The suppressive effects of intraperitoneal cocaine are augmented when evaluated in nondeprived rats

Rats suppress intake of a saccharin conditioned stimulus (CS) when paired with all drugs of abuse tested including morphine, cocaine, heroin, amphetamine, and ethanol. Although most of these drugs suppress intake when administered via a range of routes, the efficacy of cocaine is an exception. Specifically, cocaine-induced suppression of saccharin intake is much greater when administered subcutaneously than when administered intraperitoneally. The subcutaneous route of administration of cocaine, however, is somewhat problematic because, unless diluted, can cause stark necrosis. The present study, then, reexamined the effectiveness of intraperitoneal cocaine using less restrictive deprivation regimens that are known to facilitate the expression of the phenomenon. The results showed that, while only a 10- and 20-mg/kg dose of cocaine suppressed intake of the saccharin CS when evaluated in moderately water-deprived rats, all doses tested (i.e., 5, 10, and 20 mg/kg) significantly reduced CS intake when saccharin-cocaine pairings were evaluated in rats maintained on food and water ad libitum. Taken together, these data show that rats will readily avoid intake of a saccharin cue when paired with the intraperitoneal administration of cocaine and that the magnitude of the effect is augmented when examined in a need-free state.