Aa, waveform average of an extracellular recording of an LC neuron. Calibration bar: x-axis, 1 ms; and y-axis, 500 μV. Ab, raw recording of sSND discharge and the neuron in Aa during low-frequency photostimulation of the RVLM (1 Hz, 20 ms pulse). Ac, PSTH of the activity of the LC neuron in Aa during low-frequency stimulation. Inset, waveform average of sSND during the trial used to generate the PSTH. Calibration bar: x-axis, 0.1 s; and y-axis, 100 mV. Ba, as per Aa, except following intracerebroventricular (i.c.v.) administration of kynurenic acid (250 mm, 5 μl). Bb, as for Ab, following i.c.v. kynurenic acid. Bc, as for Ac, following i.c.v. kynurenic acid.