Figure 7: Effect of MPC088 photoactivation on action potential firing frequency in PNs.
From: Robust photoregulation of GABAA receptors by allosteric modulation with a propofol analogue
(a) Representative data obtained by whole-cell current-clamp recording from a PN, which was injected with 468 pA to elicit a high-frequency train of action potentials. During this current step, 10 μM GABA+30 μM trans-dominant MPC088 were applied via pressure pipette for 10 s. The cell was then exposed for 1-s durations to UV light (UV1), then blue light, and then again with UV (UV2). The entire illustrated voltage versus time trace occurs during application of GABA/MPC088. Below this trace is plotted the instantaneous firing frequency versus time; the dashed line reflects the average firing frequency during the 1-s epoch that preceded the first UV exposure. (b) Summary of results from experiments of the type shown in a. Average spike frequencies were obtained for each cell in each of five 1-s epochs, then normalized to the pre-GABA/MPC088 firing frequency (n=8 cells from 4 animals). Error bars here and in c represent the s.e.m. Repeated-measures analysis of variance on the aggregate data yielded F(3,21)=10.213, P<0.001. Red asterisks above the purple and blue bars indicate significance of the average frequency in that epoch versus the preceding epoch (for example, the asterisk above the UV1 bar refers to significance of the average firing rate in the UV1 epoch versus the GABA/MPC088 pre-UV epoch). Significance was determined from post-hoc paired-sample Student's t-tests corrected for multiple comparisons, which yielded P<0.02. (c) Summary of results from experiments similar to that described in a, but in which the cell was exposed only to the UV/blue/UV flash sequence (that is, no GABA/MPC088 applied). Data normalized to the average firing frequency during the 1-s period preceding the first UV flash (n=7 cells from three animals). Repeated-measures analysis of variance on the aggregate data yielded F(3,18)=3.057, P>0.05. Three post-hoc statistical tests were then performed as described in b; none of these yielded significance at the uncorrected 0.05 level.
