Figure 3.

Suprathreshold Excitation of Delayed Firing GRPR_excit Neurons Requires Prolonged Burst-like Input from GRP Neurons

(A) MrgprA3 fibers were stimulated with blue light (473 nm, 4 ms) and postsynaptic current or voltage responses were recorded from Grp-eGFP neurons. Left: experimental setup. Middle: EPSCs (average of five consecutive traces) and average EPSC amplitudes of 6 individual neurons. Left: burst firing in current-clamp in the same GRP neuron in response to the same blue light stimulation.

(B) Repetitive light stimulation (five 4 ms pulses at 25 intra-burst frequency, repeatedly delivered at 0.5 Hz) of Grp-ChR2 neurons mimicked burst-like firing in response to input from MrgprA3 fibers. The first burst firing response is shown at higher resolution on the right (a).

(C) Voltage responses recorded from two Grpr-eGFP neurons in response to repetitive burst-like blue light stimulation of Grp-ChR2 neurons (same stimulation as in B). (a)–(c) depict burst firing response at higher resolution at different time points of the experiment. Bar chart: incidence of GRPR neuron firing during sustained burst-like blue light stimulation (n = 14 cells from 13 animals). Paired plot: RMP before (black) and after 5 min of repetitive burst-like light stimulation (blue) (n = 14). Two-tailed paired t test, p < 0.0001. For the time course of changes in RMP and the incidence of action potentials (APs) during burst stimulation see Figure S4.

(D and E) Same as (B) and (C) but repetitive single presynaptic light stimulations at 0.5 Hz (D) (n = 6 cells from 3 animals; two-tailed paired t test, p = 0.13) or 2.5 Hz (E) (n = 6 cells from 4 animals; two-tailed paired t test, p = 0.11).

All error bars indicate SEM.