and NS, no significant difference.