Performance and extinction of lever press behavior following chronic administration of desipramine to rats

The effect of repeated administration of desipramine (DMI) on the acquisition, performance, and extinction of a lever press response for food reward was studied. Chronic administration of DMI caused a reduction in pressing under a CRF schedule both in naive and well-trained rats. Responding during extinction sessions did not differ between saline-treated rats and rats given DMI chronically. In addition, chronic administration of DMI reduced the body weight and food intake of rats on either a free-feeding or a restricted-feeding schedule. Consequently, lever pressing was also studied in a group of rats whose body weight was regulated to match the body weight of rats were administered DMI chronically. In comparison to this control group, rats administered DMI chronically responded significantly less during both reinforcement and extinction sessions. These results fail to replicate earlier reports that chronic DMI administration produces increased resistance to extinction. The results also show that assessment of food-motivated performance in rats treated chronically with DMI is difficult because of long-term changes in body weight and food intake.