Comparison of effects of bicuculline, strychnine, and picrotoxin with those of pentylenetetrazol on photically evoked afterdischarges.

The effects of bicuculline, strychnine, and picrotoxin on photically evoked afterdischarges (PhADs) in rat visual cortex were compared with those of pentylenetetrazol (a known PhAD potentiator) and a diazepam (a known PhAD suppressor) challenge. Bicuculline was found to augment PhADs in a manner similar to that found with pentylenetetrazol, with the exception that potentiation only occurred at convulsive levels whereas pentylenetetrazol augmentation occurred at both subconvulsive and convulsive levels. Diazepam suppressed bicuculline-potentiated PhADs. Picrotoxin was found to have some limited augmenting effect on PhAD activity but in a manner unlike that observed with either bicuculline or pentylenetetrazol. Strychnine had no systematic augmenting effect on PhADs. These results were discussed in terms of the possible role of GABA in thalamic systems responsible for PhAD production.