SELF-ADMINISTRATION IN RATS ALLOWED UNLIMITED ACCESS TO NICOTINE

The purpose of the present study was to develop an animal model of nic otine self-administration that more closely approximates the condition s of human nicotine use than do existing models. In most nicotine self -administration models, rats acquire self-administration during brief daily sessions in which rapid injections of a relatively high dose of the drug, 0.03 mg/kg, serve as the reinforcer. The present study exami ned nicotine self-administration in rats that acquired the behavior wh ile having virtually unlimited access to injections of a relatively lo w dose of the drug; the rats did not have any prior operant training o r shaping, Under these conditions, rats readily acquire nicotine self- administration at doses at least as low as 0.00375 mg/kg per injection , and they self-administer-throughout the active portion of their ligh t cycle. The daily nicotine intake of rats, which ranged from 0.18 to 1.38 mg/kg per day, appears to be comparable to that of human smokers.