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. 2009 Jun 24;102(2):1254–1264. doi: 10.1152/jn.00346.2009

FIG. 7.

FIG. 7.

Effects of intracellular accumulation of C17-NBD steroid analogues on GABA response potentiation in neurons. A and B: representative traces of GABA potentiation determined for 0.5 μM C17-NBD-alphaxalone (A, left) and 0.5 μM C17-NBD-3α5αA (B, left), followed by a 30-s wash in GABA alone, a 20-s wash in saline, and a reapplication of GABA alone (A and B, right) The GABA reapplication showed a larger residual current following C17-NBD-3α5αA potentiation. C: summary of effects over multiple cells treated as in A and B. Doubling the concentration of C17-NBD-alphaxalone (1 μM; middle bar) did not increase the response to a test GABA application. GABA responses to the second application are normalized to the first (original) GABA application (dotted horizontal line). Values are means ± SE (n = 10 for 0.5 μM C17-NBD-alphaxalone; n = 5 for 1 μM C17-NBD-alphaxalone; n = 11 for 0.5 μM C17-NBD-3α5αA); **P < 0.01 (unpaired t-test). D and E: representative traces of GABA potentiation by C17-NBD-alphaxalone (D) and C17-NBD-3α5αA (E) (0.5 μM), applied with GABA (0.5 μM). To speed offset of potentiation, γCDX (500 μM) was added in the GABA solution and applied for 15 s following potentiation. GABA alone was then immediately reapplied for 15 s. In cells previously exposed to C17-NBD-3α5αA, a rebound potentiation reemerged. F: summary of multiple cells treated as in D and E. Increasing C17-NBD-alphaxalone concentration to 1 μM did not increase rebound potentiation following GABA reapplication. Nonfluorescent compounds (10 μM alphaxalone and 1 μM 3α5αP) were tested with a similar protocol using a 10- to 15-s γCDX wash; a summary for rebound potentiation is shown. Rebound potentiation was normalized to the first (original) GABA application (dotted horizontal line). Values are means ± SE (n = 7 for 0.5 μM C17-NBD-alphaxalone; n = 6 for 1 μM C17-NBD-alphaxalone; n = 6 for 0.5 μM C17-NBD-3α5αA, n = 9 for 10 μM alphaxalone, n = 9 for 1 μM 3α5αP); *P < 0.05 (unpaired t-test for fluorescent compounds, paired t-test for parent steroids).