Lack of tolerance development to benzodiazepines in antagonism of the pentylenetetrazol discriminative stimulus.

In an operant procedure of lever pressing on FR 10 schedule of food reinforcement male hooded rats were trained to respond on a lever on one side of a food cup following a 20 mg/kg pentylenetetrazol (PTZ) injection and to respond on a lever on the alternate side following a 1 ml/kg saline injection. Upon acquisition of the PTZ-saline discrimination, diazepam and chlordiazepoxide were tested and found to antagonize the PTZ discriminative stimulus. The animals were then injected with 10 mg/kg diazepam or chlordiazepoxide for ten consecutive days. New dose-response curves obtained following this treatment indicated that tolerance did not develop to the antagonism of the PTZ discriminative stimulus by these benzodiazepines.