Discriminative stimulus properties of phenytoin in the pigeon: determination via a cumulative dosing procedure.

Pigeons were trained in a cumulative dosing procedure to emit one response in the presence of 15 mg/kg phenytoin and another response in the absence of phenytoin. After reliable discrimination was established, generalization tests with other anticonvulsant drugs were conducted. Ethosuximide (20-120 mg/kg) and methsuximide (25-100 mg/kg) engendered very little phenytoin-appropriate responding. Clonazepam (0.125-1 mg/kg) engendered more phenytoin-appropriate responding, but less than the training dose of phenytoin. Similar results were obtained when these drugs were administered in conventional single dose per session generalization tests. When tested in that fashion, mephenytoin (80 and 160 mg/kg) engendered some phenytoin-appropriate responding, but less than the training dose of phenytoin. Administering 10 mg/kg pentylenetetrazol in combination with 5, 10, 15, and 20 mg/kg cumulative doses of phenytoin reduced phenytoin-appropriate responding relative to levels obtained with these doses of phenytoin alone.