A protocol for inducing cortical spreading depression (SD) on rat neocortical slices in vitro, upon local application of calibrated approximately nl drops of KCl, 3M was used to elicit SD events, recorded at two different points on the slice. This in vitro model was validated by the inhibition of SD episodes by the NMDA antagonist MK-801 (20 microM), the reference SD blocker. Quinine, its stereoisomer quinidine, and mefloquine consistently inhibited the SD episodes. Quinine and quinidine, 100 and 200 microM reduced the duration, while mefloquine, 100 and 200 microM reduced the amplitude of SD events, all in a concentration-dependent manner. These compounds have been reported to block gap junctions, specifically the neuronal connexin (Cx) 36, but they also exert other cellular effects. While further investigation is warranted to settle whether SD inhibition in vitro by quinine, quinidine and mefloquine reflects an involvement of neuronal Cx36 channels in SD generation/propagation, these results bear potential drug-discovery relevance for the migraine with aura.