Effects of Chlorpromazine on a Brightness Discrimination in the Rat 1

Abstract

The effects of chlorpromazine were studied in four rats performing on a two-lever discrimination problem. 5s were trained to press one lever under conditions of a brightly illuminated stimulus light and the second lever when the stimulus light was dimly illuminated. After the accuracy of this discrimination had become consistent from day to day, chlorpromazine was administered in dosages of 0.0, 0.25, 1.0, 2.0, .3.0, or 4.0 mg/kg of body weight. Each S received each dosage on three different occasions in an ascending, mixed, and descending sequence of dosages. The major findings were: (a) Chlorpromazine in dosages ranging from 0.25 to 2.0 mg/kg decreased the accuracy of the discrimination and the rate of correct responding. (b) Over this same range of dosages, rate of incorrect responding increased. (c) Dosages larger than 2.0 mg/ kg had no further depressive effects on rate of correct responding or the accuracy of the performance but decreased to nearly zero the rate of incorrect responding.