Figure 4. MS GABAergic fibers entrain FS and LTS interneuron firing. A, Voltage-clamp responses in control (black), in the presence of iGluR and AChR antagonists (blue); and in the presence of iGluR, AChR, and GABAAR antagonists (red). Holding potential, 0 mV. B, Example responses of an FS interneuron to activation of MS GABAergic input at theta frequency (10 Hz). Mean trace, black; individual traces, gray. C, Ten consecutive responses from B on an expanded time scale. D, Normalized IPSP amplitude plotted as a function of stimulus number. E, Example response during the injection of current sufficient for maintained action potential firing without (left) and with (right) theta frequency activation of MS inputs to an FS neuron. F, Ten consecutive responses triggered from the time of each light stimulus illustrate entrainment of rebound spikes. G, Binned counts from 100 stimuli of action potentials as a function of time from the light pulse, illustrating measurement of pause time (red arrow) and frequency (blue arrow).