Pharmacology Biochemistry & Behavior, Vol. 15, pp. 485-488, 1981, Printed in the U.S.A. Low Dose Cocaine Self-Administration by Naive Rats: Effects of Body Weight and a Fixed-Time One Minute Food Delivery Schedule M. PAPASAVA, T. P. S. OEI AND G. SINGER Department of Psychology, La Trobe University Bundoora, Victoria 3083, Australia Received 12 May 1981 PAPASAVA, M., T. P. S. OEI AND G. SINGER. Low dose cocaine self-administration by naive rats: Effects t2f body weight and a fixed-time one minute food delivery schedule. PHARMAC. BIOCHEM. BEHAV. 15(3)485-488, 1981.--]'he self-administration rates of four groups of eight rats for low dose cocaine (0.1 mg/kg infusion) under free feeding and 80% body weight conditions, with and without a fixed time 1 min (FT-1) food delivery schedule, were compared with those of saline reinforced animals under the same conditions. Results indicated that (1) overall, self-administration rates were significantly greater for cocaine reinforced animals, (2) significantly higher rates of cocaine self-administration occurred in body weight reduced rats and (3) the operation of FT-1 schedule neither significantly enhanced or inhibited drug intake. In the second experiment, schedule and no schedule conditions were reversed for the sixteen 80% body weight, cocaine reinforced rats. Results showed that reversing schedule and no schedule conditions produced no significant change in drug intake. It was concluded that low dose cocaine self-administration is significantly amplified by body weight reduction. Schedule Cocaine Self-administration Body weight THE schedule-induced self-injection (SISI) procedure first reported by Lang et al. [7] has recently been utilized to in- duce self-administration of a variety of drugs by naive rats. These drugs have included heroin [8,10], methadone [10], nicotine [7], ethanol [9], and d-amphetamine [13]. Within the SISI paradigm, it has been demonstrated that the type of drug, the nutritional state of the animal and the operation of a fixed time one minute (FT-1) food pellet deliv- ery schedule, either independently or via interactions, may influence the rate of self-administration. These findings have led to the suggestion that drugs may be classified according to the interaction of factors necessary to initiate self- administration [5]. Thus far, three types of interactions have been identified. These are (1) where self-administration by rats is acquired at 80% body weight with no schedule operat- ing, but is considerably enhanced in the presence of a schedule (alcohol [9] and heroin [8,10]), (2) where self- administration is acquired only by animals at 80% body weight in the presence of an FT-1 schedule (nicotine [7] and methadone [10]), and (3) where self-administration is ac- quired only by 80% body weight animals and is inhibited by the operation of the schedule (amphetamine [13]). Several investigations have now established that intrave- nous infusions of cocaine are positively reinforcing in both rats [4, 11, 12] and monkeys [1, 3, 6] under a variety of experimental conditions. For rats, the findings indicate that optimal responding occurs within a dose range of 0.5 and 3 mg/kg, with little or no responding occurring at doses below 0.25 mg/kg [11,12]. In a recent report, however, food de- prived rats self-administered high levels of cocaine at a dose of 0.1 mg/kg [2]. These latter results would seem to indicate that the threshold for cocaine self-administration by rats is considerably lower under conditions of food deprivation. The objective of the present experiments was to examine low dose cocaine self-administration within the SISI para- digm. EXPERIMENT I: SELF-ADMINISTRATION OF COCAINE AT 100% AND 80% BODY WEIGHT WITH AND WITHOUT AN FT-1 FOOD DELIVERY SCHEDULE In this experiment, the level of cocaine reinforced self- injection at 100%, 80% body weight and 100%, 80% body weight under an FT-1 food delivery schedule was compared with saline reinforced animals under the same conditions. METHOD Animals Sixty-four naive male, Wistar albino rats, weighing ap- proximately 400 g were used. The animals were housed in- Copyright © 1981 ANKHO International Inc.~0091-3057/81/090485-04500.90/0