Fig. 2. Effects of picrotoxin and nitrous oxide on population spike amplitude. a) In the presence of 0.5 μm picrotoxin, a γ-aminobutyric acid A receptor antagonist, the ratio of second population spike/first population spike remained unchanged at a 21 ms interstimulus interval ( P = NS by paired Student t test, n = 5). b) In the presence of 0.5 μm picrotoxin, traces depict representative population spike before ( solid ) and 20 min after ( dotted ) nitrous oxide administration. Nitrous oxide did not change the second population spike in the presence of picrotoxin. c) Input-output curves for second population spike amplitude recorded before ( diamonds ) and 20 min after ( squares ) nitrous oxide administration in a single slice in the presence of 0.5 μm picrotoxin. Nitrous oxide did not change second population spike based on input/output curves. d) Nitrous oxide (picrotoxin) significantly increased the population spike ratio (ratio of second population spike/first population spike in the presence of nitrous oxide over the ratios of second population spike/first population spike in pre-nitrous oxide) ( P < 0.01 by Mann–Whitney U test, n = 5, 6, respectively).