Changes occurring in self administration of nicotine by rats over a 28-day period.

After rats at reduced body weight had established responding by lever pressing for nicotine injections under a food delivery schedule (FT60 sec) for 1 hr daily sessions for 14 days, the rate of responding was maintained over a second 14-day period even after removal of the schedule. However, the rate was not maintained by rats lever pressing for normal saline without the schedule over the second 14-day period after self administration had been established for nicotine under the schedule. Other rats maintained at reduced body weight were allowed to lever press for nicotine over a 28-day period without the food delivery schedule. Their rate of self administration increased from initially low levels until at the end of the 28-day period the rate had reached that of rats self administering nicotine adjunctive to the food delivery schedule throughout the same period. Without the schedule, rats at reduced body weight self administering normal saline or rats at normal body weight self administering nicotine, continued to lever press only at very low rates throughout the 280-day period. It is suggested that rats maintain self administration of nicotine if the behavior can be established for a critical intake of nicotine over a critical period of time. The food delivery schedule appears only to hasten the establishment of the behavior but is not essential for self administration of nicotine by rats.