Effects of candidate analgesic compounds on acid-induced depression of ICSS response rate. (a) Like ketoprofen, SNC80 selectively blocked acid-induced depression of ICSS response rate. Thus, SNC80 had little effect on total ICSS response rate in the absence of lactic acid but dose-dependently blocked acid-induced depression of total ICSS response rate. (b) Salvinorin A non-selectively decreased ICSS response rate. Thus, salvinorin A decreased total ICSS response rate in the absence of lactic acid and also exacerbated acid-induced depression of ICSS response rate. (c) Bupropion non-selectively increased ICSS response rate. Thus, bupropion blocked acid-induced depression of total ICSS response rate, but only at doses that also increased total ICSS response rate in the absence of lactic acid. Significant acid-induced depression of ICSS response rate (#P < 0.05) and significant differences in ICSS response rate with a given drug dose compared with no drug in either the presence or the absence of lactic acid (*P < 0.05) are indicated. Data adapted from refs. 31, 42 and 43 and represent the mean ± s.e.m. of values from 5–8 rats.