Figure 2: Optogenetic activation of prelimbic layer II/III pyramidal neurons in vitro.

(a) Experimental approach for combined light stimulation and whole-cell recordings from IUE-transfected layer II/III pyramidal neurons in coronal slices of P8–10 mice. (b) Left, voltage responses of a representative neuron to hyper- and depolarizing current pulses. The RMP was −73.7 mV. Right, averaged plots of the current–voltage relationship (top) and current-firing rate relationship (bottom) (n=20 neurons). (c) Top, waveform of subthreshold chirp current injection with increasing frequency from 1 to 50 Hz. Middle, voltage response of a representative neuron. Bottom, averaged plots of the impedance (n=16 neurons). (d) Top, voltage responses of a representative ChR2(ET/TC)-transfected neuron to blue light pulses (473 nm, 5.2 mW mm⁻²) of 1 (dark blue) to 100 ms (light blue) duration. Bottom, bar diagram displaying the mean firing probabilty of transfected neurons in response to blue light pulses of variable duration (n=14 neurons). (e) Top, representative phase plot of APs elicited in a transfected neuron by depolarizing current injection (grey) or a 3-ms-long light pulse (473 nm, 5.2 mW mm⁻², blue). Bottom, bar diagrams displaying the mean active membrane properties after depolarizing current injections (grey, n=18 neurons) and after light stimulation (blue, n=14 neurons). Individual values are displayed as black crosses. (f) Representative voltage responses of a transfected neuron to repetitive trains of 3-ms-long light stimuli at variable frequencies. Bar diagram displaying the mean firing probability of transfected neurons in response to repetitive light stimuli (n=14 neurons). Data are presented as mean±s.e.m. *P<0.05, **P<0.01 and ***P<0.001, two-sided t-tests. MZ, marginal zone.