Assessing Hippocampal Neuron Connectivity

Action potentials were generated in the presynaptic dGC using 5 ms square current pulses (1 nA). For connectivity analysis, 5 action potentials were induced at 20 Hz (inter-sweep-interval: 10 s; at least 30 repetitions) while recording unitary excitatory postsynaptic currents (uEPSCs) from CA3-PCs. Neurons were considered to be connected if >5% of action potentials evoked time-locked inward uEPSCs [26 (link)]. Recordings were performed in the presence of (-)-bicuculline-methiodide (10 μM, Abcam, Cambridge, UK, #ab120108) to prevent inhibitory synapse recruitment. Moreover, glutamine (200 μM, Gibco, New York, NY, USA, #11539876) was added to the recording medium to avoid synaptic depletion [27 (link)].