Figure 5

A, the effect of raising arterial pressure on the activity of recorded cells. Cells were grouped based on their sensitivity to laser light (LL) stimulation. Both LL activated (n= 26) and inhibited cells (n= 8) were virtually silenced by raising AP, but LL-insensitive cells (n= 17) were unaffected by elevated AP. *P < 0.05, **P < 0.01. B, the effect of photostimulation on the activity of recorded cells. *P < 0.05, **P < 0.01, ***P < 0.001 vs. resting frequency using paired t test. ##P < 0.01 as indicated using unpaired t test. C, grouped data from event-triggered histograms (1 ms bin) from LL activated neurons demonstrating that during 20 Hz laser stimulation, virtually all action potentials occur within 10 ms of the laser pulse onset with a large peak occurring 5 ms after the onset of the laser pulse. A subsidiary peak occurred between 9 and 10 ms representing cases when cells fired in couplets. For comparison, the same averaging of LL-insensitive cells shows no relationship with the timing of the laser pulse. D, the cumulative probability of the first evoked action potential in LL activated cells during photostimulation. This shows that virtually all laser-evoked action potentials occurred within 10 ms of the laser pulse onset. Cases in which laser pulses failed to evoke an action potential were ignored.