Effects of anticonvulsant drugs under automaintenance and negative automaintenance procedures.

The behavioral effects of phenytoin, phenobarbital, clonazepam, valproic acid, and ethosuximide were evaluated in food-deprived pigeons performing under automaintenance and negative automaintenance procedures. Under the automaintenance procedure, brief periods of key illumination were followed by food delivery without regard to the subject's behavior. In most instances, when drugs were not given this procedure engendered high rates of keypecking during almost all key illuminations (trials). Acute administrations of phenytoin (10-20 mg/kg), valproic acid (40-120 mg/kg), and ethosuximide (40-120 mg/kg) produced generally dose-dependent decreases in percent trials with a response and rate of responding. Although phenobarbital (30-60 mg/kg) and clonazepam (2.5-7.5 mg/kg) produced little obvious effect on percent trials with a response, these drugs generally increased rate of responding. Under the negative automaintenance procedure, food delivery followed only key illuminations during which keypecking did not occur. Keypecking occurred at a low rate under this procedure, with no responses occurring during the majority of key illuminations. Thus, this procedure appeared to involve responding elicited by respondent conditioning but suppressed by the response-dependent omission of food. Across the same dose ranges evaluated under the automaintenance procedure, clonazepam and phenobarbital generally increased percent trials with a response and rate of responding in dose-dependent fashion. Phenytoin similarly increased percent trials with a response but had little consistent effect on rate of responding. Ethosuximide and valproic acid failed to affect responding under this procedure.